Search Publications
Blue Stragglers in Low-Luminosity Star Clusters
Sandquist, Eric L.
We examine the blue straggler populations of 13 low-luminosity (MVt>~-6) globular clusters and two old open clusters. These clusters test blue straggler formation in environments intermediate between higher luminosity (and usually higher density) clusters and the Galactic field. The anticorrelation between the relative fre…
Direct Evidence for an Early Reionization of the Universe?
Panagia, N.; Stern, D.; Dickinson, M. +5 more
We examine the possible reionization of the intergalactic medium by the source UDF 033238.7-274839.8 (hereafter HUDF-JD2), which was discovered in deep HST/VLT/Spitzer images obtained as part of the Great Observatories Origins Deep Survey and Hubble Ultra Deep Field projects. Mobasher et al. have identified HUDF-JD2 as a massive (~6×1011
Comparison of Solar Cycle Variations of Solar p-Mode Frequencies from GONG and MDI
Chou, Dean-Yi; Serebryanskiy, Alexander
The solar p-mode frequencies change with the solar cycle. The horizontal phase velocity dependence of the relative frequency change scaled by mode mass provides depth information on the perturbations in the solar interior. Both GONG data and SOHO MDI data show that the horizontal phase velocity dependence of the scaled relative frequency change va…
A Chandra Observation of the Nearby Lenticular Galaxy NGC 5102: Where are the X-Ray Binaries?
Ponman, T. J.; Jones, C.; Kraft, R. P. +2 more
We present results from a 34 ks Chandra ACIS-S observation of the low-mass X-ray binary (LMXB) population and the hot interstellar medium (ISM) in the nearby (d=3.1 Mpc) lenticular galaxy NGC 5102, previously shown to have an unusually low X-ray luminosity. We detect 11 X-ray point sources within the D25 optical boundary of the galaxy (…
Deep Photometry of the Globular Cluster M5: Distance Estimates from White Dwarf and Main-Sequence Stars
Sarajedini, Ata; Layden, Andrew C.; Cool, Adrienne M. +1 more
We present deep VI photometry of stars in the globular cluster M5 (NGC 5904) based on images taken with the Hubble Space Telescope. The resulting color-magnitude diagram reaches below V~27 mag, revealing the upper 2-3 mag of the white dwarf cooling sequence and main-sequence stars 8 mag and more below the turnoff. We fit the main sequence to subdw…
A Study of Flare-associated X-Ray Plasma Ejections. III. Kinematic Properties
Cho, K. -S.; Moon, Y. -J.; Park, Y. D. +2 more
In this study, we have investigated the kinematic properties of flare-associated X-ray plasma ejections. First, we obtained the speed profiles of well-observed several events and compared them with the GOES soft X-ray flux profiles as well as the HXT hard X-ray flux profiles of their associated flares. Second, we have estimated the Alfvén speed at…
Photometric Confirmation of MACHO Large Magellanic Cloud Microlensing Events
Bennett, David P.; Becker, Andrew C.; Tomaney, Austin
We present previously unpublished photometry of three Large Magellanic Cloud (LMC) microlensing events and show that the new photometry confirms the microlensing interpretation of these events. These events were discovered by the MACHO Project alert system and were also recovered by the analysis of the 5.7 yr MACHO data set. This new photometry pr…
Ultraviolet Hubble Space Telescope Observations of the Jet in M87
Zepf, Stephen E.; Waters, Christopher Z.
We present new ultraviolet photometry of the jet in M87 obtained from Hubble Space Telescope (HST) WFPC2 imaging. We combine these ultraviolet data with previously published photometry for the knots of the jet in radio, optical, and X-ray and fit three theoretical synchrotron models to the full data set. The synchrotron models consistently overpre…
Helium Abundance in High-Temperature Solar Flare Plasmas
Landi, E.; Feldman, U.; Laming, J. M.
In the present work we use emission from dense plasmas late in the decay phase of flares, while the plasmas are still hot [(2-4)×106 K], to determine the absolute helium abundance in flaring solar corona. To achieve this, we make use of intensity ratios of H I and He II lines and of intensity ratios between the He II lines and the brems…
Three Criteria to Discriminate between Elementary and Composite Coronal Loops
Aschwanden, Markus J.
In this Letter, we establish three simple criteria to discriminate between elementary and composite loop structures, based on observations from high-resolution (TRACE) and low-resolution (EIT) imagers. Both data sets contain triple-filter data with a temperature diagnostic in the range of T~0.7-2.8 MK, which we use for forward-fitting of a differe…