First evidence of pulsations in Vega?. Results of today's most extensive spectroscopic search

in Astronomy and Astrophysics (2012), 537

Context. The impact of rapid rotation on stellar evolution theory remains poorly understood as of today. Vega is a special object in this context as spectroscopic and interferometric studies have shown ... [more ▼]

Context. The impact of rapid rotation on stellar evolution theory remains poorly understood as of today. Vega is a special object in this context as spectroscopic and interferometric studies have shown that it is a rapid rotator seen nearly pole one, a rare orientation particularly interesting for seismic studies. In this paper, we present a first systematic search for pulsations in Vega. <BR /> Aims: The goal of the present work is to detect for the first time pulsations in a rapidly rotating star seen nearly pole-on. <BR /> Methods: Vega was monitored in quasi-continuous high-resolution echelle spectroscopy. A total of 4478 spectra were obtained. More precisely in 2008 we obtained 1213 spectra during 19.9 h on 3 nights (26th, 27th and 29th of July 2008) with NARVAL/TBL (at R = 65 000 and R = 75 000), in 2009 we obtained 1293 spectra during 13.7 h on 3 nights (9th-11th of September 2009) with ESPaDOnS/CFHT (at R = 68 000) and in 2010 we gathered again 1972 with NARVAL/TBL during 28.8 h on five nights (July 15th-19th). This data set should represent the most extensive high S/N, high resolution quasi-continuous survey obtained on Vega as of today. Least square deconvolved (LSD) profiles were obtained for each spectrum representing the photospheric absorption profile potentially deformed by the presence of pulsations. In addition, we calculated for each spectrum a telluric line LSD profile subsequently used as radial velocity reference. LSD profile centroids were adjusted and velocity differences (stellar-telluric) determined. These residual velocities were analysed and periodic low amplitude variations, potentially indicative of stellar pulsations, detected. In a subsequent step, the temporal line profile variations during the longest (2010) data set was calculated for each individual velocity bin of 1.8 km s[SUP]-1[/SUP] by computing a 2D (velocity-frequency) Lomb-Scargle periodogram. <BR /> Results: Based on high resolution echelle spectroscopy, we have obtained indications of periodic variations of very small amplitudes within the residual radial velocity curves of Vega. All three data sets revealed the presence of residual periodic variations: 5.32 and 9.19 d[SUP]-1[/SUP] (A ≈ 6 m s[SUP]-1[/SUP]) in 2008, 12.71 and 13.25 d[SUP]-1[/SUP] (A ≈ 8 m s[SUP]-1[/SUP]) in 2009 and 5.42 and 10.82 d[SUP]-1[/SUP] (A ≈ 3-4 m s[SUP]-1[/SUP]) in 2010. However, it is too early to conclude that the variations are due to stellar pulsations, and a confirmation of the detection with a highly stable spectrograph is a necessary next step. <BR /> Conclusions: If pulsations are confirmed, their very small amplitudes show that the star would belong to a category of very "quiet" pulsators. Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers (INSU) of the Centre National de la Recherche Scientifique of France (CNRS), and at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, INSU/CNRS and the University of Hawaii. [less ▲]

First HARPSpol discoveries of magnetic fields in massive stars

in Astronomy and Astrophysics (2011), 536

In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large ... [more ▼]

In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large number of Southern massive OB stars in the field of the Galaxy and in many young clusters and associations. We report on the first discoveries of magnetic fields in two massive stars with HARPSpol - HD 130807 and HD 122451, and confirm the presence of a magnetic field at the surface of HD 105382 that was previously observed with a low spectral resolution device. The longitudinal magnetic field measurements strongly vary for HD 130807 from ~-100 G to ~700 G. Those of HD 122451 and HD 105382 are less variable with values ranging from ~-40 to -80 G, and from ~-300 to -600 G, respectively. The discovery and confirmation of three new magnetic massive stars, including at least two He-weak stars, is an important contribution to one of MiMeS objectives: the understanding of the origin of magnetic fields in massive stars and their impact on stellar structure and evolution. Based on observations collected at the European Southern Observatory, Chile (Program ID 187.D-0917). [less ▲]

Impact of the new solar abundances on the calibration of the PMS binary system RS Chamaeleontis

in Astronomy and Astrophysics (2007), 473

Context: In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to ... [more ▼]

Context: In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to reproduce the observational parameters of RS Cha with standard stellar models is to decrease the initial abundances of carbon and nitrogen derived from the GN93 solar mixture of heavy elements by a few tenths of dex. Aims: In this work, we aim to reproduce the observational properties of the RS Cha stars with stellar evolution models based on the new AGS05 solar mixture recently derived from a three-dimensional solar model atmosphere. The AGS05 mixture is depleted in carbon, nitrogen and oxygen with respect to the GN93 mixture. Methods: We calculated new stellar models of the RS Cha components using the AGS05 mixture and appropriate opacity tables. We sought models that simultaneously satisfy the observations of the two components (masses, radii, luminosities, effective temperatures and metallicity). Results: We find that it is possible to reproduce the observational data of the RS Cha stars with AGS05 models based on standard input physics. From these models, the initial helium content of the system is YË 0.255 and its age is Ë 9.13 ± 0.12 Myr. [less ▲]

Calibration of the pre-main sequence RS Chamaleontis binary system

in Astronomy and Astrophysics (2007), 465

Context: The calibration of binary systems with accurately known masses and/or radii provides powerful tools to test stellar structure and evolution theory and to determine the age and helium content of ... [more ▼]

Context: The calibration of binary systems with accurately known masses and/or radii provides powerful tools to test stellar structure and evolution theory and to determine the age and helium content of stars. We study the eclipsing double-lined spectroscopic binary system RS Cha, for which we have accurate observations of the parameters of both stars (masses, radii, luminosities, effective temperatures and metallicity). Aims: We have calculated several sets of stellar models for the components of the RS Cha system, with the aim of reproducing simultaneously the available observational constraints and to estimate the age and initial helium abundance of the system. Methods: Using the CESAM stellar evolution code, we model both components starting from the initial mass and metallicity and adjusting the input parameters and physics in order to satisfy the observational constraints. Results: We find that the observations cannot be reproduced if we assume that the abundance ratios are solar but they are satisfied if carbon and nitrogen are depleted in the RS Cha system with respect to the Sun. This is in accordance with the abundances observed in other young stars. The RS Cha system is in an evolutionary stage at the end of the PMS phase where models are not strongly sensitive to various physical uncertainties. However we show that the oscillations of these two stars, which have been detected, would be able to discriminate between different options in the physical description of this evolutionary phase. [less ▲]

RS Cha, a spectroscopic binary system as a test of stellar physics modeling during the pre-main sequence phase

in SF2A-2005: Semaine de l'Astrophysique Francaise (2005, December 01)

New spectra of the PMS eclipsing binary RS Cha obtained with the GIRAFFE spectrograph at the SAAO, allowed us to measure the metallicity and new masses of both components of RS Cha. The system is ... [more ▼]

New spectra of the PMS eclipsing binary RS Cha obtained with the GIRAFFE spectrograph at the SAAO, allowed us to measure the metallicity and new masses of both components of RS Cha. The system is therefore observationally well constrained, and modelling both stars (both with masses around 1.8 M[SUB]o[/SUB]) at the same (young) age is a severe challenge for stellar evolutionary codes. We find no evidence that our models are deficient. However accurate detection of modes and measurements of periods of the recently discovered pulsations in both components are required to constrain more severely the physical description of PMS stellar models. [less ▲]