Garching bei München, Germany
Garching bei München, Germany

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Auriere M.,CNRS Institute for research in astrophysics and planetology | Lopez Ariste A.,CNRS Institute for research in astrophysics and planetology | Mathias P.,CNRS Institute for research in astrophysics and planetology | Lebre A.,Montpellier University | And 18 more authors.
Astronomy and Astrophysics | Year: 2016

Context. Betelgeuse is an M supergiant that harbors spots and giant granules at its surface and presents linear polarization of its continuum. Aims. We have previously discovered linear polarization signatures associated with individual lines in the spectra of cool and evolved stars. Here, we investigate whether a similar linearly polarized spectrum exists for Betelgeuse. Methods. We used the spectropolarimeter Narval, combining multiple polarimetric sequences to obtain high signal-to-noise ratio spectra of individual lines, as well as the least-squares deconvolution (LSD) approach, to investigate the presence of an averaged linearly polarized profile for the photospheric lines. Results. We have discovered the existence of a linearly polarized spectrum for Betelgeuse, detecting a rather strong signal (at a few times 10-4 of the continuum intensity level), both in individual lines and in the LSD profiles. Studying its properties and the signal observed for the resonant Na i D lines, we conclude that we are mainly observing depolarization of the continuum by the absorption lines. The linear polarization of the Betelgeuse continuum is due to the anisotropy of the radiation field induced by brightness spots at the surface and Rayleigh scattering in the atmosphere. We have developed a geometrical model to interpret the observed polarization, from which we infer the presence of two brightness spots and their positions on the surface of Betelgeuse. We show that applying the model to each velocity bin along the Stokes Q and U profiles allows the derivation of a map of the bright spots. We use the Narval linear polarization observations of Betelgeuse obtained over a period of 1.4 yr to study the evolution of the spots and of the atmosphere. Conclusions. Our study of the linearly polarized spectrum of Betelgeuse provides a novel method for studying the evolution of brightness spots at its surface and complements quasi-simultaneous observations obtained with PIONIER at the VLTI. © ESO, 2016.

Tartaglia L.,National institute for astrophysics | Tartaglia L.,University of Padua | Pastorello A.,University of Padua | Sullivan M.,University of Southampton | And 45 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We report photometric and spectroscopic observations of the optical transient LSQ13zm. Historical data reveal the presence of an eruptive episode (that we label as '2013a') followed by a much brighter outburst ('2013b') three weeks later, that we argue to be the genuine supernova explosion. This sequence of events closely resemble those observed for SN 2010mc and (in 2012) SN 2009ip. The absolute magnitude reached by LSQ13zm during 2013a (MR = -14.87 ± 0.25mag) is comparable with those of supernova impostors, while that of the 2013b event (MR = -18.46 ± 0.21mag) is consistent with those of interacting supernovae. Our spectra reveal the presence of a dense and structured circumstellar medium, probably produced through numerous pre-supernova mass-loss events. In addition, we find evidence for high-velocity ejecta, with a fraction of gas expelled at more than 20 000km s-1. The spectra of LSQ13zm show remarkable similarity with those of well-studied core-collapse supernovae. From the analysis of the available photometric and spectroscopic data, we conclude that we first observed the last event of an eruptive sequence from a massive star, likely a Luminous Blue Variable, which a short time later exploded as a core-collapse supernova. The detailed analysis of archival images suggest that the host galaxy is a star-forming Blue Dwarf Compact Galaxy. © 2016 The Authors.

Klein T.,European Southern Observatories | Klein T.,Max Planck Institute for Radio Astronomy | Ciechanowicz M.,European Southern Observatories | Leinz C.,European Southern Observatories | And 6 more authors.
IEEE Transactions on Terahertz Science and Technology | Year: 2014

We report on the design and on-site performance of the recently upgraded FLASH+ instrument operated at the APEX telescope in the Chilean Atacama desert in 5100 m altitude. The dual-channel receiver allows parallel observations in the atmospheric submillimeter windows between 268 and 516 GHz. A signal of in total 16 GHz is processed simultaneously. Equipped with state-of-the-art sideband separating mixers (spin-off developments from the ALMA bands 7 and 8), its outstanding on-sky performance makes FLASH+ a most efficient spectral line mapping machine. Operation is fully automated and allows flexible remote observations from the APEX base in San Pedro de Atacama. © 2014 IEEE.

Grunhut J.H.,European Southern Observatories | Bolton C.T.,University of Toronto | McSwain M.V.,Lehigh University
Astronomy and Astrophysics | Year: 2014

Context. High-energy X-rays generated in massive binary systems can arise from several different mechanisms. Constraints on the orbital parameters of these systems are therefore necessary to properly understand and interpret the X-ray phenomena. Aims. In this study we aim to determine a spectroscopic orbit for the high-mass X-ray binary system BD +60 73=IGR J00370+6122, to infer the properties of the optical and compact companion, and to interpret the characteristics of the X-ray light curve within the context of our findings. Methods. We acquired 123 spectroscopic observations with the David Dunlap Observatory and Kitt Peak National Observatory telescopes in the optical domain. Using a cross-correlation technique, we measured the radial velocity of each of these spectra relative to the heliocentric rest-frame. An orbital solution was obtained from the resulting radial velocity measurements. Spectra of several spectral standards were also acquired to reassess the spectral classification of the optical companion. Results. The best-fit orbital parameters suggest an eccentricity of e = 0.48+0.02 -0.03 and a mass-function of f(M) = 0.009 ± 0.002, lending further support to the assumption that the companion is a low-mass compact star. We find that the X-ray maximum occurs just after the time of periastron passage, but before the time of superior conjunction when the optical companion could eclipse the compact companion. The spectrum of the optical companion is best matched by the B1Ib spectral standard HD 24398, which reaffirms the original classification. Conclusions. The mass-function combined with a plausible range of possible masses for a neutron star companion yields primary masses within the range expected for the spectral type of BD +60 73 for high orbital inclinations. The compact companion cannot be a black hole unless the supergiant has an exceptionally high mass for its B1Ib spectral type or if the inclination of its orbit is very low. The X-ray timing and characteristics can potentially be explained by accretion variations on the compact object; but this would require the companion to be a magnetar. © ESO, 2014.

Tartaglia L.,National institute for astrophysics | Tartaglia L.,University of Padua | Elias-Rosa N.,National institute for astrophysics | Pastorello A.,National institute for astrophysics | And 14 more authors.
Astrophysical Journal Letters | Year: 2016

We report the results of our follow-up campaign of the supernova impostor PSN J09132750+7627410, based on optical data covering ∼250 days. From the beginning, the transient shows prominent narrow Balmer lines with P-Cygni profiles, with a blueshifted absorption component becoming more prominent with time. Along the ∼3 months of the spectroscopic monitoring, broad components are never detected in the hydrogen lines, suggesting that these features are produced in slowly expanding material. The transient reaches an absolute magnitude M r = -13.60 ± 0.19 mag at maximum, a typical luminosity for supernova impostors. Amateur astronomers provided ∼4 years of archival observations of the host galaxy, NGC 2748. The detection of the quiescent progenitor star in archival images obtained with the Hubble Space Telescope suggests it to be an 18-20 M o white-yellow supergiant. © 2016. The American Astronomical Society. All rights reserved.

Janson M.,Princeton University | Janson M.,Max Planck Institute for Astronomy | Hormuth F.,Max Planck Institute for Astronomy | Bergfors C.,Max Planck Institute for Astronomy | And 7 more authors.
Astrophysical Journal | Year: 2012

We present the results of an extensive high-resolution imaging survey of M-dwarf multiplicity using the Lucky Imaging technique. The survey made use of the AstraLux Norte camera at the Calar Alto 2.2m telescope and the AstraLux Sur camera at the ESO New Technology Telescope in order to cover nearly the full sky. In total, 761 stars were observed (701M-type and 60 late K-type), among which 182 new and 37 previously known companions were detected in 205 systems. Most of the targets have been observed during two or more epochs, and could be confirmed as physical companions through common proper motion, often with orbital motion being confirmed in addition. After accounting for various bias effects, we find a total M-dwarf multiplicity fraction of 27% ± 3% within the AstraLux detection range of 008-6″ (semimajor axes of ∼3-227 AU at a median distance of 30pc). We examine various statistical multiplicity properties within the sample, such as the trend of multiplicity fraction with stellar mass and the semimajor axis distribution. The results indicate that M-dwarfs are largely consistent with constituting an intermediate step in a continuous distribution from higher-mass stars down to brown dwarfs. Along with other observational results in the literature, this provides further indications that stars and brown dwarfs may share a common formation mechanism, rather than being distinct populations. © 2012. The American Astronomical Society. All rights reserved.

News Article | November 22, 2015

Centaurus A is our active closest galactic neighbor at only 11 million light-years away, give or take. The galaxy itself is around 60,000 light-years across (the Milky Way is 100,000 light-years across) making it approximately "big as shit." Centaurus A also happens to be a rather weird galaxy, which is largely responsible for its photogenic nature. It's thought to be the result of two relatively normal galaxies colliding, leaving behind a brew of young blue star clusters, pinkish star-forming regions, and dark lanes of dust. At the center is a black hole with around one billion times the mass of our own Sun. As this central hole chews through left over cosmic debris, it emits a radiant waterfall of radio, X-ray, and gamma-ray energy. The image itself, a recent NASA astronomy image of the day, is actually a composite of images drawn from the Hubble Legacy Archive, the European Southern Observatories, and data from amateur astronomers and space photographers. Credit for the image assembly and processing goes to Robert Gendler and Roberto Colombari.

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