Nu Draconis
Star system in the constellation Draco
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Nu Draconis (also known as ν Dra, ν Draconis, where ν is the Greek letter nu, or as Kuma /ˈkjuːmə/) is a double star in the constellation Draco. The respective components are designated ν1 Draconis and ν2 Draconis. The second component is a spectroscopic binary star system.[15]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco |
| ν1 Dra | |
| Right ascension | 17h 32m 10.56856s[1] |
| Declination | +55° 11′ 03.2739″[1] |
| Apparent magnitude (V) | +4.88[2] |
| ν2 Dra | |
| Right ascension | 17h 32m 16.02464s[1] |
| Declination | +55° 10′ 22.6504″[1] |
| Apparent magnitude (V) | +4.88[2] |
| Characteristics | |
| ν1 Dra | |
| Evolutionary stage | main sequence[3] |
| Spectral type | A8Vm[4] (kA3hF0mF0[5]) |
| U−B color index | +0.03[2] |
| B−V color index | +0.26[2] |
| ν2 Dra | |
| Evolutionary stage | main sequence[6] |
| Spectral type | A4IVm[4] (kA3hF1mF0[5]) |
| U−B color index | +0.04[2] |
| B−V color index | +0.27[2] |
| Astrometry | |
| ν1 Dra | |
| Radial velocity (Rv) | −15.2[7] km/s |
| Proper motion (μ) | RA: +147.39[1] mas/yr Dec.: +54.31[1] mas/yr |
| Parallax (π) | 33.06±0.15 mas[1] |
| Distance | 98.7 ± 0.4 ly (30.2 ± 0.1 pc) |
| ν2 Dra | |
| Radial velocity (Rv) | −16.0[7] km/s |
| Proper motion (μ) | RA: +142.65[1] mas/yr Dec.: +62.43[1] mas/yr |
| Parallax (π) | 32.80±0.18 mas[1] |
| Distance | 99.4 ± 0.5 ly (30.5 ± 0.2 pc) |
| Orbit[8] | |
| Period (P) | 38.034 days |
| Eccentricity (e) | 0.03 |
| Semi-amplitude (K1) (primary) | 10.0 km/s |
| Details | |
| ν1 Dra | |
| Mass | 1.85[9] M☉ |
| Radius | 1.8[3] R☉ |
| Luminosity | 8.1[3] L☉ |
| Surface gravity (log g) | 4.2[10] cgs |
| Temperature | 7,533[10] K |
| Metallicity | +0.03[10] |
| Rotational velocity (v sin i) | 86[11] km/s |
| Age | 1.0[3] Gyr |
| ν2 Dra | |
| Mass | 1.61 + 0.24[9] M☉ |
| Radius | 1.812[12] R☉ |
| Surface gravity (log g) | 4.11[13] cgs |
| Temperature | 7,272[10] K |
| Rotational velocity (v sin i) | 68[11] km/s |
| Age | 1.2[6] Gyr |
| Other designations | |
| ν Draconis, ν Dra, Kuma | |
| ν1 Dra: 24 Dra, BD+55 1944, FK5 655, HD 159541, HIP 85819, HR 6554, SAO 30447[14] | |
| ν2 Dra: 25 Dra, BD+55 1945, FK5 657, HD 159560, HIP 85829, HR 6555, SAO 30450[15] | |
| Database references | |
| SIMBAD | ν Dra |
| ν1 Dra | |
| ν2 Dra | |
This star, along with β Dra (Rastaban), γ Dra (Eltanin), μ Dra (Alrakis) and ξ Dra (Grumium) were Al ʽAwāïd, "the Mother Camels", which was later known as the Quinque Dromedarii.[16]
In Chinese, 天棓 (Tiān Bàng), meaning Celestial Flail, refers to an asterism consisting of ν Draconis, ξ Draconis, β Draconis, γ Draconis and ι Herculis.[17] Consequently, the Chinese name for ν Draconis itself is 天棓二 (Tiān Bàng èr, English: the Second Star of Celestial Flail.)[18] The name Kuma was among the 14 names originating from Antonín Bečvář's 1948 Skalnate Pleso Atlas of the Heavens.[19] James B. Kaler notes that Kuma is of "obscure origin" and noting that one source had postulated it meant "at last".[20]
The two stars of the visual binary are considered to be a common proper motion pair on the basis of their very similar parallaxes, radial velocities, and proper motions, although no orbital motion can be observed.[21]
ν1 Draconis is an Am star, a slowly rotating chemically peculiar star with abnormally strong metallic absorption lines in its spectrum. Its spectral type of kA3hF0mF0 means that it would have a spectral class of A3 if determined solely from its calcium K lines, F0 if determined from its hydrogen lines, and F0 if determined from other metallic spectral lines.[5]
ν2 Draconis is a spectroscopic binary with a period of 38 days. The two stars are separated by 0.267 au on average, and they have an almost circular orbit with an eccentricity of 0.03.[22][8] The primary is also an Am star, while the secondary has a low mass and luminosity and is only inferred from the orbital movement of the more massive star.[9]