New infrared spectral indices of luminous cold stars: from early K to M-types

Abstract

We present infrared spectral indices (1.0-2.3 um) of Galactic late-type giants and red supergiants (RSGs). We used existing and new spectra obtained at resolution power R=2000 with SpeX on the IRTF telescope. While a large CO equivalent width (EW), at 2.29 um ([CO, 2.29]>45 AA) is a typical signature of RSGs later than spectral type M0, [CO] of K-type RSGs and giants are similar. In the [CO, 2.29] versus [Mg I, 1.71] diagram, RSGs of all spectral types can be distinguished from red giants, because the Mg I line weakens with increasing temperature and decreasing gravity. We find several lines that vary with luminosity, but not temperature: Si I (1.59 um), Sr (1.033 um), Fe+Cr+Si+CN (1.16 um), Fe+Ti (1.185 um), Fe+Ti (1.196 um), Ti+Ca (1.28 um), and Mn (1.29 um). Good markers of CN enhancement are the Fe+Si+CN line at 1.087 um and CN line at 1.093 um. Using these lines, at the resolution of SpeX, it is possible to separate RSGs and giants. Contaminant O-rich Mira and S-type AGBs are recognized by strong molecular features due to water vapor features, TiO band heads, and/or ZrO absorption. Among the 42 candidate RSGs that we observed, all but one were found to be late-types. 21 have EWs consistent with those of RSGs, 16 with those of O-rich Mira AGBs, and one with an S-type AGB. These infrared results open new, unexplored, potential for searches at low-resolution of RSGs in the highly obscured innermost regions of the Milky Way.

48 pages, 25 figures, accepted for publication in The Astronomical Journal

References in corpus (31)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• A massive cluster of Red Supergiants at the base of the Scutum-Crux arm
• Discovery of an Extraordinarily Massive Cluster of Red Supergiants
• The cool supergiant population of the massive young star cluster RSGC1
• The Extended IRTF Spectral Library: Expanded coverage in metallicity, temperature, and surface gravity
• A third red supergiant rich cluster in the Scutum-Crux Arm
• The X-Shooter Spectral Library (XSL): Data Release 2
• Red Supergiant Stars as Cosmic Abundance Probes: KMOS Observations in NGC 6822
• Near-IR Spectra of Red Supergiants and Giants. I- Models with Solar and with Mixing-Induced Surface Abundance Ratios
• Manganese trends in a sample of thin and thick disk stars. The origin of Mn
• MONOS: Multiplicity Of Northern O-type Spectroscopic systems. I. Project description and spectral classifications and visual multiplicity of previously known objects
• Stellar atmospheric parameters for 754 spectra from the X-shooter Spectral Library
• Red Supergiants as Cosmic Abundance Probes: The Magellanic Clouds
• Red Supergiants as Cosmic Abundance Probes: The Sculptor Galaxy NGC 300
• Red Supergiants as Cosmic Abundance Probes: massive star clusters in M83, and the mass-metallicity relation of nearby galaxies
• Red supergiants around the obscured open cluster Stephenson 2
• Empirical Bolometric Fluxes and Angular Diameters of 1.6 Million Tycho-2 Stars and Radii of 350,000 Stars with \emph{Gaia} DR1 Parallaxes
• Detailed abundances in the Galactic center: Evidence of a metal-rich alpha-enhanced stellar population
• A New Method for Measuring Metallicities of Young Super Star Clusters
• The Luminosity Function of Red Supergiants in M31
• The Red Supergiant Content of M31 and M33
• Exploring the Mass Loss Histories of the Red Supergiants
• A catalog of known Galactic K-M stars of class I, candidate RSGs, in Gaia DR2
• Quantitative Spectroscopic J-band Study of Red Supergiants in Perseus OB-1
• The Discovery of a Massive Cluster of Red Supergiants with GLIMPSE
• Effective temperatures of red supergiants estimated from line-depth ratios of iron lines in the YJ bands, 0.97--1.32 micron
• Discovery of technetium- and niobium-rich S stars: the case for bitrinsic stars
• Characterisation of red supergiants in the Gaia spectral range
• High-resolution spectroscopic study of massive blue and red supergiants in Per OB1
• Near-infrared spectroscopy of candidate red supergiant stars in clusters
• Infrared Telescope Facility (IRTF) spectral library II: New indices in Y, J, H, and L atmospheric windows

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