ADS 7251
ADS 7251 is a binary star system 6.33 parsecs (20.66 light years) from the Sun. The components are near-identical red dwarfs separated by 17″ in 2019.
ADS 7251 Location of ADS 7251 in the constellation Ursa Major | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Major |
| ADS 7251 A | |
| Right ascension | 09h 14m 22.7749s |
| Declination | +52° 41′ 11.792″ |
| Apparent magnitude (V) | 7.64 |
| ADS 7251 B | |
| Right ascension | 09h 14m 24.6828s |
| Declination | +52h 41m 10.902s |
| Apparent magnitude (V) | 7.70 |
| Characteristics | |
| ADS 7251 A (HD 79210) | |
| Spectral type | M0V |
| Apparent magnitude (B) | 9.05 |
| Apparent magnitude (G) | 6.976 |
| Apparent magnitude (J) | 4.89 |
| Apparent magnitude (H) | 3.987 |
| Apparent magnitude (K) | 3.99 |
| B−V color index | +1.41 |
| J−H color index | +0.90 |
| J−K color index | +0.90 |
| ADS 7251 B (HD 79211) | |
| Spectral type | K7V |
| Apparent magnitude (B) | 9.04 |
| Apparent magnitude (G) | 7.054 |
| Apparent magnitude (J) | 4.779 |
| Apparent magnitude (H) | 4.043 |
| Apparent magnitude (K) | 4.14 |
| B−V color index | +1.42 |
| J−H color index | +0.74 |
| J−K color index | +0.64 |
| Astrometry | |
| ADS 7251 A (HD 79210) | |
| Radial velocity (Rv) | 11.245±0.0007 km/s |
| Proper motion (μ) | RA: −1,545.787(18) mas/yr Dec.: −569.053(18) mas/yr |
| Parallax (π) | 157.8879 ± 0.0197 mas |
| Distance | 20.657 ± 0.003 ly (6.3336 ± 0.0008 pc) |
| Absolute magnitude (MV) | 8.637 |
| ADS 7251 B | |
| Radial velocity (Rv) | 12.104±0.0008 km/s |
| Proper motion (μ) | RA: −1,573.040(18) mas/yr Dec.: −659.906(19) mas/yr |
| Parallax (π) | 157.8825 ± 0.0211 mas |
| Distance | 20.658 ± 0.003 ly (6.3338 ± 0.0008 pc) |
| Absolute magnitude (MV) | 8.712 |
| Orbit | |
| Period (P) | 975 yr |
| Semi-major axis (a) | 16.725″ |
| Eccentricity (e) | 0.28 |
| Details | |
| A | |
| Mass | 0.69±0.07 M☉ |
| Radius | 0.58±0.02 R☉ |
| Luminosity | 0.0789±0.0038 L☉ |
| Surface gravity (log g) | 4.68±0.07 cgs |
| Temperature | 4,024±51 K |
| Metallicity [Fe/H] | −0.05±0.16 dex |
| Rotation | 16.3+3.5 −1.3 d |
| Rotational velocity (v sin i) | 2.9±1.2 km/s |
| Age | 1–7 Gyr |
| B | |
| Mass | 0.64±0.07 M☉ |
| Radius | 0.58±0.03 R☉ |
| Luminosity | 0.0792±0.0031 L☉ |
| Surface gravity (log g) | 4.68±0.07 cgs |
| Temperature | 4,005±51 K |
| Metallicity [Fe/H] | −0.03±0.16 dex |
| Rotation | 16.61±0.04 d |
| Rotational velocity (v sin i) | 2.3±1.5 km/s |
| Age | 1–7 Gyr |
| Other designations | |
| A: BD+53°1320, HD 79210, HIP 45343 | |
| B: BD+53°1321, HD 79211, HIP 120005 | |
| Database references | |
| SIMBAD | The system |
| A | |
| B | |
The two stars share a mildly eccentric orbit with a semimajor axis of 16.725″ and a period of 975 years. Their separation has closed from 21.1″ when they were discovered by F. G. W. Struve in 1821 to 16.9″ in 2019. Struve also documented two much fainter stars about 3′ from the two red dwarfs.
ADS 7251 A is 0.06 magnitudes (six percent) brighter than ADS 7251 B. A catalogue of MK spectral classes lists both stars as secondary standards, with ADS 7251 A being class M0V and ADS 7251 B being class K7V, noted as being unusual in the brighter star having a later spectral type. Other publications have described the stars as being both K7V, both M0V, or the primary being K7V and the secondary M0V.