Stellar and Interstellar Physics

Stars are fundamental physical probes. The Severo Ochoa project is supporting the major center goals in the Stellar and Interstellar Physics research line:

1) Identify new black hole systems and explore the physics of black holes and their progenitors; major world observatories are used by the team to obtain dynamical masses for stellar black holes in binary systems, studying accretion/outflow processes in compact binaries and test
theories predicting the orbital period evolution of these systems as a result of magnetic braking and/or gravitational radiation. Stars orbiting black holes will be used to test the behavior of gravity in the strong field regime;

2) Understand the physics and life cycle of stars, from the most massive and luminous stars that can be seen at large distances in the Universe and will lead to explosive events and the formation of black holes/ neutron stars, to the least luminous brown dwarfs which bridge the gap to the planetary domain;The goal in massive stars is to benefit from their large luminosities and intense radiation fields and use them as tools for our understanding of the low- and high-z Universe. IAC researchers have pioneered research on brown dwarfs since their discovery (Rebolo et al. 1995 Nature), the goal is now to understand the formation mechanism of these objects which compare in number with stars;

3) study chemical enrichment during the final stages of stars like the Sun; unveil the distribution of carbon (atomic and in molecular forms) in the Milky Way and other galaxies and determine the role of carbon-bearing molecules in interstellar prebiotic chemistry.

Goals:

• Discover and study black holes, neutron stars and white dwarfs in systems under strong gravity fields;
• Clarify the role of stellar winds in the most massive stars and the formation/evolution of brown dwarfs bridging the stellar and the exoplanet domain;
• Understand the final stages of Sun-like stars and unveil the distribution of carbon and the role of carbon-bearing molecules in interstellar prebiotic chemistry.

Main Scientific Outputs:

2012

• Detection of the black hole H1705-25 in quiescence using the X-ray Chandra telescope. Neutron stars are found systematically brighter than BHs in quiescence and this is interpreted as evidence for the absence of a hard surface in accreting BHs (Yang et al. 2012 MNRAS).
• Discovery with GTC of an orbital period decay in the black hole system XTE J1118+480 (González-Hernández, 2012 ApJ).
• The orbital period change of the binary white dwarfs J0651 agrees with predictions from Einstein's Theory of Relativity (The Astrophysical Journal Letters vol. 757, pp. 6)).
• IAC made front page of Nature with an article on the progenitor of Supernova 1006 (González-Hernández et al. 2012)
• Chemical enrichment. Fullerene C60 and proto-graphene (C24) detected in the planetary nebula M 1-60 and K 3-54, respectively (The Astrophysical Journal vol. 760, pp. 16).
• First T dwarfs discovered using the VISTA Hemispheric Survey (Astronomy & Astrophysics vol. 548, A53).

2013

• Researchers at the IAC discovered the fast "fall" of two stars on black holes. The X-ray binary XTE J1118+480 was observed with GTC/OSIRIS to confirm the previous discovery of its fast orbital decay. Previous observations were used to unveil the orbital decay of another black hole X-ray binary A0620-00. These two X-ray binaries, with similar black-hole masses, have short but different orbital periods and fast but different orbital-decay rates, suggesting an evolutionary sequence in the evolution of black-hole X-ray binaries.
• The spectroscopic study of nearly 80 star clusters in the nearby galaxy M33, based on GTC and WHT spectra, suggests that some mechanism has been kinematically "heating" the M33 disc. Proposed heating mechanisms include interactions with the spiral arms in the disc, mergers of mini dark matter haloes or black holes, or interactions with the nearby Andromeda galaxy (Beasley et al., in preparation).
• Active participation of researchers at the IAC in the European Southern Observatory (ESO) Large Programme VLT-FLAMES Tarantula Survey (VTFS) has led to 5 papers in 2013 (The VLT-FLAMES Tarantula Survey VIII to XII papers) studying the closest starburst-like region in the local universe.
• The IACOB spectroscopic database of Northern Galactic OB stars is now completed. First results from its scientific exploitation, concerning a modern catalogue of projected rotational velocities, has been published in Astronomy and Astrophysics (vol. 562, A135).