Search Publications
Accretion onto the Supermassive Black Hole in M87
Fabian, Andrew C.; Allen, Steven W.; Wilson, Andrew S. +2 more
Chandra X-ray observations of the giant elliptical galaxy M87 resolve the thermal state of the hot interstellar medium into the accretion (Bondi) radius of its central 3×109Msolar black hole. We measure the X-ray gas temperature and density profiles and calculate the Bondi accretion rate, MBondi~0.1Msolar
X-Ray Spectroscopic Evidence for Intermediate-Mass Black Holes: Cool Accretion Disks in Two Ultraluminous X-Ray Sources
Fabian, A. C.; Miller, J. M.; Fabbiano, G. +1 more
We have analyzed an XMM-Newton observation of the nearby spiral galaxy NGC 1313, which contains two ``ultraluminous'' X-ray (ULX) sources. We measure isotropic luminosities of LX=2.0×1040 ergs s-1 and LX=6.6×1039 ergs s-1 for NGC 1313 X-1 and X-2 (0.2-10.0 keV, assuming a distance o…
Distances and ages of NGC 6397, NGC 6752 and 47 Tuc
Grundahl, F.; Clementini, G.; Bragaglia, A. +4 more
New improved distances and absolute ages for the Galactic globular clusters NGC 6397, NGC 6752, and 47 Tuc are obtained using the Main Sequence Fitting Method. We derived accurate estimates of reddening and metal abundance for these three clusters using a strictly differential procedure, where the Johnson B-V and Strömgren b-y colours and UVES hig…
Multiplicity of Nearby Free-Floating Ultracool Dwarfs: A Hubble Space Telescope WFPC2 Search for Companions
Basri, Gibor; Bouy, Hervé; Brandner, Wolfgang +3 more
We present Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) observations of a sample of 134 ultracool objects (spectral types later than M7) coming from the Deep Near Infrared Survey (DENIS), Two Micron All Sky Survey (2MASS), and Sloan Digital Sky Survey (SDSS), with distances estimated to range from 7 to 105 pc. Fifteen new ult…
Abundances for metal-poor stars with accurate parallaxes. I. Basic data
Barbieri, M.; Claudi, R.; Carretta, E. +2 more
We present element-to-element abundance ratios measured from high dispersion spectra for 150 field subdwarfs and early subgiants with accurate Hipparcos parallaxes (errors <20%). For 50 stars new spectra were obtained with the UVES on Kueyen (VLT UT2), the McDonald 2.7 m telescope, and SARG at TNG. Additionally, literature equivalent widths wer…
CHIANTI-An Atomic Database for Emission Lines. VI. Proton Rates and Other Improvements
Young, P. R.; Mason, H. E.; Landini, M. +3 more
The CHIANTI atomic database contains atomic energy levels, wavelengths, radiative transition probabilities, and electron excitation data for a large number of ions of astrophysical interest. Version 4 has been released, and proton excitation data are now included, principally for ground configuration levels that are close in energy. The fitting pr…
A 3×109 Msolar Black Hole in the Quasar SDSS J1148+5251 at z=6.41
Willott, Chris J.; Jarvis, Matt J.; McLure, Ross J.
We present near-infrared H- and K-band spectra of the z=6.41 quasar SDSS J114816.64+525150.3. The spectrum reveals a broad Mg II λ2799 emission line with an FWHM of 6000 km s-1. From the peak wavelength of this emission line, we obtain a more accurate redshift than is possible from the published optical spectrum and determine a redshift…
Surface brightness profiles and structural parameters for 53 rich stellar clusters in the Large Magellanic Cloud
Mackey, A. D.; Gilmore, G. F.
We have compiled a pseudo-snapshot data set of two-colour observations from the Hubble Space Telescope archive for a sample of 53 rich LMC clusters with ages of 106-1010 yr. We present surface brightness profiles for the entire sample, and derive structural parameters for each cluster, including core radii, and luminosity and…
A Massive X-Ray Outflow from the Quasar PDS 456
O'Brien, P. T.; Reeves, J. N.; Ward, M. J.
We report on XMM-Newton spectroscopic observations of the luminous radio-quiet quasar PDS 456. The hard X-ray spectrum of PDS 456 shows a deep absorption trough (constituting 50% of the continuum) at energies above 7 keV in the quasar rest frame, which can be attributed to a series of blueshifted K-shell absorption edges due to highly ionized iron…
Quantitative Spectroscopy of O Stars at Low Metallicity: O Dwarfs in NGC 346
Bouret, J. -C.; Hillier, D. J.; Lennon, D. J. +5 more
We present the results of a detailed analysis of the properties of dwarf O-type stars in a metal-poor environment. High-resolution, high-quality ultraviolet and optical spectra of six O-type stars in the H II region NGC 346 have been obtained from a spectroscopic survey of O stars in the SMC. Stellar parameters and chemical abundances have been de…