HN Andromedae

Lore & Background

The HN Andromedae system is triple, revealed by periodic radial velocity variations. The primary component is a star leaving the main sequence, with an absolute magnitude Mv = −0.03 ± 0.42, and it dominates the observed spectrum. Its spectral classification is A2pSrCrEu, indicating it is a chemically peculiar Ap star with enhanced absorption lines of strontium, chromium, and europium. The other two components contribute only 0.23 magnitudes to the system's apparent magnitude; one has an orbital period of 106.3 days, and the other has an orbital period longer than 5000 days.

The variability of HN Andromedae is entirely ascribed to the primary component and is compatible with its stellar rotation, giving it the classification as an α2 Canum Venaticorum variable. Magnetic fields in this star are strong and variable, thought to occur when the magnetic dipole axis is not aligned with the rotation axis. Additionally, the distribution of metals—and consequently surface brightness—is not uniform on the surface, causing the observed brightness variation.

Reader's Guide

HN Andromedae serves as an important example of an α2 Canum Venaticorum variable within a multiple-star system. Its variability is directly linked to the primary star's rotation and misaligned magnetic dipole, which produces non-uniform surface brightness due to uneven metal distribution. The system's triple nature, with orbital periods of 106.3 days and longer than 5000 days for the companions, provides a rare opportunity to study the dynamics of chemically peculiar stars in hierarchical configurations. The primary's status as an Ap star with strong strontium, chromium, and europium lines highlights the role of magnetic fields in chemical peculiarity. The star's absolute magnitude and its departure from the main sequence offer insights into the evolutionary stage of such variables. The fact that the companions contribute only 0.23 magnitudes to the apparent brightness underscores the primary's dominance in the observed spectrum and variability. This system thus contributes to understanding stellar magnetism, rotation, and chemical inhomogeneities in variable stars.

Did You Know?

• HN Andromedae is a triple system, with the primary component dominating the observed spectrum.
• Its variability period of 69.51 days matches the rotation period of the primary star.
• The primary star is classified as A2pSrCrEu, a chemically peculiar Ap star with strong strontium, chromium, and europium lines.