Westerlund 1-20

{{short description|Red supergiant star located in the Westerlund 1 super star cluster}}

{{Sky|16|47|04.70|-|45|51|23.96}}

{{Starbox begin

|name=Westerlund 1-20

}}

{{Starbox image

|image=

{{Location mark

|image=Surprise Cloud Around Vast Star.jpg|alt=|float=center|width=300

|label=|position=right

|mark=Red circle.svg|mark_width=10|mark_link=WOH G64

|x=482|y=360

}}

|credit=ESO

|caption=Westerlund 1 super star cluster. The location of Wd 1-20 is circled.

}}

{{Starbox observe

|constell=Ara{{cite constellation|Cl* Westerlund 1 W 20}}

|dec={{DEC|-45|51|23.9}}

|ra={{RA|16|47|04.69}}

|epoch=J2000

|equinox=J2000

}}

{{Starbox character

|type=Red supergiant

|appmag_2=6.378

|appmag_2_passband=J

|appmag_3_passband=H

|appmag_3=4.381

|appmag_4=2.61

|appmag_4_passband=K

|class=M3 - M6I{{cite journal|bibcode=1987A&AS...70..311W|title=Photometry and spectroscopy of stars in the region of a highly reddened cluster in Ara|last1=Westerlund|first1=B. E.|journal=Astronomy and Astrophysics Supplement Series|year=1987|volume=70|page=311}}

}}

{{Starbox astrometry

|prop_mo_ra=−2.478

|prop_mo_dec=−4.041

|parallax=0.1690

|p_error=0.1073

|parallax_footnote={{cite Gaia EDR3|5940106007092341120}}

|dist_pc={{val|2,600|600|400|fmt=commas}} (assumed){{Cite journal|last1=Aghakhanloo|first1=Mojgan|last2=Murphy|first2=Jeremiah W.|last3=Smith|first3=Nathan|last4=Parejko|first4=John|last5=Díaz-Rodríguez|first5=Mariangelly|last6=Drout|first6=Maria R.|last7=Groh|first7=Jose H.|last8=Guzman|first8=Joseph|last9=Stassun|first9=Keivan G.|date=2020-02-21|title=Inferring the parallax of Westerlund 1 from Gaia DR2|arxiv=1901.06582|bibcode=2020MNRAS.492.2497A|journal=Monthly Notices of the Royal Astronomical Society|volume=492|issue=2|pages=2497–2509|doi=10.1093/mnras/stz3628|doi-access=free |s2cid=119465620|issn=0035-8711}}

}}

{{Starbox detail

|luminosity={{val|101,000|13,000|fmt=commas}}

|radius={{val|858|48|fmt=commas}}{{cite thesis|doi=10.11606/D.14.2019.tde-12092018-161841|title=The Red Supergiants in the Supermassive Stellar Cluster Westerlund 1|year=2019|last1=Arévalo|first1=Aura|doi-access=free}}

|temperature=3,284 - 3,550

}}

{{Starbox catalog

|names=Westerlund 1 W20, Westerlund 1 BKS D, 2MASS J16470468-4551238, Gaia EDR3 5940106007092341120

}}

{{Starbox reference

|Simbad=Cl*+Westerlund+1+W+20

}}

{{Starbox end}}

Westerlund 1-20 (abbreviated to Wd 1-20 or just W20) is a red supergiant (RSG) located in the Westerlund 1 super star cluster. Its radius was calculated to be around 965 solar radii{{Cite journal|last1=Fok|first1=Thomas K. T.|last2=Nakashima|first2=Jun-Ichi|last3=Yung|first3=Bosco H. K.|last4=Hsia|first4=Chih-Hao|last5=Deguchi|first5=Shuji|year=2012|title=Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated with Massive Clusters|journal=The Astrophysical Journal|volume=760|issue=1|page=65|arxiv=1209.6427|bibcode=2012ApJ...760...65F|doi=10.1088/0004-637X/760/1/65|s2cid=53393926}} (6.72 × 10⁸ km, 4.48 au), making it one of the largest stars discovered so far. This corresponds to a volume 899 million times bigger than the Sun. If placed at the center of the Solar System, the photosphere of Westerlund 1-20 would almost reach the orbit of Jupiter.

Image:Comparison of Radii of RSGs located in the Westerlund 1 star cluster.png star cluster.]]

The star is classified as a luminous cool supergiant emitting most of its energy in the infrared spectrum.{{Cite web|title=Cl* Westerlund 1 W 20|url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Cl*+Westerlund+1+W+20|website=Simbad}} W20 occupies the upper right corner of the Hertzsprung-Russell diagram. Using the effective temperature of 3,500 K, the bolometric luminosity of 126,000 L_☉ and the solar effective temperature of 5,772 K,{{Cite web|title=Sun Fact Sheet|url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html|last=Williams|first=D. R.|date=2013}} its radius can be calculated using the Stefan-Boltzmann law.{{nowrap|{{efn|name=radius}}}}

Westerlund 1-20 was observed to have an extended, cometary shaped nebula, similar to the other red supergiant Westerlund 1 W26. It is therefore likely that its morphology was affected by either the intracluster medium or the cluster wind of Westerlund 1.{{Cite journal|last1=Dougherty|first1=S. M.|last2=Clark|first2=J. S.|last3=Negueruela|first3=I.|last4=Johnson|first4=T.|last5=Chapman|first5=J. M.|date=2010-02-01|title=Radio emission from the massive stars in the galactic super star cluster Westerlund 1|journal=Astronomy & Astrophysics|language=en|volume=511|pages=A58|doi=10.1051/0004-6361/200913505|arxiv=0912.4165|bibcode=2010A&A...511A..58D|issn=0004-6361|doi-access=free}} The nebulae of both Westerlund 1-20 and Westerlund 1 W26 are extended outward from the cluster core and most bright at inward direction, indicating the outward cluster wind.{{citation|arxiv=1803.07008|year=2018|title=Asymmetric ejecta of cool supergiants and hypergiants in the massive cluster Westerlund 1|doi=10.1093/mnrasl/sly046 |last1=Andrews |first1=H. |last2=Fenech |first2=D. |last3=Prinja |first3=R. K. |last4=Clark |first4=J. S. |last5=Hindson |first5=L. |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=477 |issue=1 |pages=L55–L59 |doi-access=free |bibcode=2018MNRAS.477L..55A }}