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Spatial Distribution and Evolution of the Stellar Populations and Candidate Star Clusters in the Blue Compact Dwarf I Zwicky 18
Saha, A.; Tosi, M.; Clementini, G. +7 more
The evolutionary properties and spatial distribution of I Zwicky 18 (IZw18) stellar populations are analyzed by means of Hubble Space Telescope/Advanced Camera for Surveys deep and accurate photometry. A comparison of the resulting color-magnitude diagrams (CMDs) with stellar evolution models indicates that stars of all ages are present in all the…
Flares and Their Underlying Magnetic Complexity
Golub, Leon; Sylwester, Barbara; Sylwester, Janusz +5 more
SphinX (Solar PHotometer IN X-rays), a full-disk-integrated spectrometer, observed 137 flare-like/transient events with active region (AR) 11024 being the only AR on disk. The Hinode X-Ray Telescope (XRT) and Solar Optical Telescope observe 67 of these events and identified their location from 12:00 UT on July 3 through 24:00 UT 2009 July 7. We fi…
The Dark Side of QSO Formation at High Redshifts
Trenti, Michele; Hoffman, Yehuda; Shlosman, Isaac +1 more
Observed high-redshift QSOs, at z ~ 6, may reside in massive dark matter (DM) halos of more than 1012 M sun and are thus expected to be surrounded by overdense regions. In a series of 10 constrained simulations, we have tested the environment of such QSOs. The usage of constrained realizations has enabled us to address the is…
The Connection between X-Ray Binaries and Star Clusters in NGC 4449
Chandar, Rupali; Rangelov, Blagoy; Prestwich, Andrea H.
We present 23 candidate X-ray binaries with luminosities down to 1.8 × 1036 erg s-1, in the nearby starburst galaxy NGC 4449, from observations totaling 105 ks taken with the ACIS-S instrument on the Chandra Space Telescope. We determine count rates, luminosities, and colors for each source, and perform spectral fits for sour…
A Temporal Study of the Oxygen-rich Pulsating Variable Asymptotic Giant Branch Star, T Cep: Investigation on Dust Formation and Dust Properties
Onaka, Takashi; Speck, Angela K.; Guha Niyogi, Suklima
Pulsation is believed to be the leading cause of dusty mass loss from asymptotic giant branch stars. We present a temporal study of T Cep, a long-period Mira variable, using seven Infrared Space Observatory Short Wavelength Spectrometer spectra, covering a 16 month period over a single pulsation cycle. The observed spectral dust features change ov…
Suzaku Observations of the HMXB 1A 1118-61
Makishima, Kazuo; Terada, Yukikatsu; Rothschild, Richard E. +12 more
We present broadband analysis of the Be/X-ray transient 1A 1118-61 by Suzaku at the peak of its third observed outburst in 2009 January and two weeks later when the source flux had decayed by an order of magnitude. The continuum was modeled with a cutoffpl model as well as a compTT model, with both cases requiring an additional blackbody component…
HST/NICMOS Imaging of Bright High-redshift 24 µm Selected Galaxies: Merging Properties
Helou, George; Surace, Jason; Yan, Lin +4 more
We present new results on the physical nature of infrared-luminous sources at 0.5 < z < 2.8 as revealed by HST/NICMOS imaging and Infrared Spectrograph mid-infrared spectroscopy. Our sample consists of 134 galaxies selected at 24 µm with a flux of S(24 µm)>0.9 mJy. We find many (~60%) of our sources to possess an important bul…
Broad Lyα Emission from Three Nearby BL Lacertae Objects
Perlman, Eric S.; Danforth, Charles W.; Stocke, John T.
We present far-UV HST/COS spectra of four nearby BL Lac objects. BL Lac spectra are dominated by a smooth, power-law continuum which arises in a relativistic jet. However, the spectra are not necessarily featureless; weak, broad- and/or narrow-line emission is sometimes seen in high-quality optical spectra. We present detections of Lyα emission in…
Chandra Detection of SN 2010da Four Months After Outburst: Evidence for a High-mass X-Ray Binary in NGC 300
Dalcanton, J. J.; Kong, A. K. H.; Weisz, D. R. +4 more
We present the results of a 63 ks Chandra observation of the "supernova impostor" SN 2010da four months after it was first observed on 2010 May 24. We detect an X-ray source at ~7σ confidence coincident with the optical location of the outburst. Our imaging analysis has revealed a hard central point source, surrounded by soft diffuse emission exte…
Dimming of the 17th Century Sun
Ortiz, Ada; Foukal, Peter; Schnerr, Roald
Reconstructions of total solar irradiance (TSI) rely mainly on linear relations between TSI variation and indices of facular area. When these are extrapolated to the prolonged 15th-17th century Spörer and Maunder solar activity minima, the estimated solar dimming is insufficient to explain the mid-millennial climate cooling of the Little Ice Age. …