Search Publications
LINER-like Extended Nebulae in ULIRGs: Shocks Generated by Merger-Induced Flows
Colina, L.; Monreal-Ibero, A.; Arribas, S.
In this work we studied the two-dimensional ionization structure of the circumnuclear and extranuclear regions in a sample of six low-z ultraluminous infrared galaxies using integral field spectroscopy. The ionization conditions in the extranuclear regions of these galaxies (~5-15 kpc) are typical of LINERs as obtained from the Veilleux-Osterbrock…
The Homogeneity of Interstellar Elemental Abundances in the Galactic Disk
Sofia, Ulysses J.; Meyer, David M.; Cartledge, Stefan I. B. +1 more
We present interstellar elemental abundance measurements derived from Space Telescope Imaging Spectrograph echelle observations of 47 sight lines extending up to 6.5 kpc through the Galactic disk. These paths probe a variety of interstellar environments, covering ranges of nearly 4 orders of magnitude in molecular hydrogen fraction f(H2…
The ACS Virgo Cluster Survey. XI. The Nature of Diffuse Star Clusters in Early-Type Galaxies
Jordán, Andrés; Tonry, John L.; Côté, Patrick +7 more
We use HST ACS imaging of 100 early-type galaxies in the ACS Virgo Cluster Survey to investigate the nature of diffuse star clusters (DSCs). Compared to globular clusters (GCs), these star clusters have low luminosities (MV>-8) and a broad distribution of sizes (3<rh<30 pc), but they are principally characterized by …
Three-dimensional Inversion of Sound Speed below a Sunspot in the Born Approximation
Kosovichev, A. G.; Birch, A. C.; Couvidat, S.
We revise the inversion of acoustic travel times for the three-dimensional sound-speed structure below the solar NOAA Active Region 8243 of 1998 June. We benefit from recent progress in time-distance helioseismology that provides us with more reliable tools to infer subsurface solar properties. Among the improvements we implement here are the use …
Why X-Ray-selected Active Galactic Nuclei Appear Optically Dull
Rigby, J. R.; Rieke, G. H.; Pérez-González, P. G. +2 more
We investigate why half of X-ray-selected active galactic nuclei (AGNs) in deep surveys lack signs of accretion in their optical spectra. The majority of these ``optically dull'' AGNs are no more than ~6 times fainter than their host galaxies in rest-frame R band; as such, AGN lines are unlikely to be overwhelmed by stellar continuum in at least h…
The UV Scattering Halo of the Central Source Associated with η Carinae
Weis, K.; Sonneborn, G.; Smith, Nathan +8 more
We have made an extensive study of the UV spectrum of η Carinae and find that we do not directly observe the star and its wind in the UV. Because of dust along our line of sight, the UV light that we observe arises from bound-bound scattering at large impact parameters. We obtain a reasonable fit to the UV spectrum by using only the flux that orig…
ACS Photometry of Extended, Luminous Globular Clusters in the Outskirts of M31
Mackey, A. D.; Tanvir, N. R.; Ferguson, A. M. N. +6 more
A new population of extended, luminous globular clusters has recently been discovered in the outskirts of M31. These objects have luminosities typical of classical globular clusters, but much larger half-light radii. We report the first results from deep ACS imaging of four such clusters, one of which is a newly discovered example lying at a proje…
The Relation between EIT Waves and Solar Flares
Chen, P. F.
In order to determine whether EIT waves are generated by coronal mass ejections (CMEs) or pressure pulses in solar flares, 14 non-CME-associated energetic flares, which should possess strong pressure pulses in their loops, are studied. They are selected near solar minimum, as this favors the detection of EIT waves. It is found that none of these f…
A Hubble Space Telescope Archival Survey of Feathers in Spiral Galaxies
Ostriker, Eve C.; La Vigne, Misty A.; Vogel, Stuart N.
We present a survey of spiral arm extinction substructures referred to as feathers in 223 spiral galaxies using Hubble Space Telescope WFPC2 images. The sample includes all galaxies in the RC3 catalog with cz<5000 km s-1, BT<15, i<60deg, and types Sa-Sd with well-exposed broadband WFPC2 images. The detecti…
Black Hole Mass of the Ultraluminous X-Ray Source M82 X-1
Dewangan, Gulab C.; Griffiths, Richard E.; Titarchuk, Lev
We report the first clear evidence for the simultaneous presence of a low-frequency break and a QPO in the fluctuation power spectrum of a well-known ultraluminous X-ray source (ULX) in M82 using long XMM-Newton observations. The break occurs at a frequency of 34.2+6-3 mHz. The QPO has a centroid at νQPO=114.3+/-1.…