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New Infrared Spectral Indices of Luminous Cold Stars: From Early K to M Types

New Infrared Spectral Indices of Luminous Cold Stars: From Early K to M Types We present infrared spectral indices (1.0–2.3 μm) 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 μm ([CO, 2.29] ≳ 45 Å) 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 μm), Sr (1.033 μm), Fe+Cr+Si+CN (1.16 μm), Fe+Ti (1.185 μm), Fe+Ti (1.196 μm), Ti+Ca (1.28 μm), and Mn (1.29 μm). Good markers of CN enhancement are the Fe+Si+CN line at 1.087 μm and CN line at 1.093 μm. 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. Twenty-one 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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Astronomical Journal IOP Publishing

New Infrared Spectral Indices of Luminous Cold Stars: From Early K to M Types

New Infrared Spectral Indices of Luminous Cold Stars: From Early K to M Types

The Astronomical Journal , Volume 162 (5): 46 – Nov 1, 2021

Abstract

We present infrared spectral indices (1.0–2.3 μm) 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 μm ([CO, 2.29] ≳ 45 Å) 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 μm), Sr (1.033 μm), Fe+Cr+Si+CN (1.16 μm), Fe+Ti (1.185 μm), Fe+Ti (1.196 μm), Ti+Ca (1.28 μm), and Mn (1.29 μm). Good markers of CN enhancement are the Fe+Si+CN line at 1.087 μm and CN line at 1.093 μm. 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. Twenty-one 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.

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References (105)

Publisher
IOP Publishing
Copyright
© 2021. The American Astronomical Society. All rights reserved.
ISSN
0004-6256
eISSN
1538-3881
DOI
10.3847/1538-3881/ac116b
Publisher site
See Article on Publisher Site

Abstract

We present infrared spectral indices (1.0–2.3 μm) 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 μm ([CO, 2.29] ≳ 45 Å) 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 μm), Sr (1.033 μm), Fe+Cr+Si+CN (1.16 μm), Fe+Ti (1.185 μm), Fe+Ti (1.196 μm), Ti+Ca (1.28 μm), and Mn (1.29 μm). Good markers of CN enhancement are the Fe+Si+CN line at 1.087 μm and CN line at 1.093 μm. 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. Twenty-one 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.

Journal

The Astronomical JournalIOP Publishing

Published: Nov 1, 2021

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