Spectral analysis of the Chandra comet survey^*

¹ KVI atomic physics, University of Groningen, Zernikelaan 25, NL-9747 AA Groningen, The Netherlands e-mail: [bodewits;hoekstra]@kvi.nl
² Queen's University Belfast, Department of Physics and Astronomy, Belfast, BT7 1NN, UK e-mail: d.christian@qub.ac.uk
³ Atoms Beams and Plasma Group, University of Strathclyde, Glasgow, G4 0NG, UK e-mail: torney@phys.strath.ac.uk
⁴ NOAA Space Environment Center, 325 Broadway, Boulder, CO 80305, USA e-mail: murray.dryer@noaa.gov
⁵ Planetary Exploration Group, Space Department, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD 20723, USA e-mail: carey.lisse@jhuapl.edu
⁶ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany e-mail: kod@mpe.mpg.de
⁷ The University of Michigan, Department of Atmospheric, Oceanic and Space Sciences, Space Research Building, Ann Arbor, MI 48109-2143, USA e-mail: thomasz@umich.edu
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail: swolk@head.cfa.harvard.edu
⁹ NASA Ames Research Center, MS 245-3, Moffett Field, CA 9435-1000, USA e-mail: tielens@astro.rug.nl

Received: 5 March 2007
Accepted: 17 April 2007

Abstract

Aims.We present results of the analysis of cometary X-ray spectra with an extended version of our charge exchange emission model (Bodewits et al. 2006). We have applied this model to the sample of 8 comets thus far observed with the Chandra X-ray observatory and acis spectrometer in the 300–1000 eV range. The surveyed comets are C/1999 S4 (linear), C/1999 T1 (McNaught–Hartley), C/2000 WM1 (linear), 153P/2002 (Ikeya–Zhang), 2P/2003 (Encke), C/2001 Q4 (neat), 9P/2005 (Tempel 1) and 73P/2006-B (Schwassmann–Wachmann 3) and the observations include a broad variety of comets, solar wind environments and observational conditions.

Methods.The interaction model is based on state selective, velocity dependent charge exchange cross sections and is used to explore how cometary X-ray emission depend on cometary, observational and solar wind characteristics. It is further demonstrated that cometary X-ray spectra mainly reflect the state of the local solar wind. The current sample of Chandra observations was fit using the constrains of the charge exchange model, and relative solar wind abundances were derived from the X-ray spectra.

Results.Our analysis showed that spectral differences can be ascribed to different solar wind states, as such identifying comets interacting with (I) fast, cold wind, (II), slow, warm wind and (III) disturbed, fast, hot winds associated with interplanetary coronal mass ejections. We furthermore predict the existence of a fourth spectral class, associated with the cool, fast high latitude wind.