Search Publications
Microlensing Optical Depth toward the Galactic Bulge from Microlensing Observations in Astrophysics Group Observations during 2000 with Difference Image Analysis
Sumi, T.; Honda, M.; Saito, Y. +27 more
We analyze the data of the gravitational microlensing survey carried out by the Microlensing Observations in Astrophysics (MOA) group during 2000 toward the Galactic bulge (GB). Our observations are designed to detect efficient high-magnification events with faint source stars and short-timescale events, by increasing the sampling rate up to ~6 ti…
The Properties of Small Magnetic Regions on the Solar Surface and the Implications for the Solar Dynamo(s)
Title, Alan M.; Schrijver, Carolus J.; Hagenaar, Hermance J.
We find that bipolar active regions that emerge onto the Sun's surface are part of a smoothly decreasing frequency distribution that spans almost 4 orders of magnitude in flux and 8 orders of magnitude in frequency. Distributions of emergence latitude and dipole orientation narrow from nearly uniform for the smallest observed ephemeral regions (~5…
XMM-Newton Reveals the Quasar Outflow in PG 1115+080
Brandt, W. N.; Chartas, G.; Gallagher, S. C.
We report on an observation of the broad absorption line (BAL) quasar PG 1115+080 performed with the XMM-Newton observatory. Spectral analysis reveals the second case of a relativistic X-ray-absorbing outflow in a BAL quasar. The first case was revealed in a recent observation of APM 08279+5255 with the Chandra X-Ray Observatory. As in the case of…
A Tale of Two Stars: The Extreme O7 Iaf+ Supergiant AV 83 and the OC7.5 III((f)) star AV 69
Hillier, D. John; Lennon, D. J.; Smith, L. J. +5 more
We present a detailed study of AV 83, an O7 Iaf+ supergiant, and AV 69 [OC7.5 III((f))] in the SMC. The stars have similar effective temperatures and luminosities but show very different wind signatures. For our study we have used the non-LTE line-blanketed atmosphere code developed by Hillier and Miller, which explicitly allows for line blanketin…
Latitude-dependent Effects in the Stellar Wind of η Carinae
Smith, Nathan; Hillier, D. John; Gull, Theodore R. +2 more
The Homunculus reflection nebula around η Carinae provides a rare opportunity to observe the spectrum of a star from more than one direction. In the case of η Car, the nebula's geometry is known well enough to infer how line profiles vary with latitude. We present Space Telescope Imaging Spectrograph (STIS) spectra of several positions in the Homu…
Toward a Self-Consistent Model of the Ionized Absorber in NGC 3783
Elvis, M.; Nicastro, F.; Krongold, Y. +3 more
We present a detailed model for the ionized absorbing gas evident in the 900 ks Chandra HETGS spectrum of NGC 3783. The analysis was carried out with PHASE, a new tool designed to model X-ray and UV absorption features in ionized plasmas. The 0.5-10 keV intrinsic continuum of the source is well represented by a single power law (Γ=1.53) and a soft…
Hα Spectroscopy of Galaxies at z > 2: Kinematics and Star Formation
Pettini, Max; Erb, Dawn K.; Shapley, Alice E. +5 more
We present near-infrared spectroscopy of Hα emission lines in a sample of 16 star-forming galaxies at redshifts 2.0<z<2.6. Our targets are drawn from a large sample of galaxies photometrically selected and spectroscopically confirmed to lie in this redshift range. We have obtained this large sample with an extension of the broadband Un<…
New Members of the TW Hydrae Association, β Pictoris Moving Group, and Tucana/Horologium Association
Zuckerman, B.; Song, Inseok; Bessell, M. S.
We have identified five new members of the TW Hydrae association (TWA), 11 new members of the β Pic moving group, and 11 new Tucana/Horologium association members. These are the three youngest (<~30 Myr) known kinematic stellar groups near the Earth. Newly identified β Pic group members are located mostly in the northern hemisphere, and they ha…
Multiwavelength Observations of Flares on AD Leonis
Hawley, Suzanne L.; Valenti, Jeff A.; Johns-Krull, Christopher M. +9 more
We report results from a multiwavelength observing campaign conducted during 2000 March on the flare star AD Leo. Simultaneous data were obtained from several ground- and space-based observatories, including observations of eight sizable flares. We discuss the correlation of line and continuum emission in the optical and ultraviolet wavelength reg…
Locating the Launching Region of T Tauri Winds: The Case of DG Tauri
Li, Zhi-Yun; Blandford, Roger D.; Krasnopolsky, Ruben +1 more
It is widely believed that T Tauri winds are driven magnetocentrifugally from accretion disks close to the central stars. The exact launching conditions are uncertain. We show that a general relation exists between the poloidal and toroidal velocity components of a magnetocentrifugal wind at large distances and the rotation rate of the launching s…