Epoch J2000 Equinox J2000
|Right ascension||17h 09m 34.6168s|
|Declination||+33° 21′ 21.078″|
|Apparent magnitude (V)||7.27|
|B−V color index||0.523|
|Radial velocity (Rv)||-9.1 km/s|
|Proper motion (μ)||RA: -223.50 mas/yr
Dec.: -216.77 mas/yr
|Parallax (π)||23.04 ± 0.69 mas|
|Distance||142 ± 4 ly
(43 ± 1 pc)
|Absolute magnitude (MV)||4.12|
|Surface gravity (log g)||4.19|
The star is 11.9 billion years old and has a mass 0.89 times that of the Sun. At the time of the planets' discoveries, it was notable for being the lowest metallicity planet-bearing star known, with an iron-to-hydrogen ratio 21% of the solar value.
With a visual magnitude of 7.5, this star can not be observed with the unaided eye. Hence it was discovered only after the introduction of the telescope. In 1859 it was catalogued in the Bonner Durchmusterung by the Prussian astronomer F. W. Argelander, who listed an estimated visual magnitude of 7.2. In 1958 it was identified as a star with a relatively large proper motion by the Nizamiah Observatory, Hyderabad. It was suggested in 1979 that this star may lie within 25 parsecs of the Sun. (Up to that time it had never been catalogued as a nearby star.)
Beginning in 2001, this star underwent observation using the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. Changes were observed in the radial velocity motion of the star, indicating a gravitational influence from orbiting objects. Based on the motion of the star over time, astronomers were able to deduce that there are at least two planets in orbit around HD 155358.
On 10 May 2007, astronomers included Cochran from the University of Texas announced two mass type II planets orbiting the same star with the lowest metal content than any planetary host stars. Its discoveries were made by using the Hobby-Eberly Telescope, which used radial velocity to monitor the change of line of sight motion of the star caused by gravity of the planets. These two planets gravitationally interact: modelling the planets assuming their masses are the same as the empirically-determined lower limits, they exchange eccentricities on a timescale of 2700 years, and their arguments of periastron precess on a timescale of 2300 years. HD 155358 b has mass little bit less than Jupiter but more than Saturn. HD 155358 c has mass half that of Jupiter. However, more accurate masses were needed when inclinations will eventually become known. HD 155358 b orbits at 0.628 AU while c orbits at 1.224 AU.
(in order from star)
|b||>0.89 ± 0.12 MJ||0.628 ± 0.020||195.0 ± 1.1||0.112 ± 0.037||—||—|
|c||>0.504 ± 0.075 MJ||1.224 ± 0.081||530.3 ± 27.2||0.176 ± 0.174||—||—|
- "Results for HD 155358". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 2007-09-04.
- Nordstrom B., Mayor M., Andersen J., Holmberg J., Pont F., Jorgensen B.R., Olsen E.H., Udry S., Mowlavi N. (2004). "The Geneva-Copenhagen Survey of Solar neighbourhood". Centre de Données astronomiques de Strasbourg. Retrieved 2007-09-04.
- Cochran, W. et al. (2007). "A Planetary System Around HD 155358: The Lowest Metallicity Planet Host Star". The Astrophysical Journal 665 (2): 1407–1412. arXiv:0705.3228. Bibcode:2007ApJ...665.1407C. doi:10.1086/519555.
- Argelander, Friedrich W. (1902). Bonner Durchmusterung des noerdlichen Himmels (2nd ed.). Bonn.
- Goyal, A. N. (1999). "Stars with large proper motions in the astrographic zones +32° and +33° (List II)". Journal des Observateurs 41: 121. Bibcode:1958JO.....41..121G.
- Halliwell, M. J. (1979). "Possible nearby stars brighter than tenth magnitude". Astrophysical Journal Supplement Series 41: 173–190. Bibcode:1979ApJS...41..173H. doi:10.1086/190614.
- Johnson, Rebecca (May 23, 2007). "Astronomers Discover Multi-Planet System; May Alter Theories of Planet Formation". University of Texas. Retrieved 2007-09-04.
- The Extrasolar Planet Encyclopedia: HD 155358
- Extrasolar Planet Interactions by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona