View source for WASP-15b

{{Short description|Extrasolar planet orbiting WASP-15}}
{{good article}}
{{Infobox planet
| name = WASP-15b / Asye
| image = Exoplanet Comparison WASP-15 b.png
| caption = Size comparison of WASP-15b with Jupiter.
<!-- DISCOVERY           -->| discoverer = West et al. ([[SuperWASP]])<ref name="West2009"/>
| discovery_site = [[SAAO]]<ref name="West2009"/>
| discovered = April 29, 2009 (Publication date)<ref name="West2009"/>
| discovery_method = Transit<ref name="West2009"/>
<!-- DESIGNATIONS        -->
<!-- ORBITAL             -->| apsis = astron
| semimajor = {{convert|0.0499|±|0.0018|AU|km|abbr=on}}<ref name=EPE/>
| eccentricity = 0<ref name=EPE/>
| period = 3.7520656 ± 2.8e-06<ref name=EPE/> [[day|d]]
| inclination = 85.5 ± 0.5<ref name=EPE/>
| star = [[WASP-15]]
<!-- PHYS CHARS          -->| mean_radius = 1.428 ± 0.077<ref name=EPE/> {{Jupiter radius|link=y}}
| mass = 0.542 ± 0.05<ref name=EPE/> {{Jupiter mass|link=y}}
| density = {{convert|0.247|±|0.035|g/cm3|lk=on|abbr=on}}<ref name="West2009"/>
| single_temperature = 1652 ± 28<ref name="West2009"/>
<!-- ATMOSPHERE          --> 
<!-- NOTES               -->}}
'''WASP-15b''', formally named '''Asye''',<ref name=IAU /> is an [[extrasolar planet]] discovered in 2008 by the [[SuperWASP]] collaboration, which seeks to discover exoplanets that [[transit method|transit]] their host stars. The planet orbits its host star at a distance of 0.05 [[astronomical unit|AU]] every four days. The mass of this planet is about one half that of [[Jupiter]], but its radius is nearly 50% larger than Jupiter's, making the density of this planet only one quarter that of water; it is thought that some other form of heating must explain its extremely low density.<ref name="West2009"/> WASP-15b's discovery was published on April 29, 2009.

==Discovery==
WASP-15 was first observed by the WASP-South branch of the [[SuperWASP]] project, which operates from the [[South African Astronomical Observatory]], between May 4, 2006, and July 17, 2006. It was later observed by WASP-South from January 31, 2007, to July 17, 2007, and from January 31, 2008, to May 29, 2008.<ref name="West2009"/> Further analysis taken from 24,943 collected data points revealed eleven full or partial transits.<ref name="West2009"/>

Follow-up observations were conducted by a European and American science team at the 1.2&nbsp;m [[Leonhard Euler Telescope]] at [[La Silla Observatory]] in Chile, which further raised the possibility of the existence of a planet in WASP-15's orbit; use of the [[CORALIE spectrograph]] on the Euler Telescope between March 6, 2008, and July 17, 2008, revealed that the variations in [[Doppler spectroscopy|radial velocity measurements]] were not because of an [[eclipsing binary]] star system.<ref name="West2009"/>

CORALIE and the [[High Resolution Echelle Spectrometer]] (HIRES) revealed the spectrum of WASP-15, which was used to derive the star's characteristics.<ref name="West2009"/> The science team studying WASP-15 found that, after running best-fit models, WASP-15's radial velocity and transit shifts were most likely due to the existence of a planet.<ref name="West2009"/>

WASP-15's planet, WASP-15b, had one of the lowest densities known amongst extrasolar planets when it was discovered. Its discovery paper was published by the [[American Astronomical Society]] on April 29, 2009, in the ''[[Astronomical Journal]]''.<ref name="West2009"/>

==Host star==
{{main|WASP-15}}
WASP-15 is an [[Stellar classification#Class F|F-type]] star located in the [[Centaurus (constellation)|Centaurus]] constellation. It is located approximately 290 [[parsec]]s (900 [[light year]]s) from Earth and has an [[apparent magnitude]] of 10.9, making it invisible to the unaided eye. The star is 1.18 times [[solar mass|more massive]] than the Sun, and has a [[solar radius|radius]] that is 1.477 times larger than that of the Sun, making it more diffuse. WASP-15 has an [[effective temperature]] of 6300 [[Kelvin scale|K]], and is thus hotter than the Sun, although at 3.9 billion years, it is also younger. WASP-15 has a [[metallicity]] of [Fe/H] of -0.17, which means that it has 68% of the iron found in the Sun.<ref name=EPE/>

==Characteristics==
WASP-15b has a [[Jupiter mass|mass]] of 0.542 times Jupiter's mass and a [[Jupiter radius|radius]] that is 1.428 times Jupiter's radius. Due in part to its proximity to its host star, a distance of 0.0499 [[astronomical units|AU]] (7,500,000&nbsp;km), WASP-15b is greatly inflated, with a density of 0.247 g/cm<sup>3</sup>. Another factor, such as an internal heat source, is suspected to add to this extremely high radius and extremely low density.<ref name="West2009"/> WASP-15b orbits its host star every 3.7520656 days. It also has an [[orbital inclination]] of 85.5º, making it almost edge-on as seen from the Earth's perspective.<ref name=EPE/>

The study in 2012, utilizing a [[Rossiter–McLaughlin effect]], have determined the planetary orbit is strongly misaligned with the equatorial plane of the star, misalignment equal to -139.6{{±|4.3|5.2}}°. This spin-orbit angle is making orbit of WASP-15b [[Retrograde and prograde motion|retrograde]].<ref>{{citation|arxiv=1206.6105|title=Obliquities of Hot Jupiter Host Stars: Evidence for Tidal Interactions and Primordial Misalignments|year=2012|doi=10.1088/0004-637X/757/1/18 |last1=Albrecht |first1=Simon |last2=Winn |first2=Joshua N. |last3=Johnson |first3=John A. |last4=Howard |first4=Andrew W. |last5=Marcy |first5=Geoffrey W. |last6=Butler |first6=R. Paul |last7=Arriagada |first7=Pamela |last8=Crane |first8=Jeffrey D. |last9=Shectman |first9=Stephen A. |last10=Thompson |first10=Ian B. |last11=Hirano |first11=Teruyuki |last12=Bakos |first12=Gaspar |last13=Hartman |first13=Joel D. |journal=The Astrophysical Journal |volume=757 |issue=1 |page=18 |bibcode=2012ApJ...757...18A |s2cid=17174530 }}</ref>

==Naming==
In 2019 the [[International Astronomical Union|IAU]] announced as part of [[NameExoWorlds]] that WASP-15 and its planet WASP-15b would be given official names chosen by school children from [[Ivory Coast|The Ivory Coast]].<ref name=IAU /><ref name=waspnaming />

==See also==
* [[SuperWASP]]

==References==
{{reflist|refs=

<ref name=EPE>{{cite web |url=http://www.exoplanet.eu/star.php?st=WASP-15 |title=Notes for star WASP-15 |author=Jean Schneider |year=2010 |access-date=13 May 2011 |archive-url=https://web.archive.org/web/20101202051747/http://exoplanet.eu/star.php?st=WASP-15 |archive-date=2 December 2010 |url-status=dead |work=[[Extrasolar Planets Encyclopaedia]] |df=dmy-all }}</ref>

<ref name="West2009">{{ cite journal | title=The Low Density Transiting Exoplanet WASP-15b| last1=West | first1=R. G. | last2=Anderson | first2=D. R. | last3=Gillon | first3=M. | last4=Hebb | first4=L. | last5=Hellier | first5=C. | last6=Maxted | first6=P. F. L. | last7=Queloz | first7=D. | last8=Smalley | first8=B. | last9=Triaud | first9=A. H. M. J. | last10=Wilson | first10=D. M. | last11=Bentley | first11=S. J. | last12=Collier Cameron | first12=A. | last13=Enoch | first13=B. | last14=Horne | first14=K. | last15=Irwin | first15=J. | last16=Lister | first16=T. A. | last17=Mayor | first17=M. | last18=Parley | first18=N. | last19=Pepe | first19=F. | last20=Pollacco | first20=D. | last21=Segransan | first21=D. | last22=Spano | first22=M. | last23=Udry | first23=S. | last24=Wheatley
 | first24=P. J. | display-authors=1 | journal=The Astronomical Journal | volume=137 | issue=6 | pages=4834–4836 | year=2009 | arxiv=0902.2651 | bibcode=2009AJ....137.4834W | doi=10.1088/0004-6256/137/6/4834 | s2cid=119291616 }}</ref>

<ref name=IAU>
{{cite web |url=http://www.nameexoworlds.iau.org/ |title=NameExoWorlds |year=2019 |access-date=6 September 2019}}</ref>

<ref name=waspnaming>
{{cite web |url=https://wasp-planets.net/naming/ |title=Naming |year=2019 |access-date=6 September 2019}}</ref>

}}

==External links==
{{commons category-inline|WASP-15 b|WASP-15b}}
*http://wasp-planets.net/wasp-planets/

{{Sky|13|55|43|-|32|09|35|1004}}
{{Centaurus}}

{{DEFAULTSORT:WASP-15b}}
[[Category:Exoplanets discovered by WASP]]
[[Category:Exoplanets discovered in 2009]]
[[Category:Giant planets]]
[[Category:Hot Jupiters]]
[[Category:Transiting exoplanets]]
[[Category:Hydra (constellation)]]
[[Category:Exoplanets with proper names]]