CHARM2 problem?

[piellepi]

hi Celestians!
I found a strange and perhaps excessive value for the diameter of the star HIP 102276 / HD 197572 / SAO 70423 (aka X Cyg) : 3498000000 km, 5000 times the Rsun.
Don't you think it's wrong?
HIP 102276 would be the largest star in the known universe, well beyond VY Canis Majoris...
Thanks
Pierluigi

[ajtribick]

CHARM2 gives angular diameter measurements. This can result in implausible radii if the distance to the star is incorrect (in the case of this one the parallax error is comparable to the parallax itself, so there's probably a great deal of uncertainty as to the true distance). Of course the angular diameter listed in the catalogue may also be incorrect.

[Joey P.]

See https://en.wikipedia.org/wiki/Quasi-star.

«...but, with diameters of approximately 10 billion kilometres (66.85 au) or 7,187 times that of the Sun, each one would produce as much light as a small galaxy.»