Temperature Structures of Embedded Disks: Young Disks in Taurus Are Warm

Abstract

The chemical composition of gas and ice in disks around young stars sets the bulk composition of planets. In contrast to protoplanetary disks (Class II), young disks that are still embedded in their natal envelope (Class 0 and I) are predicted to be too warm for CO to freeze out, as has been confirmed observationally for L1527 IRS. To establish whether young disks are generally warmer than their more evolved counterparts, we observed five young (Class 0/I and I) disks in Taurus with the Atacama Large Millimeter/submillimeter Array, targeting2,1 , and CH 3 OH 5 K −4 K transitions at 0 48×0 31 resolution. The different freeze-out temperatures of these species allow us to derive a global temperature structure. C 17 O and H 2 CO are detected in all disks, with no signs of CO freeze-out in the inner ∼100 au and a CO abundance close to ∼10 −4 . The H 2 CO emission originates in the surface layers of the two edge-on disks, as witnessed by the especially beautiful V-shaped emission pattern in IRAS04302+2247. HDO and CH 3 OH are not detected, with column density upper limits more than 100 times lower than for hot cores. Young disks are thus found to be warmer than more evolved protoplanetary disks around solar analogs, with no CO freeze-out (or only in the outermost part of 100 au disks) or processing. However, they are not as warm as hot cores or disks around outbursting sources and therefore do not have a large gas-phase reservoir of complex molecules.

The impact of pre-main sequence stellar evolution on mid-plane snowline locations and C/O in planet forming discs

“…These criteria are consistent with our constraints of an early formation in the outer disc for HR8799b and the cooling of disc midplane as a result of stellar evolution. On the other hand if young discs are warm, as suggested by modelling (Harsono et al 2015, and our Figure 3) and by recent ALMA observations of embedded class I discs in Taurus (van 't Hoff et al 2020), this may act to inhibit gravitational instability at early stages.…”

Exploring the link between star and planet formation with Ariel

“…The distribution of H 2 CO suggests that the bulk of the observed H 2 CO in the disc is formed via gas-phase reactions. This is indicated both by the o/p ratios measured in TW Hya (Terwisscha van Scheltinga et al, 2021) and by the vertical distribution of molecular emission in the edge-on disc of IRAS 04302 where H 2 CO mostly arises from an intermediate disc layer, the so called molecular layer (Podio et al, 2020b;van't Hoff et al, 2020). However, for IRAS 04302 H 2 CO emission is detected also in the outer disc midplane, where molecules are expected to be frozen onto the dust grain icy mantles.…”

“…Fedele et al, 2013;Guilloteau et al, 2013Guilloteau et al, , 2016Öberg et al, 2010Podio et al, 2013), as well as a few S-bearing species, e.g. CS, H 2 CS, H 2 S (e.g., Phuong et al, 2018;Teague et al, 2018;Le Gal et al, 2019;Codella et al, 2020;Garufi et al, 2020b,a;Loomis et al, 2020;van't Hoff et al, 2020). The content of complex organic molecules (COMs), on the contrary, is still only poorly known because of their lower gas-phase abundances (< 10 −8 with respect to the abundance of atomic hydrogen).…”

Exploring the link between star and planet formation with Ariel

“…[51,[219][220][221][222][223]), as well as a few S-bearing species, e.g. CS, H 2 CS, H 2 S (e.g., [224][225][226][227][228][229][230][231]). The content of complex organic molecules (COMs), on the contrary, is still only poorly known because of their lower gas-phase abundances (< 10 −8 with respect to the abundance of atomic hydrogen).…”

“…The distribution of H 2 CO suggests that the bulk of the observed H 2 CO in the disc is formed via gas-phase reactions. This is indicated both by the o/p ratios measured in TW Hya [ 245 ] and by the vertical distribution of molecular emission in the edge-on disc of IRAS 04302 where H 2 CO mostly arises from an intermediate disc layer, the so called molecular layer [ 231 , 244 ]. However, for IRAS 04302 H 2 CO emission is detected also in the outer disc midplane, where molecules are expected to be frozen onto the dust grain icy mantles.…”