Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

Context. B[e] supergiants are massive post-main-sequence stars, surrounded by a complex circumstellar environment where moleculesand dust can survive. The shape in which the material is distributed around these objects and its dynamics as well as the mechanismsthat give rise to these structures are not well understood.Aims. The aim of this work is to deepen our knowledge of the structure and kinematics of the circumstellar disc of the B[e] supergiantLHA 120-S 35.Methods. High-resolution optical spectra were obtained in three different years. Forbidden emission lines, that contribute to trace thedisc at different distances from the star, are modelled in order to determine the kinematical properties of their line-forming regions,assuming Keplerian rotation. In addition, we used low-resolution near-infrared spectra to explore the variability of molecular emission.Results. LHA 120-S 35 displays an evident spectral variability in both optical and infrared regions. The P-Cygni line profiles of H i,as well as those of Fe ii and O i, suggest the presence of a strong bipolar clumped wind. We distinguish density enhancements in theP-Cygni absorption component of the first Balmer lines, which show variations in both velocity and strength. The P-Cygni profileemission component is double-peaked, indicating the presence of a rotating circumstellar disc surrounding the star. We also observeline-profile variations in the permitted and forbidden features of Fe ii and O i. In the infrared, we detect variations in the intensity ofthe H i emission lines as well as in the emission of the CO band-heads. Moreover, we find that the profiles of each [Ca ii] and [O i]emission lines contain contributions from spatially different (complete or partial) rings. Globally, we find evidence of detached multi-ring structures, revealing density variations along the disc. We identify an inner ring, with sharp edge, where [Ca ii] and [O i] linesshare their forming region with the CO molecular bands. The outermost regions show a complex structure, outlined by fragmentedclumps or partial-ring features of Ca ii and O i. Additionally, we observe variations in the profiles of the only visible absorptionfeatures, the He i lines.Conclusions. We suggest that LHA 120-S 35 has passed through the red-supergiant (RSG) phase and evolves back bluewards in theHertzsprung-Russell diagram. In this scenario, the formation of the complex circumstellar structure could be the result of the wind-wind interactions of the post-RSG wind with the previously ejected material from the RSG. The accumulation of material in thecircumstellar environment could be attributed to enhanced mass-loss, probably triggered by stellar pulsations. However, the presenceof a binary companion can not be excluded. Finally, we find that LHA 120-S 35 is the third B[e] supergiant belonging to a youngstellar cluster.Fil: Torres, Andrea Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Cidale, Lydia Sonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Kraus, M.. Tartu Observatory, Estonia; Estonia. Astronomický Ústav, Akademie Ved Ceské Republiky; República ChecaFil: Arias, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Barba, Rodolfo Hector. Universidad de La Serena; ChileFil: Maravelias, G.. Universidad de Valparaiso; Chile. Astronomický Ústav, Akademie Ved Ceské Republiky; República ChecaFil: Borges Fernandes, M.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasi

Spectroscopic behavior of some He peculiar stars

In this work we determine fundamental parameters (Teff and log g) of a sample of He-peculiar stars from the continuum energy distribution around the Balmer discontinuity. Furthermore, we search for optical line variability in some recently discovered objects.Trabajo publicado en Stefl, Stanislav; Owocki, Stanley P.; Okazaki, Atsuo T. (2007). Active OB-Stars: Laboratories For Stellar and Circumstellar Physics. ASP Conference Series, vol. 361. ISBN: 978-1-583812-29-7.Facultad de Ciencias Astronómicas y Geofísica

Modeling of molecules in circumstellar media

Las estrellas B[e] se caracterizan por poseer lı́neas espectrales en emisión, tanto de transiciones prohibidas como permitidas, producidas en el disco que rodea a la estrella. Las condiciones de temperatura ydensidad en estos discos permiten la formación de moléculas, cuya presencia se manifiesta en la observación de bandas moleculares en emisión. En este trabajo presentamos el código que hemos desarrollado que nos permite modelar las bandas en emisión de distintas moléculas diatómicas como CO, SiO, CS, SiS, NH, etc. El programatiene en cuenta los distintos isótopos que componen las moléculas, ya que éstos afectan significativamente a las bandas. Con este programa podemos obtener los espectros combinados tanto de moléculas compuestas por distintos isótopos como de la superposición de distintas moléculas. Comparando con las observaciones, podemos usar estosespectros teóricos no sólo para determinar la presencia de las moléculas, sino también otros parámetros, como la temperatura y densidad de las regiones de formación de las moléculas en el disco, la velocidad de rotación, y la región del disco en donde se encuentran las moléculas. Además los podemos utilizar para determinar la relación de abundancia de los distintos isótopos de una molécula, que puede ser utilizada para determinar la etapa evolutiva de la estrella.B[e] stars are characterized by having spectral lines in emission, both of forbiden and allowed transitions, produced in the disk that surrounds the star. The temperature and density conditions in these disks allow the formation of molecules, whose presence is manifested in the observation of molecular bands in emission. In this work we present the code that we have developed which allows us to model the emission bands of different diatomic molecules, such as CO, SiO, CS, SiS, NH, etc. The program takes into account the different isotopes that make up the molecules, since these significantly affect the bands. With this program we can obtain the combined spectra of molecules composed of different isotopes and the superposition of different molecules. Comparing with the observations, we can use these theoretical spectra not only to determine the presence of the molecules, but also other parameters, such as the temperature and density of the regions of formation of the molecules in the disk, the velocity of rotation, and the region of the disk where the molecules are found. We can also use them to determine the abundance ratio of the different isotopes of a molecule, which can be used to determine the evolutionary stage of the star.Fil: Vallverdú, Rodolfo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Kraus, M.. No especifíca;Fil: Torres, Andrea Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Arias, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina62° Reunión Anual de la Asociación Argentina de AstronomíaArgentinaAsociación Argentina de Astronomí

On the evolutionary state of massive stars in transition phases in M33

The advanced stages of several high-mass stars are characterized by episodic mass-loss shed during phases of instability.Key for assigning these stars a proper evolutionary state is to assess the composition and geometry of their ejecta alongside the stellar properties. We selected five hot luminous blue variable candidates in M33 to refine their classification, investigate their circumstellar environments, and explore their evolutionary properties. Being accessible targets in the near-infrared, we conducted medium-resolution spectroscopy with GNIRS/GEMINI in the K-band to investigate their molecular circumstellar environments. Two stars were found to display CO emission, which was modelled to emerge from a circumstellar or circumbinary Keplerian disc/ring. The identification of the carbon isotope 13C and, for one of the two stars, a significantly low 12CO/13CO ratio, implies an evolved stellar state. As both CO emission stars are highly luminous and hence do not undergo a red supergiant phase, we suggest that stripping processes and equatorial high-density ejecta due to fast rotation are responsible for the enrichment of the stellar surface with processedmaterial from the core.Acandidate B[e]SG displays an absorption CO profile, which may be attributed to a jet or stellar pulsations. The featureless infrared spectra of two stars suggest a low-density gas shell or dissipation of the molecule due to the ionizing temperature of the star. We propose spectroscopic monitoring of our targets to evaluate the stability of the CO molecule and assess the time-dependent dynamics of the circumstellar gas structures.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Infrared Spectroscopy of Be Stars: Influence of the Envelope Parameters on Brackett-Series Behaviour

The IR spectra of Be stars display numerous hydrogen recombination lines, constituting a great resource for obtaining information on the physical and dynamic structures of different regions within the circumstellar envelope. Nevertheless, this spectral region has not been analysed in depth, and there is a lack of synthetic spectra with which to compare observations. Therefore, we computed synthetic spectra with the HDUST code for different disc parameters. Here, we present our results on the spectral region that includes lines of the Brackett series. We discuss the dependence of the line series strengths on several parameters that describe the structure of the disc. We also compared model line profiles, fluxes, and EWs with observational data for two Be stars (MX Pup and p Aqr). Even though the synthetic spectra adequately fit our observations of both stars and allow us to constrain the parameters of the disc, there is a discrepancy with the observed data in the EW and flux measurements, especially in the case of MXPup. It is possible that by including Brackett lines of higher terms or adding the analysis of other series, we may be able to better constrain the parameters of the observed disc.Instituto de Astrofísica de La Plat

Determination of fundamental parameters and circumstellar properties for a sample of B[e] stars

We develop a simple model to derive theoretical continuum energy distributions for B[e] stars, consisting of a B star surrounded by an envelope made of gas and dust. We select a sample of B[e] objects for which we construct the observed energy distributions, from 0.1 to 100 μm, using available photometric and spectroscopic data. We present some preliminary fittings.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Determination of fundamental parameters and circumstellar properties for a sample of B[e] stars

We develop a simple model to derive theoretical continuum energy distributions for B[e] stars, consisting of a B star surrounded by an envelope made of gas and dust. We select a sample of B[e] objects for which we construct the observed energy distributions, from 0.1 to 100 μm, using available photometric and spectroscopic data. We present some preliminary fittings.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Macroclumping as solution of the discrepancy between Hα and P v mass loss diagnostics for O-type stars

Context. Recent studies of O-type stars have demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed. Fitting the unsaturated UV resonance lines (e.g., P v) gives drastically lower values than obtained from the Hα emission. Wind inhomogeneity (so-called "clumping") may be the main cause of this discrepancy. Aims. In a previous paper, we presented 3D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from O4 to O7) and test whether the reported discrepancies can be resolved this way. Methods. In the first step, the analyses started with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit to the observed Hα emission lines best. For the unsaturated UV resonance lines (i.e., P v) we then applied our 3D Monte-Carlo code, which can account for wind clumps of any optical depths ("macroclumping"), a non-void interclump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra were adopted from the PoWR models. The properties of the wind clumps were constrained by fitting the observed resonance line profiles. Results. Our results show that with the mass-loss rates that fit Hα (and other Balmer and He ii lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced with no problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates or to assume a subsolar phosphorus abundance or an extremely high clumping factor, unlike what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Conclusions. Macroclumping resolves the previously reported discrepancy between Hα and P v mass-loss diagnostics.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Macroclumping as solution of the discrepancy between Hα and P v mass loss diagnostics for O-type stars

Context. Recent studies of O-type stars have demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed. Fitting the unsaturated UV resonance lines (e.g., P v) gives drastically lower values than obtained from the Hα emission. Wind inhomogeneity (so-called "clumping") may be the main cause of this discrepancy. Aims. In a previous paper, we presented 3D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from O4 to O7) and test whether the reported discrepancies can be resolved this way. Methods. In the first step, the analyses started with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit to the observed Hα emission lines best. For the unsaturated UV resonance lines (i.e., P v) we then applied our 3D Monte-Carlo code, which can account for wind clumps of any optical depths ("macroclumping"), a non-void interclump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra were adopted from the PoWR models. The properties of the wind clumps were constrained by fitting the observed resonance line profiles. Results. Our results show that with the mass-loss rates that fit Hα (and other Balmer and He ii lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced with no problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates or to assume a subsolar phosphorus abundance or an extremely high clumping factor, unlike what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Conclusions. Macroclumping resolves the previously reported discrepancy between Hα and P v mass-loss diagnostics.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Modeling of emission lines in low-ionization winds of B-type stars

En el contexto de la aparición del nuevo material observacional provisto por la misión espacial Gaia, y enfocado en estrellas de tipo espectral B peculiares, se desarrolla un modelo para simular el espectro de lı́neas de elementos una vez ionizados como Ca ii y Mg ii fuera del equilibrio  termodinámico local. El cálculo se realiza para un rango de  temperaturas efectivas y gravedades superficiales, para diferentes  distribuciones de temperatura y velocidad en el material circunestelar y distintas tasas de pérdida de masa. Los perfiles sintéticos obtenidos son capaces de reproducir los rasgos generales de las lı́neas espectrales  observadas como, por ejemplo, perfiles P Cygni.Motivated by the availability of new observational material provided by Gaia mission, and focused on peculiar B-type stars, we develop a model to simulate the non-LTE line profiles of ionized elements such as Ca ii and Mg ii. The calculation is performed for a range of effective temperature and surface gravity, for different temperature and velocity distributions of the circumstellar material as well as different stellar mass-loss rates. The obtained synthetic profiles are capable of reproducing the general features of the observed spectral lines, such as P Cygni-type profiles.Fil: Mercanti, Lorena Verónica. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Cidale, Lydia Sonia. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Torres, Andrea Fabiana. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Cochetti, Yanina Roxana. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Kraus, M.. No especifíca;62º Reunión Anual de la Asociación Argentina de AstronomíaArgentinaAsociación Argentina de Astronomí