publications

2021

1. Giant white-light flares on fully convective stars occur at high latitudes

   Ekaterina Ilin, Katja Poppenhaeger,  Sarah J. Schmidt, Silva P. Järvinen, Elisabeth R. Newton, Julián D. Alvarado-Gómez, J. Sebastian Pineda, James R. A. Davenport, Mahmoudreza Oshagh, and Ilya Ilyin

   MNRAS, Oct 2021

   abstract arXiv ADS

   White-light flares are magnetically driven localized brightenings on the surfaces of stars. Their temporal, spectral, and statistical properties present a treasury of physical information about stellar magnetic fields. The spatial distributions of magnetic spots and associated flaring regions help constrain dynamo theories. Moreover, flares are thought to crucially affect the habitability of exoplanets that orbit these stars. Measuring the location of flares on stars other than the Sun is challenging due to the lack of spatial resolution. Here we present four fully convective stars observed with the Transiting Exoplanet Survey Satellite that displayed large, long-duration flares in white-light which were modulated in brightness by the stars’ fast rotation. This allowed us to determine the loci of these flares directly from the light curves. All four flares occurred at latitudes between 55\,^∘ and 81\,^∘, far higher than typical solar flare latitudes. Our findings are evidence that strong magnetic fields tend to emerge close to the stellar rotational poles for fully convective stars, and suggest that the impact of flares on the habitability of exoplanets around small stars could be weaker than previously thought.

2. Flares Big and Small: a K2 and TESS View of ASAS-SN Superflares

   Jesse Zeldes, Jason T. Hinkle, Benjamin J. Shappee, Ellis A. Avallone,  Sarah J. Schmidt, Jennifer L. van Saders, Zachary Way, Christopher S. Kochanek, and Thomas W. -S. Holoien

   arXiv e-prints, Sep 2021

   abstract arXiv ADS

   We investigate the flare-frequency distributions of 5 M-dwarfs that experienced superflares with energies in excess of 1033 erg detected by ASAS-SN. We use K2 and TESS short-cadence observations along with archival ASAS-SN data to categorise the flaring behaviour of these stars across a range of flare energies. We were able to extract a rotation period for 4 of the stars. They were all fast rotators ( Prot≤6d ), implying relative youth. We find that the flare-frequency distributions for each of the stars are well fit by a power-law, with slopes between α=1.22 and α=1.82 . These slopes are significantly flatter than those of fast-rotating M-dwarfs not selected for their superflaring activity, corresponding to an increased number of high energy flares. Despite our specific selection of superflaring stars with shallow flare-rate distributions and more power in higher-energy flares, we find that the implied UV flux is insufficient to deplete the ozone of earth-sized planets in the habitable zone around these stars. Furthermore, we find that the flares detected on the stars in our sample are insufficient to produce the UV flux needed to fuel abiogenetic processes. These results imply that given available models, even M-dwarfs selected for extreme flaring properties may have insufficient UV emission from flares to impact exolife on earth-sized planets in the habitable zones around M-dwarfs.

3. Calibration of the Hα Age-Activity Relation for M Dwarfs

   Rocio Kiman, Jacqueline K. Faherty, Kelle L. Cruz, Jonathan Gagné, Ruth Angus,  Sarah J. Schmidt, Andrew W. Mann, Daniella C. Bardalez Gagliuffi, and Emily Rice

   AJ, Jun 2021

   abstract arXiv ADS

   In this work, we calibrate the relationship between Hα emission and M dwarf ages. We compile a sample of 892 M dwarfs with Hα equivalent width (Hα EW) measurements from the literature that are either comoving with a white dwarf of known age (21 stars) or in a known young association (871 stars). In this sample we identify 7 M dwarfs that are new candidate members of known associations. By dividing the stars into active and inactive categories according to their Hα EW and spectral type (SpT), we find that the fraction of active dwarfs decreases with increasing age, and the form of the decline depends on SpT. Using the compiled sample of age calibrators, we find that Hα EW and fractional Hα luminosity (LHα/Lbol) decrease with increasing age. Hα EW for SpT ≤ M7 decreases gradually up until ∼1 Gyr. For older ages, we found only two early M dwarfs that are both inactive and seem to continue the gradual decrease. We also found 14 mid-type M dwarfs, out of which 11 are inactive and present a significant decrease in Hα EW, suggesting that the magnetic activity decreases rapidly after ∼1 Gyr. We fit LHα/Lbol versus age with a broken power law and find an index of −0.11+0.02−0.01 for ages ≲776 Myr. The index becomes much steeper at older ages, but a lack of field age-calibrators (≫1 Gyr) leaves this part of the relation far less constrained. Finally, from repeated independent measurements for the same stars, we find that 94% of them have a level of Hα EW variability ≤5 Å at young ages (<1 Gyr).

4. Flares in open clusters with K2. II. Pleiades, Hyades, Praesepe, Ruprecht 147, and M 67

   Ekaterina Ilin,  Sarah J. Schmidt, Katja Poppenhäger, James R. A. Davenport, Martti H. Kristiansen, and Mark Omohundro

   A&A, Jan 2021

   abstract arXiv ADS

   Context. Magnetic fields are a key component in the main sequence evolution of low mass stars. Flares, energetic eruptions on the surfaces of stars, are an unmistakable manifestation of magnetically driven emission. The occurrence rates and energy distributions of flares trace stellar characteristics such as mass and age. However, before flares can be used to constrain stellar properties, the flaring-age-mass relation requires proper calibration. Aims: This work sets out to quantify the flaring activity of independently age-dated main sequence stars for a broad range of spectral types using optical light curves obtained by the Kepler satellite. Methods: Drawing from the complete K2 archive, we searched 3435 ∼80 day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates. Results: We confirmed a total of 3844 flares on high probability open cluster members with ages from zero age main sequence (Pleiades) to 3.6 Gyr (M 67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-M dwarfs. We added the Hyades (690 Myr) to the sample as a comparison cluster to Praesepe (750 Myr), the 2.6 Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. We found that the flare energy distribution was similar in the entire parameter space, following a power law relation with exponent α ≈ 1.84−2.39. Conclusions: We confirm that flaring rates decline with age, and decline faster for higher mass stars. Our results are in good agreement with most previous statistical flare studies. We find evidence that a rapid decline in flaring activity occurred in M1─M2 dwarfs around the ages of the Hyades and Praesepe, when these stars spun down to rotation periods of about 10 d, while higher mass stars had already transitioned to lower flaring rates and lower mass stars still resided in the saturated activity regime. We conclude that some discrepancies between our results and flare studies that used rotation periods for their age estimates could be explained by sample selection bias toward more active stars, but others may point to the limitations of using rotation as an age indicator without additional constraints from stellar activity.

2020

1. K2 Ultracool Dwarfs Survey - VI. White light superflares observed on an L5 dwarf and flare rates of L dwarfs

   R. R. Paudel, J. E. Gizis, D. J. Mullan,  S. J. Schmidt, A. J. Burgasser, and P. K. G. Williams

   MNRAS, May 2020

   abstract arXiv ADS

   Kepler, K2 long cadence data are used to study white light flares in a sample of 45 L dwarfs. We identified 11 flares on 9 L dwarfs with equivalent durations of (1.3-198) h and total (UV/optical/IR) energies of &GreaterEqual;0.9 x 10³² erg. Two superflares with energies of >10³³ erg were detected on an L5 dwarf (VVV BD001): this is the coolest object so far on which flares have been identified. The larger superflare on this L5 dwarf has an energy of 4.6 x10³⁴ erg and an amplitude of >300 times the photospheric level: so far, this is the largest amplitude flare detected by the Kepler/K2 mission. The next coolest star on which we identified a flare was an L2 dwarf: 2MASS J08585891+1804463. Combining the energies of all the flares which we have identified on 9 L dwarfs with the total observation time which was dedicated by Kepler to all 45 L dwarfs, we construct a composite flare frequency distribution (FFD). The FFD slope is quite shallow (-0.51&pm;0.17), consistent with earlier results reported by Paudel et al. for one particular L0 dwarf, for which the FFD slope was found to be -0.34. Using the composite FFD, we predict that, in early- and mid-L dwarfs, a superflare of energy 10³³ erg occurs every 2.4 yr and a superflare of energy 10³⁴ erg occurs every 7.9 yr. Analysis of our L dwarf flares suggests that magnetic fields of &geq;0.13-1.3 kG are present on the stellar surface: such fields could suppress Type II radio bursts.

2. A Catalog of M-dwarf Flares with ASAS-SN

   Romy Rodrı́guez Martı́nez, Laura A. Lopez, Benjamin J. Shappee,  Sarah J. Schmidt, Tharindu Jayasinghe, Christopher S. Kochanek, Katie Auchettl, and Thomas W. -S. Holoien

   ApJ, Apr 2020

   abstract arXiv ADS

   We analyzed the light curves of 1376 early-to-late, nearby M dwarfs to search for white-light flares using photometry from the All-Sky Automated Survey for Supernovae. We identified 480 M dwarfs with at least one potential flare employing a simple statistical algorithm that searches for sudden increases in V-band flux. After more detailed evaluation, we identified 62 individual flares on 62 stars. The event amplitudes range from 0.12 < ΔV<2.04 mag. Using classical flare models, we place lower limits on the flare energies and obtain V-band energies spanning 2.0x10³⁰ &lesssim; E_V &lesssim; 6.9x10³⁵ erg. The fraction of flaring stars increases with spectral type, and most flaring stars show moderate to strong Hα emission. Additionally, we find that 14 of the 62 flaring stars are rotational variables, and they have shorter rotation periods and stronger Hα emission than nonflaring rotational variable M dwarfs.

2019

1. The Ultracool SpeXtroscopic Survey. I. Volume-limited Spectroscopic Sample and Luminosity Function of M7-L5 Ultracool Dwarfs

   Daniella C. Bardalez Gagliuffi, Adam J. Burgasser,  Sarah J. Schmidt, Christopher Theissen, Jonathan Gagné, Michael Gillon, Johannes Sahlmann, Jacqueline K. Faherty, Christopher Gelino, Kelle L. Cruz, and 2 more authors

   ApJ, Oct 2019

   abstract arXiv ADS

   We present a volume-limited, spectroscopically verified sample of M7−L5 ultracool dwarfs (UCDs) within 25 pc. The sample contains 410 sources, of which 93% have trigonometric distance measurements (80% from Gaia DR2) and 81% have low-resolution (R ∼ 120), near-infrared (NIR) spectroscopy. We also present an additional list of 60 sources that may be M7−L5 dwarfs within 25 pc when distance or spectral-type uncertainties are taken into account. The spectra provide NIR spectral and gravity classifications, and we use these to identify young sources, red and blue J − K S color outliers, and spectral binaries. We measure very low gravity and intermediate-gravity fractions of 2.1_-0.8%^+0.9% and 7.8_-1.5%^+1.7% , respectively; fractions of red and blue color outliers of 1.4_-0.5%^+0.6% and 3.6_-0.9%^+1.0% , respectively; and a spectral binary fraction of 1.6_-0.5% ^+0.5% . We present an updated luminosity function for M7−L5 dwarfs continuous across the hydrogen-burning limit that agrees with previous studies. We estimate our completeness to range between 69% and 80% when compared to an isotropic model. However, we find that the literature late-M sample is severely incomplete compared to L dwarfs, with completeness of 62_-7% ^+8% and 83_-9% ^+10% , respectively. This incompleteness can be addressed with astrometric-based searches of UCDs with Gaia to identify objects previously missed by color- and magnitude-limited surveys.

2. K2 Ultracool Dwarfs Survey - V. High superflare rates on rapidly rotating late-M dwarfs

   R. R. Paudel, J. E. Gizis, D. J. Mullan,  S. J. Schmidt, A. J. Burgasser, P. K. G. Williams, A. Youngblood, and K. G. Stassun

   MNRAS, Jun 2019

   abstract arXiv ADS

   We observed strong superflares (defined as flares with energy in excess of 1033 erg) on three late-M dwarfs: 2MASS J08315742+2042213 (hereafter 2M0831+2042; M7 V), 2MASS J08371832+2050349 (hereafter 2M0837+2050; M8 V), and 2MASS J08312608+2244586 (hereafter 2M0831+2244; M9 V). 2M0831+2042 and 2M0837+2050 are members of the young (700 Myr) open cluster Praesepe. The strong superflare on 2M0831+2042 has an equivalent duration (ED) of 13.7 h and an estimated energy of 1.3 × 10³⁵ erg. We observed five superflares on 2M0837+2050, on which the strongest superflare has an ED of 46.4 h and an estimated energy of 3.5 × 10³⁵ erg. This energy is larger by 2.7 orders of magnitude than the largest flare observed on the older (7.6 Gyr) planet-hosting M8 dwarf TRAPPIST-1. Furthermore, we also observed five superflares on 2M0831+2244 which is probably a field star. The estimated energy of the strongest superflare on 2M0831+2244 is 6.1 × 10³⁴ erg. 2M0831+2042, 2M0837+2050, and 2M0831+2244 have rotation periods of 0.556 ± 0.002, 0.193 ± 0.000, and 0.292 ± 0.001 d, respectively, which we measured by using K2 light curves. We compare the flares of younger targets with those of TRAPPIST-1 and discuss the possible impacts of such flares on planets in the habitable zone of late-M dwarfs.

3. Exploring the Age-dependent Properties of M and L Dwarfs Using Gaia and SDSS

   Rocio Kiman,  Sarah J. Schmidt, Ruth Angus, Kelle L. Cruz, Jacqueline K. Faherty, and Emily Rice

   AJ, Jun 2019

   abstract arXiv ADS

   We present a sample of 74,216 M and L dwarfs constructed from two existing catalogs of cool dwarfs spectroscopically identified in the Sloan Digital Sky Survey (SDSS). We cross-matched the SDSS catalog with Gaia DR2 to obtain parallaxes and proper motions and modified the quality cuts suggested by the Gaia Collaboration to make them suitable for late-M and L dwarfs. We also provide relations between Gaia colors and absolute magnitudes with spectral type and conclude that (G − G_RP) has the tightest relation to spectral type for M and L dwarfs. In addition, we study magnetic activity as a function of position on the color─magnitude diagram, finding that Hα magnetically active stars have, on average, redder colors and/or brighter magnitudes than inactive stars. This effect cannot be explained by youth alone and might indicate that active stars are magnetically inflated, binaries, and/or high metallicity. Moreover, we find that vertical velocity and vertical action dispersion are correlated with Hα emission, confirming that these two parameters are age indicators. We also find that stars below the main sequence have high tangential velocity, which is consistent with a low metallicity and old population of stars that belong to the halo or thick disk.

4. The Largest M Dwarf Flares from ASAS-SN

   Sarah J. Schmidt, Benjamin J. Shappee, Jennifer L. van Saders, K. Z. Stanek, Jonathan S. Brown, C. S. Kochanek, Subo Dong, Maria R. Drout, Stephan Frank, T. W. -S. Holoien, and 6 more authors

   ApJ, May 2019

   abstract arXiv ADS

   The All-sky Automated Survey for Supernovae (ASAS-SN) is the only project in existence to scan the entire sky in optical light approximately every day, reaching a depth of g ∼ 18 mag. Over the course of its first 4 yr of transient alerts (2013─2016), ASAS-SN observed 53 events classified as likely M dwarf flares. We present follow-up photometry and spectroscopy of all 53 candidates, confirming flare events on 47 M dwarfs, one K dwarf, and one L dwarf. The remaining four objects include a previously identified T Tauri star, a young star with outbursts, and two objects too faint to confirm. A detailed examination of the 49 flare star light curves revealed an additional six flares on five stars, resulting in a total of 55 flares on 49 objects ranging in V-band contrast from ∆V = −1 to −10.2 mag. Using an empirical flare model to estimate the unobserved portions of the flare light curve, we obtain lower limits on the V-band energy emitted during each flare, spanning log(E_V/erg)=32─35, which are among the most energetic flares detected on M dwarfs. The ASAS-SN M dwarf flare stars show a higher fraction of Hα emission, as well as stronger Hα emission, compared to M dwarfs selected without reference to activity, consistent with belonging to a population of more magnetically active stars. We also examined the distribution of tangential velocities, finding that the ASAS-SN flaring M dwarfs are likely to be members of the thin disk and are neither particularly young nor old.

5. The Near-ultraviolet Continuum Radiation in the Impulsive Phase of HF/GF-type dMe Flares. I. Data

   Adam F. Kowalski, John P. Wisniewski, Suzanne L. Hawley, Rachel A. Osten, Alexander Brown, Cecilia Fariña, Jeff A. Valenti, Stephen Brown, Manolis Xilouris,  Sarah J. Schmidt, and 1 more author

   ApJ, Feb 2019

   abstract arXiv ADS

   We present near-UV (NUV) flare spectra from the Hubble Space Telescope (HST)/Cosmic Origins Spectrograph during two moderate-amplitude U-band flares on the dM4e star GJ 1243. These spectra are some of the first accurately flux-calibrated, NUV flare spectra obtained over the impulsive phase in M dwarf flares. We observed these flares with a fleet of nine ground-based telescopes simultaneously, which provided broadband photometry and low-resolution spectra at the Balmer jump. An increase in the broadband continuum occurred with a signal-to-noise ratio >20 in the HST spectra, while numerous Fe II lines and the Mg II lines also increased but with smaller flux enhancements than the continuum radiation. These two events produced the most prominent Balmer line radiation and the largest Balmer jumps that have been observed to date in dMe flare spectra. A T = 9000 K blackbody underestimates the NUV continuum flare flux by a factor of two and is a poor approximation to the white light in these types of flare events. Instead, our data suggest that the peak of the specific continuum flux density is constrained to U-band wavelengths near the Balmer series limit. A radiative-hydrodynamic simulation of a very high energy deposition rate averaged over times of impulsive heating and cooling better explains the properties of the λ > 2500 Å flare continuum. These two events sample only one end of the empirical color-color distribution for dMe flares, and more time-resolved flare spectra in the NUV, U band, and optical from 2000 to 4200 Å are needed during more impulsive and/or more energetic flares.

6. Flares in open clusters with K2 . I. M 45 (Pleiades), M 44 (Praesepe), and M 67

   Ekaterina Ilin,  Sarah J. Schmidt, James R. A. Davenport, and Klaus G. Strassmeier

   A&A, Feb 2019

   abstract arXiv ADS

   Context. The presence and strength of a stellar magnetic field and activity is rooted in a star’s fundamental parameters such as mass and age. Can flares serve as an accurate stellar "clock"?
   Aims: To explore if we can quantify an activity-age relation in the form of a flaring-age relation, we measured trends in the flaring rates and energies for stars with different masses and ages.
   Methods: We investigated the time-domain photometry provided by Kepler’s follow-up mission K2 and searched for flares in three solar metallicity open clusters with well-known ages, M 45 (0.125 Gyr), M 44 (0.63 Gyr), and M 67 (4.3 Gyr). We updated and employed the automated flare finding and analysis pipeline Appaloosa, originally designed for Kepler. We introduced a synthetic flare injection and recovery sub-routine to ascribe detection and energy recovery rates for flares in a broad energy range for each light curve.
   Results: We collect a sample of 1761 stars, mostly late-K to mid-M dwarfs and found 751 flare candidates with energies ranging from 4 × 10³² erg to 6 × 10³⁴ erg, of which 596 belong to M 45, 155 to M 44, and none to M 67. We find that flaring activity depends both on T_eff, and age. But all flare frequency distributions have similar slopes with α ≈ 2.0-2.4, supporting a universal flare generation process. We discuss implications for the physical conditions under which flares occur, and how the sample’s metallicity and multiplicity affect our results. The detected flare indices, the stellar parameters for M 44 and M 45, and a copy of Table 4 are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A133. We also published all flares we validated, and stellar parameters used for M 44 and M 45 in the same location.

2018

1. K2 Ultracool Dwarfs Survey. IV. Monster Flares Observed on the Young Brown Dwarf CFHT-BD-Tau 4

   Rishi R. Paudel, John E. Gizis, D. J. Mullan,  Sarah J. Schmidt, Adam J. Burgasser, Peter K. G. Williams, and Edo Berger

   ApJ, Jul 2018

   abstract arXiv ADS

   We present photometric measurements of two superflares observed on a very young brown dwarf, CFHT-BD-Tau 4, observed during Campaign 13 of the Kepler K 2 mission. The stronger of the two superflares brightened by a factor of ̃48 relative to the quiescent photospheric level, with an increase in Kepler magnitude ∆ \tildeK_p=-4.20. It has an equivalent duration of ̃107 hr, a flare duration of 1.7 days, and an estimated total bolometric (ultraviolet/optical/infrared) energy up to 2.1 × 10³⁸ erg. The weaker of the two superflares is a complex (multipeaked) flare with an estimated total bolometric (UV/optical/IR) energy up to 4.7 × 10³⁶ erg. They are the strongest flares observed on any brown dwarf so far. The flare energies are strongly dependent on the value of the visual extinction parameter A _V used for extinction correction. If we apply a solar flare model to interpret the two superflares, we find that the magnetic fields are required to be stronger by as much as an order of magnitude than previous reports of field measurements in CFHT-BD-Tau 4 by Reiners et al. On the other hand, if we interpret our data in terms of accretion, we find that the requisite rate of accretion for the stronger superflare exceeds the rates that have been reported for other young brown dwarfs.

2. K2 Ultracool Dwarfs Survey. III. White Light Flares Are Ubiquitous in M6-L0 Dwarfs

   Rishi R. Paudel, John E. Gizis, D. J. Mullan,  Sarah J. Schmidt, Adam J. Burgasser, Peter K. G. Williams, and Edo Berger

   ApJ, May 2018

   abstract arXiv ADS

   We report the white light flare rates for 10 ultracool dwarfs using Kepler K2 short-cadence data. Among our sample stars, two have spectral type M6, three are M7, three are M8, and two are L0. Most of our targets are old low-mass stars. We identify a total of 283 flares in all of the stars in our sample, with Kepler energies in the range log E _Kp ˜ (29-33.5) erg. Using the maximum-likelihood method of line fitting, we find that the flare frequency distribution (FFD) for each star in our sample follows a power law with slope -α in the range -(1.3-2.0). We find that cooler objects tend to have shallower slopes. For some of our targets, the FFD follows either a broken power law, or a power law with an exponential cutoff. For the L0 dwarf 2MASS J12321827-0951502, we find a very shallow slope (-α = -1.3) in the Kepler energy range (0.82-130) × 10³⁰ erg: this L0 dwarf has flare rates which are comparable to those of high-energy flares in stars of earlier spectral types. In addition, we report photometry of two superflares: one on the L0 dwarf 2MASS J12321827-0951502 and another on the M7 dwarf 2MASS J08352366+1029318. In the case of 2MASS J12321827-0951502, we report a flare brightening by a factor of ̃144 relative to the quiescent photospheric level. Likewise, for 2MASS J08352366+1029318, we report a flare brightening by a factor of ̃60 relative to the quiescent photospheric level. These two superflares have bolometric (ultraviolet/optical/infrared) energies 3.6 × 10³³ erg and 8.9 × 10³³ erg respectively, while the full width half maximum timescales are very short,˜2 min. We find that the M8 star TRAPPIST-1 is more active than the M8.5 dwarf 2M03264453+1919309, but less active than another M8 dwarf (2M12215066-0843197).

3. 2MASS J11151597+1937266: A Young, Dusty, Isolated, Planetary-mass Object with a Potential Wide Stellar Companion

   Christopher A. Theissen, Adam J. Burgasser, Daniella C. Bardalez Gagliuffi, Kevin K. Hardegree-Ullman, Jonathan Gagné,  Sarah J. Schmidt, and Andrew A. West

   ApJ, Jan 2018

   abstract arXiv ADS

   We present 2MASS J11151597+1937266, a recently identified low-surface-gravity L dwarf, classified as an L2γ based on Sloan Digital Sky Survey optical spectroscopy. We confirm this spectral type with near-infrared spectroscopy, which provides further evidence that 2MASS J11151597+1937266 is a low-surface-gravity L dwarf. This object also shows significant excess mid-infrared flux, indicative of circumstellar material; and its strong Hα emission (EW_Hα = 560 ± 82 Å) is an indicator of enhanced magnetic activity or weak accretion. Comparison of its spectral energy distribution to model photospheres yields an effective temperature of 1724_-38⁺¹⁸⁴ K. We also provide a revised distance estimate of 37 ± 6 pc using a spectral type-luminosity relationship for low-surface-gravity objects. The three-dimensional galactic velocities and positions of 2MASS J11151597+1937266 do not match any known young association or moving group. Assuming a probable age in the range of 5-45 Myr, the model-dependent estimated mass of this object is between 7 and 21 M _Jup, making it a potentially isolated planetary-mass object. We also identify a candidate co-moving, young stellar companion, 2MASS J11131089+2110086.

4. The Time-domain Spectroscopic Survey: Target Selection for Repeat Spectroscopy

   Chelsea L. MacLeod, Paul J. Green, Scott F. Anderson, Michael Eracleous, John J. Ruan, Jessie Runnoe, William Nielsen Brand t, Carles Badenes, Jenny Greene, Eric Morganson, and 28 more authors

   AJ, Jan 2018

   abstract arXiv ADS

   As astronomers increasingly exploit the information available in the time domain, spectroscopic variability in particular opens broad new channels of investigation. Here we describe the selection algorithms for all targets intended for repeat spectroscopy in the Time Domain Spectroscopic Survey (TDSS), part of the extended Baryon Oscillation Spectroscopic Survey within the Sloan Digital Sky Survey (SDSS)-IV. Also discussed are the scientific rationale and technical constraints leading to these target selections. The TDSS includes a large “repeat quasar spectroscopy” (RQS) program delivering ̃13,000 repeat spectra of confirmed SDSS quasars, and several smaller “few-epoch spectroscopy” (FES) programs targeting specific classes of quasars as well as stars. The RQS program aims to provide a large and diverse quasar data set for studying variations in quasar spectra on timescales of years, a comparison sample for the FES quasar programs, and an opportunity for discovering rare, serendipitous events. The FES programs cover a wide variety of phenomena in both quasars and stars. Quasar FES programs target broad absorption line quasars, high signal-to-noise ratio normal broad line quasars, quasars with double-peaked or very asymmetric broad emission line profiles, binary supermassive black hole candidates, and the most photometrically variable quasars. Strongly variable stars are also targeted for repeat spectroscopy, encompassing many types of eclipsing binary systems, and classical pulsators like RR Lyrae. Other stellar FES programs allow spectroscopic variability studies of active ultracool dwarf stars, dwarf carbon stars, and white dwarf/M dwarf spectroscopic binaries. We present example TDSS spectra and describe anticipated sample sizes and results.

2017

1. The Effect of Atmospheric Cooling on Vertical Velocity Dispersion and Density Distribution of Brown Dwarfs

   Jr. Ryan, Paul A. Thorman,  Sarah J. Schmidt, Seth H. Cohen, Nimish P. Hathi, Benne W. Holwerda, Jonathan I. Lunine, Nor Pirzkal, Rogier A. Windhorst, and Erick Young

   ApJ, Sep 2017

   abstract arXiv ADS

   We present a Monte Carlo simulation designed to predict the vertical velocity dispersion of brown dwarfs in the Milky Way. We show that since these stars are constantly cooling, the velocity dispersion has a noticeable trend with the spectral type. With realistic assumptions for the initial mass function, star formation history, and the cooling models, we show that the velocity dispersion is roughly consistent with what is observed for M dwarfs, decreases to cooler spectral types, and increases again for the coolest types in our study (̃T9). We predict a minimum in the velocity dispersions for L/T transition objects, however, the detailed properties of the minimum predominately depend on the star formation history. Since this trend is due to brown dwarf cooling, we expect that the velocity dispersion as a function of spectral type should deviate from the constancy around the hydrogen-burning limit. We convert from velocity dispersion to vertical scale height using standard disk models and present similar trends in disk thickness as a function of spectral type. We suggest that future, wide-field photometric and/or spectroscopic missions may collect sizable samples of distant (̃ 1 kpc) dwarfs that span the hydrogen-burning limit. As such, we speculate that such observations may provide a unique way of constraining the average spectral type of hydrogen burning. Support for program #13266 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under the NASA contract NAS 5-26555.

2. K2 Ultracool Dwarfs Survey. II. The White Light Flare Rate of Young Brown Dwarfs

   John E. Gizis, Rishi R. Paudel, Dermott Mullan,  Sarah J. Schmidt, Adam J. Burgasser, and Peter K. G. Williams

   ApJ, Aug 2017

   abstract arXiv ADS

   We use Kepler K2 Campaign 4 short-cadence (one-minute) photometry to measure white light flares in the young, moving group brown dwarfs 2MASS J03350208+2342356 (2M0335+23) and 2MASS J03552337+1133437 (2M0355+11), and report on long-cadence (thirty-minute) photometry of a superflare in the Pleiades M8 brown dwarf CFHT-PL-17. The rotation period (5.24 hr) and projected rotational velocity (45 km s^-1) confirm 2M0335+23 is inflated (R≥slant 0.20 R_☉ ) as predicted for a 0.06 M_☉ , 24 Myr old brown dwarf βPic moving group member. We detect 22 white light flares on 2M0335+23. The flare frequency distribution follows a power-law distribution with slope -α =-1.8± 0.2 over the range 10³¹ to 10³³ erg. This slope is similar to that observed in the Sun and warmer flare stars, and is consistent with lower-energy flares in previous work on M6-M8 very-low-mass stars; taking the two data sets together, the flare frequency distribution for ultracool dwarfs is a power law over 4.3 orders of magnitude. The superflare (2.6× 10³⁴ erg) on CFHT-PL-17 shows higher-energy flares are possible. We detect no flares down to a limit of 2× 10³⁰ erg in the nearby L5γ AB Dor moving group brown dwarf 2M0355+11, consistent with the view that fast magnetic reconnection is suppressed in cool atmospheres. We discuss two multi-peaked flares observed in 2M0335+23, and argue that these complex flares can be understood as sympathetic flares, in which fast-mode magnetohydrodynamic waves similar to extreme-ultraviolet waves in the Sun trigger magnetic reconnection in different active regions.

3. Who asks questions at astronomy meetings?

   Sarah J. Schmidt, and James R. A. Davenport

   Nature Astronomy, Jun 2017

   abstract arXiv ADS

   Over the last decade, significant attention has been drawn to the gender ratio of speakers at conferences, with ongoing efforts for meetings to better reflect the gender representation in the field. We find that women are significantly under-represented, however, among the astronomers asking questions after talks.

4. K2 Ultracool Dwarfs Survey. I. Photometry of an L Dwarf Superflare

   John E. Gizis, Rishi R. Paudel,  Sarah J. Schmidt, Peter K. G. Williams, and Adam J. Burgasser

   ApJ, Mar 2017

   abstract arXiv ADS

   We report on K2 Campaign 8 measurements of a huge white light flare on the L1 dwarf SDSSp J005406.55-003101.8 (EPIC 220186653). The source is a typical L1 dwarf at a distance of ̃50 pc, probably an old hydrogen-burning star rather than a young brown dwarf. In the long (30-minute) cadence photometry, the flare peak is 21 times the flux of the stellar photosphere in the broad optical Kepler filter, which we estimate corresponds to ∆V ≈ -7.1. The total equivalent duration of the flare is 15.4 hr. We estimate that the total bolometric energy of the flare was 4 × 10³³ erg, more powerful than the previously reported Kepler white light flares for the L1 dwarf WISEP J190648.47+401106.8, but weaker than the ∆V = -11 L0 dwarf superflare ASASSN-16ae. The initial (impulsive) cooling phase is too rapid to resolve with our 30-minute cadence data, but after 1 hour the gradual cooling phase has an exponential time constant of 1.8 hr. We use template fitting to estimate that the full time-width-at-half-amplitude of the light curve is <10 minutes and that the true flare maximum reached ̃70 times the stellar photosphere, or ∆V ≈ -8. This flare is comparable to the most powerful Kepler flares observed on the active M4 dwarf GJ 1243.

5. The Late-Type Extension to MoVeRS (LaTE-MoVeRS): Proper Motion Verified Low-mass Stars and Brown Dwarfs from SDSS, 2MASS, and WISE

   Christopher A. Theissen, Andrew A. West, Guillaume Shippee, Adam J. Burgasser, and  Sarah J. Schmidt

   AJ, Mar 2017

   abstract arXiv ADS

   We present the Late-Type Extension to the Motion Verified Red Stars (LaTE-MoVeRS) catalog, containing 46,463 photometric late-type (>M5) dwarfs within the Sloan Digital Sky Survey (SDSS) footprint. Proper motions were computed for objects combining astrometry from the SDSS Data Release 12 (DR12), the Two-micron All-Sky Survey (2MASS) Point Source Catalog, and the Wide-field Infrared Survey Explorer (WISE) AllWISE data sets. LaTE-MoVeRS objects were required to have significant proper motion (μ _tot≥ 2σ _{μ tot}). Using the LaTE-MoVeRS sample and Gaia Data Release 1, we estimate Gaia will be ̃64% complete for very low-mass objects (>M5) in comparison to the combined SDSS+2MASS+WISE data set (I< 21.3). We computed photometric distances and estimated stellar effective temperatures for the LaTE-MoVeRS catalog. The majority of the dwarfs in the sample have distances < 150 pc and T_eff< 3000 K. Thirteen objects that have not been previously identified as nearby objects were identified within LaTE-MoVeRS with estimated photometric distances within 25 pc. We also identified one new object that has not been previously identified with a large amount of excess mid-infrared flux (2MASS J11151597+1937266). This object appears to be an L2γ at ˜50 pc showing spectroscopic signs of a flaring event (e.g., strong hydrogen Balmer emission lines). This object does not exhibit kinematics similar to any known kinematic association. The LaTE-MoVeRS catalog is available through SDSS CasJobs and VizieR.

2016

1. ASASSN-16ae: A Powerful White-light Flare on an Early-L Dwarf

   Sarah J. Schmidt, Benjamin J. Shappee, Jonathan Gagné, K. Z. Stanek, José L. Prieto, Thomas W. -S. Holoien, C. S. Kochanek, Laura Chomiuk, Subo Dong, Mark Seibert, and 1 more author

   ApJL, Sep 2016

   abstract arXiv ADS

   We report the discovery and classification of SDSS J053341.43+001434.1 (SDSS0533), an early-L dwarf first discovered during a powerful ∆V < -11 magnitude flare observed as part of the ASAS-SN survey. Optical and infrared spectroscopy indicate a spectral type of L0 with strong Hα emission and a blue NIR spectral slope. Combining the photometric distance, proper motion, and radial velocity of SDSS0533 yields three-dimensional velocities of (U, V, W) = (14±13, -35±14, -94±22) km s^-1, indicating that it is most likely part of the thick disk population and probably old. The three detections of SDSS0533 obtained during the flare are consistent with a total V-band flare energy of at least 4.9 × 10³³ erg (corresponding to a total thermal energy of at least E _tot > 3.7 × 10³⁴ erg), placing it among the strongest detected M dwarf flares. The presence of this powerful flare on an old L0 dwarf may indicate that stellar-type magnetic activity persists down to the end of the main sequence and on older ML transition dwarfs.

2. Examining the relationships between colour, T_eff, and [M/H] for APOGEE K and M dwarfs

   Sarah J. Schmidt, Erika L. Wagoner, Jennifer A. Johnson, James R. A. Davenport, Keivan G. Stassun, Diogo Souto, and Jian Ge

   MNRAS, Aug 2016

   abstract arXiv ADS

   We present the effective temperatures (T_eff), metallicities, and colours in Sloan Digital Sky Survey (SDSS), Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer filters, of a sample of 3834 late-K and early-M dwarfs selected from the SDSS Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectroscopic survey ASPCAP (APOGEE Stellar Parameters and Chemical Abundances Pipeline) catalogue. We confirm that ASPCAP T_eff values between 3550 < T_eff < 4200 K are accurate to ̃100 K compared to interferometric T_eff values. In that same T_eff range, ASPCAP metallicities are accurate to 0.18 dex between -1.0 <[M/H]<0.2. For these cool dwarfs, nearly every colour is sensitive to both T_eff and metallicity. Notably, we find that g - r is not a good indicator of metallicity for near-solar metallicity early-M dwarfs. We confirm that J - K_S colour is strongly dependent on metallicity, and find that W1 - W2 colour is a promising metallicity indicator. Comparison of the late-K and early-M dwarf colours, metallicities, and T_eff to those from three different model grids shows reasonable agreement in r - z and J - K_S colours, but poor agreement in u - g, g - r, and W1 - W2. Comparison of the metallicities of the KM dwarf sample to those from previous colour-metallicity relations reveals a lack of consensus in photometric metallicity indicators for late-K and early-M dwarfs. We also present empirical relations for T_eff as a function of r - z colour combined with either [M/H] or W1 - W2 colour, and for [M/H] as a function of r - z and W1 - W2 colour. These relations yield T_eff to ̃100 K and [M/H] to ̃0.18 dex precision with colours alone, for T_eff in the range of 3550-4200 K and [M/H] in the range of -0.5-0.2.

3. The Time-Domain Spectroscopic Survey: Understanding the Optically Variable Sky with SEQUELS in SDSS-III

   John J. Ruan, Scott F. Anderson, Paul J. Green, Eric Morganson, Michael Eracleous, Adam D. Myers, Carles Badenes, Matthew A. Bershady, William N. Brandt, Kenneth C. Chambers, and 20 more authors

   ApJ, Jul 2016

   abstract arXiv ADS

   The Time-Domain Spectroscopic Survey (TDSS) is an SDSS-IV eBOSS subproject primarily aimed at obtaining identification spectra of ̃220,000 optically variable objects systematically selected from SDSS/Pan-STARRS1 multi-epoch imaging. We present a preview of the science enabled by TDSS, based on TDSS spectra taken over ̃320 deg² of sky as part of the SEQUELS survey in SDSS-III, which is in part a pilot survey for eBOSS in SDSS-IV. Using the 15,746 TDSS-selected single-epoch spectra of photometrically variable objects in SEQUELS, we determine the demographics of our variability-selected sample and investigate the unique spectral characteristics inherent in samples selected by variability. We show that variability-based selection of quasars complements color-based selection by selecting additional redder quasars and mitigates redshift biases to produce a smooth quasar redshift distribution over a wide range of redshifts. The resulting quasar sample contains systematically higher fractions of blazars and broad absorption line quasars than from color-selected samples. Similarly, we show that M dwarfs in the TDSS-selected stellar sample have systematically higher chromospheric active fractions than the underlying M-dwarf population based on their Hα emission. TDSS also contains a large number of RR Lyrae and eclipsing binary stars with main-sequence colors, including a few composite-spectrum binaries. Finally, our visual inspection of TDSS spectra uncovers a significant number of peculiar spectra, and we highlight a few cases of these interesting objects. With a factor of ̃15 more spectra, the main TDSS survey in SDSS-IV will leverage the lessons learned from these early results for a variety of time-domain science applications.

2015

1. The Brown Dwarf Kinematics Project (BDKP). IV. Radial Velocities of 85 Late-M and L Dwarfs with MagE

   Adam J. Burgasser, Sarah E. Logsdon, Jonathan Gagné, John J. Bochanski, Jaqueline K. Faherty, Andrew A. West, Eric E. Mamajek,  Sarah J. Schmidt, and Kelle L. Cruz

   ApJs, Sep 2015

   abstract arXiv ADS

   Radial velocity measurements are presented for 85 late M- and L-type very low-mass stars and brown dwarfs obtained with the Magellan Echellette spectrograph. Targets primarily have distances within 20 pc of the Sun, with more distant sources selected for their unusual spectral energy distributions. We achieved precisions of 2-3 km s^-1, and combined these with astrometric and spectrophotometric data to calculate UVW velocities. Most are members of the thin disk of the Galaxy, and velocity dispersions indicate a mean age of 5.2&pm;0.2 Gyr for sources within 20 pc. We find signficantly different kinematic ages between late-M dwarfs (4.0&pm;0.2 Gyr) and L dwarfs (6.5&pm;0.4 Gyr) in our sample that are contrary to predictions from prior simulations. This difference appears to be driven by a dispersed population of unusually blue L dwarfs which may be more prevalent in our local volume-limited sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an asymmetric U velocity distribution with a net inward flow, similar to gradients recently detected in local stellar samples. Simulations incorporating brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L dwarf populations. We also find the L dwarfs to have a kinematic age-activity correlation similar to more massive stars. We identify several sources with low surface gravities, and two new substellar candidate members of nearby young moving groups: the astrometric binary DENIS J08230313-4912012AB, a low-probability member of the β Pictoris Moving Group; and 2MASS J15104786-2818174, a moderate-probability member of the 30-50 Myr Argus Association.

2. The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III

   Shadab Alam, Franco D. Albareti, Carlos Allende Prieto, F. Anders, Scott F. Anderson, Timothy Anderton, Brett H. Andrews, Eric Armengaud, Éric Aubourg, Stephen Bailey, and 294 more authors

   ApJS, Jul 2015

   abstract arXiv ADS

   The third generation of the Sloan Digital Sky Survey (SDSS-III) took data from 2008 to 2014 using the original SDSS wide-field imager, the original and an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared high-resolution spectrograph, and a novel optical interferometer. All of the data from SDSS-III are now made public. In particular, this paper describes Data Release 11 (DR11) including all data acquired through 2013 July, and Data Release 12 (DR12) adding data acquired through 2014 July (including all data included in previous data releases), marking the end of SDSS-III observing. Relative to our previous public release (DR10), DR12 adds one million new spectra of galaxies and quasars from the Baryon Oscillation Spectroscopic Survey (BOSS) over an additional 3000 deg² of sky, more than triples the number of H-band spectra of stars as part of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE), and includes repeated accurate radial velocity measurements of 5500 stars from the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The APOGEE outputs now include the measured abundances of 15 different elements for each star. In total, SDSS-III added 5200 deg² of ugriz imaging; 155,520 spectra of 138,099 stars as part of the Sloan Exploration of Galactic Understanding and Evolution 2 (SEGUE-2) survey; 2,497,484 BOSS spectra of 1,372,737 galaxies, 294,512 quasars, and 247,216 stars over 9376 deg²; 618,080 APOGEE spectra of 156,593 stars; and 197,040 MARVELS spectra of 5513 stars. Since its first light in 1998, SDSS has imaged over 1/3 of the Celestial sphere in five bands and obtained over five million astronomical spectra.

3. BOSS Ultracool Dwarfs. I. Colors and Magnetic Activity of M and L Dwarfs

   Sarah J. Schmidt, Suzanne L. Hawley, Andrew A. West, John J. Bochanski, James R. A. Davenport, Jian Ge, and Donald P. Schneider

   AJ, May 2015

   abstract arXiv ADS

   We present the colors and activity of ultracool (M7-L8) dwarfs from the Tenth Data Release of the Sloan Digital Sky Survey (SDSS). We combine previous samples of SDSS M and L dwarfs with new data obtained from the Baryon Oscillation Sky Survey (BOSS) to produce the BOSS Ultracool Dwarf (BUD) sample of 11820 M7-L8 dwarfs. By combining SDSS data with photometry from 2MASS and the Wide-field Infrared Sky Explorer (WISE) mission, we present ultracool dwarf colors from i-z to W2-W3 as a function of spectral type, and extend the SDSS-2MASS-WISE color locus to include ultracool dwarfs. The i-z, i-J, and z-J colors provide the best indication of spectral type for M7-L3 dwarfs. We also examine ultracool dwarf chromospheric activity through the presence and strength of Hα emission. The fraction of active dwarfs rises through the M spectral sequence until it reaches ̃90% at spectral type L0. The fraction of active dwarfs then declines to 50% at spectral type L5; no Hα emission is observed in the late-L dwarfs in the BUD sample. The fraction of active L0-L5 dwarfs is much higher than previously observed. The strength of activity declines with spectral type from M7 through L3, after which the data do not show a clear trend. Using one-dimensional chromosphere models, we explore the range of filling factors and chromospheric temperature structures that are consistent with Hα observations of M0-L7 dwarfs. M dwarf chromospheres have a similar, smoothly varying range of temperature and surface coverage, while L dwarf chromospheres are cooler and have smaller filling factors.

4. The Continued Optical to Mid-Infrared Evolution of V838 Monocerotis

   S. R. Loebman, J. P. Wisniewski,  S. J. Schmidt, A. F. Kowalski, R. K. Barry, K. S. Bjorkman, H. B. Hammel, S. L. Hawley, L. Hebb, M. M. Kasliwal, and 4 more authors

   AJ, Jan 2015

   abstract arXiv ADS

   The eruptive variable V838 Monocerotis (V838 Mon) gained notoriety in 2002 when it brightened nine magnitudes in a series of three outbursts and then rapidly evolved into an extremely cool supergiant. We present optical, near-infrared (near-IR), and mid-IR spectroscopic and photometric observations of V838 Mon obtained between 2008 and 2012 at the Apache Point Observatory 3.5 m, NASA IRTF 3 m, and Gemini South 8 m telescopes. We contemporaneously analyze the optical and IR spectroscopic properties of V838 Mon to arrive at a revised spectral type L3 supergiant and effective temperature T_eff̃ 2000-2200 K. Because there are no existing optical observational data for L supergiants, we speculate that V838 Mon may represent the prototype for L supergiants in this wavelength regime. We find a low level of Hα emission present in the system, consistent with interaction between V838 Mon and its B3V binary; however, we cannot rule out a stellar collision as the genesis event, which could result in the observed Hα activity. Based upon a two-component blackbody fit to all wavelengths of our data, we conclude that, as of 2009, a shell of ejecta surrounded V838 Mon at a radius of R=263+/- 10 AU with a temperature of T=285+/- 2 K. This result is consistent with IR interferometric observations from the same era and predictions from the Lynch et al. model of the expanding system, which provides a simple framework for understanding this complicated system. This publication is partially based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.

2014

1. Hα Emission From Active Equal-Mass, Wide M Dwarf Binaries

   Heather C. Gunning,  Sarah J. Schmidt, James R. A. Davenport, Saurav Dhital, Suzanne L. Hawley, and Andrew A. West

   PASP, Dec 2014

   abstract arXiv ADS

   We identify a sample of near-equal mass wide binary M dwarf systems from the SLoWPoKES catalog of common proper-motion binaries and obtain follow-up observations of their chromospheric activity as measured by the Hα emission line. We present optical spectra for both components of 48 candidate M dwarf binaries, confirming their mid-M spectral types. Of those 48 coeval pairs, we find eight with Hα emission from both components, three with weak emission in one component and no emission in the other, and 37 with two inactive components. We find that of the eleven pairs with at least one active component, only three follow the net trend of decreasing activity strength LHα/Lbol with later spectral type. The difference in quiescent activity strength between the A and B components is larger than what would be expected based on the small differences in color (mass). For five binaries with two active components, we present 47 hours of time-resolved spectroscopy, observed on the ARC 3.5-m over twelve different nights. For four of the five pairs, the slightly redder (B) component exhibits a higher level of Hα emission during the majority of the observations and the redder objects are the only components to flare. The full range of Hα emission observed on these variable mid-M dwarfs is comparable to the scatter in Hα emission found in single-epoch surveys of mid-M dwarfs, indicating that variability could be a major factor in the spread of observed activity strengths. We also find that variability is independent of both activity strength and spectral type.

2. SpeX Spectroscopy of Unresolved Very Low Mass Binaries. II. Identification of 14 Candidate Binaries with Late-M/Early-L and T Dwarf Components

   Daniella C. Bardalez Gagliuffi, Adam J. Burgasser, Christopher R. Gelino, Dagny L. Looper, Christine P. Nicholls,  Sarah J. Schmidt, Kelle Cruz, Andrew A. West, John E. Gizis, and Stanimir Metchev

   ApJ, Oct 2014

   abstract arXiv ADS

   Multiplicity is a key statistic for understanding the formation of very low mass (VLM) stars and brown dwarfs. Currently, the separation distribution of VLM binaries remains poorly constrained at small separations (<=1 AU), leading to uncertainty in the overall binary fraction. We approach this problem by searching for late-M/early-L plus T dwarf spectral binaries whose combined light spectra exhibit distinct peculiarities, allowing for separation-independent identification. We define a set of spectral indices designed to identify these systems, and we use a spectral template fitting method to confirm and characterize spectral binary candidates from a library of 815 spectra from the SpeX Prism Spectral Libraries. We present 11 new binary candidates, confirm 3 previously reported candidates, and rule out 2 previously identified candidates, all with primary and secondary spectral types in the range M7-L7 and T1-T8, respectively. We find that subdwarfs and blue L dwarfs are the primary contaminants in our sample and propose a method for segregating these sources. If confirmed by follow-up observations, these systems may add to the growing list of tight separation binaries, whose orbital properties may yield further insight into brown dwarf formation scenarios.

3. Spatially resolved measurements of H_2O, HCl, CO, OCS, SO_2, cloud opacity, and acid concentration in the Venus near-infrared spectral windows

   Giada Arney, Victoria Meadows, David Crisp,  Sarah J. Schmidt, Jeremy Bailey, and Tyler Robinson

   Journal of Geophysical Research (Planets), Aug 2014

   abstract ADS

   We observed Venus with the Apache Point Observatory 3.5 m telescope TripleSpec spectrograph (R = 3500, λ = 0.96-2.47 µm) on 1-3 March 2009 and on 25, 27, and 30 November and 2-4 December 2010. With these observations and synthetic spectra generated with the Spectral Mapping and Atmospheric Radiative Transfer model, we produce the first simultaneous maps of cloud opacity, acid concentration, water vapor (H₂O), hydrogen chloride (HCl), carbon dioxide (CO), carbonyl sulfide (OCS), and sulfur dioxide (SO₂) abundances in the Venusian lower atmosphere. Water measured at wavelengths near 1.18 µm (near-surface) averages 29 \pm 2ppm (2009) and 27 \pm 2 ppm (2010) and measured near 1.74 µm (15-30 km) averages 33 \pm 2 ppm (2009) and 32 \pm 2 ppm (2010). Water in both these altitude ranges is spatially homogeneous. Water measured near 2.4 µm (30-45 km) averages 34 \pm 2 ppm (2009) and 33 \pm 3 ppm (2010) and is spatially inhomogeneous and variable. HCl is measured near 1.74 µm to be 0.41 \pm 0.04 ppm (2009) and 0.42 \pm 0.05 ppm (2010). CO and OCS (2.3-2.5 µm; 30-45 km in altitude) are spatially inhomogeneous and show anticorrelation. CO (35 km) averages 25 \pm 3 ppm (2009) and 22 \pm 2 ppm (2010). OCS (36 km) averages 0.44 \pm 0.10 ppm (2009) and 0.57 \pm 0.12 ppm (2010). SO₂ measurements average 140 \pm 37 ppm (2009) and 126 \pm 32 ppm (2010). Many species display a hemispherical dichotomy in their distribution. We find considerable spatial variability suggesting active processes with conservation between species. The most variable regions are just below the Venus cloud deck, and these may be related to changes in atmospheric circulation or virga events.

4. Calibrating Ultracool Dwarfs: Optical Template Spectra, Bolometric Corrections, and χ Values

   Sarah J. Schmidt, Andrew A. West, John J. Bochanski, Suzanne L. Hawley, and Collin Kielty

   PASP, Jul 2014

   abstract arXiv ADS

   We present optical template spectra, bolometric corrections, and χ values for ultracool dwarfs. The templates are based on spectra from the Sloan Digital Sky Survey (SDSS) and the Astrophysical Research Consortium 3.5-m telescope. The spectral features and overall shape of the L dwarf templates are consistent with previous spectroscopic standards and the templates have a radial velocity precision of ∼10–20 km s−1. We calculate bolometric fluxes (accurate to 10–20%) for 101 late-M and L dwarfs from SDSS, 2MASS, and WISE photometry, SDSS spectra, and BT-Settl model spectra. We find that the z- and J-band bolometric corrections for late-M and L dwarfs have a strong correlation with z−J and J−KS colors respectively. The new χ values, which can be used to convert Hα equivalent widths to activity strength, are based on spectrophotometrically calibrated SDSS spectra and the new bolometric fluxes. While the measured χ values have typical uncertainties of ∼20%, ultracool dwarf models show the continuum surrounding Hα can vary by up to an order of magnitude with changing surface gravity. Our semi-empirical χ values are one to two orders of magnitude larger than previous χ values for mid- to late-L dwarfs, indicating that the upper limits for Hα activity strength on the coolest L dwarfs have been underestimated.

5. The Tenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Apache Point Observatory Galactic Evolution Experiment

   Christopher P. Ahn, Rachael Alexandroff, Carlos Allende Prieto, Friedrich Anders, Scott F. Anderson, Timothy Anderton, Brett H. Andrews, Éric Aubourg, Stephen Bailey, Fabienne A. Bastien, and 228 more authors

   ApJS, Apr 2014

   abstract arXiv ADS

   The Sloan Digital Sky Survey (SDSS) has been in operation since 2000 April. This paper presents the Tenth Public Data Release (DR10) from its current incarnation, SDSS-III. This data release includes the first spectroscopic data from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE), along with spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS) taken through 2012 July. The APOGEE instrument is a near-infrared R   22,500 300 fiber spectrograph covering 1.514-1.696 μm. The APOGEE survey is studying the chemical abundances and radial velocities of roughly 100,000 red giant star candidates in the bulge, bar, disk, and halo of the Milky Way. DR10 includes 178,397 spectra of 57,454 stars, each typically observed three or more times, from APOGEE. Derived quantities from these spectra (radial velocities, effective temperatures, surface gravities, and metallicities) are also included. DR10 also roughly doubles the number of BOSS spectra over those included in the Ninth Data Release. DR10 includes a total of 1,507,954 BOSS spectra comprising 927,844 galaxy spectra, 182,009 quasar spectra, and 159,327 stellar spectra selected over 6373.2 deg².

6. Characterizing a Dramatic ∆V~-9 Flare on an Ultracool Dwarf Found by the ASAS-SN Survey

   Sarah J. Schmidt, Jose L. Prieto, K. Z. Stanek, Benjamin J. Shappee, Nidia Morrell, Daniella C. Bardalez Gagliuffi, C. S. Kochanek, J. Jencson, T. W. -S. Holoien, U. Basu, and 12 more authors

   ApJL, Feb 2014

   abstract arXiv ADS

   We analyze a ∆V~-9 magnitude flare on the newly identified M8 dwarf SDSS J022116.84+194020.4 (hereafter SDSSJ0221) detected as part of the All-Sky Automated Survey for Supernovae. Using infrared and optical spectra, we confirm that SDSSJ0221 is a relatively nearby (d~76 pc) M8 dwarf with strong quiescent Hα emission. Based on kinematics and the absence of features consistent with low-gravity (young) ultracool dwarfs, we place a lower limit of 200 Myr on the age of SDSSJ0221. When modeled with a simple, classical flare light curve, this flare is consistent with a total U-band flare energy E_U~10³⁴ erg, confirming that the most dramatic flares are not limited to warmer, more massive stars. Scaled to include a rough estimate of the emission line contribution to the V band, we estimate a blackbody filling factor of ~10%-30% during the flare peak and ~0.5%-1.6% during the flare decay phase. These filling factors correspond to flare areas that are an order of magnitude larger than those measured for most mid-M dwarf flares. This publication is partially based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.

2013

1. Time-resolved Properties and Global Trends in dMe Flares from Simultaneous Photometry and Spectra

   Adam F. Kowalski, Suzanne L. Hawley, John P. Wisniewski, Rachel A. Osten, Eric J. Hilton, Jon A. Holtzman,  Sarah J. Schmidt, and James R. A. Davenport

   ApJs, Jul 2013

   abstract arXiv ADS

   We present a homogeneous analysis of line and continuum emission from simultaneous high-cadence spectra and photometry covering near-ultraviolet and optical wavelengths for 20 M dwarf flares. These data were obtained to study the white-light continuum components at bluer and redder wavelengths than the Balmer jump. Our goals were to break the degeneracy between emission mechanisms that have been fit to broadband colors of flares and to provide constraints for radiative-hydrodynamic (RHD) flare models that seek to reproduce the white-light flare emission. The main results from the analysis are the following: (1) the detection of Balmer continuum (in emission) that is present during all flares and with a wide range of relative contributions to the continuum flux at bluer wavelengths than the Balmer jump; (2) a blue continuum at flare maximum that is linearly decreasing with wavelength from λ = 4000-4800 Å, indicative of hot, blackbody emission with typical temperatures of T _BB   9000-14, 000 K (3) a redder continuum apparent at wavelengths longer than Hβ (λ >  4900 Å) which becomes relatively more important to the energy budget during the late gradual phase. The hot blackbody component and redder continuum component have been detected in previous studies of flares. However, we have found that although the hot blackbody emission component is relatively well-represented by a featureless, single-temperature Planck function, this component includes absorption features and has a continuum shape strikingly similar to the spectrum of an A-type star as directly observed in our flare spectra. New model constraints are presented for the time evolution among the hydrogen Balmer lines and between Ca II K and the blackbody continuum emission. We calculate Balmer jump flux ratios and compare to the solar-type flare heating predictions from RHD models. The model ratios are too large and the blue-optical (λ = 4000-4800 Å) slopes are too red in both the impulsive and gradual decay phases of all 20 flares. This discrepancy implies that further work is needed to understand the heating at high column mass during dMe flares. Based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.

2. The Baryon Oscillation Spectroscopic Survey of SDSS-III

   Kyle S. Dawson, David J. Schlegel, Christopher P. Ahn, Scott F. Anderson, Éric Aubourg, Stephen Bailey, Robert H. Barkhouser, Julian E. Bautista, Alessand ra Beifiori, Andreas A. Berlind, and 155 more authors

   AJ, Jan 2013

   abstract arXiv ADS

   The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large-scale structure. BOSS uses 1.5 million luminous galaxies as faint as i = 19.9 over 10,000 deg² to measure BAO to redshifts z < 0.7. Observations of neutral hydrogen in the Lyα forest in more than 150,000 quasar spectra (g < 22) will constrain BAO over the redshift range 2.15 < z < 3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Lyα forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance d_A to an accuracy of 1.0% at redshifts z = 0.3 and z = 0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Lyα forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate D_A (z) and H ^-1(z) parameters to an accuracy of 1.9% at z   2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS.

2012

1. The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey

   Christopher P. Ahn, Rachael Alexandroff, Carlos Allende Prieto, Scott F. Anderson, Timothy Anderton, Brett H. Andrews, Éric Aubourg, Stephen Bailey, Eduardo Balbinot, Rory Barnes, and 226 more authors

   ApJS, Dec 2012

   abstract arXiv ADS

   The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z   0.52), 102,100 new quasar spectra (median z   2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T _eff < 5000 K and in metallicity estimates for stars with [Fe/H] > -0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SEGUE-2. The astrometry error introduced in the DR8 imaging catalogs has been corrected in the DR9 data products. The next data release for SDSS-III will be in Summer 2013, which will present the first data from the APOGEE along with another year of data from BOSS, followed by the final SDSS-III data release in 2014 December.

2. Multi-wavelength Characterization of Stellar Flares on Low-mass Stars Using SDSS and 2MASS Time-domain Surveys

   James R. A. Davenport, Andrew C. Becker, Adam F. Kowalski, Suzanne L. Hawley,  Sarah J. Schmidt, Eric J. Hilton, Branimir Sesar, and Roc Cutri

   ApJ, Mar 2012

   abstract arXiv ADS

   We present the first rates of flares from M dwarf stars in both red optical and near-infrared (NIR) filters. We have studied  50,000 M dwarfs from the Sloan Digital Sky Survey (SDSS) Stripe 82 area and 1321 M dwarfs from the Two Micron All Sky Survey (2MASS) Calibration Scan Point Source Working Database that overlap SDSS imaging fields. We assign photometric spectral types from M0 to M6 using (r - i) and (i - z) colors for every star in our sample. Stripe 82 stars each have 50-100 epochs of data, while 2MASS Calibration stars have  1900 epochs. From these data we estimate the observed rates and theoretical detection thresholds for flares in eight photometric bands as a function of spectral type. Optical flare rates are found to be in agreement with previous studies, while the frequency per hour of NIR flare detections is found to be more than two orders of magnitude lower. An excess of small-amplitude flux increases in all bands exhibits a power-law distribution, which we interpret as the result of flares below our detection thresholds. In order to investigate the recovery efficiency for flares in each filter, we extend a two-component flare model into the NIR. Quiescent M0-M6 spectral templates were used with the model to predict the photometric response of flares from u to K_s . We determine that red optical filters are sensitive to flares with u-band amplitudes gsim2 mag, and NIR filters to flares with ∆u gsim 4.5 mag. Our model predicts that M0 stars have the best color contrast for J-band detections, but M4-M6 stars should yield the highest rate of NIR flares with amplitudes of ∆J >= 0.01 mag. Characterizing flare rates and photometric variations at longer wavelengths is important for predicting the signatures of M dwarf variability in next-generation surveys, and we discuss their impact on surveys such as the Large Synoptic Survey Telescope.

3. Probing the Flare Atmospheres of M Dwarfs Using Infrared Emission Lines

   Sarah J. Schmidt, Adam F. Kowalski, Suzanne L. Hawley, Eric J. Hilton, John P. Wisniewski, and Benjamin M. Tofflemire

   ApJ, Jan 2012

   abstract arXiv ADS

   We present the results of a campaign to monitor active M dwarfs using infrared spectroscopy, supplemented with optical photometry and spectroscopy. We detected 16 flares during nearly 50 hr of observations on EV Lac, AD Leo, YZ CMi, and VB 8. The three most energetic flares also showed infrared emission, including the first reported detections of Pβ, Pγ, He I λ10830, and Brγ during an M dwarf flare. The strongest flare (∆u = 4.02 on EV Lac) showed emission from Hγ, Hδ, He I λ4471, and Ca II K in the UV/blue and Pβ, Pγ, Pδ, Brγ, and He I λ10830 in the infrared. The weaker flares (∆u = 1.68 on EV Lac and ∆U = 1.38 on YZ CMi) were only observed with photometry and infrared spectroscopy; both showed emission from Pβ, Pγ, and He I λ10830. The strongest infrared emission line, Pβ, occurred in the active mid-M dwarfs with a duty cycle of  3%-4%. To examine the most energetic flare, we used the static NLTE radiative transfer code RH to produce model spectra based on a suite of one-dimensional model atmospheres. Using a hotter chromosphere than previous one-dimensional atmospheric models, we obtain line ratios that match most of the observed emission lines. Based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.

4. The Implications of M Dwarf Flares on the Detection and Characterization of Exoplanets at Infrared Wavelengths

   Benjamin M. Tofflemire, John P. Wisniewski, Adam F. Kowalski,  Sarah J. Schmidt, Praveen Kundurthy, Eric J. Hilton, Jon A. Holtzman, and Suzanne L. Hawley

   AJ, Jan 2012

   abstract arXiv ADS

   We present the results of an observational campaign which obtained high-cadence, high-precision, simultaneous optical and IR photometric observations of three M dwarf flare stars for 47 hr. The campaign was designed to characterize the behavior of energetic flare events, which routinely occur on M dwarfs, at IR wavelengths to millimagnitude precision, and quantify to what extent such events might influence current and future efforts to detect and characterize extrasolar planets surrounding these stars. We detected and characterized four highly energetic optical flares having U-band total energies of  7.8 × 10³⁰ to  1.3 × 10³² erg, and found no corresponding response in the J, H, or Ks bandpasses at the precision of our data. For active dM3e stars, we find that a  1.3 × 10³² erg U-band flare (∆U _max   1.5 mag) will induce <8.3 (J), <8.5 (H), and <11.7 (Ks) mmag of a response. A flare of this energy or greater should occur less than once per 18 hr. For active dM4.5e stars, we find that a  5.1 × 10³¹ erg U-band flare (∆U _max   1.6 mag) will induce <7.8 (J), <8.8 (H), and <5.1 (Ks) mmag of a response. A flare of this energy or greater should occur less than once per 10 hr. No evidence of stellar variability not associated with discrete flare events was observed at the level of  3.9 mmag over 1 hr timescales and at the level of  5.6 mmag over 7.5 hr timescales. We therefore demonstrate that most M dwarf stellar activity and flares will not influence IR detection and characterization studies of M dwarf exoplanets above the level of  5-11 mmag, depending on the filter and spectral type. We speculate that the most energetic megaflares on M dwarfs, which occur at rates of once per month, are likely to be easily detected in IR observations with sensitivity of tens of millimagnitudes. We also discuss how recent detections of line flux enhancements during M dwarf flares could influence IR transmission spectroscopic observations of M dwarf exoplanets.

2011

1. SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way, and Extra-Solar Planetary Systems

   Daniel J. Eisenstein, David H. Weinberg, Eric Agol, Hiroaki Aihara, Carlos Allende Prieto, Scott F. Anderson, James A. Arns, Éric Aubourg, Stephen Bailey, Eduardo Balbinot, and 234 more authors

   AJ, Sep 2011

   abstract arXiv ADS

   The Sloan Digital Sky Survey (SDSS) started a new phase in 2008 August, with new instrumentation and new surveys focused on Galactic structure and chemical evolution, measurements of the baryon oscillation feature in the clustering of galaxies and the quasar Lyα forest, and a radial velocity search for planets around  8000 stars. This paper describes the first data release of SDSS-III (and the eighth counting from the beginning of the SDSS). The release includes five-band imaging of roughly 5200 deg² in the southern Galactic cap, bringing the total footprint of the SDSS imaging to 14,555 deg², or over a third of the Celestial Sphere. All the imaging data have been reprocessed with an improved sky-subtraction algorithm and a final, self-consistent photometric recalibration and flat-field determination. This release also includes all data from the second phase of the Sloan Extension for Galactic Understanding and Exploration (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars at both high and low Galactic latitudes. All the more than half a million stellar spectra obtained with the SDSS spectrograph have been reprocessed through an improved stellar parameter pipeline, which has better determination of metallicity for high-metallicity stars.

2. A Population of X-Ray Weak Quasars: PHL 1811 Analogs at High Redshift

   Jianfeng Wu, W. N. Brandt, Patrick B. Hall, Robert R. Gibson, Gordon T. Richards, Donald P. Schneider, Ohad Shemmer, Dennis W. Just, and  Sarah J. Schmidt

   ApJ, Jul 2011

   abstract arXiv ADS

   We report the results from Chandra and XMM-Newton observations of a sample of 10 type 1 quasars selected to have unusual UV emission-line properties (weak and blueshifted high-ionization lines; strong UV Fe emission) similar to those of PHL 1811, a confirmed intrinsically X-ray weak quasar. These quasars were identified by the Sloan Digital Sky Survey at high redshift (z ≈ 2.2); eight are radio quiet while two are radio intermediate. All of the radio-quiet PHL 1811 analogs, without exception, are notably X-ray weak by a mean factor of ≈13. These sources lack broad absorption lines and have blue UV/optical continua, supporting the hypothesis that they are intrinsically X-ray weak like PHL 1811 itself. However, their average X-ray spectrum appears to be harder than those of typical quasars, which may indicate the presence of heavy intrinsic X-ray absorption. Our sample of radio-quiet PHL 1811 analogs supports a connection between an X-ray weak spectral energy distribution and PHL 1811-like UV emission lines; this connection provides an economical way to identify X-ray weak type 1 quasars. The fraction of radio-quiet PHL 1811 analogs in the radio-quiet quasar population is estimated to be <  1.2%. We have investigated correlations between relative X-ray brightness and UV emission-line properties (e.g., C IV equivalent width and blueshift) for a sample combining our radio-quiet PHL 1811 analogs, PHL 1811 itself, and typical type 1 quasars. These correlation analyses suggest that PHL 1811 analogs may have extreme wind-dominated broad emission-line regions. Observationally, the radio-quiet PHL 1811 analogs appear to be a subset (≈30%) of radio-quiet weak-line quasars (WLQs). The existence of a subset of quasars in which high-ionization "shielding gas" covers most of the broad emission-line region (BELR), but little more than the BELR, could potentially unify the PHL 1811 analogs and WLQs. The two radio-intermediate PHL 1811 analogs are X-ray bright. X-ray spectral analyses and consideration of their multiwavelength properties suggest that one of them has jet-dominated X-ray emission, while the nature of the other remains unclear.

3. The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III

   Hiroaki Aihara, Carlos Allende Prieto, Deokkeun An, Scott F. Anderson, Éric Aubourg, Eduardo Balbinot, Timothy C. Beers, Andreas A. Berlind, Steven J. Bickerton, Dmitry Bizyaev, and 170 more authors

   ApJS, Apr 2011

   abstract arXiv ADS

   Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS Data Release 8 (DR8), which was made public in 2011 January and includes SDSS-I and SDSS-II images and spectra reprocessed with the latest pipelines and calibrations produced for the SDSS-III investigations. This paper presents an overview of the four surveys that comprise SDSS-III. The Baryon Oscillation Spectroscopic Survey will measure redshifts of 1.5 million massive galaxies and Lyα forest spectra of 150,000 quasars, using the baryon acoustic oscillation feature of large-scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z < 0.7 and at z ≈ 2.5. SEGUE-2, an already completed SDSS-III survey that is the continuation of the SDSS-II Sloan Extension for Galactic Understanding and Exploration (SEGUE), measured medium-resolution (R = λ/∆λ ≈ 1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE, the Apache Point Observatory Galactic Evolution Experiment, will obtain high-resolution (R ≈ 30,000), high signal-to-noise ratio (S/N >= 100 per resolution element), H-band (1.51 μm < λ < 1.70 μm) spectra of 10⁵ evolved, late-type stars, measuring separate abundances for  15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. The Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m s^-1,  24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. As of 2011 January, SDSS-III has obtained spectra of more than 240,000 galaxies, 29,000 z >= 2.2 quasars, and 140,000 stars, including 74,000 velocity measurements of 2580 stars for MARVELS.

4. The Sloan Digital Sky Survey Data Release 7 Spectroscopic M Dwarf Catalog. I. Data

   Andrew A. West, Dylan P. Morgan, John J. Bochanski, Jan Marie Andersen, Keaton J. Bell, Adam F. Kowalski, James R. A. Davenport, Suzanne L. Hawley,  Sarah J. Schmidt, David Bernat, and 10 more authors

   AJ, Mar 2011

   abstract arXiv ADS

   We present a spectroscopic catalog of 70,841 visually inspected M dwarfs from the seventh data release of the Sloan Digital Sky Survey. For each spectrum, we provide measurements of the spectral type, a number of molecular band heads, and the Hα, Hβ, Hγ, Hδ, and Ca II K emission lines. In addition, we calculate the metallicity-sensitive parameter ζ and identify a relationship between ζ and the g - r and r - z colors of M dwarfs. We assess the precision of our spectral types (which were assigned by individual examination), review the bulk attributes of the sample, and examine the magnetic activity properties of M dwarfs, in particular those traced by the higher order Balmer transitions. Our catalog is cross-matched to Two Micron All Sky Survey infrared data, and contains photometric distances for each star. Finally, we identify eight new late-type M dwarfs that are possibly within 25 pc of the Sun. Future studies will use these data to thoroughly examine magnetic activity and kinematics in late-type M dwarfs and examine the chemical and dynamical history of the local Milky Way.

2010

1. Colors and Kinematics of L Dwarfs from the Sloan Digital Sky Survey

   Sarah J. Schmidt, Andrew A. West, Suzanne L. Hawley, and J. Sebastian Pineda

   AJ, May 2010

   abstract arXiv ADS

   We present a sample of 484 L dwarfs, 210 of which are newly discovered from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic database. We combine this sample with known L dwarfs to investigate their izJHK_S colors. Our spectroscopically selected sample has  0.1 mag bluer median J - K_S color at a given spectral type (for L0-L4) than previously known L dwarfs, which reflects a bias toward redder L dwarfs in past selection criteria. We present photometric distance relations based on i - z and i - J colors and derive distances to our L dwarf sample. We combine the distances with SDSS/2MASS proper motions in order to examine the tangential velocities. For the majority of our spectroscopic sample, we measured radial velocities and present three-dimensional kinematics. We also provide Hα detections for the fraction of our sample with sufficient quality spectra. Comparison of the velocities of our L dwarf sample to a kinematic model shows evidence for both cold and hot dynamical populations, consistent with young and old disk components. The dispersions of these components are similar to those found for M dwarfs. We also show that J - K_S color is correlated with velocity dispersion, confirming a relationship between J - K_S color and age.

2. Discovery of an Unusually Blue L Dwarf Within 10 pc of the Sun

   Sarah J. Schmidt, Andrew A. West, Adam J. Burgasser, John J. Bochanski, and Suzanne L. Hawley

   AJ, Mar 2010

   abstract arXiv ADS

   We report the discovery of an unusually blue L5 dwarf within 10 pc of the Sun from a search of Sloan Digital Sky Survey (SDSS) spectra. A spectrophotometric distance estimate of 8.0 \pm 1.6 pc places SDSS J141624.08+134826.7 among the six closest known L dwarfs. SDSS 1416+13 was overlooked in infrared color-based searches because of its unusually blue J - K _S color, which also identifies it as the nearest member of the blue L dwarf subclass. We present additional infrared and optical spectroscopy from the IRTF/SpeX and Magellan/MagE spectrographs and determine UVW motions that indicate thin disk kinematics. The inclusion of SDSS 1416+13 in the 20 pc sample of L dwarfs increases the number of L5 dwarfs by 20% suggesting that the L dwarf luminosity function may be far from complete. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

2009

1. Cool Star Oxygen Abundances from Spectral Synthesis of TiO Bands

   Sarah J. Schmidt, George Wallerstein, Vincent M. Woolf, and Jacob L. Bean

   PASP, Oct 2009

   abstract ADS

   We have used spectral synthesis of the γ R₂ 0-0 TiO band at 7054 Å to determine oxygen abundances in dwarfs previously analyzed for iron and titanium abundances from their atomic lines. With the abundances of Fe and Ti held fixed, the band profiles are sensitive to the oxygen abundances. For the late K and M dwarfs analyzed, the [O/Fe] trend agrees with previous work for higher mass stars from [Fe/H] = +0.1 to [Fe/H] = -1.5. Beyond [Fe/H] = -1.5, the TiO band becomes too weak to analyze except in cooler stars for which Ti abundances are difficult to determine because their Ti I lines are frequently blended. We find that the abundance trend derived for our stars matches those derived for solar neighborhood stars by other methods.

2007

1. Activity and Kinematics of Ultracool Dwarfs, Including an Amazing Flare Observation

   Sarah J. Schmidt, Kelle L. Cruz, Bethany J. Bongiorno, James Liebert, and I. Neill Reid

   AJ, May 2007

   abstract arXiv ADS

   We present the activity and kinematics of a representative volume-limited (20 pc) sample of 152 late-M and L dwarfs (M7-L8) photometrically selected from the Two Micron All Sky Survey (2MASS). Using new proper-motion measurements and spectrophotometric distance estimates, we calculate tangential velocities. The sample has a mean tangential velocity of <V_tan>=31.5 km s^-1, a velocity dispersion of σ_tan=20.7 km s^-1, and a maximum tangential velocity of V_tan=138.8 km s^-1. These kinematic results are in excellent agreement with previous studies of ultracool dwarfs in the local solar neighborhood. Hα emission, an indicator of chromospheric activity, was detected in 63 of 81 late-M dwarfs and in 16 of 69 L dwarfs examined. We find a lack of correlation between activity strength, measured by log(F_Hα/F_bol), and V_tan, although velocity distributions suggest that the active dwarfs in our sample are slightly younger than the inactive dwarfs. Consistent with previous studies of activity in ultracool dwarfs, we find that the fraction of Hα-emitting objects per spectral type peaks at spectral type M7 and declines through mid-L dwarfs. Activity strength is similarly correlated with spectral type for types later than M7. Eleven dwarfs out of 150 show evidence of variability, ranging from small fluctuations to large flare events. We estimate a flare cycle of  5% for late-M dwarfs and  2% for L dwarfs. Observations of strong, variable activity on the L1 dwarf 2MASS J10224821+5825453 and an amazing flare event on the M7 dwarf 2MASS J1028404-143843 are discussed.

2. Meeting the Cool Neighbors. IX. The Luminosity Function of M7-L8 Ultracool Dwarfs in the Field

   Kelle L. Cruz, I. Neill Reid, J. Davy Kirkpatrick, Adam J. Burgasser, James Liebert, Adam R. Solomon,  Sarah J. Schmidt, Peter R. Allen, Suzanne L. Hawley, and Kevin R. Covey

   AJ, Feb 2007

   abstract arXiv ADS

   We present a 20 pc, volume-limited sample of M7-L8 dwarfs created through spectroscopic follow-up of sources selected from the Two Micron All Sky Survey Second Incremental Release Point Source Catalog. In this paper we present optical spectroscopy of 198 candidate nearby ultracool dwarfs, including 12 late-M and L dwarfs likely to be within 20 pc of the Sun and 94 more distant late-type dwarfs. We have also identified five ultracool dwarfs with spectral signatures of low gravity. Combining these data with previous results, we define a sample of 99 ultracool dwarfs in 91 systems within 20 pc. These are used to estimate the J- and K-band luminosity functions for dwarfs with optical spectral types between M7 and L8 (10.5<M_J<15, 9.5<M_KS<13). We find a space density of 4.9×10^-3 pc^-3 for late-M dwarfs (M7-M9.5) and a lower limit of 3.8×10^-3 pc^-3 for L dwarfs.