BD−07 436
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cetus |
| A | |
| Right ascension | 02h 28m 37.228s |
| Declination | −07° 03′ 38.38″ |
| Apparent magnitude (V) | 10.29 |
| B | |
| Right ascension | 02h 28m 37.324s |
| Declination | −07° 03′ 41.28″ |
| Apparent magnitude (V) | 13.4 |
| Characteristics | |
| A | |
| Evolutionary stage | main-sequence star |
| Spectral type | G8V |
| B | |
| Evolutionary stage | main-sequence star |
| Spectral type | K5 |
| Astrometry | |
| A | |
| Radial velocity (Rv) | +1.44±0.17 km/s |
| Proper motion (μ) | RA: +93.708 mas/yr Dec.: −1.717 mas/yr |
| Parallax (π) | 9.4629±0.0183 mas |
| Distance | 344.7 ± 0.7 ly (105.7 ± 0.2 pc) |
| B | |
| Radial velocity (Rv) | +3.22±1.63 km/s |
| Proper motion (μ) | RA: +94.240 mas/yr Dec.: −3.787 mas/yr |
| Parallax (π) | 9.5080 ± 0.0183 mas |
| Distance | 343.0 ± 0.7 ly (105.2 ± 0.2 pc) |
| Absolute magnitude (MV) | 7.2 |
| Orbit | |
| Primary | BD−07 436A |
| Companion | BD−07 436B |
| Semi-major axis (a) | 3.3" (461+200 −140 AU) |
| Eccentricity (e) | 0.51+0.26 −0.22 |
| Inclination (i) | 77+5 −7° |
| Details | |
| BD−07 436A | |
| Mass | 0.903+0.066 −0.059 M☉ |
| Radius | 0.910+0.025 −0.023 R☉ |
| Luminosity | 0.743+0.065 −0.058 L☉ |
| Surface gravity (log g) | 4.476+0.014 −0.015 cgs |
| Temperature | 5617±72 K |
| Metallicity [Fe/H] | −0.10+0.10 −0.11 dex |
| Rotation | 15.4±0.5 |
| Rotational velocity (v sin i) | 4.0±0.2 km/s |
| Age | 7.99+1.90 −1.71 Gyr |
| BD−07 436B | |
| Mass | 0.71±0.06 M☉ |
| Radius | 0.69±0.12 R☉ |
| Surface gravity (log g) | 4.6±0.15 cgs |
| Temperature | 5570±240 K |
| Metallicity [Fe/H] | -0.11±0.19 dex |
| Rotational velocity (v sin i) | 2.8±0.5 km/s |
| Age | 7.3+4.4 −4.6 Gyr |
| Other designations | |
| WASP-77, 2MASS J02283722-0703384 | |
| A: TOI-398, TIC 1129033, TYC 4697-201-1 | |
| B: TIC 632613066 | |
| Database references | |
| SIMBAD | data |
| A | |
| B | |
BD−07 436, also known as WASP-77 since 2012, is a binary star system about 344 light-years away. The BD−07 436 system's concentration of heavy elements is similar to the Sun. Its stars display moderate chromospheric activity, including x-ray flares.
The primary is a G-type main-sequence star, BD−07 436A (WASP-77A). The star is rotating rapidly, being spun up by the tides raised by the giant planet WASP-77Ab on its close orbit. The secondary is a K-type main-sequence star BD−07 436B orbiting at a distance of 461+200
−140 AU.
When calculated using spin rates, the two components appear to have different ages, with the secondary one billion years old, while the primary's age is 0.4 billion years. When calculated from X-ray luminosity, the ages are radically different and even more inconsistent at 4.5 and >8.9 billion years respectively. These ages may be unreliable, with the spin rates and X-ray luminosities affected by binary evolution, and ages inferred from the stars' positions in the H-R diagram are 7.99 and 7.3 billion years respectively.