KK Andromedae
A faint variable star in Andromeda with rapid rotation and chemical peculiarity.
KK Andromedae (also cataloged as HD 9531) is a star in the northern constellation Andromeda. It belongs to a class of variables known as Alpha² Canum Venaticorum stars, which are chemically peculiar and show tiny brightness changes linked to their rotation. With an apparent visual magnitude of 5.90, it is just barely visible to the naked eye under clear, dark skies. Its brightness fluctuates by 0.012 magnitude over a period of 0.66 days.
Parallax measurements place this star about 437 light-years from the Sun. Interstellar dust dims its light by 0.26 magnitudes at that distance. Cowley and colleagues classified it as B9 IV in 1969, meaning it is a B-type subgiant that has exhausted the hydrogen in its core and is now expanding. Although cataloged as an Ap star with an abnormally high silicon abundance, it is actually a helium-weak chemically peculiar star.
KK Andromedae has a mass just over three times that of the Sun and a radius about 2.7 times larger. Its estimated age is 225 million years. It spins rapidly, with a projected rotational velocity of 163 km/s and a rotation period of just 16 hours. The star radiates 91 times the Sun’s luminosity from its photosphere, which has an effective temperature of 11,729 K.
- Apparent visual magnitude
- 5.90
- Variable type
- Alpha2 Canum Venaticorum
- Brightness variation
- 0.012 magnitude every 0.66 days
- Distance
- 437 light years (parallax 7.5 mas)
- Stellar classification
- B9 IV (subgiant)
- Mass
- 3.0 solar masses
- Radius
- 2.7 solar radii
- Luminosity
- 91 solar luminosities
- Effective temperature
- 11,729 K
- Projected rotational velocity
- 163 km/s
Lore & Background
KK Andromedae is a B-type subgiant star that has exhausted the hydrogen in its core and is expanding. It is catalogued as an Ap star with abnormal silicon abundance, but has been reported to actually be a helium-weak chemically peculiar star. The star spins rapidly, with a projected rotational velocity of 163 km/s and a rotation period of just 16 hours.
Its brightness varies by only 0.012 magnitude every 0.66 days, typical of Alpha2 Canum Venaticorum variables, which are thought to have surface spots of enhanced chemical elements that modulate the star's light as it rotates. The star's light is diminished by interstellar dust extinction of 0.26 magnitude.
At an estimated age of 225 million years, KK Andromedae has just over three times the Sun's mass and about 2.7 times its radius. It radiates 91 times the Sun's luminosity from its photosphere at an effective temperature of 11,729 K.
Reader's Guide
KK Andromedae is a relatively faint variable star near the limit of naked-eye visibility, with an apparent magnitude of 5.90. Its classification as an Alpha2 Canum Venaticorum variable places it among a group of chemically peculiar stars whose brightness changes are linked to rotation and surface abundance patches. The star's reported status as a helium-weak chemically peculiar star, rather than a standard silicon Ap star, highlights the ongoing complexity in classifying such objects. Its rapid rotation (163 km/s, 16-hour period) and subgiant evolutionary stage (B9 IV) provide insight into the behavior of intermediate-mass stars as they leave the main sequence. The measured parallax of 7.5 mas yields a distance of about 437 light-years, and the interstellar extinction of 0.26 magnitude is a typical correction for stars at that distance in the galactic plane. The star's age of 225 million years and its physical parameters (mass 3.0 M☉, radius 2.7 R☉, luminosity 91 L☉, temperature 11,729 K) offer a consistent picture of a moderately massive star in the late stages of core hydrogen burning or early post-main-sequence evolution.
Did You Know?
- KK Andromedae varies in brightness by only 0.012 magnitude every 0.66 days.
- It is a helium-weak chemically peculiar star, despite being catalogued as an Ap star with abnormal silicon.
- The star rotates once every 16 hours, with a projected rotational velocity of 163 km/s.
- Its light is dimmed by interstellar dust by 0.26 magnitude.
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