Phi Draconis

Phi Draconis (φ Dra / φ Draconis) is a fourth-magnitude variable star in the constellation Draco. It has the Flamsteed designation 43 Draconis. It is also a triple star system where the brightest component is a chemically peculiar Ap star.

φ Draconis
Location of φ Draconis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension  18h 20m 45.43224s[1]
Declination 71° 20′ 16.1499″[1]
Apparent magnitude (V) 4.2004[1]
Characteristics
Spectral type B8VpSi[2]
U−B color index -0.38[3]
B−V color index -0.10[3]
Variable type α² CVn[4]
Astrometry
Radial velocity (Rv)-16 [5] km/s
Proper motion (μ) RA: -5.03[1] mas/yr
Dec.: 37.86[1] mas/yr
Parallax (π)10.77 ± 0.38[1] mas
Distance300 ± 10 ly
(93 ± 3 pc)
Absolute magnitude (MV)−0.74 (−0.48/+0.94)[6]
Orbit[6]
PrimaryA
CompanionB
Period (P)307.8 yr
Semi-major axis (a)0.965"
(89.60 au)
Eccentricity (e)0.752
Inclination (i)95.6°
Orbit[6]
PrimaryAa
CompanionAb
Period (P)127.9902 d
Eccentricity (e)0.707
Inclination (i)~50°
Semi-amplitude (K1)
(primary)		29.0 km/s
Details
Aa
Mass3.3[6] M☉
Radius2.7 ± 0.2[7] R☉
Luminosity107[7] L☉
Surface gravity (log g)4.21 ± 0.08[7] cgs
Temperature11,429[7] K
Rotation1.71649[7]
Age245[6] Myr
B
Mass2.93[6] M☉
Age330[6] Myr
Other designations
φ Dra, 43 Dra, BD 71° 889, CCDM J18208+7120AB, GC 25114, HD 170000, HIP 89908, HR 6920, SAO 9084
Database references
SIMBADdata

The brightness of φ Draconis varies by about 0.04 magnitudes every 1.7 days. This is due to very strong magnetic fields at the surface of the star, and it is classified as an α² Canum Venaticorum variable.[4]

φ Draconis is a multiple star system containing three stars. The inner pair form a single-lined spectroscopic binary in an eccentric 128-day orbit. The outer star orbits the inner pair every 308 years. The outer pair can be resolved visually and have a semi-major axis of 0.752″.[6]

φ Draconis Aa is a main sequence Ap star with a spectral class of B8. The main abundance excess is silicon, although iron and chromium and also notably elevated.[8]

In Chinese astronomy, Phi Draconis is called 柱史, Pinyin: Zhùshǐ, meaning Official of Royal Archives, because this star is marking itself and stand alone in Official of Royal Archives asterism, Purple Forbidden enclosure (see : Chinese constellation).[9]

References
  1. van Leeuwen, F. (November 2007). "Hipparcos, the New Reduction" (VizieR). Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Retrieved 2010-11-22.
  2. Gray, R. O.; Corbally, C. J. (2014). "An Expert Computer Program for Classifying Stars on the MK Spectral Classification System". The Astronomical Journal. 147 (4): 80. Bibcode:2014AJ....147...80G. doi:10.1088/0004-6256/147/4/80.
  3. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. (PDF) origin: SIMBAD: 0. Bibcode:1986EgUBV........0M.
  4. 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. Bibcode:2009yCat....102025S.
  5. Evans, D. S. (1967). "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and Their Applications. 30: 57. Bibcode:1967IAUS...30...57E.
  6. Liška, J. (2016). "Analysis of the multiple system with chemically peculiar component φ Draconis". Monthly Notices of the Royal Astronomical Society. 461 (1): 939. Bibcode:2016MNRAS.461..939L. doi:10.1093/mnras/stw1355.
  7. North, P. (June 1998), "Do SI stars undergo any rotational braking?", Astronomy and Astrophysics, 334: 181–187, arXiv:astro-ph/9802286, Bibcode:1998A&A...334..181N
  8. Prvák, M.; Liška, J.; Krtička, J.; Mikulášek, Z.; Lüftinger, T. (2015). "Modelling of variability of the chemically peculiar star ϕ Draconis". Astronomy and Astrophysics. 584: A17. Bibcode:2015A&A...584A..17P. doi:10.1051/0004-6361/201526647.
  9. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 10 日

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