4 Draconis
Variable star in the constellation Draco
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4 Draconis, also known as HR 4765 and CQ Draconis, is a star about 570 light years from the Earth, in the constellation Draco.[1] It is a 5th magnitude star, so it will be faintly visible to the naked eye of an observer far from city lights.[1] It is a variable star, whose brightness varies slightly from 4.90 to 5.12 over a period of 4.66 years.[2]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Draco |
| Right ascension | 12h 30m 06.66200s[1] |
| Declination | +69° 12′ 03.9742″[1] |
| Apparent magnitude (V) | 4.90 - 5.12[2] |
| Characteristics | |
| Evolutionary stage | AGB + ?[3] |
| Spectral type | M3+ IIIa[4] |
| Variable type | Z Andromedae[2] |
| Astrometry | |
| Radial velocity (Rv) | −15[5] km/s |
| Proper motion (μ) | RA: −57.311[1] mas/yr Dec.: −50.365[1] mas/yr |
| Parallax (π) | 5.7233±0.1880 mas[1] |
| Distance | 570 ± 20 ly (175 ± 6 pc) |
| Absolute magnitude (MV) | −1.37[6] |
| Orbit[7] | |
| Primary | 4 Draconis A (red giant) |
| Name | 4 Draconis B |
| Period (P) | 1,703±3 d |
| Semi-major axis (a) | 82±4 Gm ( a⋅sin(i) ) |
| Eccentricity (e) | 0.30±0.05 |
| Periastron epoch (T) | 2442868.5 |
| Argument of periastron (ω) (primary) | 244±9° |
| Semi-amplitude (K1) (primary) | 3.67±0.19 km/s |
| Details | |
| red giant | |
| Mass | 1.64±0.2[8] M☉ |
| Radius | 111.0+9.30 −11.2[8] R☉ |
| Luminosity | 2,122±419[8] L☉ |
| Surface gravity (log g) | 1.24[8] cgs |
| Temperature | 3,718±69[8] K |
| Age | 1.97±0.57[8] Gyr |
| white dwarf | |
| Mass | ~0.8[9] M☉ |
| Radius | 0.0094[9] R☉ |
| Luminosity | (6.6–22)×10−3[9] L☉ |
| Surface gravity (log g) | 8.4[9] cgs |
| Temperature | 20,000±3,000[9] K |
| Other designations | |
| CQ Dra, HD 108907, HR 4765, HIP 60998, SAO 15816[10] | |
| Database references | |
| SIMBAD | data |
In 1967, Olin Eggen discovered that 4 Draconis is a variable star, during a multicolor photometric survey of red stars.[13] In 1973 it was given the variable star designation CQ Draconis.[14]
Until the year 1985, 4 Draconis was thought to be a normal red giant star. In 1985, Dieter Reimers announced that the International Ultraviolet Explorer had detected a hot companion to the red giant, which itself appeared to be a binary cataclysmic variable star, making the complete system a triple star.[15] However a 2003 study by Peter Wheatley et al., who examined ROSAT X-ray data for the star, concluded that the hot companion was more apt to be a single white dwarf, rather than a binary, and that the white dwarf is accreting material from the red giant.[16] There does not yet appear to be a consensus about the multiplicity; some later studies consider 4 Draconis to be a binary,[17][18] and some a triple.[19][9]
In 1987, Alexander Brown announced that 6 cm wavelength radio emission had been detected by the Very Large Array. The strength of the radio emission was variable on a timescale of weeks to months.[20]
It is possible that an outburst of 4 Draconis was the "guest star" reported by Chinese astronomers in the year 369 CE, in the constellation Zigong.[21]