HD 17156
Encyclopedia
HD 17156 is a yellow subgiant star
approximately 255 light-year
s away in the constellation
of Cassiopeia
. The apparent magnitude
is 8.17, which means it is not visible to the naked eye
but can be seen with good binoculars
. The Sun
to star distance is 255.19 ly or 78.24 pc
.
The mass of the star is 20% more massive and 47% larger than our Sun
. Based on its absolute magnitude
of 3.70 and spectral type of G0, the star is thought to be hotter than the Sun
. Based on the chromospheric
observations, it was found that the age is 5.7 ± 1.3 billion years. The total lifetime of a 1.2 sol mass star should be 1.2 -2.5 × 1010, which is under 6.4 billion years; this star is in the last stage on the main sequence
, and its nearby planets will soon be engulfed.
Based on spectral observations, the star was found to be metal-rich, 74% more metal
s than Sol. , it is thought that two extrasolar planet
s orbit the star, but only one has been confirmed.
was discovered (in 2007) using the radial velocity method. Later observations showed that this planet also transited the star.
In February 2008, a second planet, HD 17156 c
, was proposed, with a 5:1 mean motion resonance to the inner planet HD 17156 b.
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 255 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s 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....
of Cassiopeia
Cassiopeia (constellation)
Cassiopeia is a constellation in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivalled beauty. Cassiopea was one of the 48 constellations listed by the 2nd century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today...
. The apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
is 8.17, which means it is not visible to the naked eye
Naked eye
The naked eye is a figure of speech referring to human visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered "naked"...
but can be seen with good binoculars
Binoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
. The Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
to star distance is 255.19 ly or 78.24 pc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
.
The mass of the star is 20% more massive and 47% larger than our Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. Based on its absolute magnitude
Absolute magnitude
Absolute magnitude is the measure of a celestial object's intrinsic brightness. it is also the apparent magnitude a star would have if it were 32.6 light years away from Earth...
of 3.70 and spectral type of G0, the star is thought to be hotter than the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. Based on the chromospheric
Chromosphere
The chromosphere is a thin layer of the Sun's atmosphere just above the photosphere, roughly 2,000 kilometers deep....
observations, it was found that the age is 5.7 ± 1.3 billion years. The total lifetime of a 1.2 sol mass star should be 1.2 -2.5 × 1010, which is under 6.4 billion years; this star is in the last stage on the main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
, and its nearby planets will soon be engulfed.
Based on spectral observations, the star was found to be metal-rich, 74% more metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
s than Sol. , it is thought that 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 orbit the star, but only one has been confirmed.
Planetary system
It is the first star in Cassiopeia around which an orbiting planetHD 17156 b
HD 17156 b is an extrasolar planet approximately 255 light-years away in the constellation of Cassiopeia. The planet was discovered orbiting the yellow subgiant star HD 17156 in April 2007. The planet is classified as a relatively cool hot Jupiter planet slightly smaller than Jupiter but slightly...
was discovered (in 2007) using the radial velocity method. Later observations showed that this planet also transited the star.
In February 2008, a second planet, HD 17156 c
HD 17156 c
HD 17156 c is a plausible extrasolar planet approximately 255 light-years away in the constellation of Cassiopeia. The planet is thought to be orbiting the yellow giant star HD 17156. This planet has a mass of 0.063 Jupiter mass and takes about 111.314 days or 0.305 year to orbit the star,...
, was proposed, with a 5:1 mean motion resonance to the inner planet HD 17156 b.
External links
- Extrasolar Planet Interactions by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona