Mon. Not. R. Astron. Soc., 485, 1489-1507 (2019/May-2)
External photoevaporation of protoplanetary discs in Cygnus OB2: linking discs to star formation dynamical history.
WINTER A.J., CLARKE C.J. and ROSOTTI G.P.
Abstract (from CDS):
Many stars form in regions of enhanced stellar density, where stellar neighbours can have a strong influence on a protoplanetary disc (PPD) population. In particular, far-ultraviolet (FUV) flux from massive stars drives thermal winds from the outer edge of PPDs, accelerating disc destruction. Here, we present a novel technique for constraining the dynamical history of a star-forming environment using PPD properties in a strongly FUV-irradiated environment. Applying recent models for FUV-induced mass-loss rates to the PPD population of Cygnus OB2, we constrain the time since primordial gas expulsion. This is 0.5 Myr ago if the Shakura & Sunyaev α-viscosity parameter is α = 10–2 (corresponding to a viscous time-scale of τvisc ≃ 0.5 Myr for a disc of scale radius 40 au around a 1 M_☉star). This value of α is effectively an upper limit, since it assumes efficient extinction of FUV photons throughout the embedded phase. This gas expulsion time-scale is consistent with a full dynamical model that fits kinematic and morphological data as well as disc fractions. We suggest Cygnus OB2 was originally composed of distinct massive clumps or filaments, each with a stellar mass ∼104M_☉. Finally we predict that in regions of efficient FUV-induced mass-loss, disc mass Mdisc as a function of stellar host mass mstar follows a power law with Mdisc ∝mstar^β, where β exceeds ∼2.7 - steeper than correlations observed in regions of moderate FUV flux (1 < β < 1.9). This difference offers a promising diagnostic of the influence of external photoevaporation in a given region.
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
accretion, accretion discs - protoplanetary discs - circumstellar matter - stars: kinematics and dynamics - open clusters and associations: individual: Cygnus OB2
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