HD 15558

HD 15558 (HIP 11832) is a massive O-type multiple star system in Cassiopeia and is specifically in our galaxy's Heart Nebula in the open cluster IC 1805. The primary is a very massive star with and.

Physical characteristics
HD 15558 A is a spectroscopic binary system containing at least two massive luminous class O stars. The primary is an O4.5 giant star with a surface temperature over 46,800 K. It has a mass of 152 and a luminosity of 660,000, making it one of the most massive stars in the Milky Way Galaxy. The star loses 1.5×10−5 per year. The secondary is an O7V star. It has a mass of 46. The primary may itself be a double star, suggested by the improbably large mass found from the binary orbit when compared to the other stellar parameters.

The Washington Double Star Catalog lists 11 companions within one arc minute of HD 15558 A, all fainter than 10th magnitude. In addition, it lists component E just over one arc minute away; it is another hot massive star, the 9th magnitude BD+60°501 with a spectral type of O7 V(n)((f))z.