Ionizing photons from very hot stars

24 Sep

Ylva’ Götberg’s paper has been accepted for publication in the journal Astronomy and Astrophysics.  Find a link to the forthcoming paper here. She computed the first tailor made models for the structure, evolution and atmospheres of the very hot stars that can from in binary systems when a star loses its envelope by interaction with a companion.  She shows that these stars emit most of their light as ionizing photons, at wavelengths so short that none of the currently existing astronomical facilities can actually detect them.  This first paper explores how metallicity affects these stars, i.e. are stripped stars in our own galaxy different from stripped stars that formed in the early days of the universe when there were less metals available?   Stay tuned for more. Further papers to come out soon.

Mathieu Renzo on stellar winds and the final fate of stars

24 Aug

All stars lose mass, in part in the form of a stellar wind. (Even our sun does so, which most known for the beautiful aurora that can be seen) How strong these winds are is not known very well. Measurements are affected by uncertainties such as how smooth or how clumped such winds are. Mathieu Renzo undertook a very careful study to investigate how the various prescriptions for stellar winds and their uncertainties affect the final mass and structure of stars. His paper is accepted for publication and can be obtained here.

Lezing: De wonderlijke levens van de helderste sterren in ons universum

24 Oct

Tijdens deze voordracht laten sterrenkundigen Selma de Mink (UvA) en Samayra Straal (ASTRON/UvA) je kennismaken met de exotische levens van zware sterren. Ze vertellen over het dramatische einde van het leven van dit soort sterren en hoe ze hun leven na de explosie voortzetten. In het bijzonder gaan ze in op hoe ze radiostraling en de pas waargenomen zwaartekrachtsgolven gebruiken om meer te weten te komen over dit soort sterren.

Datum en tijd: woensdag 26 oktober 2016, 20:00 – 21:30
Plaats: SPUI25, Spui 25-27, 1012 XM Amsterdam
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ALMA time: “The Extreme UV of massive stars through ALMA’s eyes”

20 Oct

Extreme Ultraviolet (UV) light is blocked by our atmosphere (fortunately for us, because they are dangerous for our skin). Even from space it is very hard to measure. At the moment there is no single satellite telescope that can give information about this part of the spectrum.  Bad news for astronomers, because they really want to know how many of such ionizing photons are emitted by massive stars. Such photons play a very important role  in heating their surrounding clouds where low mass stars and their planets are still forming. These photons are also believed to have played a very big role early in the history of our Universe. They ionized the intergalactic H during the Cosmic Epoch of reionization. This made our universe transparent and ended the so-called Cosmic Dark Ages.

For this study we use a trick proposed by Scoville & Murchikova (2013) that allows to indirectly measure the extreme UV using ALMA. ALMA is an array of antennas in the dry desert of Chile (image), which can observe the sky in (sub)millimeter wavelengths, i.e. in wavelengths that are too red to see with the naked eye.   Instead of measuring the ionizing photons directly, we will measure the effect they have on the surrounding H and He gas by  measuring the “high-order recombination lines” that ALMA is sensitive too.

This proposal ALMA 2016.1.01015.S (PI De Mink) has been awarded 6.6 hours. The project design and analysis is lead by E. Muchicova (Caltech) under supervision of N. Scoville (Caltech). Image credit:  Credit ALMA/NAOJ/NRAO J. Hills

A hundred massive binaries in the Tarantula nebula: a universal phenomenon

15 Oct

screen-shot-2016-10-15-at-2-39-09-pmMassive stars are often found in close binary system, two stars that orbit each other.  So far the data samples analyzed were still relatively small and limited to stars in our own galaxy.

New results from a large extensive survey of the TMBM (Tarantula Massive Binary Monitoring) survey (PI H. Sana) contain data for over a hundred massive hot binary stars, the largest homogeneous sample to date and the first of this size outside our own galaxy.   In the first paper, Leonardo Almeida, presents the survey and first results.  The  They show that the properties are very similar as found in earlier studies. These results point at binarity being a universal phenomenon for massive stars.

The paper “The Tarantula Massive Binary Monitoring: I. Observational campaign and OB-type spectroscopic binaries” by  L.A. Almeida, H. Sana, W. Taylor, R. Barbá, A. Bonanos, P. Crowther, A. Damineli, A. de Koter, S.E. de Mink, C.J. Evans, M. Gieles, N.J. Grin, V. Hénault-Brunet, N. Langer, D. Lennon, S. Lockwood, J. Maíz Apellániz, A.F.J. Moffat, C. Neijssel, C. Norman, O.H. Ramírez-Agudelo, N.D. Richardson, A. Schootemeijer, T. Shenar, I. Soszyński, F. Tramper & J.S. Vink is available on the arxiv.