These pages document the progress of OH 1612 MHz maser monitoring programs with the Nançay Radio Telescope carried out since 2008. The goal is to determine the variability properties of all bright OH/IR stars in the Milky Way with galactic coordinates +10 < l < +150 deg and -4 < b < +4 deg. These OH/IR stars have maser peak flux densities larger than ~4 Jy. OH/IR stars show either flux variations with periods of several years and large amplitudes (hereafter L-AGB stars), or vary with small amplitudes without periodicity (hereafter S-pAGB stars).
The sample observed can be grouped according to the scientific goals pursued and the status of the monitoring program
Phase-lag distances of OH/IR stars
Measuring the phase-lag between the variations of the blue and the red-shifted OH maser peak in L-AGB stars yields the linear diameter of the circumstellar shell, in which the maser emission arises. In combination with an angular diameter obtained from mapping the shell with an interferometer a distance can be determined. This technique is used to derive distances to stars which are not accessible with optical astrometry. With some exceptions this monitoring program was completed in 2012.
Long period variable OH/IR stars (L-AGB)
These are red giants evolving on the Asymptotic Giant Branch (AGB) showing evidence for large amplitude long period variations. There are either no periods and amplitudes known yet or they are going to be re-determined.
Small amplitude or non-variable OH/IR stars (S-pAGB)
These stars possibly have left the AGB already, they are post-AGB stars (pAGB). If available at all, the lightcurves were poorly characterized at the beginning of the monitoring program. Systematic observations started in 2013.
OH/IR stars with unknown or less well determined variability properties
For these stars the variability properties are unknown or uncertain. Observations started in 2017.
For each OH/IR star a sample maser spectrum and the lightcurve based on the integrated flux is shown. If available, OH 1667 MHz sample spectra are also shown.
Usage of this material:
Use the main web page adress www.hs.uni-hamburg.de/nrt_monitoring as reference or the most recent publications on Phase-lag distances of OH/IR stars and Small amplitude or non-variable OH/IR stars (S-pAGB).