| 1. |
- Olofsson, Hans, 1952, et al.
(författare)
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HD 101584: circumstellar characteristics and evolutionary status
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 623
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Tidskriftsartikel (refereegranskat)abstract
- Context. There is growing evidence that red giant evolution is often affected by an interplay with a nearby companion, in some cases taking the form of a common-envelope evolution. Aims. We have performed a study of the characteristics of the circumstellar environment of the binary object HD 101584, that provides information on a likely evolutionary scenario. Methods. We have obtained and analysed ALMA observations, complemented with observations using APEX, of a large number of molecular lines. An analysis of the spectral energy distribution has also been performed. Results. Emissions from 12 molecular species (not counting isotopologues) have been observed, and most of them mapped with angular resolutions in the range 0 ''.1-0 ''.6. Four circumstellar components are identified: (i) a central compact source of size approximate to 0 ''.15, (ii) an expanding equatorial density enhancement (a flattened density distribution in the plane of the orbit) of size approximate to 3 '', (iii) a bipolar high-velocity outflow (approximate to 150 km s(-1)), and (iv) an hourglass structure. The outflow is directed almost along the line of sight. There is evidence of a second bipolar outflow. The mass of the circumstellar gas is approximate to 0.5 [D/1 kpc](2) M-circle dot, about half of it lies in the equatorial density enhancement. The dust mass is approximate to 0.01 [D/1 kpc](2) M-circle dot, and a substantial fraction of this is in the form of large-sized, up to 1 mm, grains. The estimated kinetic age of the outflow is approximate to 770 [D/1 kpc] yr. The kinetic energy and the scalar momentum of the accelerated gas are estimated to be 7 x 10(45) [D/1 kpc](2) erg and 10(39) [D/1 kpc](2) g cm s(-1), respectively. Conclusions. We provide good evidence that the binary system HD 101584 is in a post-common-envelope-evolution phase, that ended before a stellar merger. Isotope ratios combined with stellar mass estimates suggest that the primary star's evolution was terminated already on the first red giant branch (RGB). Most of the energy required to drive the outflowing gas was probably released when material fell towards the companion.
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| 2. |
- Tafoya, D., et al.
(författare)
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Detection of HCO+ emission toward the planetary nebula K3-35
- 2007
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Ingår i: Astronomical Journal. - 1538-3881 .- 0004-6256. ; 133:2, s. 364-369
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection, for the first time, of HCO+(J = 1 -> 0) emission, as well as marginal CO(J = 1 -> 0) emission, toward the planetary nebula (PN) K3-35 as a result of a molecular survey carried out toward this source. We also report new observations of the previously detected CO( J 2 ! 1) and water maser emission, as well as upper limits for the emission of the SiO, (HCO+)-C-13, HNC, HCN, HC3OH, HC5N, CS, HC3N, (CO)-C-13, CN, and NH3 molecules. From the ratio of CO(J = 2 -> 1) to CO(J = 1 -> 0) emission we have estimated the kinetic temperature of the molecular gas, obtaining a value of similar or equal to 20 K. Using this result we have estimated a molecular mass for the envelope of similar or equal to 0.017M(circle dot) and an HCO+ abundance relative to H-2 of 6 x 10(-7), similar to the abundances found in other PNe. K3-35 is remarkable because it is one of the two PNe reported to exhibit water maser emission, which is present in the central region, as well as at a distance of similar or equal to 5000 AU from the center. The presence of molecular emission provides some clues that could help in understanding the persistence of water molecules in the envelope of K3-35. The HCO+ emission could be arising in dense molecular clumps, which may provide the shielding mechanism that protects water molecules in this source.
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| 3. |
- Vlemmings, Wouter, 1974, et al.
(författare)
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From the ashes: JVLA observations of water fountain nebula candidates show the rebirth of IRAS 18455+0448
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 569, s. Art. no. A92-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The class of water fountain nebulae is thought to represent the stage of the earliest onset of collimated bipolar outflows during the post-asymptotic giant branch phase. They thus play a crucial role in the study of the formation of bipolar planetary nebulae (PNe). To date, 14 water fountain nebulae have been identified. The identification of more sources in this unique stage of stellar evolution will enable us to study the origin of bipolar PNe morphologies in more detail. Aims. Water fountain candidates can be identified based on the often double peaked 22 GHz H2O maser spectrum with a large separation between the maser peaks (often >100 km s-1). However, even a fast bipolar outflow will only have a moderate velocity extent in its maser spectrum when located close to the plane of the sky. In this project we aim to enhance the water fountain sample by identifying objects whose jets are aligned close to the plane of the sky. Methods. We present the results of seven sources observed with the Jansky Very Large Array (JVLA) that were identified as water fountain candidates in an Effelsberg 100≠m telescope survey of 74 AGB and early post-AGB stars. Results. We find that our sample of water fountain candidates displays strong variability in their 22 GHz H2O maser spectra. The JVLA observations show an extended bipolar H2O maser outflow for one source, the OH/IR star IRAS 18455+0448. This source was previously classified as a dying OH/IR star based on the exponential decrease of its 1612 MHz OH maser and the lack of H2O masers. We therefore also re-observed the 1612, 1665, and 1667 MHz OH masers. We confirm that the 1612 MHz masers have not reappeared and find that the1665/1667 MHz masers have decreased in strength by several orders of magnitude during the last decade. The JVLA observations also reveal a striking asymmetry in the red-shifted maser emission of IRAS 19422+3506. Conclusions. The OH/IR star IRAS 18455+0448 is confirmed to be a new addition to the class of water fountain nebulae. Its kinematic age is ~70 yr, but could be lower, depending on the distance and inclination. Previous observations indicate, with significant uncertainty, that IRAS 18455+0448 has a surprisingly low mass compared to available estimates for other water fountain nebulae. The available historical OH maser observations make IRAS 18455+0448 unique for the study of water fountain nebulae and the launch of post-AGB bipolar outflows. The other candidate sources appear high mass-loss OH/IR stars with partly radially beamed H2O masers.
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