HD 155358
Encyclopedia
HD 155358 is a low metallicity
yellow dwarf
star
approximately 43 light years away in the constellation
Hercules
. This star is known to be orbited by two extrasolar planet
s.
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.
. In 1859 it was catalogued in the Bonner Durchmusterung by the Prussia
n 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.
, 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 inclination
s will eventually become known. HD 155358 b orbits at 0.628 AU while c orbits at 1.224 AU.
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
yellow dwarf
Yellow dwarf
A G-type main-sequence star , often called a yellow dwarf, is a main-sequence star of spectral type G and luminosity class V. Such a star has about 0.8 to 1.2 solar masses and surface temperature of between 5,300 and 6,000 K., Tables VII, VIII...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
approximately 43 light years away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Hercules
Hercules (constellation)
Hercules is a constellation named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today...
. This star is known to be orbited by two extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
s.
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
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
-to-hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
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 telescopeTelescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
. In 1859 it was catalogued in the Bonner Durchmusterung by the Prussia
Prussia
Prussia was a German kingdom and historic state originating out of the Duchy of Prussia and the Margraviate of Brandenburg. For centuries, the House of Hohenzollern ruled Prussia, successfully expanding its size by way of an unusually well-organized and effective army. Prussia shaped the history...
n astronomer F. W. Argelander
Friedrich Wilhelm Argelander
Friedrich Wilhelm August Argelander was a German astronomer. He is known for his determinations of stellar brightnesses, positions, and distances.- Life and work :...
, 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
Spectrograph
A spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
on the Hobby-Eberly Telescope
Hobby-Eberly Telescope
The Hobby-Eberly Telescope is a 9.2-meter aperture telescope located at the McDonald Observatory. It combines a number of features that differentiate it from most telescope designs, resulting in greatly lowered construction costs...
at
McDonald Observatory
McDonald Observatory
The McDonald Observatory is an astronomical observatory located near the unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Fowlkes and Mount Locke in the Davis Mountains of West Texas...
. Changes were observed in the radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic 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.
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 TelescopeHobby-Eberly Telescope
The Hobby-Eberly Telescope is a 9.2-meter aperture telescope located at the McDonald Observatory. It combines a number of features that differentiate it from most telescope designs, resulting in greatly lowered construction costs...
, 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
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
on a timescale of 2700 years, and their arguments of periastron precess on a timescale of 2300 years. HD 155358 b
HD 155358 b
HD 155358 b is a gas giant planet that orbits the star HD 155358, located 142 light years away in the constellation Hercules. This planet orbits at a distance about 63% of distance between Earth and the Sun and has a moderate eccentricity. The planet mass is at least 89% of Jupiter, depending on...
has mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
little bit less than Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
but more than Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
. HD 155358 c
HD 155358 c
HD 155358 c is an extrasolar planet orbiting the star HD 155358 located 142 light years away in the constellation Hercules. This is a gas giant which orbits at 1.224 AU and takes 530.3 days to orbit HD 155358. This planet orbits in an eccentric orbit. This planet has at least half the mass of...
has mass half that of Jupiter. However, more accurate masses were needed when inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
s will eventually become known. HD 155358 b orbits at 0.628 AU while c orbits at 1.224 AU.
External links
- The Extrasolar Planet Encyclopedia: HD 155358
- Extrasolar Planet Interactions by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona