45 Herculis
A magnetic Ap star and single-lined spectroscopic binary in Hercules.
45 Herculis, also designated l Herculis and V776 Herculis, is a binary variable star located in the northern constellation Hercules. Its Flamsteed number, 45, originates from John Flamsteed’s *Historia Coelestis Britannica*, where it appears as the 45th entry in his catalog of Hercules stars. The system is faintly visible without a telescope, with a typical apparent visual magnitude of 5.22. Based on parallax measurements, it lies roughly 400 light-years from the Solar System and is moving toward Earth at a heliocentric radial velocity of −16 km/s.
The star’s spectral classification has been assigned as a late B- or early A-type chemically peculiar (Ap) star, showing abundance anomalies in chromium or silicon. It is a magnetic Ap star, though its magnetic field is unusually weak for this class. As an Alpha2 Canum Venaticorum variable, its visual magnitude fluctuates between 5.21 and 5.27. The primary star has about 2.9 times the Sun’s mass, 4.9 times its radius, and radiates 120 times the Sun’s luminosity from a photosphere with an effective temperature of 9,333 K. Its evolutionary stage is uncertain, but it is near the end of its main-sequence life—either just before, on, or shortly after the hook marking the transition to a subgiant.
Long considered a solitary star, 45 Herculis was confirmed in 2023 to be a single-lined spectroscopic binary. The two stars orbit each other every 99.51 days on a moderately eccentric path, and the secondary is likely a low-mass star.
- Bayer designation
- l Herculis
- Variable star designation
- V776 Herculis
- Flamsteed designation
- 45 Herculis
- Apparent visual magnitude
- 5.22 (baseline), ranging from 5.21 to 5.27
- Distance
- about 400 light-years
- Radial velocity
- −16 km/s
- Spectral type
- late B- or early A-type chemically peculiar (Ap star)
Lore & Background
Cowley et al. (1969) assigned this object a classification, while Abt and Morrell (1995) found a class. 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. It is an Alpha2 Canum Venaticorum variable that ranges in visual magnitude from 5.21 down to 5.27. The star has 2.9 times the mass of the Sun and 4.9 times the Sun's radius. It is radiating 120 times the Sun's luminosity from its photosphere at an effective temperature of 9,333 K. The exact evolutionary state of 45 Her is unclear, but it is near the end of its main sequence life—just before, on, or shortly after the hook that marks the transition to a subgiant. Although 45 Herculis was long thought to be a solitary star, 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.
Reader's Guide
45 Herculis is notable as a magnetic Ap star with an unusually weak magnetic field for its class, and as an Alpha2 Canum Venaticorum variable exhibiting small-amplitude brightness changes. Its classification as a chemically peculiar star with chromium or silicon anomalies places it among the interesting group of stars that show strong spectral line variations due to rotation and magnetic fields. The star's evolutionary state is uncertain but it is near the end of its main sequence life, possibly just before or during the transition to a subgiant. A significant development is the 2023 confirmation that it is a single-lined spectroscopic binary, ending its long-held status as a solitary star. The binary system has an orbital period of 99.51 days on a moderately eccentric orbit, with the secondary likely being a low-mass star. This discovery adds to the understanding of binary frequency among chemically peculiar stars. The star's Flamsteed designation originates from John Flamsteed's Historia Coelestis Britannica, and it is visible to the naked eye from the northern constellation Hercules. Its heliocentric radial velocity of −16 km/s indicates it is moving closer to the Solar System.
Did You Know?
- 45 Herculis is also designated l Herculis and V776 Herculis.
- It is an Alpha2 Canum Venaticorum variable with a magnitude range of 5.21 to 5.27.
- A 2023 study confirmed it is a single-lined spectroscopic binary with an orbital period of 99.51 days.
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