MY Cephei

File:MYCepLightCurve.png light curve for MY Cephei, plotted from ASAS-SN data{{cite web |url=https://asas-sn.osu.edu/variables/lookup |website=ASAS-SN Variable Stars Database|title=ASAS-SN Variable Stars Database|publisher=ASAS-SN |access-date=3 December 2022}}]]

Observations of the open cluster NGC 7419 in 1954 showed that four of its members were luminous red stars, most likely red supergiants. In addition, an unusually red star was found to be variable and probably an even more luminous supergiant.{{cite journal |bibcode=1955ApJ...121..637B |title=M-Type Stars in NGC 7419 |last1=Blanco |first1=V. |last2=Nassau |first2=J. J. |last3=Stock |first3=J. |last4=Wehlau |first4=W. |journal=The Astrophysical Journal |year=1955 |volume=121 |page=637 |doi=10.1086/146029 }} This star was given the variable star designation MY Cephei in 1973 in the 59th name-list of variable stars.{{cite journal |bibcode=1973IBVS..834....1K |title=59th Name-List of Variable Stars |last1=Kukarkin |first1=B. V. |last2=Kholopov |first2=P. N. |last3=Kukarkina |first3=N. P. |last4=Perova |first4=N. B. |journal=Information Bulletin on Variable Stars |year=1973 |volume=834 |page=1 }}

MY Cephei is classified as semiregular variable star of sub-type SRc, indicating it is a cool supergiant, although its pulsational period is not known. It has been observed as bright as magnitude 14.4 and as faint as magnitude 15.5. The star, along with another late red supergiant star, S Persei, are sometimes considered prototypes for the class of M6–7 supergiants.{{cite journal|bibcode=1974ApJ...193..367F|title=The open cluster NGC 7419 and its M7 supergiant IRC +60 375|journal=Astrophysical Journal|volume=193|pages=367 |last1=Fawley |first1=W. M. |last2=Cohen |first2=M. |year=1974 |doi=10.1086/153171 |doi-access=free }}

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The distance of MY Cephei is assumed to be around {{val|9,780|1,140|950|fmt=commas|ul=light years}} or {{val|3,000|350|290|fmt=commas|ul=parsecs}} based on it being a member of the NGC 7419 open cluster.{{Cite journal|last1=Davies|first1=Ben|last2=Beasor|first2=Emma R.|date=March 2020|title=The 'red supergiant problem': the upper luminosity boundary of Type II supernova progenitors|bibcode=2020MNRAS.493..468D|journal=MNRAS|language=en|volume=493|issue=1|pages=468–476|doi=10.1093/mnras/staa174|doi-access=free |arxiv=2001.06020 |s2cid=210714093}} Gaia Early Data Release 3 gives a parallax of {{val|0.3398|0.0708|ul=mas}} for MY Cep, implying a similar distance of {{val|2691|511|419|fmt=commas|ul=pc}}.{{cite journal |bibcode=2021AJ....161..147B |title=Estimating Distances from Parallaxes. V. Geometric and Photogeometric Distances to 1.47 Billion Stars in Gaia Early Data Release 3 |last1=Bailer-Jones |first1=C. A. L. |last2=Rybizki |first2=J. |last3=Fouesneau |first3=M. |last4=Demleitner |first4=M. |last5=Andrae |first5=R. |journal=The Astronomical Journal |year=2021 |volume=161 |issue=3 |page=147 |doi=10.3847/1538-3881/abd806 |arxiv=2012.05220 |s2cid=228063812 |doi-access=free }}

The spectral type of MY Cephei is given in the General Catalogue of Variable Stars as M6–7 Iab, indicating the star is an intermediate-size luminous supergiant star, although most authors gives M7–M7.5 I. Classification is difficult because of the lack of comparable standard stars, but its spectrum appears to be later than M5, earlier than VX Sagittarii when at M9, and more luminous than M7 giant stars. A 2021 study gives a spectral class of M3 based on infrared observations, and a correspondingly higher temperature.{{cite journal |bibcode=2021AJ....162..187M |title=New Infrared Spectral Indices of Luminous Cold Stars: From Early K to M Types |last1=Messineo |first1=Maria |last2=Figer |first2=Donald F. |last3=Kudritzki |first3=Rolf-Peter |last4=Zhu |first4=Qingfeng |last5=Menten |first5=Karl M. |last6=Ivanov |first6=Valentin D. |last7=Chen |first7=C. -H. Rosie |journal=The Astronomical Journal |year=2021 |volume=162 |issue=5 |page=187 |doi=10.3847/1538-3881/ac116b |arxiv=2107.03707 |s2cid=235765247 |doi-access=free }}

MY Cephei is a very luminous, cool and large extreme supergiant star, with a luminosity more than 100,000 times that of the Sun ({{solar luminosity|link=y}}) and a radius in excess of a thousand times the Sun's radius ({{solar radius|link=y}}). It is likely the most luminous, coolest, and the largest supergiant star in its open cluster, and occupies the upper-right hand corner of the Hertzsprung–Russell diagram.

A 2018 paper gives the star a temperature of {{val|3,400|fmt=commas|ul=K}}, corresponding a radius of {{solar radius|1,134}} based on a luminosity of {{solar luminosity|155,000}}.{{cite journal|bibcode=2018MNRAS.475...55B|title=The evolution of red supergiant mass-loss rates|journal=Monthly Notices of the Royal Astronomical Society|volume=475|issue=1|pages=55|last1=Beasor|first1=Emma R|last2=Davies|first2=Ben|last3=Arroyo-Torres|first3=B|last4=Chiavassa|first4=A|last5=Guirado|first5=J. C|last6=Marcaide|first6=J. M|last7=Alberdi|first7=A|last8=De Wit|first8=W. J|last9=Hofmann|first9=K. -H|last10=Meilland|first10=A|last11=Millour|first11=F|last12=Mohamed|first12=S|last13=Sanchez-Bermudez|first13=J|year=2018|doi=10.1093/mnras/stx3174|doi-access=free |arxiv=1712.01852|s2cid=55822928}} The mass of MY Cephei is uncertain, but expected to be around 14.5 times the Sun's mass ({{solar mass|link=y}}). Mass is being lost at {{solar mass|{{val|2.3|0.3|e=-5}}}} per year, one of highest mass loss rates known for a supergiant star.

A study from 2020 based on SED integration gives an unexpectedly higher bolometric luminosity of {{val|310,000|70,000|fmt=commas|u={{solar luminosity}}}}, close to the empirical upper luminosity limit of red supergiants (i.e. Humphreys–Davidson limit). This implies a higher radius of {{nowrap|{{solar radius calculator|type=LT|1=310000|Lerr=70000|2=3000|unit=y}}}} based on an effective temperature of {{val|3000|fmt=commas|u=K}} derived using the DUSTY model, considerably larger than the upper radius limit of red supergiants at roughly {{solar radius|1,500}} respectively.{{cite journal |title=The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought |display-authors=4 |author1-link=Emily Levesque|author1=Emily M. Levesque |author2=Philip Massey |author3=K. A. G. Olsen|author4=Bertrand Plez |author5=Eric Josselin|author6=Andre Maeder |author7=Georges Meynet |s2cid=15109583 |name-list-style=amp |journal=The Astrophysical Journal |volume=628 |issue=2 |date=August 2005 |pages=973–985 |doi=10.1086/430901 |bibcode=2005ApJ...628..973L|arxiv = astro-ph/0504337 }} Older studies frequently calculated even more lower temperatures and an estimated radius of {{convert|170,000,000,000,000|cm|solar radius|disp=out}}.

• NML Cygni — another late-type red supergiant or hypergiant star.
• VY Canis Majoris — another large and luminous supergiant or hypergiant star.

{{notelist|refs=

{{Efn|name=luminosity|1=Calculated using the following equation:
$10^\{0.4\backslash left(\; 4.74-\backslash left(\; \backslash text\{m\}\_\{\backslash text\{bol\}\}\; +5-5\backslash ,\backslash text\{log\}\backslash ,d\backslash right)\; \backslash right)\}$
, where m_bol is the star's apparent bolometric magnitude and d is the distance in parsecs. The values used for the m_bol are {{val|4.29|0.35}} and {{val|4.07|0.69}}, while the value used for the distance is 3,240 parsecs. }}

{{efn | name=radius2 | Applying the Stefan-Boltzmann Law with a nominal solar effective temperature of 5,772 K:

:$\backslash sqrt\{(5772/3595)^4\; *\; 158,890\}\; =\; 1,027\backslash \; R\backslash odot$.
$\backslash sqrt\{(5772/3595)^4\; *\; 194,580\}\; =\; 1,138\backslash \; R\backslash odot$}}

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{{Reflist}}

{{Stars of Cepheus}}

{{DEFAULTSORT:My Cephei}}

Category:Cepheus (constellation)

Cephei, MY

Category:M-type supergiants

Category:Semiregular variable stars

J22543171+6049388

Category:IRAS catalogue objects

Category:TIC objects