TY - JOUR A1 - Evans, C. J. A1 - Smartt, S. J. A1 - Lee, J. K. A1 - Lennon, D. J. A1 - Kaufer, A. A1 - Dufton, P. L. A1 - Trundle, C. A1 - Herrero, A. A1 - Simon Díaz, Sergio A1 - de Koter, A. A1 - Hamann, Wolf-Rainer A1 - Hendry, M. A. A1 - Hunter, I. A1 - Irwin, M. J. A1 - Korn, A. J. A1 - Kudritzki, R. P. A1 - Langer, Norbert A1 - Mokiem, M. R. A1 - Najarro, F. A1 - Pauldrach, A. W. A. A1 - Przybilla, Norbert A1 - Puls, J. A1 - Ryans, R. S. I. A1 - Urbaneja, M. A. A1 - Venn, K. A. A1 - Villamariz, M. R. T1 - The VLT-FLAMES survey of massive stars : Observations in the Galactic clusters NGC3293, NGC4755 and NGC6611 N2 - We introduce a new survey of massive stars in the Galaxy and the Magellanic Clouds using the Fibre Large Array Multi- Element Spectrograph ( FLAMES) instrument at the Very Large Telescope ( VLT). Here we present observations of 269 Galactic stars with the FLAMES- Giraffe Spectrograph ( R similar or equal to 25 000), in fields centered on the open clusters NGC3293, NGC4755 and NGC6611. These data are supplemented by a further 50 targets observed with the Fibre- Fed Extended Range Optical Spectrograph ( FEROS, R = 48 000). Following a description of our scientific motivations and target selection criteria, the data reduction methods are described; of critical importance the FLAMES reduction pipeline is found to yield spectra that are in excellent agreement with less automated methods. Spectral classifications and radial velocity measurements are presented for each star, with particular attention paid to morphological peculiarities and evidence of binarity. These observations represent a significant increase in the known spectral content of NGC3293 and NGC4755, and will serve as standards against which our subsequent FLAMES observations in the Magellanic Clouds will be compared Y1 - 2005 ER - TY - GEN A1 - Martins, Fabrice A1 - Bergemann, Maria A1 - Bestenlehner, Joachim M. A1 - Crowther, Paul A. A1 - Hamann, Wolf-Rainer A1 - Najarro, Francisco A1 - Nieva, Maria Fernanda A1 - Przybilla, Norbert A1 - Freimanis, Juris A1 - Hou, Weizhen A1 - Kaper, Lex T1 - SpS5 - II. Stellar and wind parameters T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The development of infrared observational facilities has revealed a number of massive stars in obscured environments throughout the Milky Way and beyond. The determination of their stellar and wind properties from infrared diagnostics is thus required to take full advantage of the wealth of observations available in the near and mid infrared. However, the task is challenging. This session addressed some of the problems encountered and showed the limitations and successes of infrared studies of massive stars. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 688 KW - infrared: stars KW - stars: early-type KW - stars: late-type KW - stars: fundamental parameters KW - stars: mass loss KW - stars: abundances Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-414956 SN - 1866-8372 IS - 688 ER - TY - JOUR A1 - Chougule, Abhishek A1 - Przybilla, Norbert A1 - Dimitrijevic, Milan S. A1 - Schaffenroth, Veronika T1 - The impact of improved Stark-broadening widths on the modeling of double-ionized chromium lines in hot stars JF - Contributions of the Astronomical Observatory Skalnate Pleso = Práce Astronomického Observatória na Skalnatom Plese N2 - Stellar atmosphere modeling and chemical abundance determinations require the knowledge of spectral line shapes. Spectral lines of chromium in various ionization stages are common in stellar spectra but detailed data on Stark broadening for them is scarce. Recently we reported on the first calculations of Stark widths for several 4s-4p transitions of double-ionized chromium, employing the Modified Semi-Empirical approach (MSE). In this work we present applications of the data to spectrum synthesis of Cr III lines in the ultraviolet region of hot stars. The Atlas9 model atmosphere code and the line-formation code Surface were used with the assumption of local thermodynamic equilibrium. The improvements of adopting the MSE broadening tables instead of approximate Stark broadening coefficients are investigated for a total of 56 Cr III lines visible in HST/STIS spectra of the B3 subgiant star Iota Herculis and the subdwarf B-star Feige 66. KW - line: profiles KW - stars: abundances Y1 - 2020 U6 - https://doi.org/10.31577/caosp.2020.50.1.139 SN - 1335-1842 SN - 1336-0337 VL - 50 IS - 1 SP - 139 EP - 146 PB - Astronomický Ústav SAV CY - Tatranská Lomnica ER - TY - JOUR A1 - Reindl, Nicole A1 - Bainbridge, M. A1 - Przybilla, Norbert A1 - Geier, Stephan Alfred A1 - Prvak, M. A1 - Krticka, Jiri A1 - Ostensen, R. H. A1 - Telting, J. A1 - Werner, K. T1 - Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs JF - Monthly notices of the Royal Astronomical Society N2 - The presence of ultrahigh excitation (UHE) absorption lines (e.g. OVIII) in the optical spectra of several of the hottest white dwarfs poses a decades-long mystery and is something that has never been observed in any other astrophysical object. The occurrence of such features requires a dense environment with temperatures near 10(6) K, by far exceeding the stellar effective temperature. Here we report the discovery of a new hot wind white dwarf, GALEXJ014636.8+323615. Astonishingly, we found for the first time rapid changes of the equivalent widths of the UHE features, which are correlated to the rotational period of the star (P=0.242035 d). We explain this with the presence of a wind-fed circumstellar magnetosphere in which magnetically confined wind shocks heat up the material to the high temperatures required for the creation of the UHE lines. The photometric and spectroscopic variability of GALEXJ014636.8+323615 can then be understood as consequence of the obliquity of the magnetic axis with respect to the rotation axis of the white dwarf. This is the first time a wind-fed circumstellar magnetosphere around an apparently isolated white dwarf has been discovered and finally offers a plausible explanation of the ultrahot wind phenomenon. KW - stars: AGB and post-AGB KW - stars: evolution KW - stars: magnetic field Y1 - 2018 U6 - https://doi.org/10.1093/mnrasl/sly191 SN - 0035-8711 SN - 1365-2966 VL - 482 IS - 1 SP - L93 EP - L98 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Schaffenroth, Veronika A1 - Casewell, Sarah L. A1 - Schneider, D. A1 - Kilkenny, David A1 - Geier, Stephan A1 - Heber, Ulrich A1 - Irrgang, Andreas A1 - Przybilla, Norbert A1 - Marsh, Thomas R. A1 - Littlefair, Stuart P. A1 - Dhillon, Vik S. T1 - A quantitative in-depth analysis of the prototype sdB plus BD system SDSS J08205+0008 revisited in the Gaia era JF - Monthly notices of the Royal Astronomical Society N2 - Subdwarf B stars are core-helium-burning stars located on the extreme horizontal branch (EHB). Extensive mass loss on the red giant branch is necessary to form them. It has been proposed that substellar companions could lead to the required mass loss when they are engulfed in the envelope of the red giant star. J08205+0008 was the first example of a hot subdwarf star with a close, substellar companion candidate to be found. Here, we perform an in-depth re-analysis of this important system with much higher quality data allowing additional analysis methods. From the higher resolution spectra obtained with ESO-VLT/XSHOOTER, we derive the chemical abundances of the hot subdwarf as well as its rotational velocity. Using the Gaia parallax and a fit to the spectral energy distribution in the secondary eclipse, tight constraints to the radius of the hot subdwarf are derived. From a long-term photometric campaign, we detected a significant period decrease of -3.2(8) x 10(-12) dd(-1). This can be explained by the non-synchronized hot subdwarf star being spun up by tidal interactions forcing it to become synchronized. From the rate of period decrease we could derive the synchronization time-scale to be 4 Myr, much smaller than the lifetime on EHB. By combining all different methods, we could constrain the hot subdwarf to a mass of 0.39-0.50 M-circle dot and a radius of R-sdB = 0.194 +/- 0.008 R-circle dot, and the companion to 0.061-0.071 M-circle dot with a radius of R-comp = 0.092 +/- 0.005 R-circle dot, below the hydrogen-burning limit. We therefore confirm that the companion is most likely a massive brown dwarf. KW - stars: abundances KW - stars: atmospheres KW - stars: fundamental parameters KW - stars: horizontal branch KW - stars: low-mass KW - subdwarfs Y1 - 2020 U6 - https://doi.org/10.1093/mnras/staa3661 SN - 0035-8711 SN - 1365-2966 VL - 501 IS - 3 SP - 3847 EP - 3870 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Castro, Norberto A1 - Fossati, Luca A1 - Hubrig, Swetlana A1 - Simon Díaz, Sergio A1 - Schoeller, Markus A1 - Ilyin, Ilya A1 - Carrol, Thorsten A. A1 - Langer, Norbert A1 - Morel, Thierry A1 - Schneider, Fabian R. N. A1 - Przybilla, Norbert A1 - Herrero, Artemio A1 - de Koter, Alex A1 - Oskinova, Lida A1 - Reisenegger, Andreas A1 - Sana, Hugues T1 - B fields in OB stars (BOB) Detection of a strong magnetic field in the O9.7 V star HD 54879 JF - Astronomy and astrophysics : an international weekly journal N2 - The number of magnetic stars detected among massive stars is small; nevertheless, the role played by the magnetic field in stellar evolution cannot be disregarded. Links between line profile variability, enhancements/depletions of surface chemical abundances, and magnetic fields have been identified for low-mass B-stars, but for the O-type domain this is almost unexplored. Based on FORS 2 and HARPS spectropolarimetric data, we present the first detection of a magnetic field in HD54879, a single slowly rotating O9.7 V star. Using two independent and different techniques we obtained the firm detection of a surface average longitudinal magnetic field with a maximum amplitude of about 600 G, in modulus. A quantitative spectroscopic analysis of the star with the stellar atmosphere code FASTWIND results in an effective temperature and a surface gravity of 33 000 +/- 1000K and 4.0 +/- 0.1 dex. The abundances of carbon, nitrogen, oxygen, silicon, and magnesium are found to be slightly lower than solar, but compatible within the errors. We investigate line-profile variability in HD54879 by complementing our spectra with spectroscopic data from other recent OB-star surveys. The photospheric lines remain constant in shape between 2009 and 2014, although H alpha shows a variable emission. The H alpha emission is too strong for a standard O9.7 V and is probably linked to the magnetic field and the presence of circumstellar material. Its normal chemical composition and the absence of photospheric line profile variations make HD54879 the most strongly magnetic, non-variable single O-star detected to date. KW - stars: atmospheres KW - stars: evolution KW - stars: magnetic field KW - stars: massive KW - stars: individual: HD 54879 Y1 - 2015 U6 - https://doi.org/10.1051/0004-6361/201425354 SN - 1432-0746 VL - 581 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Fossati, Luca A1 - Castro, Norberto A1 - Morel, Thierry A1 - Langer, Norbert A1 - Briquet, Maryline A1 - Carroll, Thorsten Anthony A1 - Hubrig, Swetlana A1 - Nieva, Maria-Fernanda A1 - Oskinova, Lida A1 - Przybilla, Norbert A1 - Schneider, Fabian R. N. A1 - Schoeller, Magnus A1 - Simon Díaz, Sergio A1 - Ilyin, Ilya A1 - de Koter, Alex A1 - Reisenegger, Andreas A1 - Sana, Hugues T1 - B fields in OB stars (BOB): on the detection of weak magnetic fields in the two early B-type stars beta CMa and epsilon CMa Possible lack of a "magnetic desert" in massive stars JF - Astronomy and astrophysics : an international weekly journal N2 - Only a small fraction of massive stars seem to host a measurable structured magnetic field, whose origin is still unknown and whose implications for stellar evolution still need to be assessed. Within the context of the "B fields in OB stars (BOB)" collaboration, we used the HARPSpol spectropolarimeter to observe the early B-type stars beta CMa (HD 44743; B1 II/III) and epsilon CMa (HD 52089; B1.5II) in December 2013 and April 2014. For both stars, we consistently detected the signature of a weak (<30 G in absolute value) longitudinal magnetic field, approximately constant with time. We determined the physical parameters of both stars and characterise their X-ray spectrum. For the beta Cep star beta CMa, our mode identification analysis led to determining a rotation period of 13.6 +/- 1.2 days and of an inclination angle of the rotation axis of 57.6 +/- 1.7 degrees, with respect to the line of sight. On the basis of these measurements and assuming a dipolar field geometry, we derived a best fitting obliquity of about 22 degrees and a dipolar magnetic field strength (B-d) of about 100 G (60 < B-d < 230 G within the 1 sigma level), below what is typically found for other magnetic massive stars. This conclusion is strengthened further by considerations of the star's X-ray spectrum. For epsilon CMa we could only determine a lower limit on the dipolar magnetic field strength of 13 G. For this star, we determine that the rotation period ranges between 1.3 and 24 days. Our results imply that both stars are expected to have a dynamical magnetosphere, so the magnetic field is not able to support a circumstellar disk. We also conclude that both stars are most likely core hydrogen burning and that they have spent more than 2/3 of their main sequence lifetime. A histogram of the distribution of the dipolar magnetic field strength for the magnetic massive stars known to date does not show the magnetic field "desert" observed instead for intermediate-mass stars. The biases involved in the detection of (weak) magnetic fields in massive stars with the currently available instrumentation and techniques imply that weak fields might be more common than currently observed. Our results show that, if present, even relatively weak magnetic fields are detectable in massive stars and that more observational effort is probably still needed to properly access the magnetic field incidence. KW - stars: atmospheres KW - stars: evolution KW - stars: magnetic field KW - stars: individual: epsilon CMa KW - stars: individual: beta CMa KW - stars: massive Y1 - 2015 U6 - https://doi.org/10.1051/0004-6361/201424986 SN - 0004-6361 SN - 1432-0746 VL - 574 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Hubrig, Swetlana A1 - Schoeller, Markus A1 - Fossati, Luca A1 - Morel, Thierry A1 - Castro, Neves A1 - Oskinova, Lida A1 - Przybilla, Norbert A1 - Eikenberry, Stephen S. A1 - Nieva, Maria Fernanda A1 - Langer, Norbert T1 - B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD 23478 and HD 345439 JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. Massive B-type stars with strong magnetic fields and fast rotation are very rare and pose a mystery for theories of star formation and magnetic field evolution. Only two such stars, called sigma Ori E analogues, were known until recently. A team involved in APOGEE, one of the Sloan Digital Sky Survey III programs, announced the discovery of two additional rigidly rotating magnetosphere stars, HD 23478 and HD 345439. The magnetic fields in these newly discovered sOri E analogues have not been investigated so far. Methods. In the framework of our ESO Large Programme and one normal ESO programme, we carried out low-resolution FORS 2 spectropolarimetric observations of HD 23478 and HD 345439. Results. In the measurements of hydrogen lines, we discover a rather strong longitudinal magnetic field of up to 1.5 kG in HD 23478 and up to 1.3 kG using the entire spectrum. The analysis of HD 345439 using four subsequent spectropolarimetric subexposures does not reveal a magnetic field at a significance level of 3 sigma. On the other hand, individual subexposures indicate that HD 345439 may host a strong magnetic field that rapidly varies over 88 min. The fast rotation of HD 345439 is also indicated by the behaviour of several metallic and He I lines in the low-resolution FORS 2 spectra that show profile variations already on this short time-scale. KW - stars: early-type KW - stars: fundamental parameters KW - stars: variables: general KW - stars: magnetic field KW - stars: individual: HD 23478 KW - stars: individual: HD 345439 Y1 - 2015 U6 - https://doi.org/10.1051/0004-6361/201526262 SN - 0004-6361 SN - 1432-0746 VL - 578 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Hubrig, Swetlana A1 - Fossati, Luca A1 - Carroll, Thorsten Anthony A1 - Castro, Norberto A1 - Gonzalez, J. F. A1 - Ilyin, Ilya A1 - Przybilla, Norbert A1 - Schoeller, M. A1 - Oskinova, Lida A1 - Morel, T. A1 - Langer, N. A1 - Scholz, Ralf-Dieter A1 - Kharchenko, N. V. A1 - Nieva, M. -F. T1 - B fields in OB stars (BOB): The discovery of a magnetic field in a multiple system in the Trifid nebula, one of the youngest star forming regions JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. Recent magnetic field surveys in O- and B-type stars revealed that about 10% of the core-hydrogen-burning massive stars host large-scale magnetic fields. The physical origin of these fields is highly debated. To identify and model the physical processes responsible for the generation of magnetic fields in massive stars, it is important to establish whether magnetic massive stars are found in very young star-forming regions or whether they are formed in close interacting binary systems. Methods. In the framework of our ESO Large Program, we carried out low-resolution spectropolarimetric observations with FORS 2 in 2013 April of the three most massive central stars in the Trifid nebula, HD 164492A, HD 164492C, and HD 164492D. These observations indicated a strong longitudinal magnetic field of about 500-600 G in the poorly studied component HD 164492C. To confirm this detection, we used HARPS in spectropolarimetric mode on two consecutive nights in 2013 June. Results. Our HARPS observations confirmed the longitudinal magnetic field in HD 164492C. Furthermore, the HARPS observations revealed that HD 164492C cannot be considered as a single star as it possesses one or two companions. The spectral appearance indicates that the primary is most likely of spectral type B1-B1.5 V. Since in both observing nights most spectral lines appear blended, it is currently unclear which components are magnetic. Long-term monitoring using high-resolution spectropolarimetry is necessary to separate the contribution of each component to the magnetic signal. Given the location of the system HD 164492C in one of the youngest star formation regions, this system can be considered as a Rosetta Stone for our understanding of the origin of magnetic fields in massive stars. KW - binaries: close KW - stars: early-type KW - stars: fundamental parameters KW - stars: magnetic field KW - stars: variables: general KW - stars: individual: HD 164492C Y1 - 2014 U6 - https://doi.org/10.1051/0004-6361/201423490 SN - 0004-6361 SN - 1432-0746 VL - 564 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Przybilla, Norbert A1 - Fossati, Luca A1 - Hubrig, Swetlana A1 - Nieva, M. -F. A1 - Jaervinen, S. P. A1 - Castro, Norberto A1 - Schoeller, M. A1 - Ilyin, Ilya A1 - Butler, Keith A1 - Schneider, F. R. N. A1 - Oskinova, Lida A1 - Morel, T. A1 - Langer, N. A1 - de Koter, A. T1 - B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD-57 degrees 3509 JF - Organic letters N2 - Methods. Spectropolarimetric observations with FORS2 and HARPSpol are analysed using two independent approaches to quantify the magnetic field strength. A high-S/N FLAMES/GIRAFFE spectrum is analysed using a hybrid non-LTE model atmosphere technique. Comparison with stellar evolution models constrains the fundamental parameters of the star. Results. We obtain a firm detection of a surface averaged longitudinal magnetic field with a maximum amplitude of about 1 kG. Assuming a dipolar configuration of the magnetic field, this implies a dipolar field strength larger than 3.3 kG. Moreover, the large amplitude and fast variation (within about 1 day) of the longitudinal magnetic field implies that CPD-57 degrees 3509 is spinning very fast despite its apparently slow projected rotational velocity. The star should be able to support a centrifugal magnetosphere, yet the spectrum shows no sign of magnetically confined material; in particular, emission in H alpha is not observed. Apparently, the wind is either not strong enough for enough material to accumulate in the magnetosphere to become observable or, alternatively, some leakage process leads to loss of material from the magnetosphere. The quantitative spectroscopic analysis of the star yields an effective temperature and a logarithmic surface gravity of 23 750 +/- 250 K and 4.05 +/- 0.10, respectively, and a surface helium fraction of 0.28 +/- 0.02 by number. The surface abundances of C, N, O, Ne, S, and Ar are compatible with the cosmic abundance standard, whereas Mg, Al, Si, and Fe are depleted by about a factor of 2. This abundance pattern can be understood as the consequence of a fractionated stellar wind. CPD-57 degrees 3509 is one of the most evolved He-strong stars known with an independent age constraint due to its cluster membership. KW - stars: abundances KW - stars: atmospheres KW - stars: evolution KW - stars: magnetic field KW - stars: individual: CPD-57 degrees 3509 KW - stars: massive Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527646 SN - 1432-0746 VL - 587 PB - EDP Sciences CY - Les Ulis ER - TY - GEN A1 - Morel, T. A1 - Castro, Norberto A1 - Fossati, Luca A1 - Hubrig, Swetlana A1 - Langer, N. A1 - Przybilla, Norbert A1 - Schöller, Markus A1 - Carroll, Thorsten Anthony A1 - Ilyin, Ilya A1 - Irrgang, Andreas A1 - Oskinova, Lida A1 - Schneider, Fabian R. N. A1 - Simon Díaz, Sergio A1 - Briquet, Maryline A1 - González, Jean-Francois A1 - Kharchenko, Nina A1 - Nieva, M.-F. A1 - Scholz, Ralf-Dieter A1 - de Koter, Alexander A1 - Hamann, Wolf-Rainer A1 - Herrero, Artemio A1 - Maíz Apellániz, Jesus A1 - Sana, Hugues A1 - Arlt, Rainer A1 - Barbá, Rodolfo H. A1 - Dufton, Polly A1 - Kholtygin, Alexander A1 - Mathys, Gautier A1 - Piskunov, Anatoly E. A1 - Reisenegger, Andreas A1 - Spruit, H. A1 - Yoon, S.-C. T1 - The B fields in OB stars (BOB) survey T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 821 KW - magnetic fields KW - stars: early-type KW - stars: magnetic fields KW - stars: individual (HD 164492C, CPD –57 ◦ 3509, HD 54879, β CMa, ε CMa) Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-415238 SN - 1866-8372 IS - 821 ER -