Resumen:

Very wide stellar binaries (with semi-major axes of hundreds of AU and larger) are considered useful tracers of the gravitational potential of their host, and were indeed used to place some of the first constraints on the nature of Milky Way halo dark matter in regimes not probed by microlensing. Theoretical work has shown that, if identified in dwarf galaxy hosts, a well-characterized population of wide binaries may be able to reveal with confidence whether the inner dark matter profile of these galaxies is cusped or cored, a question whose answer remains ambiguous for four decades now. However, our current census of wide binaries is restricted to a few kiloparsec distances from the Sun, and not even Gaia has the astrometric precision to identify these objects at the distances of dwarf galaxies by typical means. I will present the results of the few searches attempted so far for wide binaries in stellar systems beyond the reach of Gaia. These include our discovery and characterization of the population of wide binaries in the Galactic Bulge, at 6-10 kpc from us, and searches in dwarf galaxies at 30 and 80 kpc.

Resumen:

When the components of a binary system are close enough, one can fill its Roche lobe and start transferring mass to the companion. These mass transfer episodes affect the whole evolution of the star, being a completely different situation as if it was isolated. In this work, we study two systems with these characteristics, with the particularity that the accreting object is a black hole on both. These systems have been extensively studied in an observational way, allowing us to know their main features such as the orbital period and the masses of the components, among others. With the help of our binary evolution code, we made evolutionary models to obtain a progenitor for each system, considering the initial moment when the star is on the zero-age main sequence and the black hole is already formed. These models allow us not only to study the whole evolution of the donor star of each system but also to make some constraints about the mass transfer episodes, the orbital evolution, and the change of the black hole spin by accretion.

Resumen:

The OWN Survey is a high-resolution spectroscopic survey of Galactic massive stars accessible from the Southern hemisphere. It has been carried out since 2005, using observational facilities in Chile and Argentina. More than two hundred stars of types O and WN have been monitored to assess their multiplicity status through a systematic study of the radial velocities of their spectra. It was found that about two thirds of these objects show radial velocity variations. Fifty new multiple systems have been discovered, and their spectroscopic orbits accurately determined, effectively doubling the volume of knowledge previously existing about massive stars multiplicity. As an additional outcome, the detection of spectroscopic variability in some objects has allowed insights into magnetic fields, circumstellar material and interactions between stellar components. Thanks to the contribution of the OWN Survey, a significant pool of spectroscopic orbits is available for statistical analysis. The distribution of orbital elements (period, eccentricity, and mass ratio) observed in binaries of different luminosity classes has been investigated, leading to some preliminary conclusions regarding the formation and evolution of these systems.

Resumen:

Massive stars play a key role in the chemical evolution of the interstellar medium and thus in the metal enrichment of successive generations of stars. They also determine the dynamical and ionization state of the surrounding interstellar medium, and dominate the luminosity of star-forming regions, open clusters, spiral arms and even entire galaxies. They also have a high multiplicity (probably more than 70% of them are binaries), and are the progenitors of neutron stars and black hole binaries, which in turn are responsible for the emission of gravitational waves. However, the fundamental astrophysical parameters of massive stars are still poorly known, the mass being the most needed because of its importance in stellar evolution. To address these questions, we are carrying out a systematic observational study aimed at shedding light on the fundamental parameters of these stars. In this contribution we present new spectroscopic orbital solutions for several, already known, eccentric massive close binaries, determine the rate of their apsidal motion, and use this phenomenon, together with stellar models, to determine the masses of 14 stars. We compare the obtained masses with those obtained by the traditional eclipsing binary method, demonstrating the viability of the apsidal motion method.

Resumen:

Binary stars are very important in Astronomy. In some cases, it is possible to access, observationally and with good precision, the fundamental parameter that determines the evolution of an isolated star: its mass. In close binary systems, if close enough to each other, the evolution of the components changes completely compared to what each of them would have had in isolation, because mass loss may occur by Roche lobe overflow. As examples of objects due to binary evolution, we can cite low-mass helium white dwarfs, type Ia supernova progenitors, cataclysmic variables, the millisecond pulsar recycling model, black widows, and redbacks families, blue stragglers and yellow stragglers. On the other hand, it is within the framework of binary evolution that the formation of pairs of neutron stars and black holes is understood. In these kinds of binaries, under certain conditions, the merge of the components is a source of gravitational waves. In addition to the two stellar components, in a binary where the accretor is a compact object, there is another fundamental actor: the accretion disk. Accretion disks have been studied for decades. However, the complexity of the physical processes that occur in it means that, when modeling them, we still have a lot to explore. In this poster, we will make a brief description of the evolution of close binary systems composed of a low-mass normal star and a neutron star, using models obtained from our binary evolution code. Subsequently, we describe the thin disk treatment (“alpha” disc), where it is possible to decouple the vertical from the radial treatment (in this later, the temporal evolution is found). We present our first results and discuss the steps to follow to study the effect of neutron star irradiation on the accretion disk.

Resumen:

We present a new spectrophotometric investigation of the massive binary system HD 165246, based on high-resolution optical spectra obtained by the OWN Survey. HD 165246 is a short-period spectroscopic binary hosting a primary star of spectral type O8 V. Its light curve, as observed by the K2 satellite, reveals it is also an eclipsing system. From 2006 to 2019, the OWN Survey gathered 55 echelle spectra of HD 165246. The analysis of these data led to the detection of spectral lines arising in the secondary component, enabling a comprehensive characterization of the system. Our study yields a period of 4.59276 +/- 0.00006 days, along with absolute masses: Ma = 22.0 +/- 1.0 $M_{\odot}$ and Mb = 3.5 +/- 0.1 $M_{\odot}$, and corresponding radii: Ra = 7.0 +/- 0.1 $R_{\odot}$ and Rb = 2.2 +/- 0.03 $R_{\odot}$ for the primary and secondary components, respectively. The investigation of the evolutionary state of HD 165246, via theoretical models including rotation, suggests an age of 2 Myr for this binary system. Finally, an analysis of the tidal evolution indicates a non-circular orbit and non-synchronous rotation of the stellar components.

Resumen:

Symbiotic stars are a subclass of interacting binary systems where a compact object, typically a white dwarf (WD) or a neutron star, accretes material from an evolved giant. Accretion can occur through two primary mechanisms: wind accretion or Roche lobe overflow. Wind accretion is the dominant mechanism in most symbiotic stars [1,2], but in a small fraction of symbiotic stars, Roche lobe overflow can also occur [3]. Typical orbital periods of symbiotic stars are observed over relatively long timescales ranging from hundreds of days to decades. Shorter time-scale variability is also observed in these systems. This short-term variability in symbiotics is related to the accretion process and the formation of the accretion disk, which is crucial for understanding the evolution of these systems. The detection of periodic modulations in the optical light curves of symbiotic binaries provides evidence for the presence of magnetic white dwarfs, which plays an important role in the accretion process by truncating the accretion disk and regulating the accretion flow. We propose to do a survey with TESS of symbiotic systems to find new candidate magnetic WD in symbiotics.