| 1. |
- Roy, Alan, et al.
(författare)
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VLBI at APEX: First Fringes
- 2012
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Ingår i: Proceedings of Science. - 1824-8039. ; 2012-October
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Konferensbidrag (refereegranskat)
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| 2. |
- Desmurs, J. F., et al.
(författare)
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28 SiO j=1-0, v=1, 2 & 3 maser emission from AGB stars
- 2012
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Ingår i: Proceedings of Science. - 1824-8039. ; 2012-October
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Konferensbidrag (refereegranskat)abstract
- The v=1, 2 J=1–0 and v=1 J=2–1 are intense SiO masers, often mapped in AGB stars. Their distribution displays ring-like structures in the regions close to the star. The distribution of the v=1, 2 J=1–0 masers are similar, but the spots are rarely coincident. The v=1 J=2–1 maser ar-rises, however, from a well separated region. It has been argued that this difference can only be explained by models including overlap of two IR lines of SiO and H2O. The v=3 J=1–0 line is not expected to be affected by any line overlap, and its spot structure should be that predicted by the standard models. Our first results on the relative positions of the three lines are surprising but yet consistent with current models including line overlap.
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| 3. |
- Desmurs, J. F., et al.
(författare)
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First VLBA observations of 28SiO J=1-0, v=3 maser emission from AGB stars
- 2014
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Ingår i: Proceedings of Science. - 1824-8039. ; 2014
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Konferensbidrag (refereegranskat)abstract
- The v=1 & v=2 J=1-0 (43 GHz), and v=1 J=2-1 (86 GHz) SiO masers are intense in AGB stars. They have been mapped using VLBI displaying spots ring-like distributions. The rings of the v=1, v=2 J=1-0 masers are similar, but the spots are rarely coincident, while the v=1 J=2-1 maser arises from a well separated region farther out. The v=3 J=1-0 line is not directly affected by any line overlap and its spot structure and position, relative to the other lines, is a good test to the standard pumping models. We present simultaneous single dish and VLBI observations of the v=1, v=2, and v=3 J=1-0 maser transitions of 28SiO in several AGB stars and compare them to model predictions. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
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| 4. |
- Desmurs, J. F., et al.
(författare)
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Preliminary results on SiO v=3 J=1−0 maser emission from AGB stars
- 2012
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Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 8:5287, s. 252-253
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Konferensbidrag (refereegranskat)abstract
- We present the results of SiO maser observations at 43 GHz toward two AGB stars using the VLBA. Our preliminary results on the relative positions of the different J=1–0 SiO masers (v=1,2 and 3) indicate that the current ideas on SiO maser pumping could be wrong at some fundamental level. A deep revision of the SiO pumping models could be necessary.
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| 5. |
- Desmurs, J. F., et al.
(författare)
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SiO masers from AGB stars in the vibrationally excited v=1, v=2, and v=3 states
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 565
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Tidskriftsartikel (refereegranskat)abstract
- Context. The v = 1 and v = 2 J = 1-0 (43 GHz), and v = 1 J = 2-1 (86 GHz) SiO masers are intense in asymptotic giant branch (AGB) stars and have been mapped using very long baseline interferometry (VLBI) showing ring-like distributions. Those of the v = 1, v = 2 J = 1-0 masers are similar, but the spots are rarely coincident, while the v = 1 J = 2-1 maser arises from a well-separated region farther out. These relative locations can be explained by models tools that include the overlap of two IR lines of SiO and H2O. The v = 3 J = 1-0 line is not directly affected by any line overlap and its spot structure and position, relative to the other lines, is a good test to the standard pumping models. Aims. The aim of this project are to gain insight into the properties and the general theoretical considerations of the different SiO masers that can help to understand them. Methods. We present single-dish and simultaneous VLBI observations of the v = 1, v = 2, and v = 3 J = 1-0 maser transitions of (SiO)-Si-28 in several AGB stars. The results are compared to the predictions of radiative models of SiO masers that both include and not include the effect of IR line overlap. Results. The spatial distribution of the SiO maser emission in the v = 3 J = 1-0 transition from AGB stars is systematically composed of a series of spots that occupy a ring-like structure (as often found in SiO masers). The overall ring structure is extremely similar to that found in the other 43 GHz transitions and is very different from the structure of the v = 1 J = 2-1 maser. The positions of the individual spots of the different 43 GHz lines are, however, very rarely coincident, which in general is separated by about 0.3 AU (between 1 and 5 mas). These results are very difficult to reconcile with standard pumping models, which predict that the masers of rotational transitions within a given vibrational state require very similar excitation conditions (since the levels are placed practically at the same energy from the ground), while the transitions of different vibrational states (which are separated by an energy of 1800 K) should appear in different positions. However, models including line overlap tend to predict v = 1, v = 2, v = 3 J = 1-0 population inversion to occur under very similar conditions, while the requirements for v = 1 J = 2-1 appear clearly different, and are compatible with the observational results.
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| 6. |
- Desmurs, J.F., et al.
(författare)
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SiO v=3 J=1-0 maser emission from AGB stars
- 2013
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Ingår i: Proceedings of Science, 11th European VLBI Network Symposium & Users Meeting.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Geralt bij de Vaate, J., et al.
(författare)
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Wide bandwidth integrated 1-4 GHz feed development for VLBI and SKA
- 2012
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Ingår i: Proceedings of Science. - 1824-8039. ; 2012-October
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Konferensbidrag (refereegranskat)abstract
- Wide-band single pixel feeds such as the wide-band Eleven feed developed in Europe through Onsala Space Observatory/Chalmers are rapidly increasing in maturity. Compared to the traditional octave bandwidth feeds, wide bandwidth feeds, such as the Eleven feed, will create the possibility of significantly larger instantaneous frequency coverage observations with existing radio telescopes, such as those used in the VLBI networks, and for future radio telescopes, such as the Square Kilometre Array. This Project is supported by RadioNet3, Developments In VLBI Astronomy (DIVA).
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| 8. |
- Castro-Carrizo, A., et al.
(författare)
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Mapping the 12CO J = 1-0 and J = 2-1 emission in AGB and early post-AGB circumstellar envelopes. I. The COSAS program, first sample
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 523:4, s. A59-
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Tidskriftsartikel (refereegranskat)abstract
- We present COSAS (CO Survey of late AGB Stars), a project to map and analyze the 12CO J = 1−0 and J = 2−1 line emission in a representative sample of circumstellar envelopes around AGB and post-AGB stars. The survey was undertaken with the aim of investigating small- and large-scale morphological and kinematical properties of the molecular environment surrounding stars in the late AGB and early post-AGB phases. For this, COSAS combines the high sensitivity and spatial resolving power of the IRAM Plateau de Bure interferometer with the better capability of the IRAM 30 m telescope to map extended emission. The global sample encompasses 45 stars selected to span a range in chemical type, variability type, evolutionary state, and initial mass. COSAS provides means to quantify variations in the mass-loss rates, assess morphological and kinematical features, and to investigate the appearance of fast aspherical winds in the early post-AGB phase. This paper, which is the first of a series of COSAS papers, presents the results from the analyses of a first sample of 16 selected sources. The envelopes around late AGB stars are found to be mostly spherical, often mingled with features such as concentric arcs (R Cas and TX Cam), a broken spiral density pattern (TX Cam), molecular patches testifying to aspherical mass-loss (WX Psc, IK Tau, V Cyg, and S Cep), and also with well-defined axisymmetric morphologies and kinematical patterns (X Her and RX Boo). The sources span a wide range of angular sizes, from relatively compact (CRL 2362, OH 104.9+2.4 and CRL 2477) to very large (χ Cyg and TX Cam) envelopes, sometimes partially obscured by self-absorption features, which particularly for IK Tau and χ Cyg testifies to the emergence of aspherical winds in the innermost circumstellar regions. Strong axial structures with more or less complex morphologies are detected in four early post-AGB stars (IRAS 20028+3910, IRAS 23321+6545, IRAS 19475+3119 and IRAS 21282+5050) of the sub-sample.
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| 9. |
- Hodgson, J., et al.
(författare)
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The latest results from the global mm VLBI array
- 2012
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Ingår i: Proceedings of Science. - 1824-8039. ; 2012-October
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Konferensbidrag (refereegranskat)abstract
- The Global mm-VLBI Array (GMVA) is the highest angular resolution imaging interferometer currently available as a common user facility. It is capable of angular resolutions on the order of 40 microarcseconds. Currently 14 stations in the United States and Europe participate in global 3 mm VLBI observations. The GMVA is used for continuum and spectroscopic imaging, probing the central regions of active galaxies and the origin of jets as these regions are typically not observable at longer wavelengths due to synchrotron self-absorption. In early 2012, fringes were detected to the three stations of the Korean VLBI Network (KVN), opening the possibility of extending the baseline coverage of the VLBI array to the East. In these proceedings, we will present recent images from a monitoring program of gamma-ray blazars using the GMVA, including the sources 3C454.3 and 0235+164, and an update of its current status and abilities.
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| 10. |
- Lindqvist, Michael, 1960, et al.
(författare)
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Present status and technical directions of the EVN
- 2014
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Ingår i: Proceedings of Science. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- The European VLBI Network has evolved significantly during recent years. This has been made possible by the addition of new antennas, the introduction of the Mark 5 recording system and the emergence of high bandwidth optical fibre networks, the SFXC software correlator, and most recently, by the upgrade to digital backends at the stations. Here we describe the present status of the array and outline some of the planned future technical directions. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
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