HD 110432

HD 110432 is a Be star in the south-east of Crux, behind the center of the southern hemisphere's dark Coalsack Nebula. It has a stellar classification of B1IVe, which means it is a subgiant star of class B that displays emission lines in its spectrum. This is a variable star of the Gamma Cassiopeiae type, indicating it is a shell star with a circumstellar disk of gas about the equator, and has the variable star designation BZ Crucis. It is not known to be a member of a binary system, although it is probably a member of the open cluster NGC 4609. This star is moderately luminous in the X-ray band, with a variable energy emission of 10^32–33 erg s⁻¹ in the range 0.2−12 keV. The X-ray emission may be caused by magnetic activity, or possibly by accretion onto a white dwarf companion.^[3]

A visual band light curve for BZ Crucis, adapted from Sarty et al. (2011)^[9]

HD 110432

Location of BZ Crucis (circled). The other star shown overlapping/underlying the dark nebula is HD 109000 (HR 4771) which is a red/brown star about half the distance to the nebula, having parallax of 12.8 ± 0.05 thus about 250 light years away[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Crux
Right ascension	12h 42m 50.2656s[1]
Declination	−63° 03′ 31.048″[1]
Apparent magnitude (V)	5.24 - 5.45[2]
Characteristics
Spectral type	B1IVe[3]
U−B color index	−0.82[4]
B−V color index	+0.27[4]
Variable type	γ Cas[2]
Astrometry
Radial velocity (Rv)	+35[5] km/s
Proper motion (μ)	RA: −12.512[1] mas/yr Dec.: −3.984[1] mas/yr
Parallax (π)	2.3834±0.1228 mas[1]
Distance	1,370 ± 70 ly (420 ± 20 pc)
Absolute magnitude (MV)	−2.56[6]
Details
Mass	9.6[3] M☉
Radius	6.5±1.2[7] R☉
Luminosity	1,153[1] L☉
Surface gravity (log g)	3.5–3.9[3] cgs
Temperature	22,510–25,000[3] K
Rotational velocity (v sin i)	300–400[3] km/s
Other designations
BZ Cru, HR 4830, CD-62 671, HD 110432, GCTP, SAO 252002, FK5 3015, HIP 62027.[8]
Database references
SIMBAD	data

BZ Crucis is the bright star between the open clusters NGC 4609 and Hogg 15

Distance

The distance of 388 pc published in the 2007 new Hipparcos reduction is over twice the distance of the Coalsack Nebula.^[10] The distance from Gaia Data Release 2 is even further at 420 pc.^[1]