Carbonyl sulfide in comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp): Evidence for an extended source in Hale-Bopp

Carbonyl sulfide was detected in Comet Hale-Bopp (C/1995 O1) using high dispersion infrared spectroscopy at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Six lines (P10, P11, P12, P14, P15, and P17) of the nu(3) fundamental band near 4.85 mu m were detected on UT April 16.0, April 30.0, and May 1.2, 1997, and two additional lines (P18 and P22) were detected on April 30.0. Water was detected directly through emission lines of its nu(1)-nu(2) hot band on UT April 16.0, April 30.0, and May 1.2, with a rotational temperature of 93 +/- 16 K on May 1.2. Adopting a rotational temperature of 100 K for OCS, our derived production rates are (3.80 +/- 0.67) and (1.77 +/- 0.85) x 10(28) molecules s(-1) on April 16.0 and May 1.2, respectively. The measured production rates imply mixing ratios (Q(OCS)/Q(H2O)) of (4.58 +/- 0.77) and (2.76 +/- 1.34) x 10(-3) on April 16.0 and May 1.2, respectively. Comparison of spatial profiles for OCS, H2O, and the dust continuum derived from spectra taken less than 1 h apart suggests that on April 16.0 a significant amount of OCS (similar to 70% of the total) was released as an extended source. On April 30.0 and May 1.2 the quality of the data prevent a firm conclusion regarding an extended source contribution. If the nature of the OCS source did not change between April 16.0 and May 1.2, the weighted mean mixing ratio is (4.13 +/- 0.77) x 10(-3). We searched for lines P1 through P8 of the nu(3) band of OCS in Comet Hyakutake (C/1996 B2) on UT March 24.5, 1996. Our upper limit (3 sigma) for the OCS production rate in Hyakutake is 1.0 x 10(27) molecules s(-1) (Q(OCS)/Q(H2O) < 5.3 x 10(-3)). (C) 1998 Academic Press.