- ID:
- ivo://CDS.VizieR/J/A+A/558/A82
- Title:
- V4332 Sgr optical spectropolarimetry
- Short Name:
- J/A+A/558/A82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The eruption of V4332 Sgr was observed in 1994 and was classified as belonging to red transients of the V838 Mon type. Optical spectroscopy obtained a few years after the eruption showed a faint M-type stellar spectrum underlying numerous molecular and atomic emission features. We suggested that the central object in V4332 Sgr is now hidden in a dusty disc and that the photospheric spectrum of this object observed in the optical results from scattering of the radiation of the central star on dust grains in the circumstellar matter. The optical continuum of the object, as resulting from scattering on dust grains, is expected to be polarized. The emission features on the contrary - as observed directly from circumstellar regions, are expected to be unpolarized. We present and analyse spectropolarimetric observations of V4332 Sgr in the optical region. The continuum is linearly polarized with a typical degree of 16.6%. A clear depolarization is observed in the spectral regions where emission features contribute significantly to the observed flux. The only prominent exception is the CaI emission line at 6573{AA}, which is polarized in 21%. The results of our spectropolarimetric observations are in accord with the proposed geometry of the system and the advocated nature of the observed optical spectrum of V4332 Sgr - the continuum is not seen directly but due to scattering on dust within the disk and polar outflow, while most of the gas emission comes from the polar outflow excited by the radiation field of the central source. Additionally, the observed polarization patterns suggest a stratification of the outflow.
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- ID:
- ivo://CDS.VizieR/J/A+A/587/A42
- Title:
- weak G-band stars abundances
- Short Name:
- J/A+A/587/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Weak G-band (wGb) stars are a very peculiar class of red giants; they are almost devoided of carbon and often present mild lithium enrichment. Despite their very puzzling abundance patterns, very few detailed spectroscopic studies existed up to a few years ago, which prevented any clear understanding of the wGb phenomenon. We recently proposed the first consistent analysis of published data for a sample of 28 wGb stars and were able to identify them as descendants of early A-type to late B-type stars, although we were not able to conclude on their evolutionary status or the origin of their peculiar abundance pattern. Using new high-resolution spectra, we present the study of a new sample of wGb stars with the aim of homogeneously deriving their fundamental parameters and surface abundances for a selected set of chemical species that we use to improve our insight on this peculiar class of objects. We obtained high-resolution and high signal-to-noise spectra for 19 wGb stars in the southern and northern hemisphere that we used to perform consistent spectral synthesis to derive their fundamental parameters and metallicities, as well as the spectroscopic abundances for Li, C, ^12^C/^13^C, N, O, Na, Sr, and Ba. We also computed dedicated stellar evolution models that we used to determine the masses and to investigate the evolutionary status and chemical history of the stars in our sample. We confirm that the wGb stars are stars with initial masses in the range 3.2 to 4.2M_{sun}_. We suggest that a large fraction could be mildly evolved stars on the subgiant branch currently undergoing the first dredge-up, while a smaller number of stars are more probably in the core He burning phase at the clump. After analysing their abundance pattern, we confirm their strong nitrogen enrichment anti-correlated with large carbon depletion, characteristic of material fully processed through the CNO cycle to an extent not known in evolved intermediate-mass stars in the field and in open clusters. However, we demonstrate here that such a pattern is very unlikely owing to self-enrichment. In the light of the current observational constraints, no solid self-consistent pollution scenario can be presented either, leaving the wGb puzzle largely unsolved.
- ID:
- ivo://CDS.VizieR/J/PASP/107/617
- Title:
- YSOs and candidate protostars catalog.
- Short Name:
- J/PASP/107/617
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled a catalog of candidate protostars from the major astronomical journals up to the end of 1993. The Belchman-Ichikawa color criterion was used as the main test of an author's claim that a source should be deemed a candidate protostar. Names, positions (1950 and 2000), LSR velocities, information on whether there are associated outflows, and references are provided. This catalog is meant to update an earlier compilation by Wynn-Williams (1982).
