Publications (89) View all
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Article: Broad-band Spectroscopy of the Ongoing Large Eruption of the Luminous Blue Variable R71
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ABSTRACT: The Luminous Blue Variable (LBV) R71 is currently undergoing an eruption, which differs photometrically and spectroscopically from its last outburst in the 1970s. Valuable information on the physics of LBV eruptions can be gained by analyzing the spectral evolution during this eruption and by comparing R71's present appearance to its previous outburst and its quiescent state. Here we present the first spectra of an ongoing monitoring program with VLT/X-shooter and compare them to archival VLT/UVES and MPG/ESO-2.2m/FEROS spectra from 2002-2011. The discussed data include pre-eruption spectra in 2002 and 2005, a spectrum of the transitionary phase between quiescent and eruptive state in 2007, and spectra of the eruption in 2011-2012. The 2011-2012 spectra are dominated by strong neutral and singly ionized metal absorption lines likely formed in a large "pseudo-photosphere." We find an unusually low apparent temperature of R71 of only ~6650 K; the star resembles a late F supergiant. R71's visual lightcurve had a maximum in 2012 with mV ~ 8.7 mag. Given the uncertainty in the extinction towards R71, this corresponds to a bolometric luminosity of -9.8 mag to -10.3 mag. R71's 2011-2012 spectra do not show H I and Fe II P Cyg profiles, which were present during its last outburst in the 1970s and which are normally observed during LBV outbursts. The rise in R71's visual magnitude and the low apparent temperature of its pseudo-photosphere during the current eruption are unprecedented for this star. R71 most likely increased its bolometric luminosity by 0.4-1.3 mag compared to its quiescent state. The very low temperature of its pseudo-photosphere implies a very high-mass loss rate, a factor of 1000 higher than during the quiescence state. No fast-moving material indicative of an explosion is observed (abridged).03/2013; -
Article: The 2011 Periastron Passage of the Be Binary delta Scorpii
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ABSTRACT: We describe the results of the world-wide observing campaign of the highly eccentric Be binary system delta Scorpii 2011 periastron passage which involved professional and amateur astronomers. Our spectroscopic observations provided a precise measurement of the system orbital period at 10.8092+/- 0.0005 years. Fitting of the He II 4686A line radial velocity curve determined the periastron passage time on 2011 July 3, UT 9:20 with a 0.9--day uncertainty. Both these results are in a very good agreement with recent findings from interferometry. We also derived new evolutionary masses of the binary components (13 and 8.2 Msun) and a new distance of 136 pc from the Sun, consistent with the HIPPARCOS parallax. The radial velocity and profile variations observed in the H_alpha line near the 2011 periastron reflected the interaction of the secondary component and the circumstellar disk around the primary component. Using these data, we estimated a disk radius of 150 Rsun. Our analysis of the radial velocity variations measured during the periastron passage time in 2000 and 2011 along with those measured during the 20th century, the high eccentricity of the system, and the presence of a bow shock-like structure around it suggest that delta Sco might be a runaway triple system. The third component should be external to the known binary and move on an elliptical orbit that is tilted by at least 40 degree with respect to the binary orbital plane for such a system to be stable and responsible for the observed long-term radial velocity variations.02/2013; -
Article: Magnetometry of a sample of massive stars in Carina
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ABSTRACT: X-ray surveys of the Carina nebula have revealed a few hard and luminous sources associated with early-type stars. Such unusual characteristics for the high-energy emission may be related to magnetically-confined winds. To search for the presence of magnetic fields in these objects, we performed a limited spectropolarimetric survey using the FORS instrument. The multi-object mode was used, so that a total of 21 OB stars could be investigated during a one-night-long run. A magnetic field was detected in two objects of the sample, with a 6 sigma significance; Tr16-22 and 13. Such a detection was expected for Tr16-22, as its X-ray emission is too bright, variable and hard, compared to other late-type O or O+OB systems. It is more surprising for Tr16-13, a poorly known star which so far has never shown any peculiar characteristics. Subsequent monitoring is now needed to ascertain the physical properties of these objects and enable a full modelling of their magnetic atmospheres and winds.04/2012; -
Article: New activity in the large circumstellar disk of the Be-shell star 48 Lib
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ABSTRACT: Spectroscopic, polarimetric, and high spectral resolution interferometric data covering the period 1995-2011 are analyzed to document the transition into a new phase of circumstellar disk activity in the classical Be-shell star 48 Lib. The long-term disk evolution is described using the V/R ratio of the violet and red emission components of H alpha and Br gamma, radial velocities and profiles of He I and optical metal shell lines, multi-band BVRI polarimetry, broad-band and high-resolution interferometric visibilities and phases. Spectroscopic signatures of disk asymmetries in 48 Lib vanished in the late nineties but recovered some time between 2004 and 2007. Variations in the radial velocity and line profile of conventional shell lines correlate with the V/R behavior. They are shared by narrow absorption cores superimposed on otherwise seemingly photospheric He I lines, which may form in high-density gas at the inner disk close to the photosphere. Large radial velocity variations continued also during the V/R-quiet years. The broad H-band interferometry gives a disk diameter of (1.72+-0.2) mas (equivalent to 15 stellar radii), position angle of the disk (50+-9) deg and a relatively low disk flattening of 1.66+-0.3. Within the errors the same disk position angle is derived from polarimetric observations and from photocenter shifts across Br gamma. The high-resolution interferometric visibility and phase profiles show a double or even multiple-component structure. A preliminary estimate based on the size of the Br gamma emitting region indicates a large diameter for the disk (tens of stellar radii).02/2012; -
Article: First HARPSpol discoveries of magnetic fields in massive stars
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ABSTRACT: 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. In this Letter, 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 are strongly varying for HD 130807 from $\sim$-100 G to $\sim$700 G. Those of HD 122451 and HD 105382 are less variable with values ranging from $\sim$-40 to -80 G, and from $\sim$-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 the MiMeS objectives: the understanding of origin of magnetic fields in massive stars and their impacts on stellar structure and evolution.11/2011;
