(Last update: 3 September 13 2023)
My name is Elisson Saldanha da Gama de Almeida (E. S. G. de Almeida) and I was born in Rio de Janeiro (Brazil) on February 18, 1991. I am an astronomer working on Stellar Astrophysics, specialized in spectroscopy, interferometry, and radiative transfer modeling of massive hot stars. Besides my professional experience in Stellar Astrophysics, I have been working for private and public institutions (freelance projects) on data analysis in Diversity, Inclusion and Equity, especially in the development of computer scripts (mainly using R language).
Currently, I am a postdoctoral fellow (Fondecyt, "Fondo Nacional de Desarrollo Científico y Tecnológico") in the Massive Star Group at Instituto de Física y Astronomía, Universidad de Valparaíso (IFA/UV, Chile) under the supervision of Dr. Michel Curé. My research project concerns the hydrodynamics of winds of massive hot stars in the context of the so-called weak wind phenomenon (or "the weak wind problem"). I have been co-supervising the PhD thesis of Gonzalo Aravena Rojas (advisor: Dr. Michel Curé) at IFA/UV. To date, I work as ad hoc reviewer for The Astrophysical Journal (ApJ) and Astronomy & Astrophysics (A&A).
Since the end of my PhD, I have collaborated with the called I2C team (Intensity Interferometry at Calern) using the code CMFGEN to interpret intensity interferometric observations of hot stars. The I2C team is composed by a multidisciplinary group of researchers, comprising both astrophysicists and cold-atom physicists from Observatoire de la Côte d’Azur/Laboratoire Lagrange and Institute de Physique de Nice (Université Côte d’Azur, France), such as Dr. Robin Kaiser, Dr. Mathilde Hugbart, Dr. William Guerin, Dr. Jean-Pierre Rivet, Dr. Armando Domiciano de Souza, and Dr. Farrokh Vakili. Recently, we published an article on new intensity interferometric measurements of the LBV star P Cygni together with observations of B supergiant Rigel: E. S. G. de Almeida, M. Hugbart, A. Domiciano de Souza, J-P. Rivet, F. Vakili, A. Siciak, G. Labeyrie, O. Garde, N. Matthews, O. Lai, D. Vernet, R. Kaiser, and W. Guerin. Combined spectroscopy and intensity interferometry to determine the distances of the blue supergiants P Cygni and Rigel. MNRAS, 515:1-12, Sept. 2022 .
I am also working together with members of the Chinese Academy of Science South America Center for Astronomy (CASSACA, Chile/China), such as Dr. Massinissa Hadjara, on the topic of hot stars: for instance on studyingthe Be stars KIC 9715425 and η Centauri from the modeling of spectroscopic and spectro-interferometric observations using a large grid of radiative transfer models calculated with the code HDUST. As result of this collaboration, we published an article on the application of the photocenter displacement to study fast rotator stars: M. Hadjara; R. G. Petrov; S. Jankov; P. Cruzalèbes. A. Boskri; A. Spang; S. Lagarde; J. He; X. Chen; C. Nitschelm; E. S. G. de Almeida; G. Pereira; E. A. Michael; Q. Gao; W. Wang; I. Reyes; C. Arcos; I. Araya; M. Curé. Application limit of the photocentre displacement to fundamental stellar parameters of fast rotators - illustration on the edge-on fast rotator Regulus. MNRAS, 511:4724-4740, April 2022.
In the following, I provide a summary on my academic career in the study of massive hot stars. I have been working in the field of massive hot stars since my undergraduate course in Astronomy at Observatório do Valongo/Universidade Federal do Rio de Janeiro (Rio de Janeiro, Brazil). I defended my monograph (undergraduate) and Master thesis on this topic, both of them under the supervision of Dr. Wagner Marcolino at Observatório do Valongo, Universidade Federal do Rio de Janeiro (Brazil). During my undergraduate, my research work was funded from 2012 to 2015 by CNPq ("Conselho Nacional de Desenvolvimento Científico e Tecnológico") and by CAPES ("Conselho Nacional de Desenvolvimento Científico e Tecnológico") from 2015 to 2016 during my MSc degree.
During my PhD in Astronomy at Laboratoire Lagrange/Observatoire de la Côte d’Azur (France), I also started to work with high angular resolution observations of massive hot stars, in particular with interferometric techniques. For interpreting both spectroscopic and interferometric data, I have worked with state-of-the-art radiative transfer codes, such as CMFGEN and HDUST, allowing to constrain the physical conditions of the environments of massive hot stars, such as the density and velocity profiles.
I obtained my PhD degree in Astronomy on November 2020 at Laboratoire Lagrange/Observatoire de la Côte d’Azur (Nice, France) under the supervision of Dr. Armando Domiciano de Souza and Dr. Anthony Meilland in November 2020. My doctoral research was funded by Observatoire de la Côte d’Azur and Ville de Nice during three years between 2016 and 2019 ("Bourse Doctorale Olivier Chesneau.
The main objective of my doctoral thesis was to investigate the mass loss on different types of massive stars. I studied both massive stars for which the stellar rotation is understood to play a important role on the ejection of material from their surfaces, as the Be stars which show rotating disks, and also massive stars that lose larger amount of material through radiative line-driven winds due to their high luminosity and effective temperature, as the O-type and LBV stars.
My PhD thesis is composed of two principal publications (first-authored articles). Firstly, I investigated the so-called weak wind phenomenon in O-type stars: E. S. G. de Almeida, W. L. F. Marcolino, J. C. Bouret, and C. B. Pereira. Probing the weak wind phenomenon in Galactic O-type giants. A&A, 628:A36, Aug. 2019. For this purpose, I analysed high-resolution ultraviolet and visible spectroscopic data of late O giants (O8-9III stars) using the radiative transfer code CMFGEN, allowing then to derive their fundamental stellar and wind parameters. In this study, I was particularly interested in the determination of their wind mass-loss rate in order to compare them with the theoretical values provided by hydrodynamical simulations. One major result of this study is show for the first time that more evolved massive stars, late O giants, also present weak winds which were originally found in late O dwarfs (O8-9V stars). Furthermore, from this study, the luminosity region around log(Lstar/Lsun) = 5.2 was found to be indeed critical in the onset of weak winds in O-type stars.
In my other first-authored article, I studied the Be star o Aquarii based on visible and near-infrared spectro-interferometric observations from the CHARA/VEGA and VLTI/AMBER instruments: E. S. G. de Almeida, A. Meilland, A. Domiciano de Souza, P. Stee, D. Mourard, N. Nardetto, R. Ligi, I. Tallon-Bosc, D. M. Faes, A. C. Carciofi, D. Bednarski, B. C. Mota, N. Turner, and T. A. ten Brummelaar. Visible and near-infrared spectro-interferometric analysis of the edge-on Be star o Aquarii. A&A, 636:A110, Apr. 2020. To determine both the central star and its disk properties, I employed modeling tools of increasing complexity to interpret these interferometric datasets: geometric, kinematics and 3D non-LTE radiative transfer models calculated using the code HDUST. This allowed to draw one of the most complete pictures of a Be star and its circumstellar disk both in the visible and the near-infrared. One remarkable result from this study is to find a very similar disk extension both in the visible (Hα) and in the near-infrared (Brγ), being that an uncommon feature for Be stars disks. I showed that this feature could be related to an opacity effect for Be disks seen close to the edge-on orientation (as in the case of o Aquarii). Another interesting result of this study is the long-term disk stability of this star over many years. This result can be interpreted in terms of the very high rotational rate that was determined in my study for this star (up to 96% the critical rotational velocity). So, this suggests that the rotational rate of o Aquarii is an important source of mass injection in its disks.
Lastly, I have collaborated to study the Luminous Blue Variable star P Cygni, but based on observations with other high-angular resolution technique, the so-called intensity interferometry: J. P. Rivet, A. Siciak, E. S. G. de Almeida, F. Vakili, A. Domiciano de Souza, M. Fouché, O. , D. Vernet, R. Kaiser, and W. Guerin. Intensity interferometry of P Cygni in the H α emission line: towards distance calibration of LBV supergiant stars. MNRAS, 494(1):218–227, Feb. 2020. I analysed these intensity interferometric observations of P Cygni centered at H α using radiative transfer models calculated with CMFGEN, allowing us to provide an independent distance estimation to P Cygni. Despite being a significantly smaller distance value than the typically one adopted in the literature for this star, very recent parallax measurements of P Cygni (from Gaia eDR3) support this finding.
Starry Night, Vincent van Gogh, 1889