we propose to use the iso sws01 to observe a sample of early-type b stars to understand recently discovered discrepancies from the predictions of lte and non-lte model atmospheres. specifically, we will be searching for ir continuum excesses which trace the temperature excesses that appear to exist in the extreme outer atmospheres of some of these stars. additional information regarding the photospheric temperature structure will also be obtained from the strengths of hydrogen and helium lines. the observational evidence that there is a problem with current models comes from euve, iras and derived nebular emission measures. our research group has discoved that the b2 ii star epsilon cma is 30 times more luminous in the hydrogen lyman continuum than is predicted by model atmospheres, making it the brightest stellar object in the sky at 500 a. this data in conjunction with iras 12 and 25 micron fluxes imply a temperature excess of about 2000 k over that predicted by models. our target list includes stars which show indirect euv evidence for a temperature excess or show temperature related iras excesses. iso observations will allow us to assess the importance of non-lte effects, line blanketting and backward heating by x-ray emission. the results will affect basic assumptions in the next generation of stellar model atmospheres.
Instrument
SWS01
Temporal Coverage
1996-07-27T06:07:11Z/1997-03-27T06:36:13Z
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.
European Space Agency, CASSINELLI et al., 1999, 'IR DIAGNOSTICS OF TEMPERATURE STRUCTURE IN THE ATMOSPHERES OF EARLY B STARS', 1.0, European Space Agency, https://doi.org/10.5270/esa-7xhcfaf
