Resumen:

The Phillips relation is an empirical relationship between the peak luminosity and decline rate of Type Ia supernovae. This relation provides a powerful tool for measuring distances to distant galaxies and for probing the expansion history of the Universe. The relationship indicates that brighter SN decline more slowly than fainter ones, and therefore, their light curves have a broader peak. This correlation is thought to be due to the fact that brighter supernovae have more massive progenitor stars, which produce more radioactive nickel during the explosion, leading to a slower decline in luminosity. Despite its usefulness, the precise physical mechanism that underlies the Phillips relation is still a subject of active research. However, there are some objects that do not follow this relation. Because, if the number of this SNe increases could be dramatic for the concepts already established. We present two new SNe that do not follow this relation and have specific spectroscopic features at nebular phases that can lead some hints of the explosion mechanisms. For this reason is important subclassify them as a new family of type Ia SNe.

Resumen:

Swift J1910.2-0546 is a transient X-ray binary discovered in 2012 when the system was detected in an outburst episode. During that state, it showed the typical behaviour found in systems harbouring black holes although the nature of the compact object has not been established since. In this contribution we show a comprehensive study of Swift J1910-2-0546 using optical outburst (obtained with the INT and NOT) and quiescence data (obtained with GTC and VLT), obtaining that the donor star is later than ~G2V. We also establish constraints to the orbital period (4.6 kpc) which, together with the lack of double peak emission lines (suggesting an inclination < 35 deg) and the radial velocity estimates obtained from the H$\alpha$ line in quiescence, support the presence of a black hole in the system.

Resumen:

The Period-Luminosity relation of Cepheid variable stars is an essential tool for measuring distances in our Universe. As such, further understanding of the pulsation of Cepheids would allow for a better calibration of the extragalactic distance ladder. Being the result of the internal processes of these stars, Cepheid pulsations are not expected to be harmonic; several overtones could be excited within the star. As the overtones displace the star position in the Period-Luminosity diagram, the mixing of pulsation modes for a Cepheid population will result in an error on the calculated distance modulus. The complexity of the Cepheids light curves makes the use of a Fourier series fit inadequate, and different templates have been developed to better capture the pulsation shape. Using the available OGLE data from the Magellanic Clouds as our testing scenario, we use the fit parameters as the features for an unsupervised machine learning model to identify the pulsation modes present in each Cepheid. Then we compare the different models to see which template performs better at this identification.

Resumen:

Eclipsing binary stars, constituting approximately 70% of our Galaxy's stellar population, play a crucial role in our understanding of star cluster systems, offering unique insights into their formation, evolution, and stellar composition. In this study, we conducted an extensive investigation of eclipsing binary candidates in a specific near-infrared window using the VVV Survey (tile d040). Our primary focus was to explore the potential membership of these binaries within star clusters in the same region. Eclipsing binaries are of great significance as they offer a valuable means to estimate the distance and additional properties of their associated stellar groups, and vice versa. By analyzing Gaia DR3 and VVV databases, we thoroughly examined the structure, kinematics, and photometry of the identified star clusters, aiming to uncover any possible connections with the studied binaries and other previously identified binary systems in the same fields. This work presents our preliminary findings on cluster membership and characterizations, providing crucial insights into the intricate interplay between binary systems and star clusters.

Resumen:

Variable stars are vital in establishing the cosmic distance ladder. In particular, RR Lyrae stars (RRLs) are considered standard candles due to the relations they follow between their luminosities, metallicities, and pulsation periods. RRLs have been historically considered as tracers of old populations (older than 10 Gyr). However, recent studies in the field of the Milky Way and Magellanic Clouds (Sarbadhicary et al. 2021, Iorio and Belokurov et al. 2021) suggest the existence of RRLs in intermediate-age populations (1-8 Gyr). The existence of intermediate-age RRLs challenges our understanding as they cannot be accounted for by stellar evolution models of isolated stars, making binary evolution the prime suspect to explain their existence. Our goal in this work is to look for direct evidence of the existence of these stars by looking for RRLs in intermediate-age clusters. To this aim, we establish an inference model intended to estimate the membership probability of RRLs from the Gaia DR3 and OGLE catalogs to massive intermediate-age stellar clusters in the Large and Small Magellanic Clouds. Because the expected rate of production of these stars in any individual cluster is expected to be small, we combine the data for many clusters to infer the production rate of RRLs per unit mass in a given age range. We obtain a production rate of $\sim$10 RRLs per $10^5$ Msun for old clusters (>8 Gyr), in accordance with observations in Milky Way globular clusters, and infer a rate of $\sim < 2$ RRLs per $10^5$ Msun for intermediate-age (1-8 Gyr) clusters. Our method also allows us to build a list of RRLs with a high membership probability to intermediate-age clusters, which will require spectroscopic follow-up to confirm their membership to the clusters, and therefore confirm robustly and directly the occurrence of these stars in intermediate-age populations.

Resumen:

Type II supernovae (SNe) are the most common terminal stellar explosion in the Universe. With SNe being detected now within days after explosion, there is growing evidence that type II SNe show signs of interaction with a confined, dense cirumstellar material (CSM) in the first few days post explosion. In this work we aim to bridge the gap between single SN studies showing early-time interaction in their spectra, and the statistical studies of early-time SN light curves. We present a sample of 70 type II SNe with both early photometric data, obtained with the ATLAS survey, and spectroscopic data, obtained with the ePESSTO+ collaboration. We present an analysis of the light curves and spectra, with the extraction of parameters that help us constrain the frequency and effects of the interaction with a dense CSM. In addition, we present correlations between the extracted parameters during the first days to weeks post SN explosion.

Resumen:

Several satellites of our Milky Way have been discovered in the last decades, adding them to those twelve known for long time ago. Most of these newly discovered satellites could not be found before due to their extremely low luminosity, now known as Dwarf Spheroidals (dSph's) and Ultra faint dwarfs (UFDs). These systems are most dominated by dark matter, and they are key to explore a large variety of topics. Unfortunately, most UFDs are not suitable for extensive analysis due to the scarcity of bright stars. The available color-magnitude diagrams (CMD) of these systems are poorly populated and do not reach the sub-giant branch level in most of the cases. Their key parameters are thus derived from isochrone fits that are uncertain and degenerate in the three input parameters of age, metallicity, and distance. Our principal aim is to detect RR Lyrae variable stars, which have been found in all dSph’s studied so far. In fact, their well-known period-luminosity relation makes them ideal distance indicators for old stellar populations. The discovery of even one such star would fix the distance much better than what can be done through isochrone fit, improving measures such as luminosity and size, and allowing a better estimate of age and metallicity, among other benefits. We are probing a new method to detect the RR-lyrae stars of the UFDs that is to observe them directly, without any filter. Our aim is to successfully deal with all the issues that involves using this method to detect variable stars, such as the lack of standard stars, leading to magnitude dependencies in color and/or airmass, among others. If we are successful, we will be able to find variable stars in UFDs using only a 1-m telescope, giving new life to these increasingly forgotten telescopes.