HD 155358

Starbox begin
name=HD 155358 Starbox observe
epoch=J2000
ra=RA|17|09|34.6168cite web
title=Results for HD 155358
work=SIMBAD Astronomical Database
publisher=Centre de Données astronomiques de Strasbourg
url=http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=HD+155358&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id
accessdate=2007-09-04 ]
dec=DEC| +33|21|21.078
appmag_v=7.27
constell=Hercules Starbox character
class=G0
b-v=0.523
u-b=
variable= Starbox astrometry
radial_v=-9.1
prop_mo_ra=-223.50
prop_mo_dec=-216.77
parallax=23.04
p_error=0.69
parallax_footnote=
absmag_v=4.12 Starbox detail
mass=0.89cite web
author=Nordstrom B., Mayor M., Andersen J., Holmberg J., Pont F., Jorgensen B.R., Olsen E.H., Udry S., Mowlavi N.
year=2004
url=http://cdsarc.u-strasbg.fr/viz-bin/Cat?V/117
title=The Geneva-Copenhagen Survey of Solar neighbourhood
publisher=Centre de Données astronomiques de Strasbourg
accessdate=2007-09-04]
radius=
luminosity=
temperature=5,868
metal=21% solarcite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007ApJ...665.1407C&db_key=AST&nosetcookie=1|title=A Planetary System Around HD 155358: The Lowest Metallicity Planet Host Star|author=Cochran, W. et al.|year=2007|journal=The Astrophysical Journal|volume=665|issue=2|pages=1407–1412|doi=10.1086/519555]
gravity=4.19
rotation=
age=11.9 Gyr Starbox catalog
names=BD +33 2840, SAO 65834, Wolf 646, HIP 83949

HD 155358 is a low metalicity yellow dwarf star approximately 43 light years away in the constellation Hercules. This star is known to be orbited by two extrasolar planets.

The star is 11.9 billion years old and has a mass 0.89 times that of the Sun. It is notable for being the lowest metallicity planet-bearing star known, with an iron-to-hydrogen ratio 21% of the solar value.

Observation

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. [cite book
first=Friedrich W. | last=Argelander
authorlink=Friedrich Wilhelm Argelander | year=1902
title=Bonner Durchmusterung des noerdlichen Himmels
edition=2nd Edition | location=Bonn ] In 1958 it was identified as a star with a relatively largeproper motion by the Nizamiah Observatory, Hyderabad. [cite journal
last=Goyal | first=A. N.
title=Stars with large proper motions in the astrographic zones +32° and +33° (List II)
journal=Journal des Observateurs
year=1999 | volume=41 | pages=121
url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1958JO.....41..121G&db_key=AST
accessdate=2007-09-04 ] 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.) [cite journal
last=Halliwell | first=M. J.
title=Possible nearby stars brighter than tenth magnitude
journal=Astrophysical Journal Supplement Series
year=1979 | volume=41 | pages=173–190
url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1979ApJS...41..173H&db_key=AST
accessdate=2007-09-04
doi=10.1086/190614 ]

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. [cite news
last=Johnson | first=Rebecca | date=May 23, 2007
title=Astronomers Discover Multi-Planet System; May Alter Theories of Planet Formation
publisher=University of Texas
url=http://mcdonaldobservatory.org/news/releases/2007/0523.html
accessdate=2007-09-04]

Planetary system

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.

PlanetboxOrbit
exoplanet = b
mass = >0.895
period = 195 ± 1.1
semimajor = 0.628 ± 0.02
eccentricity = 0.112 ± 0.037PlanetboxOrbit
exoplanet = c
mass = >0.504
period = 530.3 ± 27.2
semimajor = 1.224 ± 0.081
eccentricity = 0.176 ± 0.174

References

External links

* [http://exoplanet.eu/star.php?st=HD+155358 The Extrasolar Planet Encyclopedia: HD 155358]
* [http://www.lpl.arizona.edu/~rory/research/xsp/dynamics/ Extrasolar Planet Interactions] by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona