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| {{Starbox begin
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| | name = [[Bright Star Catalogue|HR]] 8799
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| }}
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| {{Starbox image
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| | image = [[Image:Benjamin Zuckerman HR 8799 planets image Dec. 2010.jpg|250px]]
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| | caption = HR 8799 (center blob) with HR 8799e (right), HR 8799d (lower right), HR 8799c (upper right), HR 8799b (upper left) from [[W. M. Keck Observatory]]
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| }}
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| {{Starbox observe
| |
| | epoch = [[J2000.0]]
| |
| | equinox = [[J2000.0]] ([[International Celestial Reference System|ICRS]])
| |
| | constell = [[Pegasus (constellation)|Pegasus]]
| |
| | ra = {{RA|23|07|28.7150}}<ref name=sb>{{SIMBAD link|HR+8799|V* V342 Peg -- Variable Star of gamma Dor type}}, entry, [[SIMBAD]]. Accessed on line November 14, 2008.</ref>
| |
| | dec = {{DEC|+21|08|03.302}}<ref name=sb />
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| | appmag_v = 5.964<ref name=sb />
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| }}
| |
| {{Starbox character
| |
| | class = kA5 hF0 mA5 V; λ Boo<ref name="Gray1999" /><ref name="Kaye1999" />
| |
| | u-b = −0.04<ref name=bsc1>[http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=V/50/catalog&recno=8799 HR 8799], database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., [[Centre de Données astronomiques de Strasbourg|CDS]] ID [http://vizier.u-strasbg.fr/viz-bin/Cat?V/50 V/50]. Accessed on line November 14, 2008.</ref>
| |
| | b-v = 0.234<ref name=sb />
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| | variable = [[Gamma Doradus variable]]<ref name=sb />
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| }}
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| {{Starbox astrometry
| |
| | radial_v = −11.5 ± 2<ref name=sb />
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| | prop_mo_ra = {{nowrap|107.93 ± 0.60}}<ref name="vanLeeuwen2007">{{cite web|url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=113804|title=HIP 114189|work=Hipparcos, the New Reduction|author=van Leeuwen, F.|year=2007|accessdate=2008-10-13}}</ref>
| |
| | prop_mo_dec = {{nowrap|−49.63 ± 0.46}}<ref name="vanLeeuwen2007" />
| |
| | parallax = 25.38
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| | p_error = 0.70
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| | parallax_footnote = <ref name="vanLeeuwen2007" />
| |
| | absmag_v = {{nowrap|2.98 ± 0.08}}<ref name="Gray1999" />
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| }}
| |
| {{Starbox detail
| |
| | mass = {{nowrap|1.47 ± 0.30}}<ref name="Gray1999" />
| |
| | metal_fe = {{nowrap|−0.47 ± 0.10}}<ref name="Gray1999" /><ref group="note">The star is a member of the [[Lambda Boötis stars|Lambda Boötis]] class of [[peculiar star]]s, thus the observed abundance may not reflect the abundances of the star as a whole.</ref>
| |
| | gravity = {{nowrap|4.35 ± 0.05}}<ref name="Gray1999" />
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| | age = 30{{±|20|10}} million<ref name=Marois2011/>
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| | luminosity_bolometric = {{nowrap|4.92 ± 0.41}}<ref name="Gray1999" />
| |
| | rotational_velocity = {{nowrap|37.5 ± 2}}<ref name="Gray1999" />
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| | temperature = {{nowrap|7430 ± 75}}<ref name="Gray1999" />
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| | radius = {{nowrap|1.34 ± 0.05}}<ref name="Gray1999" />
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| }}
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| {{Starbox catalog
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| | names = [[GCVS|V342 Pegasi]], [[Bonner Durchmusterung|BD]]+20 5278, [[Fifth Fundamental Catalogue|FK5]] 3850, [[Boss General Catalogue|GC]] 32209, [[Henry Draper catalogue|HD]] 218396, [[Hipparcos catalogue|HIP]] 114189, [[PPM Star Catalogue|PPM]] 115157, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]] 91022, [[Tycho Catalogue|TYC]] 1718-2350-1.<ref name=sb />
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| }}
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| {{Starbox reference
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| | Simbad = HR+8799
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| | EPE = HR+8799
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| | NSTED = HR+8799
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| }}
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| {{Starbox end}}
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| | |
| '''HR 8799''' is a young (~30 million-year-old) [[main sequence|main-sequence]] [[star]] located 129 [[light year]]s (39 [[parsec]]s) away from [[Earth]] in the [[constellation]] of [[Pegasus (constellation)|Pegasus]], with roughly 1.5 times the [[Sun]]'s mass and 4.9 times its luminosity. It is part of a system that also contains a [[debris disk]] and at least four [[gas giant|massive planets]].<ref name=Marois2011/> Those planets, along with [[Fomalhaut b]], were the first [[extrasolar planet]]s whose orbital motion was confirmed via [[direct imaging]]. The designation ''HR 8799'' is the star's identifier in the [[Bright Star Catalogue]]. The star is a [[Gamma Doradus variable]]: its [[luminosity]] changes because of non-radial pulsations of its surface. The star is also classified as a [[Lambda Boötis star]], which means its surface layers are depleted in [[iron peak]] [[Chemical element|element]]s.<ref name="Gray1999">{{cite journal|title=HR 8799: A Link between γ Doradus Variables and λ Bootis Stars|author=Gray, R.O. and Kaye, A.B.|year=1999|journal=[[The Astronomical Journal]]|volume=118|issue=6|pages=2993–2996|doi=10.1086/301134|bibcode=1999AJ....118.2993G}}</ref> This may be due to the [[accretion (astrophysics)|accretion]] of [[metallicity|metal]]-poor circumstellar gas.<ref>{{cite journal|title=A Spectroscopic Search for λ Bootis and Other Peculiar A-Type Stars in Intermediate-Age Open Clusters|author=Gray, R.O. and Corbally, C.J.|year=2002|journal=[[The Astronomical Journal]]|volume=124|issue=2|pages=989–1000|doi=10.1086/341609|bibcode=2002AJ....124..989G}}</ref> It is the only known star which is simultaneously a Gamma Doradus variable, a [[Lambda Boötis star|Lambda Boötis]] type, and a [[Vega]]-like star (a star with [[infrared excess|excess infrared emission]] caused by a [[circumstellar disk]]).<ref name="Marois2008">{{cite journal |last=Marois |first=Christian |authorlink= |coauthors=''et al.'' |date=November 2008 |title=Direct Imaging of Multiple Planets Orbiting the Star HR 8799 |journal=[[Science (journal)|Science]] |volume=322 |issue=5906 |pages=1348–1352 |doi=10.1126/science.1166585 |arxiv=0811.2606 |accessdate= |quote= |pmid=19008415 |bibcode = 2008Sci...322.1348M }}</ref>
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| ==Stellar properties==
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| The star HR 8799 is a member of the [[Lambda Boötis star|Lambda Boötis]] (λ Boo) class, a group of [[peculiar star]]s with an unusual lack of metals—elements heavier than hydrogen and helium—in their upper atmosphere. Because of this special status, stars like HR 8799 have a very complex spectral type. The luminosity profile of the [[Balmer lines]] in the star's spectrum, as well as the star's [[effective temperature]], best match the typical properties of an [[F-type main sequence star|F0 V star]]. However, the strength of the [[calcium]] II K [[absorption line]] and the other metallic lines are more like those of an [[A-type main sequence star|A5 V star]]. The star's spectral type is therefore written as {{nowrap|kA5 hF0 mA5 V; λ Boo}}.<ref name="Gray1999" /><ref name="Kaye1999">{{cite journal|title=Gamma Doradus Stars: Defining a New Class of Pulsating Variables|author=Kaye, A.B. ''et al.''|year=1999|journal=[[PASP]]|volume=111|issue=761|pages=840–844|bibcode=1999PASP..111..840K|doi=10.1086/316399|arxiv = astro-ph/9905042 }}</ref>
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| Age determination of this star shows some variation based on the method used. Statistically, for stars hosting a debris disk, the luminosity of this star suggests an age of about 20–150 million years. Comparison with stars having similar motion through space gives an age in the range 30–160 million years. Given the star's position on the [[Hertzsprung–Russell diagram]] of temperature versus luminosity, it has an estimated age in the range of 30–1,128 million years. λ Boötis stars like this are generally young, with a mean age of a billion years. More accurately, [[asteroseismology]] also suggests an age of approximately a billion years.<ref>{{citation | display-authors=1 | last1=Moya | first1=A. | last2=Amado | first2=P. J. | last3=Barrado | first3=D. | last4=García Hernández | first4=A. | last5=Aberasturi | first5=M. | last6=Montesinos | first6=B. | last7=Aceituno | first7=F. | title=Age determination of the HR8799 planetary system using asteroseismology | journal=Monthly Notices of the Royal Astronomical Society: Letters | volume=405 | issue=1 | pages=L81–L85 |date=June 2010 | doi=10.1111/j.1745-3933.2010.00863.x | bibcode=2010MNRAS.405L..81M | arxiv=1003.5796 }}</ref> However, this is disputed because it would make the planets become brown dwarfs to fit into the cooling models. Brown dwarfs would not be stable in such a configuration. The best accepted value for an age of HR8799 is 30 million years, consistent with being a member of the Columba Association co-moving group of stars.<ref>{{cite paper | display-authors=1 | last1=Zuckerman | first1=B. | last2=Rhee | first2=Joseph H. | last3=Song | first3=Inseok | last4=Bessell | first4=M. S. | title=The Tucana/Horologium, Columba, AB Doradus, and Argus Associations: New Members and Dusty Debris Disks | journal=The Astrophysical Journal | volume=732 | issue=2 | month=May | year=2011 | doi=10.1088/0004-637X/732/2/61 | bibcode=2011ApJ...732...61Z | arxiv=1104.0284v1 }}</ref>
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| Detailed analysis of the star's spectrum reveals that it has a slight overabundance of [[carbon]] and [[oxygen]] compared to the Sun (by approximately 30% and 10% respectively). While some Lambda Boötis stars have [[sulfur]] abundances similar to that of the Sun, this is not the case for HR 8799; the sulfur abundance is only around 35% of the solar level. The star is also poor in elements heavier than [[sodium]]: for example, the iron abundance is only 28% of the solar iron abundance.<ref>{{cite journal|title=λ Bootis-Like Abundances in the Vega-Like, γ Doradus Type-Pulsator HD 218396|author=Kozo, Sadakane|year=2006|journal=Publications of the Astronomical Society of Japan|volume=58|issue=6|pages=1023–1032|url=http://pasj.asj.or.jp/v58/n6/580611/580611-frame.html|bibcode=2006PASJ...58.1023S}}</ref> [[Asteroseismology|Asteroseismic]] observations of other pulsating Lambda Boötis stars suggest that the peculiar abundance patterns of these stars are confined to the surface only: the bulk composition is likely more normal. This may indicate that the observed element abundances are the result of the accretion of metal-poor gas from the environment around the star.<ref>{{cite journal|title=Pulsation in λ Bootis stars|author=Paunzen, E. ''et al.''|year=1998|journal=[[Astronomy and Astrophysics]]|volume=335|pages=533–538|url=http://aa.springer.de/bibs/8335002/2300533/small.htm|bibcode=1998A&A...335..533P}}</ref>
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| Astroseismic analysis using spectroscopic data indicates that the rotational inclination of the star is constrained to be greater than or approximately equal to 40°. This contrasts with the planet's orbital inclinations, which are in roughly the same plane at an angle of about 20° ± 10°. Hence, there may be an unexplained misalignment between the rotation of the star and the orbits of its planets.<ref>{{citation | display-authors=1 | last1=Wright | first1=D. J. | last2=Chené | first2=A.-N. | last3=De Cat | first3=P. | last4=Marois | first4=C. | last5=Mathias | first5=P. | last6=Macintosh | first6=B. | last7=Isaacs | first7=J. | last8=Lehmann | first8=H. | last9=Hartmann | first9=M. | title=Determination of the Inclination of the Multi-planet Hosting Star HR 8799 Using Asteroseismology | journal=The Astrophysical Journal Letters | volume=728 | issue=1 |date=February 2011 | doi=10.1088/2041-8205/728/1/L20 | bibcode=2011ApJ...728L..20W | arxiv=1101.1590 }}</ref> Observation of this star with the [[Chandra X-ray Observatory]] indicates that it has a weak level of [[Stellar magnetic field|magnetic activity]], but the X-ray activity is much higher than that of an A-type star like [[Altair]]. This suggests that the internal structure of the star more closely resembles that of an F0 star. The temperature of the [[corona]] is about 3.0 million K.<ref>{{citation | last1=Robrade | first1=J. | last2=Schmitt | first2=J. H. M. M. | title=X-ray emission from the remarkable A-type star HR 8799 | journal=Astronomy and Astrophysics | volume=516 |date=June 2010 | doi=10.1051/0004-6361/201014027 | bibcode=2010A&A...516A..38R | arxiv=1004.1318 }}</ref>
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| ==Planetary system==
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| On November 13, 2008, Christian Marois of the National Research Council of Canada's [[Herzberg Institute of Astrophysics]] and his team announced they had directly observed three [[Extrasolar planet|planets]] orbiting the star with the [[W. M. Keck Observatory|Keck]] and [[Gemini Observatory|Gemini]] telescopes in [[Hawaii]],<ref name="Marois2008" /><ref name="Gemini2008">{{cite press release|url=http://www.gemini.edu/node/11151|title=Gemini Releases Historic Discovery Image of Planetary First Family|publisher=Gemini Observatory|date=2008-11-13|accessdate=2008-11-13}}</ref><ref name="Keck2008">{{cite press release|url=http://www.keckobservatory.org/article.php?id=231|title=Astronomers capture first images of newly-discovered solar system|publisher=W. M. Keck Observatory|date=2008-11-13|accessdate=2008-11-13}}</ref><ref name="WashPost Achenbach">{{cite news|title=Scientists Publish First Direct Images of Extrasolar Planets|first=Joel|last=Achenbach|work=[[The Washington Post]]|publisher=[[The Washington Post Company]]|date=2008-11-13|accessdate=2008-11-13|url=http://www.washingtonpost.com/wp-dyn/content/article/2008/11/13/AR2008111302267.html}}</ref> in both cases employing [[adaptive optics]] to make observations in the [[infrared]].<ref group=note>The planets are young and therefore they are still hot and bright in the [[near-infrared]] part of the spectrum .</ref> A [[precovery]] observation of the outer 3 planets was later found in infrared images obtained in 1998 by the [[Hubble Space Telescope]]'s [[Near Infrared Camera and Multi-Object Spectrometer|NICMOS]] instrument, after a newly developed image-processing technique was applied.<ref>{{cite web
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| | last = Villard
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| | first = Ray
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| | authorlink =
| |
| | coauthors = Lafreniere, David
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| | title = Hubble Finds Hidden Exoplanet in Archival Data
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| | work = [http://hubblesite.org/newscenter/ HubbleSite NewsCenter]
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| | publisher = [[NASA]]
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| | date = April 1, 2009
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| | url = http://hubblesite.org/newscenter/archive/releases/2009/15/full/
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| | accessdate = 2009-04-03}}</ref> Further observations in 2009–2010 revealed the fourth giant planet orbiting inside the first three planets at a projected separation just less than 15 AU <ref name=Marois2011/><ref name="Currie2011"/> which has now also been confirmed in multiple studies.<ref name="Skemer2012">{{cite journal |last=Skemer |first=Andrew |authorlink= |coauthors=''et al.'' |date=July 2012 |title=First Light LBT AO Images of HR 8799 bcde at 1.6 and 3.3 μm: New Discrepancies between Young Planets and Old Brown Dwarfs |journal=[[The Astrophysical Journal|ApJ]] |volume=753 |issue=1|pages=14 |arxiv=1203.2615 |bibcode = 2012ApJ...753...14S |doi = 10.1088/0004-637X/753/1/14 }}</ref>
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| The outer planet orbits inside a dusty disk like the Solar [[Kuiper belt]]. It is one of the most massive disks known around any star within 300 light years of Earth, and there is room in the inner system for [[terrestrial planet]]s.<ref name="Keck2008" /> There is an additional debris disk just inside the orbit of the innermost planet.<ref name=Marois2011/>
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| The orbital radii of planets [[HR 8799 e|e]], [[HR 8799 d|d]], [[HR 8799 c|c]] and [[HR 8799 b|b]] are 2 to 3 times those of [[Jupiter]], [[Saturn]], [[Uranus]], and [[Neptune]], respectively. Because of the [[Inverse-square law#Light and other electromagnetic radiation|inverse square law]] relating [[Electromagnetic radiation|radiation]] [[Intensity (physics)|intensity]] to distance from the source, comparable radiation intensities are present at distances <math>\scriptstyle\sqrt{4.9}</math> = 2.2 times farther from HR 8799 than from the Sun, meaning that corresponding planets in the solar and HR 8799 systems receive similar amounts of stellar radiation.<ref name=Marois2011/>
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| These objects are near the upper mass limit for classification as planets; if they exceeded 13 [[Jupiter mass]]es, they would be capable of [[deuterium]] [[nuclear fusion|fusion]] in their interiors and thus qualify as [[brown dwarf]]s under the definition of these terms used by the [[IAU]]'s Working Group on Extrasolar Planets.<ref>{{cite web|url=http://www.dtm.ciw.edu/boss/definition.html|title=Definition of a "Planet"|publisher=Working Group on Extrasolar Planets (WGESP) of the International Astronomical Union|accessdate=2008-11-16}}</ref> If the mass estimates are correct, the HR 8799 system is the first multiple-planet extrasolar system to be directly imaged.<ref name="Gemini2008" /> The orbital motion of the planets is in an anticlockwise direction and was confirmed via multiple observations dating back to 1998.<ref name="Marois2008"/> The system is more likely to be stable if the planets "e", "d" and "c" are in a 4:2:1 resonance, which would imply that the orbit the planet ''d'' has an eccentricity exceeding 0.04 in order to match the observational constraints. Planetary systems with the best-fit masses from evolutionary models would be stable if the outer three planets are in a 1:2:4 [[orbital resonance]] (similar to the [[Laplace resonance]] between Jupiter's inner three [[Galilean satellites]]: [[Io (moon)|Io]], [[Europa (moon)|Europa]] and [[Ganymede (moon)|Ganymede]] as well as three of the planets in the [[Gliese 876]] system).<ref name=Marois2011/> However, it is now believed that planet b is not in resonance with the other 3 planets. If confirmed, the HR 8799 planetary system would be the second extrasolar system to be observed with multiple resonances. The 4 planets are still glowing red hot due to their young age and are larger than Jupiter and over time they will cool and shrink to the size of 0.8 to 1.0 Jupiter radii.
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| The broadband photometry of planets b, c and d has shown that there may be significant clouds in their atmospheres,<ref name="Currie2011">{{cite journal |last=Currie |first=Thayne |authorlink= |coauthors=''et al.'' |date=March 2011 |title=A Combined Subaru/VLT/MMT 1--5 Micron Study of Planets Orbiting HR 8799: Implications for Atmospheric Properties, Masses, and Formation |journal=[[The Astrophysical Journal|ApJ]] |volume=729 |issue=2|pages=128 |arxiv=1101.1973 |bibcode = 2011ApJ...729..128C |doi = 10.1088/0004-637X/729/2/128 }}</ref> while the infrared spectroscopy of planets b and c pointed to non-equilibrium CO/CH<sub>4</sub> chemistry.<ref name=Marois2011/> Near-infrared observations with the [[Project 1640]] integral field spectrograph on the Palomar Observatory have shown that compositions between the four planets vary significantly. This is a surprise since the planets presumably formed in the same way from the same disk and have similar luminosities.<ref name=Gilliland>{{cite web|first = B. R. Oppenheimer|title= Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy|url=http://arxiv.org/abs/1303.2627|publisher=Cornell University|accessdate=12 March 2013}}</ref>
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| [[File:Spectrum of planet around HR 8799 (annotated).jpg|thumb|left|alt=Spectrum of planet around HR 8799. Credit: ESO/M. Janson.|The spectrum is that of a giant exoplanet, orbiting around the bright and very young star HR 8799, about 130 light-years away. This spectrum of the star and the planet was obtained with the NACO adaptive optics instrument on [[European Southern Observatory|ESO]]’s [[Very Large Telescope]].]]
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| <div style="float:right">
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| {{OrbitboxPlanet begin
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| | table_ref=<ref name=Marois2011/><ref name="epe">{{cite web|url=http://exoplanet.eu/star.php?st=HR+8799|title=Notes for star HR 8799|work=The Extrasolar Planets Encyclopaedia|author=Schneider, J.|accessdate=2008-10-13}}</ref>
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| | period_unit=year
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| }}
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| {{OrbitboxPlanet
| |
| | exoplanet = [[HR 8799 e|e]]
| |
| | mass = 7{{±|3|2}}
| |
| | period = ~45
| |
| | semimajor = 14.5 ± 0.5
| |
| | eccentricity = ?
| |
| | radius = ?
| |
| }}
| |
| {{OrbitboxPlanet
| |
| | exoplanet = [[HR 8799 d|d]]
| |
| | mass = 7{{±|3|2}}
| |
| | period = ~100
| |
| | semimajor = 24±0
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| | eccentricity = >0.04<ref name="Fabrycky2008">{{cite journal |title=Stability of the directly imaged multiplanet system HR 8799: resonance and masses |date=1 December 2008|pages=1408–1421 |accessdate=2008-12-02 |issue=2 |last1=Fabrycky | first1=Daniel C. |volume=710 |last2=Murray-Clay | first2=Ruth A. |doi=10.1088/0004-637X/710/2/1408 |journal=Astrophys.J. |arxiv=0812.0011|bibcode = 2010ApJ...710.1408F }}</ref><ref group="note">The eccentricity is given for the case that the planet is in a 2:1 resonance with [[HR 8799 c]], as suggested by stability constraints.</ref>
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| | inclination = 28
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| | radius = 1.2{{±|0.1|0}}
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| }}
| |
| {{OrbitboxPlanet
| |
| | exoplanet = [[HR 8799 c|c]]
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| | mass = 7{{±|3|2}}
| |
| | period = ~190
| |
| | semimajor = 38±0
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| | eccentricity = ?
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| | inclination = 28
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| | radius = 1.2{{±|0.1|0}}
| |
| }}
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| {{OrbitboxPlanet
| |
| | exoplanet = [[HR 8799 b|b]]
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| | mass = 5{{±|2|1}}
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| | period = ~460
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| | semimajor = 68±0
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| | eccentricity = ?
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| | inclination = 28
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| | radius = 1.2{{±|0.1|0.1}}
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| }}
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| {{OrbitboxPlanet disk
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| | disk = Dust disk
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| | periapsis = 6–1000
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| }}
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| {{Orbitbox end}}
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| </div>
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| {{clear}}
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| ===Planet Spectra===
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| A number of studies have used the spectra of HR8799's planets to determine their chemical compositions and constrain their formation scenarios. The first spectroscopic study of planet b (performed at near-infrared wavelengths) detected strong water absorption, which indicates a hydrogen-rich atmosphere. Weak methane and carbon monoxide absorption in this planet's atmosphere was also detected, indicating efficient vertical mixing of the atmosphere and a disequilibrium CO/CH4 ratio at the photosphere. Compared to models of planet atmospheres, this first spectrum of planet b is best matched by a model of enhanced metallicity (about 10 times the metallicity of the Sun), which may support the notion that this planet formed through core-accretion
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| .<ref>{{cite journal |last1=Barman |first1=Travis S. |last2=Macintosh |first2=Bruce |year=2011 |title=Clouds and Chemistry in the Atmosphere of Extrasolar Planet HR8799b |journal=Astrophysical Journal |volume=733 |issue=65 |pages= |publisher=AAS |doi=10.1088/0004-637X/733/1/65 |url=http://iopscience.iop.org/0004-637X/733/1/65/pdf/apj_733_1_65.pdf |accessdate=9 April 2013|arxiv = 1103.3895 |bibcode = 2011ApJ...733...65B }}</ref> | |
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| The first simultaneous spectra of all four known planets in the HR8799 system were obtained in 2012 using the Project 1640 instrument at Palomar Observatory. The near-infrared spectra from this instrument confirmed the red colors of all four planets and are best matched by models of planet atmospheres that include clouds. Though these spectra do not directly correspond to any known astrophysical objects, some of the planet spectra demonstrate similarities with L- and T-type brown dwarfs and the night-side spectrum of Saturn. The implications of the simultaneous spectra of all four planets obtained with Project 1640 are summarized as follows: Planet b contains ammonia and/or acetylene as well as carbon dioxide, but has little methane; Planet c contains ammonia, perhaps some acetylene but neither carbon dioxide nor substantial methane; Planet d contains acetylene, methane, and carbon dioxide but ammonia is not definitively detected; Planet e contains methane and acetylene but no ammonia or carbon dioxide. The spectrum of planet e is similar to a reddened spectrum of Saturn.<ref>{{cite journal |last1=Oppenheimer |first1=B.R. |last2=Baranec |first2=C. |year=2013 |title=Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy |journal=Astrophysical Journal |volume= |issue= |pages= |publisher= |doi=10.1088/0004-637X/768/1/24|url=http://arxiv.org/pdf/1303.2627v1.pdf |accessdate=9 April 2013|arxiv = 1303.2627 |bibcode = 2013ApJ...768...24O }}</ref>
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| Moderate-resolution near-infrared spectroscopy, obtained with the Keck telescope, definitively detected carbon monoxide and water absorption lines in the atmosphere of planet c. The carbon-to-oxygen ratio, which is thought to be a good indicator of the formation history for giant planets, for planet c was measured to be slightly greater than that of the host star HR8799. The enhanced carbon-to-oxygen ratio and depleted levels of C and O in planet c favor a history in which the planet formed through core accretion.<ref name="AAAS">{{cite journal |last1= Konopacky |first1= Quinn M. |last2= Barman |first2= Travis S. |year= 2013 |title=Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere |journal=Science |volume=339 |issue= |pages=1398–1401 |publisher=AAAS |doi=10.1126/science.1232003 |url=http://www.sciencemag.org/content/339/6126/1398.full.pdf |accessdate=9 April 2013|arxiv = 1303.3280 |bibcode = 2013Sci...339.1398K }}</ref> However, it is important to note that conclusions about the formation history of a planet based solely on its composition may be inaccurate if the planet has undergone significant migration, chemical evolution, or core dredging.
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| The red colors of the planets may be explained by the presence of iron and silicate atmospheric clouds, while their low surface gravities might explain the strong disequilibrium concentrations of carbon monoxide and the lack of strong methane absorption.<ref name="AAAS"/>
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| ===Debris disk===
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| [[File:HR 8799 Debris Disk.jpg|thumb|Spitzer infrared image of HR 8799's debris disk, January 2009. The small dot in the centre is the size of Pluto's orbit.]]
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| In January 2009 the [[Spitzer Space Telescope]] obtained images of the debris disk around HR 8799. Three components of the debris disk were distinguished:
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| # Warm dust (T ~ 150 K) orbiting within the innermost planet (e). The inner and outer edges of the this belt are close to 4:1 and 2:1 resonances with the planet.<ref name=Marois2011/>
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| # A broad zone of cold dust (T ~ 45 K) with a sharp inner edge orbiting just outside the outermost planet (b). The inner edge of this belt is approximately in 3:2 resonance with said planet, similar to [[Neptune]] and the [[Kuiper belt]].<ref name=Marois2011/>
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| # A dramatic halo of small grains originating in the cold dust component.
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| The halo is unusual and implies a high level of dynamic activity which is likely due to gravitational stirring by the massive planets.<ref>{{Cite doi|10.1088/0004-637X/705/1/314}}</ref> The Spitzer team says that collisions are likely occurring among bodies similar to those in our Kuiper Belt and that the three large planets may not yet have settled into their final, stable orbits.<ref name=spitzer1>{{cite web
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| | title = Unsettled Youth: Spitzer Observes a Chaotic Planetary System
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| | publisher = NASA Spitzer Space Telescope
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| | date = 2009-11-04
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| | url = http://spitzer.caltech.edu/news/1000-feature09-16-Unsettled-Youth-Spitzer-Observes-a-Chaotic-Planetary-System
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| | accessdate = 2009-11-08}}</ref>
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| In the photo, the bright, yellow-white portions of the dust cloud come from the outer cold disk. The huge extended dust halo, seen in orange-red, has a diameter of ≈ 2,000 AU. The diameter of Pluto's orbit (≈ 80 AU) is shown for reference as a dot in the centre.<ref>
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| {{Cite web
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| | title = A Picture of Unsettled Planetary Youth
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| | publisher = NASA Spitzer Space Telescope
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| | date = 2009-11-04
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| | url = http://spitzer.caltech.edu/images/2781-sig09-008-A-Picture-of-Unsettled-Planetary-Youth
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| | accessdate = 2009-11-08
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| }}</ref>
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| This disk is so thick that it threatens the young system's stability.<ref name="MooreQuillen">{{cite journal |authors=Alexander J. Moore, Alice C. Quillen |year=2013 |title=Effects of a planetesimal debris disk on stability scenarios for the extrasolar planetary system HR 8799 |arxiv=1301.2004 |bibcode = 2013arXiv1301.2004M }}</ref>
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| ===Vortex Coronagraph: Testbed for high-contrast imaging technology===
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| [[File:444226main exoplanet20100414-a-full.jpg|250px|thumb|Direct image of [[exoplanet]]s around the star [[HR8799]] using a vortex [[coronograph]] on a 1.5m portion of the [[Hale telescope]]]]
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| Up until the year 2010, [[telescope#Research telescopes|telescopes]] could only [[Methods of detecting extrasolar planets#Direct imaging|directly image]] exoplanets under exceptional circumstances. Specifically, it is easier to obtain images when the planet is especially large (considerably larger than [[Jupiter]]), widely separated from its parent star, and hot so that it emits intense infrared radiation. However in 2010 a team from [[NASA]]s [[Jet Propulsion Laboratory]] demonstrated that a [[vortex coronagraph]] could enable small scopes to directly image planets.<ref>[http://www.msnbc.msn.com/id/36528711/ns/technology_and_science-space/ New method could image Earth-like planets]</ref> They did this by imaging the previously imaged HR 8799 planets using just a 1.5 m portion of the [[Hale Telescope]].
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| ===NICMOS images===
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| In 2009, an old [[NICMOS]] image was processed to show a predicted exoplanet around the star HR 8799,<ref name=exoplanets/> thought to be about 130 [[light-years]] from Earth.<ref name=exoplanets/>
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| In 2011, around that same star, three [[exoplanets]] were rendered viewable in a NICMOS image taken in 1998, using advanced data processing.<ref name=exoplanets>[http://www.nasa.gov/mission_pages/hubble/science/elusive-planets.html NASA - Astronomers Find Elusive Planets in Decade-Old Hubble Data - 10.06.11]</ref> The exoplanets were originally discovered with the [[W. M. Keck Observatory|Keck telescopes]] and the [[Gemini North]] telescope between 2007 and 2010.<ref name=exoplanets/> The image allows the planets' orbits to be analyzed better, since they take many decades, even hundreds of Earth years to orbit their host star.<ref name=exoplanets/> In other words, the NICMOS image is especially useful because it is older.
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| ==See also==
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| * [[List of extrasolar planets]]
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| * [[Methods of detecting extrasolar planets#Direct imaging|Direct imaging of extrasolar planets]]
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| ==Notes==
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| <references group="note" />
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| ==References==
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| {{Reflist|colwidth=30em|refs=
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| <ref name=Marois2011>{{cite doi|10.1038/nature09684}}</ref>
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| }}
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| ==External links==
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| * [http://www.nasa.gov/multimedia/imagegallery/image_feature_1320.html NASA Image Gallery]
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| {{clear}}
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| {{HR 8799|state=collapsed}}
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| {{Sky|23|07|28.7150|+|21|08|03.302|129}}
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| {{Stars of Pegasus}}
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| [[Category:HR 8799]]
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| [[Category:A-type main-sequence stars]]
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| [[Category:Gamma Doradus variables]]
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| [[Category:Pegasus (constellation)]]
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| [[Category:Henry Draper Catalogue objects|218396]]
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| [[Category:Hipparcos objects|114189]]
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| [[Category:HR objects|8799]]
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| [[Category:Objects named with variable star designations|Pegasi, V342]]
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| [[Category:Planetary systems with four confirmed planets]]
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| [[Category:Lambda Boötis stars]]
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| [[Category:Circumstellar disks]]
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| {{Link GA|it}}
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