Issue |
Astron. Astrophys. Suppl. Ser.
Volume 133, Number 2, December I 1998
|
|
---|---|---|
Page(s) | 201 - 209 | |
DOI | https://doi.org/10.1051/aas:1998316 | |
Published online | 15 December 1998 |
Spectral classification of unidentified IRAS sources
with
*
1
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
Received:
4
December
1998
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
-[12] colour index. The dependence of this and of the IRAS indices on
spectral type is determined and discussed.
The mean [12]-[25] colour of the M-type stars is found to
increase monotonically from M3 to M6 and then levels off. Comparison
of the [12]-[25] colours of these faint IRAS M stars
with those of Bright Star Catalog M stars
indicates that, at all types, the mean [12]-[25] 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 [25]-[60] 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 [12]-[25] 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
© European Southern Observatory (ESO), 1998