Microquasars: disk-jet coupling in stellar-mass black holes

Microquasars provide new insights into: 1) the physics of relativistic jets from black holes, 2) the connection between accretion and ejection, and 3) the physical mechanisms in the formation of stellar-mass black holes. Furthermore, the studies of microquasars in our Galaxy can provide in the future new insights on: 1) a large fraction of the ultraluminous X-ray sources in nearby galaxies, 2) gamma-ray bursts (GRBs) of long duration in distant galaxies, and 3) the physics in the jets of blazars. If jets in GRBs, microquasars and Active Galactic Nuclei (AGN) are due to a unique universal magnetohydrodynamic mechanism, synergy of the research on these three different classes of cosmic objects will lead to further progress in black hole physics and astrophysics.Comment: 4 pages, 3 figures. To appear in Proceedings of IAU Symp. No 238 "Black Holes: from Stars to Galaxies - across the Range of Masses. Held in Prague, August 21-25, 2006. Eds. V. Karas & G. Mat

Black holes: from stars to galaxies

While until recently they were often considered as exotic objects of dubious existence, in the last decades there have been overwhelming observational evidences for the presence of stellar mass black holes in binary systems, supermassive black holes at the centers of galaxies, and possibly, intermediate-mass black holes observed as ultraluminous X-ray sources in nearby galaxies. Black holes are now widely accepted as real physical entities that play an important role in several areas of modern astrophysics. Here I review the concluding remarks of the IAU Sympposium No 238 on Black Holes, with particular emphasis on the topical questions in this area of research.Comment: Invited talk. Concluding Remarks of IAU Symposium 238: "Black Holes: From Stars to Galaxies -Across the Range of Masses". Prague 14-18 August 200

Search for neutral hydrogen with high negative velocities ejected from the galactic center

A search for neutral hydrogen in the velocity range −300>V>−1000 km s−1 has been made in the zone around the galactic nucleus. Observations of 100 points reveal no neutral hydrogen at such high velocities, with brightness temperatures exceeding 0.25 K in the latitude range |b|<1°, and 0.20 K for |b|≥1°.Instituto Argentino de Radioastronomí

An expanding high velocity hi cloud probably ejected from the galactic nucleus

An object located approximately atl=8°,b=−4° with a mean radial velocity of −212.3 km s−1 has been observed in the 21 cm neutral hydrogen line. The mean weighted velocity dispersion is 11.2 km s−1 and the total mass is estimated to be 190R2 (kpc) solar masses. We discuss possible interpretations of the origin and nature of this object. The most likely interpretation is that we observe an expanding object which has been ejected from the galactic nucleus.Instituto Argentino de Radioastronomí

Study of the outer galactic structure for 288°≤l≤310°, −7°≤b≤2°

The structure of the outer part of the Galaxy is studied, based upon 21-cm line observations of Hi in the region 288°≤l≤310°, −7°≤b≤2°. In this longitude range the galactic plane is strongly bend toward negative latitudes. The principal outer structure is a spiral arm which has a pitch angle of 10º and is formed by several concentrations differing in shape and size. There exists also a secondary concentration which could be a split from the previous structure. Possible hypotheses about the origin of the later feature are discussed.Instituto Argentino de RadioastronomíaComisión de Investigaciones Científicas de la provincia de Buenos Aire

Missing GRB host galaxies in deep mid-infrared observations: implications on the use of GRBs as star formation tracers

We report on the first mid-infrared observations of 16 GRB host galaxies performed with the Spitzer Space Telescope, and investigate the presence of evolved stellar populations and dust-enshrouded star-forming activity associated with GRBs. Only a very small fraction of our sample is detected by Spitzer, which is not consistent with recent works suggesting the presence of a GRB host population dominated by massive and strongly-starbursting galaxies (SFR >~ 100M[sun]yr^–1). Should the GRB hosts be representative of star-forming galaxies at high redshift, models of galaxy evolution indicate that >~ 50% of GRB hosts would be easily detected at the depth of our mid-infrared observations. Unless our sample suffers from a strong observational bias which remains to be understood, we infer in this context that the GRBs identified with the current techniques can not be directly used as unbiased probes of the global and integrated star formation history of the Universe

An Anomalous Velocity Neutral Hydrogen Structure Near the Galactic Center

An extensive concentration of neutral hydrogen has been observed in the fourth galactic quadrant, with a mean radial velocity of +44 km s−1 referred to the local standard of rest. At a distance ofR kpc from the Sun this structure would contain 2.5×104R2 solar masses of neutral hydrogen.Instituto Argentino de Radioastronomí

Búsqueda de nubes de hidrógeno atómico con velocidad intermedia

The región between l = 30° and l = 330° was observed in the 21 cm. line in a search for neutral hydrogen at intermediate velocities. An extensive concentration of hydrogen was observed in the fourth galactic quadrant with radial velocity of 45 Km/seg.Asociación Argentina de Astronomí

Cúmulo abierto NGC 2516 : Informe de beca

Distance and age of NGC 2516 are estimated by UBV photometry. The location of peculiar stars in colour-magnitude and colour-colour diagrams are also discussed.Asociación Argentina de Astronomí