Although my research interests began as curiosity about the hot Galatic halo, observational exigencies led me to study both the hot ISM in nearby galaxies and the X-ray emission that arises from the near-Earth environment. As a result I am deeply mired in understanding the instrumental background for XMM and other X-ray missions in astrophysics. However, in 2004, disaster struck, and we discovered that X-ray emission from the near-Earth environment can be a significant "contaminating" signal for observations of extended diffuse X-ray emission. As a result, I have gotten sidetracked into studying solar wind charge exchange emission, both in the magnetosphere and in the heliosphere (see my review article).
My interests lie primarily in the study of the hot Galactic ISM using X-ray observations, and I am particularly interested in isolating and studying the hot Galactic halo. Understanding the extent and nature of the hot Galactic halo places constraints on models of galaxy formation, will be crucial for studies of the Warm-Hot Intergalactic Medium, and may resolve the missing baryon problem. Isolating the hot Galactic halo requires characterization of the Galactic foreground components such as the Local Hot Bubble and the Galactic bulge by a combination of absorption and broad-band photometric techniques. Those foreground components are also of interest and X-ray observations directly address such active questions as the filling factor of hot gas, but can give only indirect answer to questions of the total energy or mass in the hot component. Further progress can be made only if the distance to the gas can be determined, and that can only be determined by shadowing studies.
The current generation of X-ray instruments makes possible isolation of the various emission components by spectroscopic techniques, given sufficiently long exposures and sufficiently accurate instrumental backgrounds and calibration. Thus, I have been working on the characterization of the XMM instrumental background.
However, the temporally variable solar wind charge exchange (SWCX) emission make observations quite difficult as the SWCX emission lines tend to be the strongest emission lines, which are also the lines to be used to diagnose the plasma conditions of the more distant emission. Thus, I had developed an unhealthy interest in the solar wind, the magnetosheath, and the heliosphere. This interest has consequently led to my involvement with a number of heliospheric missions to study the SWCX X-ray emission from the magnetosheath, as well as a new interest in wide-field X-ray imaging.
In parallel, I have been pursuing a study of the diffuse X-ray emission in galaxies similar to the Milky Way (M101, M83, M51, M33, M31) in order to constrain the amounts/types of emission from various structural componentsr: arms, bulge, extended spheroid, etc., as well as different emission components: star-forming regions, diffuse hot gas, unresolved stars, and other unresolved sources. I hope to get back to these studies soon!
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Co-I OWLEYE is a proposed sounding rocket to image the X-ray emission from the cusp of the magnetosheath. |
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Co-I Lobster-eye X-ray Telescope is a sounding rocket to be launched summer 2026 to test SMPO coupling to CCD detectors, in part to prepare for future MidEx proposals. |
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Co-I Line Emission Mapper was a proposed Probe class mission that would have brought high resolution (1-2 eV) imaging spectroscopy to a broad range of diffuse emission studies, allowing one to study the kinematics of hot plasmas. It's rejection for being too narrowly focussed on "a few lines in a very narrow energy band" was heartbreaking, as the soft X-ray band has one of the highest density of diagnostic lines. |
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Co-I Solar-Terrestrial Observer for the Response of the Magnetosphere was a proposed heliospheric MIDEX mission which would, among other things, use a large array of 4 cm by 4 cm slumped micropore optics to image the magnetosheath in the X-ray. STORM will be proposed again. |
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Consultant Solar wind Magnetosphere Ionosphere Link Explorer is a joint ESA/Chinese Academy of Science mission intended to image the Earth's magnetosheath in the X-ray using slumped micropore optics. SMILE is expected to launch in December 2025. |
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Co-I Lunar Environment Heliospheric X-ray Imager (LEXI) will have a mosaic of 9, 4 cm by 4 cm slumped micropore optics providing a 9 by 9 degree FOV which will be imaged by a microchannel plate detector. LEXI was launched on Blue Ghost 1 on 15 January 2025, and landed on the moon on 2 March 2025. The instrument operated until until lunar sunset on 16 March 2025. This instrument was previously flown on DXL in 2012. |
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Co-I CuPID was a 6U cubesat launched into low Earth orbit in 2020. It would have measured the width and location of the cusp in X-rays using a single 4 cm by 4 cm slumped micropore optic. The prototype of this instrument previously flew on DXL-II in 2015. The commercially provided onboard radio failed. |
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Co-I HaloSat was a 6U Cubesat, measuring the soft X-ray spectrum (0.4-8 keV) over the entire sky. Its primary goal was to measure the OVII and OVIII line emiission with a unique strategy to minimize the contributions by SWCX. Some observations also measured SWCX emission from the Earth's magnetosheath and from the heliospheric focussing cone. It used single element Si drift detectors and a colimator to restrict the FOV to roughly 10 degrees. HaloSat was launched in May 2018 and reentered in January 2021. |
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DXL-IV was launched from Wallops Space Flight Center on 9 January 2022, just hours before the untimely death of its original proposer, Michael Collier. The raw data look very good! |
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DXL-III was launched from Poker Flat Research Range in January 2018. |
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DXL-II launched in December 2015. The payload included the large area proportional counters, one with the standard C band filter, the other with a B band filter. The payload also included two smaller proportional counters with Be band filters. This payload also included the CuPID prototype, which observed in the same direction as the principle instruments. |
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DXL was launched from White Sands Missle Range on 12/12/12. It carried the same intrument which was used to create the Wisconsin All-Sky Survey. That instrument is a pair of proportional counters, each with an effective area of 500 square centimeters at 1 keV and an energy resolution similar to that of ROSAT. The flight scanned across the heliopsheric helium focussing cone to measure the strength of the SWCX emission from the cone. This observation produced a measure of the X-ray production factor of the solar wind interaction with the neutral ISM within the solar system. Using this production factor, the contribution of the heliopsheric SWCX to the soft X-ray background could be estimated. It also carried the STORM/LEXI prototype which observed perpendicular to the primary payload. |
ESAS has become even more tightly integrated into the XMM SAS, and that work continues. Some of the extensive scripting that had been part of ESAS is being shed in favor or smaller, more flexible, applications. However, the original scripts, or their counterparts are not disappearing; they will be available here once they are tested. The ESAS Cookbook for SAS 22 is now available here and on the GSFC XMM-Newton site. Planned future improvements in ESAS are listed in section 2.2; if you can think of something else that can be done to improve ESAS, please contact me.
I maintain a woodland garden in the narrow space between two rowhouses. It is filled primarily with species native to the mid-Atlantic, though it also includes some more exotic Arisaema. I also collect members of the genus amorphophallus after having seen some of their cousins (the dracunculus vulgaris) at the Cloisters.
And then there is cooking! We both have distinct Franco-Italian leanings. Here's the spread for Easter 2025. We skipped a few courses this year; for some reason we never got around to preparing either the palate cleanser for after the game, or the salad for after the roast.
Course 1: Appeteaser: Smoked trout with homemade mayonnaise.
Course 2: Soup: Chicken and tarragon tortellini in brodo.
Course 3: Pasta: Pascal ravioli - each contains a quail egg as well as the usual ricotta and spinach - under a sage pesto.
Course 4: Entree: Rabbit in phyllo.
Course 5: Game: Cornish game hen al ghiotto. The sauce is based on the cooking fluids from the fowl and some liver pate. I discovered this recipe in a restaurant in Perugia.
Course 6: Roast: Lamb, sweet potato, and asparagus.
Course 7: Dessert: Quince and plum pie. The excess of Christmas Eve and Christmas.
Course 1: Pasta: Spaghetti with oil, black pepper, and anchovies
Course 2: Main: Baccala with potatoes and picked peppers (from the garden)
Course 3: Dessert, served after midnight mass: Panettone, made from scratch.
Course 1: Appetizer: Annelini al forno, ring pasta in sauce baked in a mould. Tasty, but not much to look at. Plating could have been better.
Course 2: Soup: Made of stuff from the garden.
Course 3: Pasta: These have different names depending upon your origin: ruoti, nidi, or rotelli. A long sheet of pasta is covered with a stuffing, rolled, and baked under a besciamella. They are then sliced, plated, with a bit of sauce. Here the filling was minced pork and traditional porchetta stuffing, as was the sauce.
Course 4: Entree: This was a real disaster. The outer part was made from ground chicken and the stuffing with chanterelles. The crust was ground chicken that was put through a tamis, then combined with egg, cream, and spicing. It might as well have been made from rubber.
Course 5: Fish: A bit of silliness. Knackbrot mit sill. Yes, there was more than one piece of sill each. It was in mustard, but not nearly as good as what you get in Denmark or Sweden.
Course 6: Game: Rabbit in mustard sauce, with stoemp.
Course 7: Roast: Roasted pork shoulder, with skin, in the Danish fashion. The skin gets really crispy. Served with rice, red cabbage, and foccacia.
Course 8: Salad: Fennel and orange salad. Not our own oranges, alas, but the fennel was from the garden.
Course 9: Dessert: Apple and Raspberry pie, served with tea.
Here's last Thanksgiving
Course 0: Just the breads. One loaf of the NYT "no-knead" bread, a half batch of pane carasao, and a sfincione. I don't like hawking products, but I've found that the Sir Lancelot bread flour really is an improvement over the standard King Arthur bread flour.
Course 1: Antepaste: an escarole timbale, fried polenta under a leaf of prosciutto, and a creation that we call "piano d'oro" after the place we first had it. It is sheets of pane carasao interleaved with mushrooms and confit. Accompanied by prosecco.
Course 2: Soup: French onion soup, made according to Julia, with a toast round with melted cheese. This should have been accompanied by sherry, but we used white wine instead, a Chardonnay from Alto Adige.
Course 3: Pasta: homemade fettucine with a sauce made from the last harvest of garden peppers. It's not much to look at, but it was tasty. There's a slice of the sfincione perched on the rim of the bowl.
Course 4: Terrine: I had to grind my own chicken to get the right balance of breast and thigh. It is spiced with thyme and a standard terrine mixture, as well as shallots and cremini.
Course 5: Palate Cleanser: After the last course, we needed something to cleanse the palate! Quince compote with a drizzle of limoncello and a sprig of mint.
Course 6: Game: Salmon, done in an Italian style. Accompanied by a nice red Bordeaux from Saint Emilion. (But I'll note that the nicest Saint Emilion wines don't seem to leave Saint Emilion.)
Course 7: Roast: Confit de dinde, aspabroc from the garden, and potatoes au gratin made with Tome.
Course 8: Salad: Orange and fennel salad, and yes the fennel is out of the garden. Our oranges are not yet in season.
Course 9: Dessert: Chocolate cake with lemon buttercream frosting and chocolate ganache. Accompanied by a strong Assam.