R Crucis
Variable star in the constellation Crux
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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 between magnitudes 6.4 and 7.2. 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.[2]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Crux[2] |
| Right ascension | 12h 23m 37.68840s[3] |
| Declination | −61° 37′ 44.8570″[3] |
| Apparent magnitude (V) | 6.40 to 7.23[4] |
| Characteristics | |
| Spectral type | F6-G2Ib-II[5] or F7Ib/II[6] |
| B−V color index | 0.67±0.02[2] |
| Variable type | δ Cep[4] |
| Astrometry | |
| Radial velocity (Rv) | −13.5±3.0[2] km/s |
| Proper motion (μ) | RA: -9.404[3] mas/yr Dec.: −0.430[3] 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.[4] It is a supergiant star with a stellar classification that varies over each pulsation cycle, giving it a class range of F6-G2Ib-II.[5] 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]