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Register a new userNew infrared spectral indices of luminous cold stars: from early K to M-types
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Maria Messineo
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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.
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We present a 0.8 -5 micron spectral library of 210 cool stars observed at a resolving power of R = lambda / Delta lambda ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The stars have well established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S stars. In contrast to some other spectral libraries, the continuum shape of the spectra are measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using Two Micron All Sky Survey (2MASS) photometry. Potential uses of the library include studying the physics of cool stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically-obscured regions of galaxies, and synthetic photometry. The library is available in digital form from the IRTF website.
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