Stellar SEDs from 0.3 to 2.5 μm: Tracing the Stellar Locus and Searching for Color Outliers in the SDSS and 2MASS

By K. Covey, Željko Ivezic´, David Schlegel, Douglas P. Finkbeiner, Nikhil Padmanabhan, Robert Lupton, M. Agueros, J. Bochanski, S. Hawley, Andrew A. West and 14 more. 2007

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The Sloan Digital Sky Survey (SDSS) and Two Micron All Sky Survey (2MASS) are rich resources for studying stellar astrophysics and the structure and formation history of the Galaxy. As new surveys and instruments adopt similar filter sets, it is increasingly important to understand the properties of the ugrizJHKs stellar locus, both to inform studies of "normal" main-sequence stars and enable robust searches for point sources with unusual colors. Using a sample of ∼600,000 point sources detected by SDSS and 2MASS, we tabulate the position and width of the ugrizJHKs stellar locus as a function of g - i color, and provide accurate polynomial fits. We map the Morgan-Keenan spectral type sequence to the median stellar locus by using synthetic photometry of spectral standards and by analyzing 3000 SDSS stellar spectra with a custom spectral typing pipeline, described in the Appendix to this paper. We develop an algorithm to calculate a point source's minimum separation from the stellar locus in a seven-dimensional color space, and use it to robustly identify objects with unusual colors, as well as spurious SDSS/2MASS matches. Analysis of a final catalog of 2117 color outliers identifies 370 white-dwarf/M dwarf (WDMD) pairs, 93 QSOs, and 90 M giant/carbon star candidates, and demonstrates that WDMD pairs and QSOs can be distinguished on the basis of their J - Ks and r - z colors. We also identify a group of objects with correlated offsets in the u - g versus g - r and g - r versus r - i color-color spaces, but subsequent follow-up is required to reveal the nature of these objects. Future applications of this algorithm to a matched SDSS-UKIDSS catalog may well identify additional classes of objects with unusual colors by probing new areas of color-magnitude space.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f1436d5e547102a961861d2652228d2995022b87

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Citations in the corpus

THE SLOAN DIGITAL SKY SURVEY DATA RELEASE 7 SPECTROSCOPIC M DWARF CATALOG. I. DATA (2011, methodology): “However, when we examined the ζ values as a function of both g − r and r − z (a proxy for spectral type; see Table 2), we found a strong trend of decreasing ζ diagonal to the g − r, r − z axis and perpendicular to the stellar locus (Covey et al. 2007).”
KEPLER FLARES. I. ACTIVE AND INACTIVE M DWARFS (2014, methodology): “The spectral typing followed the procedure of Covey et al. (2007) using the Hammer software described therein.”
THE BROWN DWARF KINEMATICS PROJECT I. PROPER MOTIONS AND TANGENTIAL VELOCITIES FOR A LARGE SAMPLE OF LATE-TYPE M, L, AND T DWARFS (2008, background): “Dahn et al. (2002) and Vrba et al. (2004) both showed that MJ is well correlated with spectral type for late-type M, L, and T dwarfs (see alsoWest et al. 2005, and Covey et al. 2007).”
Automatic determination of stellar atmospheric parameters and construction of stellar spectral templates of the Guoshoujing Telescope (LAMOST) (2011, positive): “Methods in Singh et al. (1998), BailerJones (2002), Hawley et al. (2002), Covey et al. (2007), and Bazarghan & Gupta (2008) may be adopted if they could provide reliable results for GSJT observations (Wu et al. 2011b in preparation).”
Planck 2015 results - XXVIII. The Planck Catalogue of Galactic cold clumps (2015, positive): “The ﬁrst data set, based on SDSS DR7 photometry and covering 1467 PGCC sources, is that of Berry et al. (2012) who ﬁt reddening and the stellar lo-cus colours of Covey et al. (2007) to the observed photometry.”
The Early Data Release of the Dark Energy Spectroscopic Instrument (2023, background): “The PSF outliers campaign targeted point sources ( TYPE=="PSF" ) in the Legacy Surveys that lie more than 10 σ from the stellar locus in grz ( in the spirit of, e.g., Covey et al. 2007 ) .”
Trumpeting M dwarfs with CONCH-SHELL: a catalogue of nearby cool host-stars for habitable exoplanets and life (2014, neutral): “Spectral types were determined using HAMMER (Covey et al. 2007).”
THE SEGUE STELLAR PARAMETER PIPELINE. I. DESCRIPTION AND COMPARISON OF INDIVIDUAL METHODS (2007, methodology): “…that, unlike the case for most of the features in this Table, the line indices listed in rows 74 (TiO1), 75 (TiO2), 76 (TiO3), 77 (TiO4), 78 (TiO5), 79 (CaH1), 80 (CaH2), 81 (CaH3), 82 (CaOH), and 83 (Hα) are calculated following the prescription given by the “Hammer” program (Covey et al. 2007).”
THE BARYON OSCILLATION SPECTROSCOPIC SURVEY OF SDSS-III (2012, background): “…or RQSS TMC) were additionally required to match within 3′′ of a 2MASS source having 11 < K < 15.1, (J − K) > 1.25, and a 7-dimensional color distance (Covey et al. 2007) greater than 50 (this is the distance in units of χ2 to the point on the stellar locus with the same (g − i) color as the…”
X-Shooter study of accretion in Chamaeleon I (2015, positive): “The largest differences in SpT occur for K-type stars, probably because our moderateresolution blue spectra include better temperature diagnostics (e.g., Covey et al. 2007) than the low-resolution red spectra used in most previous studies of the region.”
A SUNYAEV–ZEL'DOVICH-SELECTED SAMPLE OF THE MOST MASSIVE GALAXY CLUSTERS IN THE 2500 deg2 SOUTH POLE TELESCOPE SURVEY (2011, methodology): “This was due to using Johnson filters (as opposed to Gunn-Sloan filters), and calibrating the photometry with a synthetic stellar locus (rather than the median SDSS stellar locus from Covey et al. (2007)) using the PHOENIX stellar model atmosphere library (Brott & Hauschildt 2005).”
THE KEPLER CATALOG OF STELLAR FLARES (2016, background): “Figure 4 shows the fraction of Kepler stars that have detected flares from the final sample of 4041 stars in bins of g− i color, which is a proxy for stellar temperature (Covey et al. 2007; Davenport et al. 2014b).”
WHITE-LIGHT FLARES ON COOL STARS IN THE KEPLER QUARTER 1 DATA (2010, background): “All the stars in our flare sample have SDSS and 2MASS colors, for which there are existing photometric parallax relations (Bochanski et al. 2010; Covey et al. 2007).”
ERRATUM: “THE LUMINOSITY AND MASS FUNCTIONS OF LOW-MASS STARS IN THE GALACTIC DISK. II. THE FIELD” (2010, AJ, 139, 2679) (2010, background): “The latter two cuts ensure that the stars have red colors typical of M dwarfs (Bochanski et al. 2007b; Covey et al. 2007; West et al. 2008).”
THE BLANCO COSMOLOGY SURVEY: DATA ACQUISITION, PROCESSING, CALIBRATION, QUALITY DIAGNOSTICS, AND DATA RELEASE (2012, methodology): “Testing Stellar Locus Calibration in SDSS To validate our photometric calibration algorithms, we applied exactly the same procedure to the full SDSS2MASS catalog in (Covey et al. 2007).”
A SPECTROSCOPIC CATALOG OF THE BRIGHTEST (J < 9) M DWARFS IN THE NORTHERN SKY, (2012, methodology): “Semi-automated classification using THE HAMMER To verify the accuracy and consistency of spectral typing based the spectral-index method described above, we performed independent spectral classification using the Hammer code (Covey et al. 2007).”
PROSPECTING IN LATE-TYPE DWARFS: A CALIBRATION OF INFRARED AND VISIBLE SPECTROSCOPIC METALLICITIES OF LATE K AND M DWARFS SPANNING 1.5 dex (2012, methodology): “Approximate spectral types are determined by the HAMMER software package (Covey et al. 2007).”