Spectral classification of unidentified IRAS sources with Fν(12µm)≥Fν(25µm).
IYENGAR K.V.K. and MacCONNELL D.J.
Abstract (from CDS):
Spectral types of a large number of unidentified IRAS Point Sources with Fν(12µm)≥Fν(25µm) 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 12µm 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.