The designationHAT-P-26 indicates that this was the 26th star found to have a planet by theHATNet Project.
In August 2022, this planetary system was included among 20 systems to be named by the thirdNameExoWorlds project.[8] The approved names, proposed by a team fromPuerto Rico, were announced in June 2023. HAT-P-26 is namedGuahayona and its planet is namedGuataubá, after figures fromTaíno mythology.[9]
In 2010 atransitinghot Neptune planet was detected.[4] The transiting planet HAT-P-26b was detected by theHATNet Project using telescopes located in Hawaii and Arizona. The planet is likely formed by pebble accretion mechanism.[10] 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.[11] The atmospheric composition of the planet was measured in 2019, and a water vapor volume fraction of 1.5+2.1 −0.9% 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.[12] The measured planetary temperature is equal to 563+58 −54K.
In 2023, the atmosphere of the planet was found to contain2.4%+2.9% −1.6%water vapor at a temperature of590+60 −50K.[13]
A 2019 study detectedtransit-timing variations (TTVs) of HAT-P-26b, the cause of which was unclear at that time.[14] With more data by 2023, it was suggested that the TTVs may be caused by a second planet in the system.[13] 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 inTESS data, but requires further observations to be fully confirmed.[15]
^This mass is predicted based on mass-radius relationships. If this planet is responsible for the observed TTVs it should be possible to measure its mass that way; the 2023 TTV study found a mass of about 6.36 Earths based on an assumed period of 8.47 days,[13] but if the period is actually shorter at 6.59 days the mass would be different.
^Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars".Astronomy and Astrophysics.355.Bibcode:2000A&A...355L..27H.
^abcdHartman, J. D.; Bakos, G. Á.; Kipping, D. M.; Torres, G.; Kovács, G.; Noyes, R. W.; Latham, D. W.; Howard, A. W.; Fischer, D. A.; Johnson, J. A.; Marcy, G. W.; Isaacson, H.; Quinn, S. N.; Buchhave, L. A.; Béky, B.; Sasselov, D. D.; Stefanik, R. P.; Esquerdo, G. A.; Everett, M.; Perumpilly, G.; Lázár, J.; Papp, I.; Sári, P. (2011). "HAT-P-26b: A Low-density Neptune-mass Planet Transiting a K Star".The Astrophysical Journal.728 (2): 138.arXiv:1010.1008.Bibcode:2011ApJ...728..138H.doi:10.1088/0004-637X/728/2/138.
^von Essen, C.; Wedemeyer, S.; Sosa, M. S.; Hjorth, M.; Parkash, V.; Freudenthal, J.; Mallonn, M.; Miculán, R. G.; Zibecchi, L.; Cellone, S.; Torres, A. F. (2019). "Indications for transit timing variations in the exo-Neptune HAT-P-26b".Astronomy & Astrophysics.628: A116.arXiv:1904.06360.Bibcode:2019A&A...628A.116V.doi:10.1051/0004-6361/201731966.S2CID118674293.
