SELECTING M GIANTS WITH INFRARED PHOTOMETRY: DISTANCES, METALLICITIES, AND THE SAGITTARIUS STREAM
- Key Laboratory of Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai, 200030 (China)
- Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States)
- Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Datun Road 20A, Beijing 100012 (China)
- Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen (Netherlands)
Using a spectroscopically confirmed sample of M giants, M dwarfs, and quasars from the LAMOST survey, we assess how well Wide-field Infrared Survey Explorer (WISE) and Two Micron All Sky Survey color cuts can be used to select M giant stars. The WISE bands are very efficient at separating M giants from M dwarfs, and we present a simple classification that can produce a clean and relatively complete sample of M giants. We derive a new photometric relation to estimate the metallicity for M giants, calibrated using data from the APOGEE survey. We find a strong correlation between the (W1−W2) color and [M/H], where almost all of the scatter is due to photometric uncertainties. We show that previous photometric distance relations, which are mostly based on stellar models, may be biased and devise a new empirical distance relation, investigating trends with metallicity and star formation history. Given these relations, we investigate the properties of M giants in the Sagittarius stream. The offset in the orbital plane between the leading and trailing tails is reproduced, and by identifying distant M giants in the direction of the Galactic anticenter, we confirm that the previously detected debris in the outer halo is the apocenter of the trailing tail. We also find tentative evidence supporting an existing overdensity near the leading tail in the northern Galactic hemisphere, possibly an extension to the trailing tail (so-called Branch C). We have measured the metallicity distribution along the stream, finding a clear metallicity offset between the leading and trailing tails, in agreement with models for the stream formation. We include an online table of M giants to facilitate further studies.
- OSTI ID:
- 22862933
- Journal Information:
- Astrophysical Journal, Vol. 823, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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