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Post Info TOPIC: RW Aurigae
Blobrana


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RE: RW Aurigae
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Title: The disappearing act: A dusty wind eclipsing RW Aur
Author: I. Bozhinova, A. Scholz, G. Costigan, O. Lux, C. J. Davis, T. Ray, N. F. Boardman, K. L. Hay, T. Hewlett, G. Hodosán, B. Morton

RW Aur is a young binary star that experienced a deep dimming in 2010-11 in component A and a second even deeper dimming from summer 2014 to summer 2016. We present new unresolved multi-band photometry during the 2014-16 eclipse, new emission line spectroscopy before and during the dimming, archive infrared photometry between 2014-15, as well as an overview of literature data.
Spectral observations were carried out with the Fibre-fed RObotic Dual-beam Optical Spectrograph on the Liverpool Telescope. Photometric monitoring was done with the Las Cumbres Observatory Global Telescope Network and James Gregory Telescope. Our photometry shows that RW Aur dropped in brightness to R = 12.5 in March 2016. In addition to the long-term dimming trend, RW Aur is variable on time scales as short as hours. The short-term variation is most likely due to an unstable accretion flow. This, combined with the presence of accretion-related emission lines in the spectra suggest that accretion flows in the binary system are at least partially visible during the eclipse.
The equivalent width of [O I] increases by a factor of ten in 2014, coinciding with the dimming event, confirming previous reports. The blue-shifted part of the H alpha profile is suppressed during the eclipse. In combination with the increase in mid-infrared brightness during the eclipse reported in the literature and seen in WISE archival data, and constraints on the geometry of the disk around RW Aur A we arrive at the conclusion that the obscuring screen is part of a wind emanating from the inner disk.

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Blobrana


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Astronomers search for the vanishing star

Astronomers at the University of St Andrews have observed tantalising glimpses of how our own planet may have been born. They did it by watching the longest, deepest eclipse of a young star ever seen. It suggests planets are not born slowly but emerge relatively quickly and violently.
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Blobrana


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Posts: 131433
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RW Aur A
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Title: Another deep dimming of the classical T Tauri star RW Aur A
Author: P. P. Petrov, G. F. Gahm, A. A. Djupvik, E. V. Babina, S. A. Artemenko, K. N. Grankin

Context. RW Aur A is a classical T Tauri star (CTTS) with an unusually rich emission line spectrum. In 2014 the star faded by ~ 3 magnitudes in the V band and went into a long-lasting minimum. In 2010 the star suffered from a similar fading, although less deep. 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 to gather more information on the occulting body and the cause of the phenomenon.
Methods. We collected spectra of the two components of RW Aur. Photometry was made 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 had increased in strength in certain resonance lines, and the profiles and strengths, but not fluxes, of forbidden lines had become 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/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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Blobrana


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Posts: 131433
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RE: RW Aurigae
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Title: Chandra Resolves the T Tauri Binary System RW Aur
Author: Stephen L. Skinner, Manuel Guedel

RW Aur is a multiple T Tauri system consisting of an early-K type primary (A) and a K5 companion (B) at a separation of 1.4 arcsec. RW Aur A drives a bipolar optical jet that is well-characterized optically. We present results of a sensitive Chandra observation whose primary objective was to search for evidence of soft extended X-ray emission along the jet, as has been seen for a few other nearby T Tauri stars. The binary is clearly resolved by Chandra and both stars are detected as X-ray sources. The X-ray spectra of both stars reveal evidence for cool and hot plasma. Suprisingly, the X-ray luminosity of the less-massive secondary is at least twice that of the primary and is variable. The disparity is attributed to the primary whose X-ray luminosity is at the low end of the range for classical T Tauri stars of similar mass based on established correlations. Deconvolved soft-band images show evidence for slight outward elongation of the source structure of RW Aur A along the blueshifted jet axis inside the central arcsecond. In addition, a faint X-ray emission peak is present on the redshifted axis at an offset of 1.2 +- 0.2 arcsec from the star. Deprojected jet speeds determined from previous optical studies are too low to explain this faint emission peak as shock-heated jet plasma. Thus, unless flow speeds in the redshifted jet have been underestimated, other mechanisms such as magnetic jet heating may be involved.

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Blobrana


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Posts: 131433
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RW Aurigae A
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Title: RW Aur A from the X-Wind Point of View: General Features
Authors: Chun-Fan Liu, Hsien Shang

In this paper, the RW Aur A microjet is studied from the point of view of X-wind models. The archived HST/STIS spectra of optical forbidden lines [O I], [S II], and [N II] from RW Aur A, taken in Cycle 8 with seven parallel slits along the jet axis, spaced at 0".07 apart, were analysed. Images, position-velocity diagrams, and line ratios among the species were constructed, and compared with synthetic observations generated by selected solutions of the X-wind. Prominent features arising in a steady state X-wind could be identified within the convolved images, full-widths at half maxima and high-velocity peaks on both of the redshifted and blueshifted jets. The well-known asymmetric velocity profiles of the opposite jets are built into the selected models. We discuss model selections within the existing uncertainties of stellar parameters and inclination angle of the system. In this framework, the mass-loss rates that were inferred to be decreasing along the jet axis in the literature are the results of slowly decreasing excitation conditions and electron density profiles. Despite the apparent asymmetry in terminal velocities, line intensities and mass-loss rates, the average linear momenta from the opposite sides of the jet are actually balanced. These previously hard-to-explain features of the asymmetric RW Aur A jet system now find a different but self-consistent interpretation within the X-wind framework.

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Blobrana


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Posts: 131433
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RE: RW Aurigae
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Title: Reverse Rotation of the Accretion Disk in RW Aur A: Observations and a Physical Model
Authors: D.V. Bisikalo, A.V. Dodin, P.V. Kaygorodov, S.A. Lamzin, E.V. Malogolovets, A.M. Fateeva

Speckle interferometry of the young binary system RW Aur was performed with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences using filters with central wavelengths of 550 nm and 800 nm and pass-band halfwidths of 20 nm and 100 nm, respectively. The angular separation of the binary components was 1.448" ±0.005 and the position angle of the system was 255.9° ±0.3° at the observation epoch (JD 2 454 255.9). We find using published data that these values have been changing with mean rates of +0.002"/yr and +0.02°/yr, respectively, over the past 70 years. This implies that the direction of the orbital motion of the binary system is opposite to the direction of the disk rotation in RW Aur A. We propose a physical model to explain the formation of circumstellar accretion disks rotating in the reverse direction relative to young binary stars surrounded by protoplanetary disks. Our model can explain the characteristic features of the matter flow in RW Aur A: the high accretion rate, small size of the disk around the massive component, and reverse direction of rotation.

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Blobrana


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Title: Magnetic field of young star RW Aur 
Authors: A.V. Dodin, S.A. Lamzin, G.A. Chountonov

Results of longitudinal magnetic field B_z measurements for young star RW Aur A are presented. We found that B_z in the formation region of HeI 5876 line's narrow component varies from -1.47 ± 0.15 kG to +1.10 ± 0.15 kG. Our data are consistent with a stellar rotational period of \simeq 5.6^d and with a model of two hotspots with an opposite polarity of magnetic field and with a difference in a longitude about 180°. The spot with B_z0 is below the midplane. The following upper limits for B_z (at 3\sigma{} level) were found after averaging of all our observations: 180 G for photospheric lines, 220 G and 230 G for formation regions of H_\alpha{} and [OI] 6300 lines respectively. Upper limit 600 G were found in the region where broad components of emission lines form. For two cases out of 11 we observed the field in a formation region of a blue absorption wing of NaI D lines i.e. in an outflow: B_z= - 180 ± 50 G and -810 ± 80 G. Radial velocity of RW Aur's photospheric lines averaged over all our observations is about + 10.5 km/s what is 5.5 km/s less than value derived ten years earlier by Petrov et al. (2001). In this connection, we discuss a possibility that RW Aur is not a binary but a triple system.

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Position (2000): RA 05 07 49.56625 | Dec +30° 24' 05.1774''



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