Phi Draconis

φ Draconis
	Location of φ Draconis (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Draco
Right ascension	18h 20m 45.43224s
Declination	71° 20′ 16.1499″
Apparent magnitude (V)	4.2004
Characteristics
Spectral type	B8VpSi + A4V + B9V
U−B color index	−0.38
B−V color index	−0.10
Variable type	α2 CVn
Astrometry
Radial velocity (Rv)	-16 km/s
Proper motion (μ)	RA: -5.03 mas/yr ; Dec.: 37.86 mas/yr
Parallax (π)	10.77 ± 0.38 mas
Distance	300 ± 10 ly ; (93 ± 3 pc)
Absolute magnitude (MV)	−0.74 (−0.48/+0.94)
Orbit
Primary	A
Companion	B
Period (P)	307.8 yr
Semi-major axis (a)	0.965"; (89.60 au)
Eccentricity (e)	0.752
Inclination (i)	95.6°
Orbit
Primary	Aa
Companion	Ab
Period (P)	127.9902 d
Eccentricity (e)	0.707
Inclination (i)	~50°
Semi-amplitude (K1); (primary)	29.0 km/s
Details
Aa
Mass	3.3 M☉
Radius	2.7 ± 0.2 R☉
Luminosity	107 L☉
Surface gravity (log g)	4.21 ± 0.08 cgs
Temperature	11,429 K
Rotation	1.71649
Age	245 Myr
B
Mass	2.93 M☉
Age	330 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
SIMBAD	data

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.

The brightness of φ Draconis varies by about 0.04 of a magnitude 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.^[5]

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 outermost star orbits the inner pair every 308 years. The outer pair can be resolved visually and have a semi-major axis of 0.752″.^[3]

Phi 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, φ 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 constellations).^[9]

References[]

^ ^a ^b ^c ^d ^e ^f 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. S2CID 18759600. Retrieved 2010-11-22.
^ 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.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Liška, J. (2016). "Analysis of the multiple system with chemically peculiar component φ Draconis". Monthly Notices of the Royal Astronomical Society. 461 (1): 939–947. arXiv:1606.01333. Bibcode:2016MNRAS.461..939L. doi:10.1093/mnras/stw1355.
^ ^a ^b 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.
^ ^a ^b 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.
^ 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.
^ ^a ^b ^c ^d ^e 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
^ 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. arXiv:1510.01192. Bibcode:2015A&A...584A..17P. doi:10.1051/0004-6361/201526647.
^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 10 日

External links[]

Jim Kaler's Stars, University of Illinois: PHI DRA (Phi Draconis)
An Atlas of the Universe: Multiple Star Orbits

Coordinates: 18^h 20^m 45.43^s, +71° 20′ 16.13″

[LEEUWEN-1] ^ ^a ^b ^c ^d ^e ^f 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. S2CID 18759600. Retrieved 2010-11-22.

[mk-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.

[liska-3] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Liška, J. (2016). "Analysis of the multiple system with chemically peculiar component φ Draconis". Monthly Notices of the Royal Astronomical Society. 461 (1): 939–947. arXiv:1606.01333. Bibcode:2016MNRAS.461..939L. doi:10.1093/mnras/stw1355.

[MERMILLIOD-4] 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.

[gcvs-5] 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.

[rv-6] 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.

[aaa334_181-7] 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

[prvak-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. arXiv:1510.01192. 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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Observation data Epoch J2000 Equinox J2000
Location of φ Draconis (circled)
Constellation	Draco
Right ascension	18^h 20^m 45.43224^s^[1]
Declination	71° 20′ 16.1499″^[1]
Apparent magnitude (V)	4.2004^[1]
Characteristics
Spectral type	B8VpSi^[2] + A4V + B9V^[3]
U−B color index	−0.38^[4]
B−V color index	−0.10^[4]
Variable type	α² CVn^[5]
Astrometry

Radial velocity (R_v)	-16^[6] 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
Distance	300 ± 10 ly (93 ± 3 pc)
Absolute magnitude (M_V)	−0.74 (−0.48/+0.94)^[3]

Orbit^[3]
Primary	A
Companion	B
Period (P)	307.8 yr
Semi-major axis (a)	0.965" (89.60 au)
Eccentricity (e)	0.752
Inclination (i)	95.6°
Orbit^[3]
Primary	Aa
Companion	Ab
Period (P)	127.9902 d
Eccentricity (e)	0.707
Inclination (i)	~50°
Semi-amplitude (K₁) (primary)	29.0 km/s
Details
Aa
Mass	3.3^[3] `M`_☉
Radius	2.7 ± 0.2^[7] `R`_☉
Luminosity	107^[7] `L`_☉
Surface gravity (log g)	4.21 ± 0.08^[7] cgs
Temperature	11,429^[7] K
Rotation	1.71649^[7]
Age	245^[3] Myr
B
Mass	2.93^[3] `M`_☉
Age	330^[3] 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
SIMBAD	data