HR 7578
Triple star system in the constellation Sagittarius
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HR 7578 (also known as V4200 Sagittarii) is a triple star system in the constellation of Sagittarius. Their combined apparent magnitude is 6.18,[4] making it very faintly visible to the naked eye of an observer under a dark sky, far from any city. Parallax measurements by the Gaia spacecraft put the system at 46 light-years (14.1 parsecs) away, making this a nearby system.[3]
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Sagittarius[2] |
| A | |
| Right ascension | 19h 54m 17.7453s[3] |
| Declination | −23° 56′ 27.863″[3] |
| Apparent magnitude (V) | 6.18[4] |
| Characteristics | |
| A | |
| Spectral type | K3 V + K3 V[5] + M5[6] |
| U−B color index | +0.915[7] |
| B−V color index | +1.045[7] |
| Variable type | BY Dra[4] |
| Astrometry | |
| A | |
| Radial velocity (Rv) | −5.1±0.2[8] km/s |
| Proper motion (μ) | RA: −124.476±0.067[3] mas/yr Dec.: −410.440±0.043[3] mas/yr |
| Parallax (π) | 70.857±0.019 mas[6] |
| Distance | 46.03 ± 0.01 ly (14.113 ± 0.004 pc) |
| Absolute magnitude (MV) | +5.48[2] |
| Orbit[9][6] | |
| Primary | HR 7578 Aa |
| Name | HR 7578 Ab |
| Period (P) | 46.81614±0.00003 d |
| Semi-major axis (a) | 0.3054±0.0001 AU |
| Eccentricity (e) | 0.68664±0.00006 |
| Inclination (i) | 99.048±0.007° |
| Longitude of the node (Ω) | 111.83±0.01° |
| Periastron epoch (T) | 2455441.0406±0.0003 HJD |
| Argument of periastron (ω) (secondary) | 241.056±0.011° |
| Semi-amplitude (K1) (primary) | 47.79±0.01 km/s |
| Semi-amplitude (K2) (secondary) | 48.63±0.01 km/s |
| Details | |
| HR 7578 Aa | |
| Mass | 0.87492±0.00032[6] M☉ |
| Radius | 0.86±0.04[10] R☉ |
| Luminosity | 0.35±0.02[10] L☉ |
| Temperature | 4,820±200[6] K |
| Metallicity [Fe/H] | 0.28[6] dex |
| Rotational velocity (v sin i) | 2.0[5] km/s |
| HR 7578 Ab | |
| Mass | 0.85978±0.00029[6] M☉ |
| Radius | 0.81±0.04[10] R☉ |
| Luminosity | 0.31±0.02[10] L☉ |
| Temperature | 4,820±200[6] K |
| 2MASS J19542064−2356398 (HR 7578 C) | |
| Mass | 0.173±0.020[11] M☉ |
| Radius | 0.204±0.004[11] R☉ |
| Luminosity | 0.00304±0.00083[11] L☉ |
| Surface gravity (log g) | 5.0570±0.0244[11] cgs |
| Temperature | 3,002±157[11] K |
| Other designations | |
| CD−24°15668, GJ 770, HD 188088, HIP 97944, HR 7578, SAO 188692 | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
The two main stars of HR 7578 are fairly old, older than the Pleiades but possibly younger than the Hyades.[8] The stars are between 5×108 and 2×109 years old.[8] Both are K-type main-sequence stars.[5] Both stars have a minimum mass of 0.85 ± 0.03 M☉, and are unusually metal-rich, showing high amounts of cyanide and sodium in their spectra.[8]
In 1982, Francis C. Fekel and Willet I. Beavers suggested that HR 7578 might be a variable star, based on their spectroscopic observations.[12] James T. Hooten and Douglas S. Hall confirmed that the star's brightness varies, in 1990.[13] It was given its variable star designation, V4200 Sagittarii, in 1993.[14] HR 7578 is a BY Draconis variable. This is a class of variable star whose variability comes from starspots on the stars' surfaces.
HR 7578 also has a common proper motion companion, 2MASS J19542064−2356398. It is a red dwarf that is at least 580 astronomical units from the central star system.[4] There is another star that is separated about 40″ away and is 4.4 magnitudes fainter, but is not physically associated with HR 7578.[10]