Revisiting the Transit Timing and Atmosphere Characterization of the Neptune-mass Planet HAT-P-26 b

TL;DR

This study refines the orbital and atmospheric properties of Neptune-mass planet HAT-P-26 b through extensive transit observations, revealing potential additional planets and characterizing its water content and temperature.

Contribution

It combines new and existing transit data to improve planetary parameters, detect TTV signals suggestive of additional planets, and analyze the atmosphere's water content and temperature.

Findings

TTV amplitude of 1.98 minutes suggests possible additional planet.

Atmosphere contains approximately 2.4% water vapor.

Derived temperature of the atmosphere is around 590 K.

Abstract

We present the transit timing variation (TTV) and planetary atmosphere analysis of the Neptune-mass planet HAT-P-26~b. We present a new set of 13 transit light curves from optical ground-based observations and combine them with light curves from the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST), Transiting Exoplanet Survey Satellite (TESS), and previously published ground-based data. We refine the planetary parameters of HAT-P-26 b and undertake a TTV analysis using 33 transits obtained over seven years. The TTV analysis shows an amplitude signal of 1.98 $\pm$ 0.05 minutes, which could result from the presence of an additional $0.02 M_{Jup}$ planet at the 1:2 mean-motion resonance orbit. Using a combination of transit depths spanning optical to near-infrared wavelengths, we find that the atmosphere of HAT-P-26 b contains $2.4^{+2.9}_{-1.6}$% of H$_2$O with a derived temperature of $590^{+60}_{-50}$ K.