Gliese 436

From Wikipedia, the free encyclopedia

Gliese 436
Observation data
Epoch J2000
Constellation
(pronunciation)		 Leo
Right ascension 11h 42m 11.0941s[1]
Declination +26° 42′ 23.652″[1]
Apparent magnitude (V) 10.67[2]
Characteristics
Spectral type M2.5 V[2]
B-V color index 1.52[2]
Astrometry
Radial velocity (Rv) 10[1] km/s
Proper motion (μ) RA: 896.34[1] mas/yr
Dec.: −813.70[1] mas/yr
Parallax (π) 97.73 ± 2.27[1] mas
Distance 33.4 ± 0.8 ly
(10.2 ± 0.2 pc)
Absolute magnitude (MV) 10.63[2]
Details
Mass 0.41±0.05[2] M☉
Radius 0.42[3] R☉
Luminosity 0.019[citation needed] L☉
Temperature 3318[3] K
Metallicity [M/H]=-0.32[4]
Rotation <3 km/s[2]
Age 6.5–9.9×109[5] years
Other designations
Ross 905, GJ 436, LTT 13213, GCTP 2704.10, LHS 310, AC+27:28217, Vyssotsky 616, HIP 57087.[1]

Gliese 436 is a red dwarf star approximately 33 light-years away in the constellation of Leo. As of 2004, the confirmation of at least one extrasolar planet is documented, with an unconfirmed terrestrial planet speculated to be orbiting in the system.

Contents

[edit] Star

Stellar models for this star give an estimated size of about 42% of the Sun's radius. The same model predicts a surface temperature of about 3318 K.[3] Gl 436 is older than the Sun by several billion years but it only has an abundance of heavy elements (with masses greater than helium-4) equal to 44%[4] of the Sun's. The projected rotation velocity is less than 3 km/s, and the chromosphere has only a low level of magnetic activity.[2]

This star is a member of the "old-disk population" with velocities in the galactic coordinate system of U=+44, V=−20 and W=+20 km/s.[2]

[edit] Planetary system

The star is orbited by one known extrasolar planet, designated Gliese 436 b.

Gliese 436 b has an orbital period of 2.6 Earth Days and transits the star as viewed from Earth. It has a mass of 22.2 times Earth's Mass and is roughly 55,000 km in diameter, giving it a mass and radius similar to the ice giant planets Uranus and Neptune in our solar system. In general, Doppler spectroscopy measurements do not measure the true mass of the planet, but instead measure the product msin(i), where m is the true mass and i is the inclination of the orbit (the angle between the line-of-sight and the normal to the planet's orbital plane), a quantity that is generally unknown. However, for Gliese 436 b, the transits enable the determination of the inclination, as they show that the planet's orbital plane is very nearly in the line of sight (i.e. that the inclination is close to 90 degrees). Hence the mass quoted is the actual mass. The planet is thought to be largely composed of hot ices with an outer envelope of hydrogen and helium, and is termed a "hot Neptune".[6]

In 2008, the discovery of a second planet, designated "Gliese 436 c" was announced with an orbital period of 5.2 days and an orbital semimajor axis of 0.045 AU.[7] The planet was thought to have a mass of roughly 5 Earth Masses and have a radius about 1.5 times larger than the Earth's.[8] Despite being announced in the media as being the smallest known extrasolar planet, it would still have been more massive than the three planets orbiting the pulsar PSR B1257+12, which have been known since 1992. Due to its size, the planet was thought to be a rocky, terrestrial planet.[9] Gliese 436 c was announced by Spanish scientists in April 2008 by analyzing its influence on the orbit of Gliese 436 b.[8] Further analysis showed that the transit length of the inner planet is not changing, a situation which rules out most possible configurations for this system. The existence of the planet Gliese 436 c was thus regarded as unlikely,[10] and the discovery was eventually retracted at the Transiting Planets conference in Boston, 2008.[11]

The Gliese 436 system
Planet
(in order from star)		 Mass
(MJ)		 Orbital period
(days)		 Semimajor axis
(AU)		 Eccentricity
b 22.2±1.0 2.64385±0.00009 0.0291±0.0004 0.150±0.012

[edit] References

  1. ^ a b c d e f g LHS 310. Simbad. Centre de Données astronomiques de Strasbourg. Retrieved on 2007-11-28.
  2. ^ a b c d e f g h Butler, R. Paul; Vogt, Steven S.; Marcy, Geoffrey W.; Fischer, Debra A.; Wright, Jason T.; Henry, Gregory W.; Laughlin, Greg; Lissauer, Jack J. (2004). "A Neptune-Mass Planet Orbiting the Nearby M Dwarf GJ 436" (abstract). The Astrophysical Journal 617 (1): 580-588. doi:10.1086/425173. 
  3. ^ a b c Johnson, H. M.; Wright, C. D. (1983). "Predicted infrared brightness of stars within 25 parsecs of the sun" (abstract). Astrophysical Journal Supplement Series 53: 643-711. doi:10.1086/190905. —see page 673.
  4. ^ a b Bean, Jacob L.; Benedict, G. Fritz; Endl, Michael (2006). "Metallicities of M Dwarf Planet Hosts from Spectral Synthesis" (abstract). The Astrophysical Journal 653 (1): L65-L68. doi:10.1086/510527. —for the metallicity, note that \begin{smallmatrix}10^{-0.32} = 0.44\end{smallmatrix} or 44%
  5. ^ Saffe, C.; Gómez, M.; Chavero, C. (2006). "On the Ages of Exoplanet Host Stars" (abstract). Astronomy & Astrophysics. 
  6. ^ Gillon, M.; Pont, F.; Demory, B.-O.; Mallmann, F.; Mayor, M.; Mazeh, T.; Queloz, D.; Shporer, A.; Udry, S.; Vuissoz, C. (2007). "Detection of transits of the nearby hot Neptune GJ 436 b". Astronomy and Astrophysics 472 (2): L13–L16. doi:10.1051/0004-6361:20077799. 
  7. ^ Ribas, I.; Font-Ribera, S.; Beaulieu, J. P. (2008). "A ~5 ME Super-Earth Orbiting GJ 436?: The Power of Near-Grazing Transits" arxiv:0801.3230 [astro-ph]. Retrieved on 2008-02-04.
  8. ^ a b Reuters
  9. ^ New Super-Earth is Smallest Yet. Space.com. Retrieved on 2008-04-10.
  10. ^ Alonso, R.; Barbieri, M.; Rabus, M.; Deeg, H. J.; Belmonte, J. A.;Almenara J. M. (2008). "Limits to the planet candidate GJ 436c" arxiv:0804.3030 [astro-ph]. Retrieved on 2008-05-12.
  11. ^ Schneider, J.. Notes for star GJ 436. The Extrasolar Planets Encyclopaedia. Retrieved on 2008-05-23.

[edit] External links


Sirius  This main sequence star-related article is a stub. You can help Wikipedia by expanding it.