V915 Scorpii

Did You Know?

• V915 Scorpii was given its variable-star designation in 1978.
• Its variability was first announced by the Konkoly Observatory in 1979.
• Any period associated with its variation is longer than 600 days.

Surroundings

V915 Scorpii lies within the sparse OB association Moffat 2 and is enveloped by dust and gas that produce a significant infrared excess. It is classified as a triple star: 15 arcseconds away is the Wolf-Rayet star WR 85, one of the most luminous known stars yet visually four magnitudes fainter; component C is a 10th-magnitude K-class star 17 arcseconds away; and a 14th-magnitude star lies 22 arcseconds away. Photometry and space motions indicate that only V915 Scorpii and WR 85 share the same distance, while the other two are foreground objects. Four arcminutes distant are two other probable association members: a 10th-magnitude B0 giant and an 11th-magnitude OB star. Fitting the association to a main sequence yields a highly uncertain distance of 1.8 kpc, while a kinematical distance for the bubble around WR 85 gives 2.8 kpc. Bailer-Jones et al. 2018 estimates 1,720 pc, and the parallax for WR 85 suggests a distance around that value.

Properties

V915 Scorpii has a spectral classification of K0Ia-0, indicating a massive hypergiant. Its mass is estimated at 8.5 or 14.7 solar masses, and its radius gives a volume equivalent to about 330 million times that of the Sun. It radiates a luminosity of 74,000 or 185,000 times the solar luminosity, with a surface effective temperature of 4,600 K, producing the orange color of a K-type star. Earlier spectral classifications included G5Ia, G5Ia-0, G8Ia, and K0Ia, all consistent with a luminous supergiant or hypergiant.