Distances to OH/IR stars

• Applicant: Dr. Dieter Engels
• Subject Area: Astrophysics and Astronomy
• Term: from 2012 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 213332327

I apply for a grant supporting a PostDoc position for data reduction and data analysis of radio observations of 20 OH/IR stars, for which distances are to be determined. The observations comprise a monitor program of the 1612 MHz OH maser lines, which is made since 2008 until at least end of 2012 with the Nancay Radio Telescope in France. The aim is the determination of the linear diameter of the circumstellar shell using the phase lag between the light curves of the varying OH maser lines. These observations are supplemented with interferometric measurements, which are obtained since 2010 while the stars pass the maximum of their OH maser flux density variations. These measurements are used to construct maps of the spatial distribution of the maser emission regions, to determine the angular diameter of the emitting shell. The combination of linear and angular diameter gives the distance of the star. The determination of distances to OH/IR stars is of great importance, because they are massive stars (~2-10 solar masses) in the latest evolutionary phase on the Asymptotic Giant Branch (AGB), for which the comparison with stellar evolutionary models is difficult, because of the uncertain distances and hence luminosities. The observational tests of the transition of the AGB to post-AGB evolution are therefore unsatisfactory.

• DFG Programme: Research Grants