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München, Germany

Diehl R.,Max Planck Institute for Extraterrestrial Physics | Lang M.G.,Max Planck Institute for Extraterrestrial Physics | Martin P.,Max Planck Institute for Extraterrestrial Physics | Ohlendorf H.,Max Planck Institute for Extraterrestrial Physics | And 7 more authors.
Astronomy and Astrophysics | Year: 2010

Context. The Scorpius-Centaurus association is the most-nearby group of massive and young stars. As nuclear-fusion products are ejected by massive stars and supernovae into the surrounding interstellar medium, the search for characteristic γ-rays from radioactivity is one way to probe the history of activity of such nearby massive stars on a My time scale through their nucleosynthesis. 26Al decays with a radioactivity lifetime t∼1 My, 1809 keV γ-rays from its decay can be measured with current γ-ray telescopes. Aims.We aim to identify nucleosynthesis ejecta from the youngest subgroup of Sco-Cen stars, and interpret their location and bulk motion from 26Al observations with INTEGRAL's γ-ray spectrometer SPI. Methods. Following earlier 26Al γ-ray mapping with NASA's Compton observatory, we test spatial emission skymaps of 26Al for a component which could be attributed to ejecta from massive stars in the Scorpius-Centaurus group of stars. Such a model fit of spatial distributions for large-scale and local components is able to discriminate 26Al emission associated with Scorpius-Centaurus, in spite of the strong underlying nucleosynthesis signal from the Galaxy at large. Results. We find an 26Al γ-ray signal above 5s significance, which we associate with the locations of stars of the Sco-Cen group. The observed flux of 6 × 10-5 ph cm-2 s -1 corresponds to ∼1.1 × 10-4 M⊙ of 26Al. This traces the nucleosynthesis ejecta of several massive stars within the past several million years. Conclusions.We confirm through direct detection of radioactive 26Al the recent ejection of massive-star nucleosynthesis products from the Sco-Cen association. Its youngest subgroup in Upper Scorpius appears to dominate 26Al contributions from this association. Our 26Al signal can be interpreted as a measure of the age and richness of this youngest subgroup. We also estimate a kinematic imprint of these nearby massive-star ejecta from the bulk motion of 26Al and compare this to other indications of Scorpius-Centaurus massive-star activity. © 2010 ESO. Source

Przybilla N.,Dr. Karl Remeis Sternwarte | Nieva M.-F.,Dr. Karl Remeis Sternwarte | Nieva M.-F.,Max Planck Institute for Astrophysics | Butler K.,Universitatssternwarte
Journal of Physics: Conference Series | Year: 2011

It is generally accepted that the atmospheres of cool/lukewarm stars of spectral types A and later are described well by LTE model atmospheres, while the O-type stars require a detailed treatment of NLTE effects. Here model atmosphere structures, spectral energy distributions and synthetic spectra computed with ATLAS9/SYNTHE and TLUSTY/SYNSPEC, and results from a hybrid method combining LTE atmospheres and NLTE line-formation with DETAIL/SURFACE are compared. Their ability to reproduce observations for effective temperatures between 15 000 and 35 000 K are verified. Strengths and weaknesses of the different approaches are identified. Recommendations are made as to how to improve the models in order to derive unbiased stellar parameters and chemical abundances in future applications, with special emphasis on Gaia science. Source

Sundqvist J.O.,Universitatssternwarte
Proceedings of the International Astronomical Union | Year: 2014

A quite remarkable aspect of non-interacting O-stars with detected surface magnetic fields is that they all are very slow rotators. This paper uses this unique property to first demonstrate that the projected rotational speeds of massive, hot stars, as derived using current standard spectroscopic techniques, can be severely overestimated when significant macroturbulent line-broadening is present. This may, for example, have consequences for deriving the statistical distribution of rotation rates in massive-star populations. It is next shown how such macroturbulence (seemingly a universal feature of hot, massive stars) is present in all but one of the magnetic O-stars, namely NGC 1624-2. Assuming then a simple model in which NGC 1624-2's exceptionally strong, large-scale magnetic field suppresses atmospheric motions down to layers where the magnetic and gas pressures are comparable, first empirical constraints on the formation depth of this enigmatic hot-star macroturbulence is derived. The results suggest it originates in the thin sub-surface convection zone of massive stars, consistent with a physical origin due to, e.g., stellar pulsations excited by the convective motions. Copyright © International Astronomical Union 2015. Source

Herdin A.,Universitatssternwarte | Paunzen E.,Masaryk University | Netopil M.,Masaryk University
Astronomy and Astrophysics | Year: 2016

Context. The chemically peculiar (CP) stars of the upper main sequence are well suited for investigating the impact of magnetic fields and diffusion on the surface layers of slowly rotating stars. They can even be traced in the Magellanic Clouds and are important to the understanding of the stellar formation and evolution. Aims. A systematic investigation of the near-infrared (NIR), 2MASS JHKs, photometry for the group of CP stars has never been performed. Nowadays, there is a great deal of data available in the NIR that reach very large distances. It is therefore very important for CP stars to be unambiguously detected in the NIR region and for these detections to be used to derive astrophysical parameters (age and mass) by applying isochrone fitting. Furthermore, we investigated whether the CP stars behave in a different way to normal-type stars in the various photometric diagrams. Methods. For our analysis, we carefully compiled a sample of CP and apparently normal (non-peculiar) type stars. Only stars for which high-quality (i.e. with low error levels), astrometric, and photometric data are available were chosen. In total, 639 normal and 622 CP stars were selected and further analysed. All stars were dereddened and calibrated in terms of the effective temperature and absolute magnitude (luminosity). Finally, isochrone fitting was applied. Results. No differences in the astrophysical parameters derived from 2MASS and Johnson UBV photometry were found. Furthermore, no statistical significant deviations from the normal type stars within several colour-colour and colour-magnitude diagrams were discovered. Therefore, it is not possible to detect new CP stars with the help of the photometric 2MASS colours only. A new effective temperature calibration, valid for all CP stars, using the (V - KS)0 colour was derived. © ESO, 2015. Source

Paunzen E.,Masaryk University | Netopil M.,Masaryk University | Netopil M.,Universitatssternwarte | Maitzen H.M.,Universitatssternwarte | And 3 more authors.
Astronomy and Astrophysics | Year: 2014

Context. The chemically peculiar (CP) stars of the upper main sequence are mainly characterized by strong overabundances of heavy elements. Two subgroups (CP2 and CP4) have strong local magnetic fields which make them interesting targets for astrophysical studies. This star group, in general, is often used for the analysis of stellar formation and evolution in the context of diffusion as well as meridional circulation. Aims. In continuation of a long term study of CP stars (initiated in the 1980s), we present new results based on photoelectric measurements for ten open clusters that are, with one exception, younger than 235 Myr. Observations in star clusters are favourable because they represent samples of stars of constant age and homogeneous chemical composition. Methods. The very efficient tool of Δa photometry was applied. It samples the flux depression at 5200 Å typically for CP stars. In addition, it is able to trace emission line Be/Ae and λ Bootis stars. Virtually all CP2 and CP4 stars can be detected via this tool, and it has been successfully applied even in the Large Magellanic Cloud. For all targets in the cluster areas, we performed a kinematic membership analysis. Results. We obtained new photoelectric Δa photometry of 304 stars from which 207 objects have a membership probability higher than 50%. Our search for chemically peculiar objects results in fifteen detections. The stars have masses between 1.7 M · and 7.7 M· and are between the zero-and terminal-age-main-sequence. We discuss the published spectral classifications in the light of our Δa photometry and identify several misclassified CP stars. We are also able to establish and support the nature of known bona fide CP candidates. Conclusions. It is vital to use kinematic data for the membership determination and also to compare published spectral types with other data, such as Δa photometry. There are no doubts about the accuracy of photoelectric measurements, especially for stars brighter than 10th magnitude. The new and confirmed CP stars are interesting targets for spectroscopic follow-up observations to put constraints on the formation and evolution of CP stars. © 2014 ESO. Source

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