HR Carinae

HR Car

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Carina
Right ascension	10h 22m 53.84074s
Declination	−59° 37′ 28.3774″
Apparent magnitude (V)	8.42 (7.0 - 8.8)
Characteristics
Spectral type	LBV
U−B color index	−0.22
B−V color index	+0.92
Variable type	LBV
Astrometry
Proper motion (μ)	RA: -6.87 mas/yr Dec.: +2.33 mas/yr
Parallax (π)	1.69 ± 0.82 mas
Distance	5.2k pc
Absolute magnitude (MV)	-8.4
Absolute bolometric magnitude (Mbol)	-9.4
Details
Mass	25 M☉
Radius	100 R☉
Luminosity	416,000-790,000 L☉
Temperature	7,900-21,900 K
Rotational velocity (v sin i)	150 km/s
Other designations
HR Car, HD 90177, HIP 50843, SAO 238005, CD-59 3044, GC 14276, MWC 202, AAVSO 1019-59
Database references
SIMBAD	data

HR Carinae is a luminous blue variable star located in the constellation Carina. It is surrounded by a vast nebula of ejected nuclear-processed material because this star has a multiple shell expanding atmosphere. This star is among the most luminous stars in the Milky Way. It has very broad emission wings on the Balmer lines, reminiscent from the broad lines observed in the spectra of O and Wolf–Rayet stars. A distance of 5 kpc and a bolometric magnitude of -9.4 put HR Car among the most luminous stars of the galaxy.

Discovery

HR Carinae was first noticed at the start of the 20th century because of its H_β emission. It was placed in Secchi class I, corresponding to modern A and F-type stars. It was catalogued in 1933 as a Be star and was discovered to be variable in 1940. A more detailed spectroscopic study gave it the type B2eq with emission line of hydrogen, helium, and ionised iron and P Cygni profiles on some lines.

By 1970, HR Carinae and the similar variable AG Carinae were recognised as being related to the P Cygni variables, unstable hot supergiants. The group was formally recognised as S Doradus variables to avoid confusion with the P Cygni spectral features shared with other types of star. HR Carinae became one of the best-studied examples of the class, clearly showing the brightness and spectral variations that came to characterise the stars known as luminous blue variables.

Brightness variation

HR Carinae undergoes spectral variations apparently correlated with the light variations similarly to other luminous blue variables. It has undergone several outbursts during which the visual brightness increases and the temperature drops, but the bolometric luminosity remains approximately constant. The visual brightness increased erratically but consistently during the later decades of the 20th century to a record peak of mag 6.8, then dropped straight to a record minimum of mag 8.8 by 2010.

Characteristics

HR Carinae has a temperature around 21,000K when quiescent and the spectrum is of an early B hypergiant, but in outburst it cools to below 8,000K.

HR Carinae is a lot like Eta Carinae, both luminous blue variables, and both surrounded by ejected material. HR Carinae is also likely to be a binary system with a similar separation, period, and ratio of component sizes to Eta Carinae. However, the Eta Carinae system is more massive and more luminous.

It has been identified as a possible type IIb supernova candidate in modelling of the fate of stars 20 to 25 times the mass of the Sun (with LBV status as the predicted final stage beforehand).