Columbia University Department of Astronomy/Department of Physics New York, New York 10027 This report covers the period September 2002 through Mordecai MacLow from the American Museum of August 2003 and comprises an account of astronomical Natural History. Postdoctoral Research Scientists research carried out in the Department of Astronomy appointments were held by David Alves, Marc Audard, and the Department of Physics. Edward Baltz, Martin Bureau, Fernando Camilo, Soizik Faculty and Research Associates were James Donguy, Jason Koglin, Richard Easther, Masanori Applegate, Elena Aprile, Norman Baker, Andrei Kobayashi, William Kinney, Stephen Lawrence, Patrick Beloborodv, Arlin Crotts, Karl-Ludwig Giboni, Eric Cseresnjes, Caleb Scharf and Jacob Vink. Paul Vanden Gotthelf, Charles Hailey, Zoltan Haiman, Jules Bout (NRAO) and Deepto Chakrabarty (MIT) were Halpern, David Helfand, Lam Hui, Steven Kahn, visiting research scientists. Laura Kay (Barnard), Amber Miller, Lloyd Motz Helfand continued as Chair of the Astronomy (Emeritus), Reshmi Mukherjee (Barnard), Robert Department, Paerels continued as Director of the Novick (Emeritus), Frederik Paerels, Joseph Patterson, Columbia Astrophysics Laboratory, Weinberg continued Kevin Prendergast (Emeritus), Andrew Rasmussen, as Chair of the Physics Department, and Kay continued Malvin Ruderman, Daniel Savin, Edward Spiegel, as Chair of the Physics and Astronomy Department at Jacqueline van Gorkom and David Windt. Faculty Barnard. Halpern continued as Director of the MDM members at Biosphere 2 are Karen Schwarz, Philip Observatory. Yecko and Catharine Garmany. Norman Baker retired in July 2003. New faculty appointments include David 1 Stars and Stellar Evolution Schiminovich and Janna Levin (Barnard). The Center for Backyard Astrophysics accumulated Graduate students participating in research were 800 nights of observation during 2002-3. This Antara Basu-Zych, Douglas Bramel, Tzu-Ching Chang, is a network of astronomers, primarily amateur, who Aeree Chung, James Chonko, Alessandro Curioni, Mark do stellar photometry with small telescopes in their Dijkstra, Akimi Fujita, Suvi Gezari, Eilat Glikman, backyards. Columbia personnel included J. Patterson, Mark Jackson, Miranda Jackson, Benjamin Johnson, J. Kemp, and C. Espaillat. We typically observe a Moo Kwang (Ryan) Joung, Ali Kinkhabwala, Maurice star steadily for a few months, trying to amass the Leutenegger, Yuexing Li, Adam Lidz, Andrei Mesinger, densest possible coverage by stressing long observations Nestor Mirabal, Kaya Mori, Anthony Mroczkowski, and distribution of observers in longitude. This provides Stephen Muchovej, James Don Neill, Kaixuan Ni, John a time series well suited to the study of periodic signals, Peterson, Andreea Petric, Pietro Reviglio, Jacob Noel- and immunized from the “aliasing” problems inherent Storr, David Spiegel, Ben Sugerman, Shen Wang, Haitao in data from a single site. Our long-time observers Yu, Michel Zamojski. Undergraduates participating are in Belgium, Denmark, Maryland, Arizona, Illinois, in research were Anne Abramson, Eve Armstrong, New Zealand, South Africa, and Australia. During Ibrahima Bah (Lafayette), Randy Berkowitz, Tiany this period, new nodes were established in Uzbekistan, Christatos (Barnard), Maya Cohen (Barnard), Benjamin Canada, Utah, and Connecticut. Most programs involve Collins, Alexander Cosmas (Columbia Engineering), the study of cataclysmic variables, justly famous for the Catherine Espaillat, Regina Flores (Barnard), Amy many periods present in their light curves. Goldman (Barnard), Rebecca Grossman (Barnard), Through the study of “superhumps” in the light Karina Hamalainen (Barnard), Susan Hu, Paul Jawlik curves of dwarf novae, we succeeded in measuring (Biosphere), David Krohn, Floris Lugt (visiting accretion-disk precession rates in 30 new stars, and from Kapteyn Institute, Groningen), Sharlissa Moore calibrated a scheme for measuring mass ratios from those (Biosphere), Marcia Sanders (Barnard), Rachel Semple rates. We also obtained a tight constraint of the mass- Schuchter (Barnard), Samuel Singer (Biosphere), Dana radius relation of the secondary stars in cataclysmics. Stern (Barnard), Jin Suh, T.T. Tao, Gisela Telis, and The secondaries have an average radius of 18 6% Pauline Wang (Barnard). Research sta assistants greater than the radius of a theoretical ZAMS star. This include Alex Bergier, Alan Gersch, Mala Mateen and small expansion may be due to the star’s mass loss on a Adam Fallon. timescale close to its thermal timescale. Tzu-Ching Chang, Akimi Fujita, Ali Kinkhabwala, Large data sets, comprising typically 300 hr Ben Sugerman and John Peterson received Ph.D. over 60 nights, have been collected on many other degrees. short-period stars to study accretion-disk precession and Appointments during 2002–2003 were held by white-dwarf pulsation. Their study and understanding Adjunct Professors Michael Allison from the Goddard will keep us busy for years to come. Institute for Space Studies, and Michael Shara and Leutenegger, Kahn and collaborators D. Cohen, R. 1 Kramer, and J. Reed (Swarthmore), and S. Owocki most active show an inverse FIP eect. (Delaware) are studying the proles of emission lines Audard collaborated with M. Gudel (Paul Scherrer in the Chandra HETGS and XMM-Newton RGS X-ray Institut), and other colleagues to study the coronal X- spectra of O-type stars. A simple empirical model is ray emission of the binary Coronae Borealis. While used to t the proles. The prole shapes are found the secondary (a young solar analog) is a typical coronal to be generally consistent with emission from shocks star, the primary (an A-type star) is not magnetically distributed throughout the stellar wind. However, the active and thus is X-ray dark. XMM-Newton obtained characteristic optical depths inferred are systematically a deep light curve of the secondary eclipse thanks too small by about an order of magnitude. This result to its sensitive EPIC cameras. Gudel, Audard, and poses problems for our understanding of X-ray emission collaborators constructed two-dimensional maps of the from hot stars. X-ray brightness on and around CrB B using iterative Paerels and student researcher Telis reduced the eclipse mapping reconstruction codes. The maps reveal X-ray spectroscopy of the LMC Supersoft X-ray similar distribution of X-ray bright regions and large Source CAL 83. A high signal-to-noise spectrum areas with little ux, showing the inhomogeneity of the obtained with the XMM-Newton RGS exists, which corona of the young solar analog. shows intricate, and probably only partially resolved, Audard, M. Gudel (Paul Scherrer Institut), and absorption structure. The spectrum is complemented by S. Skinner (Univ. of Colorado) studied the X-ray a deep exposure with the Chandra LETGS, which covers emission of the nearby are star UV Ceti. For the the band out to the long wavelength ISM absorption rst time Chandra was able to separate X-rays from cuto. Both spectra agree perfectly in the area of overlap each component of this detached binary. Audard and around the carbon K edge; the increased bandwidth colleagues found that, despite their similar spectral will increase the diagnostic leverage. Quantitative types (dM5.5e), their X-ray activity dier drastically: interpretation, to be pursued based on dedicated model the B component showed enhanced magnetic activity, atmosphere calculations, will yield an estimate for the displaying several large ares and even a huge, short are luminosity and mass accretion rate of the white dwarf, with a peak luminosity a hundred times the low-level X- and establish whether this type of binary is a viable ray emission. On the other hand, UV Cet A showed candidate progenitor for Ia supernovae. weak modulation; however, its low-level ux was similar Paerels, Kahn, M. Sako (Stanford), and collabora- to UV Cet B. Numerous radio observations of the UV tors at ISAS in Japan, interpreted the Compton recoil Ceti binary system have also shown that the coronae spectrum rst identied in the Fe K uorescent emis- of the two components dier signicantly. While the sion of the massive binary GX301-2, as observed in the dierences remain unexplained, they could be related to high resolution Chandra HETGS spectrum of the source. the magnetospheric congurations. UV Cet B is indeed The detailed shape of the feature probes the conditions spatially resolved in the the radio. in the Compton-thick gas surrounding the uorescent Audard, J.-U. Ness (Hamburger Sternwarte), and source. A detailed treatment of the scattering with a colleagues have systematically investigated the opacity dedicated Monte Carlo simulation indicates that the en- eects and coronal densities in stellar coronae. Line tire sky, as seen from the photon source, is lled with ratios of some Fe Ne-like lines are sensitive to optical cold scattering electrons. The eects of a nite elec- depth. The observed ratios in a large sample of tron temperature, and of multiple Compton scattering, coronal stars displaying a wide range of magnetic activity are clearly detected. High resolution X-ray spectroscopy showed no evidence for opacity eects, implying that has therefore now also given us a quantitative probe of the spatially unresolved X-ray emission of magnetically the dense, near-neutral gas in the stellar wind, which is active stars is in average optically thin. Coronal densities otherwise only observable in the heavily saturated reso- on the other hand showed a dierent picture: low nance absorption lines in the