arXiv subjects

J. G. Cuby

Publications and source records attributed to J. G. Cuby.

24 records · Page 2Linked to original sources

arXiv2001

An unusually massive stellar black hole in the Galaxy

Here we report a measurement of the orbital period and mass function of GRS 1915+105 which allow us to deduce a mass of 14 +- 4 solar masses for its black hole. This large mass provides a challenge for black hole formation scenarios in binaries, since black holes with masses above 5-7 solar masses are hard to explain. Also, the mass estimate allows us to understand the unique X-ray variability of GRS 1915+105 as being due to instabilities of a radiation-pressure dominated disk radiating near the Eddington limit. Finally, several models are constrained which relate observable X-ray properties to the spin of black holes in microquasars. Once further calibrated, these relations may soon turn into a valuable tool to study relativistic effects in strong gravitational fields.

astro-ph↗

arXiv2001

Identification of the donor in the X-ray binary GRS 1915+105

We report on the results of medium-resolution spectroscopy of GRS 1915+105 in the near-infrared H and K band using the 8m VLT at ESO. We clearly identify absorption bandheads from 12CO and 13CO. Together with other features this results in a classification of the mass-donating star in this binary as a K-M III star, clearly indicating that GRS 1915+105 belongs to the class of low-mass X-ray binaries (LMXB).

astro-ph↗

arXiv2001

Kinematics of Molecular Gas in the Nucleus of NGC1068, from H2 line emission observed with VLT

We present results about the distribution and kinematics of the molecular environment of the AGN in NGC1068, over a 1.5'' x 3.5'' region around the central engine in NGC1068, derived from H2 line emission detected with ISAAC at VLT/ANTU on ESO/Paranal. The H2 emitting molecular gas is found to be distributed along the East-West direction and with two main peak emission (knots) located at a distance of about 70 pc from the central engine. The eastern H2 knot is more intense than the western one. The line profiles mapped across the entire 1.5'' x 3.5'' region, at a spatial resolution of 0.3'' x 0.45'', appear to be quite complex with either a blue or red wing. At first order, we find a velocity difference of 140 km/s between the two knots; if interpreted as quasi-keplerian velocity, this implies a central enclosed mass of 10^8 solar masses.

astro-ph↗

arXiv2000

Identification of the donor in GRS 1915+105

We report on the results of medium-resolution spectroscopy of GRS 1915+105 in the H and K band using the 8m VLT at ESO. We clearly identify absorption bandheads from CO12 and CO13. Together with other features this results in a classification of the donor as a K-M III star.

astro-ph↗

arXiv1999

Discovery of a faint Field Methane Brown Dwarf from ES0 NTT and VLT observations

We report the discovery of an isolated brown dwarf with similar properties to the binary object Gliese 229B and to the newly discovered field brown dwarf SDSS 1624+00. Although exhibiting similar colors, its magnitude of ~20.5 is about 6 and 5 magnitudes fainter than Gliese 229B and SDSS 1624+00 respectively. This is the third methane brown dwarf reported to date, the second isolated one in the field and by far the most distant at ~ 100 pc. Its IR spectrum, although at low S/N given the faintness of the object, is remarkably similar to those of the 2 other methane brown dwarfs.

astro-ph↗

arXiv1999

Counts, Sizes and Colors of Faint Infrared Selected Galaxies

Deep J and Ks band images covering a $5\times5$ arcmin area centered on the NTT Deep Field have been obtained during the Science Verification of SOFI at the NTT. These images were made available via the Web in early June. The preliminary results we have obtained by the analysis of these data are the following: 1) the counts continue to rise with no evidence of a turnover or of a flattening down to the limits of the survey (Ks=22.5 and J=24); 2) we find a slope $dlog(N)/dm\sim$0.37 in agreement with most of the faintest surveys but much steeper than the Hawaii survey; 3) fainter than Ks$\sim19$ and J$\sim20$, the median J-K color of galaxies shows a break in its reddening trend turning toward bluer colors; 4) faint bluer galaxies also display a larger compactness index, and a smaller apparent size.

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