OBJECTIVE 2: HOW ARE VOLATILES AND ORGANICS PROCESSED IN PROTO- PLANETARY DISKS?
Lead: Ilaria Pascucci
The objective of our team is to characterize the physical and chemical evolution of protoplanetary disks and their time-varying inventories of volatiles. We will carry out surveys of planet-forming disks to establish how fundamental properties such as disk masses, disk lifetimes, and stellar accretion rates change as a function of age and stellar mass. At the same time we will characterize the distribution of the main molecular carriers of C, H, and N in disks. We will combine state-of-the-art astrochemical models with physical models for gas and dust evolution to identify the key processes that influence the availability of organics and volatiles in disks.
PROJECT 2.1: PROTOPLANETARY DISK MASSES AS A FUNCTION OF AGE AND STELLAR MASS
Lead: Josh Eisner
In Project 2.1 we will study the distribution of protoplanetary disks as a function of age, stellar mass, and environment by using ALMA and the EVLA to target systems spanning a range of evolutionary stages and environments. This study will focus on two surveys: one targeting richly clustered star forming regions where large numbers of sources can be observed simultaneously; and another targeting sources at very young ages. The former will allow a statistical study of disk properties as a function of cluster age and environment. The latter will assess to which extent dust grain processing is affecting the measured versus actual disk mass budget, and allow corrections to be made to the larger survey results.
Our aim is to characterize the initial distribution of mass in protoplanetary disks, and to investigate how disk mass depends on stellar or environmental properties. The disk mass distribution constrains the masses of planets that may ultimately form, and is a critical initial condition for models of planet formation. We will use ALMA, the largest millimeter-wavelength telescope in the world, for most of this work. We are also obtaining ancillary data from other telescopes to help constrain stellar properties of the objects of interest.
PROJECT 2.2: PHYSICAL DISK EVOLUTION
Lead: Ilaria Pascucci
In Project 2.2 we will carry out observations to answer the following two questions: A) What is the lifetime and mass evolution of protoplanetary disks near massive stars? B) How much mass is lost via central star-driven photoevaporation?
For goal A we will carry out optical and near-infrared spectroscopy of the richly clustered star-forming regions identified in Project 2.1. With these observations we will homogeneously re-compute stellar properties and mass accretion rates. Combining this dataset with available infrared surveys and the ALMA data from Project 2.1 we will estimate the disk mass loss as a function of age and radial distance from O stars.
For goal B we will acquire high-resolution optical and mid-infrared spectroscopy for a sample of protoplanetary disks in different evolutionary stages and belonging to star-forming regions with no massive stars. We will identify gas lines tracing slow thermal winds driven by the central star high energy photons. By sampling gas lines at different critical densities we will empirically constrain wind temperature and density and thus estimate mass loss rates. The availability of sources tracing different evolutionary stages will enable us to establish when internal photoevaporation starts to dominate over viscous accretion.
PROJECT 2.3 GASEOUS VOLATILES IN PROTOPLANETARY DISKS: PROBES OF ICY PLANETESIMAL FORMATION AND THE SYNTHESIS OF PREBIOTIC MOLECULES IN DISKS
Lead: Joan Najita
In Project 2.3, we take advantage of recent advancements in our ability to probe the gaseous disk within the snow line. Our project focuses on two main goals. In Project 2.3A we will probe poorly constrained planet formation and disk transport processes, i.e., solid migration and planetesimal formation. Because these processes can either enrich the inner disk in oxygen (e.g., via the rapid transport water ice inward via aerodynamic drag) or deprive it of oxygen (e.g., by locking up water ice beyond the snow line through the formation of large planetesimals or protplanets), they can affect the C/O ratio of the gaseous disk within the snow line. We will attempt to measure the C/O ratio of the gaseous inner disk in order to diagnose these effects. In Project 2.3B we will determine the molecular carriers of N, which bears on the ability of disks to synthesize molecules of biological interest.
PROJECT 2.4: CHEMICAL PROCESSING OF PLANETARY MATERIALS IN DYNAMIC PROTO- PLANETARY DISKS
Lead: Fred Ciesla
Protoplanetary disks are dynamic objects, through which mass is transported to be accreted by the central star during its final stages of growth. This dynamical evolution leads to constantly evolving conditions within the disk, with solids and gas being pushed and jostled through a range of physical environments as a result. This can lead to significant chemical evolution of primitive materials prior to their incorporation into planets.
In this project, we will combine state-of-the-art models to understand the coupled dynamical and chemical evolution of protoplanetary disk materials. We will follow the paths of disk materials through different disk environments, tracking the chemical changes that occur over time. This is a brand approach to studying protoplanetary disk evolution, that allows us to understand chemical processing on very fine scales.
Our focus will be to apply our models to study the processing of volatiles and organics in protoplanetary disks and how such materials are made available to forming planets. We will consider a wide range of disk structures and the influence of different stellar types to understand the full diversity of outcomes that are possible for stars in our galaxy. Models will be refined as our predictions are compared to disk observations and meteoritic analyses carried out as part of the EOS studies.