BX Boötis
A magnetic CP star and Alpha² CVn variable in Boötes.
BX Boötis, a star in the northern constellation Boötes, sits near the threshold of naked-eye visibility with an apparent visual magnitude of 6.35. Parallax measurements place it roughly 512 light-years away, and interstellar dust dims its light by 0.13 magnitudes. The star is moving toward the Sun at a heliocentric radial velocity of −11 km/s.
Its variability was likely first noted by Gerhard Robert Miczaika, who reported in a 1954 IAU publication on photoelectric measurements of spectrum variables. He described a magnetic-field variable, HD 133129, as varying in magnitude with a small amplitude. However, a typographical error appears to have occurred: the star in question was actually HD 133029, not HD 133129. In 1972, Kukarkin and colleagues gave the star its variable-star designation, BX Boötis, citing Miczaika’s announcement.
BX Boötis is a magnetic CP star, classified as an A-type main-sequence star. Its spectrum shows very weak helium lines and strong overabundances of silicon and all heavier elements except nickel. It is an Alpha² Canum Venaticorum variable, with its magnitude fluctuating between 6.33 and 6.41 over a period of 2.88756 days.
The star is 235 million years old, with a projected rotational velocity of 30 km/s. It has 2.7 times the Sun’s mass and 2.5 times its radius. Its photosphere radiates about 72 times the Sun’s luminosity at an effective temperature of 9,164 K.
- Apparent visual magnitude
- 6.35 (nominal)
- Distance
- 512 light years
- Radial velocity
- −11 km/s
- Variability type
- Alpha² Canum Venaticorum
- Magnitude range
- 6.33 to 6.41
- Period
- 2.88756 days
- Spectral type
- A-type main-sequence star
- Mass
- 2.7 M☉
- Radius
- 2.5 R☉
- Luminosity
- 72 L☉
Lore & Background
The variability of BX Boötis was probably discovered by Gerhard Robert Miczaika, announced in a 1954 IAU publication discussing photo-electric measurements of spectrum variables. Miczaika wrote that 'The magnetic-field variable HD 133129 is likewise variable in magnitude with a small amplitude.' However, HD 133129 is not BX Boötis; HD 133029 is. Kukarkin et al. apparently concluded there was a typographical error in Miczaika's announcement, because they cited his 1954 announcement when they gave BX Boötis its variable star designation in 1972.
This is a magnetic CP star with a stellar classification indicating an A-type main-sequence star. Its spectrum shows very weak helium lines but strong overabundances of silicon and all heavier elements except nickel. It is classified as an Alpha² Canum Venaticorum variable, varying in magnitude from 6.33 to 6.41 over a period of 2.88756 days. The star is 235 million years old, with a projected rotational velocity of 30 km/s, and has 2.7 times the mass and 2.5 times the radius of the Sun, radiating about 72 times the Sun's luminosity at an effective temperature of 9,164 K.
Reader's Guide
BX Boötis is notable as a magnetic CP star and an Alpha² Canum Venaticorum variable, a class of stars that exhibit both photometric and spectral variations tied to strong magnetic fields and chemical peculiarities. Its discovery history involves a probable typographical error in the original announcement by Gerhard Robert Miczaika, where the star HD 133129 was mistakenly named instead of HD 133029; this confusion was later resolved by Kukarkin et al. when they assigned the variable star designation in 1972. The star's spectrum, with weak helium lines and strong overabundances of silicon and heavier elements except nickel, makes it a key example of chemically peculiar stars that inform models of atomic diffusion and magnetic field effects in stellar atmospheres. Its small-amplitude brightness variations over a 2.88756-day period, combined with a projected rotational velocity of 30 km/s, provide constraints on the geometry of its magnetic field and surface abundance patches. At a distance of about 512 light years and with an extinction of 0.13 magnitudes, it remains a useful target for studying the interplay between rotation, magnetism, and chemical anomalies in A-type stars.
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