1,949 research outputs found
A Spectroscopic and Photometric Study of the Metal-Poor, Pulsating, Post-AGB Binary HD 46703
The metal-poor post-AGB star HD 46703 is shown to be a single-line
spectroscopic binary with a period of 600 days, a high velocity of -94 km/s,
and an orbital eccentricity of 0.3. Light curve studies show that it also
pulsates with a period of 29 days. High-resolution, high signal-to-noise
spectra were used for a new abundance study. The atmospheric model determined
is T(eff) = 6250 K, log(g) = 1.0, V(t) = 3.0 km/s, and a metal abundance of
[M/H] = -1.5. A low carbon abundance and lack of s-process element enhancement
indicate that the star has not experienced third dredge-up on the AGB. The
sulfur and zinc abundances are high compared with iron, and the chemical
abundances show a clear anti-correlation with condensation temperature. The
abundance depletion pattern is similar to that seen in other post-AGB binaries,
and, like them, is attributed to the chemical fractionation of refractory
elements onto dust stored in a circumbinary disk and the re-accretion of
volatiles in the stellar atmosphere. The infrared excess is small but the
excess energy distribution is very similar to what can expected from a disk. HD
46703 joins the growing list of depleted, post-AGB stars which are likely
surrounded by a dusty and stable circumbinary disk.Comment: Machine readable files not include
HD172481: a super lithium-rich metal-deficient post-AGB binary with a red AGB companion
We present in this paper a study on the peculiar supergiant HD172481. Its
spectral type (F2Ia), high galactic latitude (b=-10.37), circumstellar dust,
high radial velocity and moderate metal deficiency ([Fe/H]=-0.55) confirm the
post-AGB character of this object. A detailed chemical analysis shows slight
but real s-process overabundances, however no CNO-enhancement was detected.
Furthermore, the spectral energy distribution and the TiO bands in the red part
of the spectrum reveal a red luminous companion. The luminosity ratio of the
hot F type component and this cool M type companion L(F)/L(M) is derived for a
reddening of E(B-V)=0.44 (L(F)/L(M)=1.8) and indicates that the companion must
also be strongly evolved and probably evolving along the AGB. Neither our
photometric data-set, nor our radial velocity monitoring show evidence for
orbital variability which may indicate that the period is too large for direct
binary interaction. Most interestingly, a strong lithium resonance line is
detected, which yields an abundance of log(Li)=3.6. Several explanations for
this large lithium content are explored.Comment: 11 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
Monitoring evolved stars for binarity with the HERMES spectrograph
Binarity is often invoked to explain peculiarities that can not be explained
by the standard theory of stellar evolution. Detecting orbital motion via the
Doppler effect is the best method to test binarity when direct imaging is not
possible. However, when the orbital period exceeds the duration of a typical
observing run, monitoring often becomes problematic. Placing a high-throughput
spectrograph on a small semi- robotic telescope allowed us to carry out a
radial-velocity survey of various types of peculiar evolved stars. In this
review we highlight some findings after the first four years of observations.
Thus, we detect eccentric binaries among hot subdwarfs, barium, S stars, and
post- AGB stars with disks, which are not predicted by the standard binary
interaction theory. In disk objects, in addition, we find signs of the on-
going mass transfer to the companion, and an intriguing line splitting, which
we attribute to the scattered light of the primary.Comment: To appear in the proceedings of the conference "Setting a new
standard in the analysis of binary stars", A. Tkachenko (ed.), European
Astron. Soc. Publ. Se
IRAS\,11472-0800: an extremely depleted pulsating binary post-AGB star
We focus here on one particular and poorly studied object, IRAS11472-0800. It
is a highly evolved post-Asymptotic Giant Branch (post-AGB) star of spectral
type F, with a large infrared excess produced by thermal emission of
circumstellar dust. We deploy a multi-wavelength study which includes the
analyses of optical and IR spectra as well as a variability study based on
photometric and spectroscopic time-series. The spectral energy distribution
(SED) properties as well as the highly processed silicate N-band emission show
that the dust in IRAS11472-0800 is likely trapped in a stable disc. The
energetics of the SED and the colour variability show that our viewing angle is
close to edge-on and that the optical flux is dominated by scattered light.
With photospheric abundances of [Fe/H] = -2.7 and [Sc/H]=-4.2, we discovered
that IRAS11472-0800 is one of the most chemically-depleted objects known to
date. Moreover, IRAS11472-0800 is a pulsating star with a period of 31.16 days
and a peak-to-peak amplitude of 0.6 mag in V. The radial velocity variability
is strongly influenced by the pulsations, but the significant cycle-to-cycle
variability is systematic on a longer time scale, which we interpret as
evidence for binary motion. We conclude that IRAS11472-0800 is a pulsating
binary star surrounded by a circumbinary disc. The line-of-sight towards the
object lies close the the orbital plane making that the optical light is
dominated by scattered light. IRAS11472-0800 is one of the most
chemically-depleted objects known so far and links the dusty RV\,Tauri stars to
the non-pulsating class of strongly depleted objects.Comment: 12 pages, 14 figures Accepted for publication in A&A Main Journa
A study of the s-process in the carbon-rich post-AGB stars IRAS06530-0213 and IRAS08143-4406 on the basis of VLT-UVES spectra
In an effort to extend the still limited sample of s-process enriched
post-AGB stars, high-resolution, high signal-to-noise VLT+UVES spectra of the
optical counterparts of the infrared sources IRAS06530-0213 and IRAS08143-4406
were analysed. The objects are moderately metal deficient by [Fe/H]=-0.5 and
-0.4 respectively, carbon-rich and, above all, heavily s-process enhanced with
a [ls/Fe] of 1.8 and 1.5 respectively. Especially the spectrum of
IRAS06530-0213 is dominated by transitions of s-process species, and therefore
resembling the spectrum of IRAS05341+0852, the most s-process enriched object
known so far. The two objects are chemically very similar to the 21micron
objects discussed in Van Winckel & Reyniers (2000). A homogeneous comparison
with the results of these objects reveals that the relation between the third
dredge-up efficiency and the neutron nucleosynthesis efficiency found for the
21micron objects, is further strengthened. On the other hand, a detailed
comparison with the predictions of the latest AGB models indicates that the
observed spread in nucleosynthesis efficiency is certainly intrinsic, and
proves that different C-13 pockets are needed for stars with comparable mass
and metallicity to explain their abundances.Comment: 14 pages, 10 figures, accepted for publication in A&A; Table 4 is
available at ftp://ftp.ster.kuleuven.ac.be/dist/maarten/filescds/ pending
upload to CD
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