Alpha Equulei
  | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Equuleus |
| Right ascension | 21h 15m 49.437s[1] |
| Declination | +05° 14′ 52.41″[1] |
| Apparent magnitude (V) | +3.919[2] (4.476 + 4.496)[3] |
| Characteristics | |
| Spectral type | G7III + kA3hA4mA9[4] |
| U−B color index | +0.284[2] |
| B−V color index | +0.529[2] |
| Astrometry | |
| Radial velocity (Rv) | −16.458±0.027[5] km/s |
| Proper motion (μ) | RA: +49.747 mas/yr[1] Dec.: −89.846 mas/yr[1] |
| Parallax (π) | 18.11±0.24 mas[5] |
| Distance | 180 ± 2 ly (55.2 ± 0.7 pc) |
| Absolute magnitude (MV) | +0.146 (0.689 + 1.159)[3] |
| Orbit[5] | |
| Period (P) | 98.80450±0.00035 days |
| Semi-major axis (a) | 0.66±0.02 au[3] |
| Eccentricity (e) | 0.00417±0.00076 |
| Inclination (i) | 151.52±0.28° |
| Longitude of the node (Ω) | 216.57±0.16° |
| Periastron epoch (T) | 2,457,277.7±1.7 |
| Argument of periastron (ω) (primary) | 102.9±6.3° |
| Semi-amplitude (K1) (primary) | 16.190±0.036 km/s |
| Semi-amplitude (K2) (secondary) | 18.92±0.61 km/s |
| Details | |
| A | |
| Mass | 2.20±0.16[5] M☉ |
| Radius | 9.20±0.01[6] R☉ |
| Luminosity | 47.9+12.4 −9.8[3] L☉ |
| Surface gravity (log g) | 3.08±0.11[5] cgs |
| Temperature | 5,160±65[6] K |
| Metallicity [Fe/H] | +0.11±0.06[6] dex |
| Rotational velocity (v sin i) | 5.53±0.14[6] km/s |
| Age | 1.0–1.2[5] Gyr |
| B | |
| Mass | 1.883±0.083[5] M☉ |
| Radius | 2.60±0.03[6] R☉ |
| Luminosity | 26.9+3.3 −2.9[3] L☉ |
| Surface gravity (log g) | 3.87±0.15[5] cgs |
| Temperature | 8,260±218[6] K |
| Metallicity [Fe/H] | +0.14±0.16[6] dex |
| Rotational velocity (v sin i) | 25.88±3.45[6] km/s |
| Age | 1.0–1.2[5] Gyr |
| Other designations | |
| Kitalphar, 8 Equulei, HR 8131, HD 202447, BD+04 4635, HIP 104987, SAO 126662, FK5 800, GC 29735 | |
| Database references | |
| SIMBAD | data |
Alpha Equulei (α Equulei, abbreviated Alpha Equ, α Equ), officially named Kitalpha /kɪˈtælfə/,[7][8] is the brightest star in the constellation of Equuleus. It is a binary system with an orbital period of 98.8 days and a sky separation of a few milliarcseconds, too small to be resolved with the naked eye.
Nomenclature
[edit]α Equulei (Latinised to Alpha Equulei) is the star's Bayer designation.
It bore the traditional name Kitalpha (rarely Kitel Phard or Kitalphar), a contraction of the Arabic name قطعة الفرس qiṭ‘a(t) al-faras—"a piece of the horse". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[9] to catalogue and standardize proper names for stars. The WGSN approved the name Kitalpha for α Equulei A on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[8]
In Chinese, 虚宿 (Xū Sù), meaning Emptiness, is an asterism consisting of Alpha Equulei and Beta Aquarii.[10] Consequently, the Chinese name for Alpha Equulei itself is 虛宿二 (Xū Sù èr, English: the Second Star of Emptiness).[11]
Properties
[edit]The overall appearance of α Equulei is a G-type giant[12] with an apparent magnitude of +3.92,[2] but it is a spectroscopic binary consisting of two individual stars.[6]
The primary star is a G7 giant about fifty times more luminous than the Sun.[3] It has an effective temperature of 5,160 K and a radius of 9.2 times greater than the Sun.[6]
The secondary is an A-type main-sequence star that is about 27 times as luminous as the Sun.[3] It has an effective temperature of 8,260 K and a radius 2.60 times greater than the Sun. It is a chemically peculiar Am star.[4][6]
The two stars revolve in a circular orbit every 98.8 days. Their respective orbital velocities allow their masses to be calculated at 2.3 M☉ and 2.0 M☉, respectively.[4]
References
[edit]- 1 2 3 4 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- 1 2 3 4 Cousins, A. W. J. (1984). "Standardization of Broadband Photometry of Equatorial Standards". South African Astronomical Observatory Circulars. 8: 59. Bibcode:1984SAAOC...8...59C.
- 1 2 3 4 5 6 7 Piccotti, Luca; Docobo, José Ángel; Carini, Roberta; Tamazian, Vakhtang S.; Brocato, Enzo; Andrade, Manuel; Campo, Pedro P. (2020-02-01). "A study of the physical properties of SB2s with both the visual and spectroscopic orbits". Monthly Notices of the Royal Astronomical Society. 492 (2): 2709–2721. Bibcode:2020MNRAS.492.2709P. doi:10.1093/mnras/stz3616. ISSN 0035-8711.
- 1 2 3 Griffin, R. E. M.; Griffin, R. F. (2002). "Composite spectra Paper 11: α Equulei, an astrometric binary with an Am secondary". Monthly Notices of the Royal Astronomical Society. 330 (2): 288. Bibcode:2002MNRAS.330..288G. doi:10.1046/j.1365-8711.2002.05030.x.
- 1 2 3 4 5 6 7 8 9 Halbwachs, J-L; Kiefer, F; Lebreton, Y; Boffin, H M J; Arenou, F; Le Bouquin, J-B; Famaey, B; Pourbaix, D; Guillout, P; Salomon, J-B; Mazeh, T (2020-08-01). "Masses of the components of SB2 binaries observed with Gaia – V. Accurate SB2 orbits for 10 binaries and masses of the components of 5 binaries". Monthly Notices of the Royal Astronomical Society. 496 (2): 1355–1368. doi:10.1093/mnras/staa1571. ISSN 0035-8711.
- 1 2 3 4 5 6 7 8 9 10 11 Romanovskaya, Anna; Zvyagintsev, Sergey (2025-08-06). "Abundance Analysis of the Spectroscopic Binary α Equulei". Galaxies. 13 (4): 88. Bibcode:2025Galax..13...88R. doi:10.3390/galaxies13040088. ISSN 2075-4434.
- ↑ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
- 1 2 "IAU Catalog of Star Names". Retrieved 28 July 2016.
- ↑ "IAU Working Group on Star Names (WGSN)". International Astronomical Union. Archived from the original on 10 June 2016. Retrieved 22 May 2016.
- ↑ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- ↑ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2011-01-29 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ↑ Ginestet, N.; Carquillat, J. M.; Jaschek, C. (1999). "Spectral classifications in the near infrared of stars with composite spectra. III. Study of a sample of 137 objects with the Aurelie spectrograph". Astronomy and Astrophysics Supplement. 134 (3): 473. Bibcode:1999A&AS..134..473G. doi:10.1051/aas:1999444.
