there appears to be several similarities between two classes of chemically-peculiar stars: the fe-deficient post-agb stars and the barium and tc-poor s stars. they are binaries with non-zero eccentricities and periods ranging from one to several years, with one component having evolved off the agb. current scenarios for the evolution of low-mass binary systems indicate that barium and s systems may be the descendants of the post-agb binaries. moreover, dust seems to play a key role in these systems. as far as fe-poor post-agb stars are concerned, their photospheric abundance peculiarities resemble the elemental depletions in the gas phase of the ism. it became thus clear that their low fe contents are not primordial. they were instead acquired in the course of the binary evolution by a process of re-accretion of circumstellar gas, depleted in refractory elements which remained trapped in the non-accreted dust phase. as far as barium and s stars are concerned, the two closest systems exhibit complex lightcurves which share some similarities with those of binary post-agb stars. in particular, the observed light variations suggest that dust may be scattering the red-giant light at some orbital phases and obscuring it at other phases. the eclipsing-like behaviour has been attributed to dust as well, since the present white dwarf companion is too cool and too faint to contribute significantly to the system light. existing ir data already suggest that a moderate amount of dust is present in these barium and s systems. by deriving the energy distribution of the dust with unprecedented detail and accuracy using isophot and sws, this program aims at a better understanding of the properties of the dust (size, chemical type, location in the system and mass loss history) present in these two classes of chemically-peculiar binary stars. it should thus also shed some light on the exact relationships between these classes.
Instrument
PHT03 , PHT37 , PHT38 , PHT39
Temporal Coverage
1996-08-26T22:12:04Z/1996-12-15T12:15:07Z
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, JORISSEN et al., 1999, 'DUST IN BINARIES CONTAINING CHEMICALLY PECULIAR GIANTS: LINKING BARIUM AND S STARS TO POST-AGB STARS', 1.0, European Space Agency, https://doi.org/10.5270/esa-w74s0md
