CW Octantis

CW Octantis, also known as HD 148542, is a solitary, white hued variable star located in the southern circumpolar constellation Octans. It has an apparent magnitude of 6.03, allowing it to be faintly visible to the naked eye. Parallax measurements from Gaia DR3 place the object at a distance of 629 light years. It appears to be receding from the Solar System with a heliocentric radial velocity of 7.1 km/s.

CW Octantis

A light curve for CW Octantis, plotted from TESS data[1]
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Octans
Right ascension	17h 00m 58.51777s[2]
Declination	−86° 21′ 51.4707″[2]
Apparent magnitude (V)	6.03±0.01[3]
Characteristics
Evolutionary stage	subgiant[4]
Spectral type	A3 IV[5]
U−B color index	+0.02[6]
B−V color index	+0.05[6]
Variable type	α2 CVn[7]
Astrometry
Radial velocity (Rv)	7.1±0.5[8] km/s
Proper motion (μ)	RA: +8.413 mas/yr[2] Dec.: −0.032 mas/yr[2]
Parallax (π)	5.1828±0.0486 mas[2]
Distance	629 ± 6 ly (193 ± 2 pc)
Absolute magnitude (MV)	−0.36[9]
Details
Mass	2.98±0.05[4] M☉
Radius	4.64[10] R☉
Luminosity	111[11] L☉
Surface gravity (log g)	3.45±0.07[12] cgs
Temperature	8,791[13] K
Metallicity [Fe/H]	+0.6[14] dex
Rotation	≈2.8 days[13]
Rotational velocity (v sin i)	92±6[13] km/s
Age	188±4[4] Myr
Other designations
26 G. Octantis[15], CW Octantis, CD−86°100, CPD−86°333, FK5 921, GC 22519, HD 148542, HIP 83255, HR 6139, SAO 258751[16]
Database references
SIMBAD	data

CW Octantis has a stellar classification of A3 IV, indicating that it is an evolved A-type star heading towards the red giant branch. Zorec and Royer (2012) model it as a dwarf star that has just reached the end of its main sequence lifetime.^[4] It has 2.98 times the mass of the Sun^[4] and 4.6 times its radius.^[10] It radiates 111 times the luminosity of the Sun^[11] from its photosphere at an effective temperature of 8,791 K.^[13] CW Octantis is estimated to be 188 million years old.^[4]

This object is classified as a Alpha² Canum Venaticorum variable.^[7] Most stars of this class have chemical peculiarities in their spectra, but CW Octantis seems to be ordinary. Renson and Manfroid (2009) consider its peculiarity status to be doubtful.^[17] Nevertheless, CW Octantis fluctuates between 6.05 and 6.07 in the Hipparcos passband within 2.63 days.^[18] It takes 2.8 days to complete a full a rotation, which corresponds to a projected rotational velocity of 92 km/s.^[13]