54 Aurigae
A multiple star system with an eclipsing binary and a disputed companion.
54 Aurigae, a multiple star system in the northern constellation Auriga, lies roughly 800 light-years from the Sun. With a combined apparent visual magnitude of 6.02, it appears to the unaided eye as a faint, blue-white point of light. The system is receding from the Sun at a heliocentric radial velocity of about +19 km/s.
Resolved into two visible stars, the pair has magnitudes of 6.22 and 7.82, separated by 0.8 arcseconds. First identified as a double in 1843, the separation then measured 0.7 arcseconds. Although the secondary’s parallax has not been measured independently, it shares a common proper motion with the brighter star, so the two are presumed to form a binary system. The brighter component is classified as spectral type B7 III—a hot giant—though it has also been listed as B7/8 III/V, suggesting it might instead be a main-sequence star. For the fainter star, most sources offer no separate spectral classification, but it has been noted as either DA1 (a white dwarf) or K4V (a red dwarf).
The brighter component of this visible pair is itself an eclipsing binary with a period of 1.8797 days and a primary eclipse depth of 0.03 magnitudes. It radiates 315 times the Sun’s luminosity from its photosphere, which has an effective temperature of 11,083 K (10,810 °C; 19,490 °F). Its projected rotational velocity is 65 km/s (40 mi/s).
- Distance
- 800 light-years (51,000,000 AU)
- Combined apparent magnitude
- 6.02
- Heliocentric radial velocity
- +19 km/s
- Component magnitudes
- 6.22 and 7.82
- Separation
- 0.8″ (discovered 1843 at 0.7″)
- Spectral class brighter
- B7 III (also given as B7/8 III/V)
- Spectral class fainter
- DA1/K4V (white dwarf or red dwarf)
- Eclipsing binary period
- 1.8797 days
- Primary eclipse depth
- 0.03 magnitudes
- Luminosity brighter component
- 315 times solar
Lore & Background
54 Aurigae was resolved into two visible components in 1843, when the separation was measured at 0.7″; it has since widened to 0.8″. The brighter star (magnitude 6.22) and fainter star (magnitude 7.82) share a common proper motion and are assumed to form a binary, though no separate parallax exists for the secondary. The brighter component is classified as spectral type B7 III, indicating a hot giant star, but it has also been given as B7/8 III/V, suggesting it may be a main sequence star. The fainter star lacks a consistent spectral classification; it has been listed as DA1/K4V, meaning it could be either a white dwarf or a red dwarf.
Reader's Guide
The significance of 54 Aurigae lies in its multiple-star nature and the eclipsing binary within its brighter component. The system's combined magnitude of 6.02 makes it a naked-eye target, while the 1.8797-day eclipsing binary with a shallow primary eclipse depth of 0.03 magnitudes provides a subtle photometric variation. The uncertainty in the spectral classification of both the brighter star (giant vs. main sequence) and the fainter companion (white dwarf vs. red dwarf) highlights the challenges in characterizing such systems. The common proper motion between the two visible stars supports their physical association, but the lack of a separate parallax for the secondary leaves room for doubt. The system's heliocentric radial velocity of +19 km/s indicates it is moving away from the Sun. Its legacy is as a modest but instructive example of a hierarchical multiple star system, where the brighter component itself is a close binary, and the outer companion's nature remains ambiguous.
Did You Know?
- 54 Aurigae was discovered as a double star in 1843 with a separation of 0.7″.
- The fainter star has been classified as either a white dwarf (DA1) or a red dwarf (K4V).
- The system is moving away from the Sun at a radial velocity of about +19 km/s.
More in Binary and Multiple Stars, Part 2 1-24
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