we propose to obtain grating scans over the full iso range of the remarkable emission line star mwc349. from radio imaging and spectroscopy in the near ir it is known that this star is surrounded by a dense disk; hydrogen recombination line masers are also located on this disk. the most plausible model for mwc349 is that of a massive star on the zams, which has left its parental molecular cloud, but is still surrounded by the accretion disk from which it formed. mwc349 is thus a unique laboratory to study the accretion disks around massive stars. the iso data will enable us to model this disk in much more detail than currently possible. first, they will define the sed in the critical wavelength region around 50 micron, where the contributions from the disk and the free-free emission from the wind merge. the sed in this region can be used to model the overall physical parameters of the disk (dust mass, temperature range, accretion rate, luminosity, dimensions) as well as the properties of the region where the wind is accelerated. from the results of ground-based observations in the mid-ir we expect that silicate features from the dust in the disk and numerous fine structure lines will be detected in the grating spectra. analysis of these lines will allow us to infer the temperature and range of densities in the ionized region, and to determine the ionizing spectrum independently from near-ir data, which suffer from a large amount of extinction. lower excitation lines probe the photodissociation region at the transition from the dense disk to the ionized wind, whose characteristics remain largely unknown to date. rotational lines from h_2 and hd will be detectable, if the disk has an average density of at least 10^7 cm^-3; this value has actually been inferred for the ionized skin of the disk. if densities are indeed as high as suggested by near-ir spectroscopy, namely 10^10 cm^-3, the hydrogen lines at 28, 17 and 12 micron will even be detectable by fp scans. we will therefore perform such scans, in order to study the disk rotation law.
Instrument
LWS01
Temporal Coverage
1996-11-08T21:34:21Z/1996-11-08T23:09:39Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
