X Rays From the Solar System and Beyond IV
Presiding: C M Lisse, University of Maryland/Applied Physics Laboratory, Johns Hopkins University; P Beiersdorfer, Lawrence Livermore National Laboratory
P44A-01 15:30h
Charge Exchange Of Solar Wind Alpha Particles In Cometary Atmospheres
Cometary far ultraviolet and soft X-ray emission can provide detailed insight in the interaction between comets and the solar wind. Using the two complementary experimental techniques of photon emission spectroscopy and translation energy spectroscopy we have studied state selective charge exchange in collisions between fully ionized helium and target gasses characteristic for cometary atmospheres. Experiments were performed at velocities typical for the solar wind (200-1500 km/s). From the experimental data cross sectional data sets are produced that are used for modeling the interaction of solar wind alpha particles with cometary atmospheres. Our model results demonstrate how the solar wind velocity and how cometary properties such as the composition of its atmosphere, the outgassing rate and the heliocentric distance are reflected in the helium line emission.
http://www.kvi.nl/~atf
P44A-02 15:45h
X-ray Emissions from Jupiter as Observed with XMM-Newton
We present two XMM-Newton observations of Jupiter, which were carried out in April and November 2003 for 110 and 250 ks (or 3 and 7 planet rotations) respectively. X-ray images taken with XMM-Newton EPIC CCD cameras show prominent emission, essentially all confined to the 0.2 - 2.0 keV band, from Jupiter's auroral spots; their spectra can be modelled with a combination of unresolved emission lines, including most prominently those of highly ionised oxygen (OVII and OVIII). Emission from the equatorial regions of the planet's disk is also observed. Its spectrum is consistent with that of solar X-rays scattered in the planet's upper atmosphere. More remarkably, we find that in November 2003 a large solar X-ray flare, taking place on the Sun's Jupiter-facing side, is associated with a corresponding feature in the Jovian X-ray lightcurve of the equatorial regions. Jupiter's X-ray emissions are spectrally resolved with XMM-Newton Reflection Grating Spectrometer (RGS). The high energy resolution provided by RGS allows us to clearly separate the OVII and OVIII lines in the spectra, and to identify most of the auroral emission with the lower ionisation line. The North auroral spot emission is deeply modulated at the planet's rotation period. Moreover, the X-ray emission from Jupiter's disk displays prominent line contribution due to FeXVII, in addition to an OVIII component. Our temporal and spectral findings suggest that the non-auroral X-ray emission from Jupiter is directly controlled by the Sun. On the other hand, the spectral results presented here support the hypothesis that Jupiter's auroral emissions originate from the capture and acceleration of solar wind ions in the planet's magnetosphere, followed by X-ray production by charge exchange.
P44A-03 16:00h
Ion emission spectra in the Jovian X-ray Aurora
X-ray and EUV emission spectra of energetic sulfur and oxygen ions precipitating into the Jovian atmosphere are investigated. The charge distributions of Oq+ and Sq+ ions are computed for different initial energies of the solar wind and magnetospheric ions with updated cross sections for stripping, electron capture, and target ionization processes. Results of Monte Carlo simulations of the energy-charge relaxation of precipitating ions are compared with the equilibrium charge model. Spectra of emitted X-ray and EUV photons are obtained for the sulfur and oxygen ion fluxes with different initial energies, and photon yield functions are computed for the brightest spectral lines. Theoretical spectra are used to determine the initial energy distributions of precipitating ions from the X-ray spectra detected by the Chandra and XMM-Newton X-ray telescopes. Spectral contributions of the magnetospheric and solar wind ions are compared.
P44A-04 16:15h
X-rays from Saturn and its Rings
In January 2004 Saturn was observed by Chandra ACIS-S in two exposures, 00:06 to 11:00 UT on 20 January and 14:32 UT on 26 January to 01:13 UT on 27 January. Each continuous observation lasted for about one full Saturn rotation. These observations detected an X-ray flare from the Saturn's disk and indicate that the entire Saturnian X-ray emission is highly variable -- a factor of ~4 variability in brightness in a week time. The Saturn X-ray flare has a time and magnitude matching feature with the solar X-ray flare, which suggests that the disk X-ray emission of Saturn is governed by processes happening on the Sun. These observations also unambiguously detected X-rays from Saturn's rings. The X-ray emissions from rings are present mainly in the 0.45-0.6 keV band centered on the atomic O Kα fluorescence line at 525 eV: indicating the production of X-rays due to oxygen atoms in the water icy rings. The characteristics of X-rays from Saturn's polar region appear to be statistically consistent with those from its disk X-rays, suggesting that X-ray emission from the polar cap region might be an extension of the Saturn disk X-ray emission.
P44A-05 16:30h
Scattering of Solar X-Rays by Jupiter and Saturn
Soft X-ray emission has been observed from the disks of both Jupiter and Saturn, as well as from the auroral regions of these planets. The low-latitude disk emission as observed by ROSAT, the Chandra X-Ray Observatory, and XMM-Newton appears to be uniformly distributed across the disk and to be correlated with solar activity. These characteristics suggest that the source of the disk x-rays are: (1) elastic scattering of solar X-rays by atmospheric neutrals (2) absorption of solar X-rays in the carbon K-shell followed by fluorescent emission. The carbon atoms are found in methane molecules located below the homopause. In this paper we present the results of calculations of the scattering albedo and of the emitted x-ray intensity for a range of atmospheric abundances and for a number of solar irradiance spectra. The model calculations are compared with recent x-ray observations of Jupiter and Saturn.
P44A-06 16:45h
X-Ray Spectroscopy of Optically Bright Planets with the Chandra Observatory
Since its launch in July 1999, Chandra's Advanced CCD Imaging Spectrometer (ACIS) has observed several planets (Venus, Mars, Jupiter and Saturn) and 6 comets. At 0.5 arc-second spatial resolution, ACIS detects individual x-ray photons with good quantum efficiency (25% at 0.6 KeV) and energy resolution (20% FWHM at 0.6 KeV). However, the ACIS CCDs are also sensitive to optical and near-infrared light, which is absorbed by optical blocking filters (OBFs) that eliminate optical contamination from all but the brightest extended sources, e.g., planets. Jupiter at opposition subtends ~45 arc-seconds (90 CCD pixels.) Since Chandra is incapable of tracking a moving target, the planet takes 10 - 20 kiloseconds to move across the most sensitive ACIS CCD, after which the observatory must be re-pointed. Meanwhile, the OBF covering that CCD adds an optical signal equivalent to ~110 eV to each pixel that lies within the outline of the Jovian disk. This has three consequences: (1) the observatory must be pointed away from Jupiter while CCD bias maps are constructed; (2) most x-rays from within the optical image will be misidentified as charged-particle background and ignored; and (3) those x-rays that are reported will be assigned anomalously high energies. The same also applies to the other planets, but is less serious since they are either dimmer at optical wavelengths, or they show less apparent motion across the sky, permitting reduced CCD exposure times: the optical contamination from Saturn adds ~15 eV per pixel, and from Mars and Venus ~30 eV. After analyzing a series of short Jupiter observations in December 2000, ACIS parameters were optimized for the February 2003 opposition. CCD bias maps were constructed while Chandra pointed away from Jupiter, and the subsequent observations employed on-board software to ignore any pixel that contained less charge than that expected from optical leakage. In addition, ACIS was commanded to report 5 × 5 arrays of pixel values surrounding each x-ray event, and the outlying values were employed during ground processing to correct for the optical contamination.