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Evidence for the Formation of a Large-Scale Current Sheet in a Solar Flare
Holman, Gordon D.; Sui, Linhui
We present X-ray evidence for the formation of a large-scale current sheet in a flare observed by the Ramaty High-Energy Solar Spectroscopic Imager on 2002 April 15. The flare occurred on the northwest limb, showing a cusp-shaped flare loop in the rise phase. When the impulsive rise in hard X-rays (>25 keV) began, the cusp part of the coronal s…
Detection of Nine M8.0-L0.5 Binaries: The Very Low Mass Binary Population and Its Implications for Brown Dwarf and Very Low Mass Star Formation
Close, Laird M.; Biller, Beth; Siegler, Nick +1 more
Use of the highly sensitive Hokupa'a/Gemini curvature wave front sensor has allowed direct adaptive optics (AO) guiding on very low mass (VLM) stars with SpT = M8.0-L0.5. A survey of 39 such objects detected nine VLM binaries (seven of which were discovered for the first time to be binaries). Most of these systems are tight (separation <5 AU) a…
Shapelets - I. A method for image analysis
Refregier, Alexandre
We present a new method for the analysis of images, a fundamental task in observational astronomy. It is based on the linear decomposition of each object in the image into a series of localized basis functions of different shapes, which we call `shapelets'. A particularly useful set of complete and orthonormal shapelets is that consisting of weigh…
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…