# HD 28185

HD 28185
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Eridanus
Right ascension 04h 26m 26.32s[1]
Declination –10° 33′ 02.9″[1]
Apparent magnitude (V) +7.81
Characteristics
Spectral type G5V
U−B color index ?
B−V color index 0.750
Variable type none
Astrometry
Proper motion (μ) RA: 84.42 ± 0.84[1] mas/yr
Dec.: –57.66 ± 0.72[1] mas/yr
Parallax (π) 23.62 ± 0.87[1] mas
Distance 138 ± 5 ly
(42 ± 2 pc)
Absolute magnitude (MV) +4.68[note 1]
Details
Mass 0.99 ± 0.07 M
Luminosity (visual, LV) 1.15[note 2] L
Temperature 5705 K
Metallicity 173%
Rotation 30 days
Age 7.5 Gyr
Other designations
BD–10°919, SAO 149631, HIP 20723, GSC 05317-00733
Database references
Extrasolar Planets
Encyclopaedia
data

HD 28185 is a yellow dwarf star similar to our Sun located about 138 light-years away from Earth in the constellation Eridanus. The designation HD 28185 refers to its entry in the Henry Draper catalogue. The star is known to possess one long-period extrasolar planet.

## Distance and visibility

According to measurements from the Hipparcos astrometric satellite, HD 28185 has a parallax of 23.62 milliarcseconds,[1] which corresponds to a distance of 42 parsecs (138 light-years). Since the star is located further than 25 parsecs from Earth, it is not listed in the Gliese Catalogue of Nearby Stars. With an apparent magnitude of 7.81, the star is not visible with the naked eye, though it can be seen using binoculars.

## Stellar characteristics

HD 28185 is similar to our Sun in terms of mass, radius, and luminosity. The star is on the main sequence and is generating energy by fusing hydrogen in its core. The spectral type of G5V implies HD 28185 is cooler than the Sun. 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, 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 our Sun.[2] The higher luminosity and longer rotation period favour an older age for the star.

## Planetary system

In 2001 an extrasolar planet similar in size to Jupiter designated HD 28185 b was discovered in orbit around the star with a period of 1.04 years.[2][3] Unlike many long-period extrasolar planets, it has a low orbital eccentricity.[4] The planet experiences similar insolation to Earth, which has led to speculations about the possibilities for habitable moons.[5][6] In addition, numerical simulations suggest that low-mass planets located in the gas giant's Trojan points would be stable for long periods.[7] The planet's existence was independently confirmed by the Magellan Planet Search Program in 2008.[8]

The star also shows evidence of a long-term radial velocity trend, which may indicate the presence of an additional outer companion.[9]

The HD 28185 system[2]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
b ≥5.7 MJ 1.031 ± 0.060 383 ± 2 0.07 ± 0.04

## Notes

1. ^ Derived from apparent magnitude and parallax: $\scriptstyle M_V=m_V-5\log_{10}\left(\frac{100}{\pi}\right)$
2. ^ Derived from absolute visual magnitude: $\scriptstyle \frac{L_\ast}{L_{\odot}}=100^{(M_{V_\odot}-M_{V_\ast})/5}$

## References

1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.Vizier catalog entry
2. ^ a b c
3. ^ "Exoplanets: The Hunt Continues!" (Press release). Garching, Germany: European Southern Observatory. April 4, 2001. Retrieved December 27, 2012.
4. ^ Butler, R. P. et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal 646 (1): 505–522. arXiv:astro-ph/0607493. Bibcode:2006ApJ...646..505B. doi:10.1086/504701.
5. ^ Mullen, L. (2001). "Extrasolar Planets with Earth-like Orbits". Retrieved 22 July 2006.
6. ^ Jones, Barrie W.; Sleep, P. Nick; Underwood, David R. (2006). "Habitability of Known Exoplanetary Systems Based on Measured Stellar Properties". The Astrophysical Journal 649 (2): 1010–1019. arXiv:astro-ph/0603200. Bibcode:2006ApJ...649.1010J. doi:10.1086/506557.
7. ^ Schwarz, R.; Dvorak, R.; Süli, Á.; Érdi, B. (2007). "Survey of the stability region of hypothetical habitable Trojan planets". Astronomy and Astrophysics 474 (3): 1023–1029. Bibcode:2007A&A...474.1023S. doi:10.1051/0004-6361:20077994.
8. ^ Minniti, Dante et al. (2009). "Low-Mass Companions for Five Solar-Type Stars From the Magellan Planet Search Program". The Astrophysical Journal 693 (2): 1424–1430. arXiv:0810.5348. Bibcode:2009ApJ...693.1424M. doi:10.1088/0004-637X/693/2/1424.
9. ^ Chauvin, G.; Lagrange, A.-M.; Udry, S.; Fusco, T.; Galland, F.; Naef, D.; Beuzit, J.-L.; Mayor, M. (2006). "Probing long-period companions to planetary hosts. VLT and CFHT near infrared coronographic imaging surveys". Astronomy and Astrophysics 456 (3): 1165–1172. arXiv:astro-ph/0606166. Bibcode:2006A&A...456.1165C. doi:10.1051/0004-6361:20054709.