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Simultaneous Observations of Comet C/2002 T7 (LINEAR) with the Berkeley-Illinois-Maryland Association and Owens Valley Radio Observatory Interferometers: HCN and CH_3OH

Hogerheijde, Michiel R. and Qi, Chunhua and de Pater, Imke and Blake, Geoffrey A. and Friedel, D. N. and Forster, J. R. and Palmer, Patrick and Remijan, Anthony J. and Snyder, L. E. and Wright, M. C. H. (2009) Simultaneous Observations of Comet C/2002 T7 (LINEAR) with the Berkeley-Illinois-Maryland Association and Owens Valley Radio Observatory Interferometers: HCN and CH_3OH. Astronomical Journal, 137 (6). pp. 4837-4845. ISSN 0004-6256. https://resolver.caltech.edu/CaltechAUTHORS:20090828-083521932

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Abstract

We present observations of HCN J = 1-0 and CH_3OH J(K_a, K_c) = 3(1, 3)-4(0, 4) A+ emission from comet C/2002 T7 (LINEAR) obtained simultaneously with the Owens Valley Radio Observatory (OVRO) and Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometers. We combined the data from both arrays to increase the (u, v) sampling and signal to noise of the detected line emission. We also report the detection of CH_3OH J(K_a, K_c) = 8(0, 8)-7(1, 7) A^+ with OVRO data alone. Using a molecular excitation code that includes the effects of collisions with water and electrons, as well as pumping by the Solar infrared photons (for HCN alone), we find a production rate of HCN of 2.9 × 10^(26) s^(–1) and for CH_3OH of 2.2 × 10^(27) s^(–1). Compared to the adopted water production rate of 3 × 10^(29) s^(–1), this corresponds to an HCN/H_2O ratio of 0.1% and a CH_3OH/H_2O ratio of 0.7%. We critically assess the uncertainty of these values due to the noise (~10%), the uncertainties in the adopted comet model (~50%), and the uncertainties in the adopted collisional excitation rates (up to a factor of 2). Pumping by Solar infrared photons is found to be a minor effect for HCN, because our 15" synthesized beam is dominated by the region in the coma where collisions dominate. Since the uncertainties in the derived production rates are at least as large as one-third of the differences found between comets, we conclude that reliable collision rates and an accurate comet model are essential. Because the collisionally dominated region critically depends on the water production rate, using the same approximate method for different comets may introduce biases in the derived production rates. Multiline observations that directly constrain the molecular excitation provide much more reliable production rates.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-6256/137/6/4837DOIArticle
http://www.iop.org/EJ/abstract/1538-3881/137/6/4837/PublisherArticle
ORCID:
AuthorORCID
Qi, Chunhua0000-0001-8642-1786
de Pater, Imke0000-0002-4278-3168
Blake, Geoffrey A.0000-0003-0787-1610
Remijan, Anthony J.0000-0001-9479-9287
Additional Information:© 2009 The American Astronomical Society. Received 2008 May 28; accepted 2009 March 25; published 2009 April 29. We are indebted to the staffs of BIMA and OVRO for making the observations possible. Frank Bensch is thanked for useful discussions about the required adaptations of the molecular excitation code. Fred Lahuis is thanked for help with the vibrational spectroscopy. The Netherlands Research School for Astronomy (NOVA) is acknowledged for a bezoekersbeurs for Imke de Pater to Leiden. The anonymous referee is thanked for many useful comments that greatly improved the manuscript.
Subject Keywords:comets: individual (LINEAR C/2002 T7); molecular processes; radio lines: solar system; techniques: interferometric
Issue or Number:6
Record Number:CaltechAUTHORS:20090828-083521932
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20090828-083521932
Official Citation:Simultaneous Observations of Comet C/2002 T7 (LINEAR) with the Berkeley-Illinois-Maryland Association and Owens Valley Radio Observatory Interferometers: HCN and CH3OH Michiel R. Hogerheijde, Chunhua Qi, Imke de Pater, Geoffrey A. Blake, D. N. Friedel, J. R. Forster, Patrick Palmer, Anthony J. Remijan, L. E. Snyder, and M. C. H. Wright 2009 The Astronomical Journal 137 4837-4845 doi: 10.1088/0004-6256/137/6/4837.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15384
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:08 Sep 2009 21:12
Last Modified:09 Mar 2020 13:19

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