Distances to OH/IR stars
Zusammenfassung der Projektergebnisse
Determining distances of optically highly obscured giant stars using the phase-lag technique is unrivaled, at least beyond distances of 2 kiloparsec. We obtained new determinations of the linear diameter of their OH maser shells from 20 stars with the aid of a up to nine years long monitoring program. For half of the stars new angular diameters are currently available from an ongoing imaging program with the radio interferometers eMERLIN and eVLA. The distances obtained so far have an uncertainty ≈20%. Compared to a previous similar program carried out in the early 1980s the current program allows to address systematic errors, which are due to the only partly justified assumption of perfect spherical symmetry and of geometrical thin OH maser shells. Due to the time-consuming observing program and the complex analysis it is anticipated that the distances derived from this program will be the best available for long time to come. They are instrumental for obtaining luminosities of these stars, serving as benchmarks for evolutionary models of giant stars. The program suffered from a slower than anticipated progress in obtaining the interferometric maps. A major reason was the slow commissioning of the interferometers, which underwent a major upgrade in ~2010 and beyond. The detailed analysis of the data OH 26.5+0.6 revealed that the OH maser shells need to be modelled for each star individually, to interpret the phase lags from different parts of the velocity profile and to derive the extent of the shell from the distribution of the OH maser emission in the maps.
Projektbezogene Publikationen (Auswahl)
- 2012, 1612 MHz OH maser monitoring with the Nancay Radio Telescope, In: Cosmic masers - From OH to HO, lAU Symposium 287, p. 254-255
Engels D., Gerard E., Hallet N.
(Siehe online unter https://doi.org/10.1017/S1743921312007077) - 2014, Phase-lag distance of OH 83.4-0.9 from eMERLIN and NRT observations. 12th European VLBI Network Symposium and Users Meeting
Etoka S., Engels D., Gerard E., Richards A.M.S.
- 2015, Phase-lag distances of OH masing AGD stars, In: Why Galaxies Care About AGB Stars III, Eds. F. Kerschbaum, R. F. Wing, and J. Hron. ASP Conference Series, Vol. 497, p.473
Engels D., Etoka S., Gerard E., Richards A.M.S.
- 2017, Distances of Stars by mean of the Phaselag Method, In: Astrophysical Masers: Unlocking the Mysteries of the Universe, Eds. A. Tarchi, M.J. Reid and P. Castangia, lAU Symposium 336, 2017
Etoka S., Engels D., Gerard E., Richards A.M.S.
(Siehe online unter https://doi.org/10.1017/S1743921317009826)
