Phi Persei

Phi Persei (Phi Per, φ Persei, φ Per) is a class B2Vep fourth-magnitude star in the constellation Perseus, location about 720 light-years from Earth.

φ Persei
Location of φ Persei (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Perseus
Right ascension 01h 43m 39.63792s[1]
Declination 50° 41′ 19.4328″[1]
Apparent magnitude (V) 4.06[2] (3.96 - 4.11[3])
Characteristics
Spectral type B2Vep[4] + sdO[5]
U−B color index −0.92[2]
B−V color index −0.04[2]
Variable type γ Cas[3]
Astrometry
Radial velocity (Rv)+0.80[6] km/s
Proper motion (μ) RA: +24.59[1] mas/yr
Dec.: −14.01[1] mas/yr
Parallax (π)4.54 ± 0.20 mas[1]
Distance720 ± 30 ly
(220 ± 10 pc)
Absolute magnitude (MV)−3.11[7]
Orbit[7][8]
Period (P)126.6731 days
Semi-major axis (a)5.89 mas
Inclination (i)77.6°
Longitude of the node (Ω)295.7°
Periastron epoch (T)2456110.03
Semi-amplitude (K1)
(primary)		9.97 km/s
Semi-amplitude (K2)
(secondary)		81.3 km/s
Details
A
Mass9.6[9] M☉
Radius5.5 - 8.0[7] R☉
Luminosity14,454[9] L☉
Surface gravity (log g)4.46[10] cgs
Temperature29,300[9] K
Rotational velocity (v sin i)440[10] km/s
B
Mass1.14[11] M☉
Radius1.3[11] R☉
Luminosity6,310[9] L☉
Surface gravity (log g)4.2[9] cgs
Temperature53,000[11] K
Age57±9[9] Myr
Other designations
φ Persei, φ Per, Phi Per, 54 Andromedae, BD+49°444, FK5 57, GC 2102, HD 10516, HIP 8068, HR 496, PPM 26670, SAO 22554
Database references
SIMBADdata

System
φ Persei in optical light

Phi Persei is spectroscopic binary consisting of a blue main sequence primary of class B2 and a hot subdwarf secondary. The two stars have an orbit of 217 days and are separated by about 200 R☉.[9] Phi Persei is a runaway star and extrapolating its space velocity backwards by the modelled age of the system (57 million years) places it within the Alpha Persei cluster.[5]

The primary star rotates rapidly with a projected equatorial velocity of 440 km/s. Due to its rapid rotation, the primary star has a polar radius about 5.5 R☉ and an equatorial radius of about 8.0 R☉. With an effective temperature of nearly 30,000 K, it has a bolometric luminosity nearly 15,000 times higher than the Sun. The rapidly-spinning star is surrounded by a circumstellar disk. The binary orbit, the spin of the primary star, and the disk are all seen nearly edge-on. There are no eclipses, but models of the system show that the disk significantly obscures the primary star.[5] The primary formed as a 3.8 M☉ star and has accreted material from its companion.[9]

The secondary star is also a class O subdwarf, hotter than the primary but smaller and less massive. It is proposed that it is the core of a 7 M☉ star, with the outer layers stripped as it expanded away from the main sequence. Its luminosity is higher than expected for a normal 1.2 M☉ helium star, which suggests it may have evolved to helium shell burning.[9] Although the subdwarf has a bolometric luminosity about half that of the primary, it emits most of its radiation as ultraviolet, being only about 3% as bright as the primary at visible wavelengths.[5]

Variability
A blue-light light curve for Phi Persei, adapted from Božić et al. (1995)[12]

Phi Persei is a variable star with both rapid and longterm variations in its brightness and spectrum. Variations occur on a daily timescale which may be related to the rotation of the primary star. Any variations originating with the secondary are difficult to detect due to its comparative faintness. Slower variations, including deep fades, are also seen. Some of the variations may correspond to the orbital period, possibly eclipses of gas streams or hot spots, but the occasional deep fades do not match any particular orbital phase. The variations are classified as γ Cassiopeiae-type, shell stars with eruptions and irregular fading.[12]

Naming

Flamsteed followed Ptolemy in treating φ Persei as being in Andromeda and gave it the designation 54 Andromedae. It is isolated from the main stars of Perseus, but lies within its formal borders.[13]

In Chinese, 天大將軍 (Tiān Dà Jiāng Jūn), meaning Heaven's Great General, refers to an asterism consisting of φ Persei, γ Andromedae, 51 Andromedae, 49 Andromedae, χ Andromedae, υ Andromedae, τ Andromedae, 56 Andromedae, β Trianguli, γ Trianguli and δ Trianguli. Consequently, the Chinese name for φ Persei itself is 天大將軍二 (Tiān Dà Jiāng Jūn èr, English: the Second Star of Heaven's Great General.).[14]

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Vizier catalog entry
  2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. 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.
  4. Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.
  5. Mourard, D.; Monnier, J. D.; Meilland, A.; Gies, D.; Millour, F.; Benisty, M.; Che, X.; Grundstrom, E. D.; Ligi, R.; Schaefer, G.; Baron, F.; Kraus, S.; Zhao, M.; Pedretti, E.; Berio, P.; Clausse, J. M.; Nardetto, N.; Perraut, K.; Spang, A.; Stee, P.; Tallon-Bosc, I.; McAlister, H.; Ten Brummelaar, T.; Ridgway, S. T.; Sturmann, J.; Sturmann, L.; Turner, N.; Farrington, C. (2015). "Spectral and spatial imaging of the Be+sdO binary ϕ Persei". Astronomy & Astrophysics. 577: A51. arXiv:1503.03423. Bibcode:2015A&A...577A..51M. doi:10.1051/0004-6361/201425141. S2CID 16766856.
  6. Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication. Carnegie Institution for Science. Bibcode:1953GCRV..C......0W. LCCN 54001336.
  7. Gies, Douglas R.; Bagnuolo, William G.; Ferrara, Elizabeth C.; Kaye, Anthony B.; Thaller, Michelle L.; Penny, Laura R.; Peters, Geraldine J. (1998). "Hubble Space Telescope Goddard High Resolution Spectrograph Observations of the Be + sdO Binary φ Persei". The Astrophysical Journal. 493 (1): 440–450. Bibcode:1998ApJ...493..440G. doi:10.1086/305113. S2CID 121635926.
  8. "Sixth Catalog of Orbits of Visual Binary Stars". Archived from the original on 1 August 2017. Retrieved 29 December 2016.
  9. Schootemeijer, A.; Götberg, Y.; De Mink, S. E.; Gies, D.; Zapartas, E. (2018). "Clues about the scarcity of stripped-envelope stars from the evolutionary state of the sdO+Be binary system φ Persei". Astronomy and Astrophysics. 615: A30. arXiv:1803.02379. Bibcode:2018A&A...615A..30S. doi:10.1051/0004-6361/201731194. S2CID 59471417.
  10. Zorec, J.; Frémat, Y.; Domiciano De Souza, A.; Royer, F.; Cidale, L.; Hubert, A.-M.; Semaan, T.; Martayan, C.; Cochetti, Y. R.; Arias, M. L.; Aidelman, Y.; Stee, P. (2017). "Critical study of the distribution of rotational velocities of Be stars". Astronomy & Astrophysics. 595: A132. arXiv:1702.07684. Bibcode:2016A&A...595A.132Z. doi:10.1051/0004-6361/201628760.
  11. Krtička, J.; Kubát, J.; Krtičková, I. (2016). "Stellar wind models of subluminous hot stars". Astronomy & Astrophysics. 593: A101. arXiv:1607.04445. Bibcode:2016A&A...593A.101K. doi:10.1051/0004-6361/201628433. S2CID 118390374.
  12. Božić, H.; Harmanec, P.; Horn, J.; Koubský, P.; Scholz, G.; McDavid, D.; Hubert, A. M.; Hubert, H. (December 1995). "Toward a consistent model of the B0.5IVe + sdO binary φ Persei". Astronomy and Astrophysics. 304: 235–257.
  13. Wagman, M. (August 1987). "Flamsteed's Missing Stars". Journal for the History of Astronomy. 18 (3): 212. Bibcode:1987JHA....18..209W. doi:10.1177/002182868701800305. S2CID 118445625.
  14. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 10 日
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