viernes 01 de diciembre
SALÓN DORADO (120)
10:20 - 11:00
COFFEE BREAK
11:00 - 12:30
G: Stars and Stellar Physics
Stellar Structure and Evolution II
Chair: Julia Arias
#053 |
Lithium depletion in solar analogs: age, mass, and planet effects
Anne Rathsam
1
;
Jorge Meléndez
1
;
Gabriela Silva
1
;
Giulia Martos
1
1 - Universidade de São Paulo.
Resumen:
Lithium is an essential element for Stellar Astrophysics because it is depleted at somewhat low temperatures which are easily reached in the interior of stars. According to standard models, the base of the convection zone of main sequence solar-type stars does not reach deep enough inside the star to burn Li. However, it is observed that older field solar analogs present a lower Li content, indicating that part of the Li present in the stars is taken towards inner regions through non-standard mixture processes. In this work, we determined Li abundances for a sample of 153 solar analogs, exploring the dependence of Li with age, mass and convective mass. The high-quality (R $=$ 115000; 270 $\leq$ SNR $\leq$ 1000) spectra used in this project were taken with ESO’s HARPS spectrograph. We employed the method of high precision differential spectroscopy, measuring equivalent widths of spectral lines to determine atmospheric parameters and infer masses and ages. The Li abundance was determined via spectral synthesis. We found a strong correlation between lithium abundance and age, and also a clear link between low lithium abundances and lower masses (and higher convective masses). We added another high-precision HARPS sample of solar analogs studied in our group to consider the effect of planets on Li in a sample of 194 stars and we report that planet hosts have on average Li abundances -0.3 dex lower than non-planet hosts with similar parameters, with a significance above 99\% for our results.
#068 |
Multiple Element Abundance Fitting Software, MEAFS
Matheus J. Castro
1
;
Heitor Ernandes
2
;
Beatriz Barbuy
1
1 - Institute of Astronomy, Geophysics and Atmospheric Sciences of the University of São Paulo.
2 - Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University.
Resumen:
Deriving chemical abundances from spectra is one of the great jobs in astronomy. The chemical evolution of the Galaxy can be studied through the abundance of chemical elements of stars of different stellar populations. The applications are diverse, deriving abundances in a spectrum can help us predict, for example, which is the future of stars like the Sun will be like. Each star has a chemical signature depending on the conditions of its formation, its mass and age.
The analysis is a job that demands time and precision. Commonly, for a robust work, it is necessary to analyse hundreds of spectral lines, which can take days or months to adjust all of them. For each line, it is necessary to run programs that generate synthetic spectra of stars several times, changing the chemical abundance of the element being analysed in order to better fit the model with the observed spectrum.
MEAFS (Multiple Element Abundance Fitting Software) is a code being developed in \textit{Python} and \textit{C} that aims to fit abundances automatically and for multiple elements in a single execution. It is also able to adjust the convolution, the continuum and the wavelength shift of the synthetic spectrum for the best fit with the observed spectrum. Not only does it faster than the manual way, it is in principle also more accurate than an average person.
The code is under development and currently MEAFS can run the \textit{Turbospectrum} (Plez, 2012) spectrum generator. The version to use the code \textit{PFANT} (Barbuy et al., 2018) is aso in progress.
The current version with \textit{Turbospectrum} was tested with spectra of the star CS 31082-001 and the analysis of 260 spectral lines takes around two hours. The code is validated for clear and unblended lines as shown in Ernandes et al. (2023).
#508 |
New insights on weak winds in massive stars from hydrodynamical simulations
Elisson Saldanha da Gama de Almeida
1
;
Michel Curé
1
;
Catalina Arcos
1
;
María Laura Arias
2
;
Marcelo Borges Fernandes
3
;
Wagner Marcolino
4
;
Lydia Cidale
2
1 - Instituto de Física y Astronomía/Universidad de Valparaíso.
2 - Instituto de Astrofísica de La Plata (CONICET-UNLP).
3 - Observatório Nacional.
4 - Observatório do Valongo/Universidade Federal do Rio de Janeiro.
Resumen:
Although the theoretical bases of line-driven winds were set around half a century ago, it is still uncertain what are the real mass-loss rates among different luminosity classes of O stars. One severe issue is the so-called weak wind phenomenon, where the empirical mass-loss rates ($\dot{M}$) of late O stars (O8-9V and O8-9III) are lower by $10^{2}$ than theoretical predictions from Vink’s mass loss recipe. In this work, we present our ongoing results on weak winds in late O dwarfs and giants using hydrodynamical simulations with the code HYDWIND. These hydrodynamical results are used as input parameters in state-of-the-art non-LTE radiative transfer codes, CMFGEN and FASTWIND, to calculate synthetic spectra and test them against observations in the UV and visible regions. In Fig. 1, we show our preliminary results based on H$\alpha$ spectroscopy for the weak wind star HD 46202 (O9V). The observed H$\alpha$ line profile is well reproduced using both codes with the solved hydrodynamics by HYDWIND. This happens when we consider the last fast wind solution, that is, increasing the value of the line-force parameter $\delta$ (from the CAK-theory) before obtaining a $\delta$-slow wind solution ($\delta >$ 0.25-0.30). In this case, our derived $\dot{M}$ for this star is $\sim$$3\mathrm{E}{-10}$ $M_\odot$ yr\textsuperscript{-1} (weak wind regime). For comparison, this value is about $10^{2}$ lower than the one from Vink’s mass loss recipe. In conclusion, these results indicate that weak winds could be explained from first principles (solving the wind motion equation), deserving additional constraints from spectral regions other than the UV and visible. We also discuss our perspectives of exploring weak winds in the infrared region, especially using the Br$\alpha$ line profile, since we had allocated time to observe late O dwarfs and giants with the GEMINI/GNIRS and ESO/CRIRES instruments, to be performed during the second semester of 2023.
#366 |
Constraining the physics of rotation in stellar interiors
Facundo Moyano
1
1 - University of Geneva, Switzerland.
Resumen:
Thanks to space-borne missions like Kepler and TESS, and new asteroseismic techniques developed in recent years, the rotation rate in stellar interiors was obtained for hundreds of stars in different evolutionary phases. This revealed a strong disagreement between stellar models and observations, pointing to a missing physical process in stellar evolution models with rotation. The treatment of rotation in stellar interiors affects both the transport of angular momentum and chemical elements, and hence can change several outputs of stellar models such as the surface chemical composition, surface rotational velocities, and even affect the predicted rotational periods of neutron stars and spins of black holes. Therefore improving our understanding of angular momentum transport processes in stellar interiors is fundamental to improve stellar models and make better predictions. In this talk I will review the status of the problem with emphasis on recent constraints obtained with asteroseismic techniques and its interplay with spectroscopic data. I will then present the main physical candidates proposed to solve the inconsistency between models and observations, with particular emphasis on magnetic fields present in stellar interiors.
#330 |
Pulsating stars in the inner Galactic VVV globular clusters
Javier Alonso-García
1
1 - Universidad de Antofagasta / MAS.
Resumen:
The globular clusters in the innermost regions of the Milky Way are affected by high, differential extinction. Their physical parameters are therefore not as reliably measured as their counterparts of the outer halo. Extinction effects are highly diminished in near-infrared observations, like the ones provided by the Vista Variables in the Via Lactea (VVV) survey and its extension, the VVV-X. More than 50 known Galactic globular clusters located towards the inner Milky Way lie in the region surveyed by the VVV and the VVV-X. Their multi-epoch observations allow us to search and characterize the pulsating stars contained in these star clusters. The tight near-infrared period-luminosity-metallicity relations of these variable stars allow a better parametrization of the globular clusters to which they belong. In my contribution, I will present our current, ongoing analyses of the pulsating stars in some of these poorly known objects within the framework of the VVV and VVV-X.
12:30 - 14:30
LUNCH
15:20 - 16:00
COFFEE BREAK
16:00 - 17:30
D: High Energy Phenomena and Fundamental Physics
Gamma Rays, Black Holes, and Neutron Stars
Chair: Luis Núñez
#067 |
Simulations of the long-term magnetic field evolution in neutron star cores
Francisco Castillo
1
;
Mikhail Gusakov
2
;
Juan Alejandro Valdivia
3
;
Andreas Reisenegger
1
1 - Universidad Metropolitana de Ciencias de la Educación.
2 - Ioffe Institute.
3 - Universidad de Chile.
Resumen:
The evolution of the magnetic field in neutron stars is strongly related to their internal structure. In the NS core, there is a fluid mixture of neutrons, protons, and electrons (joined by other species at increasing densities) that scatter off each other through strong and electromagnetic interactions, causing effective friction forces, and can also convert into each other by weak interactions (‘‘Urca reactions’’). Likely, the dominant process evolving the magnetic field there is ambipolar diffusion, i.e., the joint motion of the charged particles and the magnetic field relative to the neutrons, driven by the Lorentz force and controlled by frictional forces and pressure gradients. Here, we present simulations of the long-term evolution of the magnetic field in the interior of an isolated, axially symmetric neutron star core, under ambipolar diffusion.
Special attention is given to the characterization of the newly developed numerical approach, different physical processes involved, as well as their corresponding timescales, which happen to be in agreement with our numerical estimates.
#304 |
Formation of binary compact objects in young star clusters with PeTar and SEVN
Gastón Escobar
1
;
Giuliano Iorio
1
;
Sara Rastello
1
;
Michela Mapelli
2
1 - University of Padova.
2 - University of Heidelberg.
Resumen:
The currently-growing LIGO-Virgo data provides an excellent opportunity to investigate the demography of gravitational-wave sources and their production channels. Gravitational-waves detected by LIGO-Virgo are originated in the coalescence of two compact objects, as black holes (BHs) or neutron stars (NSs). Compact-object binaries that merge in less than a Hubble time may arise as the last evolutionary stage of binary stars evolved in isolation. In addition, dynamically active and dense environments, such as star clusters, provide several mechanisms to produce or enhance these merger episodes via dynamical channels. Research in this topic is addressed performing population-synthesis simulations of binary systems and direct N-body star-cluster simulations. In this talk we will show our recently developed tool to compute both dynamics and binary evolution integrated together, which uses the group's population-synthesis code SEVN (Stellar EVolution N-body) within the state-of-the-art N-body code PeTar. SEVN uses a set of precomputed stellar tracks to interpolate the evolution of star properties on the fly. This is a change of paradigm in the field, since most population synthesis codes rely on fitting formulas to stellar evolution tracks run more than 20 years ago. We will show our results on the demography of binary compact objects, as binary BHs (BBHs) and BH-NSs, formed in young star clusters ($10^{4-5}~M_{\odot}$), and confront the results with those which use past stellar-evolution prescriptions.
#405 |
The binary black holes of LIGO and Virgo
Javier Roulet
1
1 - California Institute of Technology.
Resumen:
With approximately a hundred detections to date, the discoveries of compact binary mergers by the LIGO and Virgo gravitational-wave detectors have opened a new observational window to the Universe. These data have been made publicly available, enabling their independent analysis by the community. In this talk I will describe various such analyses carried by our group.
A first layer involves searching for signals. We have developed a detection pipeline implementing original solutions to mitigate systematics in the detectors, with which we were able to confirm previous detections and make new ones.
A second stage requires estimating signal parameters (masses, spins, location...). We have developed algorithms to improve the efficiency and robustness of this process, and implemented them in an open-source code `cogwheel`.
Lastly, considering the parameters of all events as a whole we can describe the statistical properties of the observed population of binary black holes and compare against predictions of candidate formation mechanisms. For example, I will show that the observed proportion of events with spins aligned versus anti-aligned with the orbit disfavors the hypothesis that the spin distribution is isotropic.
#011 |
On the formation of NS-NS and NS-BH binaries from binary-driven hypernov
Laura Marcela Becerra
1
;
Jorge Rueda
2
1 - Universidad Industrial de Santander.
2 - International Center of Relativistic Astrophysics.
Resumen:
The binary-driven hypernova (BdHN) model is a proposed explanation for long gamma-ray bursts (GRBs) associated with type Ic supernovae (SNe) in which a binary system consisting of a carbon-oxygen (CO) star and a neutron star (NS) companion in close orbit undergoes a series of physical episodes. The event is triggered by the core collapse of the CO star, leading to a supernova (SN) explosion that forms a newborn NS (hereafter $\nu$NS) at its center. The SN accretes at super-Eddington rates on the $\nu$NS and the NS companion, leading to a binary system classified as type I when the NS forms a black hole (BH), type II when the NS becomes only a more massive NS, and type III when the orbital separation is too large for the companion NS to play any role in the GRB. With smooth hydrodynamics simulations, in this work, we investigate the binary parameters that determine whether the $\nu$NS or the NS companion reaches the point of gravitational collapse into a BH during the accretion process, as well as the time it takes for collapse to occur since the SN explosion. We also examine whether the system remains gravitationally bound after the SN explosion, leading to an NS-NS binary in BdHN II, an NS-BH binary in BdHN I, or if it disrupts altogether. We determine the maximum orbital period of the initial CO-NS binary that can remain bound after a BdHN event and calculate the characteristic parameters of the resulting NS-NS binaries.Overall, our findings shed light on the physical mechanisms driving BdHN and provide insight into the potential outcomes of such cataclysmic events in binary systems.
#558 |
Flare-induced feedback on the broad line region, the study case of PKS2004-447
Eleonora Sani
1
1 - ESO - Chile.
Resumen:
PKS2004-447 is a rare hybrid between a gamma-ray emitting narrow-line Seyfert 1 and a compact steep-spectrum radio source.
It harbors a relatively small supermassive black hole accreting at typical NLS1s' Eddington ratio and, as our recent observations show, it connects these two classes of objects in the AGN evolution framework. PKS 2004-447 underwent, for the first time, a gamma-ray flare in 2019 mainly caused by the relativistic jet, which altered the broad line region with a flux excess redshifted by 250 km/s observed in the Balmer, Paschen, and He I permitted lines. This new emission feature was no longer visible 1.5 years later, suggesting a causal connection with the flare. The emission lines coming from the same atomic transition series show a similar velocity offset for this "red excess", but the offset changes for different line series. This discovery suggests that the relativistic jet can affect the physics of the BLR in this peculiar AGN, and that flaring activity can lead to the formation of additional and localized broad emission components. Our results highlight the importance of optical spectroscopy for flaring jetted AGN, and that our understanding of the jet-BLR -connection is still very limited.
#147 |
Binary synthesis of merging compact object populations from evolving initial conditions
Lucas M. de Sá
1
;
Antônio Bernardo
1
;
Riis R. A. Bachega
1
;
Livia S. Rocha
1
;
Jorge E. Horvath
1
1 - Institute of Astronomy, Geophysics and Atmospheric Sciences - University of São Paulo.
Resumen:
Over the past few years, the steadily growing catalog of compact object mergers observed by the LVK Collaboration has allowed for a picture of the properties of these events as a population to start to emerge. One invaluable tool in the exploitation of this growing catalog has been rapid binary population synthesis (BPS), which allows for predictions for the rate of observed mergers and their properties, as well as for constraining the initial conditions of stellar/binary formation and evolutionary models by comparing the results with observations. While much has been done in BPS to constrain the evolutionary models, the initial conditions have been comparatively neglected. Chiefly, this ignores the long-expected trend of the initial mass function (IMF) to become top-heavy at high redshift, i.e., to produce more compact object progenitors. One such model for a varying IMF is the integrated-galaxy wide IMF (IGIMF). In this work, we employ the IGIMF and correlated orbital parameter distributions to perform the population synthesis of compact object mergers with the code COMPAS. We are able to generate populations consistent with star formation rate, metallicity and IMF evolution with redshift, such that we are able to study how observed merger rates and other properties vary with redshift. We find an overall tendency of merging binaries to be more massive the older they are and the higher the merger redshift is. We also find support for a peak in the merger rate of binary black holes (BBHs) between redshift ~2 and ~1. We compare this trend to the current LVK constraints on the merger evolution of the BBH merger rate. Our work provides a framework for redshift-dependent population synthesis broadly speaking, and for testing IMF variations in particular.
