# Stars

We present a summary of the posters of this astronomical topic. If you want to see the full poster, click on the document:

Title: Variable O’Connell effect in the binary system OGLE-216305

Garcés, Juan

J. Garcés and R.E. Mennickent. Universidad de Concepción, Departamento de Astronomía.

Abstract: We present a preliminary photometric study of the OGLE-BLG-ECL-216305 eclipsing binary system. In total, we have 6417 observation epochs of OGLE III-IV I-band. We find that the orbital period is decreasing at a rate of $dP/dt = -8\times 10^{-9}$. In addition, the orbital light curve shows changes in its morphology, mainly in the brightness of the first and second quadratures. When one reaches a maximum, the other reaches a minimum and this occurs cyclically. Through a theoretical model of the different light curves we can explain the phenomenon with cold spots on the surface of the secondary star.

poster_miniatura - Juan Garces Letelier.pptx

Click here to see the full poster (Garcés, Juan)

Title: Characterizing the morphology of the debris disk around the low-mass star

GSC 07396-00759

Adam, Christian

C. Adam, J. Olofsson, R. G. van Holstein, A. Bayo, J. Milli, A. Boccaletti, Q. Kral, C. Ginski, Th. Henning, M. Montesinos, N. Pawellek, A. Zurlo, M. Langlois, A. Delboulbé, A. Pavlov, J. Ramos, L. Weber, F. Wildi, F. Rigal, J. -F. Sauvage

Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile

Núcleo Milenio Formación Planetaria - NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile

Escuela de Ciencias, Universidad Viña del Mar, Viña del Mar, Chile

Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden, The Netherlands

European Southern Observatory, Alonso de Córdova 3107, Casilla, 19001, Vitacura, Santiago, Chile

LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne

Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France

Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France

Geneva Observatory, University of Geneva, Chemin des Mailettes 51, 1290 Versoix, Switzerland

Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary

Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

Anton Pannekoek Institute for Astronomy, Science Park 904, 1098 XH Amsterdam, The Netherlands

DOTA, ONERA, Université Paris Saclay, 91123, Palaiseau France

Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Avenida Ejercito 441, Santiago, Chile

Aix Marseille Université, CNRS, LAM - Laboratoire d’Astrophysique de Marseille, UMR 7326, 13388, Marseille, France

CRAL, UMR 5574, CNRS, Université de Lyon, Ecole Normale Supérieure de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07, France

Escuela de Ingeniería Industrial, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile

Abstract: Debris disks have commonly been studied around intermediate-mass stars, as their intense radiation fields are believed to efficiently remove the small dust grains that are constantly replenished by collisions. For low-mass M stars, the irradiation field is generally much weaker, while stellar winds can be strong. Thus, stellar winds are most likely the dominant, yet poorly constrained, mechanism driving the rapid removal of particles. In our poster, we present new polarimetric observations (VLT/SPHERE IRDIS) of the disk around the young M-type star GSC 07396-00759. Using radiative transfer modeling, we find a highly inclined disk (i ≈ 84.3°) with a radius of ≈ 107 au, an anisotropic scattering factor g ≈ 0.6 and small micron-sized dust grains with sizes s > 0.3μm. The results, however, also indicate that using a given scattering theory might not be sufficient to fully explain key aspects, like the shape of the phase function or the dust grain size. However, we find that the average mass-loss rate of GSC 07396-00759 can be up to 500 times stronger than that of the Sun, supporting the idea that stellar winds from low-mass stars can evacuate small dust grains efficiently.

poster_miniatura_adam_christian_stars - Christian Adam.pdf

Click here to see the full poster (Adam, Christian)

Title: Study of the V1001 Cen system using spectroscopic and photometric observations.

Calderon Paul Adrian

P. Calderón and R. E. Mennickent

Abstract: The Double Periodic Variables (DPVs) are binary stars showing orbital periods between one and a few tens of days. They are characterized by an additional long cyclic variability of length tens to hundreds of days. We present the result of the photometric and spectroscopic investigation of the poorly known DPV V1001 Cen (HD 125104). The short orbital periodicity and the cyclic variability were decoupled and they are studied separately. The radial velocity of the binary was determined from the time-resolved spectroscopic data. We present basic physical parameters for V1001 Cen and propose future studies to enlighten this interesting binary.

Stars_Binary systems_P.Calderon_poster_miniatura - Paul Calderon.pptx

Click here to see the full poster (Calderon Paul Adrian)

Title: Comparing self-consistent solutions for electron temperature and gas distributions in Be disks.

Concha Astorga, David Alfonso Enrique

Concha, David, Universidad de Valparaíso ; Arcos,Catalina, Universidad de Valparaíso

Abstract: Be stars are very rapidly rotating massive B-type stars expelling material from their photosphere under a process that is still not fully understood. The material is placed in a thin equatorial disk in keplerian rotation and the disk growing is governed by viscosity. In this work, we compare the results from two self-consistent Non-LTE radiative transfer codes, HDUST (Carciofi & Bjorkman 2006, 2008) and BEDISK & BERAY (Sigut & Jones 2007,Sigut 2011), that calculate the electron temperature and gas density distribution in the disk, assuming similar distributions but with different physical processes.

resumenposterfinal - DAVID ALFONSO ENRIQUE CONCHA ASTORGA.pdf

Click here to see the full poster (Concha Astorga,David Alfonso Enrique)

Title: Determination of disk parameters of Be star HD 45725

Figueroa Tapia, Felipe Ignacio

F. Figueroa-Tapia, C. Arcos, M. Curé: Instituto de Física y Astronomía, Universidad de Valparaíso, Chile

I. Araya: Centro de Investigación DAiTA Lab, Universidad Mayor, Chile

Abstract: Classical Be stars are B-type main sequence stars holding a geometrically thin equatorial disk rotating in a quasi-Keplerian way. The gas disk is responsible for the observed emission lines and IR-excess in the SED. The properties of the disk, e.g., density structure, size and inclination, can be studied by modeling the H$\alpha$ line-emission. In this work, we studied the disk of the Be star HD 45725 ($\beta$ Mon A) using the 3-dimensional Monte Carlo NLTE radiative transfer code HDUST, in order to obtain the disk parameters. We determine the best-fitting model through the comparison between the model and the observed H$\alpha$ line-emission. For this work, we fixed the stellar parameters, T_{pole} = 20880 K, R_{pole} = 4.32 R_{\sun}, and stellar mass M_{\star} = 6.62 M_{\sun}. Using a parametric ad-hoc model for the disk density, we found a disk size of 120 R_{\star}, a volumetric density rho = 1*0^{-11} g*cm^{-3}, and a power-law density exponent of n = 1.5, which are close to the study made by from Arcos et al., 2017 using the code BEDISK.

FigueroaTapia-summary - FELIPE IGNACIO FIGUEROA.pdf

Click here to see the full poster (Figueroa Tapia, Felipe Ignacio)

Title: An interactive python code to obtain measurements over emission an absorption spectral lines.

Herrera Figueroa, Felipe Alberto Isaías

Felipe Herrera Figueroa, Universidad de Valparaíso; Yanina López Bonilla, Universidad de Valparaíso; Catalina Arcos, Universidad de Valparaíso.

Abstract: Be stars are fast rotating massive stars capable of forming and dissipating an equatorial thin and optically thick circumstellar gas disk. The gas disk is rotating in a Keplerian motion and is responsible for showing emission lines in the spectra of these stars. Information about the disk and the star can be determined through the study of these variations over time. In order to analyze variations in the spectra of BeSS (Neiner et al. 2011) and BeSOS (Arcos et al. 2018) databases, we developed a routine in python to automatically normalize the spectra to the continuum and to correct for the barycentric velocity. We also developed an interactive python code, called BeROBOT, to make quick and easy measurements on absorption and emission lines.

RESUMEN_HerreraLopez2021.pptx - FELIPE ALBERTO ISAÍAS HERRERA.pdf

Click here to see the full poster (Herrera Figueroa, Felipe Alberto Isaías)

Title: Self-consistent synthetic Hα lines in the study of the Wind Momentum-Luminosity relationship for massive stars.

Machuca, Natalia

Natalia Machuca A.(Universidad de Valparaíso), Michel Curé O.(Universidad de Valparaíso), Ignacio Araya G.(Universidad Mayor), Pedro Escarate M.(Pontificia Universidad Católica de Valparaíso), Sara Cuellar O.(Pontificia Universidad Católica de Valparaíso)

Abstract: Radiation driven winds theories predict a relation between the momentum of the wind and the stellar luminosity (Dmom ~ Lstar). However, this relation seems to vary as a function of the spectral type. The momentum of the wind is defined as: Dmom = v∞Ṁ√Rstar where v∞ is the wind terminal velocity, Ṁ is the mass-loss rate and Rstar is the stellar radius. In this work, we aim to study for the first time the Wind Momentum-Luminosity relationship (WLR) using the hydrodynamics self-consistently in the NLTE radiative transport calculations. We developed a code that uses a χ2 test to determine the model that most closely resembles the Hα observed line of 25 OB-type stars in the ISOSCELES grid. This grid is based on the hydrodynamic code HYDWIND and the radiative transfer code FASTWIND. In this first step, we used a Dmom estimated exclusively with Hα line at 6563 Å. The next steps are to use more spectral lines and find the WLR for different metallicities.

Machuca_Stars_Summary - NATALIA PAMELA MACHUCA ARROYO.pdf

Click here to see the full poster (Machuca, Natalia)

Title: Disk-star interactions: misalignment vs coplanarity

Medina, Bruno

Bruno Medina, Amelia Bayo, Larissa Antunes, Gabriel Corvalan, Christian Adam

Transition disks are a class of protoplanetary disks first thought to host large dust cavities as interpreted from the lack of near-infrared excess in their SEDs, and later confirmed via high-resolution continuum imaging. These cavities in the disk might be caused by photoevaporation processes, planet formation, or other mechanisms. In the single-isolated star picture of star formation, the disk plane should be perpendicular to the axis of rotation of the star and hence the resulting planetary orbits should follow similar configurations. However, different perturbations can break the alignment. In Francis & Van der Marel (2020), the authors studied a sample of 34 resolved transition disk systems, some with multiple rings, where they measured their mutual orientations.

By gathering and analyzing archival lightcurves and high-resolution spectra of the individual stars or binaries in the sample, we aim at determining the inclinations of the central star (or multiple) of each system. Our final goal is to compare those orientations with the ones of the different components of the disks. We present some early results for the vsini and period estimates for part of the sample.

poster_miniatura_BMedina - Bruno Medina.pptx

Click here to see the full poster (Medina, Bruno)

Title: The limits of the Solar Events amplitudes: the occurrence of strong flares from the point of view of the underlying dynamo mechanism

Popova, Elena

E. Popova (Centro de Investigación en Astronomía, Universidad Bernardo O’Higgins, Chile),

R. Sagdeev (University of Maryland, USA)

Abstract: Powerful flares with energy releases much above of 10 in 32 erg are very rare events compared to habitual display of Solar activity, routine monitoring of which is already within the reach by the existing Space Weather network (even with a certain degree of predictability). However, much less is known about the scenarios of rare events (like for example the well-known Carrington-1859) or even on hypothetical Superflares, potentially extending the energy limits by orders of magnitude higher. We discuss various options for underlying physical mechanisms and their potential realization in the framework of Solar Physics (comparative analysis with other stars models is useful).

poster_miniaturaPopova - Elena Popova.pdf

Click here to see the full poster (Popova, Elena )

Title: A High Resolution View of Protoplanetary Disks: analysis of the AS 209 disk using the deconvolution tool Frankenstein as brightness profile reconstructor

Mellado Tenorio, María Jesús

Laura Pérez, Anibal Sierra, María Jesús Mellado y Adolfo Carvalho.

Abstract: We studied the dust continuum emission of the protoplanetary disk around the T Tauri star AS 209, one of the most unusual sources of DSHARP (Disk Substructures at High Angular Resolution Project), due to the notable difference between the internal and external substructure of the disk, and the symmetrical nature of the rings. With observations at wavelengths of 1.25mm and 3mm, we used the Frankenstein open software (Jennings et al., 2020) to infer radial profiles of emission at these wavelengths and properly constrain physical properties of the solids in this disk (maximum dust grain size, a_max, and dust surface density, sigma). We studied the effect of Frank hyperparameters and disk geometry on the radial profile modeled by Frank by obtaining a large number of fittings and deriving error bars, to account for the reliability of this method. Then, we analyzed the spectral index of the emission and obtain the radial profiles for a_max and sigma that best explains the radial profile constrained with Frank, using a likelihood probability model. Finally, we discern if the rings observed in AS209 are consistent with dust trapping models, important signature of planetary formation.

Poster_SOCHIAS_min_MJMT - María Jesús Mellado Tenorio.pptx

Click here to see the full poster (Mellado Tenorio, María Jesús )