HD 123657
Star in the constellation Boötes
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HD 123657 (BY Boötis) is a star in the northern constellation of Boötes, near the end of the handle of the Big Dipper. It is a fifth-magnitude star, and can be spotted to the unaided eye in sufficiently dark skies, far from light pollution. Based on stellar parallax measurements, it is about 540 light-years distant.
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Boötes |
| Right ascension | 14h 07m 55.755s[1] |
| Declination | +43° 51′ 16.03″[1] |
| Apparent magnitude (V) | 4.98–5.33[2][3] |
| Characteristics | |
| Evolutionary stage | AGB[4] |
| Spectral type | M4.5III[5] |
| U−B color index | 1.66[6] |
| B−V color index | 1.58[6] |
| R−I color index | 1.66[6] |
| Variable type | LB[5] |
| Astrometry | |
| Radial velocity (Rv) | −36.24[7] km/s |
| Proper motion (μ) | RA: +11.443 mas/yr[1] Dec.: −30.812 mas/yr[1] |
| Parallax (π) | 6.0110±0.1554 mas[1] |
| Distance | 540 ± 10 ly (166 ± 4 pc) |
| Absolute magnitude (MV) | −0.90[8] |
| Details | |
| Mass | 3.96[9] M☉ |
| Radius | 131.7+3.4 −3.5[10] R☉ |
| Luminosity | 1,600±130[11] L☉ |
| Surface gravity (log g) | 0.66[12] cgs |
| Temperature | 3,444±125[11] K |
| Metallicity [Fe/H] | −0.03[13] dex |
| Other designations | |
| BY Boötis, HD 123657, HIP 69038, HR 5299, GSC 03040-00969, TYC 3040-969-1, BD+44°2325, IRAS 14059+4405, IRC +40253, SAO 44901 | |
| Database references | |
| SIMBAD | data |
This is a slow irregular variable with an apparent magnitude varying between 4.98 and 5.33.[2][3] The variability of the brightness of HD 123657 was announced by Joel Stebbins and Charles Morse Huffer in 1928, based on observations made at Washburn Observatory.[15] The star was given its variable star designation, BY Boötis, in 1973.[16]
HD 123657 has a spectral classification of M4.5III,[5] placing it as a cool red giant that exhausted its hydrogen supply. It has expanded to over 132 times the size of the Sun,[10] now radiating 1,600 times its luminosity at a cool photosphere that has an effective temperature of 3,400 K.[11]