Analysis of colour and polarimetric variability of RW Aur A in 2010–2018

Abstract

Results of U BV RIJHKLM photometry and V RI polarimetry of a young star RW Aur A observed during unprecedented long and deep (up to ∆V ≈ 5 mag) dimming events in 2010-11 and 2014-18 are presented. The polarization degree p of RW Aur A at this period has reached 30 per cent in the I band. As in the case of UX Ori type stars (UXORs), the so-called 'bluing effect' in the colour-magnitude V versus V − R c , V − I c diagrams of the star and a strong anticorrelation between p and brightness were observed. But the duration and the amplitude of the eclipses as well as the value and orientation of polarization vector in our case differ significantly from that of UXORs. We concluded that the dimmings of RW Aur A occurred due to eclipses of the star and inner regions of its disc by the axisymmetric dust structure located above the disc and created by the disc wind. Taking into account both scattering and absorption of stellar light by the circumstellar dust, we explain some features of the light curve and the polarization degree -magnitude dependence. We found that near the period of minimal brightness mass-loss rate of the dusty wind was > 10 −9 M ⊙ yr −1 .

Exploring the dimming event of RW Aurigae A through multi-epoch VLT/X-shooter spectroscopy

“…We find good agreement with the observations for a max ∼ 150 µm, Q tot = Q abs + 0.12Q sca (green curve in the bottom panel of Fig. 7); the effective albedo is ∼ 0.7 in the visual range, consistent with the polarimetry results analysed most recently by Dodin et al (2019). If the scattering is less efficient, a max needs to be larger.…”

“…The first hypothesis is a dust-laden wind (e.g. Petrov et al 2015;Dodin et al 2019). Facchini et al (2016) (and earlier France et al 2014 have detected narrow absorption lines at ∼ −60 km s −1 in the optical Na and K doublets, and in the N i, Si ii, and Si iii UV lines.…”

“…This indicates that while the star has been occulted, most of the circumstellar material has not, and thus constrains the location of the occulting body. Recent models by Dodin et al (2019) account for the increase in the polarisation fraction due to scattering by a dust layer in a disc wind. This study agrees with our results and locates the dust screen close to the star.…”

The Weakening Outburst of the Young Eruptive Star V582 Aur

“…The light curves and the color evolution of V582 Aur show striking similarity to those of an other well known young stellar object, RW Aur A (Dodin et al 2019, and the references therein). The physical reason for the behavior of RW Aur A is still debated.…”

Classical T Tauri stars: accretion, wind, dust

“…The authors assumed that decreases in brightness in the visible range were caused by the appearance of hot dust in the disk wind of RW Aur A at a temperature of about 1000 K. A similar interpretation was previously proposed by Grinin et al (2009) to explain the deep minimum of the T Tauri star V1184 Tau, where the decrease in brightness in the optical range with constant or slightly increased emission in the K band was caused by an increase in the disk thickness near the dust evaporation zone as a result of amplification of the disk wind. Dodin et al (2019) recorded a significant increase in the linear polarization of RW Aur A during deep minima in 2010-2011 and 2014-2018. The value and orientation of the polarization vector indicated that the star and inner regions of the accretion disk were shielded by the axial symmetric dusty disk wind.…”