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A Variability Study of Y Dwarfs: A Spitzer Space Telescope Program

Trucks, Jesica Lynn
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564689621551064

Abstract Details

2019, Doctor of Philosophy, University of Toledo, Physics.
I present the results of a search for variability in 14 Y dwarfs consisting 2 epochs of observations, each taken with Spitzer for 12 hours at [3.6] immediately followed by 12 hours at [4.5], separated by 122–464 days and found that Y dwarfs are variable. We used not only periodograms to characterize the variability but we also utilized Bayesian analysis. We found that using different methods to detect variability gives different answers making survey comparisons difficult. We determined the variability fraction of Y dwarfs to be between 37% and 74%. While the mid-infrared light curves of Y dwarfs are generally stable on time scales of months, we have encountered a few that vary dramatically on those time scales. When we combined the variability frac- tions of L and T dwarfs with our variability fractions of Y dwarfs the results support the standard paradigm which suggests that clouds are responsible for the observed variability because of the cloudy→cloud free→cloudy nature of the LTY spectral se- quence. We have determined the rotation periods of 5 Y dwarfs ranging from 2.44 hours to 8.42 hours, with two additional tentative periods. We also considered the oblateness of Y dwarfs as rotation period is one factor in its calculation. One of our targets WISE 0359−54 has a very small period so we showed that depending on its’ mass it could have an oblateness comparable to that of Jupiter or Saturn. We also determined that with its short, consistent period across all four light curves, it would make a perfect candidate for future variability studies with JWST. Interestingly we found that our survey failed to detect any small amplitude variability (< 0.5%) even though it is sensitive down to 0.2%, but is not due to observational bias. We con- firmed that the maximum amplitude increases as a function of spectral type. We find that the average [4.5]/[3.6] amplitude ratio is less than unity which suggests that hot spots may be the physical mechanism of the observed variability. As [3.6] and [4.5] probe similar atmospheric layers unsurprisingly we find no phase changes in the light curves for WISE 0359−54.
Michael Cushing (Committee Chair)
S. Thomas Megeath (Committee Member)
Rupali Chandar (Committee Member)
Richard Irving (Committee Member)
Stanimir Metchev (Committee Member)
103 p.
Astronomy; Astrophysics

Recommended Citations

Citations

  • Trucks, J. L. (2019). A Variability Study of Y Dwarfs: A Spitzer Space Telescope Program [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564689621551064

    APA Style (7th edition)

  • Trucks, Jesica. A Variability Study of Y Dwarfs: A Spitzer Space Telescope Program. 2019. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564689621551064.

    MLA Style (8th edition)

  • Trucks, Jesica. "A Variability Study of Y Dwarfs: A Spitzer Space Telescope Program." Doctoral dissertation, University of Toledo, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564689621551064

    Chicago Manual of Style (17th edition)

toledo1564689621551064
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© 2019, all rights reserved.
This open access ETD is published by University of Toledo and OhioLINK.