Eta Capricorni
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Double star η Capricorni |
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| η cap in the constellation "Capricorn" | ||||||||||||||||||||||||||||||||
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Observation dates equinox : J2000.0 , epoch : J2000.0 |
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| AladinLite | ||||||||||||||||||||||||||||||||
| Constellation | Capricorn | |||||||||||||||||||||||||||||||
| Right ascension | 21 h 04 m 24.301 s | |||||||||||||||||||||||||||||||
| declination | -19 ° 51 ′ 17.97 ″ | |||||||||||||||||||||||||||||||
| Apparent brightness | 4.90 likes | |||||||||||||||||||||||||||||||
| Astrometry | ||||||||||||||||||||||||||||||||
| Radial velocity | (23.8 ± 2) km / s | |||||||||||||||||||||||||||||||
| parallax | (20.20 ± 0.82) mas | |||||||||||||||||||||||||||||||
| distance | (161 ± 7) ly ((49.5 ± 2) pc ) |
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| Proper movement : | ||||||||||||||||||||||||||||||||
| Rec. Share: | (−37.62 ± 0.90) mas / a | |||||||||||||||||||||||||||||||
| Dec. portion: | (−24.95 ± 0.88) mas / a | |||||||||||||||||||||||||||||||
| orbit | ||||||||||||||||||||||||||||||||
| period | (27.85 ± 0.15) a | |||||||||||||||||||||||||||||||
| Major semi-axis | 0.265 mas | |||||||||||||||||||||||||||||||
| eccentricity | 0.410 | |||||||||||||||||||||||||||||||
| Orbit inclination | 162.6 ° | |||||||||||||||||||||||||||||||
| Argument of the node | 171.1 ° | |||||||||||||||||||||||||||||||
| Epoch of the periastron | 2002.46 | |||||||||||||||||||||||||||||||
| Argument of the periapsis | 238.2 ° | |||||||||||||||||||||||||||||||
| Individual data | ||||||||||||||||||||||||||||||||
| Names | A; B. | |||||||||||||||||||||||||||||||
| Observation data: | ||||||||||||||||||||||||||||||||
| Apparent brightness | A. | 5.02 likes | ||||||||||||||||||||||||||||||
| B. | 7.39 likes | |||||||||||||||||||||||||||||||
| Typing: | ||||||||||||||||||||||||||||||||
| Spectral class | A. | A4 V | ||||||||||||||||||||||||||||||
| B. | F2 V | |||||||||||||||||||||||||||||||
| B − V color index | A. | 0.18 | ||||||||||||||||||||||||||||||
| U − B color index | A. | 0.05 | ||||||||||||||||||||||||||||||
| Physical Properties: | ||||||||||||||||||||||||||||||||
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Absolute bol. Brightness M bol |
A. | 1.39 likes | ||||||||||||||||||||||||||||||
| B. | 3.62 likes | |||||||||||||||||||||||||||||||
| Dimensions | A. | 2.0 M ☉ | ||||||||||||||||||||||||||||||
| B. | 1.2 M ☉ | |||||||||||||||||||||||||||||||
| Effective temperature | A. | 8460 K | ||||||||||||||||||||||||||||||
| B. | 6890 K | |||||||||||||||||||||||||||||||
| Other names and catalog entries |
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Eta Capricorni (η Cap) is a close double star in the constellation Capricorn . It has an apparent magnitude of 4.90 mag and its distance is approximately 160 light years .
The two components of the binary star may be a white and a white and yellow main sequence star . Together they are about 3 times as heavy as the sun with a mass ratio of about 5: 3 and they orbit each other in about 28 years.
The star is sometimes referred to with the proper name “Armus” (from Latin armus , “upper arm, shoulder blade”), as it can be found in the constellation of Capricorn in the area of his shoulder.
Scientific research
With a coverage of the star by the Moon on 15 November 1950, found independently by several observers in South Africa, that this was done in two stages. Then William Stephen Finsen measured the star in October of the following year at the Union Observatory in Johannesburg with a micrometer on a 67 cm telescope and identified it as a double star. At this point he was able to measure a distance between the components of 0.34 arc seconds.
In the period from 1976 to 2011, a large number of measurements were carried out at Eta Capricorni with speckle interferometers , mostly on 4 m telescopes, and another measurement was also made with the astrometry satellite Hipparcos . There have already been several details about the spectral class of this star, but a photometric study with different color filters in 2000 showed the values A4 V and F2 V for the spectral types of the two components A and B of the star.
In a study from 2012, revised orbital elements were presented for several binary stars identified by Finsen, including Eta Capricorni, and estimates of the masses of the stars involved were made using the latest observational data. For Eta Capricorni, various calculation methods were used to find the values given above for the total mass and the mass ratios.
Individual evidence
- ^ A b c VizieR: Hipparcos, the New Reduction (van Leeuwen, 2007) - The Astrometric Catalog
- ↑ VizieR: General Catalog of Stellar Radial Velocities (Wilson, 1953)
- ↑ a b c d J. A. Docobo, M. Andrade: Dynamical and physical properties of 22 binaries discovered by WS Finsen. In: Monthly Notices of the Royal Astronomical Society. Vol. 428, 2013, doi: 10.1093 / mnras / sts045 , pp. 321–339, oxfordjournals.org (PDF; 991 kB).
- ↑ a b VizieR: Stellar Photometry in Johnson's 11-color system (Ducati, 2002) - Photometric data in the UBVRIJHKLMN colors
- ↑ a b c Th. Ten Brummelaar, BD Mason, HA McAlister, LC Roberts Jr., NH Turner, WI Hartkopf, WG Bagnuolo Jr .: Binary Star Differential Photometry Using the Adaptive Optics System at Mount Wilson Observatory. In: The Astronomical Journal. Vol. 119, 2000, doi: 10.1086 / 301338 , pp. 2403-2414 bibcode : 2000AJ .... 119.2403T
- ^ WS Finsen: New Double Stars (III). In: Monthly Notes of the Astronomical Society of South Africa. Vol. 10, 1951, p. 106, bibcode : 1951MNSSA..10..106F