HAT-P-26

HAT-P-26 is a K-type main-sequence star about 466 ly away. A survey in 2015 did not find any stellar companions in orbit around it, although a red dwarf companion with a temperature 4000$14.1$ K is suspected on wide orbit.

Nomenclature
The designation HAT-P-26 indicates that this was the 26th star found to have a planet by the HATNet Project.

In August 2022, this planetary system was included among 20 systems to be named by the third NameExoWorlds project. The approved names, proposed by a team from Puerto Rico, were announced in June 2023. HAT-P-26 is named Guahayona and its planet is named Guataubá, after figures from Taíno mythology.

Planetary system
In 2010 a transiting hot Neptune like planet was detected. The transiting planet HAT-P-26b was detected by the HATNet Project using telescopes located in Hawaii and Arizona. The planet is likely formed by pebble accretion mechanism. The transmission spectrum of HAT-P-26b was taken in 2015, with the best fit favouring either a cloudless atmosphere or an atmosphere with a low-lying cloud deck. The atmospheric composition of the planet was measured in 2019, and a water vapor volume fraction of 1.5$$% was detected. HAT-P-26 is carbon depleted, with a C/O ratio constrained to less than 0.33. Also, the planet's atmosphere contains light metal hydrides. The measured planetary temperature is equal to 563$$ K.

In 2019, a transit timing variation analysis of HAT-P-26b indicated the possible presence of a second planet in the system on a wide, 1141-days orbit.

In 2023, the atmosphere of the planet was confirmed to contain 12$$% steam at 590$$K.