Optical identification and BVRI photometry of a few 'unidentified' IRAS sources of a late type stellar nature

Abstract

A search for the optical counterparts of 21 'unidentified' IRAS sources was carried out using the Palomar Observatory Sky Survey (POSS), European Space Observatory (ESO) and Space Engineering Research Center (SERC) Sky Survey prints. The sources selected for study were of a late type stellar nature with circumstellar dust shells as revealed by their flux densities in the IRAS survey bands. CCD photometric observations of these IRAS sources were carried out in the BVRI bands with the 1.02 m telescope at the Vainu Bappu Observatory (VBO), of the Indian Institute of Astrophysics (IIA) at Kavalur. Spectroscopic observations of three of the brighter sources (viz., 04184 + 2008, 07593 - 1452 and 12387 - 3717) were carried out in the wavelength range 6300-11000 A using the 2.3 m telescope of IIA at VBO, Kavalur. BVRI photometric measurements aimed towards understanding the evolutionary stage of these sources indicate that they have higher values of B-V for their V-I colors compared to those of main sequence and giant stars indicating their advanced stage of evolution associated with a high mass loss rate and the consequent high extinction experienced by them in the B band, due to circumstellar dust. Color-color diagrams of (12) - (25) versus V-I and (25) - (60) versus V-I show that they can be used to distinguish proto-planetaries and planetaries from sources with continuously falling spectra as they exhibit distinctly higher (12) - (25) and (25) - (60) at all V-I.