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The eccentric accretion disc of the black hole A0620-00
We present spectroscopic observations of the quiescent black hole binaryA0620-00 with the 6.5-m Magellan Clay telescope at Las CampanasObservatory. We measure absorption-line radial velocities of thesecondary and make the most precise determination to date (K2= 435.4 +/- 0.5kms-1). By fitting the rotational broadeningof the secondary, we refine the mass ratio to q = 0.060 +/- 0.004; theseresults, combined with the orbital period, imply a minimum mass for thecompact object of 3.10 +/- 0.04Msolar. Although quiescenceimplies little accretion activity, we find that the disc contributes 56+/- 7 per cent of the light in B and V, and is subject to significantflickering. Doppler maps of the Balmer lines reveal bright emission fromthe gas stream-disc impact point and unusual crescent-shaped features.We also find that the disc centre of symmetry does not coincide with thepredicted black hole velocity. By comparison with smoothed particlehydrodynamics (SPH) simulations, we identify this source with aneccentric disc. With high signal-to-noise ratio (S/N), we pursuemodulation tomography of Hα and find that the aforementionedbright regions are strongly modulated at the orbital period. Weinterpret this modulation in the context of disc precession, and discusscases for the accretion disc evolution.This paper includes data gathered with the 6.5-m Magellan telescopelocated at Las Campanas Observatory, Chile.E-mail: jneilsen@cfa.harvard.edu (JN); dsteeghs@cfa.harvard.edu (DS);svrtilek@cfa.harvard.edu (SDV)
| Observations of Star-Forming Regions with the Midcourse Space Experiment
We have imaged seven nearby star-forming regions, the Rosette Nebula,the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5,with the Spatial Infrared Imaging Telescope on the Midcourse SpaceExperiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and21.3 μm. The large angular scale of the regions imaged (~7.2-50deg2) makes these data unique in terms of the combination ofsize and resolution. In addition to the star-forming regions, twocirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the southGalactic pole (MSXBG 239) were also imaged. Point sources have beenextracted from each region, resulting in the identification over 500 newsources (i.e., no identified counterparts at other wavelengths), as wellas over 1300 with prior identifications. The extended emission from thestar-forming regions is described, and prominent structures areidentified, particularly in W3 and Orion. The Rosette Nebula isdiscussed in detail. The bulk of the mid-infrared emission is consistentwith that of photon-dominated regions, including the elephant trunkcomplex. The central clump, however, and a line of site toward thenorthern edge of the cavity show significantly redder colors than therest of the Rosette complex.
| Dwarf K and M stars of small proper motion found in a large spectroscopic survey
More than 2000 candidates for K and M dwarf status, generally havingproper motions that are either unknown or less than 0.2 arcsec perannum, have been identified in an objective-prism survey covering theentire sky north of declination - 25 degrees and more than 10 degreesfrom the galactic plane. More than 95 percent have no previousindication that they are dwarfs. Several dozen appear to be visualdouble stars.
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