Investigating the magnetospheric accretion process in the young pre-transitional disk system DoAr 44 (V2062 Oph)

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2020

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European Southern Observatory

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item.page.issne

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Instituto de Fisica y Astronomia

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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 ( ˙Macc = 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 (H , H , HeI 1083 nm, Pa ) 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 800G 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.

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STARS: PRE-MAIN SEQUENCE, STARS: VARIABLES: T TAURI, HERBIG AE/BE, STARS: MAGNETIC FIELD, STARS: FORMATION, ACCRETION, ACCRETION DISKS

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