View source for Upsilon Andromedae b

{{Short description|Extrasolar planet in the Andromeda constellation}}
{{Infobox planet
| name = Upsilon Andromedae b / Saffar
| image = Upsilon Andromedae b comparison.png
| caption = Size comparison of Jupiter with Upsilon Andromedae b
<!-- DISCOVERY           -->
| discoverer = [[Geoffrey Marcy|Marcy]] ''et al.''
| discovery_site = [[California and Carnegie Planet Search|California and Carnegie<br/> Planet Search]]<br/>{{flag|United States}}
| discovered = June 23, 1996
| discovery_method = [[Radial velocity]]
<!-- DESIGNATIONS        -->
<!-- ORBITAL             -->
| apsis = astron
| aphelion = {{val|0.0601|ul=AU}}
| perihelion = {{val|0.0587|ul=AU}}
| semimajor = {{val|0.0594|0.0003|ul=AU}}<ref name=Pizkorz2017/>
| eccentricity = {{val|0.012|0.005}}<ref name=Pizkorz2017/>
| period = {{val|4.617111|0.000014|fmt=none|ul=d}}<ref name=Pizkorz2017/><br/>({{convert|4.617111|d|year h|disp=out|lk=on}})
| inclination = {{val|24|4}}<ref name=Pizkorz2017/>
| time_periastron = {{val|2450034.05|0.33|fmt=commas}}<ref name=Pizkorz2017/>
| arg_peri = {{val|44.11|25.56}}<ref name=Pizkorz2017/>
| semi-amplitude = {{val|70.51|0.37}}<ref name=Pizkorz2017/>
| star = [[Upsilon Andromedae A]]
<!-- PHYS CHARS          -->
| mass = {{val|1.70|0.33|0.24}}<ref name=Pizkorz2017/> {{Jupiter mass|link=y}}
| mean_radius = ~1.8<ref name=Deitrick2014/>{{Jupiter radius|link=y}}
<!-- ATMOSPHERE          --> 
<!-- NOTES               -->}}

'''Upsilon Andromedae b''' ('''υ Andromedae b''', abbreviated '''Upsilon And b''', '''υ And b'''), formally named '''Saffar''' {{IPAc-en|'|s|æ|f|ɑr}}, is an [[extrasolar planet]] approximately 44 [[light-year]]s away from the [[Sun]] in the [[constellation]] of [[Andromeda (constellation)|Andromeda]]. The planet orbits its host star, the [[F-type main-sequence star]] [[Upsilon Andromedae]] A, approximately every five days. Discovered in June 1996 by [[Geoffrey Marcy]] and [[R. Paul Butler]], it was one of the first [[hot Jupiter]]s to be discovered. It is also one of the first non-resolved planets to be detected directly. Upsilon Andromedae b is the innermost-known planet in its [[planetary system]].

In July 2014 the [[International Astronomical Union]] launched [[NameExoWorlds]], a process for giving proper names to certain exoplanets and their host stars.<ref>[http://www.iau.org/news/pressreleases/detail/iau1404/ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars]. IAU.org. 9 July 2014</ref> The process involved public nomination and voting for the new names.<ref>{{Cite web |url=http://nameexoworlds.iau.org/process |title=NameExoWorlds The Process |access-date=2015-09-05 |archive-date=2015-08-15 |archive-url=https://web.archive.org/web/20150815025117/http://nameexoworlds.iau.org/process |url-status=dead }}</ref> In December 2015, the IAU announced the winning name was Saffar for this planet.<ref>[http://www.iau.org/news/pressreleases/detail/iau1514/ Final Results of NameExoWorlds Public Vote Released], International Astronomical Union, 15 December 2015.</ref> The winning name was submitted by the Vega Astronomy Club of [[Morocco]] and honours the 11th-century astronomer [[Ibn al-Saffar]] of [[Muslim Spain]].<ref>{{Cite web |url=http://nameexoworlds.iau.org/names |title=NameExoWorlds The Approved Names |access-date=2016-01-17 |archive-date=2018-02-01 |archive-url=https://web.archive.org/web/20180201043609/http://nameexoworlds.iau.org/names |url-status=dead }}</ref>

== Discovery ==
Upsilon Andromedae b was detected by the variations in its star's [[radial velocity]] caused by the planet's [[gravity]]. The variations were detected by making sensitive measurements of the [[Doppler shift]] of Upsilon Andromedae's [[spectrum]]. The planet's existence was announced in January 1997, together with [[55 Cancri b]] and the planet orbiting [[Tau Boötis]].<ref>{{cite journal | display-authors=1 | last1=Butler | first1=R. Paul | last2=Marcy | first2=Geoffrey W. | last3=Williams | first3=Eric | last4=Hauser | first4=Heather | last5=Shirts | first5=Phil | title=Three New 51 Pegasi-Type Planets | journal=[[The Astrophysical Journal]] | volume=474 | issue=2 | date=1997 | pages=L115–L118 | doi=10.1086/310444 | bibcode=1997ApJ...474L.115B | doi-access=free }}</ref>

Like [[51 Pegasi b]], the first extrasolar planet discovered around a normal star, Upsilon Andromedae b orbits very close to its star, closer than [[Mercury (planet)|Mercury]] does to the Sun. The planet takes 4.617 [[day]]s to complete an orbit, with a [[semimajor axis]] of 0.0595 [[Astronomical unit|AU]].<ref>{{cite journal | display-authors=1 |last1=Butler |first1=R. P. |last2=Wright |first2=J. T. |last3=Marcy |first3=G. W. |last4=Fischer |first4=D. A. |last5=Vogt |first5=S. S. |last6=Tinney |first6=C. G. |last7=Jones |first7=H. R. A. |last8=Carter |first8=B. D. |last9=Johnson |first9=J. A. |last10=McCarthy |first10=C. |last11=Penny |first11=A. J. | doi=10.1086/504701 | title=Catalog of Nearby Exoplanets | journal=[[The Astrophysical Journal]] | volume=646 | issue=1 | pages=505–522 | date=2006 | bibcode=2006ApJ...646..505B|arxiv = astro-ph/0607493 |s2cid=119067572 }} ([http://exoplanets.org/planets.shtml web version])</ref>

A limitation of the radial velocity method used to detect Upsilon Andromedae b is that only a lower limit on the [[mass]] can be found. The [[true mass]] may be much greater depending on the [[inclination]] of the orbit. A mass of {{Jupiter mass|link=y|1.70}} and an inclination of 24° were later found using high-resolution [[astronomical spectroscopy|spectroscopy]].<ref name=Pizkorz2017/>

== Physical characteristics ==
[[File:Saffar_(Upsilon_Andromedae_b).jpg|thumb|200px|An artist's impression of Upsilon Andromedae b and its parent star]]
Given the planet's high mass, it is likely that Upsilon Andromedae b is a [[gas giant]] with no [[solid]] surface.

The [[Spitzer Space Telescope]] measured the planet's [[temperature]], and found that the difference between the two sides of Upsilon Andromedae b is about 1,400 degrees Celsius, ranging from minus 20 to 230 degrees to about 1,400 to 1,650 °C.<ref>{{cite journal | first = J | last = Harrington |author2=Hansen BM |author3=Luszcz SH |author4=Seager S |author5=Deming D |author6=Menou K |author7=Cho JY |author8=Richardson LJ | date = October 27, 2006 | title = The phase-dependent infrared brightness of the extrasolar planet upsilon Andromedae b | journal = Science | volume = 314 | issue = 5799 | pages = 623–6 | pmid = 17038587 | doi = 10.1126/science.1133904|arxiv = astro-ph/0610491 |bibcode = 2006Sci...314..623H | s2cid = 20549014 }}</ref> The temperature difference has led to speculation that Upsilon Andromedae b is [[tidal locked]] with the same side always facing Upsilon Andromedae A.

[[David Sudarsky]] had, on the assumption that the planet is similar to Jupiter in composition and that its environment is close to [[chemical equilibrium]], predicted Upsilon Andromedae b to have reflective [[cloud]]s of [[silicate minerals|silicates]] and [[iron]] in its upper [[atmosphere]].<ref>{{cite journal |last1=Sudarsky |first1=David |authorlink1=David Sudarsky |last2=Burrows |first2=Adam |last3=Hubeny |first3=Ivan |display-authors=1 |date=2003 |title=Theoretical Spectra and Atmospheres of Extrasolar Giant Planets |journal=[[The Astrophysical Journal]] |volume=588 |issue=2 |pages=1121–1148 |arxiv=astro-ph/0210216 |bibcode=2003ApJ...588.1121S |doi=10.1086/374331 |s2cid=16004653}}</ref> The cloud deck instead absorbs the star's radiation; between that and the hot, high-pressure gas surrounding the mantle, exists a [[stratosphere]] of cooler gas.<ref>{{cite journal |title=Spectrum and atmosphere models of irradiated transiting extrasolar giant planets|date=2008 |author1=Ivan Hubeny |author2=Adam Burrows |doi=10.1017/S1743921308026458 |journal=Proceedings of the International Astronomical Union |volume=4 |pages=239 |arxiv=0807.3588|bibcode=2009IAUS..253..239H |s2cid=13978248 }}</ref> The outer shell of dark, opaque, hot cloud is assumed to consist of [[vanadium oxide|vanadium]] and [[titanium oxide]]s, but other compounds like [[tholin]]s cannot be ruled out yet.

The chemical elements in the atmosphere can be studied by finding their absorption lines in the thermal spectrum of the planet; given typical planet temperatures, the spectrum has its peak at infrared wavelengths. So far, only [[water vapor]] has been detected in this planet, while [[carbon monoxide]] and [[methane]] are still under the detection limit.<ref name=Pizkorz2017/>

The planet is unlikely to have large [[natural satellite|moons]], since [[tidal force]]s would either eject them from orbit or destroy them on short timescales compared to the age of the system.<ref>{{cite journal|bibcode=2002ApJ...575.1087B|author=Barnes, J.|author2=O'Brien, D.|title=Stability of Satellites around Close-in Extrasolar Giant Planets|journal=[[The Astrophysical Journal]]|volume=575|issue=2|pages=1087–1093|date=2002|doi=10.1086/341477|arxiv = astro-ph/0205035 |s2cid=14508244 }}</ref>

The planet (with [[51 Pegasi b]]) was deemed a candidate for direct imaging by [[Planetpol]].<ref name=lucas>{{cite journal|last1=Lucas|first1=P. W.|last2=Hough|first2=J. H.|last3=Bailey|first3=J. A.|last4=Tamura|first4=M.|last5=Hirst|first5=E.|last6=Harrison|first6=D.|title=Planetpol polarimetry of the exoplanet systems 55 Cnc and τ Boo|journal=Monthly Notices of the Royal Astronomical Society|date=11 February 2009|volume=393|issue=1|pages=229–244|doi=10.1111/j.1365-2966.2008.14182.x|doi-access=free |arxiv = 0807.2568 |bibcode = 2009MNRAS.393..229L |s2cid=8684361 }}</ref> Preliminary results from polarimetric studies indicate that the planet has a predominately blue color, is 1.36 times as large and 0.74 times as massive as Jupiter, meaning that the mean density is 0.36g/cm<sup>3</sup>. It has a [[geometric albedo]] of 0.35 in visible light.<ref>{{cite arXiv |eprint=1109.3116 |title=Upsilon Andromedae b in polarized light: New constraints on the planet size, density and albedo |author1=S.V. Berdyugina |author2=A.V. Berdyugin |author3=V. Piirola |date=14 September 2011 |class=astro-ph.EP}}</ref> In 2016–2017 the direct detection of the planetary thermal emission was claimed, but the detection was questioned in 2021.<ref>{{citation|arxiv=2109.13275|year=2021|title=Reinvestigation of the Multiepoch Direct Detections of HD 88133 b and Upsilon Andromedae B|doi=10.3847/1538-3881/ac2a2c |last1=Buzard |first1=Cam |last2=Piskorz |first2=Danielle |last3=Lockwood |first3=Alexandra C. |last4=Blake |first4=Geoffrey |last5=Barman |first5=Travis S. |last6=Benneke |first6=Björn |last7=Bender |first7=Chad F. |last8=Carr |first8=John S. |journal=The Astronomical Journal |volume=162 |issue=6 |page=269 |bibcode=2021AJ....162..269B |s2cid=238198093 |doi-access=free }}</ref> Tidal heating models predict a similar mass for the planet.<ref name=Deitrick2014>{{cite journal |display-authors=1 | first1=R. | last1=Deitrick | first2=R. | last2=Barnes | first3=B. | last3=McArthur | first4=T. R. | last4=Quinn | first5=R. | last5=Luger | first6=A. | last6=Antonsen | first7=G. F. | last7=Benedict |title=The Three-dimensional Architecture of the υ Andromedae Planetary System | journal=The Astrophysical Journal | volume=798 | issue=1 | date=January 2015 | page=46 | doi=10.1088/0004-637X/798/1/46 | bibcode=2015ApJ...798...46D| arxiv=1411.1059 | s2cid=118409453 }}</ref>

== Host star ==
{{main|Upsilon Andromedae#Upsilon Andromedae A}}
The planet orbits a ([[Stellar classification#Class F|F-type]]) [[star]] named Titawin (Upsilon Andromedae A). The star has a mass of 1.27 {{Solar mass|link=y}} and a radius of around 1.48 {{Solar radius|link=y}}. It has a temperature of 6,074 [[Kelvin|K]] and is 3.12 billion years old. In comparison, the Sun is about 4.6 billion years old. The star is slightly metal-rich, with a [[metallicity]] ([Fe/H]) of 0.09, or about 123% of the solar amount. Its luminosity ({{solar luminosity|link=y}}) is 3.57 times that of the Sun.

The star's [[apparent magnitude]], or how bright it appears from Earth's perspective, is 4.09. Therefore, Upsilon Andromedae can be seen with the naked eye.

=== Effect on the parent star ===
[[File:UAndAb full.jpg|thumb|200px|left|Artist's impression of the hot spot, shown in orange hues]]
Upsilon Andromedae b appears to be responsible for increased [[chromospheric activity]] on its parent star. Observations suggest that there is a "hot spot" on the star around 169 degrees away from the sub-planetary point. This may be the result of interactions between the [[magnetic field]]s of the planet and the star. The mechanism may be similar to that responsible for the activity of [[RS Canum Venaticorum variable]] stars, or the interaction between Jupiter and its moon [[Io (moon)|Io]].<ref>{{cite journal | url=http://www.iop.org/EJ/article/0004-637X/622/2/1075/61179.html | title=Hot Jupiters and Hot Spots: The Short- and Long-term Chromospheric Activity on Stars with Giant Planets | display-authors=1 | last1=Shkolnik | first1=E. | last2=Walker | first2=G. A. H. | last3=Bohlender | first3=D. A. | last4=Gu | first4=P.-G. | last5=Kürster | first5=M. | journal=The Astrophysical Journal | volume=622 | issue=2 | date=2005 | pages=1075–1090 | doi=10.1086/428037 | bibcode=2005ApJ...622.1075S|arxiv = astro-ph/0411655 | s2cid=3043910 }}</ref>

{{clear left}}

== See also ==
* [[55 Cancri b]]
* [[Tau Boötis b]]
* [[List of exoplanets discovered before 2000]]

== References ==
{{Reflist|refs=
<ref name=Pizkorz2017>{{cite journal |display-authors=1 | first1=D. | last1=Pizkorz | first2=B. | last2=Benneke | first3=N. R. | last3=Crockett | first4=A. C. | last4=Lockwood | first5=G. A. | last5=Blake | first6=T. S. | last6=Barman | first7=C. F. | last7=Bender | first8=J. S. | last8=Carr | first9=J. A. | last9=Johnson |title=Detection of Water Vapor in the Thermal Spectrum of the Non-transiting Hot Jupiter Upsilon Andromedae b |journal=The Astronomical Journal |volume=154 | issue=2 | pages=78 | date=August 2017 |doi=10.3847/1538-3881/aa7dd8 | bibcode=2017AJ....154...78P| arxiv=1707.01534 | s2cid=19960378 | doi-access=free }}</ref>
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<ref name="McArthur2010">{{cite journal | url=http://hubblesite.org/pubinfo/pdf/2010/17/pdf.pdf |display-authors=1 | last1=McArthur |first1=Barbara E.| last2=Benedict |first2=G. Fritz| last3=Barnes |first3=Rory| last4=Martioli |first4=Eder| last5=Korzennik |first5=Sylvain| last6=Nelan |first6=Ed| last7=Butler |first7=R. Paul | title=New Observational Constraints on the ''υ'' Andromedae System with Data from the ''Hubble Space Telescope'' and ''Hobby Eberly Telescope'' |journal=The Astrophysical Journal |volume=715 |issue=2 |pages=1203 | date=2010 |format=PDF | doi=10.1088/0004-637X/715/2/1203 |bibcode=2010ApJ...715.1203M }}</ref>-->
}}

== External links ==
* {{cite web |url=http://www.physics.sfsu.edu/~gmarcy/planetsearch/upsand/upsand.html |title=A Triple-Planet System Orbiting Ups Andromedae |access-date=2008-06-23 |work=[[San Francisco State University]] |publisher=[[Lick Observatory]]}}
* {{cite web |url=http://www.spacedaily.com/news/extrasolar-05t.html |title=Mystery Solved: How The Orbits Of Extrasolar Planets Became So Eccentric |access-date=2008-06-23 |work=SpaceDaily |date=2005-04-14}}
* {{cite web |url=http://www.spitzer.caltech.edu/Media/releases/ssc2006-18/release.shtml |title=NASA's Spitzer Sees Day and Night on Exotic World |access-date=2008-06-23 |work=[[NASA]] |publisher=[[Spitzer Space Telescope]] |date=2006-10-12 |archive-url = https://web.archive.org/web/20071022061634/http://www.spitzer.caltech.edu/Media/releases/ssc2006-18/release.shtml |archive-date = October 22, 2007}}
* {{cite encyclopedia |url=http://www.daviddarling.info/encyclopedia/U/upsAnd.html |title=Upsilon Andromedae |access-date=2008-06-23 |encyclopedia=The Internet Encyclopedia of Science}}
* {{cite web |url=http://www.astro.uiuc.edu/~kaler/sow/upsand.html |title=Upsilon Andromedae |access-date=2008-06-23 |work=The Planet Project |url-status=dead |archive-url=https://web.archive.org/web/20080518004158/http://www.astro.uiuc.edu/~kaler/sow/upsand.html |archive-date=2008-05-18 }}
* {{cite web |url=http://www.solstation.com/stars2/ups-and.htm |title=Upsilon Andromedae 2 |access-date=2008-06-23 |work=SolStation}}
* {{cite web |url=http://cfa-www.harvard.edu/afoe/upsAnd.html |title=The Upsilon Andromedae Planetary System |access-date=2008-06-23 |work=[[Harvard-Smithsonian Center for Astrophysics]]}}

{{Upsilon Andromedae}}
{{Andromeda (constellation)}}
{{Good article}}

{{Sky|01|36|47.8|+|41|24|20|43.9}}

{{DEFAULTSORT:Upsilon Andromedae b}}
[[Category:Upsilon Andromedae]]
[[Category:Exoplanets discovered in 1996]]
[[Category:Giant planets]]
[[Category:Hot Jupiters]]
[[Category:Exoplanets detected by radial velocity]]
[[Category:Exoplanets with proper names]]