CD Crucis

CD Crucis

A light curve for CD Crucis, adapted from Marchenko et al. (1998)[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Crux
Right ascension	12h 43m 50.99768s[2]
Declination	−63° 05′ 14.8029″[2]
Apparent magnitude (V)	10.81[3] (10.71 - 10.82[4])
Characteristics
Spectral type	WN6o + O5V[5]
U−B color index	−0.19[3]
B−V color index	+0.83[3]
Variable type	Eclipsing binary[4]
Distance		approx. 14,000 ly (approx. 4,300 pc)
Absolute magnitude (MV)	−6.2 (−5.2 + −5.7[8])
Semi-amplitude (K1) (primary)		263 ± 4 km/s
Semi-amplitude (K2) (secondary)	218 ± 9 km/s
Details
WR
Mass	42.6 ± 3.6[10] M☉
Radius	5[10] R☉
Luminosity	127,000[5] L☉
O
Mass	51.0 ± 2.8[10] M☉
Radius	12[10] R☉
Luminosity	880,000[5] L☉
AAVSO  1238-62
Database references
SIMBAD	data

CD Crucis, also known as HD 311884, is an

CD Cru is composed of two massive and highly luminous stars aligned so that they eclipse each other as they orbit every 6 days and 6 hours. One is a hot blue O-type main sequence star of spectral type O5V that is 57 times as massive as the Sun, while the other is an even hotter Wolf–Rayet star of spectral type WN6 that is 48 times as massive as the Sun. The WR star dominates the spectrum but is less bright, so which star is considered the primary varies. For clarity the components are referred to as WR and O^[5][9]

Hogg 15

Hogg 15 is a small faint open cluster that has been calculated to lie about 4.2 kpc away. CD Cru is considered a likely member of the cluster, in which case it would be the brightest member by over a magnitude. It lies outside the central two arc-minute condensation of the cluster, but well within the outer bounds discovered for the member stars. The cluster is calculated to be only eight million years old.^[11]

The brighter and closer cluster

Properties

The WR component is five times the radius of the sun, but its high temperature means it is over 100,000 times more luminous. Its mass is determined from the orbital motion to be 42.6 M_☉.

The O star is larger at 12 R_☉, more luminous at 880,000 L_☉, and more massive at 51 M_☉. Although the stars are only separated by around 68 R_☉, they are well separated because of their small size.

References