3 research outputs found
Multi-wavelength interferometry of evolved stars using VLTI and VLBA
We report on our project of coordinated VLTI/VLBA observations of the
atmospheres and circumstellar environments of evolved stars. We illustrate in
general the potential of interferometric measurements to study stellar
atmospheres and envelopes, and demonstrate in particular the advantages of a
coordinated multi-wavelength approach including near/mid-infrared as well as
radio interferometry. We have so far made use of VLTI observations of the near-
and mid-infrared stellar sizes and of concurrent VLBA observations of the SiO
maser emission. To date, this project includes studies of the Mira stars S Ori
and RR Aql as well as of the supergiant AH Sco. These sources all show strong
silicate emission features in their mid-infrared spectra. In addition, they
each have relatively strong SiO maser emission. The results from our first
epochs of S Ori measurements have recently been published and the main results
are reviewed here. The S Ori maser ring is found to lie at a mean distance of
about 2 stellar radii, a result that is virtually free of the usual uncertainty
inherent in comparing observations of variable stars widely separated in time
and stellar phase. We discuss the status of our more recent S Ori, RR Aql, and
AH Sco observations, and present an outlook on the continuation of our project.Comment: 9 pages, to appear in the proceedings of the ESO workshop "The Power
of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation
VLTI Instrumentation", ESO Astrophysics Symposi
Mid-infrared interferometric observations of four oxygen-rich Mira variables
We present an investigation of the dust formation process in the atmospheres of the oxygen-rich AGB stars RR Aql, S Ori, GX Mon and R Cnc using spatially and spectrally resolved mid-infrared interferometric observations. We successfully compared multi epoch observations to a radiative transfer model of the dust shells, where the central stellar intensity profile is described by a series of dust-free dynamic model atmospheres based on self-excited pulsation models. We show that the Al2O3 shells have inner radii between 1.9 and 2.2 stellar photospheric radii, and that the silicate shells have inner radii between 4.1 and 4.6 stellar photospheric radii. The best-fit photospheric angular diameters are consistent with independent estimates. The model dust temperatures at the inner radii of 1.9–2.2 stellar radii and 4.1–4.6 stellar radii are consistent with dust condensation temperatures of Al2O3 and silicates, respectively