Westerlund 1-243
{{Short description|Luminous blue variable star undergoing an eruptive phase in Westerlund 1}}
{{Sky|16|47|7.503|-|45|52|29.152}}
{{Starbox begin
| name = Westerlund 1-243
}}
{{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
|x=452|y=433
}}
| caption=Westerlund 1 super star cluster. The location of Wd 1-243 is circled.
| credit=ESO
}}
{{Starbox observe
| epoch = J2000
| equinox = J2000
| constell = Ara
}}
{{Starbox character
| appmag_1_passband = J
| appmag_2_passband = H
| appmag_3_passband = K
}}
{{Starbox astrometry
| parallax = 0.0119
| p_error = 0.0812
| dist_ly = 13,400
}}
{{Starbox detail
| mass = 40
| radius = 376.9
| luminosity = 730,000
| gravity = ~0.65
| temperature = ~8,500
| rotational_velocity = 10
| age_myr = {{val|10.4|1.3|1.2}}
}}
{{Starbox catalog
| names = Westerlund 1 W 243, Westerlund 1 BKS G, 2MASS J16470749-4552290, Gaia DR3 5940105830990286208
}}
{{Starbox reference
| Simbad = Cl*+Westerlund+1+W+243}}
{{Starbox end}}
Westerlund 1-243 or Wd 1-243 is a luminous blue variable (LBV) star undergoing an eruptive phase located within the outskirts of the super star cluster Westerlund 1. Located about {{convert|13400|ly|pc|abbr=on}} from Earth, it has a luminosity of 0.73 million {{solar luminosity|link=y}} making it one of the most luminous stars known.
Observation
Westerlund 1-243 is the second brightest star in Westerlund 1, behind only Westerlund 1-4.
It is one of several different hypergiant stars in Westerlund 1. It may also have a companion star, possibly an O-type supergiant.
=Spectrum=
Westerlund 1-243 displays a complex, time-varying spectrum with emission lines of hydrogen, helium and Lyman-α pumped metals, forbidden lines of nitrogen and iron, and a large number of absorption lines from neutral and singly-ionized metals. Many lines are complex emission/absorption blends, with significant spectral evolution occurring on timescales of just a few days.
Properties
Westerlund 1-243 has a temperature of ~8,500 K determined from modelling the absorption line spectrum. It has expanded to a radius of {{solar radius|376.9|link=y}}, and a Rosseland radius of {{solar radius|450}}. It is radiating at a luminosity of {{solar luminosity|730,000}}. It is losing mass at a rate of {{solar mass|{{val|6.1|e=-7}}}}/yr.
=Evolution=
Westerlund 1-243 is believed to be either in an advanced pre-red supergiant LBV phase, or has evolved through the RSG phase and returned to the blue side of the HR diagram. In the future it is expected to evolve toward a WR phase. The K-band spectrum also implies a higher temperature than that of a typical yellow hypergiant and suggests that Westerlund 1-243 may be evolving back towards a hotter state.
References
{{reflist|refs=
{{cite Gaia DR3|5940105830990286208}}
}}
{{Stars of Ara}}