Volume 530, June 2011
|Number of page(s)||5|
|Published online||28 April 2011|
Letters to the Editor
UJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique (IPAG) UMR 5274, 38041 Grenoble, France
2 Dep. de Física Teórica, Fac. de Ciencias, UAM Campus Cantoblanco, 28049 Madrid, Spain
3 University of Vienna, Dept. of Astronomy, Türkenschanzstr. 17, 1180 Vienna, Austria
4 School of Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK
5 UK Astronomy Technology Centre, Royal Observatory, Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
6 Max Planck Institute for Astronomy, Königstuhl 17 69117, Heidelberg, Germnay
7 Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
8 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
9 Eureka Scientific and Exoplanets and Stellar Astrophysics Lab, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771, USA
10 Clemson University, Clemson, SC, USA
11 Department of Physics & Astronomy, The Open University, Milton Keynes MK7 6AA, UK
12 The Rutherford Appleton Laboratory, Chilton, Didcot, OX11 OQL, UK
13 SOFIA-USRA, NASA Ames Research Center, Mailstop 211-3 Moffett Field CA 94035 USA
Received: 9 February 2011
Accepted: 12 April 2011
Despite its importance in the thermal balance of the gas and in the determination of primeval planetary atmospheres, the chemistry in protoplanetary discs remains poorly constrained with only a handful of detected species. We observed the emission from the disc around the Herbig Be star HD 100546 with the PACS instrument in the spectroscopic mode on board the Herschel Space Telescope as part of the GAS in Protoplanetary Systems (GASPS) programme and used archival data from the DIGIT programme to search for the rotational emission of CH+. We detected in both datasets an emission line centred at 72.16 μm that most likely corresponds to the J = 5−4 rotational emission of CH+. The J = 3−2 and 6−5 transitions are also detected albeit with lower confidence. Other CH+ rotational lines in the PACS observations are blended with water lines. A rotational diagram analysis shows that the CH+ gas is warm at 323 K with a mass of ~3 × 10-14−5 × 10-12 M⊙. We modelled the CH+ chemistry with the chemo-physical code ProDiMo using a disc density structure and grain parameters that match continuum observations and near- and mid-infrared interferometric data. The model suggests that CH+ is most abundant at the location of the disc rim at 10−13 AU from the star where the gas is warm, which is consistent with previous observations of hot CO gas emission.
Key words: protoplanetary disks / astrochemistry
Herschel is an ESA space observatory with science instruments provided by Principal Investigator consortia. It is open for proposals for observing time from the worldwide astronomical community.
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2011
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