15 February 2009
World’s Most Precise Stellar Spectrograph Gets Polarised Vision
The very successful HARPS spectrograph, attached to ESO’s 3.6-metre telescope at La Silla, Chile, has just been enhanced with a new capability: the most precise polarimeter in the world. The polarimeter was designed by Frans Snik from Utrecht University, the Netherlands. The instrument was shipped to Chile in May 2009, and it is now officially ready for use by the astronomical community. The HARPS polarimeter enables observations of magnetic fields in stars of various masses, temperatures and ages. It is also important for the discovery of new exoplanets: due to its extremely high sensitivity, it will allow astronomers to distinguish between a true planet and a similar signal from a stellar spot.
For the full press release in English see
www.eso.org.
Een Nederlandse versie van het persbericht is te vinden op
www.astronomie.nl.
21 December 2009
Utrecht University and
SRON
Netherlands Institute for Space Research have signed an agreement on
cooperation in the fields of astrophysics and Earth and planetary
science. The institutes have been cooperating for years, but now
tangible commitments have been made regarding joint research
programms. SRON will also contribute to the education activities of
the Faculty of Science of Utrecht University.
SRON press release
7 December 2009
ISAS, Japan, have found for the first time a nebula of ultra high energy electrons around a magnetar. A magnetar is a neutron star (or pulsar) with an ultra-high magnetic field, hundred times higher than ordinary pulsars.
Rapidly rotating neutron stars pour out a constant stream of highly energetic electrons, which form a nebula around the pulsar. These so-called pulsar wind nebulae are ubiquitous in the galaxy and can be observed with radio and X-ray telescopes. The brightness of these nebulae relates directly to the energy being lost by the pulsar itself,
which depends on how fast the pulsar rotates and the strength of its magnetic field.
So far now pulsar wind nebula was seen around magnetars. This is puzzling, because
the magnetars have very high magnetic fields, although they seem to rotate slowly. This
slow rotation should not be important, because magnetars slow down quickly. So in the recent past they should have been rapidly rotating, producing very strong pulsar wind nebulae.
With the new discovery Vink and Bamba open the way to investigate the early history of magnetars. Do magnetars produce less powerful winds during their early
evolution, or are they just born slowly spinning?
The study has been published in the
Astrophysical Journal Letters of December 2009.
A dutch version of the press release can be found at astronomie.nl
21 November 2009
An international team of astronomers, lead by Selma de Mink, PhD student at Utrecht University, have marked binary stars as the main suspects for contaminating globular clusters. About 150 of such globular clusters orbit the Milky Way, the Galaxy we live in. They consist of hundred thousands of stars, held together by their mutual gravitational interaction. These stars are among the oldest in the Milky Way, and a large fraction of them have a peculiar chemical composition: They contain much more nitrogen, sodium and aluminium than expected, but they are not massive enough to produce these elements themselves. For that reason astronomers assume that an earlier generation of more massive stars have contaminated the stars with these elements.
Up to now two sorts of stars were suspected for the contamination: red supergiants, or rapidly rotating stars. However, there was not enough evidence for either suspects. Red supergiant don't produce enough sodium, and rapidly rotating stars are too rare to explain the large scale contamination.
In a paper published in Astronomy & Astrophysics the team lead by Selma de Mink argue now that the main suspects are massive binary stars. These can efficiently shed gas with the peculiar chemical composition found in globular cluster stars. Since the density of stars in the centers of globular cluster is very high, that stars regularly encounter each other and even collide. It is therefore likely that almost all massives stars during their lives interact with other stars, forming a binary system, in which the massive star loses its sodium rich outer layers, thereby contaminating its surroundings.
Information in dutch can be found at www.astronomie.nl.
3 November 2009
Dr. Jorit Leenaarts, who received his PhD from Utrecht University in 2007, has received an prestiguous Veni Fellowship from NWO, the Netherlands Science Foundation. He received this fellowship for his project entitled: "The formation of spectral lines in the solar chromosphere".
Further information (in dutch) can be found at www.astronomie.nl.
25 June 2009
Thanks to a unique "ballistic study" that combines data from ESO's Very Large Telescope and NASA's Chandra X-ray Observatory, astronomers lead by Eveline Helder and Jacco Vink from Utrecht University have now solved a long-standing mystery of the Milky Way’s particle accelerators. They show in a paper published in Science that cosmic rays from our galaxy are very efficiently accelerated in the remnants of exploded stars.
For more information see here the original press release issued by ESO.
25 March 2009
In a study authored by Selma de Mink, a PhD student from Utrecht, a surprisingly simple explanation is presented for why the close stellar binary system M33-X7 has a black hole that is much more massive than explained by standard models. De Mink has investigated the mixing processes in such fast rotating, very compact binary systems and concluded from that that the binary system does not expand, but on the contrary remain small, and, therefore, do not result in mass accretion. The results are published in Astronomy & Astrophysics.
The scientific publication can be found here. For more information see the original press release (in dutch).
www.eso.org