Iota1 Librae
Quadruple star system with a variable B-type subgiant primary.
Iota1 Librae is a quadruple star system in the constellation Libra. It is a Bayer designation star with an apparent magnitude of 4.54, located 379 light years from Earth. The system is notable for containing an Alpha2 Canum Venaticorum variable star, a spectroscopic binary, and two additional stellar companions.
- Apparent magnitude
- 4.54
- Distance
- 379 light years
- Spectral type (primary)
- B-type subgiant with silicon overabundance
- Variable type
- Alpha2 Canum Venaticorum
- Magnitude range
- 4.53 to 4.56
- Orbital period (inner pair)
- 23.512 years
- Eccentricity (inner pair)
- 0.2440
Lore & Background
The inner pair of Iota1 Librae, components Aa and Ab, form a spectroscopic binary with an orbital period of 23.512 years and an eccentricity of 0.2440. The brighter member has a stellar classification indicating it is a B-type subgiant star with an overabundance of silicon in the photosphere. It is a variable star of the Alpha2 Canum Venaticorum type, with a magnitude that varies from 4.53 to 4.56, and its spectrum likewise shows variability. The secondary component is of class B9. The two stars are very close together, separated by 0.129 arcseconds, with respective magnitudes of 5.10 and 5.60.
The two other stars are components C and D, separated by 57.8 arcseconds from AB and 2.058 arcseconds from each other. Their combined spectrum is G5IV, and each star has masses of 0.98 and 0.91 solar masses, with magnitudes 10.40 and 10.90, respectively. Due to its position on the ecliptic, Iota1 Librae is sometimes obscured by the Moon or planets; a lunar occultation took place on April 4, 2012.
Reader's Guide
Iota1 Librae's significance lies in its quadruple nature and the variability of its primary component. As an Alpha2 Canum Venaticorum variable, the primary star exhibits small but measurable brightness changes linked to its strong silicon overabundance and magnetic field, making it a target for studies of chemically peculiar stars. The system's hierarchical architecture—a close spectroscopic binary paired with a wider binary of solar-type stars—provides a laboratory for understanding multiple-star formation and dynamical evolution. Its location near the ecliptic allows occasional occultations by the Moon and planets, events that can refine astrometric measurements. For observers, the system is visible to the naked eye under dark skies, with best evening observation between May and September from both hemispheres. The system's Bayer designation and its listing in multiple catalogs (including BD-19 4047, 074392, 134759, and 5652) ensure its continued study in stellar astronomy.
Did You Know?
- Iota1 Librae is a quadruple star system located 379 light years from Earth.
- The primary star is an Alpha2 Canum Venaticorum variable with a magnitude range of 4.53 to 4.56.
- A lunar occultation of Iota1 Librae occurred on April 4, 2012.
Frequently Asked Questions
What is Iota1 Librae?
Iota1 Librae is a quadruple star system in the constellation Libra that carries a Bayer designation. It lies approximately 379 light years from Earth and presents an apparent magnitude of about 4.54 to the naked eye.
What type of variable star is Iota1 Librae?
The system is classified as an Alpha2 Canum Venaticorum variable, meaning its small brightness swings (4.53 to 4.56 mag) come from rotating surface inhomogeneities on the B-type subgiant primary rather than from pulsation. The underlying driver is a change in hydrogen-alpha emission as the star turns.
How is the Iota1 Librae system structured?
Four stars make up the system: a tight spectroscopic binary whose inner pair completes an orbit every 23.512 years, plus two wider stellar companions. The primary of that inner binary is the variable B-type subgiant.
What is unusual about Iota1 Librae's primary star?
The primary is a B-type subgiant that displays a measurable silicon overabundance compared to a normal stellar composition. That chemical peculiarity, paired with its Alpha2 CVn variability, makes it a useful laboratory for studying how surface inhomogeneities alter a star's light.
Why do variable-star enthusiasts care about Iota1 Librae?
It provides a relatively nearby (379 ly) example of an Alpha2 CVn-type variable embedded in a four-star configuration, letting observers study how multiple-star dynamics coexist with surface-activity-driven dimming. Its narrow 0.03-mag amplitude also makes it a rewarding target for careful differential photometry.
More in Variable Stars, Part 6 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced