| 1. |
- Abellan, F.J., et al.
(författare)
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Core-shifts and proper-motion constraints in the S5 polar cap sample at the 15 and 43 GHz bands
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 614
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Tidskriftsartikel (refereegranskat)abstract
- We have studied a complete radio sample of active galactic nuclei with the very-long-baseline-interferometry (VLBI) technique and for the first time successfully obtained high-precision phase-delay astrometry at Q band (43 GHz) from observations acquired in 2010. We have compared our astrometric results with those obtained with the same technique at U band (15 GHz) from data collected in 2000. The differences in source separations among all the source pairs observed in common at the two epochs are compatible at the 1σ level between U and Q bands. With the benefit of quasi-simultaneous U and Q band observations in 2010, we have studied chromatic effects (core-shift) at the radio source cores with three different methods. The magnitudes of the core-shifts are of the same order (about 0.1 mas) for all methods. However, some discrepancies arise in the orientation of the core-shifts determined through the different methods. In some cases these discrepancies are due to insufficient signal for the method used. In others, the discrepancies reflect assumptions of the methods and could be explained by curvatures in the jets and departures from conical jets.
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| 2. |
- Abellán, F. J., et al.
(författare)
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Very Deep inside the SN 1987A Core Ejecta : Molecular Structures Seen in 3D
- 2017
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Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing. - 2041-8205 .- 2041-8213. ; 842:2
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Tidskriftsartikel (refereegranskat)abstract
- Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outward through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks ("nickel heating"). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.
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| 3. |
- Alberdi, A., et al.
(författare)
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The high-frequency compact radio structure of the peculiar quasar 4C 39.25
- 1997
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Ingår i: Astronomy and Astrophysics. - : Springer-Verlag. - 0004-6361 .- 1432-0746. ; 327:2, s. 513-521
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Tidskriftsartikel (refereegranskat)abstract
- We present new high angular resolution images of the compact non-thermal radio source 4C 39.25 obtained from VLBI observations at λ1.3cm, λ7mm, and λ3mm wavelengths. These maps and Gaussian model-fits show that the milli-arcsecond to sub-milliarcsecond structure of 4C 39.25 consists of a complex bent core-jet structure with embedded moving and stationary VLBI components. Facilitated by the small observing beams and high angular resolutions obtained at mm-wavelengths, we measured the relative positions of the jet components with an accuracy of a few hundred micro-arcseconds. This allows the detailed followup of the ongoing merging process of a westward superluminally moving component (b_) with a stationary component a_, located at ~2.9 mas east of the putative core d_. In contrast to the other components of the structure with steeper spectra, the westernmost component d_ exhibits an inverted spectrum peaking between λ7mm and λ3mm, thus further supporting its identification as the VLBI core, self-absorbed at longer wavelengths. From two VLBI maps obtained nearly simultaneously at λ7mm and λ1.3cm, we made the first spectral index map of 4C 39.25 in this wavelength regime. The main characteristics of the spectral index distribution of the jet are pronounced changes of the spectral index between orientations parallel and transverse to the jet axis. Near the merging components a_ and b_ the spectral index steepens with increasing separation from d_. However, in the bridge of emission c_, which connects d_ with a_ and b_, the spectral index gradient has a direction transverse to the jet axis, suggesting a frequency dependent jet curvature and edge-brightening. A brief discussion of this behaviour within current jet models is presented.
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| 4. |
- Alberdi, Antxon, et al.
(författare)
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The jet of the Low Luminosity AGN of M81. Evidence of Precession
- 2013
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 61
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Konferensbidrag (refereegranskat)abstract
- In this contribution, we summarize our main results of a big campaign of global VLBI observations of the AGN in M81 (M81*) phase-referenced to the radio supernova SN 1993J. Thanks to the precise multi-epoch and multi-frequency astrometry, we have determined the normalized core-shift of the relativistic jet of M81* and estimated both the magnetic field and the particle density at the jet base. We have also found evidence of jet precession in M81* coming from the systematic time evolution of the jet orientation correlated with changes in the overall flux density.
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| 5. |
- Arroyo-Torres, B., et al.
(författare)
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VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 566
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The main goal of this research is to determine the angular size and the atmospheric structures of cool giant stars (epsilon Oct, beta Peg, NU Pav, psi Peg, and gamma Hya) and to compare them with hydrostatic stellar model atmospheres, to estimate the fundamental parameters, and to obtain a better understanding of the circumstellar environment. Methods. We conducted spectro-interferometric observations of epsilon Oct, beta Peg, NU Pav, and psi Peg in the near-infrared K band (2.13-2.47 mu m), and gamma Hya (1.9-2.47 mu m) with the VLTI/AMBER instrument at medium spectral resolution (similar to 1500). To obtain the fundamental parameters, we compared our data with hydrostatic atmosphere models (PHOENIX). Results. We estimated the Rosseland angular diameters of epsilon Oct, beta Peg, NU Pav, psi Peg, and gamma Hya to be 11.66 +/- 1.50 mas, 16.87 +/- 1.00 mas, 13.03 +/- 1.75 mas, 6.31 +/- 0.35 mas, and 3.78 +/- 0.65 mas, respectively. Together with distances and bolometric fluxes (obtained from the literature), we estimated radii, effective temperatures, and luminosities of our targets. In the beta Peg visibility, we observed a molecular layer of CO with a size similar to that modeled with PHOENIX. However, there is an additional slope in absorption starting around 2.3 m. This slope is possibly due to a shell of H2O that is not modeled with PHOENIX (the size of the layer increases to about 5% with respect to the near-continuum level). The visibility of psi Peg shows a low increase in the CO bands, compatible with the modeling of the PHOENIX model. The visibility data of epsilon Oct, NU Pav, and gamma Hya show no increase in molecular bands. Conclusions. The spectra and visibilities predicted by the PHOENIX atmospheres agree with the spectra and the visibilities observed in our stars (except for beta Peg). This indicates that the opacity of the molecular bands is adequately included in the model, and the atmospheres of our targets have an extension similar to the modeled atmospheres. The atmosphere of beta Peg is more extended than that predicted by the model. The role of pulsations, if relevant in other cases and unmodeled by PHOENIX, therefore seems negligible for the atmospheric structures of our sample. The targets are located close to the red limits of the evolutionary tracks of the STAREVOL model, corresponding to masses between 1 M-circle dot and 3 M-circle dot. The STAREVOL model fits the position of our stars in the Hertzsprung-Russell (HR) diagram better than the Ekstrom model does. STAREVOL includes thermohaline mixing, unlike the Ekstrom model, and complements the latter for intermediate-mass stars.
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| 6. |
- Arroyo-Torres, B., et al.
(författare)
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VLTI/AMBER Studies of the Atmospheric Structure and Fundamental Parameters of Red Giant and Supergiant Stars
- 2015
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Ingår i: WHY GALAXIES CARE ABOUT AGB STARS III. - : ASTRONOMICAL SOC PACIFIC. - 9781583818794 ; , s. 91-96
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present recent near-IR interferometric studies of red giant and super giant stars, which are aimed at obtaining information on the structure of the atmospheric layers and constraining the fundamental parameters of these objects. The observed visibilities of six red supergiants (RSGs), and also of one of the five red giants observed, indicate large extensions of the molecular layers, as previously observed for Mira stars. These extensions are not predicted by hydrostatic PHOENIX model atmospheres, hydrodynamical (RED) simulations of stellar convection, or self-excited pulsation models. All these models based on parameters of RSGs lead to atmospheric structures that are too compact compared to our observations. We discuss how alternative processes might explain the atmospheric extensions for these objects. As the continuum appears to be largely free of contamination by molecular layers, we can estimate reliable Rosseland angular radii for our stars. Together with distances and bolometric fluxes, we estimate the effective temperatures and luminosities of our targets, locate them in the HR diagram, and compare their positions to recent evolutionary tracks.
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| 7. |
- Arroyo-Torres, B., et al.
(författare)
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VLTI/AMBER studies of the atmospheric structure and fundamental parameters of red giant and supergiant stars
- 2015
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Ingår i: Why Galaxies Care about AGB Stars III: A Closer Look in Space and Time. Proceedings of ASP Conference Series. - 9781583818794 ; 497, s. 91-96
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present recent near-IR interferometric studies of red giant and supergiant stars, which are aimed at obtaining information on the structure of the atmospheric layers and at constraining the fundamental parameters of these objects. The observed visibilities of the red supergiants (RSGs) and also of one red giant indicate large extensions of the molecular layers, as those previously observed for Mira stars. These extensions are not predicted by hydrostatic PHOENIX model atmospheres, hydrodynamical (RHD) simulations of stellar convection, or self-excited pulsation models. All these models based on parameters of RSGs lead to atmospheric structures that are too compact compared to our observations. We discuss how alternative processes might explain the atmospheric extensions for these objects. As the continuum appears to be largely free of contamination by molecular layers, we can estimate reliable angular Rosseland radii of our stars. Together with distances and bolometric fluxes, we estimate the effective temperatures and luminosities of our targets, locate them in the HR diagram, and compare their positions to recent evolutionary tracks.
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| 8. |
- Arroyo-Torres, B., et al.
(författare)
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What causes the large extensions of red supergiant atmospheres? : Comparisons of interferometric observations with 1D hydrostatic, 3D convection, and 1D pulsating model atmospheres
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 575
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Tidskriftsartikel (refereegranskat)abstract
- Aims. This research has two main goals. First, we present the atmospheric structure and the fundamental parameters of three red supergiants (RSGs), increasing the sample of RSGs observed by near-infrared spectro-interferometry. Additionally, we test possible mechanisms that may explain the large observed atmospheric extensions of RSGs. Methods. We carried out spectro-interferometric observations of the.RSGs V602 Car, EID 95687, and EID 183589 in the near-infrared K-band (1.92-2.47 mu m) with the VLTI/AMBER instrument at medium spectral resolution (R similar to 1500). To categorize and comprehend the extended atmospheres, we compared our observational results to predictions by available hydrostatic PHOENIX, available 3D convection, and new 1D self-excited pulsation models of RSGs. Results. Our near-infrared flux spectra of V602 Car, HD 95687, and HD 183589 are well reproduced by the PHOENIX model atmospheres. The continuum visibility values are consistent with a limb-darkened disk as predicted by the PHOENIX models, allowing us to determine the angular diameter and the fundamental parameters of our sources. Nonetheless, in the case of V602 Car and HD 95686, the PHOENIX model visibilities do not predict the large observed extensions of molecular layers, most remarkably in the CO bands. Likewise, the 3D convection models and the ID pulsation models with typical parameters of RSGs lead to compact atmospheric structures as well, which are similar to the structure of the hydrostatic PHOENIX models. They can also not explain the observed decreases in the visibilities and thus the large atmospheric molecular extensions. The full sample of our RSGs indicates increasing observed atmospheric extensions with increasing luminosity and decreasing surface gravity, and no correlation with effective temperature or variability amplitude. Conclusions. The location of our RSG sources in the Hertzsprung-Russell diagram is contirm.ed to be consistent with the red limits of recent evolutionary tracks. The observed extensions of the atmospheric layers of our sample of RSGs are comparable to those of Mira stars. This phenomenon is not predicted by any of the considered model atmospheres including as 311) convection and new 1D pulsation models of.RSGs. This confirms that neither convection nor pulsation alone can levitate the molecular atmospheres of.RSGs. Our observed correlation of atmospheric extension with luminosity supports a scenario of radiative acceleration on Doppler-shifted molecular lines.
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| 9. |
- Azulay, R., et al.
(författare)
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Binary stars in loose associations: AB Dor B and HD 160934
- 2014
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Ingår i: Proceedings of the 11th Scientific Meeting of the Spanish Astronomical Society - Highlights of Spanish Astrophysics VIII, SEA 2014. ; , s. 447-452
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Konferensbidrag (refereegranskat)abstract
- Precise determination of dynamical masses of pre-main- sequence (PMS) stars is necessary to calibrate PMS stellar evolutionary models, whose predictions are in disagreement with measurements for masses below 1.2 Msun. Binary stars in young, nearby loose associations are particularly good candidates, since all members share a common age. We present phase-reference VLBI observations of two binary systems that belong to the AB Doradus moving, HD 160934 A/c and AB Dor Ba/Bb, from which we have measured both the relative and absolute orbital motion. Accordingly, we obtained precise estimates of the mass of the components of these binaries (ranging from 0.25 to 0.7 Msun). We will show how these measurements provide precise calibration points for testing PMS models of low-mass stars.
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| 10. |
- Azulay, R., et al.
(författare)
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Binary stars in moving groups
- 2014
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Ingår i: Proceedings of Science. - 1824-8039. ; 2014
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Konferensbidrag (refereegranskat)abstract
- Precise determination of dynamical masses of pre-main-sequence (PMS) stars is necessary to calibrate PMS stellar evolutionary models, whose predictions are in disagreement with measurements for masses below 1.2M⊙. Binary stars in young, nearby loose associations are particularly good candidates, since all members share a common age. We present phase-reference EVN observations of the binary system HD 160934 A/c, that belongs to the ABDoradus moving group, from which we have measured both the relative and absolute orbital motion. Accordingly, we obtained precise estimates of the mass of the components of this binary. Also we report on other PMS binary systems as EKDra and AB DorB. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
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