| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cetus[1] |
| A | |
| Right ascension | 02h 28m 37.228s[2] |
| Declination | −07° 03′ 38.38″[2] |
| Apparent magnitude (V) | 10.29[3] |
| B | |
| Right ascension | 02h 28m 37.324s[4] |
| Declination | −07° 03′ 41.28″[4] |
| Apparent magnitude (V) | 13.4[3] |
| Characteristics | |
| A | |
| Evolutionary stage | main-sequence star[5] |
| Spectral type | G8V[6] |
| B | |
| Evolutionary stage | main-sequence star[5] |
| Spectral type | K5[6] |
| Astrometry | |
| A | |
| Radial velocity (Rv) | +1.44±0.17[2] km/s |
| Proper motion (μ) | RA: +93.708[2] mas/yr Dec.: −1.717[2] mas/yr |
| Parallax (π) | 9.4629±0.0183 mas[2] |
| Distance | 344.7 ± 0.7 ly (105.7 ± 0.2 pc) |
| B | |
| Radial velocity (Rv) | +3.22±1.63[4] km/s |
| Proper motion (μ) | RA: +94.240[4] mas/yr Dec.: −3.787[4] mas/yr |
| Parallax (π) | 9.5080±0.0183 mas[4] |
| Distance | 343.0 ± 0.7 ly (105.2 ± 0.2 pc) |
| Absolute magnitude (MV) | 7.2[5] |
| Orbit[6][7] | |
| 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[8] | |
| 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[9] |
| Rotational velocity (v sin i) | 4.0±0.2 km/s |
| Age | 7.99+1.90 −1.71[10] Gyr |
| BD−07 436B | |
| Mass | 0.71±0.06[5] M☉ |
| Radius | 0.69±0.12[5] R☉ |
| Surface gravity (log g) | 4.6±0.15[5] cgs |
| Temperature | 5570±240[7] K |
| Metallicity [Fe/H] | -0.11±0.19[5] dex |
| Rotational velocity (v sin i) | 2.8±0.5[5] km/s |
| Age | 7.3+4.4 −4.6[10] Gyr |
| Other designations | |
| WASP-77, 2MASS J02283722-0703384[11] | |
| 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,[5] 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.[6]
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.[9] The secondary is a K-type main-sequence star BD−07 436B orbiting at a distance of 461+200
−140 AU.[7]
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.[5] When calculated from X-ray luminosity, the ages are radically different and even more inconsistent at 4.5 and >8.9 billion years respectively. [6] 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.[10]
In 2012 a transiting hot Jupiter planet b was detected on a very tight, circular orbit.[5] The planet may have an extended gaseous envelope and is losing mass.[6] Its equilibrium temperature is 1715+26
−25 K,[8] the nightside temperature is 1786±84 K,[12] and dayside planetary temperature is 1842+34
−33 K.[13]
Water vapour was detected on the planetary dayside of WASP-77Ab, indicating C/O ratio similar to solar or even lower.[14]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| Ab | 1.667+0.068 −0.064 MJ |
0.02335+0.00045 −0.00043 |
1.36002854±0.00000062 | 0.0074+0.0069 −0.0049 |
88.91+0.74 −0.95° |
1.230+0.031 −0.029 RJ |
