R Crucis

R Crucis is a variable star in the southern constellation of Crux. It has a yellow-white hue and is often too faint to see with the naked eye, having an apparent visual magnitude that fluctuates around 6.89.^[3] This object is located at a distance of approximately 1,600 light years from the Sun based on parallax,^[7] but it is drifting closer with a radial velocity of −13.5 km/s.^[3]

R Crucis

A visual band light curve for R Crucis, adapted from Dean et al. (1977)[1]
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Crux
Right ascension	12h 23m 37.68840s[2]
Declination	−61° 37′ 44.8570″[2]
Apparent magnitude (V)	6.89[3]
Characteristics
Spectral type	F6-G2Ib-II[4] or F7Ib/II[5]
B−V color index	0.67±0.02[3]
Variable type	δ Cep[6]
Astrometry
Radial velocity (Rv)	−13.5±3.0[3] km/s
Proper motion (μ)	RA: -9.404[2] mas/yr Dec.: −0.430[2] mas/yr
Parallax (π)	1.98±0.54 mas[7]
Distance	approx. 1,600 ly (approx. 500 pc)
Details
Radius	44.6[8] R☉
Surface gravity (log g)	1.65[9] cgs
Temperature	5,812±22[9] K
Metallicity [Fe/H]	+0.06[9] dex
Other designations
R Cru, AAVSO 1218-61, CD−60°4138, HD 107805, HIP 60455, SAO 251878[10]
Database references
SIMBAD	data

This is a Classical Cepheid, or Delta Cephei variable, that ranges in brightness from visual magnitude 6.40 down to 7.23 with a period of 5.82575 days.^[6] It is a supergiant star with a stellar classification that varies over each pulsation cycle, giving it a class range of F6-G2Ib-II.^[4] The star has a mean radius 44.6 times the radius of the Sun (44.6 R_☉), but the radius varies by 5 R_☉ during each pulsation.^[11] It has a near solar metallicity and the atmospheric abundances indicate it is likely past first dredge-up.^[9]

A candidate companion star has been detected at an angular separation of 7.6″, which corresponds to a projected separation of 6,330 AU. The Hubble WFC3 shows a closer companion at a separation of 1.9″.^[12] The system is a source for X-ray emission but the contributing component is unclear.^[13]