NOAO >   Observing Info >   Approved Programs >   2009A-0098

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Proposal Information for 2009A-0098


PI: Bettina Posselt, Harvard-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 Mancini Pires, University of Sao Paulo
CoI: Fred Walter, SUNY-Stony Brook University

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.Precisely known 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 the 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 very large (up to 200 pc) due to a crude extinction model. The known steep increase in the extinction in the direction RX J0806.4-4123 stands out among the X-ray thermal NSs. 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 neighboring well- selected stars. Spectral types and luminosity classes of these stars will be obtained by already approved 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.


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