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==> In this proposal, more time is being requested for DLAMBERT.DLL002
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This proposal is a continuation of another one already performed by ISO. It
deals with the atmospheres of cool dwarf stars whose chemical compositions are
unique clues to the early evolution of the Galaxy. Contemporary analyses of
spectra depend on model stellar atmospheres computed usually from a set of
simplifying assumptions, and only few attempts have been made to derive
atmospheric structures as directly as possible from observations, i.e. to
construct empirical atmospheres. This study is motivated by the power of ISO
photometry to measure the temperature in the upper photospheric layers: the
opacity in the infrared is provided by the free-free transitions of the H- ion
and scales as wavelength-squared. Hence, a large range of depths is sampled
by the flux between 3 to 120 micron. Previous studies of optical line and
continuous spectra suggest that theoretical model atmospheres do not yet
adequately represent the real atmospheres of cool dwarf stars.
The cool metal-poor star Gmb1830 (HD103095) was observed in 3.6, 4.85, 7.3,
11, 16, and 60 micron by our group with ISOPHOT (proposal DLL002), providing
very good data for the shorter wavelength filters, and showing that it was
possible to detect this very faint source in the longest wavelength filter.
We propose now to complement these data by observing the metal-rich star
Epsilon Eri (HD22049, with similar stellar parameters than Gmb1830) in these
six filters plus the 25 and 90 micron filters, for making a direct comparison
of the IR flux distribution in both objects and having a detailed photometric
information of Epsilon Eri. Most of these observations were already included
in the former proposal, but it was not possible to carry them out within the
allocated observing time due to the errors contained in the cookbook for
computing exposure times, and to the change of sensitivity of the ISOPHOT
detectors once in orbit compared to their pre-flight values.