Imaging the water snowline in protostellar envelopes

Imaging the water snowline in protostellar envelopes

Author:

van 't Hoff

Abstract:

Determining the locations of the major snowlines in protostellar environments is crucial to fully understand the planet formation process and its outcome. Despite being located far enough from the central star to be spatially resolved with ALMA, the CO snowline remains difficult to detect directly in protoplanetary disks. Instead, its location can be derived from N2H+ emission, when chemical effects like photodissociation of CO and N2 are taken into account. The water snowline is even harder to observe than that for CO, because in disks it is located only a few AU from the protostar, and from the ground only the less abundant isotopologue H182O can be observed. Therefore, using an indirect chemical tracer, as done for CO, may be the best way to locate the water snowline. A good candidate tracer is HCO+, which is expected to be particularly abundant when its main destructor, H2O, is frozen out. Comparison of H182O and H13CO+ emission toward the envelope of the Class 0 protostar IRAS2A shows that the emission from both molecules is spatially anticorrelated, providing a proof of concept that H13CO+ can indeed be used to trace the water snowline in systems where it cannot be imaged directly.

The maximum mass of planetary embryos formed in core-accretion models

The maximum mass of planetary embryos formed in core-accretion models 

Author:

Alibert

Abstract:

We compute the maximum mass a growing planetary embryo can reach depending on the size of accreted planetesimals or pebbles, to infer the possibility of growing the cores of giant planets, and giant planets themselves. We compute the internal structure of the gas envelope of planetary embryos, to determine the core mass that is necessary to bind an envelope large enough to destroy planetesimals or pebbles while they are gravitationally captured. We also consider the effect of the advection wind originating from the protoplanetary disk, following the results of Ormel et al. (2015). We show that for low mass pebbles, once the planetary embryo is larger than ~1 Mearth, the envelope is large enough to destroy and vaporize pebbles completely before they can reach the core. The material constituting pebbles is therefore released in the planetary envelope, and later on dispersed in the protoplanetary disk, if the advection wind is strong enough. As a consequence the growth of the planetary embryo is stopped at a mass that is so small that Kelvin-Helmholtz accretion cannot lead to the accretion of significant amounts of gas. For larger planetesimals, a similar process occurs but at much larger mass, of the order of ten Earth masses, and is followed by rapid accretion of gas. If the effect of the advection is as efficient as described in Ormel al. (2015), the combined effect of the vaporization of accreted solids in the envelope of forming planetary embryos, and of this advection wind, prevents the growth of the planets at masses smaller or similar to the Earth mass in the case of formation by pebble accretion, up to a distance of the order of 10 AU. In the case of formation by accretion of large mass planetesimals, the growth of the planetary core is limited at masses ~10 Mearth but further growth of the planet can proceed by gas accretion.

Formation of Close-in SuperEarths by Giant Impacts

Formation of Close-in Super-Earths by Giant Impacts: Effects of Initial Eccentricities and Inclinations of Protoplanets

Authors:
Matsumoto et al

Abstract:
Recent observations have revealed the eccentricity and inclination distributions of close-in super-Earths. These distributions have the potential to constrain their formation processes. In the in-situ formation scenario, the eccentricities and inclinations of planets are determined by gravitational scattering and collisions between protoplanets on the giant impact stage. We investigate the effect of the initial eccentricities and inclinations of protoplanets on the formation of close-in super-Earths. We perform N-body simulations of protoplanets in gas-free disks, changing the initial eccentricities and inclinations systematically. We find that while the eccentricities of protoplanets are well relaxed through their evolution, the inclinations are not. When the initial inclinations are small, they are not generally pumped up since scattering is less effective and collisions occur immediately after orbital crossing. On the other hand, when the initial inclinations are large, they tend to be kept large since collisional damping is less effective. Not only the resultant inclinations of planets, but also their number, eccentricities, angular momentum deficit, and orbital separations are affected by the initial inclinations of protoplanets.

Imaging Protoplanets in Transition Disks

Imaging protoplanets: observing transition disks with non-redundant masking

Authors:

Sallum et al

Abstract:

Transition disks, protoplanetary disks with inner clearings, are promising objects in which to directly image forming planets. The high contrast imaging technique of non-redundant masking is well posed to detect planetary mass companions at several to tens of AU in nearby transition disks. We present non-redundant masking observations of the T Cha and LkCa 15 transition disks, both of which host posited sub-stellar mass companions. However, due to a loss of information intrinsic to the technique, observations of extended sources (e.g. scattered light from disks) can be misinterpreted as moving companions. We discuss tests to distinguish between these two scenarios, with applications to the T Cha and LkCa 15 observations. We argue that a static, forward-scattering disk can explain the T Cha data, while LkCa 15 is best explained by multiple orbiting companions.