| 1. |
- Dermine, Tyl, et al.
(författare)
-
Barium stars revisited
- 2010
-
Ingår i: International Conference on Binaries - In Celebration of Ron Webbink's 65th Birthday. - : AIP. - 9780735408692 ; 1314, s. 61-62
-
Konferensbidrag (refereegranskat)abstract
- The barium overabundances observed at the surface of barium stars originate from accretion long ago from the wind of a companion AGB star. However, this scenario cannot explain their high eccentricities and short orbital periods that have remained a mystery for decades. We investigate how kicks imparted to the white-dwarf at its birth or the presence of a circumbinary disk can solve this problem.
|
|
| 2. |
- Kluska, J., et al.
(författare)
-
VLTI images of circumbinary disks around evolved stars
- 2020
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11446
-
Konferensbidrag (refereegranskat)abstract
- The new generation of VLTI instruments (GRAVITY, MATISSE) aims to produce routinely interferometric images to uncover the morphological complexity of different objects at high angular resolution. Image reconstruction is, however, not a fully automated process. Here we focus on a specific science case, namely the complex circumbinary environments of a subset of evolved binaries, for which interferometric imaging provides the spatial resolution required to resolve the immediate circumbinary environment. Indeed, many binaries where the main star is in the post-asymptotic giant branch (post-AGB) phase are surrounded by circumbinary disks. Those disks were first inferred from the infrared excess produced by dust. Snapshot interferometric observations in the infrared confirmed disk-like morphology and revealed high spatial complexity of the emission that the use of geometrical models could not recover without being strongly biased. Arguably, the most convincing proof of the disk-like shape of the circumbinary environment came from the first interferometric image of such a system (IRAS08544-4431) using the PIONIER instrument at the VLTI. This image was obtained using the SPARCO image reconstruction approach that enables to subtract a model of a component of the image and reconstruct an image of its environment only. In the case of IRAS08544-4431, the model involved a binary and the image of the remaining signal revealed several unexpected features. Then, a second image revealed a different but also complex circumstellar morphology around HD101584 that was well studied by ALMA. To exploit the VLTI imaging capability to understand these targets, we started a large programme at the VLTI to image post-AGB binary systems using both PIONIER and GRAVITY instruments.
|
|
| 3. |
- Tout, Christopher A., et al.
(författare)
-
HV2112, a Thorne-A >> ytkow object or a super asymptotic giant branch star
- 2014
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 1745-3933 .- 1745-3925. ; 445:1, s. 36-40
-
Tidskriftsartikel (refereegranskat)abstract
- The very bright red star HV2112 in the Small Magellanic Cloud could be a massive Thorne-A >> ytkow object (TA >> O), a supergiant-like star with a degenerate neutron core. With a luminosity of over 10(5) L-aS (TM), it could also be a super asymptotic giant branch (SAGB) star, a star with an oxygen/neon core supported by electron degeneracy and undergoing thermal pulses with third dredge up. Both TA >> Os and SAGB stars are expected to be rare. Abundances of heavy elements in HV2112's atmosphere, as observed to date, do not allow us to distinguish between the two possibilities based on the latest models. Molybdenum and rubidium can be enhanced by both the irp-process in a TA >> O or by the s-process in SAGB stars. Lithium can be generated by hot bottom burning at the base of the convective envelope in either. HV2112's enhanced calcium could thus be the key determinant. Neither SAGB stars nor TA >> Os are known to be able to synthesize their own calcium but it may be possible to produce it in the final stages of the process that forms a TA >> O, when the degenerate electron core of a giant star is tidally disrupted by a neutron star. Hence, it is more likely, on a fine balance, that HV2112 is indeed a genuine TA >> O.
|
|
