149 research outputs found
Non-thermal processes in colliding-wind massive binaries: the contribution of Simbol-X to a multiwavelength investigation
Several colliding-wind massive binaries are known to be non-thermal emitters
in the radio domain. This constitutes strong evidence for the fact that an
efficient particle acceleration process is at work in these objects. The
acceleration mechanism is most probably the Diffusive Shock Acceleration (DSA)
process in the presence of strong hydrodynamic shocks due to the
colliding-winds. In order to investigate the physics of this particle
acceleration, we initiated a multiwavelength campaign covering a large part of
the electromagnetic spectrum. In this context, the detailed study of the hard
X-ray emission from these sources in the SIMBOL-X bandpass constitutes a
crucial element in order to probe this still poorly known topic of
astrophysics. It should be noted that colliding-wind massive binaries should be
considered as very valuable targets for the investigation of particle
acceleration in a similar way as supernova remnants, but in a different region
of the parameter space.Comment: 4 pages, 2 figures, to appear in Proc. of the Second Internqtionql
Simbol-X Symposium, held in Paris (France
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
An XMM-Newton observation of the multiple system HD 167971 (O5-8V+O5-8V+(O81)) and the young open cluster NGC6604
We discuss the results of two XMM-Newton observations of the open cluster NGC 6604 obtained in April and September 2002. We concentrate mainly on the multiple system HD 167971 (O5- 8V + O5- 8V + (O8I)). The soft part of the EPIC spectrum of this system is thermal with typical temperatures of about 2 x 106 to 9 x 106 K. The nature ( thermal vs. non-thermal) of the hard part of the spectrum is not unambiguously revealed by our data. If the emission is thermal, the high temperature of the plasma (similar to 2.3 x 10(7) to 4.6 x 10(7) K) would be typical of what should be expected from a wind-wind interaction zone within a long period binary system. This emission could arise from an interaction between the combined winds of the O5- 8V + O5- 8V close binary system and that of the more distant O8I companion. Assuming instead that the hard part of the spectrum is non-thermal, the photon index would be rather steep (similar to 3). Moreover, a marginal variability between our two XMM-Newton pointings could be attributed to an eclipse of the O5 - 8V + O5 - 8V system. The overall X-ray luminosity points to a significant X-ray luminosity excess of about a factor 4 possibly due to colliding winds. Considering HD 167971 along with several recent X-ray and radio observations, we propose that the simultaneous observation of non-thermal radiation in the X-ray (below 10.0 keV) and radio domains appears rather unlikely. Our investigation of our XMM-Newton data of NGC 6604 reveals a rather sparse distribution of X-ray emitters. Including the two bright non-thermal radio emitters HD 168112 and HD 167971, we present a list of 31 X-ray sources along with the results of the cross-correlation with optical and infrared catalogues. A more complete spectral analysis is presented for the brightest X-ray sources. Some of the members of NGC 6604 present some characteristics suggesting they may be pre-main sequence star candidates
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 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
Radial velocities, dynamics of stars and nebulosities with GAIA and VLT-GIRAFFE
Proceedings GSD2008 conference, submitted to ANThis document is divided in two parts. The first part deals with the radial velocities (RV) distributions for B-type stars and nebulosities observed with the VLT-GIRAFFE in the Large and Small Magellanic Clouds towards the open clusters NGC2004 and NGC330. Thanks to the resolution of GIRAFFE spectra, we found that the RV distribution for the nebulosities in the LMC is bi-modal. This bi-modality can be interpreted, in term of dynamics, by the expansion of the LMC4 superbubble. The second part deals with the GAIA space mission and the determination of the radial velocities by using Radial Velocity Spectrometer (RVS) spectra. The methods to determine the radial velocities are presented as well as preliminary results on simulated RVS spectra
The Gaia satellite: a tool for Emission Line Stars and Hot Stars
The Gaia satellite will be launched at the end of 2011. It will observe at
least 1 billion stars, and among them several million emission line stars and
hot stars. Gaia will provide parallaxes for each star and spectra for stars
till V magnitude equal to 17. After a general description of Gaia, we present
the codes and methods, which are currently developed by our team. They will
provide automatically the astrophysical parameters and spectral classification
for the hot and emission line stars in the Milky Way and other close Local
Group galaxies such as the Magellanic Clouds.Comment: SF2A2008, session GAIA, invited tal
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
Luminous blue variables: An imaging perspective on their binarity and near environment
Luminous blue variables (LBVs) are rare massive stars with very high
luminosity. They are characterized by strong photo-metric and spectroscopic
variability related to transient eruptions. The mechanisms at the origin of
these eruptions is not well known. In addition, their formation is still
problematic and the presence of a companion could help to explain how they
form. Aims. This article presents a study of seven LBVs (about 20% of the known
Galactic population), some Wolf-Rayet stars, and massive binaries. We probe the
environments that surround these massive stars with near-, mid-, and
far-infrared images, investigating potential nebula/shells and the companion
stars. Methods. To investigate large spatial scales, we used seeing-limited and
near diffraction-limited adaptive optics images to obtain a differential
diagnostic on the presence of circumstellar matter and to determine their
extent. From those images, we also looked for the presence of binary companions
on a wide orbit. Once a companion was detected, its gravitational binding to
the central star was tested. Tests include the chance projection probability,
the proper motion estimates with multi-epoch observations, flux ratio, and star
separations. Results. We find that two out of seven of LBVs may have a wide
orbit companion. Most of the LBVs display a large circumstellar envelope or
several shells. In particular, HD168625, known for its rings, possesses several
shells with possibly a large cold shell at the edge of which the rings are
formed. For the first time, we have directly imaged the companion of LBV stars
The Gaia-ESO Survey: Homogenisation of stellar parameters and elemental abundances
The Gaia-ESO Survey is a public spectroscopic survey that targeted ≳105 stars covering all major components of the Milky Way from the end of 2011 to 2018, delivering its final public release in May 2022. Unlike other spectroscopic surveys, Gaia-ESO is the only survey that observed stars across all spectral types with dedicated, specialised analyses: from O (Teff ~ 30 000–52 000 K) all the way to K-M (≳3500 K). The physics throughout these stellar regimes varies significantly, which has previously prohibited any detailed comparisons between stars of significantly different types. In the final data release (internal data release 6) of the Gaia-ESO Survey, we provide the final database containing a large number of products, such as radial velocities, stellar parameters and elemental abundances, rotational velocity, and also, for example, activity and accretion indicators in young stars and membership probability in star clusters for more than 114 000 stars. The spectral analysis is coordinated by a number of working groups (WGs) within the survey, each specialised in one or more of the various stellar samples. Common targets are analysed across WGs to allow for comparisons (and calibrations) amongst instrumental setups and spectral types. Here we describe the procedures employed to ensure all survey results are placed on a common scale in order to arrive at a single set of recommended results for use by all survey collaborators. We also present some general quality and consistency checks performed on the entirety of the survey results.This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR) in the form of the grant “Premiale VLT 2012”. L. Magrini and M. Van der Swaelmen acknowledge support by the WEAVE Italian consortium, and by the INAF Grant “Checs”. A.J. Korn acknowledges support by the Swedish National Space Agency (SNSA). A. Lobel acknowledges support in part by the Belgian Federal Science Policy Office under contract no. BR/143/A2/BRASS and by the European Union Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Marie Sklodowska-Curie grant Agreement No. 823734. D.K. Feuillet was partly supported by grant no. 2016-03412 from the Swedish Research Council. D. Montes acknowledges financial support from the Agencia Estatal de Investigacion of the Ministerio de Ciencia, Innovation through project PID2019-109522GB-C54 /AEI/10.13039/501100011033. E. Marfil acknowledges financial support from the European Regional Development Fund (ERDF) and the Gobierno de Canarias through project ProID2021010128. J.I. Gonzalez Hernandez acknowledges financial support from the Spanish Ministry of Science and Innovation (MICINN) project PID2020-117493GB-I00. M. Bergemann is supported through the Lise Meitner grant from the Max Planck Society and acknowledges support by the Collaborative Research centre SFB 881 (projects A5, A10), Heidelberg University, of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation). This project has received funding from the European Research Council (ERC) under the European Union, Horizon 2020 research and innovation programme (Grant agreement No. 949173). P. Jofré acknowledges financial support of FONDECYT Regular 1200703 as well as Nucleo Mile-nio ERIS NCN2021_017. R. Smiljanic acknowledges support from the National Science Centre, Poland (2014/15/B/ST/03981). S.R. Berlanas acknowledges support by MCIN/AEI/10.13039/501100011033 (contract FJC 2020-045785-I) and NextGeneration EU/PRTR and MIU (UNI/551/2021) through grant Margarita Salas-ULL. T. Bensby acknowledges financial support by grant No. 2018-04857 from the Swedish Research Council. T. Merle is supported by a grant from the Foundation ULB. T. Morel are grateful to Belgian F.R.S.-FNRS for support, and are also indebted for an ESA/PRODEX Belspo contract related to the Gaia Data Processing and Analysis Consortium and for support through an ARC grant for Concerted Research Actions financed by the Federation Wallonie-Brussels. W. Santos acknowledges FAPERJ for a Ph.D. fellowship. H.M. Tabernero acknowledges financial support from the Agencia Estatal de Investigation of the Ministerio de Ciencia, Innovation through project PID2019-109522GB-C51/AEI/10.13039/501100011033
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