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- Petrov, P. P., et al.
(författare)
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Another deep dimming of the classical T Tauri star RW Aurigae A
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 577
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Tidskriftsartikel (refereegranskat)abstract
- Context. RWAur A is a classical T Tauri star (CTTS) with an unusually rich emission line spectrum. In 2014 the star faded by similar to 3 mag in the V band and went into a long-lasting minimum. In 2010 the star underwent a similar fading, although less pronounced. These events in RW Aur A are very unusual among the CTTS, and have been attributed to occultations by passing dust clouds. Aims. We want to find out if any spectral changes took place after the last fading of RW Aur A with the intention of gathering more information on the occulting body and the cause of the phenomenon. Methods. We collected spectra of the two components of RW Aur. The photometry was performed before and during the minimum. Results. The overall spectral signatures reflecting emission from accretion flows from disk to star did not change after the fading. However, blue-shifted absorption components related to the stellar wind increased in strength in certain resonance lines, and the profiles and strengths but not the fluxes of forbidden lines became drastically different. Conclusions. The extinction through the obscuring cloud is grey indicating the presence of large dust grains. At the same time, there are no traces of related absorbing gas. The cloud occults the star and the interior part of the stellar wind, but not the wind or jet further out. The dimming in 2014 was not accompanied by changes in the accretion flows at the stellar surface. There is evidence that the structure and velocity pattern of the stellar wind did change significantly. The dimmings could be related to passing condensations in a tidally disrupted disk, as proposed earlier, but we also speculate that large dust grains have been stirred up from the inclined disk into the line of sight through the interaction with an enhanced wind.
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| 2. |
- Petrov, P. P., et al.
(författare)
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Dynamics of wind and the dusty environments in the accreting T Tauri stars RY Tauri and SU Aurigae
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 483:1, s. 132-146
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Tidskriftsartikel (refereegranskat)abstract
- Classical T Tauri stars with ages of less than 10 Myr possess accretion discs. Magnetohydrodynamic processes at the boundary between the disc and the stellar magnetosphere control the accretion and ejections gas flows. We carried out a long series of simultaneous spectroscopic and photometric observations of the classical T Tauri stars, RY Tauri and SU Aurigae, with the aim to quantify the accretion and outflow dynamics at time-scales from days to years. It is shown that dust in the disc wind is the main source of photometric variability of these stars. In RY Tau, we observed a new effect: during events of enhanced outflow, the circumstellar extinction becomes lower. The characteristic time of changes in outflow velocity and stellar brightness indicates that the obscuring dust is near the star. The outflow activity in both stars is changing on a time-scale of years. Periods of quiescence in the variability of the H alpha profile were observed during the 2015-2016 period in RY Tau and during the 2016-2017 period in SU Aur. We interpret these findings in the framework of the magnetospheric accretion model, and we discuss how the global stellar magnetic field can influence the long-term variations of the outflow activity.
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| 3. |
- Gahm, Gösta F., 1942-, et al.
(författare)
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Expanding shells around young clusters - S 171/Be 59
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 663
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Tidskriftsartikel (refereegranskat)abstract
- Context. Some HII regions that surround young stellar clusters are bordered by molecular shells that appear to expand at a rate inconsistent with our current model simulations. In this study we focus on the dynamics of Sharpless 171 (including NGC 7822), which surrounds the cluster Berkeley 59. Aims. We aim to compare the velocity pattern over the molecular shell with the mean radial velocity of the cluster for estimates of the expansion velocities of different shell structures, and to match the observed properties with model simulations. Methods. Optical spectra of 27 stars located in Berkeley 59 were collected at the Nordic Optical Telescope, and a number of molecular structures scattered over the entire region were mapped in 13CO(1- 0) at Onsala Space Observatory. Results. We obtained radial velocities and MK classes for the clustera's stars. At least four of the O stars are found to be spectroscopic binaries, in addition to one triplet system. From these data we obtain the mean radial velocity of the cluster. From the 13CO spectra we identify three shell structures, expanding relative to the cluster at moderate velocity (4 km s- 1), high velocity (12 km s- 1), and in between. The high-velocity cloudlets extend over a larger radius and are less massive than the low-velocity cloudlets. We performed a model simulation to understand the evolution of this complex. Conclusions. Our simulation of the Sharpless 171 complex and Berkeley 59 cluster demonstrates that the individual components can be explained as a shell driven by stellar winds from the massive cluster members. However, our relatively simple model produces a single component. Modelling of the propagation of shell fragments through a uniform interstellar medium demonstrates that dense cloudlets detached from the shell are decelerated less efficiently than the shell itself. They can reach greater distances and retain higher velocities than the shell.
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| 5. |
- Grinin, V. P., et al.
(författare)
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Modelling UX Ori star eclipses based on spectral observations with the Nordic Optical Telescope - I. RR Tau
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 524:3, s. 4047-4061
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Tidskriftsartikel (refereegranskat)abstract
- Based on observations obtained with the Nordic Optical Telescope (NOT) we investigate the spectral variability of the Herbig Ae star RR Tau. This star belongs to the UX Ori family, characterized by very deep fadings caused by the screening of the star with opaque fragments (clouds) of the protoplanetary discs. At the moments of such minima one observes strong spectral variability due to the fact that the dust cloud occults, for an observer, not only the star but also a part of the region where the emission spectrum originates. We calculated a series of obscuration models to interpret the observed variability of the H a line parameters. We consider two main obscuration scenarios: (1) the dust screen rises vertically above the circumstellar disc, and (2) the screen intersects the line-of-sight moving azimuthally with the disc. In both cases, the model of the emission region consists of a compact magnetosphere and a magnetocentrifugal disc wind. Comparison with observations shows that the first scenario explains well the variability of the radiation flux, the equivalent width, as well as the asymmetry of the H a line during eclipses, while the second scenario explains them only partly. This permits us to suggest that in the case of RR Tau, the main causes of the eclipses are either a structured disc wind, or the charged dust lifted along the field lines of the poloidal component of the magnetic field of the circumstellar disc.
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| 9. |
- de Val-Borro, M., et al.
(författare)
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Modelling circumbinary gas flows in close T Tauri binaries star
- 2011
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 413:4, s. 2679-2688
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Tidskriftsartikel (refereegranskat)abstract
- Young close binaries open central gaps in the surrounding circumbinary accretion disc, but the stellar components may still gain mass from gas crossing through the gap. It is not well understood how this process operates and how the stellar components are affected by such inflows. Our main goal is to investigate how gas accretion takes place and evolves in close T Tauri binary systems. In particular, we model the accretion flows around two close T Tauri binaries, V4046 Sgr and DQ Tau, both showing periodic changes in emission lines, although their orbital characteristics are very different. In order to derive the density and velocity maps of the circumbinary material, we employ two-dimensional hydrodynamic simulations with a locally isothermal equation of state. The flow patterns become quasi-stable after a few orbits in the frame corotating with the system. Gas flows across the circumbinary gap through the corotating Lagrangian points, and local circumstellar discs develop around both components. Spiral density patterns develop in the circumbinary disc that transport angular momentum efficiently. Mass is preferentially channelled towards the primary and its circumstellar disc is more massive than the disc around the secondary. We also compare the derived density distribution to observed line profile variability. The line profile variability tracing the gas flows in the central cavity shows clear similarities with the corresponding observed line profile variability in V4046 Sgr, but only when the local circumstellar disc emission was excluded. Closer to the stars normal magnetospheric accretion may dominate, while further out the dynamic accretion process outlined here dominates. Periodic changes in the accretion rates on to the stars can explain the outbursts of line emission observed in eccentric systems such as DQ Tau.
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