Seminars
2023
Lunes 18/12 - 11:00 hs (Salón Meridiano - FCAG - UNLP): Luis Lomellí Nuñez (Observatorio de Valongo, UFRJ, Brasil)
Tìtulo: "Stellar populations in nearby galaxies"
Resumen: The stellar clusters are one the most visible characteristics in galaxies. Studies have found that late-galaxies show a two distinct populations of stellar clusters (e.g. Simanton et al. 2015a), a component older (globular clusters) and other younger (open clusters). Studying the different populations of star clusters in galaxies can give us clues about the evolution and current state of galaxies (Pérez et al. 2013). In the framework of the hierarchical model of galaxy formation, the current state of galaxies is preceded by a great history of interactions and mergers of smaller elements. A consequence of this model of galaxy formation is a continuous formation of stars, therefore stellar clusters of all ages in galaxies should be observed. However the detection and study of the stellar clusters is observational it has focused in old clusters (e.g., Zepf & Ashman 1993, Ashman & Zepf 1998, Brodie & Strader 2006 and references in) and in young clusters (e.g, Larsen & Richtler 1999, Bica et al. 2003). On the other hand, in recent years with the help of the HST, works about a new star clusters class has been done (e.g., Whitmore et al. 1999 (Antennae), Mayya et al. 2008 (M82), Santiago-Cortés et al. 2010 (M81) ) such works have studied a new class of stellar clusters: super stellar clusters (SSC). They have characteristics similar to the globular clusters (mass, compactibility, etc.), being the main candidates to be an evolutionary state previous to the GCs as such, therefore to be intermediate age clusters. In this seminar we will talk about the properties of the different stellar clusters.
Jueves 14/12 - 10:00 hs (Salón Meridiano - FCAG - UNLP): Pablo Astudillo Sotomayor (Universidad de Concepción, Chile)
Tìtulo: "Los orígenes de las Galaxias Ultra Difusas: Caracterización de su población de cúmulos globulares en distintos entornos"
Resumen: Las galaxias ultra difusas (UDGs, por sus siglas en inglés) son un subconjunto de galaxias de bajo brillo superficial caracterizadas por sus grandes radios efectivos (r_e > 1,5 kpc). Estas galaxias se han encontrado en una gran variedad de entornos, incluyendo el campo, grupos y cúmulos de galaxias. Las diferentes propiedades de las UDGs y sus cúmulos globulares (GCs) en función del entorno han planteado la cuestión del papel del medioambiente en la evolución de las UDGs y la influencia del mismo en su población de CGs. En esta presentación, hablaremos de nuestro trabajo en curso para estudiar las propiedades de las UDGs y sus CGs en diferentes entornos utilizando a estos ùltimos como partículas trazadoras para restringir sus orígenes.
Viernes 24/11 - 13:00 hs (Salón Meridiano - FCAG - UNLP): Felipe de Almeida Fernandes (IAG, Universidad de Sao Paulo, Brasil)
Título: Hunting for the first stars in the Universe with S-PLUS (Video)
Resumen: Metal-poor stars are key to our understanding of the early stages of chemical evolution in the Universe. New multifilter surveys, such as the Southern Photometric Local Universe Survey (S-PLUS), are greatly advancing our ability to select low-metallicity stars in our Galaxy. In a series of papers, we have selected and analyzed a sample of 522 metal-poor candidates in S-PLUS. Follow-up observations in Blanco and Gemini South telescopes, using the COSMOS and GMOS spectrographs, confirmed that 92% of the selected stars have [Fe/H] < -1, while 83% have [Fe/H] < -2, and 15% [Fe/H] < -3. Our sample also includes two stars with spectroscopic metallicity below -4. Based on this sample, we proposed further selection criteria by combining S-PLUS and Gaia DR3 data and showed that we were able to improve the purity of the selection, achieving fractions of 99.5% and 91% for [Fe/H] ≤ -1 and [Fe/H] ≤ -2, respectively. We also performed high-resolution spectroscopic follow-ups for two peculiar stars in the sample: i) SPLUS J2104−0049 was observed in the Magellan-Clay telescope and found to be the ultra metal-poor star ([Fe/H] < -4) with the lowest ever detected carbon abundance (at the time of our publication). ii) More recently, SPLUS J1424-2542 was observed during the system verification of the GHOST instrument, installed at the Gemini South telescope. Our preliminary results reveal that this star is not only a metal-poor star with low carbon abundance, but is also enriched in r-process elements.
Miércoles 27/09 - 13:00 hs (Salón Meridiano - FCAG - UNLP): Clecio R. de Bom (CBPF, Brasil)
Título: Follow-up of Gravitational Waves and explosive transients: optimized strategies and prospects for novel discoveries (Video)
Resumen: Transient astrophysical phenomena have a range of interest that goes through different fields of astrophysics and cosmology and are one of the most interesting subjects in time-domain and multi-messenger astronomy. Those fields has undergone a revolution over the past years. With the detection of an electromagnetic counterpart to the gravitational wave (GW) event GW170817 from a binary neutron stars merger, new techniques and resources to study astrophysical transients in the multi-messenger context have increased. Unique in its design sensitivity, the current LIGO-Virgo-KAGRA (O4) season is expected to explore ∼7x more detections of Binary Neutron star (BNS) events than O3. EM follow-up of many O4 events should require telescopes with limited Target-of-Opportunity (ToO) availability.
We present the S-PLUS Transient Extension Program (STEP), an explosive transient survey conducted in the Southern Hemisphere using data from the Southern Photometric Local Universe Survey (S-PLUS) Main Survey. Additionally, we address the problem of optimally identifying all kilonovae. We optimize our strategy for kilonova confirmation while minimizing telescope time. For a wide range of kilonova parameters, corresponding to a fainter, redder kilonova compared to GW170817/AT2017gfo we find that the discovery probability with the DECam is ∼80% at the nominal BNS gravitational wave detection limit for O4, a ∼30% improvement compared to the O3 strategy. For AT2017gfo-like kilonova, we find ∼90% probability out to 330 Mpc.
Furthermore, as most expected events are Binary Black Holes, we explore the possibility of Standard Sirens in association with AGN flares. Our formalism requires GW localization area monitoring only without needing ToO spectra since we don't require identifying the host of each BBH merger. Thus, a hybrid method between bright and dark sirens is explored. We simulate O4 season and derive the expected constraints in H0, Omega_m, and w.
2022
Miércoles 7/12 - 12:30 hs (Salón Meridiano - FCAG - UNLP): Laerte Sodré (IAG, Universidad de Sao Paulo, Brasil)
Título: The Giant Magellan Telescope and the new challenges of Brazilian Astronomy (Video)
Resumen: The Giant Magellan Telescope (GMT) is one of the new giant telescopes currently under construction. The State of São Paulo is a member of the consortium responsible for its construction, thanks to the support of the state funding agency FAPESP. In this seminar I will present the project and the challenges faced by our group to participate in the development of its instruments.
Miércoles 30/11 - 12:30 hs (Salón Meridiano - FCAG - UNLP): Vitor Cernic (IAG, Universidad de Sao Paulo, Brasil)
Título: The S-PLUS Survey and the study of stellar populations in galaxies (Video)
Resumen: The Southern Photometric Local Universe Survey (S-PLUS) is a 12-band survey conducted with the T80-South telescope, at Cerro Tololo, Chile, that has observed tens of millions of stars, galaxies and other objects since 2016. In this talk, I will describe the S-PLUS survey and present a Deep Learning approach to investigate the stellar population of galaxies using S-PLUS photometry. Indeed, we obtain parameters like stellar mass and mean stellar ages by training the algorithm to emulate the results of the STARLIGHT spectral synthesis code using the 12 S-PLUS magnitudes instead of a spectrum.