Infrared spectral properties of M giants

Abstract

We observed a sample of 20 M giants with the Infrared Spectrograph on the Spitzer Space Telescope. Most show absorption structure at 6.6-6.8 um which we identify as water vapor, and in some cases, the absorption extends from 6.4 um into the SiO band at 7.5 um. Variable stars show stronger H2O absorption. While the strength of the SiO fundamental at 8 um increases monotonically from spectral class K0 to K5, the dependence on spectral class weakens in the M giants. As with previously studied samples, the M giants show considerable scatter in SiO band strength within a given spectral class. All of the stars in our sample also show OH band absorption, most noticeably in the 14-17 um region. The OH bands behave much like the SiO bands, increasing in strength in the K giants but showing weaker dependence on spectral class in the M giants, and with considerable scatter. An examination of the photometric properties reveals that the V-K color may be a better indicator of molecular band strength than the spectral class. The transformation from Tycho colors to Johnson B-V color is double-valued, and neither B-V nor BT-VT color increases monotonically with spectral class in the M giants like they do in the K giants.

arXiv comment16 pages, 18 figures, 8 tables, and a few words. The on-line spectra are available at http://isc.astro.cornell.edu/~sloan/library/standards and will be hosted at IRSA and ViZier

References in corpus (17)

• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Spitzer Space Telescope Mission
• The Infrared Spectrograph on the Spitzer Space Telescope
• A three-dimensional Galactic extinction model
• Warming early Mars with CO2 and H2
• Pixie Dust: The Silicate Features in the Diffuse Interstellar Medium
• Classification of 2.4-45.2 Micron Spectra from the ISO Short Wavelength Spectrometer
• The COBE DIRBE Point Source Catalog
• Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei
• Water in K and M giant stars unveiled by ISO
• Detection of Water Vapor in the Photosphere of Arcturus
• Spectral Calibration in the Mid-Infrared: Challenges and Solutions
• Hipparcos calibration of the tip of the Red Giant Branch
• The K giant star Arcturus: the hybrid nature of its infrared spectrum
• Water vapor on supergiants. The 12 micron TEXES spectra of mu Cephei
• Systematic trend of water vapour absorption in red giant atmospheres revealed by high resolution TEXES 12 micron spectra
• IRS-TR 12001: Spectral Pointing-Induced Throughput Error and Spectral Shape in Short-Low Order 1

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