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2022-03-08 Karina Mauco Coronado and Justyn Campbell-White (ESO)

Speaker: Karina Mauco Coronado

Title: Testing external photoevaporation in the σ-Orionis cluster with spectroscopy and disk mass measurements

Abstract: The evolution of protoplanetary disks is regulated by an interplay of several processes, either internal to the system or related to the environment. Mounting theoretical work shows
that OB stars play a key role in planet formation by externally photoevaporating the protoplanetary disks in massive clusters, where most planets form. Yet observational confirmation lags due to difficulties in detecting externally driven photoevaporative winds.

Since disk evolution can be summarized by the mass accreted onto the star (over the system age) divided by the present-day disk mass, i.e τ_acc ~ M_acc /M_disk , the best way forward
is to combine the power of spectroscopic observations (to get M acc and line prolies) with ALMA (to get the disk masses) to robustly test theoretical predictions. Only external photoevaporation yields τ_acc >> 1 by dramatically reducing M_disk. The primary goal, then, is to characterize the extent of the photoevaporated region in the mid-age (~3-5 Myr) σ-Orionis cluster.

We study a sample of 50 targets located at increasing distances from the central massive OB-system σ-Ori. We found clear evidence of external photoevaporation with τ_acc > 1 for many sources, several of which also showed strong [NII] forbidden emission lines characteristic of highly ionized material. Furthermore, we find a tentative dependence on stellar mass: within 0.5 pc (on projected distance) to σ-Ori, massive stars in our sample (M_* > 0.4 M_sun) have very low disk masses, whereas father out they appear to have well-distributed masses. This is not observed in the less massive stars in our sample, where the dependence of disk mass on projected distance is basically flat.

Speaker: Justyn Campbell-White

Title: Investigating the link between winds/outflows, disk substructures and protoplanets

Abstract: Protoplanetary disks are now routinely observed around young stars but the planets they produce remain elusive to detect. So far, we have only one confirmed detection of protoplanets in the disk of PDS 70, with some tentative results (e.g. AB Aur). Yet disk structures are found almost ubiquitously across the sample of resolved disks. We are investigating the potential relationship between inner disk winds and outflows, as traced by the [OI] 6300 A emission line, and the presence and type of disk substructures. We aim to determine whether or not the various substructures are the direct results of protoplanet formation.

I will present new results from recent and archival observations of PDS 70. In order to investigate such connections between winds, substructures and planets, we turn to the one system where we have certainly detected the planets. We have carefully applied established techniques to the high-resolution spectra to reveal previously unseen forbidden emission profiles. These results suggest a moderate wind originating from the inner disk. We compare these results and measurements of the mass accretion rate and disk properties to those of other weakly accreting young stars and those with transition disks.

I will also highlight our recent result on the empirically determined position of the Li ~6708 A photospheric absorption feature, which is commonly used for radial velocity calibration in young stars and therefore could affect subsequent emission line kinematic measurements.