HD 224801
An Alpha2 Canum Venaticorum variable star in Andromeda.
HD 224801, also called CG Andromedae, is a variable star of the Alpha2 Canum Venaticorum type, located in the constellation Andromeda. It lies about 188 parsecs (610 light-years) from Earth, and its apparent brightness shifts between magnitudes 6.32 and 6.42 over a cycle of roughly 3.74 days.
This star is a chemically peculiar Ap star with a strong magnetic field. Its spectral type is given as A0IIspSiSrHg, meaning it is a bright giant with narrow absorption lines and unusually strong lines of silicon, strontium, and mercury, while calcium and manganese lines are weaker than expected. Other sources classify it as B9pSiEu, noting strong lines of silicon and europium, which implies a slightly different blackbody temperature.
The variability of CG Andromedae was first detected in 1951 and announced by Sanford S. Provin in 1953. Like other Alpha2 Canum Venaticorum variables, it shows changes in both luminosity and spectral line strength, both with the same 3.74-day period. This is thought to result from an uneven distribution of elements across the star’s surface, causing patchy surface brightness. A shorter variation, just over two hours long and with an amplitude of 0.011 magnitudes, has also been observed in its light curve. However, with a temperature of 11,000 K, the star lies outside the instability strip where rapidly oscillating Ap stars are usually found. Magnetohydrodynamic waves traveling through the star may explain this short-period variability.
- Constellation
- Andromeda
- Distance
- approximately 188 parsecs (610 ly)
- Apparent magnitude range
- 6.32 to 6.42
- Variability period
- approximately 3.74 days
- Spectral type
- A0IIspSiSrHg (also reported as B9pSiEu)
- Temperature
- 11,000 K
Lore & Background
CG Andromedae's variability was detected in 1951 and announced by Sanford S. Provin in 1953. Like other Alpha2 Canum Venaticorum variables, it shows a variation of luminosity and a variation in the strength of spectral lines with the same period of approximately 3.74 days. This is thought to be caused by an inhomogeneous distribution of elements on the star's surface, leading to an inhomogeneous surface brightness.
The star is also a chemically peculiar Ap star with a strong magnetic field. Its spectral type is given as A0IIspSiSrHg, indicating a bright giant with narrow absorption lines and unusually strong lines of silicon, strontium, and mercury, while calcium and manganese lines are weaker than expected. Other sources report stronger lines of silicon and europium, giving a spectral classification B9pSiEu, which implies a slightly different temperature for the blackbody emission.
A shorter period, slightly longer than 2 hours, with an amplitude of 0.011 magnitudes has been observed in the light curve. However, with a temperature of 11,000 K, the star lies outside the instability strip where rapidly oscillating Ap stars are located. Magnetohydrodynamic waves propagating in the star could explain this observed variability.
Reader's Guide
CG Andromedae serves as an example of an Alpha2 Canum Venaticorum variable, a class of stars whose variability is linked to chemical peculiarities and strong magnetic fields. The star's approximately 3.74-day period, observed in both brightness and spectral line strength, supports the model of an inhomogeneous surface element distribution causing uneven brightness. Its dual spectral classifications (A0IIspSiSrHg and B9pSiEu) reflect ongoing uncertainty in its precise temperature and chemical makeup, with different sources emphasizing different strong lines (silicon, strontium, mercury versus silicon and europium). The detection of a shorter, 2-hour period with a small amplitude of 0.011 magnitudes is notable because the star's temperature of 11,000 K places it outside the typical instability strip for rapidly oscillating Ap stars, suggesting that magnetohydrodynamic waves, rather than pulsation, may drive this rapid variability. This makes CG Andromedae a valuable object for studying the interplay between magnetic fields, chemical spots, and non-pulsational oscillations in chemically peculiar stars.
Did You Know?
- CG Andromedae varies between apparent magnitudes 6.32 and 6.42 over approximately 3.74 days.
- The star has a spectral type reported as both A0IIspSiSrHg and B9pSiEu, reflecting different chemical line strengths.
Frequently Asked Questions
What is HD 224801 and where can I find it in the sky?
HD 224801, also catalogued as CG Andromedae, is a pulsating variable star located in the constellation Andromeda. It is a member of the Alpha2 Canum Venaticorum family, a group of chemically peculiar stars that dim and brighten in a regular rhythm.
How does HD 224801's brightness change and how long is its cycle?
The star's apparent magnitude swings between 6.32 and 6.42 as it pulses, completing one full cycle in roughly 3.74 days. That narrow range makes it a subtle target for dedicated visual or photometric monitoring rather than casual stargazing.
How far away is HD 224801 from Earth?
It sits approximately 188 parsecs, or about 610 light-years, from our solar system. At that distance and with a peak magnitude near 6.4, it is at the very limit of naked-eye visibility under ideal dark-sky conditions.
What makes HD 224801's chemical composition unusual?
Its spectral label A0IIspSiSrHg flags anomalously strong absorption lines of silicon, strontium, and mercury, while calcium and manganese lines are weaker than a normal A-type giant would show. The star also hosts a strong magnetic field, a hallmark of chemically peculiar Ap stars.
What is HD 224801's temperature and luminosity class?
The star radiates at an effective temperature of roughly 11,000 kelvin and carries a luminosity class II, marking it as a bright giant rather than a main-sequence star. Some catalogues alternatively list its spectrum as B9pSiEu, reflecting the difficulty of pinning down its exact classification given the peculiar line strengths.
More in Variable Stars, Part 2 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced