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Post Info TOPIC: Comet C/2006 W3 (Christensen)


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RE: Comet C/2006 W3 (Christensen)
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Title: Herschel observations of gas and dust in comet C/2006 W3 (Christensen) at 5 AU from the Sun
Author: M. de Val-Borro, D. Bockelée-Morvan, E. Jehin, P. Hartogh, C. Opitom, S. Szutowicz, N. Biver, J. Crovisier, D. C. Lis, L. Rezac, Th. de Graauw, D. Hutsemékers, C. Jarchow, M. Kidger, M. Küppers, L. M. Lara, J. Manfroid, M. Rengel, B. M. Swinyard, D. Teyssier, B. Vandenbussche, C. Waelkens

We aimed to measure the H2O and dust production rates in C/2006 W3 (Christensen) with the Herschel Space Observatory at a heliocentric distance of ~ 5 AU. We have searched for emission in the H2O and NH3 ground-state rotational transitions at 557 GHz and 572 GHz, simultaneously, with HIFI onboard Herschel on UT 1.5 September 2010. Photometric observations of the dust coma in the 70 and 160 {\mu}m channels were acquired with the PACS instrument on UT 26.5 August 2010. A tentative 4-{\sigma} H2O line emission feature was found in the spectra obtained with the HIFI wide-band and high-resolution spectrometers, from which we derive a water production rate of 2.0(5) x 10^27 molec. s^-1. A 3-{\sigma} upper limit for the ammonia production rate of <1.5 x 10^27 molec. s^-1 is obtained taking into account the contribution from all hyperfine components. The blueshift of the water line detected by HIFI suggests preferential emission from the subsolar point. However, it is also possible that water sublimation occurs in small ice-bearing grains that are emitted from an active region on the nucleus surface at a speed of ~ 0.2 km s^-1. The dust thermal emission was detected in the 70 and 160 {\mu}m filters, with a more extended emission in the blue channel. The dust production rates, obtained for a dust size distribution index that explains the fluxes at the photocenters of the PACS images, lie in the range 70-110 kg s^-1. Scaling the CO production rate measured post-perihelion at 3.20 and 3.32 AU, these values correspond to a dust-to-gas production rate ratio in the range 0.3-0.4. The dust production rates derived in August 2010 are roughly one order of magnitude lower than in September 2009, suggesting that the dust-to-gas production rate ratio remained approximately constant during the period when the activity became increasingly dominated by CO outgassing.

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Title: A study of the distant activity of comet C/2006 W3 (Christensen) using Herschel and ground-based radio telescopes
Authors: D. Bockelée-Morvan, P. Hartogh, J. Crovisier, B. Vandenbussche, B.M. Swinyard, N. Biver, D.C. Lis, C. Jarchow, R. Moreno, D. Hutsemékers, E. Jehin, M.K. Küppers, L.M. Lara, E. Lellouch, J. Manfroid, M. de Val-Borro, S. Szutowicz, M. Banaszkiewicz, F. Bensch, M.I. Blecka, M. Emprechtinger, T. Encrenaz, T. Fulton, M. Kidger, M. Rengel, C. Waelkens, E. Bergin, G.A. Blake, J.A.D.L. Blommaert, J. Cernicharo, L. Decin, P. Encrenaz, T. de Graauw, S. Leeks, A.S. Medvedev, D. Naylor, R. Schieder, N.Thomas

Comet C/2006 W3 (Christensen) was observed in November 2009 at 3.3 AU from the Sun with Herschel. The PACS instrument acquired images of the dust coma in 70- and 160-micrometers filters, and spectra covering several H2O rotational lines. Spectra in the range 450-1550 GHz were acquired with SPIRE. The comet emission continuum from 70 to 672 micrometers was measured, but no lines were detected. The spectral energy distribution indicates thermal emission from large particles and provides a measure of the size distribution index and dust production rate. The upper limit to the water production rate is compared to the production rates of other species (CO, CH3OH, HCN, H2S, OH) measured with the IRAM 30-m and Nancay telescopes. The coma is found to be strongly enriched in species more volatile than water, in comparison to comets observed closer to the Sun. The CO to H2O production rate ratio exceeds 220%. The dust to gas production rate ratio is on the order of 1.

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Ephemeris
Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   mag
2009 12 25 19 33.78 -17 21.7 4.445 3.534 19.7 5.4 13.7
2009 12 30 19 36.83 -17 53.4 4.496 3.557 15.2 4.2 13.8
2010 01 04 19 39.92 -18 23.7 4.541 3.579 10.7 2.9 13.8
2010 01 09 19 43.04 -18 52.8 4.578 3.602 6.3 1.7 13.9
2010 01 14 19 46.18 -19 21.0 4.609 3.626 2.3 0.6 13.9
2010 01 19 19 49.30 -19 48.4 4.632 3.650 3.3 0.9 14.0
2010 01 24 19 52.39 -20 15.4 4.648 3.674 7.5 2.0 14.0
2010 01 29 19 55.43 -20 42.1 4.657 3.699 12.0 3.2 14.0


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Comet C/2006 W3 (Christensen) Magnitude= 9.0mag
Best seen from 18.4h -19.7h
RA=19h10m10  Dec= -7°20.3' (J2000)
Distance to Sun= 3.31AU 
Distance to Earth= 3.40AU 
Elongation= 76°
hourly motion: dRA=  1.0"/h  dDec=-38.1"/h

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Ephemeris
Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   mag
2009 09 26 19 19.57 +02 20.1 2.781 3.224 107.3 17.3 12.3
2009 10 01 19 16.33 +00 23.4 2.878 3.236 101.9 17.6 12.4
2009 10 06 19 13.84 -01 25.1 2.979 3.249 96.6 17.8 12.5
2009 10 11 19 12.04 -03 05.6 3.083 3.263 91.3 17.8 12.6
2009 10 16 19 10.86 -04 38.6 3.190 3.277 86.1 17.7 12.7
2009 10 21 19 10.26 -06 04.5 3.297 3.292 81.0 17.4 12.8
2009 10 26 19 10.18 -07 23.6 3.404 3.307 76.0 17.0 12.9
2009 10 31 19 10.56 -08 36.6 3.511 3.323 71.0 16.4 12.9


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Ephemeris
Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   mag

2009 09 01 19 49.15 +13 53.8 2.409 3.174 132.0 13.7 11.9
2009 09 06 19 41.31 +11 23.6 2.464 3.182 127.7 14.5 12.0
2009 09 11 19 34.46 +08 57.7 2.531 3.192 122.9 15.3 12.1
2009 09 16 19 28.58 +06 37.8 2.606 3.202 117.9 16.1 12.1
2009 09 21 19 23.64 +04 25.0 2.690 3.213 112.6 16.8 12.2
2009 09 26 19 19.57 +02 20.1 2.781 3.224 107.3 17.3 12.3


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Ephemeris

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   m1    

2009 08 02 20 53.98 +27 54.8 2.343 3.137 134.3 13.4 11.8
2009 08 07 20 41.71 +25 56.4 2.321 3.141 137.1 12.7 11.8
2009 08 12 20 29.78 +23 45.7 2.312 3.146 138.8 12.3 11.8
2009 08 17 20 18.40 +21 25.1 2.317 3.152 139.1 12.2 11.8
2009 08 22 20 07.76 +18 57.5 2.334 3.158 137.9 12.4 11.8
2009 08 27 19 57.98 +16 26.0 2.365 3.166 135.4 12.9 11.9



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Ephemeris
Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   mag    

2009 04 09 22 48.52 +33 58.5 3.915 3.242 42.1 12.0 13.1
2009 04 14 22 49.91 +34 02.0 3.875 3.230 44.0 12.5 13.0
2009 04 19 22 51.00 +34 07.3 3.829 3.218 46.3 13.0 13.0
2009 04 24 22 51.78 +34 14.4 3.777 3.207 48.9 13.7 12.9
2009 04 29 22 52.19 +34 22.8 3.720 3.197 51.8 14.3 12.9



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