Research

animation
Here is a subset of the ALMA data in our L1641 sample. These are continuum images at 1.33 mm which trace the cold dust in the disks.

Understanding Protoplanetary Disk Evolution in the Lynds 1641 Disk Population

Many factors impact protoplanetary disk evolution, including the age of the system and the local environment. Younger systems often have more massive disks with a large population of small dust grains located in the upper layers of the disk atmosphere, giving the disk a flared shape. As the system evolves, the dust grains will settle to the disk midplane, collide, and grow into pebbles and then planetesimals and eventually, terrestrial planets or the cores of giant planets. If the disk is in a dense stellar environment or is located near a massive star, the disk can be truncated, leading to small disks with less mass. I’m interested in how disks evolve in general, searching for trends with age, location, stellar mass, etc.
The Lynds 1641 (L1641) region is located in the Orion Molecular Cloud A. L1641 is young (~1 Myr) and populous (with an estimated 1600 stars with disks and more evolved systems). This region extends along a filament south of the Orion Nebula Cluster, such that must of the region is far enough from the massive stars in the ONC that it does not show signs of being photoevaporated from the outside. In Grant et al. 2018, we analyzed far-infrared photometry of disks in this region from the Herschel Space Observatory and found that despite their young ages, the disks in L1641 already showed signs of dust evolution. My coauthors and I recently were awarded time with the Atacama Large Millimeter Array (ALMA) to study L1641 at radio wavelengths which trace the cold dust in these disks. We will present our results in an upcoming paper.

Accretion in Intermediate-Mass Stars

Accretion occurs when the gas in the protoplanetary disk falls onto the stellar surface. It is a critical mechanism that both heats the disk and clears it of material. Understanding how this accretion takes place and under what conditions has important implications for disk evolution. The mechanism is well-understood for low-mass stars. In these systems, the hot gas is funneled onto the star via the star’s magnetic field lines. However, more massive stars do not have strong magnetic fields and it is unknown how accretion occurs in these systems. These stars are called Herbig Ae/Bes after the man who discovered them (George Herbig) and due to their spectral types (A and B). Stars that are even higher mass evolve so quickly that we cannot see how they accrete material because the stars are often so embedded in the molecular cloud that we cannot get a clear picture. Therefore, Herbig Ae/Be stars are the link to understanding how high-mass star formation proceeds.
I have performed a survey of Herbig Ae/Be stars with the Lowell Discovery Telescope, NASA’s Infrared Telescope Facility, and Gemini South using the near-infrared spectrographs iSHELL and IGRINS. These observations include a Hydrogen line that is formed as material travels from the disk onto the star. I am using this data to look for accretion trends with stellar mass, age of the system, disk morphology (whether the disk has any holes or gaps), and more. I am also modeling this data with a radiative transfer model of accretion flows, allowing us to probe properties of the accretion flow. The results of this survey will be presented in two upcoming papers.