HAT-P-26 is a K-type main-sequence star located about 466lk=onNaNlk=on away in the constellation of Virgo. A survey in 2015 did not find any stellar companions in orbit around it, although a red dwarf companion with a temperature is suspected on wide orbit.
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.[1] 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.
In 2010 a transiting hot Neptune 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.[2] 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 2023, the atmosphere of the planet was found to contain water vapor at a temperature of .
A 2019 study detected transit-timing variations (TTVs) of HAT-P-26b, the cause of which was unclear at that time. With more data by 2023, it was suggested that the TTVs may be caused by a second planet in the system. In 2024, a candidate second planet, about twice the size of Earth and slightly farther from the star than planet b, was detected by transit in TESS data, but requires further observations to be fully confirmed.