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 152 M_☉ and 660,000 L_☉.

HD 15558

An H-alpha image of the Heart Nebula. HD 15558 is located at the centre of the cluster, circled.
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Cassiopeia[1]
Right ascension	02h 32m 42.537s[2]
Declination	61° 27′ 21.57″[2]
Apparent magnitude (V)	7.87[3]
Characteristics
Spectral type	O4.5III(f)[4] (O5.5III(f) + O7V[5])
U−B color index	−0.55[3]
B−V color index	+0.43[3]
V−R color index	+0.38[3]
R−I color index	+0.40[3]
J−H color index	+0.18[3]
Astrometry
Radial velocity (Rv)	−45.10±1.50[6] km/s
Proper motion (μ)	RA: −0.478[2] mas/yr Dec.: −0.849[2] mas/yr
Parallax (π)	0.5764±0.0662 mas[2]
Distance	approx. 5,700 ly (approx. 1,700 pc)
Absolute magnitude (MV)	−0.79[1]
Orbit
Period (P)	442 days[5] (1.2 [5] yr)
Semi-major axis (a)	726 R☉[5]
Eccentricity (e)	0.37±0.07[5]
Argument of periastron (ω) (secondary)	120[5]°
Details
Mass	>152±51[5] M☉
Radius	16.4[7] R☉
Luminosity	~660,000[5] L☉
Surface gravity (log g)	3.7[7] cgs
Temperature	39,500[7] K
Age	0.7-3[5][8] Myr
secondary
Mass	46±11[5] M☉
Radius	5.6[7] R☉
Other designations
HD 15558, HIP 11832, SAO 12326, IDS 02251+6101, TYC 4046-44-1, UBV 2530, GCRV 1424, 2MASS J02324253+6127215, WDS J02327+6127, PPM 13720, BD+60°502, GSC 04046-00044, CCDM J02327+6127, IC 1805 148
Database references
SIMBAD	data

HD 15558 in the cluster IC 1805

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 M_☉ and a luminosity of 660,000 L_☉, making it one of the most massive stars in the Milky Way Galaxy. The star loses 1.5×10⁻⁵ M_☉ per year.^[8] The secondary is an O7V star. It has a mass of 46 M_☉. 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.^[5]

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.^[4][9]

See also

• List of most massive stars
• List of most luminous stars