Search Publications
Stellar Populations in the Nuclei of Late-Type Spiral Galaxies
Ho, L. C.; Rix, H. -W.; Shields, J. C. +5 more
As part of an ongoing effort to study the stellar nuclei of very late type, bulge-less spirals, we present results from a high-resolution spectroscopic survey of nine such nuclear star clusters, undertaken with the VLT UVES. We fit the spectra with population synthesis models and measure Lick-type indices to determine mean luminosity-weighted ages…
Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters
Whitmore, Bradley C.; Kavelaars, J. J.; Baum, William A. +4 more
We present new (B, I) photometry for the globular cluster systems in eight brightest cluster galaxies (BCGs), obtained with the ACS/WFC camera on the Hubble Space Telescope. In the very rich cluster systems that reside within these giant galaxies, we find that all have strongly bimodal color distributions that are clearly resolved by the metallici…
Near-Infrared and Star-forming Properties of Local Luminous Infrared Galaxies
Pérez-González, Pablo G.; Ryder, Stuart D.; Colina, Luis +3 more
We use Hubble Space Telescope (HST) NICMOS continuum and Paα observations to study the near-infrared and star formation properties of a representative sample of 30 local (d~35-75 Mpc) luminous infrared galaxies (LIRGs, infrared [8-1000 µm] luminosities of logLIR=11-11.9 Lsolar). The data provide spatial resolutions of 2…
Magnetoacoustic Portals and the Basal Heating of the Solar Chromosphere
McIntosh, Scott W.; Cacciani, Alessandro; Armstrong, James D. +3 more
We show that inclined magnetic field lines at the boundaries of large-scale convective cells (supergranules) provide ``portals'' through which low-frequency (<5 mHz) magnetoacoustic waves can propagate into the solar chromosphere. The energy flux carried by these waves at a height of 400 km above the solar surface is found to be a factor of 4 g…
The N2K Consortium. IV. New Temperatures and Metallicities for More than 100,000 FGK Dwarfs
Strader, Jay; Laughlin, Gregory; Ammons, S. Mark +3 more
We have created specialized target lists for radial velocity surveys that are biased toward stars that (1) possess planets and (2) are easiest to observe with current detection techniques. We use a procedure that uniformly estimates fundamental stellar properties of Tycho 2 stars, with errors, using spline functions of broadband photometry and pro…
The Hard X-Ray Spectral Slope as an Accretion Rate Indicator in Radio-quiet Active Galactic Nuclei
Maiolino, Roberto; Brandt, W. N.; Kaspi, Shai +2 more
We present new XMM-Newton observations of two luminous and high accretion rate radio-quiet active galactic nuclei (AGNs) at z~2. Together with archival X-ray and rest-frame optical spectra of three sources with similar properties, as well as 25 moderate-luminosity radio-quiet AGNs at z<0.5, we investigate, for the first time, the dependence of …
The Proper Treatment of Coronal Mass Ejection Brightness: A New Methodology and Implications for Observations
Vourlidas, Angelos; Howard, Russell A.
With the complement of coronagraphs and imagers in the SECCHI suite, we will follow a coronal mass ejection (CME) continuously from the Sun to Earth for the first time. The comparison, however, of the CME emission among the various instruments is not as easy as one might think. This is because the telescopes record the Thomson-scattered emission f…
The Star-forming Torus and Stellar Dynamical Black Hole Mass in the Seyfert 1 Nucleus of NGC 3227
Genzel, R.; Tacconi, L. J.; Sternberg, A. +7 more
We report R~4300 VLT SINFONI adaptive optics integral field K-band spectroscopy of the nucleus of the Seyfert 1 galaxy NGC 3227 at a spatial resolution of 0.085" (7 pc). We present the morphologies and kinematics of emission lines and absorption features and give the first derivation of a black hole mass in a Seyfert 1 nucleus from stellar dynamic…
Different Power-Law Indices in the Frequency Distributions of Flares with and without Coronal Mass Ejections
Howard, R. A.; Gopalswamy, N.; Yashiro, S. +1 more
We investigated the frequency distributions of flares with and without coronal mass ejections (CMEs) as a function of flare parameters (peak flux, fluence, and duration of soft X-ray flares). We used CMEs observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) mission and soft X-ray …
Unveiling Supergiant Fast X-Ray Transient Sources with INTEGRAL
Hill, A. B.; Bird, A. J.; Ubertini, P. +9 more
Supergiant high-mass X-ray binaries (SGXBs) are believed to be rare objects, as stars in the supergiant phase have a very short lifetime and to date only about a dozen of them have been discovered. They are known to be persistent and bright X-ray sources. INTEGRAL is changing this classical picture, as its observations are revealing the presence o…