Astronomy:OU Andromedae

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Short description: Rotationally variable star in the constellation Andromeda
OU Andromedae
OUAndLightCurve.png
The light curve of an X-ray flare observed in 2001 by the Chandra X-ray Observatory is shown. This flare is believed to have been produced by a coronal mass ejection. (Adapted from Argiroffi et al., 2019[1])
Observation data
Equinox J2000.0]] (ICRS)
Constellation Andromeda
Right ascension  23h 49m 40.9598s[2]
Declination +36° 25′ 31.0082″[2]
Apparent magnitude (V) 5.87 - 5.94[3]
Characteristics
Spectral type G1 IIIe[4]
Apparent magnitude (G) 5.6187[2]
Apparent magnitude (J) 4.723[5]
Apparent magnitude (H) 4.208[5]
Apparent magnitude (K) 4.097[5]
B−V color index 0.79[4]
Variable type FK Com[3]
Astrometry
Radial velocity (Rv)−1.89±0.25[2] km/s
Proper motion (μ) RA: −0.858±0.094[2] mas/yr
Dec.: −47.402±0.078[2] mas/yr
Parallax (π)7.1692 ± 0.0677[2] mas
Distance455 ± 4 ly
(139 ± 1 pc)
Details[6]
Mass2.85 M☉
Radius9.46 R☉
Luminosity71.2 L☉
Surface gravity (log g)2.8 cgs
Temperature5,360 K
Metallicity [Fe/H]−0.07 dex
Rotation24.3 days
Rotational velocity (v sin i)21.5 km/s
Age645 – 891[7] Myr
Other designations
2MASS J23494097+3625309, FK5 3914, HIP 117503, SAO 73535, BD+35°5110, HR 9024, HD 223460, PPM 89159
Database references
SIMBADdata

OU Andromedae (also HR 9024) is a rotationally variable star in the constellation Andromeda. Varying between magnitudes 5.87 and 5.94, it has been classified as an FK Comae Berenices variable, but the classification is still uncertain. It has a spectral classification of G1IIIe, meaning that it is a giant star that shows emission lines in its spectrum.[3] It is also likely in its horizontal branch phase of evolution.[7]

In 1985, Jeffrey Hopkins et al. discovered that HR 9024 is a variable star, with a period of ~23.3 days.[8] It was given the variable star designation OU Andromedae in 1986.[9] Paola Testa et al. reported that the star showed X-ray flare activity, in 2007.[10]

Fast rotation

The spin rate of OU Andromedae is unusually high for an evolved star of this type, showing a projected rotational velocity of 21.5 km/s. One possible explanation is that it may have engulfed a nearby giant planet, such as a hot Jupiter, since an infrared excess has been observed.[4] Another explanation relies on its strong magnetic field; if OU Andromedae was an Ap star during its main sequence stage of evolution, it could have retained both the strong magnetic field and the fast rotation of Ap stars.[6]

X-ray source

OU Andromedae is a bright X-ray source, due to the activity of its corona; it's estimated that solar-like active regions cover 30% of the surface. This is another effect of the strong magnetic field, which produces an uninterrupted flaring activity that generates a large volume of hot plasma at coronal temperatures (~7.5×106 K).[11]

References

  1. ↑ Argiroffi, C.; Reale, F.; Drake, J. J.; Ciaravella, A.; Testa, P.; Bonito, R.; Miceli, M.; Orlando, S. et al. (August 2019). "A stellar flare-coronal mass ejection event revealed by X-ray plasma motions". Nature Astronomy 3: 742–748. doi:10.1038/s41550-019-0781-4. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  3. ↑ 3.0 3.1 3.2 "OU And database entry". Combined General Catalog of Variable Stars. CDS. http://webviz.u-strasbg.fr/viz-bin/VizieR-S?V*%20OU%20And. 
  4. ↑ 4.0 4.1 4.2 Rodrigues da Silva, R. et al. (March 2015). "On the Nature of Rapidly Rotating Single Evolved Stars". The Astrophysical Journal 801 (1): 6. doi:10.1088/0004-637X/801/1/54. 54. Bibcode: 2015ApJ...801...54R. 
  5. ↑ 5.0 5.1 5.2 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E. et al. (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. http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/246. 
  6. ↑ 6.0 6.1 Borisova, A.; Aurière, M.; Petit, P.; Konstantinova-Antova, R.; Charbonnel, C.; Drake, N. A. (June 2016). "The different origins of magnetic fields and activity in the Hertzsprung gap stars, OU Andromedae and 31 Comae". Astronomy & Astrophysics 591: 15. doi:10.1051/0004-6361/201526726. A57. Bibcode: 2016A&A...591A..57B. 
  7. ↑ 7.0 7.1 Stock, S.; Reffert, S.; Quirrenbach, A. (August 2018). "Precise radial velocities of giant stars. X. Bayesian stellar parameters and evolutionary stages for 372 giant stars from the Lick planet search". Astronomy & Astrophysics 616: 15. doi:10.1051/0004-6361/201833111. A33. Bibcode: 2018A&A...616A..33S. 
  8. ↑ Hopkins, J. L.; Boyd, L. J.; Genet, R. M.; Hall, D. S. (March 1985). "Discovery of Variability in HR 9024". Information Bulletin on Variable Stars 2684: 1. Bibcode: 1985IBVS.2684....1H. https://ibvs.konkoly.hu/pub/ibvs/2601/2684.pdf. Retrieved 7 February 2023. 
  9. ↑ Kholopov, P. N.; Samus, N. N.; Kazarovets, E. V.; Kireeva, N. N. (August 1987). "The 68th Name-List of Variable Stars". Information Bulletin on Variable Stars 3058: 1. Bibcode: 1987IBVS.3058....1K. https://ibvs.konkoly.hu/pub/ibvs/3001/3058.pdf. Retrieved 7 February 2023. 
  10. ↑ Testa, Paola; Reale, Fabio; Garcia-Alvarez, David; Huenemoerder, David P. (July 2007). "Detailed Diagnostics of an X-Ray Flare in the Single Giant HR 9024". The Astrophysical Journal 663 (2): 1232–1243. doi:10.1086/518241. Bibcode: 2007ApJ...663.1232T. https://iopscience.iop.org/article/10.1086/518241. Retrieved 7 February 2023. 
  11. ↑ Gondoin, P. (October 2003), "The corona of HD 223460 (HR 9024)", Astronomy and Astrophysics 409: 263–274, doi:10.1051/0004-6361:20030978, Bibcode: 2003A&A...409..263G 



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