Eta Crucis

Eta Crucis (η Crucis) is a solitary^[7] star in the southern constellation of Crux. It can be seen with the naked eye, having an apparent visual magnitude of 4.14^m.^[2] Based upon parallax measurements,^[1] η Crucis is located at a distance of 64 light-years. The system made its closest approach about 1.6 million years ago when it achieved perihelion at a distance of roughly 26 light years.^[8]

η Crucis

Location of Mimosa (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Crux
Right ascension	12h 06m 52.89814s[1]
Declination	−64° 36′ 49.4305″[1]
Apparent magnitude (V)	4.14[2]
Characteristics
Spectral type	F2 V[3]
U−B color index	+0.00[2]
B−V color index	+0.35[2]
Astrometry
Radial velocity (Rv)	+13.13±0.26[1] km/s
Proper motion (μ)	RA: +34.270 mas/yr[1] Dec.: −36.902 mas/yr[1]
Parallax (π)	50.7919±0.1049 mas[1]
Distance	64.2 ± 0.1 ly (19.69 ± 0.04 pc)
Absolute magnitude (MV)	2.67[4]
Details[1]
Mass	1.51±0.04 M☉
Radius	1.854±0.005 R☉
Luminosity	6.901+0.027 −0.029 L☉
Surface gravity (log g)	4.01±0.00 cgs
Temperature	6,830[5] K
Metallicity [Fe/H]	−0.04[3] dex
Rotational velocity (v sin i)	46.1±2.3[4] km/s
Age	1.63±0.29 Gyr
Other designations
η Cru, CD−63°2145, GJ 455.2, GJ 9388, HD 105211, HIP 59072, HR 4616, SAO 251742.[6]
Database references
SIMBAD	data

This is an F-type main sequence star with a stellar classification of F2 V.^[3] It has 151% of the Sun's mass, 185% of the Sun's radius and shines with 6.9 times the luminosity of the Sun from its outer atmosphere^[1] with an effective temperature of 6,830 K.^[5]

Eta Crucis has a pair of visual companions. Component B is a magnitude 11.80 star located at an angular separation of 48.30″ along a position angle of 300°, as of 2010. Component C has a magnitude of 12.16 and lies at an angular separation of 35.50″ along a position angle of 194°, as of 2000.^[9]

Debris disk

Image of the debris disk with the REASONS survey^[10]

A debris disk around Eta Crucis was initially inferred from observations from the Spitzer Space Telescope that showed a significant infrared excess at a wavelength of 70 μm, which was atribuited to the presence of a circumstellar disk.^[11] A further analysis of the IR excess show that the circumstellar disk around Eta Crucis is divided in a warm dust disk and a cold debris disk.^[12]

The warm disk is positioned at 13 astronomical units (AU) from Eta Crucis and has a temperature of 170 K (−103 °C). The grains that make this dust disk are milimiter-sized. It is believed this disk (and its particles) originated from both in-situ collisions of planetesimals in a region similar to the Solar System's asteroid belt and from comet delivery, where more distant planetesimals were transported to the inner region by gravitational interactions with other planets. Comet delivery could also suggest the presence of planets formed by comet interactions.^[12]

The cold disk is characterized by a narrow ring that is 24 AU wide, with an average distance of 134 AU and an inner edge of 85 AU. Its temperature is estimated at 43 K (−230.2 °C). Observations suggest the particles making up it are of large-size.^[12] An image of the cold disk was presented in 2025 as part of the REsolved ALMA and SMA Observations of Nearby Stars (REASONS) survey.^[10]

The Eta Crucis planetary system^[12]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (years)	Eccentricity	Inclination	Radius
Warm disk	13 AU				—	—
Cold disk	133.7±1.6 AU				67.0±0.7°	—