Gas and dust productions of Comet 103P/Hartley 2 from millimetre observations: Interpreting rotation-induced time variations

Comet 103P/Hartley 2 made a close approach to the Earth in October 2010. It was the target of an extensive observing campaign including ground- and orbit-based observatories and was visited by the Deep Impact spacecraft in the framework of its mission extension EPOXI. We present observations of HCN and CH_3OH emission lines conducted with the IRAM Plateau de Bure interferometer on 22–23, 28 October and 4, 5 November 2010 at 1.1, 1.9 and 3.4 mm wavelengths. The thermal emission from the dust coma and nucleus is detected simultaneously. Interferometric images with unprecedented spatial resolution of ∼100 to ∼500 km are obtained. A sine–wave like variation of the thermal continuum is observed in the 23 October data, that we associate with the nucleus thermal light curve. The nucleus contributes up to 30–55% of the observed continuum emission. The dust thermal emission is used to measure the dust production rate. The inferred large dust-to-gas ratio (in the range 2–6) can be explained by the unusual activity of the comet for its size, which allows decimeter size particles and large boulders to be entrained by the gas due to the small nucleus gravity. The rotational temperature of CH_3OH is measured with beam radii from ∼150 km to ∼1500 km. We attribute the increase from ∼35 K to ∼46 K with increasing beam size to radiative processes. The HCN production rate displays strong rotation-induced temporal variations, varying from ∼0.3 × 10^(25) s^(−1) to ∼2.0 × 10^(25) s^(−1) in the 4–5 November period. The HCN production curve, as well as the CO_2 and H_2O production curves measured by EPOXI, are interpreted with a geometric model which takes into account the complex rotational state of 103P/Hartley 2 and its shape. The HCN and H_2O production curves are in phase, showing that these molecules have common sources. The ∼1.7 h delay, in average, of the HCN and H_2O production curves with respect to the CO_2 production curve suggests that HCN and H_2O are mainly produced by subliming icy grains. The scale length of production of HCN is determined to be on the order of 500–1000 km, implying a mean velocity of 100–200 m s^(−1) for the icy grains producing HCN. From the time evolution of the insolation of the nucleus, we show that the CO_2 production is modulated by the insolation of the small lobe of the nucleus. The three-cycle pattern of the production curves reported earlier is best explained by an overactivity of the small lobe in the longitude range 0–180°. The good correlation between the insolation of the small lobe and CO_2 production is consistent with CO_2 being produced from small depths below the surface. The time evolution of the velocity offset of the HCN lines, as well as the displacement of the HCN photocenter in the interferometric maps, are overall consistent with this interpretation. Other localized sources of gas on the nucleus surface are also suggested

CSO BROADBAND MOLECULAR LINE SURVEYS II: INTIAL CORRELATION ANALYSIS RESULTS FOR COMPLEX ORGANIC MOLECULES

Author Institution: Emory University, Department of Chemistry, Atlanta, Georgia 30322As was presented in the previous talk, we have conducted 25 broadband line surveys of interstellar sources in the $\lambda$=1.3 mm band using the Caltech Submillimeter Observatory. Using the results from the spectral analysis of these observations, the influence of physical environment on molecular complexity can be examined. Our broader research goal is to improve astrochemical models to the point where accurate predictions of complex molecular inventory can be made based on the physical and chemical environment of a given source. The CSO observations include a statistically-significant sample of sources, cover a range of physical environments, and target selected frequency windows containing transitions from a set of known complex organic molecules. We are now analyzing these line surveys to search for correlations between the relative abundances of organic molecules and the physical properties of the source (i.e. temperature, density, mass, etc.), as well as correlations between sets of molecules. Here we present the results from the initial quantitative analysis of these surveys, as well as chemical trends that have been determiend. The implications of these results for astrochemical models will also be discussed

A Comparison of c-C3H2 and l-C3H2 in the Spiral Arm Clouds

International audienceUsing the IRAM 30-m telescope, we observed molecular absorption lines from c-C<SUB>3</SUB>H<SUB>2</SUB> produced in diffuse clouds toward the high-mass star forming regions W51 e1/e2 and W49N to determine the abundance ratio between the cyclic and linear isomers of C<SUB>3</SUB>H<SUB>2</SUB> (N<SUB>c</SUB>/N<SUB>l</SUB>). The abundance ratio is found to be 3-5 in the sources where l-C<SUB>3</SUB>H<SUB>2</SUB> was previously detected. A possible source of uncertainty in the determination of N<SUB>c</SUB>/N<SUB>l</SUB> is related to the estimate of N(c-C<SUB>3</SUB>H<SUB>2</SUB>). The main goal of this paper is verification of this hypothesis

A Comparison of c-C3H2 and l-C3H2 in the Spiral Arm Clouds

International audienceUsing the IRAM 30-m telescope, we observed molecular absorption lines from c-C<SUB>3</SUB>H<SUB>2</SUB> produced in diffuse clouds toward the high-mass star forming regions W51 e1/e2 and W49N to determine the abundance ratio between the cyclic and linear isomers of C<SUB>3</SUB>H<SUB>2</SUB> (N<SUB>c</SUB>/N<SUB>l</SUB>). The abundance ratio is found to be 3-5 in the sources where l-C<SUB>3</SUB>H<SUB>2</SUB> was previously detected. A possible source of uncertainty in the determination of N<SUB>c</SUB>/N<SUB>l</SUB> is related to the estimate of N(c-C<SUB>3</SUB>H<SUB>2</SUB>). The main goal of this paper is verification of this hypothesis

First Solar System Observations with Herschel

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First Solar System Observations with Herschel

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First Solar System Observations with Herschel

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The Effect of an Increased Elemental D/H Ratio on Deuterium Fractionation in the Cold Interstellar Medium

International audienceMeasurements using the Far Ultraviolet Spectroscopic Explorer (FUSE) show that the gas-phase D/H ratio in the solar neighborhood is highly variable and suggest that the elemental abundance of deuterium in the Galactic disk may be higher than previously thought. We investigate in this Letter the possible consequences of such an enhanced D/H ratio on the deuterium fractionation in singly and multiply deuterated molecules in cold, dense gas. We show that a modest increase in the elemental abundance of deuterium can lead to significant enhancements in abundances of multiply deuterated species

Low Abundance of Hydrogen Isocyanide in Comet 73P-B/Schwassmann-Wachmann 3

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