Gliese 436

Gliese 436

Starbox begin
name = Gliese 436
Starbox observe
epoch=J2000
ra=RA|11|42|11.0941cite web
url=http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=LHS+310
title=LHS 310
work=Simbad
publisher=Centre de Données astronomiques de Strasbourg
accessdate=2007-11-28
]
dec=DEC| +26|42|23.652
appmag_v=10.67
constell=Leo
Starbox character
class=M2.5 Vcite journal
last=Butler
first=R. Paul
coauthors=Vogt, Steven S.; Marcy, Geoffrey W.; Fischer, Debra A.; Wright, Jason T.; Henry, Gregory W.; Laughlin, Greg; Lissauer, Jack J.
title=A Neptune-Mass Planet Orbiting the Nearby M Dwarf GJ 436
journal=The Astrophysical Journal
year=2004
volume=617
issue=1
pages=580–588
url=http://adsabs.harvard.edu/abs/2004ApJ...617..580B
accessdate=2007-11-28
doi=10.1086/425173
format=abstract
]
b-v=1.52
u-b=
variable=
Starbox astrometry
radial_v=10
prop_mo_ra=896.34
prop_mo_dec=−813.70
parallax=97.73
p_error=2.27
parallax_footnote=
absmag_v=10.63
Starbox detail
mass=0.41±0.05
radius=0.42cite journal
last=Johnson
first=H. M.
coauthors=Wright, C. D.
title=Predicted infrared brightness of stars within 25 parsecs of the sun
journal=Astrophysical Journal Supplement Series
year=1983
volume=53
pages=643–711
url=http://adsbit.harvard.edu/abs/1983ApJS...53..643J
accessdate=2007-11-28
doi=10.1086/190905
format=abstract
—see page 673.]
luminosity=0.019fact|date=December 2007
temperature=3318
metal= [M/H] =-0.32cite journal
last=Bean | first=Jacob L.
coauthors=Benedict, G. Fritz; Endl, Michael
title=Metallicities of M Dwarf Planet Hosts from Spectral Synthesis
journal=The Astrophysical Journal
year=2006 | volume=653 | issue=1 | pages=L65–L68
url=http://adsabs.harvard.edu/abs/2006astro.ph.11060B
accessdate=2007-11-28
doi=10.1086/510527
format=abstract
—for the metallicity, note that egin{smallmatrix}10^{-0.32} = 0.44end{smallmatrix} or 44%]
rotation=<3 km/s
age=6.5&ndash;9.9&times;109cite journal
last=Saffe
first=C.
coauthors=G&oacute;mez, M.; Chavero, C.
title=On the Ages of Exoplanet Host Stars
journal=Astronomy & Astrophysics
year=2006
url=http://fr.arxiv.org/abs/astro-ph/0510092
accessdate=2007-11-28
format=abstract
]
Starbox catalog
names=Ross 905, GJ 436, LTT 13213, GCTP 2704.10, LHS 310, AC+27:28217, Vyssotsky 616, HIP 57087.

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.

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. 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% 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.

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.

Planetary system

The star is orbited by one known extrasolar planet, designated Gliese 436 b. Other planets outside its orbit have been proposed.

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 m sin 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". [cite journal
url = http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...472L..13G&db_key=AST&nosetcookie=1
author = Gillon, M.; Pont, F.; Demory, B.-O.; Mallmann, F.; Mayor, M.; Mazeh, T.; Queloz, D.; Shporer, A.; Udry, S.; Vuissoz, C.
title = Detection of transits of the nearby hot Neptune GJ 436 b
journal = Astronomy and Astrophysics
volume = 472
issue = 2
pages = L13–L16
year = 2007
doi = 10.1051/0004-6361:20077799
]

In June 2007, Gliese 436 b's eccentricity was narrowed to 0.15 +/-0.012. This was deemed improbable unless another planet of similar mass existed close to it.Cite arXiv|author=Deming, D. "et al."|title=Spitzer Transit and Secondary Eclipse Photometry of GJ 436b|eprint=0707.2778|class=astro-ph|year=2007] PlanetboxOrbit
exoplanet = b
mass = 0.041±0.05
period = 2.64385±0.00009
semimajor = 0.0291±0.0004
eccentricity = 0.150±0.012

Possible second planet

In 2008, a second planet, designated "Gliese 436 c" was claimed to have been discovered; with an orbital period of 5.2 days and an orbital semimajor axis of 0.045 AU. [cite arXiv | author = Ribas, I.; Font-Ribera, S.; Beaulieu, J. P. | title = A ~5 ME Super-Earth Orbiting GJ 436?: The Power of Near-Grazing Transits | year = 2008 | eprint = 0801.3230 | class = astro-ph | accessdate = 2008-02-04] 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. 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. [cite web | url=http://www.space.com/scienceastronomy/080409-smallest-exoplanet.html | title=New Super-Earth is Smallest Yet |work=Space.com | accessdate=2008-04-10] Gliese 436 c was announced by Spanish scientists in April 2008 by analyzing its influence on the orbit of Gliese 436 b. [http://www.reuters.com/article/scienceNews/idUSL0956988620080409 Reuters] ] 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. Also, if it did orbit at these parameters, the system would be the only "Unstable" orbit on UA's [http://www.lpl.arizona.edu/~rory/research/xsp/dynamics/ Extrasolar Planet Interactions] chart. The existence of this "Gliese 436 c" was thus regarded as unlikely, [cite arXiv
author = Alonso, R.; Barbieri, M.; Rabus, M.; Deeg, H. J.; Belmonte, J. A.;Almenara J. M.
title = Limits to the planet candidate GJ 436c
year = 2008
eprint = 0804.3030
class = astro-ph
accessdate = 2008-05-12
] and the discovery was eventually retracted at the Transiting Planets conference in Boston, 2008. [cite web
url = http://exoplanet.eu/star.php?st=GJ+436
title = Notes for star GJ 436
work = The Extrasolar Planets Encyclopaedia
author = Schneider, J.
accessdate = 2008-09-07
]

Despite the retraction, studies have concluded that the possibility that there is an additional planet orbiting Gliese 436 remains plausible. [Cite arXiv|author=Jacob L. Bean and Andreas Seifahrt|title=Observational Consequences of the Recently Proposed Super-Earth Orbiting GJ436|eprint=0806.3270v2|class=astro-ph|year=2008] With the aid of an unnoticed transit automatically recorded at NMSU on January 11, 2005 and observations by amateur astronomers, it has been suggested that there is a trend of increasing inclination of the orbit of Gliese 436 b, though this trend remains unconfirmed. This trend is compatible with a perturbation by a planet of less than 12 Earth masses on an orbit within about 0.08 AU of the star.Cite arXiv|author=Jeffrey L. Coughlin "et al."|title=New Observations and a Possible Detection of Parameter Variations in the Transits of Gliese 436b| eprint=0809.1664v1| class=astro-ph| year=2008]

References

External links

*cite web
url=http://exoplanet.eu/star.php?st=GJ+436
title=Notes for star GJ 436
work=The Extrasolar Planets Encyclopaedia
accessdate=2008-08-06

*cite web
url=http://www.solstation.com/stars2/gl436.htm
title=Gliese 436 / AC+27 28217
publisher=SolStation company
accessdate=2007-11-28


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