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Register a new userX-shooter, NACO, and AMBER observations of the LBV Pistol Star footnote{Based on ESO runs 85.D-0182A, 085.D-0625AC}
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Added by
Christophe Martayan
Publication date
2010
fields
Physics
and research's language is
English
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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.
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Several studies have shown recently that at low metallicity B-type stars rotate faster than in environments of high metallicity. This is a typical case in the SMC. As a consequence, it is expected that a larger number of fast rotators is found in the SMC than in the Galaxy, in particular a higher fraction of Be/Oe stars. Using the ESO-WFI in its slitless mode, the data from the SMC open clusters were examined and an occurrence of Be stars 3 to 5 times larger than in the Galaxy was found. The evolution of the angular rotational velocity at different metallicities seems to be the main key to understand the specific behavior and evolution of these stars. According to the results from this WFI study, the observational clues obtained from the SMC WR stars and massive stars, and the theoretical predictions of the characteristics must have the long gamma-ray burst progenitors, we have identified the low metallicity massive Be and Oe stars as potential LGRB progenitors. To this end, the ZAMS rotational velocities of the SMC Be/Oe stars were determined and compared to models. The expected rates and the numbers of LGRB were then calculated and compared to the observed ones. Thus, a high probability was found that low metallicity Be/Oe stars can be LGRB progenitors. In this document, we describe the different steps followed in these studies: determination of the number of Be/Oe stars at different metallicities, identification of the clues that lead to suppose the low metallicity Be/Oe stars as LGRB progenitors, comparison of models with observations.
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.
We performed high-resolution optical spectroscopy and X-ray observations of the recently identified Mira-type symbiotic star EF Aql. Based on high-resolution optical spectroscopy obtained with SALT, we determine the temperature ($sim $55 000 K) and the luminosity ($sim$ 5.3 $L_odot$) of the hot component in the system. The heliocentric radial velocities of the emission lines in the spectra reveal possible stratification of the chemical elements. We also estimate the mass-loss rate of the Mira donor star. Our Swift observation did not detect EF Aql in X-rays. The upper limit of the X-ray observations is 10$^{-12}$ erg cm$^{-2}$ s$^{-1}$, which means that EF Aql is consistent with the faintest X-ray systems detected so far. Otherwise we detected it with the UVOT instrument with an average UVM2 magnitude of 14.05. During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter. The periodogram analysis of the V-band data reveals an improved period of 320.4$pm$0.3 d caused by the pulsations of the Mira-type donor star. The spectra are available upon request from the authors.
Aims. We study the enigmatic B[e] star MWC 300 to investigate its disk and binary with milli-arcsecond-scale angular resolution. Methods. We observed MWC 300 with the VLTI/AMBER instrument in the H and K bands and compared these observations with temperature-gradient models to derive model parameters. Results. The measured low visibility values, wavelength dependence of the visibilities, and wavelength dependence of the closure phase directly suggest that MWC 300 consists of a resolved disk and a close binary. We present a model consisting of a binary and a temperature-gradient disk that is able to reproduce the visibilities, closure phases, and spectral energy distribution. This model allows us to constrain the projected binary separation (~4.4 mas or ~7.9 AU), the flux ratio of the binary components (~2.2), the disk temperature power-law index, and other parameters.
(abridged) Strongly star-forming galaxies of subsolar metallicities are typical of the high-redshift universe. Here we therefore provide accurate data for two low-z analogs, the well-known low-metallicity emission-line galaxies Haro 11 and ESO 338-IG 004. On the basis of Very Large Telescope/X-shooter spectroscopic observations in the wavelength range 3000-24000AA, we use standard direct methods to derive physical conditions and element abundances. Furthermore, we use X-shooter data together with Spitzer observations in the mid-infrared range to attempt to find hidden star formation. We derive interstellar oxygen abundances of 12 + log O/H = 8.33+/-0.01, 8.10+/-0.04, and 7.89+/-0.01 in the two HII regions B and C of Haro 11 and in ESO 338-IG 004, respectively. The observed fluxes of the hydrogen lines correspond to the theoretical recombination values after correction for extinction with a single value of the extinction coefficient C(Hbeta) across the entire wavelength range from the near-ultraviolet to the NIR and mid-infrared for each of the studied HII regions. Therefore there are no emission-line regions contributing to the line emission in the NIR range, which are hidden in the optical range. The agreement between the extinction-corrected and CLOUDY-predicted fluxes implies that a HII region model including only stellar photoionisation is able to account for the observed fluxes, in both the optical and NIR ranges. All observed spectral energy distributions (SEDs) can be reproduced quite well across the whole wavelength range by model SEDs except for Haro 11B, where there is a continuum flux excess at wavelengths >1.6mum. It is possible that one or more red supergiant stars are responsible for the NIR flux excess in Haro 11B. We find evidence of a luminous blue variable (LBV) star in Haro 11C.
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