Spectral classification of unidentified IRAS sources with *
Indian Institute of Astrophysics, Bangalore 560 034, India
2 Computer Sciences Corporation, System Sciences Division, Space Telescope Science Institute, Baltimore, Maryland, U.S.A.
Send offprint request to: K.V.K. Iyengar
Accepted: 5 June 1998
Spectral types of a large number of unidentified IRAS Point Sources with were determined; the majority are faint, oxygen-rich (M-type) or carbon-rich giant stars. The Guide Star Catalog has been used to find the photographic magnitudes of the newly classified IRAS sources with quality-3 flux densities at 12 m in order to determine their Bj - colour index. The dependence of this and of the IRAS indices on spectral type is determined and discussed. The mean - colour of the M-type stars is found to increase monotonically from M3 to M6 and then levels off. Comparison of the - colours of these faint IRAS M stars with those of Bright Star Catalog M stars indicates that, at all types, the mean - index of the former group is higher than that of the latter by at least 0.2 magnitude, and this is found to be significant at the 95% confidence level. Comparison of the quality-3, mean - colours of the newly-classified, faint M stars with those of BSC stars over the same spectral type also shows the same trend. Possible reasons for this difference are discussed. The percentage of variable sources as a function of spectral type is seen to sharply increase from a nearly constant value of about 25% for sources of spectral type M3 to M7 to a value of about 50% at M10. The mean - colours of the IRAS unidentified sources (within the limits of the errors on their mean values) appear to be rather insensitive to the degree of variability.
Key words: stars: AGB / stars: carbon / stars: late-type / stars: mass-loss / infrared: stars
Table 6 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130 79 128 5) or via http://cdsweb.u-strasbg.fr/Abstract.html
© European Southern Observatory (ESO), 1998