HD 28185 is similar to the Sun in terms of mass, radius, and luminosity. The spectral type of G6.5IV-V[3] implies HD 28185 is cooler than the Sun, and that the star is on the main sequence and is generating energy by fusinghydrogen in its core. Like the majority of extrasolar planet host stars, HD 28185 is metal-rich relative to the Sun, containing around 173% of the solar abundance of iron. The star rotates slower than the Sun, with a period of around 30 days,[5] compared to 25.4 days for the Sun.
Based on the star's chromospheric activity, HD 28185 is estimated to have an age of around 2,900 million years. On the other hand, evolutionary models give an age of around 7,500 million years and a mass 0.99 times that of the Sun.[5] The higher luminosity and longer rotation period favour an older age for the star. As of 2024[update], the most recent estimate is about 8,300 million years, based on the star's observed physical properties.[4]
Planetary system
In 2001, an extrasolar planet more massive than Jupiter, designated HD 28185 b, was discovered in orbit around the star with a period of 1.04 years.[5][7] Unlike many long-period extrasolar planets, it has a low orbital eccentricity.[8] The planet experiences similar insolation to Earth, which has led to speculations about the possibilities for habitablemoons.[9][10] In addition, numerical simulations suggest that low-mass planets located in the gas giant's Trojan points would be stable for long periods.[11] The planet's existence was independently confirmed by the Magellan Planet Search Program in 2008.[12]
The star also shows evidence of a long-term radial velocity trend, which may indicate the presence of an additional outer companion.[13] In 2022, the presence of an outer companion (HD 28185 c) was confirmed using a combination of radial velocity and astrometry, with the proposed mass of nearly 20 times that of Jupiter being in the range of brown dwarfs.[14] However, this was revised by a 2024 follow-up study which found HD 28185 c to be a planet with a mass 6 times that of Jupiter, comparable to HD 28185 b.[4]
^ abGray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Bubar, E. J.; McGahee, C. E.; O'Donoghue, A. A.; Knox, E. R. (July 2006). "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637. S2CID119476992.