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

Screen Shot 2014-10-26 at 5.50.52 AMThis 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.)

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)

Transition to Amsterdam

I am heading to amsterdam as a MacGillabry Fellow to start a new Research group there  A very welcome to Manos Zapartas (Starting as a PhD student Oct 1st), Abel Schootemeijer (starting as a MSc student Oct 1st) and Ylva Goetberg (starting as a PhD student Nov 1st ). More soon.

A night at Palomar Observatory searching for exoplanets

Just spent a night at Mount Palomar Observatory at the 200 inch (5.1 meter) telescope.  Quite amazing that this mountain, just 2.5 hours from Los Angeles, is the location of the telescope, which used to be the most important telescope for about 4 decades until 1992.

I joined a team lead by Ben Oppenheimer (American Museum of National History) that build a special instrument that can not only detect planets (which is very challenging because it is sitting right next to a very bright star) but also get some information about the properties of the planet through its spectrum (which is even more challenging to get).  The museum made a very nice short video explaining how this works: “Seeing planets like never before”.

Unfortunately, the weather was not very good: it was clear, but the strong winds made the air too turbulent.   So, no new discoveries tonight, but for me a very useful and special experience.

The incidence of stellar mergers (ApJ, in press)

Incidence of mergers and other products among a typical population of massive stars.

A merger between two stars may sound like an exotic event, but for massive stars this is not rare at all.  About a quarter has a companion that is so close that the two stars will coalesce to form a new rejuvenated star (Sana, de Mink, de Koter et al. Science 2012). In this paper we simulate the evolution of the stars and their interaction processes.  We predict the incidence of stellar mergers and other products of binary evolution among a typical stellar population. Furthermore we show that these products typically appear to be single stars.

De Mink, Sana, Langer, Izzard & Schneider, ApJ 2014

iPTF workshop in Santa Barbara

iptf_2013_smallhttp://ptf.caltech.edu/iptf/

Most massive stars in young starclusters are binary products (new paper, ApJ in press)

Age for which the most massive star of the cluster is expected to be a binary product, based on monte carlo simulations

70% of all O-stars is expected to interact with a binary companion during it’s life. The mass changes resulting from such interactions and stellar winds leave characteristic signatures in stellar mass function of young star clusters. Using these we model the mass functions of the Arches and Quintuplet cluster accounting for binary interaction and derive an age of 3.5+/-0.7 Myr and 4.8+/-0.1 Myr.  Based on our simulations, we expect the most massive 9+/-3 stars in Arches and 8+/-3 in Quintuplet to be the product of binary evolution. We propose this as a solution to the long standing age controversy for these clusters and we discuss the implications for the upper stellar mass limit

ApJ in press,  SCHNEIDER,  IZZARD, DE MINK , LANGER, STOLTE, DE KOTER, GVARAMADZE, HUSSMANN, LIERMANN & SANA

Job openings: PhD / Postdoc position in Amsterdam

If you are interested in doing your PhD or a Postdoc position in Amsterdam and work with me on massive stars and binarity, apply by December 1st following these instructions:  http://jobregister.aas.org/node/45919

The position is for four years with a highly competitive salary in comparison to the US and most other European countries. The position comes with generous  resources to travel to international schools and conferences.

Excitement: first data from Hubble to search for little siblings of massive stars

Today the first data of my very first own Hubble proposal is coming in. I feel excited as a child.  Especially since I am from the generation that grew up as children with pictures from Hubble.  And now, finally the first data is coming in.  Still unprocessed and it is not yet clear how good the data is, but it looks so pretty already.

Continue reading

New insight in the latest evolutionary stages of the hottest and most luminous stars (new paper accepted for A&A)

The location of the oxygen sequence Wolf-Rayet star DR1 in the Hertzsprung-Russel Diagram.

The most massive stars end are believed to end their lives as Wolf-Rayet stars, very hot and luminous. In this study the spectrum of an extremely hot and bright ionizing Wolf-Rayet star, DR1, is analyzed. The star is embedded in the hottest known HII region known and located in the metal-poor local group galaxy IC 1613.

The star is of the rare oxygen sequence subtype (WO). Only 8 of such stars are known, but they may have been more common in the earlier metal poor universe. Detailed analysis of the spectrum provides evidence that WO stars do not form an evolutionary sequence with carbon rich Wolf-Rayet stars (WC) as was previously thought.

On the nature of WO stars: a quantitative analysis of the WO3 star DR1 in IC 1613? by  Tramper, Grafener, Hartoog, Sana, de Koter, Vink, Ellerbroek, Langer, Garcia, Kaper, and de Mink, A&A 2013 in press.

Globular clusters: Simple after all? (new paper accepted for MNRAS)

Globular clusters are old compact systems containing up to a about a million of stars. How so many stars form in such a small area still remains unclear.  A particular puzzling feature is that effectively all globular cluster appear to harbor more than one stellar population within them.

In this paper we propose that a first generation of massive stars polluted their lower mass sisters while they were still fully convective PMS stars.  While details still need to be worked out, a very attractive feature of this scenario is that it provides a solution for the long standing mass budget problem.

A mass weighted initial mass function illustrates the mass budget problem and how accretion onto PMS stars can solve this.

Early Disc Accretion as the Origin of Abundance Anomalies in Globular Clusters“, by Bastian, Lamers, de Mink, Longmore, Goodwin & Gieles, 2013, MNRAS in press.

Hubble takes first data taken for the LEGUS (Legacy ExtraGalactic UV Survey)