My astrophysical research interests are broadly focus on white dwarf stars, the final chapter of the lives for about 97% of stars in the Universe, including our own Sun in T-minus 5 billion years. My greatest interest in studying these ancient, retired stars is to learn about the planetary systems they harbor. In particular, I am looking for the carcasses of extrasolar asteroid and rocky planets manifest as clouds of debris orbiting very close to the star. I study how the planetary debris orbits around the star to learn about the dynamics of these remnant planetary systems and take an inventory of the chemical species within the debris to test the geochemical similarity between these rocks and those in our Solar System.

Here I highlight the published research projects I have contributed to, including peer-reviewed journal articles and research posters.

My ORCiD is available at:

ORCID iD icon

First-authored Refereed Publications:

Joseph Guidry, Zachary Vanderbosch, JJ Hermes, et al. 2021, ApJ, 912, 125 - I Spy Transits and Pulsations: Empirical Variability in White Dwarfs Using Gaia and the Zwicky Transient Facility

In our paper we use anomalous levels of excess scatter in Gaia DR2 and the Zwicky Transient Facility photometry as a proxy for variability. We use our variability metrics to rank ~12,100 white dwarf stars centered on a parameter space known as the ZZ Ceti instability strip, where hydrogen-atmosphere (DA) white dwarfs are observed to pulsate. As a proof of concept, we investigated the top 1% (121 white dwarfs) ranked by our metrics, recovering 39 white dwarfs previously known to “go bump in the night.” Our follow-up high-speed photometry from the McDonald Observatory 2.1m Telescope confirmed variability in 33 out of 33 observed candidates from the top 1%, further establishing our efficacy and sensitivty. Most excitingly, in the top 1% we recovered the two white dwarfs previously known to host transiting planetary debris (WD 1145+017 - top right, and ZTF J0139+5245, top left) and find evidence in our follow-up photometry (right) and ZTF light curves (left) for 5 more systems demonstrating transits on varying timescales. We obtained indetifying spectra for three of systems, ruling out variability indicative of a cataclysmic variable, while SDSS J0107+2107 and SBSS 1232+536 exhibited metal pollution in prior SDSS spectra. These objects should be closesly monitored to confirm their candicacy and probe for substrcutres and repeating patterns in observations of future transits. Lastly, we cofirm 29 new ZZ Ceti pulsators, find possible the closest known polar at ~56 pc away (ZTF J0146+4914), and one possible spotted-magnetic variable white dwarf (ZTF J0534+7707). Hope you enjoy the results!

Transiting Debris Systems

Refereed Publications as Contributing Author:

Farihi, J., Hermes, J. J., Marsh, T. R., …, Guidry, J. A. (author 6/14), et al. 2022, MNRAS, 511, 1647.

Relentless and complex transits from a planetesimal debris disc.*

Vanderbosch, Z. P., Rappaport, S., Guidry, J. A., et al. 2021, ApJ, 917, 41.

Recurring Planetary Debris Transits and Circumstellar Gas around White Dwarf ZTF J0328-1219.

Kupfer, T., Prince, T. A., van Roestel, J., …, Guidry, J. A. (author 18/21), et al. 2021, MNRAS, 505, 1254.

Year 1 of the ZTF high-cadence Galactic plane survey: strategy, goals, and early results on new single-mode hot subdwarf B-star pulsators.

Research Posters:

Joseph Guidry, Zachary Vanderbosch, JJ Hermes, Mike Montgomery - Searching for Color Changes During Outburst

This worked has been presented at multiple conferences, inlcuding the TASC5/KASC12 (the TESS and Kepler Asteroseismic Consortiums), and Bash Fest 2019 and the Undergrad Research Forum at UT Austin. Using Pan-STARRS multicolor photometry and K2 photometry, we attempted to assess the changes of color as a result of outburst for two outbursting ZZ Ceti whit dwarfs. Aside from confirming the expectation that white dwarfs are indeed bluer during at the peaks of pulsations than in troughs or in quiescence, definitive results have been found yet. It appears new Pan-STARRS pipelines offered by the Mikulski Archive have developed a work around that plagued our analysis.

You can view our poster here.