HR 6819
HR 6819, also known as HD 167128 or QV Telescopii (abbreviated QV Tel), is a double star system in the southern constellation of Telescopium. It is in the south-western corner of the constellation, near Pavo to the south and Ara to the west. The system appears as a variable star that is dimly visible to the naked eye with an apparent magnitude that ranges from 5.32 down to 5.39, which is comparable to the maximum brightness of the planet Uranus. It is about 1,120 light years from the Sun, and is drifting farther away at a rate of 9.4 km/s. Due to its location in the sky, it is visible only to observers south of 33°N latitude.
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Telescopium |
| Right ascension | 18h 17m 07.53243s |
| Declination | −56° 01′ 24.0576″ |
| Apparent magnitude (V) | 5.36 (5.32 to 5.39) |
| Characteristics | |
| Evolutionary stage | giant |
| Spectral type | B3IIIpe or B3II/III |
| B−V color index | −0.050±0.018 |
| Variable type | Be |
| Astrometry | |
| Radial velocity (Rv) | +9.13±0.78 km/s |
| Proper motion (μ) | RA: −4.021±0.111 mas/yr Dec.: −13.071±0.104 mas/yr |
| Parallax (π) | 2.7122 ± 0.1187 mas |
| Distance | 1,200 ± 50 ly (370 ± 20 pc) |
| Absolute magnitude (MV) | −1.47 |
| Orbit | |
| Primary | Stripped B giant |
| Companion | Be star |
| Period (P) | 40.335±0.007 d |
| Eccentricity (e) | 0 (fixed) |
| Inclination (i) | 32±4 (49±2)° |
| Longitude of the node (Ω) | 32.4±0.9° |
| Semi-amplitude (K1) (primary) | 60.4±1.0 km/s |
| Semi-amplitude (K2) (secondary) | 4.0±0.8 km/s |
| Details | |
| Stripped B giant | |
| Mass | 0.46±0.26 M☉ |
| Radius | 4.4±0.4 R☉ |
| Luminosity | 1,122+291 −231 L☉ |
| Surface gravity (log g) | 2.8±0.2 cgs |
| Temperature | 16,000±1,000 K |
| Rotational velocity (v sin i) | 50±1 km/s |
| Be star | |
| Mass | 7±2 (fixed) M☉ |
| Radius | 3.9±0.7 R☉ |
| Luminosity | 2,239+580 −460 L☉ |
| Temperature | 20,000±2,000 K |
| Rotational velocity (v sin i) | 180±10 km/s |
| Age | 50 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
A May 2020 study hypothesized that the system contained two stars and a black hole, which would have been the closest known black hole, and the first one in a system visible to the naked eye. A study in July of the same year concluded that rather than a triple system it was much more likely to be a black hole and a star orbiting at one distance from here and another star at a different distance. Three further papers in 2020 and one in 2022 concluded that HR 6819 is simply a binary system with two main-sequence stars and no black hole at all.