Search for Hydroxyl in Southern Cold IRAS Sources

Details Search for Hydroxyl in Southern Cold IRAS Sources Search for Hydroxyl in Southern Cold IRAS Sources

Aug 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...275..510s&link_type=abstract

Astronomy and Astrophysics, Vol.275, NO.2/AUG(II), P. 510, 1993

Astronomy and Astrophysics

Astrophysics

17

Evolved Stars, Oh Radio Lines, Maser Emission, Infrared Radiation - Circumstellar Shells

Scientific paper

We searched for OH in a sample of 53 objects selected from the IRAS Point Source Catalog. According to their color properties, the sources have the cool envelopes (temperature Tenv ≍ 150-300 K) of objects in evolution between OH/IR stars and planetary nebulae (PN). The sources were chosen from within the southern sky with declinations (δ < - 30°.
We sought the OH radical at the frequencies of 1612, 1665 and 1667 MHz with a 3O-m antenna at the Instituto Argentino de Radioastronomia (IAR).
We found OH radiation in emission and/or absorption towards thirteen of the sources, among which are two known bipolar nebulae. Furthermore, we suggest the following identifications: two possible cloud sources with absorption in three OH lines and PN color at the positions of IRAS 16115 - 5044 and IRAS 16279-4757, respectively (new detections); four OH/IR stars with symmetric double peaked profiles and low variability, one of them a new detection (IRAS 17106-3046); a possible star in transition between oxygen to carbon-rich (IRAS 16279-4757, new detection); two OH/IR stars with high mass loss rates and variability (previously reported) in possible transition to bipolar nebulae; and two new pre-PN candidates with very cold envelopes and irregular OH profiles (IRAS 17579 -3121 and 18025-3906). For IRAS 10197-5750 (Roberts 22) there is evidence of an uneven distribution of the matter surrounding the star. Its OH-variability was studied and a tentative light curve with a 7.2 yr period was constructed.
Among the non-detections there are carbon star candidates and a few possible PN without the conditions needed for supporting maser operation. On the other hand there is no apparent difference in the color properties of non- detections and detections.
We present evidence for radiative pumping of the 1612 maser line. The mean efficiency is <ɛ> = 0.13, assuming that the 35 μm line is the only pump line. Mass loss rates between 3 10-6 and 5 10-5 Msun yr-1 were estimated for the 10 objects detected with double peaked 1612 MHz lines. The importance of the mass loss process for understanding the evolutionary stage of the objects and its influence on OH line shapes is discussed.

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