lunes 27 de noviembre
SALÓN ROJO (150)
10:35 - 11:15
COFFEE BREAK
11:15 - 12:45
G: Stars and Stellar Physics
Star formation and young stars I
Chair: Mauricio Tapia
#062 |
Accurate young star mass determinations and their implication for theoretical evolutionary models
Laurent Loinard
1
1 - Instituto de Radioastronomia y Astrofisica, Universidad Nacional Autónoma de Mexico.
Resumen:
Using interferometric radio observations (particularly long baseline interferometry - VLBI), it is possible to accurately constrain the mass of young stars in binary and multiple stellar systems. This provides strong constraints for stellar evolution models since the location of the stars in the HR diagram can then be compared directly with the tracks for the appropriate masses. In this talk, I will present several young star mass measurements based on VLBI observations and discuss the implications for evolutionary models. I will particularly focus on intermediate mass stars (M > 2 Sun) where constraints are rare. I will also briefly discuss mass constrains for long period multiple systems based on conventional radio interferometry, which are highly complementary of VLBI measurements by providing access to a different region of the parameter space.
#138 |
Survival of fossil fields during the pre-main sequence evolution of intermediate-mass stars
Dominik Schleicher
1
;
Juan Pablo Hidalgo
2
;
Daniele Galli
3
1 - Universidad de Concepción.
2 - Universidad de Concepcion.
3 - Arcetri Astrophysical Observatori.
Resumen:
Chemically peculiar Ap and Bp stars host strong large-scale magnetic fields in the range of $200$~G up to $30$~kG, which are often considered to be the origin of fossil magnetic fields. We assess the evolution of such fossil fields during the star formation process and the pre-main sequence evolution of intermediate stars, considering fully convective models, models including a transition to a radiative protostar and models with a radiative core. We also examine the implications of the interaction between the fossil field and the core dynamo. We employ analytic and semi-analytic calculations combined with current observational constraints. For fully convective models, we show that magnetic field decay via convection can be expected to be very efficient for realistic parameters of turbulent resistivities. Based on the observed magnetic field strength - density relation, as well as the expected amount of flux loss due to ambipolar diffusion, it appears unlikely that convection could be suppressed via strong enough magnetic fields. On the other hand, a transition from a convective to a radiative core could very naturally explain the survival of a significant amount of flux, along with the presence of a critical mass. We show that in some cases, the interaction of a fossil field with a core dynamo may further lead to changes in the surface magnetic field structure. In the future, it will be important to understand in more detail how the accretion rate evolves as a function of time during the formation of intermediate-mass protostars, including its impact on the protostellar structure.
#575 |
Inferring the sub-stellar and stellar Initial Mass Function of Nearby Young Moving Groups
Rafael Bertolotto
1
;
Juan José Downes
1
;
Genaro Suárez
2
1 - Universidad de la República, Uruguay.
2 - American Museum of Natural History.
Resumen:
The solar neighborhood is populated with Nearby ($\textless 200$ pc) Young
($\textless 100$ Myr) stellar co-Moving Groups (NYMG; e.g. Torres et al., 2006;
Gagné et al., 2018; Kerr et al., 2021). Although their origin is a matter of
debate, their ages could be one order of magnitude smaller than their
dynamical times around the Galaxy which supports the idea of these
groups as remnants of stellar populations dispersing in the galactic disc.\\
The NYMGs are ideal candidates for the observational study of the Initial
Mass Function (IMF) because of their proximity and low extinction, and
because their youth guarantees that only their very massive stars
have evolved out of the main sequence. Then, their mass distribution
equals the IMF in most of the stellar and sub-stellar mass ranges.
However, only a few determinations of the IMF of these groups have been
done so far (e.g. Gagné et al., 2017) due to the observational challenge of
their wide spatial distribution. \\
In this talk, I will present a robust determination of the IMF of 5 NYMGs
in the mass range $0.04 \textless M/M_\odot \textless 5$.
The selection of members was made with a clustering code
based on the DBSCAN algorithm (Ester et al., 1996) for the detection of
NYMGs using data from Gaia DR3 (Gaia Collaboration et al., 2022) astrometry and photometry.
I will present the validation process of this tool which allowed us to quantify the fraction
of completeness and contamination from old stars in each of the detected NYMGs.
Finally, I will discuss how the resulting IMF compares with previous determinations
for the NYMGs and the solar neighborhood, and its interpretation in the context of the dispersion of the NYMGs.
#382 |
Unpuzzling the star formation scenario of the Canis Major stellar nursery
João Victor Corrêa Rodrigues
1
;
Jane Gregorio-Hetem
1
;
Thaís Santos-Silva
1
1 - Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo (IAG/USP).
Resumen:
The Canis Major Association OB1/R1 (CMa) is an interesting region to study the effects of supernovae (SN) in star formation. Evidence indicates that at least three such events affected the environment and evolution processes of young stellar objects in the CMa. This ongoing work aims to unpuzzle the star formation history of CMa and improve the survey of young low-mass stars in the region, especially toward the star FZ CMa. Probably this stellar population is mixed, lying between two clusters in different age ranges: one group associated with the star Z CMa ($\leq$5 Myr) and the other associated with the star GU CMa ($\geq$10 Myr). The survey is still incomplete, although it is crucial to investigate the possibility of triggering and/or inhibiting star formation by SN or even the early destruction of circumstellar disks. To characterize this population, we analyzed optical spectra (R $\sim$ 4400), acquired with the Gemini South telescope in the multi-object mode, searching for typical features of this evolutionary phase, such as Li absorption (6708 \AA) and H$\alpha$ emission. We have over a hundred candidate stars available, with $\sim$ 20\% of them being counterparts of X-ray sources. We present the spectral classification and estimates of physical parameters of these stars derived from spectral analysis. By using the equivalent width of the H$\alpha$ line, we have distinguished in our sample the Classical T Tauri (CTT), which are disk-bearing stars, from the Weak-line T Tauri (WTT) that do not have an active accretion disk. Previous results based on infrared sources indicate a low fraction of disk-bearing stars compared to other star-forming regions at the same age. In addition, we explored multi-band photometric data by constructing different color-color diagrams. These data have been compared to evolutionary models to identify color excesses that are related to the accretion process.
#477 |
Star formation history of Canis Major OB1 III: stellar group contents revealed by Gaia
Thais Santos-Silva
1
;
Hélio Perottoni
2
;
Felipe Almeida-Fernandes
1
;
Jane Gregorio-Hetem
1
;
Vera Jatenco-Pereira
1
;
Claudia Mendes de Oliveira
1
1 - Universidade de São Paulo.
2 - Nicolaus Copernicus Astronomical Center.
Resumen:
Our previous works, based on X-ray and infrared data, we found that Canis Major OB1 (CMa OB1) is a Galactic stellar association having a very intriguing star-formation scenario, which probably had at least three star formation episodes.
In order to better understand the association stellar population and its star formation history, I recently conducted a study using a clustering code that employs five-dimensional data from the Gaia DR2 catalog to identify physical groups in the vicinity of CMa OB1 and to obtain their astrometric parameters. Additionally, we estimated the age of these groups using two different isochrone-fitting methods.
With this, we confirm the existence of 15 star groups with distances between 570 and 1650 pc, of which 10 are previously known clusters and five are new open cluster candidates. We identified that four younger groups (< 20 Myr), CMa05, CMa06, CMa07 and CMa08, are CMa OB1 contents. While CMa06 coincides with the star formation region very well studied by our group, CMa R1, CMa08, one of the new candidate clusters, may be the progenitor cluster of runaway stars that indicate the existence of different star formation episodes in the association.
Since the youngest group, CMa06, is still immersed in the remaining material of the molecular cloud associated with the Sh 2-262 nebula, it continues to form stars, on the other hand CMa05, CMa07, and CMa08 seem to be in more evolved stages of evolution, with no recent star-forming activity.
The results of this work fit well in a monolithic scenario of star formation, with a common formation mechanism, and having suffered multiple episodes of star formation. This suggests that the hierarchical model alone, which explains the populations of other parts of the same association, is not sufficient to explain its whole formation history.
#364 |
Cores and filaments in MHD simulations of massive protoclusters
María Valentina García Alvarado
1
;
Jonathan Tan
2
;
Chia-Jung Hsu
3
1 - Universidad de los Andes.
2 - Chalmers University of Technology/University of Virginia.
3 - Chalmers University of Technology.
Resumen:
The main processes that trigger the collapse and fragmentation of giant molecular clouds (GMCs) in star-forming regions are poorly understood. Collisions between giant molecular clouds (GMCs) have been proposed as a mechanism to compress gas to trigger the birth of massive star clusters and associations and thus be potentially relevant to the formation of most stars in galaxies. The spatial distributions of dense gas cores within protoclusters generated by such collisions may encode important diagnostic information about the process and the environmental properties of the parent clouds. To investigate this, we carried out 3D numerical simulations of magnetized turbulent GMCs. Non-colliding cases were also considered. The projected 2D mass surface density structures of the clouds, including cases after applying simulated ALMA observations, were analyzed. In particular, dense cores were identified with the dendrogram method, and the Minimum Spanning Tree (MST) of the cores was computed. We compared the results from clouds with different initial magnetic (B-) field strengths, ranging from 10 to 50 micro G. The number and mass fraction of dense cores are suppressed in the more strongly magnetized and non-colliding cases. We consider various MST statistics, including the Q parameter, how these evolve during the simulations, and their potential ability to diagnose magnetic and collisional conditions. We also examine mass segregation, including detailed properties of the most massive cores, which relates to the question of whether or not massive stars tend to form in more central locations in protoclusters. Finally, we study the properties of the filaments within and around the protoclusters, including their widths, mass per unit lengths, energy balance, and magnetic field strengths and orientations.
12:45 - 14:30
LUNCH
15:50 - 16:30
COFFEE BREAK
16:30 - 18:15
G: Stars and Stellar Physics
Star formation and young stars II
Chair: Jesús Hernández
#034 |
Towards a Better Determination of Stellar Parameters in the Pre-Main Sequence Phase in the era of Large Spectroscopic Surveys: SDSS APOGEE-2 and Milky Way Mapper
Carlos Román-Zúñiga
1
;
Jesús Hernández
1
;
Marina Kounkel
2
;
Lucia Adame
1
;
Ricardo Lopez-Valdivia
1
;
Corina Zepeda
1
;
Sergio González
1
;
Itzarel Hernández
1
;
Sergio Sánchez
1
;
Karla Peña
3
1 - Instituto de Astronomía, Universidad Nacional Autónoma de México.
2 - University of North Florida.
3 - Universidad de Antofagasta.
Resumen:
We are in the monumental era of large optical and infrared spectroscopic surveys (e.g. Gaia, SDSS, LAMOST, Gaia-ESO, GALAH, WHT-WEAVE). Fiber spectroscopy allows now to obtain high quality spectra for hundreds of stars at a time, and the use of infrared detectors opens the field for the study of young stars in star forming regions within our reach. The pre-main sequence phase of stellar evolution is not as well characterized as the main-sequence or the red-giant branch. Young star spectra are affected by dust extinction from the parental cloud gas, by the presence of circumstellar material and diverse effects associated with accretion and variability.
Using spectra from the SDSS APOGEE-2 and Milky Way Mapper surveys, we are building up one of the largest systematic census of pre-main sequence stars (see e.g. Román-Zúñiga et al. 2023, Kounkel et al. 2023). One of our main goals is to increase the precision in the parameter determination for young stars. For this goal we participate in the development of tools (e.g. neural networks: APOGEE Net - Sprague et al 2022, unsupervised model fitting: TONALLI- Adame et al. 2023) aiming to reduce model dependent discrepancies and degeneracies in the $\mathrm{T_{eff}}$, $\log{g}$, [Fe/H] space. We are also applying methodologies to understand and reduce the effects of extinction and disks in spectral classification (Zepeda et al i.p.) and to determine precise metal abundances with BACCHUS (Lopez-Valdivia et al i.p.)
We discuss these methodologies, show our current efforts and results in the construction of better young star catalogs, and we will share our plans to use them along with kinematic data (e.g. combining APOGEE radial velocities with proper motions from Gaia), to understand the evolution of nearby young star clusters. We will also discuss strategies and details to be considered (e.g. model dependencies) in current big data treatments.
#174 |
Identifying T Tauri stars in the Milky Way using machine learning and LAMOST spectra
Cesar Dagoberto Millan Valderrama
1
;
Jesús Hernández
2
;
Beatriz Sabogal
1
;
Alejandro García
1
1 - Universidad de los Andes.
2 - Universidad Nacional Autónoma de México, Instituto de Astronomía.
Resumen:
T Tauri stars (TTS) are young, low-mass stars ($< 2M_{\odot}$) in pre-main sequence phase, considered precursors to planetary systems. Their youth is robustly indicated by the presence of LiI absorption line in their optical spectra. TTS can be divided into two categories: classical TTS (CTTS) displaying $H_{\alpha}$ line emission due to a circumstellar disk, and weak-line TTS (WTTS) where the $H_{\alpha}$ line is relatively weak and attributed to chromospheric activity.
The Chinese Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) provides a large amount of spectra in the wavelength range of 3700 to 9000 \AA, with approximately 10 million low-resolution spectra ($R\approx1800$) available in DR8.
In this study we present the results of detecting and classifying TTS in the Orion Star Forming Complex using machine learning (ML) techniques and LAMOST spectra. We used over 5000 kinematic candidates selected by using proper motion and parallax data from the GAIA DR3 database. Our main training sample consisted of 342 TTS from the Ori OB1a substellar association, as reported by Hernandez et al. (2023). To ensure the robustness of the classifiers, we also included a set of non-TTS (field stars) in the training sample. Automatic equivalent width measurements were performed on 18 spectral features, including $H_{\alpha}$ and LiI lines, as well as TiO and VO bands.
We implemented two ML classifiers: a binary model to classify whether a target is a TTS or not, and a multiclass model to assign a spectral type to the detected TTS. We employed the Monte Carlo method for error propagation to determine probabilities during the classification process. To assess the classifiers' performance, we used the F1 score, which yielded a value of 0.91. In a preliminary classification of 766 stars, we successfully identified 249 TTS. These TTS candidates were visually inspected, confirming an accuracy of 0.94.
#060 |
A TESS SURVEY OF FLARE ACTIVITY AND STELLAR ROTATION OF YOUNG STELLAR OBJECTS IN THE TAURUS REGION
Maria Gracia Batista
1
;
Giovanni Pinzón
1
;
Jesús Hernández
2
1 - Universidad Nacional de Colombia.
2 - Instituto de Astronomía Universidad Nacional Autónoma de México.
Resumen:
Flares and superflares are eruptive events related to magnetic reconnection in the star’s magnetosphere where, a high burst of energy and electromagnetic radiation is released. Flares can affect the formation and early evolution of planets close to their host star, especially during their formation around Young Stellar Objects (YSOs). In this work, we present the most numerous survey of flare detection on YSOs up to date, with the majority of them classified as T Tauri Stars (TTSs). Our sample belongs to the Taurus region at $\sim$140 parsecs with an age range of $\sim$1-15 Myr. We studied flare characteristics such as duration, peak amplitude, bolometric luminosity and energy released.
We examined 643 light curves using TESS observations with a 2 minutes cadence in sectors 43 and 44. As a result, we detected 1704 flares over a sample of 346 stars, representing almost 67\% of the known low-mass members of Taurus. Also, we estimated the mean bolometric flare energy and amplitude for stars with multiple flares. Our measurements of flares in the optical range were related with the luminosity in Rx and UV bands, finding correlations between them. From LAMOST and FAST spectra, we measured H$\alpha$ equivalent widths of the sampled stars and later classified them by the presence of accretion disk. Additionally, we calculated the R$_{HK}$ factor and compared the chromospheric activity with the flare features alongside the age, mass, and type of TTSs.
#192 |
Damping of surface Alfvén waves in accretion disks
Natália Fernanda de Souza Andrade
1
;
Vera Jatenco Silva Pereira
1
1 - Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG-USP).
Resumen:
The transport of angular momentum and matter is essential for the evolution of astrophysical disks, particularly protostellar disks. Recently, several works investigated the role of non-ideal MHD effects in those objects and their impact on angular momentum transport. On the other
hand, the damping of Alfvén waves was already proposed as a viable mechanism for disk heating, increasing its ionization fraction and, consequently, the region of the disk subject to Magneto-Rotational Instability. In this work, we analyze the role of the resonant damping of surface Alfvén waves in protostellar disks with a local approximation, which allows us to describe the radial shear associated with the differential rotation as a linear velocity. We consider the Alfvén waves propagation and dissipation/amplification in the presence of both viscosity and dissipative non-ideal MHD effects. In general, we find that the effectiveness of these processes is independent of the dissipation coefficients, as already obtained in previous works, and, depending on the propagation properties of the wave, can lead to damping or the development of instability. We also quickly compared the damping rate obtained with our mechanism and the turbulent damping, already studied in the literature as a source for non-thermal disk heating. We found that, under reasonable conditions, the resonant damping is more effective than the turbulent damping in heating the disk, indicating that the proposed mechanism can decrease the dead zone extent. We are now performing a more robust numerical analysis to fully describe the effect of the resonant damping of surface Alfvén waves over the ionization fraction and transport of angular momentum in those disks.
#562 |
H$\alpha$ emitters in the Magellanic Clouds: searching for Be stars using high-resolution multi-band photometry
Felipe Navarete
1
;
Pedro Ticiani dos Santos
2
;
André Figueiredo
2
;
Alex Carciofi
2
1 - NOIRLab/SOAR Telescope.
2 - University of São Paulo.
Resumen:
Classical Be stars are a subset of main-sequence B-type stars associated with viscous Keplerian decretion disks responsible for their emission lines. In addition, fast rotation is a fundamental ingredient for the existence of Be stars, as they are the fastest among non-degenerate stars. To date, three scenarios try to explain the spin-up mechanism and the existence of Be stars: Be stars are born as fast rotators; the spin-up would occur during the evolution of a binary system; or they would start as slow rotators, increasing their rotation throughout their evolution. Even though all scenarios may play a role in the origin of Be stars, discriminating the relative prevalence of each scenario is a key step towards a better understanding of these objects.
In this talk, I will present the analysis of BVRI+Halpha photometry of NGC\,330, a young stellar cluster in the Small Magellanic Cloud (SMC), observed at the 4-m SOAR telescope (Chile) using the SOAR Adaptive Optics Module Imager (SAMI). Thanks to the depth and the high angular resolution (0.30''-0.40'') of the images, the entire massive stellar population up to early A-type stars are disentangled and resolved at SMC distances. Alongside well-consolidated models of B+Be stars (BeATLAS), SAMI observations provide an excellent dataset to search, identify and classify Be stars. With supervised machine learning classification models, a Be/(Be+B) fraction of approximately 50\% was found for stars up to V=18.5 mag, and 20\% for the whole B spectral type range, a considerably larger fraction of Be candidates than previously reported from high-resolution spectroscopic works in the literature ($\approx$30\%). Combined with the analysis of further young open clusters in the Magellanic Clouds, this survey will provide crucial evidence for understanding the Be phenomenon as a function of metallicity and age, putting critical observational constraints on the origin of these massive stellar objects.
#150 |
Analysis of the parameters in the evolution of viscous accretion disks in Be stars for the L spectral band.
Fredy Orjuela
1
;
Beatriz Sabogal
1
;
Alejandro Garcia
1
;
Leandro Rimulo
1
1 - Universidad de los Andes.
Resumen:
In this study, we analyzed a sample of 24 Be stars located in the northern galactic region. Utilizing the IRAF software, we measured crucial emission line fluxes, including Br-Alpha, Pf-Gamma, and Hu 14 in the L band of the spectrum. These measurements enabled us to construct the observational Lenorzer diagram, providing valuable insights into the star group.
To gain further understanding, we employed the HDUST code to generate a grid of BeAtlas stellar models. By investigating correlations among five parameters in these disk models, we revealed a positive association between n-Sigma (parameter potential law-surface density), n-M (parameter potential law-Mass of Star), and Sigma-M parameters. This observation suggests that disks with higher or lower Sigma density are linked to stronger or weaker recombination processes, respectively. Consequently, we could classify disks into optically thick or thin regions based on this information.
Interestingly, the parameter associated with disk inclination does not appear to be decisive in model selection. This finding led to a restriction of parameters in the models present in Be star disks.
In conclusion, our oral presentation offers a comprehensive approach to understanding and characterizing circumstellar disks in Be stars, providing relevant information for future research on these dynamic astronomical systems.
#200 |
Chemical complexity in simulations of circumstellar discs formation
Sebastián Aguilar
1
;
Stefano Bovino
1
;
Alessandro Lupi
2
1 - Universidad de Concepción.
2 - Università degli Studi di Milano-Bicocca.
Resumen:
In the search for a more efficient modeling of complex chemistry in numerical simulations new studies have adopted a new method known as post-processing routines. A commonly used approach to simulate chemistry, particularly useful when considering demanding simulations where on-the-fly (OTF) chemistry models mean more computational resources which cannot be approached. This method enables the simulation of chemistry over the raw simulation’s dynamic history, alleviating the use of computational resources compared to OTF chemistry while accurately capturing the evolution of chemical species.
In this study we aim to validate the efficiency of post-processing routines presented in Bovino et al. 2019 (ApJ, 887, 224). By employing the chemistry package KROME to analyze and recover the abundances of different chemical species over the simulation data obtained from Bate 2019 (MNRAS, 484, 2341), specifically, investigating the solar metallicity scenario.
The primary objective of this project is to comprehensively study the evolution of complex chemistry in circumstellar and protoplanetary discs. By meticulously tracing the evolution of the simulations' discs and analyzing the chemistry on different samples, we can accurately replicate the dynamical and chemical evolution before and after the formation of stars in the simulation. Through this research, we anticipate gaining deeper insights into complex chemical processes that shape the early stages of protoplanetary systems.
#066 |
Unveiling the structural content of NGC 6357 via kinematics and NIR variability
Camila Ordenes-Huanca
1
;
Manuela Zoccali
1
;
Amelia Bayo
2
;
Jorge Cuadra
3
;
Rodrigo Contreras Ramos
1
1 - PUC - MAS.
2 - ESO Garching.
3 - UAI - NPF.
Resumen:
NGC 6357, a star-forming region located at a distance of approximately $1.7$ kpc from the Sun, is composed of giant molecular clouds as well as three prominent star clusters. It also hosts three HII regions, very massive stars and thousands of YSOs in different evolutionary stages. We present VVVX PMs for $1681$ young stars in this region and observe that they cluster around two mean PM values, giving rise to two kinematically different populations of stars. One of them is spatially related to dusty regions and its components have projected movements along the filaments of the area. These suggests that it is a younger population and could be related to a triggered star formation process developed in the molecular material of the region and powered by the expansion of the ionized gas. In addition, due to accretion episodes and because of the presence of cool spots on their surface, YSOs are known to be highly variable in terms of brightness. Using VVVX data, with a baseline of approximately eight years, we studied their flux changes: a unique follow-up of these stars in this region. Using the $K_s$-band, we can overcome its extreme levels of extinction and compile, for the first time, a catalogue of $775$ light curves associated to young stars. Each of them has been classified according to the $Q$ and $M$ values, related to the physical process that dominates the variability. We linked these categories to the different kinematical populations and observe that hints of an age difference can also be observed through the different classes.
