AD Andromedae
Eclipsing binary with ellipsoidal stars and a proposed third body.
AD Andromedae (AD And) is an eclipsing binary star system in the constellation Andromeda, classified as a Beta Lyrae variable. It is notable for its nearly one-day orbital period and the ellipsoidal shapes of its two close main sequence stars, which cause mutual eclipses that dim the system's light by 0.62 magnitudes during the primary eclipse and 0.58 during the secondary.
Quick Facts
- Maximum apparent visual magnitude
- 11.2
- Variable star classification
- Beta Lyrae
- Orbital period
- 20 minutes less than one day
- Spectral type of components
- A0V
Facts from the source article.
Lore & Background
The AD Andromedae system consists of two close main sequence stars of spectral type A0V. They orbit so close to each other that their gravitational interaction distorts them into ellipsoidal shapes. The orbital plane is aligned with our line of sight, so each star eclipses the other as it passes in front, producing the observed brightness variations.
A third body with a minimum mass of 2.21 solar masses has been proposed to exist in the system, but it has not been detected, and its light contribution should be significant. One possible explanation is that two unseen, less massive and luminous stars orbit close to each other instead.
A cyclic variation of 14.3 years in the orbital period has been reported, which could be an effect of another body orbiting in the system. AD Andromedae received its variable star designation in 1927.
Reader's Guide
AD Andromedae is significant as an eclipsing binary of the Beta Lyrae type, a class of close binaries where the components are distorted by tidal forces. Its nearly one-day period and the small difference in eclipse depths (0.62 vs. 0.58 magnitudes) indicate that the two stars are similar in brightness and size. The proposed third body, with a minimum mass of 2.21 solar masses, remains undetected, highlighting the challenges in confirming multiple-star systems through photometric data alone. The 14.3-year cyclic variation in the orbital period further suggests gravitational influence from an unseen companion, though the exact nature—whether a single star or a close pair—is unresolved. This system exemplifies the complexities of close binary evolution and the search for additional components in variable star systems. Its designation in 1927 places it among the early recognized variable stars, contributing to the foundational catalog of eclipsing binaries.
Frequently Asked Questions
How long is AD Andromedae's orbital period?
The pair completes one full orbit in roughly 23 hours and 40 minutes, meaning it falls about 20 minutes short of a full day. This extremely tight period keeps the two stars so close that their mutual gravity visibly reshapes each other.
How much does AD Andromedae dim during its eclipses?
The primary eclipse reduces the system's apparent visual magnitude by 0.62, while the secondary eclipse accounts for a 0.58-magnitude dip. At maximum brightness the pair reaches a visual magnitude of 11.2, far beyond what the unaided eye can detect.
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