Search Publications
The Redshift and the Ordinary Host Galaxy of GRB 970228
Bloom, J. S.; Djorgovski, S. G.; Kulkarni, S. R.
The gamma-ray burst of 1997 February 28 (GRB 970228) ushered in the discovery of the afterglow phenomenon. Despite intense study of the nearby galaxy, however, the nature of this galaxy and the distance to the burst eluded the community. Here we present the measurement of the redshift of the galaxy, the putative host galaxy of GRB 970228, and, bas…
Cusped Mass Models of Gravitational Lenses
Keeton, C. R.; Kochanek, C. S.; Muñoz, J. A.
Recent observations of galaxy luminosity profiles and dark matter simulations find luminosity and mass distributions characterized by central cusps rather than finite core radii. We introduce and implement a set of cusped ellipsoidal lens models that include limits similar to the Jaffe, Hernquist, η and NFW models and apply them to the gravitation…
A Study of Chromospheric Oscillations Using the SOHO and TRACE Spacecraft
Wilhelm, Klaus; Judge, Philip G.; Tarbell, Theodore D.
We analyze line and continuum time-series data of the solar atmosphere, with between 10 and 60 s cadence, using the MDI and SUMER instruments on the SOHO spacecraft and the UV bandpasses on the TRACE satellite. The co-aligned data sets sample spectral features formed from photosphere to the middle transition region, spanning five decades in pressu…
Old Stellar Populations of the Small Magellanic Cloud
Dolphin, Andrew E.; Schommer, Robert A.; Mateo, Mario +4 more
We present WFPC2 and ground-based VI photometry of NGC 121 and a nearby field in the outer SMC. For NGC 121, we measure a true distance modulus of µ0=18.96+/-0.04 (distance of 61.9+/-1.1 kpc), age of 10.6+/-0.5 Gyr, metallicity of [Fe/H]=-1.03+/-0.06, and initial mass of 4.1+/-0.4×105 Msolar, assuming a Salpe…
Evidence for the Heating of Atomic Interstellar Gas by Polycyclic Aromatic Hydrocarbons
Dale, Daniel A.; Malhotra, Sangeeta; Helou, George +2 more
We report a strong correlation between the [C II] 158 µm cooling line and the mid-infrared flux in the 5-10 µm range in a wide variety of star-forming galaxies. The mid-infrared flux is dominated by the aromatic features in emission (AFEs), which are thought to arise from large polycyclic aromatic hydrocarbons (PAHs) and are generally …
The Discovery of a Second Luminous Low-Mass X-Ray Binary in the Globular Cluster M15
White, Nicholas E.; Angelini, Lorella
We report an observation by the Chandra X-Ray Observatory of 4U 2127+119, the X-ray source identified with the globular cluster M15. The Chandra observation reveals that 4U 2127+119 is in fact two bright sources, separated by 2.7". One source is associated with AC 211, the previously identified optical counterpart to 4U 2127+119, a low-mass X-ray …
Erupting Solar Magnetic Flux Ropes: Theory and Observation
Thompson, B. J.; Chen, J.; Howard, R. A. +2 more
Measurements of coronograph (LASCO) and extreme-ultraviolet (EIT) images are presented for 11 coronal mass ejection (CME) events. Detailed measurements of these events, selected because they have flux-rope-like morphological features, show excellent agreement with results from a theoretical model of erupting flux-rope dynamics. Here, data are used…
An XMM-Newton Observation of the Luminous Seyfert 1 Galaxy Markarian 509
Reeves, James; Nayakshin, Sergei; O'Brien, Paul +3 more
We present the spectral analysis of an early XMM-Newton observation of the luminous Seyfert 1 galaxy Mrk 509. We find the hard (2-10 keV) continuum slope, including reflection, to be somewhat flatter (Γ=1.75) than that of a typical broad-line Seyfert 1 galaxy. The most obvious feature in the hard X-ray spectrum is a narrow emission line near 6.4 k…
Spectroscopic Diagnostics of Nanoflare-heated Loops
Klimchuk, J. A.; Cargill, P. J.
To evaluate the usefulness of spectroscopic techniques for diagnosing realistic solar plasmas and to better understand the physical origin of coronal heating, we have simulated observations of model coronal loops that are heated randomly and impulsively by nanoflares. We find that the emission measures, densities, and filling factors that are infe…
Far-Ultraviolet and Hα Imaging of Nearby Spiral Galaxies: The OB Stellar Population in the Diffuse Ionized Gas
Hoopes, Charles G.; Bothun, Gregory D.; Walterbos, René A. M.
We have compared Hα and far-ultraviolet (FUV) images of 10 nearby spirals, with the goal of understanding the contribution of field OB stars to the ionization of the diffuse ionized gas (DIG) in spiral galaxies. The FUV images were obtained by the Ultraviolet Imaging Telescope (UIT), and the Hα images were obtained using various ground-based teles…