The star is about 15% smaller than the Sun in both mass and radius and radiates slightly less than half the Sun's luminosity from its photosphere. It has a spectral type of K1V and an effective temperature of 5,131 K (4,858 °C; 8,776 °F), giving the star an orange hue. It is 9.6+3.8 −3.9 billion years old, making it much older than the Solar System. The star has a solar-like metallicity and displays similar amounts of stellar activity to the Sun,[7] though when the star was only 150 million years old, it may have emitted between 3.7 and 127 times the high-energy luminosity of the Sun in the present day.[3]
Planetary system
In May 2019, a pair of exoplanets were discovered to revolve around HD 15337 through transit observations by the TESSspace telescope, namely HD 15337 b and c.[3] The two planets are far closer to their host star than Mercury is to the Sun (0.3871 AU[9]), which heats them up to equilibrium temperatures of 1,001 K (728 °C; 1,342 °F) and 642 K (369 °C; 696 °F),[3] respectively, both of which are hot enough to melt lead (m.p. 327 °C[10]).
The inner planet, HD 15337 b, has a mass of 1.770 R🜨 and a mass of 6.519 ME. This places its density at 6.458 g/cm3,[6] meaning it is denser than Earth (5.513 g/cm3[11]) and very likely to be a rockysuper-Earth.[3] The outer planet, c, is only slightly more massive than b at 6.792 ME, but possesses a radius over 40% larger, which makes it much less dense at 2.303 g/cm3,[6] suggesting a mini-Neptune-like composition with a thick (>0.01 ME[6]) gaseous envelope probably consisting of hydrogen and helium.[7] This striking difference in the structure of the two planets in spite of their similar masses implies that the two planets are on opposite sides of the small planet radius gap, making the HD 15337 system a prime target for research in planetary formation and evolution.[3][7]
In 2024, the planetary parameters of both planets were precisely gauged through photometric observations by CHEOPS and radial velocity measurements by HARPS. As a result, the uncertainties of HD 15337 b's mass and radius were each reduced to less than 2% and 7%, which put the planet among the most accurately characterized terrestrial exoplanets at the time. Additionally, the radius of HD 15337 c was constrained to within a 3% margin of error.[6]
^Høg, E.; et al. (February 2000). "The Tycho-2 Catalogue of the 2.5 Million Brightest Stars". Astronomy and Astrophysics. 355 (1): L27–L30. Bibcode:2000A&A...355L..27H.
^Williams, David R. (16 March 2017). "Earth Fact Sheet". NASA/Goddard Space Flight Center. Archived from the original on 8 May 2013. Retrieved 26 July 2018.
