Identification of IRAS Sources in the Outer Disk of the Galaxy

Details Identification of IRAS Sources in the Outer Disk of the Galaxy Identification of IRAS Sources in the Outer Disk of the Galaxy

Apr 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aj....113.1315j&link_type=abstract

Astronomical Journal v.113, p. 1315-1327 (1997)

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18

Scientific paper

Near infrared imaging and photometric observations at J, H and K (or K') bands were performed toward 95 IRAS sources in the outer disk of the Galaxy most of which had been searched for SiO maser emission and are candidates for variable late-type stars with cold circumstellar envelopes. Low resolution optical spectroscopic observations were made to 19 stars of them for classifying the spectral types. Thirty-eight of them, for which counterparts were not found at I band brighter than 19mag, were taken near infrared images for identification. All are identified in the near-infrared images brighter than 16 mag at K' band except two that could be in the faint phase of variation when observed. So most of the IRAS late-type stars perhaps have a near-infrared counterpart although many have no optical counterpart. In the near-infrared color-color diagram, the stars with O-rich and C-rich circumstellar envelopes(CSEs) are separated from each other. The stars with C-rich CSE are redder than those with O-rich CSE in general but there are three very red stars in this sample being SiO maser sources, i.e. with O-rich CSE. By combining the near-infrared colors and IRAS color, the two types of circumstellar envelopes are discriminated. 48 percent are stars with C-rich CSE in the entire sample and the number ratios of C-rich to O-rich stars are 14:43 and 32:6 for the optically identified and unidentified groups respectively. This indicates an increasing proportion of C-rich stars with galacto-centric distance and stellar evolutionary stage. The result is applied to explain the low detection rate of SiO maser emission in a similar and bigger sample in the outer disk of the Galaxy.

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