28 Cancri
Binary star in the constellation Cancer
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28 Cancri is a star system in the zodiac constellation of Cancer. It is a variable star with the designation CX Cancri, and is close to the lower limit of visibility with the naked eye, having a mean apparent visual magnitude of 6.05.[3] The annual parallax shift seen from Earth's orbit is 8.5 mas, which provides a distance estimate of about 384 light years. It is moving away from the Sun with a radial velocity of around +9 km/s.[6]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cancer |
| Right ascension | 08h 28m 36.78530s[2] |
| Declination | +24° 08′ 41.7179″[2] |
| Apparent magnitude (V) | 6.05[3] |
| Characteristics | |
| Spectral type | F0 Vn[4] |
| U−B color index | +0.13[3] |
| B−V color index | +0.22[3] |
| Variable type | δ Sct[5] |
| Astrometry | |
| Radial velocity (Rv) | +9.0±4.3[6] km/s |
| Proper motion (μ) | RA: −30.946[2] mas/yr Dec.: −39.719[2] mas/yr |
| Parallax (π) | 8.4885±0.1539 mas[2] |
| Distance | 384 ± 7 ly (118 ± 2 pc) |
| Absolute magnitude (MV) | 0.41[7] |
| Details | |
| Mass | 2.36±0.11[8] M☉ |
| Radius | 3.7[2] R☉ |
| Luminosity | 44[2] L☉ |
| Surface gravity (log g) | 3.61[2] cgs |
| Temperature | 7,516+52 −103[8] K |
| Metallicity [Fe/H] | +0.16[9] dex |
| Rotational velocity (v sin i) | 133[8] km/s |
| Age | 737[2] Myr |
| Other designations | |
| 28 Cnc, CX Cnc, BD+24°1931, HD 71496, HIP 41574, HR 3329, SAO 80204[10] | |
| Database references | |
| SIMBAD | data |
Based upon proper motion variation, this is an astrometric binary system with high likelihood (99.8%).[11] The visible component has a stellar classification of F0 Vn,[4] indicating it is a F-type main-sequence star with "nebulous" lines due to rapid rotation.
In 1973, John R Percy announced that 28 Cancri might be a variable star.[12] Stephen John Horan et al. confirmed that the star's brightness varies, in 1974.[13] In 1979, it was given its variable star designation.[14] It is a Delta Scuti variable star with a period of 0.0960 days and an amplitude of 0.020 in magnitude.[15] With 2.4 times the mass of the Sun it is spinning with a high projected rotational velocity of 133 km/s. 28 Cancri is radiating roughly 44 times the Sun's luminosity from its photosphere at an effective temperature of around 7,516 K.