Imaging & Spectroscopy

Hazy With A Chance Of Star Spots: Constraining The Atmosphere Of The Young Planet, K2-33b

By Keith Cowing
Press Release
November 16, 2022
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Hazy With A Chance Of Star Spots: Constraining The Atmosphere Of The Young Planet, K2-33b
Top: Stacked phase-folded light curve of K2- 33 observed in K2 (pink), MEarth (blue), Spitzer/Channel 1 (purple), Spitzer/Channel 2 (orange), and HST (green). The HST data here is the white light curve. Data points correspond to the light curve binned in phase using a bin size of 10, 200, 1500, and 1500 for K2, MEarth, Channel 1, and Channel 2, respectively. Solid line corresponds to the bestfit (highest likelihood) model from our MCMC fit. Typical error bars are derived from scatter in the out-of-transit data points. The transit depth for the optical wavelengths is ∼ 2 times deeper than the transit depth for the near-infrared wavelengths. Bottom: Residuals using the binned points. — astro-ph.EP

Although all-sky surveys have led to the discovery of dozens of young planets, little is known about their atmospheres. Here, we present multi-wavelength transit data for the super Neptune-sized exoplanet, K2-33b — the youngest (~10 Myr) transiting exoplanet to-date.

We combined photometric observations of K2-33 covering a total of 33 transits spanning >2 years, taken from K2, MEarth, Hubble, and Spitzer. The transit photometry spanned from the optical to the near-infrared (0.6-4.5μm), enabling us to construct a transmission spectrum of the planet.

We find that the optical transit depths are nearly a factor of two deeper than those from the near-infrared. This difference holds across multiple datasets taken over years, ruling out issues of data analysis and unconstrained systematics. Surface inhomogeneities on the young star can reproduce some of the difference, but required spot coverage fractions (>60%) are ruled out by the observed stellar spectrum(<20%).

We find a better fit to the transmission spectrum using photochemical hazes, which were predicted to be strong in young, moderate-temperature, and large-radius planets like K2-33b. A tholin haze with CO as the dominant gaseous carbon carrier in the atmosphere can reasonably reproduce the data with small or no stellar surface inhomogeneities, consistent with the stellar spectrum. The HST data quality is insufficient for the detection of any molecular features. More observations would be required to fully characterize the hazes and spot properties and confirm the presence of CO suggested by current data.

Pa Chia Thao, Andrew W. Mann, Peter Gao, Dylan A. Owens, Andrew Vanderburg, Elisabeth R. Newton, Yao Tang, Matthew J. Fields, Trevor J. David, Jonathan M. Irwin, Tim-Oliver Husser, David Charbonneau, Sarah Ballard

Comments: Accepted to AJ. 26 pages, 14 figures, 6 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2211.07728 [astro-ph.EP] (or arXiv:2211.07728v1 [astro-ph.EP] for this version)
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Submission history
From: Pa Chia Thao
[v1] Mon, 14 Nov 2022 19:57:14 UTC (5,296 KB)

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