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John J. Bochanski

Publications and source records attributed to John J. Bochanski.

At least 19 recordsLinked to original sources

New and Known Moving Groups And Clusters Identified in a Gaia Co-Moving Catalog

We present a re-organization of the Oh et al. (2017b) (Oh17) wide, co-moving catalog of 4,555 groups of stars (10,606 individual objects) identified in the Tycho Gaia Astrometric Survey (TGAS) into new and known co evolving groups of stars in the Milky Way. We use the BANYAN Σ kinematic analysis tool to identify 1,015 individual stars in the Oh17 catalog that yielded a >80% probability in one of 27 known associations (e.g. the AB Doradus moving group, Columba, Upper Scorpius) in the vicinity of the Sun. Among the 27 groups uncovered by Oh17 that had > 10 connected components, we find that 6 are newly discovered. We use a combination of Tycho, Gaia, 2MASS, WISE, Galex, and ROSAT photometry as well as Gaia parallaxes to determine that these new groups are likely older than the Pleiades but younger than ~1 Gyr. Using isochrone fitting we find that the majority of these new groups have solar type stars and solar type metallicity. Among the 35 Oh17 groups with 5 - 9 members, we find that 19 also appear new and co-moving, with one group well within 100pc (range of 77 - 90 pc). For known star forming regions, open clusters, and moving groups identified by Oh17, we find that the majority were broken up into pieces over several Oh17 groups (e.g. Lower Centaurus Crux members are spread over 26 Oh17 groups) however we found no correlation with positions of the groups on color magnitude diagrams therefore no substructure of the association correlated with the Oh17 designated group. We find that across the 27 groups tested by BANYAN Σ there were 400 new members to 20 different associations uncovered by Oh17 that require further vetting.

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Fundamental Properties of Co-Moving Stars observed by $Gaia$

We have estimated fundamental parameters for a sample of co-moving stars observed by $Gaia$ and identified by Oh et al. (2017). We matched the $Gaia$ observations to the 2MASS and WISE catalogs and fit MIST isochrones to the data, deriving estimates of the mass, radius, [Fe/H], age, distance and extinction to 9,754 stars in the original sample of 10,606 stars. We verify these estimates by comparing our new results to previous analyses of nearby stars, examining fiducial cluster properties, and estimating the power-law slope of the local present-day mass function. A comparison to previous studies suggests that our mass estimates are robust, while metallicity and age estimates are increasingly uncertain. We use our calculated masses to examine the properties of binaries in the sample, and show that separation of the pairs dominates the observed binding energies and expected lifetimes.

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An empirical template library of stellar spectra for a wide range of spectral classes, luminosity classes, and metallicities using SDSS BOSS spectra

We present a library of empirical stellar spectra created using spectra from the Sloan Digital Sky Survey's Baryon Oscillation Spectroscopic Survey (BOSS). The templates cover spectral types O5 through L3, are binned by metallicity from -2.0 dex through +1.0 dex and are separated into main sequence (dwarf) stars and giant stars. With recently developed M dwarf metallicity indicators, we are able to extend the metallicity bins down through the spectral subtype M8, making this the first empirical library with this degree of temperature \emph{and} metallicity coverage. The wavelength coverage for the templates is from 3650 Angstroms through 10200 Angstroms at a resolution better than R~2000. Using the templates, we identify trends in color space with metallicity and surface gravity, which will be useful for analyzing large data sets from upcoming missions like LSST. Along with the templates, we are releasing a code for automatically (and/or visually) identifying the spectral type and metallicity of a star.

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New views of the distant stellar halo

Currently only a small number of Milky Way (MW) stars are known to exist beyond 100 kpc from the Galactic center. Though the distribution of these stars in the outer halo is believed to be sparse, they can provide evidence of more recent accretion events than in the inner halo and help map out the MW's dark matter halo to its virial radius. We have re-examined the outermost regions of 11 existing stellar halo models with two synthetic surveys: one mimicking present-day searches for distant M giants and another mimicking RR Lyrae (RRLe) projections for LSST. Our models suggest that color and proper motion cuts currently used to select M giant candidates for follow-up successfully remove nearly all halo dwarf self-contamination and are useful for focusing observations on distant M giants, of which there are thousands to tens of thousands beyond 100 kpc in our models. We likewise expect that LSST will identify comparable numbers of RRLe at these distances. We demonstrate that several observable properties of both tracers, such as proximity of neighboring stars, proper motions, and distances (for RRLe) could help us separate different accreted structures from one another. We also discuss prospects for using ratios of M giants to RRLe as a proxy for accretion time, which in the future could provide new constraints on the recent accretion history of our Galaxy.

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

Radial velocity measurements are presented for 85 late M- and L-type very low mass stars and brown dwarfs obtained with the Magellan Echellette (MagE) 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, 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$0.2 Gyr for sources within 20 pc. We find significantly different kinematic ages between late-M dwarfs (4.0$\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.

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

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 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 sq. deg 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 measured abundances of 15 different elements for each star. In total, SDSS-III added 2350 sq. deg 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 sq. deg; 618,080 APOGEE spectra of 156,593 stars; and 197,040 MARVELS spectra of 5,513 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.

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BOSS Ultracool Dwarfs I: Colors and Magnetic Activity of M and L dwarfs

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 the Two Micron All Sky Survey and the Wide-Field Infrared Sky Explorer 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 H$α$ emission. The fraction of active dwarfs rises through the M spectral sequence until it reaches $\sim$90% at spectral type L0. The fraction of active dwarfs then declines to 50% at spectral type L5; no H$α$ 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 H$α$ 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.

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A New Sample of Cool Subdwarfs from SDSS: Properties and Kinematics

We present a new sample of M subdwarfs compiled from the 7th data release of the Sloan Digital Sky Survey. With 3517 new subdwarfs, this new sample significantly increases the number of spectroscopically confirmed low-mass subdwarfs. This catalog also includes 905 extreme and 534 ultra sudwarfs. We present the entire catalog including observed and derived quantities, and template spectra created from co-added subdwarf spectra. We show color-color and reduced proper motion diagrams of the three metallicity classes, which are shown to separate from the disk dwarf population. The extreme and ultra subdwarfs are seen at larger values of reduced proper motion as expected for more dynamically heated populations. We determine 3D kinematics for all of the stars with proper motions. The color-magnitude diagrams show a clear separation of the three metallicity classes with the ultra and extreme subdwarfs being significantly closer to the main sequence than the ordinary subdwarfs. All subdwarfs lie below (fainter) and to the left (bluer) of the main sequence. Based on the average $(U,V,W)$ velocities and their dispersions, the extreme and ultra subdwarfs likely belong to the Galactic halo, while the ordinary subdwarfs are likely part of the old Galactic (or thick) disk. An extensive activity analysis of subdwarfs is performed using H$α$ emission and 208 active subdwarfs are found. We show that while the activity fraction of subdwarfs rises with spectral class and levels off at the latest spectral classes, consistent with the behavior of M dwarfs, the extreme and ultra subdwarfs are basically flat.

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The Most Distant Stars in the Milky Way

We report on the discovery of the most distant Milky Way (MW) stars known to date: ULAS J001535.72$+$015549.6 and ULAS J074417.48$+$253233.0. These stars were selected as M giant candidates based on their infrared and optical colors and lack of proper motions. We spectroscopically confirmed them as outer halo giants using the MMT/Red Channel spectrograph. Both stars have large estimated distances, with ULAS J001535.72$+$015549.6 at $274 \pm 74$ kpc and ULAS J074417.48$+$253233.0 at 238 $\pm$ 64 kpc, making them the first MW stars discovered beyond 200 kpc. ULAS J001535.72$+$015549.6 and ULAS J074417.48$+$253233.0 are both moving away from the Galactic center at $52 \pm 10$ km s$^{-1}$ and $24 \pm 10$ km s$^{-1}$, respectively. Using their distances and kinematics, we considered possible origins such as: tidal stripping from a dwarf galaxy, ejection from the MW's disk, or membership in an undetected dwarf galaxy. These M giants, along with two inner halo giants that were also confirmed during this campaign, are the first to map largely unexplored regions of our Galaxy's outer halo.

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

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 $\sim$10--20 km s$^{-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 $J-K_S$ colors respectively. The new $χ$ values, which can be used to convert H$α$ 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 $\sim$20\%, ultracool dwarf models show the continuum surrounding H$α$ 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 H$α$ activity strength on the coolest L dwarfs have been underestimated.

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

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 microns. 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 square degrees.

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Hunting The Most Distant Stars in the Milky Way: Methods and Initial Results

We present a new catalog of 404 M giant candidates found in the UKIRT Infrared Deep Sky Survey (UKIDSS). The 2,400 deg$^2$ available in the UKIDSS Large Area Survey Data Release 8 resolve M giants through a volume four times larger than that of the entire Two Micron All Sky Survey. Combining near-infrared photometry with optical photometry and proper motions from the Sloan Digital Sky Survey yields an M giant candidate catalog with less M dwarf and quasar contamination than previous searches for similarly distant M giants. Extensive follow-up spectroscopy of this sample will yield the first map of our Galaxy's outermost reaches over a large area of sky. Our initial spectroscopic follow-up of $\sim$ 30 bright candidates yielded the positive identification of five M giants at distances $\sim 20-90$ kpc. Each of these confirmed M giants have positions and velocities consistent with the Sagittarius stream. The fainter M giant candidates in our sample have estimated photometric distances $\sim 200$ kpc (assuming $[Fe/H]$ = 0.0), but require further spectroscopic verification. The photometric distance estimates extend beyond the Milky Way's virial radius, and increase by $\sim 50\%$ for each 0.5 dex decrease in assumed $[Fe/H]$. Given the number of M giant candidates, initial selection efficiency, and volume surveyed, we loosely estimate that at least one additional Sagittarius-like accretion event could have contributed to the hierarchical build-up of the Milky Way's outer halo.

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The Sloan digital sky survey data release 7 spectroscopic m dwarf catalog iii: The spatial dependence of magnetic activity in the galaxy

We analyze the magnetic activity of 59,318 M dwarfs from the Sloan Digital Sky Survey (SDSS) Data Release 7. This analysis explores the spatial distribution of M dwarf activity as a function of both vertical distance from the Galactic plane (Z) and planar distance from the Galactic center (R). We confirm the established trends of decreasing magnetic activity (as measured by H-alpha emission) with increasing distance from the mid-plane of the disk and find evidence for a trend in Galactocentric radius. We measure a non-zero radial gradient in the activity fraction in our analysis of stars with spectral types dM3 and dM4. The activity fraction increases with R and can be explained by a decreasing mean stellar age with increasing distance from the Galactic center.

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The Very Short Period M Dwarf Binary SDSS J001641-000925

We present follow-up observations and analysis of the recently discovered short period low-mass eclipsing binary, SDSS J001641-000925. With an orbital period of 0.19856 days, this system has one of the shortest known periods for an M dwarf binary system. Medium-resolution spectroscopy and multi-band photometry for the system are presented. Markov chain Monte Carlo modeling of the light curves and radial velocities yields estimated masses for the stars of M1 = 0.54 +/- 0.07 Msun and M2 = 0.34 +/- 0.04 Msun, and radii of R1 = 0.68 +/- 0.03 Rsun and R2 = 0.58 +/- 0.03 Rsun respectively. This solution places both components above the critical Roche overfill limit, providing strong evidence that SDSS J001641-000925 is the first verified M-dwarf contact binary system. Within the follow-up spectroscopy we find signatures of non-solid body rotation velocities, which we interpret as evidence for mass transfer or loss within the system. In addition, our photometry samples the system over 9 years, and we find strong evidence for period decay at the rate of dP/dt ~8 s/yr. Both of these signatures raise the intriguing possibility that the system is in over-contact, and actively losing angular momentum, likely through mass loss. This places SDSS J001641-000925 as not just the first M-dwarf over-contact binary, but one of the few systems of any spectral type known to be actively undergoing coalescence. Further study SDSS J001641-000925 is on-going to verify the nature of the system, which may prove to be a unique astrophysical laboratory.

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Mapping the Local Halo: Statistical Parallax Analysis of SDSS Low-Mass Subdwarfs

We present a statistical parallax study of nearly 2,000 M subdwarfs with photometry and spectroscopy from the Sloan Digital Sky Survey. Statistical parallax analysis yields the mean absolute magnitudes, mean velocities and velocity ellipsoids for homogenous samples of stars. We selected homogeneous groups of subdwarfs based on their photometric colors and spectral appearance. We examined the color-magnitude relations of low-mass subdwarfs and quantified their dependence on the newly-refined metallicity parameter, zeta. We also developed a photometric metallicity parameter, delta(g-r), based on the g-r and r-z colors of low-mass stars and used it to select stars with similar metallicities. The kinematics of low-mass subdwarfs as a function of color and metallicity were also examined and compared to main sequence M dwarfs. We find that the SDSS subdwarfs share similar kinematics to the inner halo and thick disk. The color-magnitude relations derived in this analysis will be a powerful tool for identifying and characterizing low-mass metal-poor subdwarfs in future surveys such as GAIA and LSST, making them important and plentiful tracers of the stellar halo.

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

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 SDSS-III Sloan Extension for Galactic Understanding and Exploration-2 (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 Apache Point Observatory Galactic Evolution Experiment (APOGEE) along with another year of data from BOSS, followed by the final SDSS-III data release in December 2014.

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An H-band Spectroscopic Metallicity Calibration for M Dwarfs

We present an empirical near-infrared (NIR) spectroscopic method for estimating M dwarf metallicities, based on features in the H-band, as well as an implementation of a similar published method in the K-band. We obtained R~2000 NIR spectra of a sample of M dwarfs using the NASA IRTF-SpeX spectrograph, including 22 M dwarf metallicity calibration targets that have FGK companions with known metallicities. The H-band and K-band calibrations provide equivalent fits to the metallicities of these binaries, with an accuracy of +/- 0.12 dex. We derive the first empirically calibrated spectroscopic metallicity estimate for the giant planet-hosting M dwarf GJ 317, confirming its super-solar metallicity. Combining this result with observations of eight other M dwarf planet hosts, we find that M dwarfs with giant planets are preferentially metal-rich compared to those that host less massive planets. Our H-band calibration relies on strongly metallicity-dependent features in the H-band, which will be useful in compositional studies using mid to high resolution NIR M dwarf spectra, such as those produced by multiplexed surveys like SDSS-III APOGEE. These results will also be immediately useful for ongoing spectroscopic surveys of M dwarfs.

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Refined Metallicity Indices for M Dwarfs Using the SLoWPoKES Catalog of Wide, Low-mass Binaries

We report the results from spectroscopic observations of 113 ultra-wide, low-mass binary systems, composed largely of M0--M3 dwarfs, from the SLoWPoKES catalog of common proper motion pairs identified in the Sloan Digital Sky Survey. Radial velocities of each binary member were used to confirm that they are co-moving and, consequently, to further validate the high fidelity of the SLoWPoKES catalog. Ten stars appear to be spectroscopic binaries based on broad or split spectral features, supporting previous findings that wide binaries are likely to be hierarchical systems. We measured the Hα equivalent width of the stars in our sample and found that components of 81% of the observed pairs has similar Hα levels. The difference in Hα equivalent width amongst components with similar masses was smaller than the range of Hα variability for individual objects. We confirm that the Lepine et al. ζ(CaH2+CaH3, TiO5) index traces iso-metallicity loci for most of our sample of M dwarfs. However, we find a small systematic bias in ζ, especially in the early-type M dwarfs. We use our sample to recalibrate the definition of ζ. While representing a small change in the definition, the new ζ is a significantly better predictor of iso-metallicity for the higher mass M dwarfs.

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