Resumen:

Mass transfer in binary star systems is thought to be the main formation channel for Blue Stragglers: apparently rejuvenated main-sequence stars that lie above and to the blue of the turn-off point in a star cluster color-magnitude diagram, where single star evolution predicts a paucity of stars. But the impact of mass transfer on the accretor's observed properties has yet to be constrained. Aiming to predict the accretor's observational properties, we present an analytical model describing the aftermath of direct mass accretion in binary stars. We confront our model with hydrodynamical simulations of binary mass transfer, allowing for predictions of the observed properties of post-mass transfer accretors as a function of the progenitor binary's orbital parameters. In this talk, we present preliminary results, which quantify how the initial orbital parameters of the system shape the surface temperature and rotation of the accretor.

Resumen:

Blue-straggler stars (BSS) are peculiar objects found in various stellar systems. They exhibit characteristics of youth, higher temperature, and greater mass than expected according to standard stellar evolution. Moreover, they occupy a position above and to the left of the main sequence turn-off point in the optical color-magnitude diagrams (CMDs). The prevailing consensus is that BSS were originally main-sequence stars that acquired additional mass via mass transfer from an evolving primary star through Roche lobe overflow and/or via collisions involving single, binary, or triple stars. Based on the recent publication of a fresh catalog of BSS in Galactic Open Clusters (OC) using Gaia DR2 data (Gaia Collaboration et al. 2018), we conducted a study focusing specifically on the short-period BSS found in the OC Collinder 261. Our investigation delved into the potential of mass transfer in binary systems in accounting for the presence and properties of these stars. We used an adaptation of the binary evolution code presented in Benvenuto \\\\& De Vito (2003), which allowed us to perform comprehensive calculations on the structure of both stars within the binary system, as well as the orbital evolution and mass transfer rate simultaneously. Our investigation included the study of several parameters, such as the initial mass of both stars, the initial orbital period, and the efficiency of mass transfer. The aim is to identify potential progenitor candidates matching CMD observations at the same age as that determined for Collinder 261. We found that binary evolution serves as a viable mechanism for producing these BSS and that the efficiency of mass transfer plays a key role in accurately matching the fainter objects.

Resumen:

Symbiotic stars (SySt) are evolved binary systems in which a white dwarf (WD) accretes mass from a giant star. This stellar configuration causes light curve variability and other phenomena like recurrent nova eruptions and jets, turning SySt good laboratories for many binary interaction phenomena. Here we deal with the problem of the SySt population and its controversial relation with type Ia supernovae (SNe Ia) in the galaxies of the Local Group. Since a fraction of the WDs can be massive ($>$ 1 M$_\odot$) in some SySt, accretion might be enough to reach the Chandrasekar mass. Due to this condition, SySt have been considered as potential SNe Ia progenitors. This contribution is an attempt to pave the SySt-SN Ia relation adopting two approaches: an empirical, based on the distribution and dynamics of the SySt in the Galaxy; and a statistical that applies to the Galaxy and dwarf galaxies in the Local Group. Per galaxy, the main parameters involved are the initial mass function, the zero age main sequence binary system’s semi-major axis and mass ratio distributions, the binary fraction and the mean metallicity. Our results show an estimated Galactic SySt population ranging from the minimum empirical threshold value of $\sim 10^3$ to an expected statistical amount of $\sim 2\text{--}4 \times 10^4$. For Local Group dwarfs galaxies, the expected SySt population ranges from 2 to 4 orders of magnitudes lower, depending mainly on the galaxies’ bolometric luminosity. Concerning the SNe Ia events, we show that SySt are not the main progenitors. Either way, we infer that it is still expected that a few percent of the SNe Ia might have symbiotic progenitors in the Milky Way, while the majority of the – low-luminosity – dwarfs galaxies did not experience symbiotic type Ia supernovae.

Resumen:

Blue straggler stars (BSS) are exotic objects that are present in all stellar environments, but their nature and formation channels are still partially unknown. This work presents an observational and theoretical effort made to contribute to a better understanding of the properties of BSS in open clusters (OCs), enhance membership-based BS statistics, and shed light on which formation mechanism is the most predominant from a macro scale point of view. Two are the sides that define our work. From one side, we will present the most comprehensive and homogeneous catalog of the BSS population in a sample of more than 400 OCs, critically revisiting the relationship of the stragglers and cluster's host parameters, but also comparing them with a suite of composite evolutionary sequences derived from binary evolutionary models. From the other side, we will describe the different type of binaries we found among the straggler population, and how they relate with the different formation scenarios. By combining observational data and theoretical modeling we will show that binary evolution is the most viable scenario to form stragglers in Galactic star clusters.

Resumen:

Runaway stars are objects observed with high velocities thought to be ejected from star clusters. There are two competing mechanisms for their production: SN-based ejections in binaries, where one companion explodes leaving no remnant and launching the other companion at the instantaneous orbital velocity, and the disintegration of triples which produces a recoiled runaway binary (RB) and a runaway star (RS), ignoring collisions which happen rarely. We examine runaway star formation in the old open cluster M67 in this work, with a focus on triple disintegration, using data from the Gaia DR3 survey. We create a systematic methodology to look for the computed number of candidate runaway pairs we expect to observe. We use our criteria to search for these pairs in a circular field of view surrounding M67, and create a catalog using our highest probability pairs. Preliminary results could reveal a number of interesting runaway star candidates for the triple disintegration scenario considered in this study, which we identify for radial-velocity follow-up.