Theta Apodis
Star in the constellation Apus
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Theta Apodis is a variable star in the southern circumpolar constellation of Apus. Its identifier is a Bayer designation that is Latinized from θ Apodis, and abbreviated Tet Aps or θ Aps, respectively. This is a variable star with an apparent visual magnitude range of 4.65 to 6.20,[4] which, according to the Bortle Dark-Sky Scale, means it is a faint star but visible to the naked eye from dark suburban skies. The distance to Theta Apodis is approximately 390 light-years (120 parsecs), based upon parallax measurements made from the Gaia telescope.[1] It is unusual in that it is a red star with a high proper motion (greater than 50 milliarcseconds a year).[11]
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Apus |
| Right ascension | 14h 05m 19.881s[1] |
| Declination | −76° 47′ 48.34″[1] |
| Apparent magnitude (V) | 4.65 - 6.20[2] |
| Characteristics | |
| Evolutionary stage | AGB[3] |
| Spectral type | M7 III[4] |
| U−B color index | +1.07[5] |
| B−V color index | +1.48[5] |
| Variable type | SRb[4] |
| Astrometry | |
| Radial velocity (Rv) | +9.0[6] km/s |
| Proper motion (μ) | RA: −88.586 mas/yr[1] Dec.: −32.655 mas/yr[1] |
| Parallax (π) | 8.3808±0.3574 mas[1] |
| Distance | 390 ± 20 ly (119 ± 5 pc) |
| Absolute magnitude (MV) | 0.7[4] |
| Details | |
| Mass | 1.0±0.3[7] M☉ |
| Radius | 208[8] R☉ |
| Luminosity | 3,050±460[7] L☉ |
| Surface gravity (log g) | +0.0[7] cgs |
| Temperature | 2,850±160[7] K |
| Metallicity [Fe/H] | −0.20[9] dex |
| Other designations | |
| θ Apodis, Theta Aps, AAVSO 1355-76, CD−76°615, FK5 1363, HD 122250, HIP 68815, HR 5261, SAO 257112[10] | |
| Database references | |
| SIMBAD | data |
Benjamin Apthorp Gould announced that Theta Apodis is a variable star, in 1879.[13] It is a semiregular pulsating variable and its brightness changes over a range of 0.56 magnitudes with a period of 119[4] days. A longer period of around 1,000 days has also been detected.[12]
This is an evolved red giant that is currently on the asymptotic giant branch,[14] with a stellar classification of M7 III.[4] It shines with a luminosity approximately 3879 times that of the Sun and has a surface temperature of 3,131 K.[8] It is losing mass at the rate of 1.1 × 10−7 times the mass of the Sun per year through its stellar wind. Dusty material ejected from this star is interacting with the surrounding interstellar medium, forming a bow shock as the star moves through the galaxy. The stand-off distance for this front is located at about 0.134 ly (0.041 pc) from Theta Apodis.[14]
Theta Apodis has been identified as an astrometric binary, indicating that it has an orbiting companion that causes gravitational perturbation of the primary star.[15]