Editing Algol (section)

{{short description|Eclipsing variable star in the constellation Perseus}}
{{about|the star|the programming languages|ALGOL|other uses}}
{{good article}}
{{Use British English|date=February 2017}}
{{Starbox begin
 | name = Algol
}}
{{Starbox image
 | image =
{{Location mark
|image = Perseus constellation map.svg
|float = center
|alt =
|label =
|position = right
|width = 280
|mark = Red circle.svg
|mark_width = 12
|mark_link = Algol
|x = 644
|y = 663
}}
|caption = Location of β Persei (circled)
}}
{{Starbox observe
 | epoch = J2000
 | ra = {{RA|03|08|10.13245}}<ref name=hipparcos/>
 | dec = {{DEC|+40|57|20.3280}}<ref name=hipparcos>{{cite journal|bibcode=2007A&A...474..653V|title=Validation of the new Hipparcos reduction|journal=Astronomy and Astrophysics|volume=474|issue=2|pages=653–664|last1=Van Leeuwen|first1=F.|year=2007|doi=10.1051/0004-6361:20078357|arxiv = 0708.1752 |s2cid=18759600}}</ref>
 | appmag_v = 2.12<ref name=ducati>{{cite journal|bibcode=2002yCat.2237....0D|title=VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system|journal=CDS/ADC Collection of Electronic Catalogues|volume=2237|pages=0|last1=Ducati|first1=J. R.|year=2002}}</ref> (- 3.39<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|pages=02025|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009|display-authors=etal}}</ref>)
 | constell=[[Perseus (constellation)|Perseus]]
}}
{{Starbox character
 | engvar = en-UK
 | class = '''Aa1''': B8V<ref name=lestrade1993/><br />'''Aa2''': K0IV<ref name=lestrade1993/><br />'''Ab''': F1V<ref name=frank2022/> {{nowrap|(kA4hA9.5mF0:<ref name=fletcher2964>{{cite journal |bibcode=1964AJ.....69..357F |title=Spectrophotometry of Algol |last1=Fletcher |first1=Emery S. |journal=The Astronomical Journal |year=1964 |volume=69 |page=357 |doi=10.1086/109284 }}</ref>)}}
 | b-v=−0.05<ref name=ducati/>
 | u-b=−0.37<ref name=ducati/>
 | variable=[[Algol variable|EA/SD]]<ref name=gcvs/>
}}
{{Starbox astrometry
 | radial_v = 3.7
 | prop_mo_ra = 2.99<ref name=hipparcos/>
 | prop_mo_dec = −1.66<ref name=hipparcos/>
 | parallax = 34.7
 | p_error = 0.6
 | parallax_footnote = <ref name=xu>{{Cite journal |last1=Xu |first1=Shuangjing |last2=Zhang |first2=Bo |last3=Reid |first3=Mark J. |last4=Zheng |first4=Xingwu |last5=Wang |first5=Guangli |date=2019-04-20 |title=Comparison of Gaia DR2 Parallaxes of Stars with VLBI Astrometry |arxiv=1903.04105 |journal=The Astrophysical Journal |volume=875 |issue=2 |pages=114 |doi=10.3847/1538-4357/ab0e83 |doi-access=free |bibcode=2019ApJ...875..114X |issn=0004-637X}}</ref>

|dist_footnote=<ref name=xu/>
}}
{{Starbox astrometry|no_heading=y
 | component1 = A or Aa1
 | absmag_v = −0.07<ref name=soderhjelm>{{cite journal|bibcode=1980A&A....89..100S|year = 1980|title = Geometry and dynamics of the Algol system|journal = Astronomy and Astrophysics|volume = 89|issue = 1–2|pages = 100|last1 = Soderhjelm|first1 = S.}}</ref>
}}
{{Starbox astrometry|no_heading=y
 | component1 = B or Aa2
 | absmag_v = 2.9<ref name=soderhjelm/>
}}
{{Starbox astrometry|no_heading=y
 | component1 = C or Ab
 | absmag_v = 2.3<ref name=soderhjelm/>
}}
{{Starbox orbit
| reference = <ref name=baron/>
| primary = A or Aa1
| name = B or Aa2
| period =
| period_unitless = 2.867328 days
| axis = 0.00215
| axis_unitless =
| eccentricity = 0
| inclination = 98.70
| node = 43.43
| periastron =
| periarg = <!--Argument of periastron (in degrees), secondary -->
| periarg_primary =
| k1 =
| k2 = <!-- Velocity semi-amplitude (secondary in SB2), in km/s -->
}}
{{Starbox orbit
| reference = <ref name=baron/>
| primary = Aa
| name = Ab
| period =
| period_unitless = 680.168 days
| axis = 0.09343
| axis_unitless =
| eccentricity = 0.227
| inclination = 83.66
| node = 132.66
| periastron = 2446927.22
| periarg = <!--Argument of periastron (in degrees), secondary -->
| periarg_primary = 310.02
| k1 =
| k2 = <!-- Velocity semi-amplitude (secondary in SB2), in km/s -->
}}
{{Starbox detail
 | component1 = A or Aa1
 | mass = 3.17 ± 0.21<ref name=baron>{{cite journal|bibcode=2012ApJ...752...20B|title=Imaging the Algol Triple System in the H Band with the CHARA Interferometer|journal=The Astrophysical Journal|volume=752|issue=1|pages=20|last1=Baron|first1=F.|last2=Monnier|first2=J. D.|last3=Pedretti|first3=E.|last4=Zhao|first4=M.|last5=Schaefer|first5=G.|last6=Parks|first6=R.|last7=Che|first7=X.|last8=Thureau|first8=N.|last9=Ten Brummelaar|first9=T. A.|last10=McAlister|first10=H. A.|last11=Ridgway|first11=S. T.|last12=Farrington|first12=C.|last13=Sturmann|first13=J.|last14=Sturmann|first14=L.|last15=Turner|first15=N.|year=2012|doi=10.1088/0004-637X/752/1/20|arxiv = 1205.0754 |s2cid=11110989}}</ref>
 | radius = 2.73 ± 0.20<ref name=baron/>
 | luminosity = 182<ref name=soderhjelm/>
 | temperature = 13,000<ref name=zavala>{{cite journal|bibcode=2010ApJ...715L..44Z|title=The Algol Triple System Spatially Resolved at Optical Wavelengths|journal=The Astrophysical Journal Letters|volume=715|issue=1|pages=L44–L48|last1=Zavala|first1=R. T.|last2=Hummel|first2=C. A.|last3=Boboltz|first3=D. A.|last4=Ojha|first4=R.|last5=Shaffer|first5=D. B.|last6=Tycner|first6=C.|last7=Richards|first7=M. T.|last8=Hutter|first8=D. J.|year=2010|doi=10.1088/2041-8205/715/1/L44|arxiv = 1005.0626 |s2cid=118573026}}</ref>
 | gravity = 4.0<ref name=zavala/>
 | metal =
 | rotational_velocity = 49<ref name=tomkin>{{cite journal|bibcode=1985PASP...97...51T|title=The rotation of the primary of Algol|journal=Publications of the Astronomical Society of the Pacific|volume=97|pages=51|last1=Tomkin|first1=J.|last2=Huisong|first2=T.|year=1985|doi=10.1086/131493|s2cid=119392903 |doi-access=free}}</ref>
 | age_myr = 570<ref name=soderhjelm/>
}}
{{Starbox detail|no_heading=y
 | component1 = B or Aa2
 | mass = {{val|0.70|0.08}}<ref name=baron/>
 | radius = {{val|3.48|0.28}}<ref name=baron/>
 | luminosity = 6.92<ref name=soderhjelm/>
 | temperature = 4,500<ref name=zavala/>
 | gravity = 3.5<ref name=zavala/>
 | metal =
 | rotation =
 | age =
}}
{{Starbox detail|no_heading=y
 | component1 = C or Ab
 | mass = {{val|1.76|0.15}}<ref name=baron/>
 | radius = {{val|1.73|0.33}}<ref name=baron/>
 | luminosity = 10.0<ref name=soderhjelm/>
 | temperature = 7,500<ref name=zavala/>
 | gravity = 4.5<ref name=zavala/>
 | metal =
 | rotation =
 | age =
}}
{{Starbox catalog
 | names = Algol, Gorgona, Gorgonea&nbsp;Prima, Demon&nbsp;Star, El&nbsp;Ghoul, β&nbsp;Persei, β&nbsp;Per, 26&nbsp;Persei, [[Star catalogue#BD/CD/CPD|BD]]+40°673, [[Fifth Fundamental Catalogue|FK5]]&nbsp;111, [[Boss General Catalogue|GC]]&nbsp;3733, [[Henry Draper catalogue|HD]]&nbsp;19356, [[Hipparcos catalogue|HIP]]&nbsp;14576, [[Bright Star Catalogue|HR]]&nbsp;936, [[PPM Star Catalogue|PPM]]&nbsp;45864, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;38592.
}}
{{Starbox reference
|Simbad = Algol
}}
{{Starbox end}}
'''Algol''' {{IPAc-en|ˈ|æ|l|g|ɒ|l}},<ref>{{OED|Algol}}</ref> designated '''Beta Persei''' ('''β&nbsp;Persei''', abbreviated '''Beta&nbsp;Per''', '''β&nbsp;Per'''), known colloquially as the '''Demon Star''', is a bright [[multiple star]] in the [[constellation]] of [[Perseus (constellation)|Perseus]] and one of the first non-[[nova]] [[variable star]]s to be discovered.

Algol is a [[triple star|three-star system]], consisting of Beta Persei&nbsp;Aa1, Aa2, and&nbsp;Ab – in which the hot luminous primary β Persei&nbsp;Aa1 and the larger, but cooler and fainter, β Persei&nbsp;Aa2 regularly pass in front of each other, causing eclipses. Thus Algol's [[apparent magnitude|magnitude]] is usually near-constant at&nbsp;2.1, but regularly dips to 3.4 every 2.86 days during the roughly 10-hour-long partial eclipses. The secondary eclipse when the brighter primary star [[occultation|occults]] the fainter secondary is very shallow and can only be detected photoelectrically.<ref>{{cite web |date=January 1999 | url = http://www.aavso.org/vstar/vsots/0199.shtml | title = Beta Persei (Algol) | publisher = AAVSO  | access-date = 31 July 2006 |archive-url = https://web.archive.org/web/20060708092301/http://www.aavso.org/vstar/vsots/0199.shtml |archive-date = 8 July 2006}}</ref>

Algol gives its name to its class of eclipsing variable, known as [[Algol variable]]s.