Topical Group on EUV and X-Ray Emission from Comets, Planets, and Heliospheric Gas

January 16-17, 2003

Organizers: Vasili Kharchenko and Alex Dalgarno

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Schedule

Thursday January 16 (M340 Conference Room, 160 Concord Avenue, 3rd Floor)

8:30-8:50 a.m. Coffee

Session 1: Kate Kirby, Chair

8:50-9:00 a.m. Kate Kirby, Introduction
9:00 -9:30 a.m. Thomas Cravens, " X-Ray Emission in the Solar System"

9:30 - 9:50 a.m. Discussion

9:50 -10:10 a.m., Scott J. Wolk, " Chandra's View of the Solar System"

10:10 -10:25 a.m. Discussion
10:25 - 10:40 a.m. Coffee break
10:40 - 11:10 a.m. Randall Gladstone, "Soft X-ray Emissions from the Jovian System"

11:10 -11:30 a.m. Discussion

11:30 -12:00 noon. David R. Schultz, "Atomic Physics Data for Jovian UV/X-ray Emission"

12:00 -12:20 p.m. Discussion

12:20 -2:00 p.m. Lunch

Session 2: David Schultz, Chair

2:00 - 2:30 p.m. Paul Feldman, "Spectroscopy of Cometary and Planetary Atmospheres
in the 900-1200 A Spectral Range with the FUSE"

2:30- 2:45 p.m. Discussion
2:45- 3:15 p.m. Casey Lisse, "Observations of EUV and X-ray Emission from Comets"

3:15- 3:30 p.m. Discussion
3:30-3:45 p.m. Refreshments
3:45- 4:00 p.m. Damian Christian, "Analysis and Results from the Chandra LETG Observations of C/2000 WM1 (LINEAR)"

4:00- 4:10 p.m. Discussion
4:10 - 4:40 p.m. Ara Chutjian, "Measurement of Charge-Exchange Cross Sections for the
Interaction of Solar-Wind Ions with Neutral Atoms and Molecules"

4:40-4:55 p.m. Discussion
4:55 -5:25 p.m. Phillip Stancil, "The Status of Charge Transfer Calculations Relevant
to EUV/X-ray Emission in the Solar System''

5:25 -5:40 p.m. Discussion

5:40 p.m. Reception in Perkin Lobby

Friday, January 17 (Phillips Auditorium 9:00 - 12:30)

Session 3: Nancy Brickhouse, Chair

9:00-9:30 a.m. Brad Wargelin, "Spectral Evidence for Geocoronal X Rays from Chandra Observations of the 'Dark' Moon

9:30 -9:45 a.m. Discussion

9:45-10:15 a.m. Richard J. Edgar, "Spectroscopic Observations of the Diffuse Soft X-ray Background"

10:15 - 10:30 a.m. Discussion
10:30 - 10:40 a.m. Coffee break
10:40- 11:10 a.m. Jason B. Greenwood, "Recent Laboratory Measurements of Charge Exchange Relevant to Cometary and Heliospheric EUV and Soft X-ray Emissions"
11:10-11:25 a.m. Discussion
11:25-11:55 a.m. Endre Takács, "Spectroscopy of Highly Charged Ions at the NIST Electron
Beam Ion Trap"

11:55-12:10 a.m. Discussion
12:10-12:30 a.m. Alex Dalgarno, "Transition Probabilities of Helium-like Ions"

12:30- 12:40 a.m. Discussion

12:40 -2:00 p.m. Lunch

Session 4: Casey Lisse, Chair

(Classroom, Building A, [A-101])

2:00 - 2:30 p.m. John C. Raymond, "X-ray and UV Spectral Predictions of Models for Cometary

2:30 -2:50 p.m. Discussion
2:50 - 3:20 p.m. Nancy S. Brickhouse, "The Astrophysical Plasma Emission Code and Database"
3:20-3:40 p.m. Discussion
3:40- 3:55 p.m. Refreshments
3:55-4:15 p.m. Vasili Kharchenko, "Spectra of Cascading Photons for the Charge Transfer Mechanism: Correlation between UV, EUV and X-ray Photons"

4:15 -4:25 p.m. Discussion
4:25 -5:30 p.m. Summarizing discussion

Participants

Dr. Nancy S. Brickhouse HEA Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 06 Cambridge, MA 02138 nbrickhouse@cfa.harvard.edu   Dr. Damian Christian Dept. of Physics & Astronomy The Johns Hopkins University 3400 North Charles Street Baltimore, MD 21218-2686 damian@pha.jhu.edu Prof. Ara Chutjian Jet Propulsion Laboratory 4800 Oak Grove, MS 121-114 Pasadena CA 91109 ara.chutjian@jpl.nasa.gov Prof. Thomas Cravens University of Kansas Department of Physics and Astronomy 1251 Wescoe Hall Drive Lawrence, KS 66045 cravens@ku.edu   Prof. Alex Dalgarno ITAMP Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 14 Cambridge, MA 02138 adalgarno@cfa.harvard.edu   Dr. Richard J. Edgar HEA Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 70 Cambridge, MA 02138 redgar@cfa.harvard.edu Prof. Paul D. Feldman Department of Physics & Astronomy Johns Hopkins University Baltimore, MD 21218 pdf@pha.jhu.edu Dr. G. Randall Gladstone Southwest Research Institute Space Science and Engineering Division P.O. Drawer 28510 San Antonio, TX 78228 randy.gladstone@swri.org Dr. Jason Greenwood Department of Pure and Applied Physics Queen's University Belfast Belfast BT7 1NN j.greenwood@qub.ac.uk Dr. Michael Juda Chandra X-ray Observatory Center, HEA Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 70 Cambridge, MA 02138 mjuda@cfa.harvard.edu   Prof. Quentin C. Kessel Department of Physics, U-3046 University of Connecticut Storrs, CT 06269 quentin.kessel@uconn.edu   Dr. Kate Kirby ITAMP Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 14 Cambridge, MA 02138 kkirby@cfa.harvard.edu   Dr. Vasili Kharchenko ITAMP, AMP Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 14 Cambridge, MA 02138 vkharchenko@cfa.harvard.edu Dr. Casey Lisse Department of Astronomy University of Maryland College Park, MD 20742 lisse@astro.umd.edu Dr. John C. Raymond SSP Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 15 Cambridge, MA 02138 jraymond@cfa.harvard.edu David R. Schultz Physics Division Oak Ridge National Laboratory M.S. 6372, Bldg. 6000 P.O. Box 2008 Oak Ridge, TN 37831-6372 schultzd@ornl.gov Prof. Winthrop W. Smith Physics Department, U-3046 University of Connecticut Storrs, CT 06269-3046 winthrop.smith@uconn.edu Prof. Phillip Stancil Department of Astronomy and Physics University of Georgia, Athens GA 30602 stancil@hal.physast.uga.edu Dr. Endre Takács NIST Atomic Physics Division 100 Bureau Drive, Stop 8421 Gaithersburg, MD 20899-842 National Institute of Standards and Technology Gaithersburg, MD 20899 Endre.Takacs@nist.gov   Dr. Bradford Wargelin Chandra X-ray Observatory Center, HEA Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 70 Cambridge, MA 02138 bwargelin@cfa.harvard.edu   Dr. Scott J. Wolk Chandra X-ray Observatory Center, HEA Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 70 Cambridge, MA 02138 swolk@cfa.harvard.edu

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Abstracts

Brickhouse	Christian	Chutjian	Cravens
Dalgarno	Edgar	Feldman	Gladstone
Greenwood	Kharchenko	Lisse	Raymond
Schultz	Stancil	Takács	Wargelin
Wolk

The Astrophysical Plasma Emission Code and Database Nancy S. Brickhouse HEA Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 06 Cambridge, MA 02138 The Astrophysical Plasma Emission Database (APED) is a publicly available atomic database of particular use for X-ray spectral modeling of collisionally ionized plasmas. At the present time the Astrophysical Plasma Emission Code (APEC) calculates emission spectra in collisional ionization equilibrium. Our next goal is to produce models for non-equilibrium ionization plasmas with various applications. I will describe what's in the database and how charge exchange rate data might be incorporated.

Analysis and Results from the Chandra LETG Observations of C/2000 WM1 (LINEAR) Christian, D.J.*, Lisse, C., Wolk, S. and Dennerl, K. *Dept. of Physics and Astronomy The Johns Hopkins University 3400 North Charles Street Baltimore, MD 21218-2686 C/2000 WM1 was observed with the Chandra LETG on Dec 31, 2001. Four pointings tracking the Comet were conducted keeping the Comet's 0th order image centered on chip S2 for a total exposure of 34 ksec. We present preliminary analysis of the dispersed and pulse-height spectra.

Measurement of Atomic Collision Parameters Involving Highly-Charged Ions in Astronomical Objects A. Chutjian Jet Propulsion Laboratory and California Institute of Technology 4800 Oak Grove, MS 121-114 Pasadena CA 91109 X-ray emissions are produced by the interaction of solar-wind ions with cometary, planetary and (possibly) circumstellar neutral species. They are also produced by the collisional excitation of highly-charged ions (HCIs) in the sun and stars. To interpret the former within the model of an HCI-comet (say) neutral interaction, one requires charge-exchange and X-ray emission cross sections. For the latter, one requires collisional excitation cross sections and Einstein A-values. Using the JPL HCI Facility, we will present a sample of measurements of absolute cross sections for single and double charge exchange of HCIs with neutral atoms and molecules, as well as results for collisional excitation and lifetimes in HCIs.

X-Ray Emission in the Solar System T. E. Cravens University of Kansas, Lawrence, KS 66045 Many objects in the solar system produce x-rays, including the Sun, Venus, Earth, Mars, Jupiter, and comets. A number of emission mechanisms account for this x-ray emission including scattering and fluorescence of solar x-rays, impact excitation of atoms and molecules by energetic electrons and ions, and by charge transfer of highly charged ions with neutrals. A brief review is provided of x-ray sources and emission mechanisms in the solar system. In particular, x-rays are produced when highly charged solar wind ions (e.g., O7+, C6+, Fe12+,.) undergo charge transfer collisions with neutral atoms and molecules they might encounter in space. The ion resulting from such a collision is almost always highly excited and emits an extreme ultraviolet (EUV) or soft x-ray photon. X-ray emission from comets, from the terrestrial geocorona, and from the heliosphere has been attributed to this solar wind charge exchange (SWCX) mechanism. It is also possible that the SWCX mechanism can explain Jovian auroral x-rays, although the solar wind ions would require considerable acceleration in this case.

Transition Probabilities of Helium-like Ions  Alex Dalgarno ITAMP Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 14 Cambridge, MA 02138 A summary of atomic data on the radiative transitions of helium-like ions will be presented together with a brief discussion of the emission spectra resulting from electron capture by hydrogenic ions.

Spectroscopic Observations of the Diffuse Soft X-ray Background 1Richard J. Edgar and 2Wilton T. Sanders(University of Wisconsin) 1HEA Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 70 Cambridge, MA 02138 2University of Wisconsin The Diffuse X-Ray Spectrometer (DXS), which flew as an attached payload on the Space Shuttle Endeavour in January 1993, obtained spectra of the low-energy X-ray (44-83 Angstrom) diffuse background near the Galactic plane from longitudes 150 < l < 300 degrees with better than 3 Angstrom spectral and ~15 degree spatial resolution. We discuss the spectral properties of this emission, atomic physics needs for the interpretation of these data, and discuss the possibility that a part of the emission may arise from the heliosphere. We will also discuss observations of the oxygen lines (the O VII helium alpha complex and/or the O VIII Lyman alpha line) in the diffuse x-ray background with Chandra. A discussion of the difficulty of using contemporary instruments for such measurements will be included.

Spectroscopy of Cometary and Planetary Atmospheres in the 900-1200 A Spectral Range with the FUSE Satellite Paul D. Feldman Department of Physics and Astronomy Johns Hopkins University Baltimore, Maryland 21218   The spectral band, resolution, and sensitivity of the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, launched in June 1999, provide a unique capability to study the principal atoms, ions and molecules in a variety of planetary environments. The wavelength region from 905 to1187 A is observed at a spectral resolution of 0.3 A or less. This talk will describe the instrumental capabilities of FUSE and review recent observations and results on the atmospheres of Earth and Mars, polar aurora on Jupiter and Saturn, the Io plasma torus, and cometary comae.

Soft X-ray Emissions from the Jovian System  G. Randall Gladstone Southwest Research Institute Space Science and Engineering Division P.O. Drawer 28510 San Antonio, TX 78228 Jovian auroral soft x-ray emissions were first observed by Metzger et al. [1983] using the Einstein observatory and were extensively studied with ROSAT [e.g., Waite et al. 1995; Gladstone et al. 1998]. From limited spectral information and more extensive imaging data, the x-ray emissions were thought to result from charge exchange and excitation of precipitating energetic (>1MeV per nucleon) sulfur and oxygen ions from just outside the region of the Io Plasma Torus. However, this view has been overturned by recent high-spatial-resolution observations made with Chandra [Gladstone et al. 2001]. It is now established that the particles responsible for Jupiter's auroral x-ray emissions originate in the outer magnetosphere, and furthermore, that they pulsate with a ~45-minute period. The source of the responsible particles is not clear - it is possible that they are solar wind ions rather than from Io. X-ray emissions are also observed in the equatorial regions of Jupiter [Waite et al. 1997].

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Recent Laboratory Measurements of Charge Exchange Relevant to Cometary and Heliospheric EUV and Soft X-ray Emissions Jason B. Greenwood Department of Pure and Applied Physics Queen's University Belfast Belfast BT7 1NN While X-ray emission from charge exchange of C, N and O solar wind ions has been observed by the new generation of X-ray telescopes, laboratory simulations of these collisions has proceeded in parallel. A review of laboratory measurements in this area will be made and of recent work at JPL. This includes a summary of all experimental data obtained for charge exchange of alpha particles which influences the intensity of EUV emission observed from comets and the first results of total charge exchange cross sections for iron charge states. Although transitions in iron charge states are unresolved in the cometary X-ray spectra obtained so far, they are expected to provided significant yields at energies < 300eV.

Spectra of Cascading Photons for the Charge Transfer Mechanism: Correlation Between UV, EUV and X-ray Emissions Vasili Kharchenko ITAMP Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 14 Cambridge, MA 02138 Spectra of cascading photons induced in charge transfer collisions of heavy solar wind (SW) ions with the heliospheric and cometary neutral gas are calculated. Relative intensities of spectral lines of individual SW ions, colliding with H, H2, He, CO2, and H2O atoms and molecules, are computed at different SW velocities. It is shown that relative numbers of UV, EUV, and X-ray photons emitted by excited SW ions may be used for determination of ion velocities and neutral gas composition. Synthetic spectra of UV, EUV and X-ray emission induced by the charge transfer mechanism are evaluated at different composition of the solar wind.

Observations of EUV and X-ray Emission from Comets Casey Lisse Department of Astronomy University of Maryland College Park, MD 20742 The unexpected discovery of x-ray emission from Comet Hyakutake in March 1996 (Lisse et al. 1996) produced a number of questions about the physical mechanism producing the radiation. The original detection and subsequent observations have shown that the very soft (best fit thermal bremsstrahlung model kT $\sim$ 0.2 keV) emission is due to an interaction between the solar wind and the comet's atmosphere. Using the results from the more than 17 comets detected to date in x-rays, we report here on the latest results on cometary x-ray emission, including new results from Chandra, and show that charge exchange between highly ionized minor ions in the solar wind and neutral gases in the cometary coma is the most likely operative mechanism. We then use this result to study a number of problems of astrophysical interest: the nature of the cometary coma, other possible sources of x-ray emission in the solar system, the structure of the solar wind in the heliosphere, and the source of the local x-ray background.

X-ray and UV Spectral Predictions of Models for Cometary X-rays John C. Raymond SSP Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 15 Cambridge, MA 02138 The two models for X-ray emission from comets are charge transfer into excited states of highly ionized metals and collisional excitation by electrons. The latter model is only beginning to reach the stage of quantitative spectral predictions, but it is worthwhile to contrast the observable differences between the predictions of the two models.

Atomic Physics Data for Jovian UV/X-ray Emission David R. Schultz Physics Division Oak Ridge National Laboratory M.S. 6372, Bldg. 6000 P.O. Box 2008 Oak Ridge, Tennessee 37831-6372 After briefly mentioning our recent work to model UV/x-ray emission from Jupiter originating from Iogenic ion precipitation [Liu & Schultz 1999 ApJ 526, 538; Liu & Schultz 2000 ApJ 530, 500; Kharchenko et al. 2003 in preparation] I will describe in some detail the atomic physics data that has been computed enabling this work. This data results from very large calculations of the state-selective (n,l) single charge transfer, transfer-ionization, pure double capture, and autoionizing double capture cross sections across a broad collision energy range for all oxygen and sulfur ionization stages colliding with the principal Jovian atmosphere gas, molecular hydrogen. (All data will be included on the ORNL/UGA charge transfer database for astrophysics, www-cfadc.phy.ornl.gov/astro/ps/data). These data form the basis for computing the UV/X-ray emission from radiatively relaxing Iogenic ions. Also required are similarly extensive results for ionization (a principal energy loss mechanism determining the slowing down of the precipitating ions) and ion stripping (which, combined with charge transfer, determines the charge state evolution of precipitating ions). Some of the theoretical advances required to perform these calculations, along with some of the studies used to benchmark them, will be described. A look forward towards the data that is being computed, or could be computed, to extend this project, or for other related work such as for x-ray emission from comets or for the soft x-ray background, will be given. Close collaboration with Phillip Stancil, Milun Rakovic, Weihong Liu, and Vasili Kharchenko is acknowledged as is past support from the NASA ADP, PA, and AISRP programs and the US DOE.

The Status of Charge Transfer Calculations Relevant to EUV/X-ray Emission in the Solar System P.C. Stancil*, D. R. Schultz, J. G. Wang, M. J. Rakovic', and R. Ali *Department of Astronomy and Physics University of Georgia, Athens GA 30602 A summary of current results for calculations of charge changing collisions of highly charged solar-wind and Iogenic ions with neutral H, He, H2, CO, and H2O will be given. Emphasis will be placed on state-selective cross sections and departures from statistical l- and triplet/singlet-distributions. The results are obtained using a variety of theoretical methods for collision energies less than 10 keV/u. The validity of the methods will be discussed and comparison to experiment will be made where possible for the case of total and n-resolved cross sections. New x-ray emission cascade models for single electron capture, true double electron capture, and autoionizing double capture, constructed with our n,l-resolved charge transfer data, will be presented and compared to recent triple-coincidence COLTRIMS measurements. Finally, plans for future calculations will be summarized. We acknowledge past support for this work from the NASA AISR Program, NASA grant NAG5-9088, and the US DoE.

Spectroscopy of Highly Charged Ions at the NIST Electron Beam Ion Trap E. Takács[1,2] J.D. Gillaspy[1], L.P. Ratliff[1], E. Silver[3], K. Makónyi[1], H. Tawara[1], 1 National Institute of Standards and Technology, Gaithersburg, MD 2 University of Debrecen, Debrecen, Hungary 3 Smithsonian Astrophysical Observatory, Cambridge, MA The NIST electron beam ion trap (EBIT) is capable of producing the full range of ion charge states responsible for the x-ray and EUV emission in astrophysical and solar environments. The ions can be trapped and studied in situ using different spectroscopic methods, ranging from precision Bragg crystal spectroscopy through broadband x-ray microcalorimetry and grating spectroscopy. Instruments available for use cover, cumulatively, the entire spectral range from the visible to the hard x-ray. In addition, the NIST EBIT is equipped with an ion extraction and transport system for ion beam collision experiments and to assist in the interpretation of the spectra of the trapped ions. The present talk will highlight the capabilities and recent results of our laboratory, including our latest studies involving x-ray emission during collisions of few-electron ions with neutral gases. Our first attempts to model these collision experiments will be presented.

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Spectral Evidence for Geocoronal X Rays from Chandra Observations of the "Dark" Moon B. Wargelin, A. Dalgarno, M. Juda, V. Kharchenko, and M. Markevitch Harvard-Smithsonian Center for Astrophysics 60 Garden Street Cambridge, MA 02138 The Chandra X-ray Observatory observed the partially illuminated Moon during a series of observations with the ACIS CCD detector in July and September 2001. The intention was to block "cosmic" X rays and observe the unilluminated portion of the Moon to determine the detector background. Another background measurement was conducted in September 2002 with ACIS in a "stowed" position (not exposed to the sky). When comparing the dark Moon and ACIS-stowed data, faint line-like excess emission around 600 eV is observed in some of the Moon data, providing strong evidence for charge exchange between solar wind ions and neutral hydrogen in the geocorona.

Chandra's View of the Solar System Scott J. Wolk   Chandra X-ray Observatory Center, HEA Division Harvard-Smithsonian Center for Astrophysics 60 Garden Street, MS 70 Cambridge, MA 02138 I will provide a summary broad and shallow summary several comet and planetary observation performed by the Chandra X-ray observatory. I expect to focus on results from Venus, Mars and the comet Ikeya-Zhang in the inner solar system. In the outer Solar system I will report on result from Jupiter which include the detection of several moons.

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