Search Publications
Mass-dependent Color Evolution of Field Galaxies back to z~3 over the Wide Range of Stellar Mass
Yamada, T.; Kajisawa, M.
We use deep multiband optical and near-infrared data for four general fields, GOODS-South, HDF-North/South, and IRAC UDF in GOODS-North to investigate the evolution of the observed rest-frame U-V color of field galaxies as a function of the stellar mass evaluated by fitting the galaxy spectral models to the observed broadband SEDs. In these four f…
Estimating the Thickness of the Heliosheath from CELIAS/HSTOF and Voyager 1 Data
Hsieh, K. C.; Hilchenbach, M.; Czechowski, A. +2 more
We use recent Voyager 1 measurements of the ion fluxes beyond the termination shock and the SOHO HSTOF/CELIAS measured fluxes of the energetic neutral hydrogen and helium at 1 AU to estimate the neutral hydrogen column density NH in the heliosheath. Our best estimate is NH=1.13×1014 cm-2. The result corr…
Subarcsecond Resolution Mid-Infrared Observations of Super Star Clusters in the Antennae (NGC 4038/4039)
Schaerer, D.; Wang, Z.; Brandl, B. R. +3 more
We present ground-based subarcsecond mid-infrared imaging and spectroscopy of young super star clusters in the overlap region of the merging galaxies NGC 4038/4039 (the Antennae) obtained with the VLT Imager and Spectrometer for mid-InfraRed (VISIR). With its unprecedented spatial resolution, VISIR begins for the first time to resolve the H II/pho…
Coronal Heating and Photospheric Turbulence Parameters: Observational Aspects
Romano, P.; Abramenko, V. I.; Pevtsov, A. A.
In this study, the soft X-ray luminosity of the solar corona, measured by the Yohkoh spacecraft for 104 well-developed and decaying active regions, is compared to the magnetic field parameters determined from SOHO MDI high-resolution magnetograms. We calculate and compare (1) two area-independent characteristics of the magnetic field: the index (α…
Tracing the Dynamical History of the Globular Cluster 47 Tucanae
Sills, Alison; Beccari, Giacomo; Guhathakurta, Puragra +3 more
We use two stellar populations in the globular cluster 47 Tucanae to trace its dynamical history: blue stragglers and low-mass main-sequence stars. We assumed that the blue stragglers were formed through stellar collisions in all regions of the cluster. We find that in the core of the cluster, models of collisional blue stragglers agree well with …
On the Fraction of X-Ray-obscured Quasars in the Local Universe
Wang, J. X.; Jiang, P.
Recent wide-area hard X-ray and soft gamma-ray surveys have shown that the fraction of X-ray-obscured active galactic nuclei (AGNs) in the local universe significantly decreases with intrinsic luminosity. In this Letter we point out that two corrections have to be made to the samples: (1) radio-loud AGNs have to be excluded, since their X-ray emis…
Multiwavelength Studies of the Optically Dark Gamma-Ray Burst 001025A
Cline, T.; Hurley, K.; Schartel, N. +18 more
We identify the fading X-ray afterglow of GRB 001025A from XMM-Newton observations obtained 1.9-2.3 days, 2 yr, and 2.5 yr after the burst. The nondetection of an optical counterpart to an upper limit of R=25.5, 1.20 days after the burst, makes GRB 001025A a ``dark'' burst. Based on the X-ray afterglow spectral properties of GRB 001025A, we argue …
On the Nature of the Hard X-Ray Source IGR J2018+4043
Kennea, J. A.; Terrier, R.; Rauw, G. +13 more
We found a very likely counterpart to the recently discovered hard X-ray source IGR J2018+4043 in the multiwavelength observations of the source field. The source, originally discovered in the 20-40 keV band, is now confidently detected also in the 40-80 keV band, with a flux of (1.4+/-0.4)×10-11 ergs cm-2 s-1. A 5…
A Blue Straggler Binary with Three Progenitors in the Core of a Globular Cluster?
Knigge, C.; Long, K. S.; Gilliland, R. L. +3 more
We show that the X-ray source W31 in the core of the globular cluster 47 Tucanae is physically associated with the bright blue straggler BSS 7. The two sources are astrometrically matched to 0.061", with a chance coincidence probability of less than 1%. We then analyze optical time-series photometry obtained with the Hubble Space Telescope (HST) a…
Evolution of the X-Ray Jets from 4U 1755-33
Wijnands, R.; Tomsick, J. A.; Kaaret, P. +4 more
We report on new X-ray observations of the large-scale jets recently discovered in X-rays from the black hole candidate 4U 1755-33. Our observations in 2004 show that the jets found in 2001 are still present in X-rays. However, sensitive radio observations in 2004 failed to detect the jets. We suggest that synchrotron radiation is a viable emissio…