Westerlund 2 images selected as Hubbles 25th Birthday Image

30 Apr


Data of Westerlund 2 were obtained from the HST proposal 13038: A. Nota (ESA/STScI), E. Sabbi and C. Christian (STScI), E. Grebel and P. Zeidler (Astronomisches Rechen-Institut Heidelberg), M. Tosi (INAF, Osservatorio Astronomico di Bologna), A. Bonanos (National Observatory of Athens, Astronomical Institute), and S.E. de Mink (University of Amsterdam)

Discovery of the first high mass X-ray binary in the Taruntula Nebula

17 Mar
Mark A. Garlic /  space-art.co.uk
Artist impression of a Be-X-ray binary: Mark A. Garlic / space-art.co.uk

The bright star VFTS 399 turned out to be more interesting than its not-so-catchy name suggests. While classified as “apparent single star”, it stood out by its rapid rotation and, as turned out when inspecting data from the Chandra Satellite, by its  exceptionally bright in X-rays.  In this paper lead by Simon Clark, we conclude this VFTS399 is most likely the secondary star in a binary system.  It is about 20 times more massive than the sun, rapidly rotating and probably shedding material from its equator by the centrifugal effect.  Its companion star is now gone and left a neutron star when it exploded as a supernova.  The neutron star appears to be the second pulsar in this region. The other neutron star is about 200 light years away.

The VLT-FLAMES Tarantula survey XX. The nature of the X-ray bright emission line star VFTS 399,  Clark et al. 2015, accepted for publication in Astronomy and Astrophysics, http://arxiv.org/abs/1503.00930

Discovery of nine runaway stars with strange rotation rates

20 Feb

Screen Shot 2015-02-20 at 1.07.24 PMEvans et al. investigated the nearly 300  B-type stars in the Tarantula nebula measuring their velocities toward and away from us using the Doppler effect.  Nine stars have extreme velocities and are candidate runaway stars. 

They appear to have strange rotation rates: either they spin very very fast or very slow.  The most extreme case is star VFTS 358, which is moving at 100 km/s. It is a very rapid rotator and shows peculiar surface chemistry.  This is very suggestive of the so-called “binary ejection scenario”.  Likely, the star was member of a close binary where it was enriched and spun up by its companion star. When the companion died (in a supernova explosion), star VFTS 358 was ejected, now flying through space all by it self.

The VLT-FLAMES Tarantula Survey XVIII. Classifications and radial velocities of the B-type stars, C. J. Evans, et al. A&A, 574, A13, 2015 http://adsabs.harvard.edu/abs/2015A%26A…574A..13E


News: Marie Curie Grant

5 Feb

EU_logoVery good news, the European Commission decided to support part of our research for the next two years through a Marie Skłodowska-Curie Research Fellowship.



New Paper Accepted: Mystery of the Blue Supergiants

8 Dec

Screen Shot 2014-12-08 at 9.49.34 PMBlue super giants are stars that are too bright and too big. Stellar models predict that they should be very rare and yet we find many of them.  We don’t know if they are regular main sequence stars burning hydrogen, whether they are in the helium burning phase or whether they are on verge of exploding…. the progenitor of supernova 1987a was a blue supergiant.  In this paper lead by Catherine McEnvoy and Philip Dufton (Belfast) we investigate the properties of blue super giants in the Tarantula survey.  Never before we had such a well studied set of these stars. From this sample we learn that  we have under estimated how big and cool massive stars get on the main sequence. An extension down to 20,000 K is suggested.

“The VLT-FLAMES Tarantula Survey XX: Atmospheric Parameters and Nitrogen Abundances to investigate the Role of binarity and the width of the Main Sequence”   C.M. McEvoy, P. L. Dufton, C. J. Evans, V. M. Kalari, N. Markova, S. Simón-Díaz, J. Vink, N. Walborn, P. A. Crowther, A. de Koter, S. E. de Mink, P. R. Dunstall, V. Hénault-Brunet, A. Herrero, N. Langer, D. J. Lennon, J. Maíz Apellániz, F. Najarro,, J. Puls, H. Sana, F. R. N. Schneider, W. D. Taylor, accpeted for publication in Astronomy and Astrophysics

New Paper: Hubble Legacy Extra Galactic UV Survey (accepted for publ.)

25 Oct

LEGUSThis Hubble Space Telescope Treasury program is imaging 50 nearby galaxies in full color resolving many of their stars, star clusters and associations. Science goals: (1) quantify how the clustering of star formation evolves both in space and time, (2) discriminate among models of star cluster evolution, (3) investigate the effects of starformation history on the UV starfornation rate calibrations, (4) explore the impacts of environment on star formation and cluster evolution across the full range of galactic and ISM properties, (5) investigate UV-excess globular clusters across multiple environments, (6) study the environment surrounding supernovae.

Description of the survey (Calzetti et al. 2014 accepted for publ. in AJ). Link to LEGUS website.

New Paper: Rotating stars up to 500 Solar Masses (accepted for publ.)

21 Oct

Screen Shot 2014-10-21 at 9.45.15 AMGrowing evidence for the existence of very massive stars (up to 500 Solar Masses) motivated the development of corresponding stellar evolution models accounting for a wide range of rotation rates (0 to 550 km/s), masses (from 70 to 500 M⊙), LMC composition covering the hydrogen burning phase.  In Kohler et al. we discuss the many peculiar phenomena, homogenous evolution, inflation, mass loss.  We find that mass loss and spin down prevents the formation of pair instability supernovae and long gamma-ray burst, for these high masses.

Koehler, Langer, de Koter, de Mink, Crowther et al. accepted for publication in A&A (2014)