R Aquarii
Star in the constellation of Aquarius
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R Aquarii (R Aqr) is a variable star in the constellation Aquarius.[11]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 23h 43m 49.46343s[1] |
| Declination | −15° 17′ 04.1763″[1] |
| Apparent magnitude (V) | 5.2 - 12.4[2] |
| Characteristics | |
| Spectral type | M5e-M8.5e + pec[2] |
| U−B color index | −0.62[3] |
| B−V color index | +1.98[3] |
| Variable type | Mira + Z And[2] |
| Astrometry | |
| Radial velocity (Rv) | −22.0[4] km/s |
| Proper motion (μ) | RA: +40.587[1] mas/yr Dec.: −30.411[1] mas/yr |
| Parallax (π) | 4.59±0.24 mas[5] |
| Distance | 848 ± 88 ly (260±27 pc)[6] |
| Orbit[7] | |
| Period (P) | 15,943±471 days |
| Semi-major axis (a) | 0.071 - 0.084" (14.2 - 16.8 AU) |
| Eccentricity (e) | 0.25±0.07 |
| Inclination (i) | 70° |
| Details | |
| A | |
| Mass | 1.0[6] M☉ |
| Radius | 430[7] R☉ |
| Luminosity | 4,780[8] L☉ |
| Surface gravity (log g) | −0.5[8] cgs |
| Temperature | 2,800[8] K |
| B | |
| Mass | 0.75[6] M☉ |
| Radius | >0.1[9] R☉ |
| Luminosity | 5-20[10] L☉ |
| Temperature | 60,000[10] K |
| Other designations | |
| R Aqr, BD−16°6352, HD 222800, HIP 117054, HR 8992, SAO 165849 | |
| Database references | |
| SIMBAD | data |
R Aquarii is a symbiotic star containing a red giant primary and a white dwarf secondary in a binary system.[6] The orbital period is approximately 44 years.[7] The main star is a Mira variable, and varies in brightness by a factor of several hundred and with a period of slightly more than a year; this variability was discovered by Karl Ludwig Harding in 1810. The total range of 5.2 - 12.4 is a variation of 750 times in brightness, from a naked eye star to one beyond the range of binoculars. The pulsations occur every 390 days but are not entirely regular.[2] It is one of the nearest symbiotic stars and a well-known jet source.[12] The two components have been resolved at a separation of 55 mas.[13]
By its gravitational pull, the white dwarf draws in material from the red giant and occasionally ejects some of the surplus in loops to form the nebula seen in the linked image.[14] The whole system appears reddened because it is situated in a very dusty region of space, and its blue light is absorbed before reaching Earth.[citation needed]
The nebula around R Aquarii is also known as Cederblad 211.[15] It is possible that the nebula is the remnant of a nova-like outburst, which may have been observed by Japanese astronomers, in the year 930 AD.[16] It is reasonably bright but small and dominated by its central star. Visual observations are difficult and rare.[17] The central region of the jet shows an ejection that took place around 190 years ago, as well as much younger structures.[18] Another jet launched in January 2020 was announced by a 2025 publication. The expansion rate of the jet constrains the distance of the system to 260 ± 27 parsecs (848 ± 88 ly).[6]
