Delta Coronae Borealis

Delta Coronae Borealis, Latinized from δ Coronae Borealis, is a variable star in the constellation Corona Borealis. Its apparent magnitude varies regularly between apparent magnitude 4.57 and 4.69, and it is around 170 light-years distant.

δ Coronae Borealis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Corona Borealis
Right ascension  15h 49m 35.64682s[1]
Declination +26° 04′ 06.2065″[1]
Apparent magnitude (V) 4.57 - 4.69[2]
Characteristics
Spectral type G5III-IV Fe-1[3]
U−B color index +0.32[4]
B−V color index +0.78[4]
Variable type RS CVn?[2]
Astrometry
Radial velocity (Rv)−20.356±0.035[5] km/s
Proper motion (μ) RA: -78.83[1] mas/yr
Dec.: -65.28[1] mas/yr
Parallax (π)19.7137 ± 0.1820[6] mas
Distance165 ± 2 ly
(50.7 ± 0.5 pc)
Absolute magnitude (MV)+1.18[7]
Details
Mass2.4[8] M☉
Radius7.4[8] R☉
Luminosity34.3[8] L☉
Surface gravity (log g)3.29[7] cgs
Temperature5,180[8] K
Metallicity [Fe/H]−0.12[7] dex
Rotation59[8] days
Rotational velocity (v sin i)4.56[7] km/s
Age851[7] Myr
Other designations
δ CrB, 10 Coronae Borealis, BD+26° 2737, HD 141714, HIP 77512, HR 5889, SAO 84019[9]
Database references
SIMBADdata

δ Coronae Borealis is a yellow giant star of spectral type G3.5III that is around 2.4 times as massive as the Sun and has swollen to 7.4 times its radius. It has a surface temperature of 5180 K.[10] For most of its existence, Delta Coronae Borealis was a blue-white main sequence star of spectral type B before it ran out of hydrogen fuel in its core. Its luminosity and spectrum suggest it has just crossed the Hertzsprung gap, having finished burning core hydrogen and just begun burning hydrogen in its shell. It is a strong source of X-rays due to its hot corona.[11]

In 1989, it was noticed that the brightness of δ Coronae Borealis is not constant. Approximately every 45 days, its brightness changes sinusoidally between 4.57 and 4.69, too small to be noticed without close monitoring. The evolutionary state of the star and its probably rotation period mean that the variations may be due to its rotation with different parts of the surface having spots or different temperatures. This would make it an RS Canum Venaticorum variable.[12] The period has since been refined to 59 days and this is now accepted as the star's rotation period.[8]

References
  1. van Leeuwen, F. (2007). "Validation of the New Hipparcos Reduction". Astronomy and Astrophysics. 474 (2): 653–64. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1: B/gcvs. Bibcode:2009yCat....102025S.
  3. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins Catalog of Revised MK Types for the Cooler Stars". The Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  4. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data., 0 (1986): 0. Bibcode:1986EgUBV........0M.
  5. Niedzielski, A.; Deka-Szymankiewicz, B.; Adamczyk, M.; Adamów, M.; Nowak, G.; Wolszczan, A. (2016). "The Penn State - Toruń Centre for Astronomy Planet Search stars". Astronomy and Astrophysics. 585: A73. Bibcode:2016A&A...585A..73N. doi:10.1051/0004-6361/201527362.
  6. 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.
  7. Niedzielski, A.; Deka-Szymankiewicz, B.; Adamczyk, M.; Adamów, M.; Nowak, G.; Wolszczan, A. (2016). "The Penn State - Toruń Centre for Astronomy Planet Search stars". Astronomy and Astrophysics. 585: A73. Bibcode:2016A&A...585A..73N. doi:10.1051/0004-6361/201527362.
  8. Gondoin, P. (2005). "The X-ray activity of the slowly rotating G giant δ CrB". Astronomy and Astrophysics. 431 (3): 1027–1035. Bibcode:2005A&A...431.1027G. doi:10.1051/0004-6361:20041991.
  9. "del CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 25 February 2017.
  10. Gondoin, P. (2005). "The X-ray activity of the slowly rotating G giant δ CrB". Astronomy & Astrophysics. 431 (3): 1027–35. Bibcode:2005A&A...431.1027G. doi:10.1051/0004-6361:20041991.
  11. Kaler, James B. "Delta Coronae Borealis". Stars. University of Illinois. Retrieved 21 November 2014.
  12. Fernie, J. D. (1987). "Delta Coronae Borealis : A chromospherically active giant ?". Publications of the Astronomical Society of the Pacific. 99: 183. Bibcode:1987PASP...99..183F. doi:10.1086/131975.
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