63 Andromedae
A chemically peculiar variable star in Andromeda.
63 Andromedae, also known by its variable star designation PZ Andromedae, is a star in the constellation Andromeda that belongs to the Alpha2 Canum Venaticorum class of variables. Its apparent magnitude of roughly 5.6 makes it just visible to the naked eye. Parallax measurements place it about 382 light-years from Earth, based on an annual shift of 8.53 milliarcseconds.
The star is classified as spectral type B9VpSi, meaning it is a main-sequence star with a peculiar chemical composition—specifically, unusually strong silicon lines in its spectrum. Despite its B-type spectral class, it is considered an Ap star, a group known for intense spectral lines of certain heavy elements and powerful magnetic fields. These chemical oddities arise from atmospheric stratification caused by the star’s slow rotation.
63 Andromedae has about three times the Sun’s mass and 2.4 times its radius. It shines with 110 times the Sun’s luminosity, and its photosphere has an effective temperature of roughly 11,967 K.
Its brightness fluctuates by about 0.05 magnitudes over a period of 4.189 days, a variation thought to be linked to its rotation. This behavior defines it as an Alpha2 Canum Venaticorum variable, named after the first such star studied.
To the naked eye, 63 Andromedae appears as part of a faint, compact asterism alongside 64 and 65 Andromedae, which lie to the southwest and west. Together, these stars form a rectangular projection at the extreme edge of the constellation’s official boundaries. To the north, west, and east, the region corresponds to an arm or hand of Perseus—mythologically, Andromeda’s rescuer, who saved her from the sea monster, which forever retreats beyond Pisces and Cetus. The nearest star in the commonly drawn asterism representing the princess herself is 51 Andromedae, to the east. With an apparent magnitude of 3.57, it shines about two magnitudes—or 6.3 times—brighter than 63 Andromedae.
- Apparent magnitude
- about 5.6
- Distance
- 382 light years
- Spectral type
- B9VpSi
- Mass
- 3 times the Sun's mass
- Radius
- 2.4 times the Sun's radius
- Luminosity
- 110 times the Sun's luminosity
- Effective temperature
- 11,967 K
- Variation period
- 4.189 days
- Brightness variation
- 0.05 magnitudes
Lore & Background
63 Andromedae is an Alpha2 Canum Venaticorum variable star, a type named after the first example studied. Its spectral type is B9VpSi, indicating it is a chemically peculiar main sequence star with abnormally strong silicon lines. Although it has a B-type spectral class, it is known as an Ap star, a class of stars with very strong spectral lines of certain heavy elements and strong magnetic fields. The chemical peculiarities are caused by stratification in the atmosphere due to slow rotation.
The star varies in brightness by about 0.05 magnitudes with a period of 4.189 days, believed to occur as it rotates. To the naked eye, it figures as a faint, dense asterism with 64 and 65 Andromedae (southwest and west), which together justify a rectangular projection of the constellation. North, west and east are an arm/hand of Perseus, whose character is related in traditional mythology as Andromeda's saviour, saving her from the sea monster. The closest star in the asterisms commonly drawn up to represent the princess herself is 51 Andromedae, to the east, which shines at an apparent magnitude of 3.57, two magnitudes or 6.3 times brighter.
Reader's Guide
63 Andromedae is significant as an Alpha2 Canum Venaticorum variable star, a class characterized by brightness variations linked to rotation and chemical peculiarities. Its spectral type B9VpSi and classification as an Ap star highlight its strong magnetic fields and atmospheric stratification due to slow rotation, which produce abnormally strong silicon lines. With a mass three times that of the Sun and a radius 2.4 times larger, it radiates 110 times the Sun's luminosity at an effective temperature of 11,967 K. Its brightness variation of 0.05 magnitudes over 4.189 days is typical for this variable type. The star's location in the constellation Andromeda, forming a faint asterism with 64 and 65 Andromedae, and its mythological association with Perseus and the princess Andromeda, add to its contextual interest. At an apparent magnitude of about 5.6, it is visible to the naked eye under good conditions, and its distance of 382 light years is determined from an annual parallax shift of 8.53 mas.
Did You Know?
- It has a spectral type of B9VpSi, indicating abnormally strong silicon lines.
- The star has 3 times the mass of the Sun and 2.4 times the Sun's radius.
- Its variable star designation is PZ Andromedae.
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