Search Publications
Multi-Epoch Multi-Wavelength Study of an Ultraluminous X-ray Source in M101: The Nature of the Secondary
Liu, Jifeng
Ultraluminous X-ray sources are non-nuclear point sources in external galaxies with LX = 2 × 1039-1041 erg s-1, and thus are possibly stellar black holes with special radiation mechanisms or intermediate mass black holes of 100-105 M sun. To measure their dynamical mass, one needs t…
The Extragalactic Distance Scale Without Cepheids. II. Surface Brightness Fluctuations
Sakai, Shoko; Mould, Jeremy
Distances of galaxies in the Hubble Space Telescope (HST) Key Project are based on the Cepheid period-luminosity relation. An alternative basis is the tip of the red giant branch (TRGB). Using archival HST data, we calibrate surface brightness fluctuations using 16 galaxies with TRGB branch measurements. The TRGB and Cepheid distance scales are sh…
New Fe IX Line Identifications Using Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation and Hinode/EIS Joint Observations of the Quiet Sun
Young, P. R.; Landi, E.
In this work, we study joint observations of Hinode/EUV Imaging Spectrometer (EIS) and Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation of Fe IX lines emitted by the same level of the high energy configuration 3s 23p 54p. The intensity ratios of these lines are dependent on atomic physics …
Two Rapidly Variable Galactic X-ray Transients Observed with Chandra, XMM-Newton, and Suzaku
Heinke, C. O.; Grindlay, J. E.; Tomsick, J. A. +1 more
We have identified two moderately bright, rapidly variable transients in new and archival X-ray data near the Galactic center. Both objects show strong, flaring variability on timescales of tens to thousands of seconds, evidence of NH variability, and hard spectra. XMMU J174445.5-295044 is seen at 2-10 keV fluxes of 3 × 10-11…
Impact of a Radius and Composition Variation on Stratification of the Solar Subsurface Layers
Lefebvre, S.; Turck-Chièze, S.; Nghiem, P. A. P.
Several works have reported changes of the Sun's subsurface stratification inferred from f-mode or p-mode observations. Recently, a nonhomologous variation of the subsurface layers with depth and time has been deduced from f-modes. Progress on this important transition zone between the solar interior and the external part supposes a good understan…
Different Types of Ultraluminous X-Ray Sources in NGC 4631
Soria, Roberto; Ghosh, Kajal K.
We have re-examined the most luminous X-ray sources in the starburst galaxy NGC 4631, using XMM-Newton, Chandra, and ROSAT data. The most interesting source is a highly variable supersoft ultraluminous X-ray source (ULX). We suggest that its bolometric luminosity ~ a few 1039 erg s-1 in the high/supersoft state: this is an or…
Asymmetry of Helicity Injection Flux in Emerging Active Regions
Alexander, David; Tian, Lirong
Observational and modeling results indicate that typically the leading magnetic field of bipolar active regions (ARs) is often spatially more compact, while more dispersed and fragmented in following polarity. In this paper, we address the origin of this morphological asymmetry, which is not well understood. Although it may be assumed that, in an …
X-Ray Searches for Emission from the WHIM in the Galactic Halo and the Intergalactic Medium
Bregman, Joel N.; Putman, Mary E.; Irwin, Jimmy A. +3 more
At least 50% of the baryons in the local universe are undetected and predicted to be in a hot dilute phase (105-107 K) in low and moderate overdensity environments. We searched for the predicted diffuse faint emission through shadowing observations whereby cool foreground gas absorbs more distant diffuse emission. Observation…
Mid-UV Narrow-Band Indices of Evolved Simple Stellar Populations
Bressan, A.; Chavez, M.; Bertone, E. +1 more
We explore the properties of selected mid-ultraviolet (1900-3200 Å) spectroscopic indices of simple stellar populations. We incorporate the high-resolution UVBLUE stellar spectral library into an evolutionary population synthesis code, based on the most recent Padova isochrones. We analyze the trends of UV indices with respect to age and chemical …
Low-Mass X-ray Binaries and Globular Clusters in Early-Type Galaxies. II. Globular Cluster Candidates and Their Mass-Metallicity Relation
Humphrey, Philip J.
We present an astrometry and photometry catalogue of globular cluster (GC) candidates detected with the Hubble Space Telescope Wide Field Planetary Camera 2 in a sample of 19 early-type galaxies, appropriate for comparison with the low-mass X-ray binary populations observed with Chandra. In a companion paper, we present the Chandra data and invest…