Millimeter Observations of Vibrationally Excited CS toward IRC +10216: A New Circumstellar Maser?

Details Millimeter Observations of Vibrationally Excited CS toward IRC +10216: A New Circumstellar Maser? Millimeter Observations of Vibrationally Excited CS toward IRC +10216: A New Circumstellar Maser?

Dec 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...544..881h&link_type=abstract

The Astrophysical Journal, Volume 544, Issue 2, pp. 881-888.

Astronomy and Astrophysics

Astronomy

9

Stars: Circumstellar Matter, Masers, Radio Lines: Stars, Stars: Agb And Post-Agb, Stars: Individual (Irc +10216)

Scientific paper

New observations of vibrationally excited CS in its v=1 state have been conducted toward the circumstellar shell of IRC +10216 using the NRAO 12 m telescope and the CSO. The J=3-->2, 6-->5, and 7-->6 transitions in the v=1 level at 146, 292, and 340 GHz have been detected toward this object, and the J=2-->1 and 5-->4 lines were also reobserved. After accounting for contamination from other species, these CS transitions all exhibit line profiles that are narrower (ΔV1/2~10 km s-1) than those displayed by most molecules in IRC +10216, indicating an origin in the inner stellar envelope. The J=3-->2 line is particularly narrow (ΔV1/2~1-2 km s-1), and consists of two separate velocity components at VLSR~-26 and -22 km s-1. These characteristics are suggestive of weak maser action in this transition. The narrow line widths observed in the other transitions indicate a source size <~0.5", which implies a CS column density in the v=1 state of ~2-6×1016 cm-2. The ground-state (v=0) column density is therefore on the order of 0.8-2×1018 cm-2 for Tvib=500 K. The fractional abundance of CS relative to H2 is consequently f~3-7×10-5 at ~14 R*. Such a high abundance close to the stellar photosphere is strong evidence that CS is a ``parent'' molecule in IRC +10216, as suggested by infrared studies of the v=0-->1 vibrational transition and interferometric observations.

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