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Research Interests
Research Interests
I am primarily protoplanetary disks and how their geometry and evolution can be used to study planet formation. Within protoplanetary disks there are a variety of subjects that I am particuarly interested in studying in the future:
Missaligned protoplanetary disks and what mechanisms cause the inner and outer disk to be missaligned.
YSO's that exhibit Dippers in their light curve and linking variable shaddowing we observe in PDI imaging to the occurance of dippers to indirectly study in the inner disk.
Using PDI and ALMA gas observations to constrain the relative heights of small dust grains and gas in protoplanetary disks.
Measuring and constraining dust polarization fraction to measure dust properties in protoplanetary disks.
I am also interested in exoplanet detection (via direct imaging), fundamental stellar parameters and abundances (especially Lithium), Young Stellar Object variability, and many many more! Frankly if its Astronomy related, its fascinating!
Below you will find a short description of current and previous projects I have worked on.
GPI Project
GPI Project
We have obtained scattered light near-IR images of 44 pre/transitional protoplanetary disks with the Gemini Planet Imager (GPI). Our goals are to investigate the structure of the disk and how it relates to the planet formation process and timescale. The survey is called Gemini-LIGHTS and you can find more information here. We will compare these near-IR observations to near-IR and radio interferometric (VLT/MATISSE, SMA, ALMA) observations. Look for the first major paper from the project Fall 2021!
Small Dust Grains and Gas Heights in Protoplanetary Disks
Small Dust Grains and Gas Heights in Protoplanetary Disks
Traditionally, only two of the three dimentions (radial and azimuthal) in protoplanetary disks can be directly probed. However, with the advent of high contrast PDI imaging and ALMA, we can now directly measure the height of protoplanetary disks. Even more, we can compare the height of gas and the small dust grains (1 micron) in protplanetary disk.
I published the first direct comparison of the gas and small dust grain height distributions in protoplanetary disks. I measured the scale height and flare parameter β of the small dust grain scattering surface and 12CO gas emission surface for three protoplanetary disks: IM Lup, HD 163296, and HD 97048 (CU Cha). For two systems, IM Lup and HD 163296, the 12CO gas and small dust grains at small radii from the star have similar heights, but at larger radii (>100 au), the dust grain scattering surface height is lower than the 12CO gas emission surface height. In the case of HD 97048, the small dust grain scattering surface has similar heights to the 12CO gas emission surface at all radii. I ran a protoplanetary disk radiative transfer model of a generic protoplanetary disk with TORUS and showed that there is no difference between the observed scattering surface and 12CO emission surface. I also performed analytical modeling of the system and found that gas-to-dust ratios larger than 100 could explain the observed difference in IM Lup and HD 163296. I am exited to collaborate and work on future observations of gas emission and near-infrared scattered-light observations to search for similar trends in other protoplanetary disks.
Disk and Jet Variability of
HD 163296
Disk and Jet Variability of
HD 163296
We present two new epochs of Hubble Space Telescope/Space Telescope Imaging Spectrograph coronagraphic imaging, along with multi-epoch optical, near-IR, and radio monitoring, of the HD 163296 system. We find ansae features identified in earlier epoch HST imagery are a 4th ring, that resides at a radial distance of 330 au. We observe surface brightness variations in the 4th ring on <3 month timescales, including large-scale, azimuthally asymmetric changes. This variability resembles earlier at a semi-major axis distance of 3.25" (330 au). We determine the scale height of the dust is 64 au studies of the innermost disk ring (0.66", 67 au), suggesting a common origin. We find no evidence for the ejection of new HH-knots predicted to occur in 2018. Moreover, our non-detection of older HH-knots indicate the knots could be experiencing less shock-heating. We also detect one clear dipper event in our optical light curve from 2018. Using the time-scale and spatial extent of disk illumination changes we observe, we estimate the source of this shadowing resides within 0.5 au from the star, must extend at least 0.08 au above the midplane of the disk, and has an azimuthal extent of 0.26 au. We estimate the source of the dipper event reaches a scale height of 0.37 au above the midplane at 0.41 au, and has an azimuthal extent of 0.3 au. We suggest these similarities could indicate the same (or similar) mechanisms are responsible for producing both dippers and variable ring illumination in the system.
SEEDS Survey Disk Imaging
SEEDS Survey Disk Imaging
The Strategic Exploration for Exoplanets and Disks with Subaru (SEEDS) survey searched for protoplanetary disks, debris disks, and directly imaged planets. For example, we detected a transitional disk around DoAr 28 utilizing near-IR polarimetric imagery (Rich et al. 2015). Previously, DoAr 28 had an inferred gap size of 15 AU based on SED modeling. We detected no gap in our imagery down to 13 AU, and we performed Monte Carlo Radiative Transfer (MCRT) modeling and found that the SED and imagery has a gap more consistent with 8 AU (Rich et al. 2015).
A handful of protoplanetary disks exhibit non-azimuthal changes in disk flux over time which is attributed to the outer portion of the disk being shadowed by the inner portion of the system. For example, HD 163296 has a protoplanetary disk that has been well observed (eg. HST/STIS, Gemini/GPI, VLT/SPHERE, ALMA, VLA) over the past 20 years. We compared our new 2011 Subaru/HiCIAO polarmetirc imaging to archival images (Gemini/GPI, VLT/SPHERE, VLT/NACO) of the system and found that the morphology of scattered light from the disk changes within a 4-year timescale (Rich et al. 2019). Our 2011 HiCIAO image (Figure on the right) is 2.7x dimmer on the NW-major axis compared to the VLT/SPHERE image (Muro-Arena et al. 2018). The cause of the morphology change is most likely due to a precession of an inclined inner disk, a warp in the inner disk, or a clumpy disk wind. We performed MCRT modeling using Hochunk3D (Whitney et al. 2013) where we found the best fit model by comparing it to our scattered light 2011 HiCIAO imagery and contemporaneous near-IR spectra and non-contemporaneous photometry. We found that a disk wind model is consistent with the observed scattered light imagery and the contemporaneous SED. Future modeling that includes an inclined disk and future observations that continue to monitor the changing illumination of HD 163296 are necessary to pin down the scattered light morphology of HD 163296.
Hierarchical Triple System: VHS1256
Hierarchical Triple System: VHS1256
Nearby M dwarf VHS J125601.92-125723.9 (VHS 1256) has a previously detected planetary mass companion of 11 Mjup (VHS 1256 b; Gauza et al. 2015). We performed follow up high-contrast observations at the Subaru Telescope using the Infrared Camera and Spectrograph (IRCS) along with the A0188 Adaptive Optics system. L’ and M bandpass images and revealed that the central star was in fact not a single star but a similar mass binary shown in the Figure to the left (Rich et al. 2016). In the figure, VHS 1256 is in the box insert and the centeral binary is shown in the main image.
We estimate that the system is 200 Myr old, based on the non-detection of lithium in the primary stars. Additionally, we estimate that the masses of the stars comprising the central binary are at least 58 Mjup each. Moreover, we find that some of the properties of VHS 1256 are inconsistent with the recent suggestion that it is a member of the AB Dor moving group. VHS 1256 b occupies nearly the same near-infrared position in the color–magnitude diagram as HR 8799 bcde and has a comparable L′ brightness. We estimate the mass range of VHS 1256 b to be from 10.5 Mjup to 26.2 Mjup. Our detection limits rule out companions more massive than VHS 1256 b exterior to 6–8 au, placing significant limits on and providing some evidence against a second, more massive companion that may have scattered the wide-separation companion to its current location. VHS 1256 is most likely a very low-mass hierarchical triple system and could be the third such system in which all components reside in the mass regime of
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