Chemical abundances of fast-rotating massive stars. I. Description of the methods and individual results

Aims: Recent observations have challenged our understanding of rotational mixing in massive stars by revealing a population of fast-rotating objects with apparently normal surface nitrogen abundances. However, several questions have arisen because of a number of issues, which have rendered a reinvestigation necessary; these issues include the presence of numerous upper limits for the nitrogen abundance, unknown multiplicity status, and a mix of stars with different physical properties, such as their mass and evolutionary state, which are known to control the amount of rotational mixing. Methods: We have carefully selected a large sample of bright, fast-rotating early-type stars of our Galaxy (40 objects with spectral types between B0.5 and O4). Their high-quality, high-resolution optical spectra were then analysed with the stellar atmosphere modelling codes DETAIL/SURFACE or CMFGEN, depending on the temperature of the target. Several internal and external checks were performed to validate our methods; notably, we compared our results with literature data for some well-known objects, studied the effect of gravity darkening, or confronted the results provided by the two codes for stars amenable to both analyses. Furthermore, we studied the radial velocities of the stars to assess their binarity. Results: This first part of our study presents our methods and provides the derived stellar parameters, He, CNO abundances, and the multiplicity status of every star of the sample. It is the first time that He and CNO abundances of such a large number of Galactic massive fast rotators are determined in a homogeneous way.Comment: accepted for publication by A&

Massive Stars in the Gaia-ESO Survey

The Gaia-ESO Survey (GES) is an ambitious project to study the formation and evolution of the Milky Way and its stellar populations. It is led by Gerry Gilmore and Sofia Randich and includes about 350 Co-Investigators. During 300 nights (spread over 5 years) of order 10^5 Giraffe spectra and 10^4 UVES spectra will be taken. As part of the survey, about 13 clusters will be observed that were chosen specifically for their massive-star content. We report on the preliminary analysis of GES data from two such clusters: NGC 3293 and NGC 6705. We determine stellar parameters for the B-type stars in NGC 3293 and compare the A-type stars population between the two clusters. We also use a repeat observation to study binarity and use the radial velocity information to study cluster membership in NGC 3293. We also list our plans for future observations, which include the Carina nebula region

X-shooter, NACO, and AMBER observations of the LBV Pistol Star \footnote{Based on ESO runs 85.D-0182A, 085.D-0625AC}

We present multi-instruments and multi-wavelengths observations of the famous LBV star Pistol Star. These observations are part of a larger program about early O stars at different metallicities. The Pistol star has been claimed as the most massive star known, with 250 solar masses. We present the preliminary results based on X-Shooter spectra, as well as the observations performed with the VLTI-AMBER and the VLT-NACO adaptive optics. The X-shooter spectrograph allows to obtain simultaneously a spectrum from the UV to the K-band with a resolving power of $\sim$15000. The preliminary results obtained indicate that Pistol Star has similar properties of Eta Car, including shells of matter, but also the binarity. Other objects of the program, here briefly presented, were selected for their particular nature: early O stars with mass discrepancies between stellar evolution models and observations, discrepancies with the wind momentum luminosity relation.Comment: Poster at the 39th LIAC, submitted version of the proceeding

Fases de actividad y quietud en estrellas Be de cumulos abiertos galacticos: una mirada con WISE

Fil: Granada, Anahi. Instituto de Astrofisica de La Plata, CONICET–UNLP, ArgentinaFil: Jones, Carol. Department of Physics and Astronomy, The University of Western Ontario, CanadaFil: Sigut, Thomas Aaron. Department of Physics and Astronomy, The University of Western Ontario, CanadaFil: Semaan, Thierry. Geneva Observatory, University of Geneva, SuizaFil: Georgy, Cyril. Geneva Observatory, University of Geneva, SuizaFil: Meynet, Georges. Geneva Observatory, University of Geneva, SuizaFil: Ekstrom, Sylvia. Geneva Observatory, University of Geneva, SuizaWISE (Wide-Field Infrared Survey Explorer) photometry is very useful for studying known Be stars from open clusters, and also detect new Be candidates that can then be studied spectroscopically. Through the modelling of near infrared photometry of star plus disc systems with Bedisk/Beray codes, we adequately describe the photometric characteristics of Be stars in seventeen galactic open clusters with ages between 10 and 100 Myr. The location of the stars Be in WISE colour-magnitude and colour-colour diagrams, permits the classification in two groups: active stars (those that are surrounded by a developed disc) and quiescent objects (in a stage without a detectable disk). This allows us to study how often Be stars are in these different phases. We find that about half of the Be stars in the studied clusters are in an active phase, and that this fraction it is dependent on the spectral type. The location of the stars with a disc developed in the colour diagram magnitude requires mass loss rates that are in accordance with expected values for stellar models in rapid rotation.La fotometría de WISE (Wide-Field Infrared Survey Explorer) resulta muy  útil para estudiar estrellas Be conocidas de cúmulos abiertos, y también para detectar nuevas candidatas a estrellas Be que pueden luego ser estudiadas espectroscópicamente. A través del modelado de fotometría infrarroja de sistemas estrella más disco con los códigos BeDisk/Beray, describimos adecuadamente las características fotométricas de estrellas Be en diecisiete cúmulos abiertos galácticos con edades entre 10 y 100 Myr. La ubicación de las estrellas Be en Diagramas color-magnitud y color-color de WISE, permite separarlas en dos grupos: estrellas activas, aquellas que están rodeadas de un disco desarrollado, e inactivas o quietas, es decir en una etapa sin disco detectable. Esto nos permite estudiar la frecuencia con que las estrellas Be se encuentran en estos estados diferentes. Encontramos que alrededor de la mitad de las estrellas Be en los cúmulos estudiados está en una fase activa, y que esta fracción es dependiente del tipo espectral. La ubicación de las estrellas con un disco desarrollado en el diagrama color-magnitud requiere tasas de pérdida de masa que están de acuerdo con valores esperados para modelos estelares en rotación rápida

High-angular resolution observations of the Pistol Star

First results of near-IR adaptive optics (AO)-assisted imaging, interferometry, and spectroscopy of this Luminous Blue Variable (LBV) are presented. They suggest that the Pistol Star is at least double. If the association is physical, it would reinforce questions concerning the importance of multiplicity for the formation and evolution of extremely massive stars.Comment: poster at IAUS27

Caractéristiques spectrales et pulsationnelles d'étoiles Be à l'aide de données sol (VLT/GIRAFFE et X-SHOOTER) et espace (CoRoT)

Be stars are early-type stars having near critical rotation. They are surrounded by an equatorial disc fed by discrete mass-loss ejections from the central star. Be stars are good laboratories to study, on one hand, the impact of rotation on pulsations and, on the other hand, the role of pulsation on the recurrent mass ejections. During this thesis we focused on faint Be stars located in the first exoplanetary fields CoRoT satellite. In a first step we have identified the stars presenting the Be phenomenon among all the variable stars observed by CoRoT. We have thus been able to provide a sample of forty Be stars.Thanks to ground-based spectroscopic observations at VLT with GIRAFFE and X-SHOOTER instruments we have studied th spectral properties of half of them and determined their fundamental parameters by taking into account the effects of rapid rotation. Using the CoRoT light curves we have determined the frequencies and amplitudes of the pulsations that characterize the treated stars and studied their temporal variations. We have studied attentively the newly discovered stars presenting light outbursts. Thanks to the carried spectroscopic and photometric studies we have been able to investigate the properties of pulsations according to the stellar location in the HR diagram, and could identify some common properties among the Be stars of our sample.Les étoiles Be sont des étoiles chaudes à rotation quasi-critique qui sont entourées d'un disque circumstellaire alimenté par des éjections discrètes de matière. Les étoiles Be sont de bons laboratoires pour étudier l'impact de la rotation rapide sur les pulsations stellaires et aussi du rôle des pulsations sur le phénomène récurrent des éjections de matière. Au cours de cette thèse nous nous sommes intéressé à l'étude des étoiles Be observées dans les premiers champs d'exoplanètes du satellite CoRoT. La première étape de ce travail a été d'identifier les étoiles Be parmi toutes les étoiles variables observées par le satellite. Nous avons constitué ainsi une liste d'une quarantaine d'étoiles Be. Grâce à des observations spectroscopiques obtenues au VLT avec les instruments GIRAFFE et X-SHOOTER nous avons pu étudier les propriétés spectrales d'une vingtaine de ces objets et déterminer leurs paramètres fondamentaux en tenant compte des effets de la rotation rapide. Nous avons étudié ensuite les courbes de lumières CoRoT de ces étoiles pour déterminer les fréquences et les amplitudes des pulsations qui les caractérisent. Nous avons étudié la variation des fréquences et amplitudes dans le temps. Cette étude porte une attention particulière aux nouvelles étoiles découvertes présentant des sursauts de lumière, signes d'éjections récurrentes de matière. Grâce à nos études spectroscopiques et photométriques nous avons pu établir de nouvelles caractéristiques des spectres de fréquences en fonction de la position des étoiles dans le diagramme HR, et mettre en évidence quelques comportements communs parmi les étoiles Be étudiées

Caractéristiques spectrales et pulsationnelles d'étoiles Be à l'aide de données sol (VLT/GIRAFFE et X-SHOOTER) et espace (CoRoT)

Les étoiles Be sont des étoiles chaudes à rotation quasi-critique qui sont entourées d'un disque circumstellaire alimenté par des éjections discrètes de matière. Les étoiles Be sont de bons laboratoires pour étudier l'impact de la rotation rapide sur les pulsations stellaires et aussi du rôle des pulsations sur le phénomène récurrent des éjections de matière. Au cours de cette thèse nous nous sommes intéressé à l'étude des étoiles Be observées dans les premiers champs d'exoplanètes du satellite CoRoT. La première étape de ce travail a été d'identifier les étoiles Be parmi toutes les étoiles variables observées par le satellite. Nous avons constitué ainsi une liste d'une quarantaine d'étoiles Be. Grâce à des observations spectroscopiques obtenues au VLT avec les instruments GIRAFFE et X-SHOOTER nous avons pu étudier les propriétés spectrales d'une vingtaine de ces objets et déterminer leurs paramètres fondamentaux en tenant compte des effets de la rotation rapide. Nous avons étudié ensuite les courbes de lumières CoRoT de ces étoiles pour déterminer les fréquences et les amplitudes des pulsations qui les caractérisent. Nous avons étudié la variation des fréquences et amplitudes dans le temps. Cette étude porte une attention particulière aux nouvelles étoiles découvertes présentant des sursauts de lumière, signes d'éjections récurrentes de matière. Grâce à nos études spectroscopiques et photométriques nous avons pu établir de nouvelles caractéristiques des spectres de fréquences en fonction de la position des étoiles dans le diagramme HR, et mettre en évidence quelques comportements communs parmi les étoiles Be étudiées.Be stars are early-type stars having near critical rotation. They are surrounded by an equatorial disc fed by discrete mass-loss ejections from the central star. Be stars are good laboratories to study, on one hand, the impact of rotation on pulsations and, on the other hand, the role of pulsation on the recurrent mass ejections. During this thesis we focused on faint Be stars located in the first exoplanetary fields CoRoT satellite. In a first step we have identified the stars presenting the Be phenomenon among all the variable stars observed by CoRoT. We have thus been able to provide a sample of forty Be stars.Thanks to ground-based spectroscopic observations at VLT with GIRAFFE and X-SHOOTER instruments we have studied th spectral properties of half of them and determined their fundamental parameters by taking into account the effects of rapid rotation. Using the CoRoT light curves we have determined the frequencies and amplitudes of the pulsations that characterize the treated stars and studied their temporal variations. We have studied attentively the newly discovered stars presenting light outbursts. Thanks to the carried spectroscopic and photometric studies we have been able to investigate the properties of pulsations according to the stellar location in the HR diagram, and could identify some common properties among the Be stars of our sample.PARIS-Observatoire (751142302) / SudocSudocFranceF

NGC 3293 revisited by the Gaia-ESO Survey

In the framework of the Gaia-ESO survey we have determined the fundamental parame- ters of a large number of B-type stars in the Galactic, young ope n cluster NGC 3293. The determination of the stellar parameters is based on medium- resolution spectra obtained with FLAMES/GIRAFFE at ESO-VLT. As a second step, we adopted the acc urate parameters to determine the chemical abundances of these hot stars. We pre sent a comparison of our results with those obtained by the ’VLT-FLAMES survey of massive sta rs’ (Evans et al. 2005). Our study increases the number of objects analysed and provides an extended view of this cluster

A Pulsational Study of a Sample of CoRoT Faint Be Stars

International audienceWe present an intensive study of a sample of 12 Be stars in the first exo-planetary fields of the CoRoT mission. The aim is to understand the short-term variability in Be stars. We use both spectroscopic and photometric data: VLT-GIRAFFE spectra to derive the fundamental parameters and CoRoT light curves to search for low-amplitude frequencies. This allows us to locate the stars in the HR diagram and compare their positions in the instability strip with those of other pulsating B stars. From VLT-GIRAFFE observations we determined the stellar parameters by fitting the observed spectra with non-LTE stellar atmosphere models. The observed spectra were corrected for veiling effects due to circumstellar material and for rotational effects. We estimated the rotational frequency using the corrected fundamental parameters. For the CoRoT light curves, we determined all significant frequencies and compared the main frequencies with the rotational frequency. We also investigated the variation of the frequencies and amplitudes with time and, in particular, during outbursts. This is the first time that a statistical study with space data has been performed for Be stars. Our study suggests that rotational modulation is not the cause of short-term photometric variability in Be stars