X Trianguli Australis
Variable star in the constellation Triangulum Australe
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X Trianguli Australis is a star in the southern constellation Triangulum Australe. It is a red-hued carbon star approximately 1,140 light years (350 parsecs) from Earth.[1] It is a semi-regular variable star with two periods of around 385 and 455 days, and is of spectral type C5.5(Nb).[8] It ranges from magnitude 5.03 to 6.05, making it faintly visible to the naked eye under excellent observing conditions.[9] The discovery by Louisa Dennison Wells that the star is a variable star, was announced in 1898.[10] Its designation is from the variable star designation developed by German astronomer Friedrich Wilhelm Argelander.
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Triangulum Australe |
| Right ascension | 15h 14m 19.17550s[1] |
| Declination | −70° 04′ 46.1133″[1] |
| Apparent magnitude (V) | +5.75[2] |
| Characteristics | |
| Evolutionary stage | AGB[3] |
| Spectral type | C5.5[4] |
| B−V color index | 3.271±0.019[2] |
| Variable type | Lb[5] |
| Astrometry | |
| Radial velocity (Rv) | −3.2±1.5[6] km/s |
| Proper motion (μ) | RA: +3.932 mas/yr[1] Dec.: −8.402 mas/yr[1] |
| Parallax (π) | 2.8588±0.1525 mas[1] |
| Distance | 1,140 ± 60 ly (350 ± 20 pc) |
| Absolute magnitude (MV) | −1.97[2] |
| Details[3] | |
| Mass | 1.5 or 2 M☉ |
| Radius | 535[a] R☉ |
| Luminosity (bolometric) | 12,815 L☉ |
| Surface gravity (log g) | −0.79 or −0.51 cgs |
| Temperature | 2,650 K |
| Other designations | |
| X TrA, AAVSO 1504-69, CPD−69°2267, HD 134453, HIP 74582, HR 5644, SAO 253062[7] | |
| Database references | |
| SIMBAD | data |
It is a cool star, with of a surface effective temperature of 2,650 K (2,380 °C), yet luminous, emitting 13,000 times the luminosity of the Sun. Its angular diameter was measured at 13.82×10−3 arcseconds, which at its distance give a diameter 540 times that of the Sun.[3][a] If placed at the center of the Solar System, it would stretch out farther than Mars' orbit. Its absolute magnitude is −1.97.[2]
Notes
- Calculated multiplying the angular diameter (in arcseconds) to the distance in parsecs: 0.01382 • 360 = diameter of 4.975 AU, which multiplied by 107.5 to convert from AU to R☉ give 535 R☉.