NOAO >   Observing Info >   Approved Programs >   2009B-0170

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Proposal Information for 2009B-0170


PI: Bettina Posselt, Havard-Smithsonian Center for Astrophysics, bposselt@cfa.harvard.edu
Address: High-Energy, 60 Garden Street, Cambridge, MA 02138, USA

CoI: Christian Motch, Observatoire Astronomique de Strasbourg
CoI: Patrick Slane, CfA
CoI: Frank Haberl, Max-Planck-Institut fuer extraterrestrische Physik
CoI: Adriana M. Pires, Univeristy of Sao Paulo

Title: Constraining the radius of the neutron star RX J0806.4-4123

Abstract: Radio-quiet X-ray thermal neutron stars (NSs) are the only NS class allowing a direct view onto the star's surface. Good distances are mandatory for checking the validity of NS atmosphere models and to determine radii (important to constrain the equation of state). In previous work we estimated distances of these NSs from well-known (low) X-ray absorption together with a 3D-ISM model. The resulting distance of RX J0806.4-4123, 240 pc marks this object as a quark star candidate with very small radius. However, the uncertainty is huge (up to 200 pc) due to a crude extinction model. A detailed extinction model will allow to determine a very well-constrained distance. We want to establish the distance to RX J0806.4-4123 via the reddening of neighbouring well- selected stars. Spectral types and luminosity classes of these stars will be obtained by on-going VLT observations. Together with the proposed photometry we expect to derive a distance with 20% accuracy or better, thus allowing to exclude either a quark star or a stiff equation of state. \bf This previously approved proposal is re-submitted due to bad weather conditions during recent observations (see page 6).


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