R Apodis
Variable star in the constellation Apus
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R Apodis (HD 131109; HR 5540; 18 G. Apodis) is a solitary star[9] in the constellation Apus. It is faintly visible to the naked eye as an orange-hued point of light with an apparent magnitude of 5.36.[2] Parallax measurements imply a distance of 413 light-years[1] and it is drifting closer with a heliocentric radial velocity of −31.2 km/s.[6] At its current distance, R Apodis' brightness is diminished by an interstellar extinction of 0.26 magnitudes[10] and it has an absolute magnitude of −0.22.[7]
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Apus |
| Right ascension | 14h 57m 52.98352s[1] |
| Declination | −76° 39′ 45.5569″[1] |
| Apparent magnitude (V) | 5.36±0.01[2] |
| Characteristics | |
| Spectral type | K4 III:[3] |
| B−V color index | +1.44[4] |
| Variable type | constant[5] |
| Astrometry | |
| Radial velocity (Rv) | −31.20±0.08[6] km/s |
| Proper motion (μ) | RA: −69.161 mas/yr[1] Dec.: −16.583 mas/yr[1] |
| Parallax (π) | 7.8879±0.0867 mas[1] |
| Distance | 413 ± 5 ly (127 ± 1 pc) |
| Absolute magnitude (MV) | −0.22±0.16[7] |
| Details[6] | |
| Mass | 1.10±0.18 M☉ |
| Radius | 33.9±0.9[1] R☉ |
| Luminosity | 293+9 −10[1] L☉ |
| Surface gravity (log g) | 1.99±0.05 cgs |
| Temperature | 4,318±18 K |
| Metallicity [Fe/H] | −0.29±0.05 dex |
| Rotational velocity (v sin i) | 2.64±0.45 km/s |
| Age | 5.68±2.42 Gyr |
| Other designations | |
| 18 G. Apodis[8], R Aps, CD−76°688, CPD−76°924, FK5 3175, GC 20057, HD 131109, HIP 73223, HR 5540, SAO 257212 | |
| Database references | |
| SIMBAD | data |
HD 131109 was the first star observed to be variable in the constellation; It was first discovered in 1873 by Benjamin Apthorp Gould. Later, it was hastily given the variable star designation R Apodis in a 1907 variable star catalogue despite it being a suspected variable star at the time.[11] However, observations conducted in a 1952 field star survey revealed that R Apodis was not variable at all.[12] Keenan & Pitts (1980) found that it varied between magnitudes 5.5 and 6.1, but this was never confirmed.[13] Hipparcos photometric data revealed that R Apodis indeed had a constant brightness.[14] It has since been listed as a class CST: in the General Catalog of Variable Stars.[5]
R Apodis has a stellar classification of K4 III:,[3] indicating that it is an evolved K-type giant that has ceased hydrogen fusion at its core and left the main sequence. However, there is uncertainty about the luminosity class. It has a comparable mass to the Sun at 1.1 solar masses but, at the age of 5.68 billion years, it has expanded to 23 times the radius of the Sun.[6] It radiates 293 times the luminosity of the Sun[1] from its enlarged photosphere at an effective temperature of 4,318 K.[6] R Apodis is metal deficient with an iron abundance roughly half of the Sun's[6] and it spins slowly with a projected rotational velocity lower than 1.3 km/s.[15]