HD 7924
Star in the constellation Cassiopeia
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HD 7924 is a single[9] star located 55.5[2] light years away from the Sun in the northern constellation of Cassiopeia, near the northern constellation border with Cepheus. It has an orange hue and is only visible by means of binoculars or a telescope due to a low apparent visual magnitude of 7.167.[3] The star is drifting closer to the Sun with a radial velocity of –22.81 km/s,[2] and is expected to approach to within 9.3 light-years in around 711,700 years.[10]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cassiopeia[1] |
| Right ascension | 01h 21m 59.11373s[2] |
| Declination | +76° 42′ 37.0383″[2] |
| Apparent magnitude (V) | 7.167[3] |
| Characteristics | |
| Evolutionary stage | main sequence |
| Spectral type | K0.5V[4] |
| Apparent magnitude (B) | 8.005[3] |
| Apparent magnitude (J) | 5.618[5] |
| Apparent magnitude (H) | 5.231[5] |
| Apparent magnitude (K) | 5.159[5] |
| B−V color index | +0.826±0.006[1] |
| Astrometry | |
| Radial velocity (Rv) | −22.81±0.12[2] km/s |
| Proper motion (μ) | RA: −34.767±0.016[2] mas/yr Dec.: −32.724±0.019[2] mas/yr |
| Parallax (π) | 58.8125±0.0168 mas[2] |
| Distance | 55.46 ± 0.02 ly (17.003 ± 0.005 pc) |
| Absolute magnitude (MV) | 6.04[1] |
| Details[6] | |
| Mass | 0.81±0.01 M☉ |
| Radius | 0.74±0.01 R☉ |
| Luminosity | 0.364±0.001 L☉ |
| Surface gravity (log g) | 4.6±0.01 cgs |
| Temperature | 5,216±13 K |
| Metallicity [Fe/H] | −0.15±0.03 dex |
| Rotational velocity (v sin i) | 0.9[7] km/s |
| Age | 3.0±1.8 Gyr |
| Other designations | |
| BD+75°58, GJ 56.5, HD 7924, HIP 6379, SAO 4386, PPM 4675, TYC 4494-1346-1, GCRV 766, GSC 04494-01396, 2MASS J01215911+7642372[8] | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
| ARICNS | data |
This is a K-type main-sequence star with a stellar classification of K0.5V.[4] Low-level chromospheric activity has been detected, with the star showing spots and an activity cycle.[9] The star is about three[6] billion years old and is spinning with a projected rotational velocity of just 0.9 km/s.[7] It has 81% of the mass of the Sun and 74% of the Sun's radius. The metal content is about seven-tenths as much as the Sun. It is radiating 36.4% of the luminosity of the Sun from its photosphere at an effective temperature of 5,216 K.[6]
Planetary system
In 2009, a super-Earth exoplanet was found in orbit around the star.[11] In 2015, two more planets were discovered, and the mass of the original planet was revised downwards slightly.[12][9] It is possible that planets c and d are in the 8:5 mean motion resonance.[13] All of the planets lie below the star's habitable zone.[9]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥ 8.68±0.52 M🜨 | 0.05664±0.00068 | 5.39792±0.00025 | 0.058 +0.056 −0.040 |
— | — |
| c | ≥ 7.86±0.72 M🜨 | 0.1134±0.0014 | 15.299±0.0033 | 0.098 +0.096 −0.069 |
— | — |
| d | ≥ 6.44±0.79 M🜨 | 0.1551±0.0019 | 24.451±0.016 | 0.21 +0.13 −0.12 |
— | — |