Astronomy:Alpha1 Capricorni
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| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Capricornus[1] |
| Right ascension | 20h 17m 38.869s[2] |
| Declination | −12° 30′ 29.56″[2] |
| Apparent magnitude (V) | 4.27[3] + 8.60[4] |
| Characteristics | |
| Evolutionary stage | Supergiant[5] |
| Spectral type | G3 Ib[6] |
| U−B color index | +0.70[3] |
| B−V color index | +1.07[3] |
| Variable type | Constant[1] |
| Astrometry | |
| Radial velocity (Rv) | −25.79±0.15[5] km/s |
| Proper motion (μ) | RA: +21.709[2] mas/yr Dec.: +1.643[2] mas/yr |
| Parallax (π) | 4.0157 ± 0.1072[2] mas |
| Distance | 810 ± 20 ly (249 ± 7 pc) |
| Absolute magnitude (MV) | −1.90[1] |
| Details[5] | |
| Mass | 5.3 M☉ |
| Radius | 36.3±2.0 R☉ |
| Luminosity | 1,047 L☉ |
| Surface gravity (log g) | 1.75 cgs |
| Temperature | 5,119±15 K |
| Metallicity [Fe/H] | −0.02 dex |
| Rotational velocity (v sin i) | 7.3[6] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha1 Capricorni is a binary star system dominated by a highly luminous star in the constellation of Capricornus, north of the ecliptic. It has the traditional star names Prima Giedi (/ˌpraɪmə ˈdʒiːdi/) and Algiedi Prima (/æˈdʒiːdi ˈpraɪmə/). The Bayer designation Alpha1 Capricorni is Latinized from α1 Capricorni, and abbreviated Alpha1 Cap or α1 Cap. The system is separated from the brighter Alpha2 Capricorni by 0.11° of the sky, a gap resolvable with the naked eye,[8] similar to Mizar and Alcor. Both are not to be confused with much fainter 3 Capricorni nor somewhat fainter Nu Capricorni which are 3 to 6 times the angular distance apart than separate the two Alpha stars, respectively.
The primary star is a yellow hued supergiant star with a stellar classification of G3 Ib.[6] It has an apparent magnitude of +4.3; bright enough to make it visible to the naked eye. The star is located at a distance of approximately 810 light-years (250 pc) 870 light years from the Solar System based on parallax measurements,[2] but is drifting closer with a radial velocity of −26 km/s.[5] The star is past first dredge-up and has already evolved through the Cepheid instability strip; it may be about to do so a second time.[5] It has 5.3 times the mass and 36 times the radius of the Sun, and is radiating around 1,047 times the Sun's luminosity from its photosphere at an effective temperature of 5,119 K.[5]
The Hipparcos satellite in about the year 2000 found a previously undetected companion at an angular separation of 0.65″ from the primary.[9] This magnitude 8.60 star forms a binary pair with α1 Capricorni.[4] Three other faint visual companion stars lie within one arc-minute, so are unresolveable in small telescopes. The brightest of these is 10th magnitude and on this basis it has often been considered as an optical binary. Separation is increasing rapidly due to great proper motion of the primary star.[9]
References
- ↑ 1.0 1.1 1.2 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A XHIP record for this object at VizieR.
- ↑ 2.0 2.1 2.2 2.3 2.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 3.0 3.1 3.2 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues 2237: 0. Bibcode: 2002yCat.2237....0D.
- ↑ 4.0 4.1 Eggleton, Peter; Tokovinin, A. (2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society 389 (2): 869. doi:10.1111/j.1365-2966.2008.13596.x. Bibcode: 2008MNRAS.389..869E.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Usenko, I. A. et al. (November 2015). "Spectroscopic studies of four southern-hemisphere G-K supergiants: HD 192876 (α1 Cap), HD 194215 (HR 7801), HD 206834 (c Cap), and HD 222574 (104 Aqr)". Astronomy Letters 41 (11): 660–676. doi:10.1134/S1063773715110067. Bibcode: 2015AstL...41..660U.
- ↑ 6.0 6.1 6.2 Smiljanic, R. et al. (April 2006). "CNO in evolved intermediate mass stars". Astronomy and Astrophysics 449 (2): 655–671. doi:10.1051/0004-6361:20054377. Bibcode: 2006A&A...449..655S.
- ↑ Rumrill, H. B. (1936). "Star Name Pronunciation". Publications of the Astronomical Society of the Pacific 48 (283): 139. doi:10.1086/124681. Bibcode: 1936PASP...48..139R.
- ↑ Harrington, Philip S. (1990). Touring the Universe through Binoculars: A Complete Astronomer's Guidebook. Wiley Science Editions. 79. Turner Publishing Company. ISBN 9781620459492. https://books.google.com/books?id=So3uEAAAQBAJ&pg=PT72. The separation is 378″, or 0.105°.
- ↑ 9.0 9.1 Mason, Brian D. et al. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal 122 (6): 3466. doi:10.1086/323920. Bibcode: 2001AJ....122.3466M.
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