Skills (2)
Publications (5) View all
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Article: Unveiling the structure and kinematics of B[e] stars' disks from FEROS and CRIRES spectra
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ABSTRACT: We are investigating the circumstellar material for a sample of B[e] stars using high spectral resolution data taken in the optical and near-infrared regions with ESO/FEROS and ESO/CRIRES spectrographs, respectively. B[e] stars are surrounded by dense disks of still unknown origin. While optical emission lines from [O I] and [Ca II] reflect the disk conditions close to the star (few stellar radii), the near-infrared data, especially the CO band emission, mirror the characteristics in the molecular part of the disk farther away from the star (several AU). Based on our high resolution spectroscopic data, we seek to derive the density and temperature structure of the disks, as well as their kinematics. This will allow us to obtain a better understanding of their structure, formation history and evolution. Here we present our preliminary results.12/2012; -
Article: The sudden appearance of CO emission in LHA 115-S 65
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ABSTRACT: Molecular emission has been detected in several Magellanic Cloud B[e] supergiants. In this Letter, we report on the detection of CO band head emission in the B[e] supergiant LHA 115-S 65, and present a K-band near-infrared spectrum obtained with the Spectrograph for INtegral Field Observation in the Near-Infrared (SINFONI; R=4500) on the ESO VLT UT4 telescope. The observed molecular band head emission in S 65 is quite surprising in light of a previous non-detection by McGregor et al. 1989, as well as a high resolution (R=50000) Gemini/Phoenix spectrum of this star taken nine months earlier showing no emission. Based on analysis of the optical spectrum by Kraus et al. 2010, we suspect that the sudden appearance of molecular emission could be due to density build up in an outflowing viscous disk, as seen for Be stars. This new discovery, combined with variability in two other similar evolved massive stars, indicates an evolutionary link between B[e] supergiants and LBVs.07/2012; -
Article: A new observational tracer for high-density disc-like structures around B[e] supergiants
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ABSTRACT: The disc formation mechanism of B[e] supergiants is one of the puzzling phenomena in massive star evolution. Rapid stellar rotation seems to play an important role for the non-spherically symmetric mass-loss leading to a high-density disc or ring-like structure of neutral material around these massive and luminous objects. The radial density and temperature structure as well as the kinematics within this high-density material are, however, not well studied. Based on high-resolution optical spectra of a sample of B[e] supergiants in the Magellanic Clouds we especially searched for tracers of the kinematics within their discs. Besides the well-known [O I] lines, we discovered the [Ca II] {\lambda}{\lambda}7291, 7324 lines that can be used as a complementary set of disc tracers. We find that these lines originate from very high-density regions, located closer to the star than the [O I] {\lambda}5577 line-forming region. The line profiles of both the [O I] and the [Ca II] lines indicate that the discs or rings of high-density material are in Keplerian rotation. We estimate plausible ranges of disc inclination angles for the sample of B[e] supergiants and suggest that the star LHA 120-S 22 might have a spiral arm rather than a disc.03/2012; -
Article: Molecular emission from GG Car's circumbinary disk
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ABSTRACT: The appearance of the B[e] phenomenon in evolved massive stars such as B[e] supergiants is still a mystery. While these stars are generally found to have disks that are cool and dense enough for efficient molecule and dust condensation, the origin of the disk material is still unclear. We aim at studying the kinematics and origin of the disk in the eccentric binary system GG Car, whose primary component is proposed to be a B[e] supergiant. Based on medium- and high-resolution near-infrared spectra we analyzed the CO-band emission detected from GG Car. The complete CO-band structure delivers information on the density and temperature of the emitting region, and the detectable 13CO bands allow us to constrain the evolutionary phase. In addition, the kinematics of the CO gas can be extracted from the shape of the first 12CO band head. We find that the CO gas is located in a ring surrounding the eccentric binary system, and its kinematics agrees with Keplerian rotation with a velocity, projected to the line of sight, of (80\pm 1) km/s. The CO ring has a column density of (5\pm 3)x10^21 cm^-2 and a temperature of 3200\pm 500 K. In addition, the material is chemically enriched in 13CO, which agrees with the primary component being slightly evolved off the main sequence. We discuss two possible scenarios for the origin of the circumbinary disk: (i) non-conservative Roche lobe overflow, and (ii) the possibility that the progenitor of the primary component could have been a classical Be star. Neither can be firmly excluded, but for Roche lobe overflow to occur, a combination of stellar and orbital parameter extremawould be required.11/2012; -
Article: Fundamental parameters of B supergiants from the BCD system
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ABSTRACT: Context. Effective temperatures of early-type supergiants are important to test stellar atmosphere- and internal structure-models of massive and intermediate mass objects at different evolutionary phases. However, these $T_{\rm eff}$ values are more or less discrepant depending on the method used to determine them.Aims. We aim to obtain a new calibration of the $T_{\rm eff}$ parameter for early-type supergiants as a function of observational quantities that are: a) highly sensitive to the ionization balance in the photosphere and its gas pressure; b) independent of the interstellar extinction; c) as much as possible model-independent.Methods. The observational quantities that best address our aims are the ($\lambda_1, D$) parameters of the BCD spectrophotometric system. They describe the energy distribution around the Balmer discontinuity, which is highly sensitive to $T_{\rm eff}$ and $\log g$. We perform a calibration of the ($\lambda_1, D$) parameters into $T_{\rm eff}$ using effective temperatures derived with the bolometric-flux method for 217 program stars, whose individual uncertainties are on average $|\Delta T_{\rm eff}|/T_{\rm eff}^f$ $=$ $0.05$.Results. We obtain a new and homogeneous calibration of the BCD ($\lambda_1, D$) parameters for OB supergiants and revisit the current calibration of the ($\lambda_1, D$) zone occupied by dwarfs and giants. The final comparison of calculated with obtained $T_{\rm eff}$ values in the $(\lambda_1,D)$ calibration show that the latter have total uncertainties, which on average are $\epsilon_{T_{\rm eff}}/T_{\rm eff}^f$ $\simeq$ $\pm0.05$ for all spectral types and luminosity classes.Conclusions. The effective temperatures of OB supergiants derived in this work agree on average within some 2000 K with other determinations found in the literature, except those issued from wind-free non-LTE plane-parallel models of stellar atmospheres, which produce effective temperatures that can be overestimated by up to more than 5000 K near $T_{\rm eff}=25\,000$ K. Since the stellar spectra needed to obtain the ($\lambda_1, D$) parameters are of low resolution, a calibration based on the BCD system is useful to study stars and stellar systems like open clusters, associations or stars in galaxies observed with multi-object spectrographs and/or spectro-imaging devices.http://dx.doi.org/10.1051/0004-6361/200811147.
