BP Boötis

Lore & Background

The star, often called HD 140728 before it was known to be variable, was transferred from Boötes to Quadrans Muralis. Later, when the International Astronomical Union officially recognised constellations, Quadrans Muralis became obsolete, so this star was moved back to Boötes. In 1962, William Wehlau announced that the star's brightness varied, based on observations made from 1958 through 1960.

BP Boötis is an Ap star with a stellar classification showing abundance anomalies of silicon and chromium. It is an Alpha2 Canum Venaticorum variable that varies in brightness by 0.02 magnitude over a period of 1.3 days. The distribution of silicon across the surface appears to be associated with the magnetic field of the star, with depleted regions appearing around the magnetic poles.

The star is 170 million years old with a projected rotational velocity of 69 km/s, having a rotation period of 1.29557 days. It has 2.6 times the mass of the Sun and 2.7 times the Sun's radius. The star is radiating 65 times the luminosity of the Sun from its photosphere at an effective temperature of 9,954 K.

Reader's Guide

BP Boötis is significant as an example of an Alpha2 Canum Venaticorum variable, a class of chemically peculiar Ap stars whose brightness variations are linked to strong magnetic fields and uneven surface distributions of elements. Its small amplitude of 0.02 magnitude and short period of 1.3 days make it a typical representative of this type. The star's history of being moved between constellations—first from Boötes to the now-obsolete Quadrans Muralis, then back—reflects the evolution of official constellation boundaries. The discovery of its variability by William Wehlau in 1962, based on observations from 1958 through 1960, added to the growing catalog of magnetic chemically peculiar stars. The association between silicon distribution and magnetic field geometry, with depleted regions at the magnetic poles, provides insight into the processes that create abundance patches on such stars. Its measured rotation period of 1.29557 days and projected rotational velocity of 69 km/s help constrain models of stellar rotation and magnetic field alignment. At 170 million years old, it is a relatively young star, and its physical parameters—mass 2.6 times the Sun, radius 2.7 times the Sun, luminosity 65 times the Sun, and effective temperature 9,954 K—place it firmly among the intermediate-mass chemically peculiar stars that are key to understanding stellar magnetism and diffusion.

Did You Know?

• BP Boötis varies in brightness by only 0.02 magnitude over 1.3 days.
• The star was moved from Boötes to Quadrans Muralis and later back to Boötes.
• Its silicon distribution is depleted near the magnetic poles.