Iota Cassiopeiae

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]

ι Cassiopeiae

The Bayer-designated stars in Cassiopeia. Iota Cassiopeiae is circled.
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
BD+66° 213, HD 15089, HIP 11569, HR 707, SAO 12298
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

Components

A light curve for Iota Cassiopeiae, plotted from TESS data^[11]

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]

References

1. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27 – L30. Bibcode:2000A&A...355L..27H.
2. Drummond, Jack; Milster, Scott; Ryan, Patrick; Roberts, Jr., Lewis C. (2003). "ι Cassiopeiae: Orbit, Masses, and Photometry from Adaptive Optics Imaging in the I and H Bands". The Astrophysical Journal. 585 (2): 1007. Bibcode:2003ApJ...585.1007D. doi:10.1086/346224.
3. Christou, Julian C.; Drummond, Jack D. (2006). "Measurements of Binary Stars, Including Two New Discoveries, with the Lick Observatory Adaptive Optics System". The Astronomical Journal. 131 (6): 3100. Bibcode:2006AJ....131.3100C. doi:10.1086/503255.
4. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
5. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
6. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Washington. Bibcode:1953GCRV..C......0W.
7. van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
8. Tokovinin, A. (2021). "Inner and Outer Orbits in 13 Resolved Hierarchical Stellar Systems". The Astronomical Journal. 161 (3): 144. arXiv:2101.02976. Bibcode:2021AJ....161..144T. doi:10.3847/1538-3881/abda42. S2CID 231419112.
9. De Rosa, R. J.; Patience, J.; Vigan, A.; Wilson, P. A.; Schneider, A.; McConnell, N. J.; Wiktorowicz, S. J.; Marois, C.; Song, I.; MacIntosh, B.; Graham, J. R.; Bessell, M. S.; Doyon, R.; Lai, O. (2012). "The Volume-limited A-Star (VAST) survey - II. Orbital motion monitoring of A-type star multiples". Monthly Notices of the Royal Astronomical Society. 422 (4): 2765. arXiv:1112.3666. Bibcode:2012MNRAS.422.2765D. doi:10.1111/j.1365-2966.2011.20397.x. S2CID 102487103.
10. Aurière, M.; Wade, G. A.; Silvester, J.; Lignières, F.; Bagnulo, S.; Bale, K.; Dintrans, B.; Donati, J. F.; Folsom, C. P.; Gruberbauer, M.; Hui Bon Hoa, A.; Jeffers, S.; Johnson, N.; Landstreet, J. D.; Lèbre, A.; Lueftinger, T.; Marsden, S.; Mouillet, D.; Naseri, S.; Paletou, F.; Petit, P.; Power, J.; Rincon, F.; Strasser, S.; Toqué, N. (2007). "Weak magnetic fields in Ap/Bp stars". Astronomy and Astrophysics. 475 (3): 1053. arXiv:0710.1554. Bibcode:2007A&A...475.1053A. doi:10.1051/0004-6361:20078189. S2CID 54850596.
11. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
12. Rakos, Karl D. (1962). "Photoelectric investigation of magnetic and spectrum variable stars". Bulletin / Lowell Observatory. 5 (12): 227–256. Bibcode:1962LowOB...5..227R. Retrieved 10 October 2024.
13. Tokovinin, A. A. (1997). "MSC - a catalogue of physical multiple stars". Astronomy and Astrophysics Supplement Series. 124: 75–84. Bibcode:1997A&AS..124...75T. doi:10.1051/aas:1997181. (HR 707 Archived 2021-02-05 at the Wayback Machine)