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Register a new userInterferometric imaging of the sulfur-bearing molecules H2S, SO and CS in comet C/1995 O1 (Hale-Bopp)
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We present observations of rotational lines of H2S, SO and CS performed in comet C/1995 O1 (Hale-Bopp) in March 1997 with the Plateau de Bure interferometer (IRAM). The observations provide informations on the spatial and velocity distributions of these molecules. They can be used to constrain their photodissociation rate and their origin. We use a radiative transfer code which allows us to compute synthetic line profiles and interferometric maps, to be compared to the observations. Both single-dish spectra and interferometric spectral maps show a day/night asymmetry in the outgassing. From the analysis of the spectral maps, including the astrometry, we show that SO and CS present in addition a jet-like structure that may be the gaseous counterpart of the dust high-latitude jet observed in optical images. A CS rotating jet is also observed. Using the astrometry provided by continuum radio maps obtained in parallel, we conclude that there is no need to invoke of nongravitational forces acting on this comet, and provide an updated orbit. The radial extension of H2S is found to be consistent with direct release from the nucleus. SO displays an extended radial distribution. Assuming that SO2 is the parent of SO, the photodissociation rate of SO is measured to be 1.5 E-4 s-1 at 1 AU from the Sun. This is lower than most laboratory-based estimates and may suggest that SO is not solely produced by SO2 photolysis. From the observations of J(2-1) and J(5-4) CS lines, we deduce a CS photodissociation rate of 1 to 5 E-5 s-1. The photodissociation rate of CS2, the likely parent of CS, cannot be constrained due to insufficient resolution, but our data are consistent with published values. These observations illustrate the cometary science that will be performed with the future ALMA interferometer.
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On 30.14 March 1997 we observed the EUV spectrum of the bright comet C/1995 O1 (Hale-Bopp) at the time of its perihelion, using our EUVS sounding rocket telescope/spectrometer. The spectra reveal the presence H Ly beta, O+, and, most notably, Argon. Modelling of the retrieved Ar production rates indicates that comet Hale-Bopp is enriched in Ar relative to cosmogonic expectations. This in turn indicates that Hale-Bopps deep interior has never been exposed to the 35-40 K temperatures necessary to deplete the comets primordial argon supply.
The long-term brightness evolution of the great comet C/1995 O1 (Hale-Bopp) presented a remarkable opportunity to study the behavior of its coma over four years. We used approximately 2200 total visual magnitudes published in the International Comet Quarterly taken from 17 observers during the period of 1995 July - 1999 September to create a secular lightcurve. In order to account for observer differences, we present a novel algorithm to reduce scatter and increase precision in a lightcurve compiled from many sources. It is implemented in a publicly available code, ICQSPLITTER. This code addresses the differences among observers by using a self-consistent statistical approach, leading to a sharper lightcurve, and improving the precision of the measured slopes. To first order, the comets lightcurve approximately follows a r$^{-4}$ response for both pre- and post-perihelion distances. Interestingly, the pre-perihelion data are better fit with a fifth-order polynomial with inflection points at 4.0, 2.6, 2.1 and 1.1 au. We analyze these specific regions and find that they are associated with physical phenomena in the comets evolution. Contrary to other reports, the lightcurve shows no evidence for the comet having been in outburst at discovery. Afrho values derived from the visual lightcurve data are consistent with a r$^{-1.5}$ dependence on heliocentric distance, which is similar in shape to those derived from spectroscopy and narrow-band photometry. We present correlation equations for visual magnitudes and CO and H2O production rates, which are consistent with the pre-perihelion visual magnitudes increasing almost entirely due to CO outgassing until a heliocentric distance of about 2.6 - 3.0 au. We also present two correlation equations that should prove highly useful for observation planning and data analysis, and can be generalized to be applicable to other comets.
We report the discovery of X-ray emission from comet C/1995 O1 (Hale-Bopp) by the LECS instrument on-board BeppoSAX on 1996 September 10--11. The 0.1--2.0 keV luminosity decayed by a factor of 2 on a timescale of ~10 hr with a mean value of 5.10E16 erg s-1. The spectrum is well fit by a thermal bremsstrahlung model with a temperature of 0.29 +/- 0.06 keV, or a power-law with a photon index of 3.1 +{0.6} -{0.2}. The lack of detected C and O line emission places severe constraints on many models for cometary X-ray emission, especially those which involve X-ray production in cometary gas. The luminosity is a factor of at least 3.4 greater than measured by Extreme Ultraviolet Explorer (EUVE) 4 days later. This difference may be related to the emergence from the nucleus on 1996 September 9 of a dust-rich cloud. Over the next few days the cloud continued to expand becoming increasingly tenuous, until it had reached an extent of ~3.10E5 km (or ~2 arcmin) by the start of EUVE observation. We speculate that the observed reduction in X-ray intensity is evidence for dust fragmentation. These results support the view that cometary X-ray emission arises from the interaction between solar X-rays and cometary dust.
We present an observational study of the sulfur (S)-bearing species towards Orion KL at 1.3 mm by combining ALMA and IRAM-30,m single-dish data. At a linear resolution of $sim$800 au and a velocity resolution of 1 $mathrm{km, s^{-1}, }$, we have identified 79 molecular lines from 6 S-bearing species. In these S-bearing species, we found a clear dichotomy between carbon-sulfur compounds and carbon-free S-bearing species in various characteristics, e.g., line profiles, spatial morphology, and molecular abundances with respect to $rm H_2$. Lines from the carbon-sulfur compounds (i.e., OCS, $^{13}$CS, H$_2$CS) exhibit spatial distributions concentrated around the continuum peaks and extended to the south ridge. The full width at half maximum (FWHM) linewidth of these molecular lines is in the range of 2 $sim$ 11 $mathrm{km, s^{-1}, }$. The molecular abundances of OCS and H$_2$CS decrease slightly from the cold ($sim$68 K) to the hot ($sim$176 K) regions. In contrast, lines from the carbon-free S-bearing species (i.e., SO$_2$, $^{34}$SO, H$_2$S) are spatially more extended to the northeast of mm4, exhibiting broader FWHM linewidths (15 $sim$ 26 $mathrm{km, s^{-1}, }$). The molecular abundances of carbon-free S-bearing species increase by over an order of magnitude as the temperature increase from 50 K to 100 K. In particular, $mathrm{^{34}SO/^{34}SO_2}$ and $mathrm{OCS/SO_2}$ are enhanced from the warmer regions ($>$100 K) to the colder regions ($sim$50 K). Such enhancements are consistent with the transformation of SO$_2$ at warmer regions and the influence of shocks.
We surveyed 20 AGB stars of different chemical types using the APEX telescope, and combined this with an IRAM 30 m and APEX survey of CS and SiS emission towards over 30 S-type stars. For those stars with detections, we performed radiative transfer modelling to determine abundances and abundance distributions. We detect CS towards all the surveyed carbon stars, some S-type stars, and the highest mass-loss rate oxygen-rich stars ($> 5times 10^{-6}$ Msol yr$^{-1}$). SiS is detected towards the highest mass-loss rate sources of all chemical types ($> 8times 10^{-7}$ Msol yr$^{-1}$). We find CS peak fractional abundances ranging from ~ $ 4times 10^{-7}$ to ~ $2times 10^{-5}$ for the carbon stars, from ~ $ 3times 10^{-8}$ to ~ $1times 10^{-7}$ for the oxygen-rich stars and from ~ $ 1times 10^{-7}$ to ~ $8times 10^{-6}$ for the S-type stars. We find SiS peak fractional abundances ranging from ~ $ 9times 10^{-6}$ to ~ $ 2times 10^{-5}$ for the carbon stars, from ~ $ 5times 10^{-7}$ to ~ $ 2times 10^{-6}$ for the oxygen-rich stars, and from ~ $ 2times 10^{-7}$ to ~ $ 2times 10^{-6}$ for the S-type stars. We derived Si$^{32}$S/Si$^{34}$S = 11.4 for AI Vol, the only star for which we had a reliable isotopologue detection. Overall, we find that wind density plays an important role in determining the chemical composition of AGB CSEs. It is seen that for oxygen-rich AGB stars both CS and SiS are detected only in the highest density circumstellar envelopes and their abundances are generally lower than for carbon-rich AGB stars by around an order of magnitude. For carbon-rich and S-type stars SiS was also only detected in the highest density circumstellar envelopes, while CS was detected consistently in all surveyed carbon stars and sporadically among the S-type stars.
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