| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Octans |
| Right ascension | 05h 26m 06.19562s [2] |
| Declination | −86° 23′ 17.7741″ [2] |
| Apparent magnitude (V) | 6.4 –13.2 [3] |
| Characteristics | |
| Spectral type | M5.5e [4] (M5.3e –M8.4e [3] ) |
| Variable type | Mira [5] |
| Astrometry | |
| Radial velocity (Rv) | 46±5 [6] km/s |
| Proper motion (μ) | RA: 0.540 mas/yr [2] Dec.: 31.079 mas/yr [2] |
| Parallax (π) | 1.7152±0.0862 mas [2] |
| Distance | 1,900 ± 100 ly (580 ± 30 pc) |
| Details | |
| Mass | 6.6 [7] M☉ |
| Radius | 466 [7] R☉ |
| Luminosity | 9,304 [8] L☉ |
| Temperature | 2,571 [8] K |
| Other designations | |
| R Octantis, CD−86°52, CPD−86°72, HD 40857, HIP 25412 [9] | |
| Database references | |
| SIMBAD | data |
R Octantis, also known as HD 40857, is a solitary, red hued variable star located in the southern circumpolar constellation Octans. It has an apparent magnitude that varies in-between 6.4 and 13.2 within 405 days. [3] At is maximum, it is barely visible to the naked eye. The object is located relatively far at a distance of about 1,900 light years based on parallax measurements from Gaia DR3, [2] but is receding with a heliocentric radial velocity of 46 km/s . [6]
R Octantis has been known to have a peculiar spectra since 1892. [10] It was revealed to have emission lines in its spectrum in a 1954 paper [11] and was found to be a long period variable a year later. [12] In 1966, R Octantis was officially classified as a Mira variable. [4] Later observations reveal it to have an overabundance of oxygen on its outer layers. [13]
The object has an average stellar classification of M5.5e, indicating that it is a M-type star with emission lines in its spectrum. [4] However, this can range from M5.3 to M8.4e. [3] It is currently on the asymptotic giant branch, generating energy by fusing hydrogen and helium shells around an inert carbon core. As a result, it has expanded to 466 times the radius of the Sun. [7] R Octantis radiates over 9,000 times the luminosity of the Sun from its photosphere at an effective temperature of 2,571 K , [8] which is cooler than most Mira variables.
