Research

I'm primarily an observational astronomer, studying star and planet formation. I am interested in everything about how the interactions between young stars, their disks, and the larger circumstellar environment, can affect the formation of planets around them. 

FU Ori Outburster Observations:

The primary work of my thesis is with Prof. Lynne Hillenbrand, focused on outbursting Young Stellar Objects (YSOs). I seek to expand our understanding of the innermost regions of the accretion disks of FUor objects, which are YSOs with accretion rates up to 10,000 times greater than those of T Tauri Stars. During their outbursts, the inner disks of the objects reach temperatures of 6,000 - 8,000 K and the emission from the disk is 100 times brighter than the star. These outbursts play a crucial role in how young stars acquire their mass. Furthermore, due to the extreme conditions of the inner disk during outburst, the additional heating may lead to interesting chemistry in the outer disk or have serious consequences for any potential new-born planets within 1 AU!

When the disk is in outburst, the very hot midplane supports a plane-parallel atmosphere almost like an unraveled star. The disk also has a temperature profile similar to those we observe in other astrophysical accretion disks. We can take advantage of these two facts  to model the spectrum of the disk by adding up several pre-calculated stellar spectrum models (or observed templates), where the effective temperatures of the spectra represent different temperature annuli in the disk. With this model, we can compare with observations to constrain the evolution of certain disk parameters, which in turn tells us about the physics of the outbursts. I describe this in more detail below. 

Protoplanetary Disk Imaging:

I also work with Prof. Laura Perez at Universidad de Chile, studying the millimeter emission from protoplanetary disks. The 0.5 mm to 5 mm continuum emission in protoplanetary disks is dominated by thermal emission from dust grains. Observations with the Atacama Large Millimeter Array, or ALMA, allow us to observe this thermal emission at high sensitivity and high angular resolution. High angular resolution continuum images show us that the spatial distribution of dust in protoplanetary disks is not always smooth. In fact it almost always show some structure beyond a simple power law relation with radius, such as huge spirals or dark gaps and bright rings. This is what we call "substructure".

There are several models for what may cause substructure in disks but the one that I (and many others!) find particularly exciting is the possibility that it may be formed by planet-disk interactions. If so, studying these features can help us to understand the properties of planets that have only just recently formed! 

Publications I have been involved in and led can be found at this ADS library.

Some more details:

High Resolution Spectroscopy of FU Ori Objects:

My work with FU Ori objects is based on simultaneously modeling their spectral energy distributions (SEDs) and high resolution optical/NIR spectra to break degeneracies that arise from modeling only one or the other. Using our modeling infrastructure, we have been able to produce new constraints on the physical parameters of three FU Ori objects: V960 Mon (Carvalho et al. 2023 a,b), HBC 722 (Carvalho et al. (2024a), and RNO 54 (Hillenbrand, Carvalho, et al. 2023). For V960 Mon and HBC 722, we have also measured the post-outburst evolution of components in the disk system. 

Constraining the physical parameters of FU Ori objects is critical to informing our understanding of the population of objects to answer questions like: 

• Is there a particular mass range for these objects?

• Is there a minimum accretion rate for an outburst disk to show an FU Ori-like spectrum?

• How large can the viscous accretion-heated region of the disk be? 

Our constraints on the evolution of disk components, including the outflows and inner/outer boundaries of the disk help to constrain the physics of the outburst and ultimately what set of instabilities may be active during and outburst. 

Using our infrastructure and detailed comparison between existing models of winds in the literature, we are able to construct a picture of these systems that includes each of the individual components we identify. An example of this is shown in the cartoon below, detailed the components of the HBC 722 outbursting disk. 

High Angular Resolution Imaging of Protoplanetary Disks:

My work with millimeter imaging of protoplanetary disks aims to understand the spatial distribution of dust properties in the disks and how dust trapping in disks can set the stage for planetesimal formation via the streaming instability. We are able to constrain dust properties by observing bright, nearby disks at high sensitivity and high angular resolution in multiple bands. The models we use are based on the model in Sierra et al. (2021) and incorporate both absorption and scattering to better constrain dust properties in regions with high optical depth. 

An example of this work is summarized in the Poster below, which I presented at the 2023 Gordon Research Conference: Origins of Solar Systems.