Abstract
Context. Young stars interact with their accretion disk through their strong magnetosphere. Aims. We aim to investigate the magnetospheric accretion/ejection process in the young stellar system DoAr 44 (V2062 Oph). Methods. We monitored the system over several rotational cycles, combining high-resolution spectropolarimetry at both optical and near-IR wavelengths with long-baseline near-IR inteferometry and multicolor photometry. Results. We derive a rotational period of 2.96 d from the system’s light curve, which is dominated by stellar spots. We fully characterize the central star’s properties from the high signal-to-noise, high-resolution optical spectra we obtained during the campaign. DoAr 44 is a young 1.2 M⊙ star, moderately accreting from its disk (Ṁacc = 6.5 10−9 M⊙ yr−1), and seen at a low inclination (i ≃ 30°). Several optical and near-IR line profiles probing the accretion funnel flows (Hα, Hβ, HeI 1083 nm, Paβ) and the accretion shock (HeI 587.6 nm) are modulated at the stellar rotation period. The most variable line profile is HeI 1083 nm, which exhibits modulated redshifted wings that are a signature of accretion funnel flows, as well as deep blueshifted absorptions indicative of transient outflows. The Zeeman-Doppler analysis suggests the star hosts a mainly dipolar magnetic field, inclined by about 20° onto the spin axis, with an intensity reaching about 800 G at the photosphere, and up to 2 ± 0.8 kG close to the accretion shock. The magnetic field appears strong enough to disrupt the inner disk close to the corotation radius, at a distance of about 4.6 R⋆ (0.043 au), which is consistent with the 5 R⋆ (0.047 au) upper limit we derived for the size of the magnetosphere in our Paper I from long baseline interferometry. Conclusions. DoAr 44 is a pre-transitional disk system, exhibiting a 25–30 au gap in its circumstellar disk, with the inner and outer disks being misaligned. On a scale of 0.1 au or less, our results indicate that the system is steadily accreting from its inner disk through its tilted dipolar magnetosphere. We conclude that in spite of a highly structured disk on the large scale, perhaps the signature of ongoing planetary formation, the magnetospheric accretion process proceeds unimpeded at the star-disk interaction level.
Highlights
T Tauri stars are low-mass pre-main sequence stars at an early stage of their evolution
We monitored the variability of the young stellar object, DoAr 44, over several rotational periods using several complementary observational techniques to investigate the physics of accretion onto the star in a pre-transitional disk system
How does accretion proceed from the outer disk to the inner scales through the gap? Is the star-disk interaction process fed in the same way or differently from what is observed in classical T Tauri stars with continuous circumstellar disks? If the pre-transitional nature of disks is the signature of ongoing planet formation in the disk, does this process affect accretion on any scale?
Summary
T Tauri stars are low-mass pre-main sequence stars at an early stage of their evolution. For a few million years, they accrete. The so-called classical T Tauri stars (cTTSs) have specific properties, such as a rich emission-line spectrum, large photometric variability, and a strong continuum excess flux superimposed onto a late-type photospheric spectrum (Herbig 1962). The unique properties of this class of objects eventually vanish as the disk dissipates on a timescale of a few million years, and the young stellar object transitions to a weak-line T Tauri star (wTTS, Ménard et al 1999). Many of the specific properties of cTTSs are thought to derive from the accretion process
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