HD 224801

HD 224801, also known as CG Andromedae, is an Alpha² Canum Venaticorum variable star in the constellation Andromeda. Located approximately 188 parsecs (610 ly) away, the star varies between apparent magnitudes 6.32 and 6.42 over a period of approximately 3.74 days.

HD 224801
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension  00h 00m 43.6346s[1]
Declination +45° 15′ 12.00222″[1]
Apparent magnitude (V) 6.32 – 6.42[2]
Characteristics
Spectral type A0IIspSiSrHg[3]
Apparent magnitude (B) 6.299[4]
Apparent magnitude (V) 6.347[4]
Apparent magnitude (G) 6.3299[1]
Apparent magnitude (J) 6.407[5]
Apparent magnitude (H) 6.506[5]
Apparent magnitude (K) 6.511[5]
U−B color index -0.35[6]
B−V color index -0.0425[4]
Variable type Alpha² CVn[7]
Astrometry
Radial velocity (Rv)−1.00±2.2[8] km/s
Proper motion (μ) RA: 17.683±0.099[1] mas/yr
Dec.: 0.919±0.065[1] mas/yr
Parallax (π)5.3162 ± 0.0768[1] mas
Distance614 ± 9 ly
(188 ± 3 pc)
Details
Temperature11,000[3] K
Rotational velocity (v sin i)30[6] km/s
Other designations
CG Andromedae, BD+44° 4538, HIP 63, HR 9080, SAO 53568, TYC 3246-2388-1.
Database references
SIMBADdata

Spectrum

CG Andromedae is also a chemically peculiar star with a strong magnetic field, or Ap star, with a spectral type A0IIspSiSrHg. This means that it's a bright giant star that shows narrow absorption lines and unusual strong lines of silicium, strontium and mercury. Calcium and manganese lines are weaker than expected instead.[3] Other sources report that the stronger lines are of silicium and europium, thus giving a spectral classification B9pSiEu, which has just a slightly different temperature for the blackbody emission in addition to the different lines.[2]

Variability

Like in Alpha² Canum Venaticorum variable stars, CG Andromedae shows a variation of luminosity and one in the strength of spectral lines with the same period of approximately 3.74 days.[7] It is thought that this is caused by an inhomogeneous distribution of elements on the surface of the star, which cause an inhomogeneous surface brightness.

A shorter period, slightly longer than 2 hours, with an amplitude of 0.011 magnitudes has been observed in the light curve of CG Andromedae; however, with a temperature of 11,000 K, it lies outside the instability strip of the HR diagram where rapidly oscillating Ap stars are located. Magnetohydrodynamic waves propagating in the star could explain the observed variability.[3]

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References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. CG And, database entry, Combined General Catalog of Variable Stars (GCVS4.2, 2004 Ed.), N. N. Samus, O. V. Durlevich, et al., CDS ID II/250 Accessed on line 2018-10-17.
  3. Abt, H. A.; Morrell, N. A. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". Astrophysical Journal Supplement. 99: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.
  4. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000), "The Tycho-2 catalogue of the 2.5 million brightest stars", Astronomy & Astrophysics, 355: L27–L30, Bibcode:2000A&A...355L..27H.
  5. Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; et al. (June 2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues (2246): II/246. Bibcode:2003yCat.2246....0C.
  6. Renson, P.; Manfroid, J. (2009). "Catalogue of Ap, HgMn and Am stars". Astronomy and Astrophysics. 498 (3): 961–966. Bibcode:2009A&A...498..961R. doi:10.1051/0004-6361/200810788.
  7. VSX (4 January 2010). "CG Andromedae". AAVSO Website. American Association of Variable Star Observers. Retrieved 9 October 2014.
  8. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
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