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Variable star in the constellation Cassiopeiae From Wikipedia, the free encyclopedia
Iota Cassiopeiae (ι Cas, ι Cassiopeiae) is a star system in the constellation Cassiopeia. The system has a combined apparent magnitude of 4.53,[citation needed] making it visible to the naked eye. Based on its parallax, it is located about 133 light-years (41 parsecs) from Earth.[7]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cassiopeia |
| ι Cas A | |
| Right ascension | 02h 29m 03.960s[1] |
| Declination | +67° 24′ 08.70″[1] |
| Apparent magnitude (V) | 4.61[1] (4.65 / 8.48)[2] |
| ι Cas B | |
| Right ascension | 02h 29m 03.567s[1] |
| Declination | +67° 24′ 07.01″[1] |
| Apparent magnitude (V) | 6.87[1] |
| ι Cas C | |
| Right ascension | 02h 29m 05.086s[1] |
| Declination | +67° 24′ 05.53″[1] |
| Apparent magnitude (V) | 9.05[3] (9.14 / 11.84)[3] |
| Characteristics | |
| U−B color index | +0.03[4] |
| B−V color index | +0.12[4] |
| ι Cas A | |
| Spectral type | A3p / G6[2] |
| Variable type | α2 CVn[5] |
| ι Cas B | |
| Spectral type | F5[2] |
| ι Cas C | |
| Spectral type | K4 / M2[3] |
| U−B color index | +0.18[4] |
| B−V color index | +0.72[4] |
| Astrometry | |
| Radial velocity (Rv) | 1.2 ± 2[6] km/s |
| Proper motion (μ) | RA: -26.61[7] mas/yr Dec.: 38.21[7] mas/yr |
| Parallax (π) | 22.22 ± 0.08 mas[8] |
| Distance | 146.8 ± 0.5 ly (45.0 ± 0.2 pc) |
| Absolute magnitude (MV) | 1.62 ± 0.07 (Aa) 5.60 ± 0.17 (Ab)[9] |
| Orbit[8] | |
| Primary | ι Cas Aa |
| Companion | ι Cas Ab |
| Period (P) | 48.72 ± 0.45 yr |
| Semi-major axis (a) | 0.423 ± 0.004″ |
| Eccentricity (e) | 0.637 ± 0.004 |
| Inclination (i) | 148.2 ± 1.3° |
| Longitude of the node (Ω) | 176.6 ± 1.8° |
| Periastron epoch (T) | B 1993.21 ± 0.05 |
| Argument of periastron (ω) (secondary) | 328.2 ± 1.9° |
| Orbit[8] | |
| Primary | ι Cas A |
| Companion | ι Cas B |
| Period (P) | 2400 yr |
| Semi-major axis (a) | 6.50″ |
| Eccentricity (e) | 0.40 |
| Inclination (i) | 102.9 ± 0.3° |
| Longitude of the node (Ω) | 188.0 ± 0.9° |
| Periastron epoch (T) | B 940 ± 47 |
| Argument of periastron (ω) (secondary) | 113.3 ± 3.4° |
| Details | |
| ι Cas Aa | |
| Mass | 1.98[8] M☉ |
| Radius | 2.3 ± 0.4[10] R☉ |
| Luminosity | 24[10] L☉ |
| Temperature | 8360 ± 275[10] K |
| Rotation | 1.74033 d[10] |
| Rotational velocity (v sin i) | 48[10] km/s |
| Age | 100[9] Myr |
| ι Cas Ab | |
| Mass | 0.98[8] M☉ |
| ι Cas B | |
| Mass | 1.28[8] M☉ |
| Temperature | 6540[3] K |
| ι Cas Ca | |
| Temperature | 4520 ± 20[3] K |
| ι Cas Cb | |
| Temperature | 3590 ± 45[3] K |
| Other designations | |
| ι Cas A: TYC 4058-1504-1 | |
| ι Cas B: TYC 4058-1504-2 | |
| ι Cas C: TYC 4058-1505-1 | |
| Database references | |
| ι Cas AB | |
| ι Cas A | |
| ι Cas B | |
| ι Cas C | |
Iota Cassiopeiae is known to be a quintuple star system. The brightest star system, ι Cassiopeiae A, contains a white-colored A-type main-sequence star with a mean apparent magnitude of +4.61.[1] The primary is itself a tighter binary star system. The two stars were resolved by adaptive optics.[citation needed] These are designated Aa and Ab (although confusingly they may also be labeled as A and Aa, respectively).[citation needed] The primary is classified as an Alpha2 Canum Venaticorum-type variable star and the brightness of the system varies from magnitude +4.45 to +4.53 with a period of 1.74 days,[5] because of its magnetic field.[10] The variability in brightness was first detected by Karl D. Rakos in 1962, although its spectrum was known to be variable from earlier observations.[12] The fainter companion is a G-type star with a mass of 0.98 M☉.[8] The orbital period of the system is about 49 years.[8]
ι Cassiopeiae B is a yellow-white F-type main sequence dwarf with an apparent magnitude of +6.87.[1] It orbits around ι Cassiopeiae A approximately every 2,400 years with a semi-major axis of around 6.5 arcseconds, but the orbit is not very well constrained.[8] This object may be causing Kozai–Lidov cycles in the inner orbital pair.[8]
ι Cassiopeiae C is itself another binary, designated Ca and Cb,[8] or just C and c.[3] It comprises two stars, a K-type star and an M-type star.[3] It is currently at an angular distance of about 7 arcseconds from the AB pair.[13] Since the semimajor axis of the AB orbit is about 6.5 arcseconds, the true semimajor axis of C's orbit around them is thought to be significantly larger than 7 arcseconds.[8]
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