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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) Identifying new black hole systems and exploring 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) Understanding 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 and 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) Studying the chemical enrichment during the final stages of stars like the Sun; unveiling 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:

2016

  • Measurements of [C/Fe] and [N/Fe] have been carried out for 95 individual Red Giant Branch stars in the Sculptor dwarf spheroidal galaxy. This is the first time that [N/Fe] was measured for such a large number of stars in a galaxy of that type (Lardo, Battaglia et al. 2016).
  • Confirmation of 100 late-M (M5-L1) subdwarfs by cross-matching large-scale imaging surveys: 2MASS, SDSS, and UKIDSS. The study has provided spectral types and 3D space motions for all the sources under investigation (Lodieu et al. 2016).
  • IAC researchers have published the first atlas of OB-type stars at metallicities lower than that of the Small Magellanic Cloud (Camacho et al., 2016). The observations were performed with GTC-OSIRIS and represent the first study of a massive resolved stellar population in galaxies at low metallicity.
  • Discovery of two of the most massive contact binaries known, providing the first detailed characterization of these systems, probable progenitors of gravitational wave sources (GU Mon - Lorenzo et al. 2016 and VFTS 352 – Almeida et al., 2015).
  • The IAC team working on nucleosynthesis in giant stars has found the first evidence that the most massive, evolved AGB (asymptotic giant branch) stars play a fundamental role in the contamination of the interstellar medium, from which successive generations of stars have formed. This team has also shed light on the production of oxygen nuclei in low-mass planetary nebulae.

  • IAC researchers have found that the discrepancy between the abundances of a given element determined from collisionally excited and recombination lines in HII regions seems to have a dependence with metallicity. A strong connection between the abundance discrepancy problem and the binarity of the central star in planetary nebulae has also been identified.
  • A team of experts in asteroseismology at the IAC, together with the rest of the SONG collaboration, has published a detailed study of the spectrum of oscillations of the star μ Her based on some 30,000 spectra collected in 2014 and 2015. The investigation detected a total of 49 oscillation modes.
  • An IAC team working in the APOGEE project has uncovered multiple transitions of the rare-earth element neodymium in the H band. This discovery makes it possible to determine the abundance of this element in tens of thousands of stars observed with the APOGEE instrument (Hasselquist et al. 2016).
  • The first public data release from Gaia (Gaia Collaboration 2016) has already provided new insight into the dynamical effects that has led to the correlation between Galactic rotation and chemical composition known to be present in the stellar populations in the Galactic disk (Allende Prieto, et al. 2016).

 

2017

  • Discovery of the most metal-poor substellar object until now (Zhang et al. 2017b).
  • An extensive search for the coolest members of young open clusters has been carried out, obtaining deep optical and near-infrared spectroscopy of cool brown dwarfs in the Upper Sco association (paper submitted to MNRAS; Lodieu et al. 2017).
  • An IAC team has reported the extremely fast orbital period decay of the black hole X-ray binary (BHXB) Nova Muscae 1991. There is no standard evolutionary model able to explain the fast decay rate of this system, thus having strong implications on the evolution and lifetime of these BHXBs (González Hernández et al. 2017).
  • Discovery of a new L5 member of the Hyades cluster with chromospheric activity detected with GTC/OSIRIS spectroscopy (Perez-Garrido et al. 2017).
  • The IACOB spectroscopic database of Northern Galactic OB stars allowed the discovery of the magnetic field decay associated with the evolution of massive stars (Schneider et al. 2016).  This catalog provided as well the observations for a pioneer study on the macro-turbulence broadening in OB stars (Simón-Díaz et al., 2017; Godart et al., 2017).
  • IAC researchers have determined the physical properties for a sample of nearly 200 massive stars in a single star formation region, 30 Dor, in the Large Magellanic Cloud, which is witnessing the most intense star formation ever observed among those where individual stars can be resolved (Sabin-Sanjulian et al., 2017; Ramirez-Agudelo et al., 2017). The investigations to date show that it is necessary to improve the stellar evolution models for massive stars, as well as the models for radiation-driven winds.
  • The IAC led a study in which 44 new massive stars have been discovered, 11 of them O-type stars, in Cygnus (Berlanas et al., in preparation).

 

Previous Results (2012-2015)

MINECO
IAC
Contact: severoochoa@iac.es
Instituto de Astrofisica de Canarias. C/ Via Láctea s/n 38200, La Laguna. Canary Islands. Spain.
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