45 Herculis

45 Herculis is a binary variable star in the northern constellation Hercules. It has the Bayer designation l Herculis and the variable star designation V776 Herculis. The Flamsteed designation for this star comes from the publication Historia Coelestis Britannica by John Flamsteed. It is the 45th star in Flamsteed list of stars in the constellation Hercules, and is visible to the naked eye with a baseline apparent visual magnitude of 5.22.^[3] Parallax measurements show this star to be about 400 light-years away from the Solar System.^[2] It is moving closer to the Earth with a heliocentric radial velocity of −16 km/s.^[15]

45 Herculis

An ultraviolet band light curve for V776 Herculis, adapted from Burke and Barr (1981)[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Hercules
Right ascension	16h 47m 46.41942s[2]
Declination	+05° 14′ 48.2789″[2]
Apparent magnitude (V)	5.22[3]
Characteristics
Spectral type	A1 Vp Si[4] or B9p Cr[5]
U−B color index	+0.005[6]
B−V color index	−0.025[6]
Variable type	α2 CVn[7]
Astrometry
Radial velocity (Rv)	−13.13±0.09[8] km/s
Proper motion (μ)	RA: −18.802[2] mas/yr Dec.: −38.735[2] mas/yr
Parallax (π)	8.1955±0.2169 mas[2]
Distance	400 ± 10 ly (122 ± 3 pc)
Absolute magnitude (MV)	−0.18[9]
Orbit[8]
Period (P)	99.51 ± 0.10 d
Eccentricity (e)	0.445 ± 0.020
Argument of periastron (ω) (primary)	167.1 ± 4.2°
Semi-amplitude (K1) (primary)	4.75 ± 0.12 km/s
Details
Mass	2.85±0.11[10] M☉
Radius	4.3[11] R☉
Luminosity	129.7[8] L☉
Surface gravity (log g)	3.55[12] cgs
Temperature	9,400[8] K
Metallicity [Fe/H]	0.10[12] dex
Rotation	4.116476 ± 0.000022
Rotational velocity (v sin i)	35.5[13] km/s
Age	351–469[8] Myr
Other designations
l Her, 45 Her, V776 Herculis, BD+05°3272, HD 151525, HIP 82216, HR 6234, SAO 121865, WDS 16478+0515[14]
Database references
SIMBAD	data

Cowley et at. (1969) assigned this object a classification of B9p Cr,^[5] while Abt and Morrell (1995) found a class of A1 Vp Si.^[4] Both indicate this is a late B- or early A-type chemically peculiar, or Ap star, with abundance anomalies in chromium or silicon. It is classified as a magnetic Ap star, although its magnetic field is unusually weak for a star of this class.^[8] It is an Alpha² Canum Venaticorum variable that ranges in visual magnitude from 5.21 down to 5.27.^[7] The star has 2.9^[10] times the mass of the Sun and 4.9^[11] times the Sun's radius. It is radiating 120^[9] times the Sun's luminosity from its photosphere at an effective temperature of 9,333 K.^[12]

Although 45 Herculis was long thought to be a solitary star,^[16] a 2023 study confirmed that 45 Herculis is a single-lined spectroscopic binary. The pair of stars orbit each other every 99.51 days on a moderately eccentric orbit. The secondary star is likely a low-mass star.^[8]