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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)
| 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.
| Catalogue of early-type stars measured in a narrow-band photometric system
A compilation of the photoelectric measurements in the Barbier-Morguleffsystem is presented. The catalogue includes data for 773 stars ofspectral type 08 to F6. 706 stars have been measured at least twice.
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