Abstract Details

Name: Supriyo Ghosh
Affiliation: SNBNCBS
Conference ID: ASI2017_706
Title : The Near-Infrared Spectral Calibration of Late-type Giant Stars from medium resolution HK-band Spectra
Authors and Co-Authors : Supriyo Ghosh$^{*}$, Soumen Mondal$^{*}$, Ramkrishna Das$^{*}$ \affil{$^{*}$ S. N. Bose National Centre for Basic Sciences, Salt Lake, Kolkata-700106}
Abstract Type : Poster
Abstract Category : Stars,ISM and the Galaxy
Abstract : We present here moderate resolution ($\lambda$/$\Delta\lambda$ $\approx$ 1200) spectra of K-M type giant stars including few AGB stars covering 1.50-1.84 and 1.95-2.45 $\mu$m, observed with TIFR Near Infrared Spectrometer and Imager (TIRSPEC) on 2.0-m Himalaya Chandra Telescope (HCT) at IAO, Hanle, Ladakh, India. We measured equivalent widths of some important spectral features - NaI doublet at 2.2062 $\mu$m, CaI triplet at 2.2631 $\mu$m, $^{12}CO$ firstovertone band-head at 2.2935 $\mu$m, and a spectral index represents the overall shape of the spectra due to $H_2O$ opacity (the $H_2O$-K2 index). We have calibrated here the empirical relationship between fundamental parameters and equivalent widths of those features and $H_2O$-K2 index for giant stars from TIRSPEC observations and archival NIR spectral library, observed with medium-resolution ($\lambda$/$\Delta\lambda$ $\approx$ 2000) SpeX instrument at 3.0-m NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The trends of observed spectral features with respect to a physical parameters are compared with BT-NextGen Phoenix Model atmosphere. We found that the $H_2O$-K2 index are tightly correlated with spectral type in later M class giants stars and hence it is a powerful tool for subclass greater than M5 giants stars. We also discuss the difference in behaviour between giant stars and AGB stars in our presentation. This study of K-M type stars help us to derive the fundamental parameters of these class of objects to understand their formation and evolution, and would be extremely helpful to constrain the theoretical models.