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Region around γ Cygni, with RW Cygni annotated on the full-size image (north is right)
Epoch J2000 Equinox J2000
|Right ascension||20h 28m 50.59095s|
|Declination||39° 58′ 54.4268″|
|Apparent magnitude (V)||8.05 - 9.70|
|Parallax (π)||0.91 ± 1.03 mas|
|Absolute magnitude (MV)||-6.41|
|Radius||680 - 980 R☉|
|Diameter||680 - 980 D☉|
RW Cygni is a semiregular variable star in the constellation Cygnus, about a degree east of 2nd magnitude γ Cygni. Its apparent magnitude varies between 8.05 and 9.70 and its spectral type between M2 and M4.
The Hipparcos parallax for RW Cygni is 0.91 mas but with a very large margin of error. RW Cygni is assumed to be a member of the Cygnus OB9 Stellar Association and therefore around 3,600 light-years from the solar system.
RW Cygni is a red supergiant with a bolometric luminosity around 150,000 L☉. Its spectral type is given in the General Catalogue of Variable Stars as M2-4Ia-Iab, and one of the most recent catalogues of MK spectral classifications gives M3-M4Ia-Iab. The effective temperature is directly calculated to be 3,600 K, giving a radius of 980 D☉. An alternate calculation gives a higher temperature of 3,920 K and a correspondingly lower radius of 680 D☉. Using the more conservative figure, if it was placed at the center of Solar System, it would be extend past the orbit of Mars and into the Asteroid Belt.
The initial mass of RW Cygni has been estimated from its position relative to theoretical stellar evolutionary tracks to be around 20 M☉. Observations of its atmosphere suggest that it is losing mass at a rate of ×10−9 M☉ per year. 3.2
RW Cygni is classified as a semiregular variable star. It is given the subtype SRc, indicating that it is a cool supergiant. Its brightness varies from extremes of magnitude +8.0 and +9.5 with a period of 580 ± 80 days. No long secondary period has been detected.
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