Quantitative spectral classification of galactic disc K-M stars from spectrophotometric measurements

Details Quantitative spectral classification of galactic disc K-M stars from spectrophotometric measurements Quantitative spectral classification of galactic disc K-M stars from spectrophotometric measurements

Apr 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997mnras.286..500m&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 286, Issue 2, pp. 500-512.

Astronomy and Astrophysics

Astronomy

25

Stars: Fundamental Parameters, Stars: Late-Type

Scientific paper

New spectral observations for 47 southern galactic red supergiants obtained with the new RUBIKON spectrophotometer (developed at the Astronomisches Institut der Ruhr-Universitat Bochum) at the Bochum 61-cm telescope on La Silla are presented. The spectra range from 4800 to 7700 A and their resolution is 10 A. The mean error of absolute fluxes is 0.028 mag and that of relative fluxes 0.021 mag. The spectra will be available at the Strasbourg Stellar Database (CDS). Together with data taken from recently published spectral catalogues, the new observations have been used to define spectral indices as measures of the strengths of the following features: Fe i+TiOalpha_1, Mgb+TiOalpha_0, NaD+TiOgamma'_1, TiOgamma'_0 and TiOgamma_1 systems. The indices have been checked against errors introduced by reductions, interstellar reddening and different resolutions of different spectral catalogues, and have been found to be very insensitive to all these effects. Therefore, different catalogues may be combined without any loss of accuracy and homogeneity. The mean error of a single index has been found to be 0.011 mag. For stars from K4 to M7, a strong temperature dependence is found for all indices. For the Fe i+TiO and especially the Mgb+TiO features, a strong dependence on luminosity has also been observed. These indices therefore have been combined to form a luminosity index, while the others together form a spectral index. The combined indices have been calibrated in terms of MK data using the stepwise linear regression technique, and may be used for quantitative two- dimensional spectral classification of late K- and M-type stars. The mean error of the classification is 0.6 of spectral subtype and 0.8 of luminosity class, which is much higher than would be expected from the uncertainty of the indices alone (which, e.g., for an M4 giant correspond to an uncertainty of 0.1 of spectral subtype and 0.3 of luminosity class). This may be explained by the uncertainty of the original MK classifications and the variability of some programme stars.

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