LN Andromedae

Lore & Background

LN Andromedae was added to the General Catalogue of Variable Stars after a 1979 report indicated its blue magnitude varied by about 0.025 every 28 minutes. Such rapid variability was unknown for any class of variable star at the time, but its position in the Hertzsprung–Russell diagram at the main-sequence end of the β Cephei instability strip suggested high-overtone radial pulsations as a likely cause. However, follow-up studies failed to reproduce the rapid variations or detect any significant brightness changes, and the star is now listed as probably constant.

In the Washington Double Star Catalog, LN And has a faint optical companion star of apparent magnitude 9.88, located 7.5″ away. The separation has increased from 4.0″ when the pair was discovered as a double in 1828. The two stars share the same Hipparcos identifier HIP 113802 and have very similar parallaxes and proper motions, suggesting a possible physical association despite the optical designation.

Analysis of Hipparcos photometry revealed variability of about 0.0059 magnitudes with a main period of 3.25 days. The statistical threshold for these variations is met by only 0.01% of stars, indicating a very low probability that the signal is due to chance.

Reader's Guide

LN Andromedae's significance lies in its history as a suspected variable star that ultimately proved to be probably constant, illustrating the challenges of confirming low-amplitude variability. The initial 1979 report of rapid 28-minute variations with an amplitude of 0.025 magnitudes in the blue band was unprecedented for any known variable class, prompting its inclusion in the General Catalogue of Variable Stars. However, subsequent studies failed to replicate the signal, leading to its reclassification as probably constant. This case highlights the importance of follow-up observations in variable star astronomy, especially for claims of unusual or rapid variability. The star's position near the β Cephei instability strip in the Hertzsprung–Russell diagram remains interesting, as it suggests that if variability were present, high-overtone radial pulsations would be the likely mechanism. The Hipparcos photometry detected extremely low-amplitude variations (0.0059 mag) with a 3.25-day period at a statistical significance level met by only 0.01% of stars, leaving open the possibility of very subtle intrinsic variability. The optical companion, with its increasing separation since 1828 and shared proper motion, adds a further layer of interest to this otherwise unremarkable B2V star.

Did You Know?

• LN Andromedae was added to the General Catalogue of Variable Stars after a 1979 report of 28-minute brightness variations, but follow-up studies found no significant variability.
• The star has an optical companion of magnitude 9.88, whose separation from LN And increased from 4.0″ in 1828 to 7.5″.
• Hipparcos photometry detected variations of about 0.0059 magnitudes with a 3.25-day period, at a statistical threshold met by only 0.01% of stars.
• LN Andromedae is a B2V main-sequence star with an effective temperature of 18,090 K, located 458 parsecs away.