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Created page with "{{Night Sky | image = | designation =VV Cep<br/>HD 208816<br/>HIP 108317 | rightascension =21<sup>h</sup> 56<sup>m</sup> 39.1438<sup>s</sup><ref name=simbad>{{c..."
{{Night Sky
| image =
| designation =VV Cep<br/>HD 208816<br/>HIP 108317
| rightascension =21<sup>h</sup> 56<sup>m</sup> 39.1438<sup>s</sup><ref name=simbad>{{cite web|url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=VV+Cephei|title=VV Cephei|accessdate=January 30, 2020|work=Simbad Astronomical Database|publisher=simbad.u-strasbg.fr}}</ref><ref name=hip>
{{cite journal
|last1=van Leeuwen |first1=Floor
|display-authors=3
|title=Validation of the new Hipparcos reduction
|journal=Astronomy and Astrophysics
|volume=474
|issue=2|page=653-664|date=2007
|doi=10.1051/0004-6361:20078357
|bibcode=2007A&A...474..653V
|ref=harv
}} {{arXiv|0708.1752}}</ref>
| declination =+63° 37′ 32.0174″<ref name=simbad/><ref name=hip/>
| distance =2452.36 ly<ref name=universeguide>{{cite web|url=https://www.universeguide.com/star/vvcephei|title=VV Cephei (Supergiant Star) Star Facts|accessdate=January 30, 2020|publisher=universeguide.com}}</ref>
| constellation =Cepheus
| type =Supergiant{{!}}Supergiant star
| dimensions =
| magnitude =Apparent Mag: +5.11<ref name=universeguide/><br/>Absolute Mag: -6.93 / -4.27<ref name=universeguide/>
| redshift =
| radvelocity =-18.7 ± 0.9 km/s<ref name=simbad/>
| propmotion =RA: -0.25 mas/yr<ref name=simbad/><ref name=hip/><br/>Dec: -2.56 mas/yr<ref name=simbad/><ref name=hip/>
| parallax =1.33 ± 0.20 mas<ref name=simbad/><ref name=hip/>
}}
'''VV Cephei''' (VV Cep, HD 208816, HIP 108317, BD+62 2007) is a [[Supergiant|supergiant star]] in the [[constellation]] of [[Cepheus]].<ref name=illinois>{{cite web|url=http://stars.astro.illinois.edu/sow/vvcep.html|title=VV Cephei|accessdate=January 30, 2020|publisher=stars.astro.illinois.edu|work=Stars|author=Jim Kaler|date=May 21, 2013}}</ref> Along with [[Mu Cephei]], VV Cephei is one of the largest [[star]]s in the night sky. It is actually an [[eclipsing binary]] system of two stars with the longest known period of 7,430 days, or 20.4 years.<ref name=variablePaper>
*{{cite journal
|last1=Hoppkins |first1=Jeffrey L.
|last2=Bennett |first2=Phillip D.
|last3=Pollmann |first3=Ernst
|display-authors=3
|title=VV Cephei Eclipse Campaign 2017/19
|journal=The Society for Astronomical Sciences 34th Annual Symposium on Telescope Science
|volume=
|issue=|page=83-90|date=2015
|doi=
|bibcode=2015SASS...34...83H
|ref=harv
}}
*{{cite web|url=https://britastro.org/sites/default/files/attachments/VV+Cephei+Eclipse+Campaign+2017.pdf|title=VV Cephei Eclipse Campaign 2017/19 PDF|accessdate=January 30, 2020|publisher=britastro.org}}
</ref> The two stars are designated VV Cephei A and VV Cephei B repectively to distinguish them, with VV Cephei A being the larger of the two. The high [[declination]] of VV Cephei means that it is a [[circumpolar]] system that can always be seen in the northern hemisphere.
==Properties and Structure==
The VV Cephei system is situated 2452.36 [[light year]]s away from [[Earth]].<ref name=universeguide/> The system is composed of two stars, a red [[supergiant]] VV Cephei A and a blue dwarf VV Cephei B, with their [[orbit]]s align to Earth such that one star can pass in front of the other. This results in the light from the two stars periodically dimming as one obscures light from the other. The dimming follows a cycle of 7,430 days (or 20.4 years) making it the second longest period for a [[variable star]] known, the longest being that of [[Epsilon Aurigae]] and a period of 9,890 days.<ref name=variablePaper/> The eclipse produced when the red supergiant passes in front of the blue dwarf lasts about 2 years and reduced the brightness of the system by 20%.<ref name=illinois/> As of 2019 the most recent eclipse began in August 2017. The long timescale over which an orbit occurs makes the system difficult to study.
The stars have a highly [[eccentric]] orbit with a [[semi-major axis]] of 25 [[Astronomical unit|astronomical units]] and an eccentricity of 0.346.<ref name=wright>{{cite journal
|last1=Wright |first1=K. O.
|display-authors=3
|title=The System of VV Cephei Derived from an Analysis of the Hα Line
|journal=Journal of the Royal Astronomical Society of Canada
|volume=71
|issue=|page=152|date=1977
|doi=
|bibcode=1977JRASC..71..152W
|ref=harv
}}
</ref> This means the distance between the two stars varies between 17 AU up to 34 AU.<ref name=illinois/> The is thought to be some form of mass transfer between the stars with a jet of material travelling from the larger VV Cephei A to VV Cephei B. Up to a few hundreths of a solar mass of material is thought to be transfered between the stars each year.<ref name=illinois/>
VV Cephei A is thought to have a [[mass (science)|mass]] of 20 [[solar mass]]es and a radius approximately 1,000 times that of the [[Sun]], though more older measurements place it higher at 1,600 times the solar radius.<ref name=variablePaper/><ref name=contellationguide>{{cite web|url=https://www.constellation-guide.com/constellation-list/cepheus-constellation/|title=Cepheus Constellation|accessdate=January 30, 2020|publisher=constellation-guide}}</ref> For a comparison, if it were to replace the Sun in our [[solar system]], its surface would easily extend to the orbit of [[Saturn]] or possibly [[Uranus]].<ref>{{cite web|url=https://thesciencearchives.miraheze.org/wiki/VV_Cephei|title=VV Cephei|accessdate=January 30, 2020|publisher=thesciencearchives.miraheze.org|date=November 24, 2018}}</ref> The temeprature of its surface it thought to be in the range 3,300-3,650 kelvin and its [[luminosity]] is estimated to be 400,000 larger than the Sun's.<ref name=illinois/> The star is a pulsating semi-regular variable star and changes in brightness by several hundredths to a few tenths of magnitude as it pulsates. These changes take place over several times periods 58, 118, and 349 days as well as an additional one of 13.7 years. VV Cephei A's shape is not thought to be spherical, but something closer to a teardrop shape, though more subtle. The star is sufficiently larger that there is a [[Doppler-shift]] in the [[hydrogen]]-alpha line in the star's spectrum. This is causes by the star's rotation as one side of the star is rotating towards us and so light from that side is [[blueshift|blue shifted]] whereas light from the side rotating away from us is [[redshift|red shifted]].<ref name=variablePaper/>
Although smaller than VV Cephei A, VV Cephei B is still quite large compared to the Sun with an estimated mass in the neighbourhood of 19 solar masses and radius of 13 solar radii.<ref>{{cite journal
|last1=Hutchings |first1=J. B.
|last2=Wright |first2=K. O.
|display-authors=3
|title=Rotationally extended stellar envelopes - III. The Be component of VV Cephei
|journal=Monthly Notices of the Royal Astronomical Society
|volume=155
|issue=|page=203|date=1971
|doi=10.1093/mnras/155.2.203
|bibcode=1971MNRAS.155..203H
|ref=harv
}}</ref><ref name=variablePaper/> The star dominates the spectrum of the VV Cephei system in the [[ultraviolet]] and at higher wavelengths whereas VV Cephei A dominated in the [[infrared]]. The star appears blue-white in color and its class is a B6 dwarf.<ref name=illinois/>
==References==
{{reflist}}
{{Stars}}
[[Category:Astronomy]]
[[Category:Stars]]
| image =
| designation =VV Cep<br/>HD 208816<br/>HIP 108317
| rightascension =21<sup>h</sup> 56<sup>m</sup> 39.1438<sup>s</sup><ref name=simbad>{{cite web|url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=VV+Cephei|title=VV Cephei|accessdate=January 30, 2020|work=Simbad Astronomical Database|publisher=simbad.u-strasbg.fr}}</ref><ref name=hip>
{{cite journal
|last1=van Leeuwen |first1=Floor
|display-authors=3
|title=Validation of the new Hipparcos reduction
|journal=Astronomy and Astrophysics
|volume=474
|issue=2|page=653-664|date=2007
|doi=10.1051/0004-6361:20078357
|bibcode=2007A&A...474..653V
|ref=harv
}} {{arXiv|0708.1752}}</ref>
| declination =+63° 37′ 32.0174″<ref name=simbad/><ref name=hip/>
| distance =2452.36 ly<ref name=universeguide>{{cite web|url=https://www.universeguide.com/star/vvcephei|title=VV Cephei (Supergiant Star) Star Facts|accessdate=January 30, 2020|publisher=universeguide.com}}</ref>
| constellation =Cepheus
| type =Supergiant{{!}}Supergiant star
| dimensions =
| magnitude =Apparent Mag: +5.11<ref name=universeguide/><br/>Absolute Mag: -6.93 / -4.27<ref name=universeguide/>
| redshift =
| radvelocity =-18.7 ± 0.9 km/s<ref name=simbad/>
| propmotion =RA: -0.25 mas/yr<ref name=simbad/><ref name=hip/><br/>Dec: -2.56 mas/yr<ref name=simbad/><ref name=hip/>
| parallax =1.33 ± 0.20 mas<ref name=simbad/><ref name=hip/>
}}
'''VV Cephei''' (VV Cep, HD 208816, HIP 108317, BD+62 2007) is a [[Supergiant|supergiant star]] in the [[constellation]] of [[Cepheus]].<ref name=illinois>{{cite web|url=http://stars.astro.illinois.edu/sow/vvcep.html|title=VV Cephei|accessdate=January 30, 2020|publisher=stars.astro.illinois.edu|work=Stars|author=Jim Kaler|date=May 21, 2013}}</ref> Along with [[Mu Cephei]], VV Cephei is one of the largest [[star]]s in the night sky. It is actually an [[eclipsing binary]] system of two stars with the longest known period of 7,430 days, or 20.4 years.<ref name=variablePaper>
*{{cite journal
|last1=Hoppkins |first1=Jeffrey L.
|last2=Bennett |first2=Phillip D.
|last3=Pollmann |first3=Ernst
|display-authors=3
|title=VV Cephei Eclipse Campaign 2017/19
|journal=The Society for Astronomical Sciences 34th Annual Symposium on Telescope Science
|volume=
|issue=|page=83-90|date=2015
|doi=
|bibcode=2015SASS...34...83H
|ref=harv
}}
*{{cite web|url=https://britastro.org/sites/default/files/attachments/VV+Cephei+Eclipse+Campaign+2017.pdf|title=VV Cephei Eclipse Campaign 2017/19 PDF|accessdate=January 30, 2020|publisher=britastro.org}}
</ref> The two stars are designated VV Cephei A and VV Cephei B repectively to distinguish them, with VV Cephei A being the larger of the two. The high [[declination]] of VV Cephei means that it is a [[circumpolar]] system that can always be seen in the northern hemisphere.
==Properties and Structure==
The VV Cephei system is situated 2452.36 [[light year]]s away from [[Earth]].<ref name=universeguide/> The system is composed of two stars, a red [[supergiant]] VV Cephei A and a blue dwarf VV Cephei B, with their [[orbit]]s align to Earth such that one star can pass in front of the other. This results in the light from the two stars periodically dimming as one obscures light from the other. The dimming follows a cycle of 7,430 days (or 20.4 years) making it the second longest period for a [[variable star]] known, the longest being that of [[Epsilon Aurigae]] and a period of 9,890 days.<ref name=variablePaper/> The eclipse produced when the red supergiant passes in front of the blue dwarf lasts about 2 years and reduced the brightness of the system by 20%.<ref name=illinois/> As of 2019 the most recent eclipse began in August 2017. The long timescale over which an orbit occurs makes the system difficult to study.
The stars have a highly [[eccentric]] orbit with a [[semi-major axis]] of 25 [[Astronomical unit|astronomical units]] and an eccentricity of 0.346.<ref name=wright>{{cite journal
|last1=Wright |first1=K. O.
|display-authors=3
|title=The System of VV Cephei Derived from an Analysis of the Hα Line
|journal=Journal of the Royal Astronomical Society of Canada
|volume=71
|issue=|page=152|date=1977
|doi=
|bibcode=1977JRASC..71..152W
|ref=harv
}}
</ref> This means the distance between the two stars varies between 17 AU up to 34 AU.<ref name=illinois/> The is thought to be some form of mass transfer between the stars with a jet of material travelling from the larger VV Cephei A to VV Cephei B. Up to a few hundreths of a solar mass of material is thought to be transfered between the stars each year.<ref name=illinois/>
VV Cephei A is thought to have a [[mass (science)|mass]] of 20 [[solar mass]]es and a radius approximately 1,000 times that of the [[Sun]], though more older measurements place it higher at 1,600 times the solar radius.<ref name=variablePaper/><ref name=contellationguide>{{cite web|url=https://www.constellation-guide.com/constellation-list/cepheus-constellation/|title=Cepheus Constellation|accessdate=January 30, 2020|publisher=constellation-guide}}</ref> For a comparison, if it were to replace the Sun in our [[solar system]], its surface would easily extend to the orbit of [[Saturn]] or possibly [[Uranus]].<ref>{{cite web|url=https://thesciencearchives.miraheze.org/wiki/VV_Cephei|title=VV Cephei|accessdate=January 30, 2020|publisher=thesciencearchives.miraheze.org|date=November 24, 2018}}</ref> The temeprature of its surface it thought to be in the range 3,300-3,650 kelvin and its [[luminosity]] is estimated to be 400,000 larger than the Sun's.<ref name=illinois/> The star is a pulsating semi-regular variable star and changes in brightness by several hundredths to a few tenths of magnitude as it pulsates. These changes take place over several times periods 58, 118, and 349 days as well as an additional one of 13.7 years. VV Cephei A's shape is not thought to be spherical, but something closer to a teardrop shape, though more subtle. The star is sufficiently larger that there is a [[Doppler-shift]] in the [[hydrogen]]-alpha line in the star's spectrum. This is causes by the star's rotation as one side of the star is rotating towards us and so light from that side is [[blueshift|blue shifted]] whereas light from the side rotating away from us is [[redshift|red shifted]].<ref name=variablePaper/>
Although smaller than VV Cephei A, VV Cephei B is still quite large compared to the Sun with an estimated mass in the neighbourhood of 19 solar masses and radius of 13 solar radii.<ref>{{cite journal
|last1=Hutchings |first1=J. B.
|last2=Wright |first2=K. O.
|display-authors=3
|title=Rotationally extended stellar envelopes - III. The Be component of VV Cephei
|journal=Monthly Notices of the Royal Astronomical Society
|volume=155
|issue=|page=203|date=1971
|doi=10.1093/mnras/155.2.203
|bibcode=1971MNRAS.155..203H
|ref=harv
}}</ref><ref name=variablePaper/> The star dominates the spectrum of the VV Cephei system in the [[ultraviolet]] and at higher wavelengths whereas VV Cephei A dominated in the [[infrared]]. The star appears blue-white in color and its class is a B6 dwarf.<ref name=illinois/>
==References==
{{reflist}}
{{Stars}}
[[Category:Astronomy]]
[[Category:Stars]]