21 Canum Venaticorum
A faint white-hued variable star in Canes Venatici.
BK Canum Venaticorum, also known by its Flamsteed designation 21 Canum Venaticorum, is a single variable star in the northern constellation Canes Venatici. Located about 279 light-years from the Sun, it appears to the naked eye as a faint white-hued point of light with a baseline apparent visual magnitude of +5.14. This star is classified as an Alpha2 Canum Venaticorum type variable, with its brightness fluctuating by 0.04 magnitudes over a 0.767-day period. Its variability was first noted in 1984 by Juraj Zverko, and it received its variable star designation in 1987.
The star is a B-type subgiant, according to Garrison et al. (1994), with a stellar classification that includes the suffix notation for a Silicon star. However, Cowley et al. (1969) listed it as an A-type main-sequence star, with a colon indicating some uncertainty. It is a marginally chemically-peculiar star, showing weaker than normal helium absorption lines and helium line variability. The widths of the lines of ionized silicon vary with a period of 0.88 days. With an estimated age of around 201 million years, 21 Canum Venaticorum spins at a relatively high projected rotational velocity of 96 km/s. It has 2.73 times the mass of the Sun and 2.8 times its radius, radiating 72 times the Sun’s luminosity from its photosphere at an effective temperature of 11,036 K.
- Distance
- 279 light years
- Apparent magnitude
- +5.14
- Spectral type
- B-type subgiant (Garrison et al. 1994); A-type main-sequence with uncertainty (Cowley et al. 1969)
- Variable star designation
- BK Canum Venaticorum
- Variable type
- Alpha2 Canum Venaticorum
- Brightness variation
- 0.04 magnitudes over 0.767 days
- Age
- 201 million years
Lore & Background
21 Canum Venaticorum is classified as an Alpha2 Canum Venaticorum type variable star, and its brightness varies by 0.04 magnitudes over a period of 0.767 days. Its variability was discovered in 1984 by Juraj Zverko and it was given its variable star designation in 1987. The star is a marginally chemically-peculiar star with weaker than normal helium absorption lines and displaying helium line variability. The widths of the lines of ionized silicon vary with a period of 0.88.
Reader's Guide
21 Canum Venaticorum is notable as a chemically peculiar star of the Alpha2 Canum Venaticorum type, a class of variables that exhibit strong magnetic fields and abundance anomalies. Its variability, discovered in 1984, adds to the understanding of such stars, which are important for studying stellar magnetism and chemical diffusion processes. The star's spectral classification shows some uncertainty, with one source listing it as a B-type subgiant and another as an A-type main-sequence star, reflecting the challenges in classifying chemically peculiar objects. Its helium line variability and varying silicon line widths provide clues to the inhomogeneous distribution of elements on its surface, likely driven by its magnetic field. With a relatively high projected rotational velocity of 96 km/s and an age of 201 million years, it represents a moderately young star that has not yet evolved far from the main sequence. The star's brightness variation of only 0.04 magnitudes makes it a subtle variable, detectable only through precise photometry.
More in Variable Stars, Part 5 1-24
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