AI Phoenicis

AI Phoenicis is a variable star in the constellation of Phoenix. An Algol-type eclipsing binary, its apparent magnitude is constant at 8.58 for most of the time, sharply dropping to 9.35 during primary eclipse and to 8.89 during secondary eclipse.[2] The system's variability was discovered by W. Strohmeier in 1972.[8] From parallax measurements by the Gaia spacecraft, the system is located at a distance of 560 light-years (171 parsecs) from Earth,[1] in agreement with earlier estimates based on its luminosity (173 ± 11 parsecs).[3]

AI Phoenicis
Observation data
Epoch J2000      Equinox J2000
Constellation Phoenix
Right ascension 01h 09m 34.19s[1]
Declination −46° 15′ 56.07″[1]
Apparent magnitude (V) 8.58 – 9.35[2]
Characteristics
Spectral type K0IV + F7V[3]
Variable type Algol[2]
Astrometry
Radial velocity (Rv)−0.750 ± 0.012[4] km/s
Proper motion (μ) RA: +56.27[1] mas/yr
Dec.: +0.70[1] mas/yr
Parallax (π)5.8336 ± 0.0262[1] mas
Distance559 ± 3 ly
(171.4 ± 0.8 pc)
Absolute magnitude (MV)A: 3.29 ± 0.17[3]
B: 3.06 ± 0.13[3]
Orbit
Period (P)24.592483 ± 0.000017 days[5]
Semi-major axis (a)47.855 ± 0.019 R☉[4]
Eccentricity (e)0.1821 ± 0.0051[5]
Inclination (i)88.502 ± 0.039[5]°
Argument of periastron (ω)
(secondary)		110.73 ± 0.78[5]°
Semi-amplitude (K1)
(primary)		51.16 ± 0.03[4] km/s
Semi-amplitude (K2)
(secondary)		49.11 ± 0.02[4] km/s
Details
Metallicity [Fe/H]−0.14 ± 0.1[6] dex
Age4.39 ± 0.32[5] Gyr
Primary
Mass1.2473 ± 0.0039[5] M☉
Radius2.912 ± 0.014[5] R☉
Luminosity4.86+0.52
−0.46[3] L☉
Surface gravity (log g)3.595 ± 0.014[3] cgs
Temperature5,010 ± 120[3] K
Rotational velocity (v sin i)6 ± 1[6] km/s
Secondary
Mass1.1973 ± 0.0037[5] M☉
Radius1.835 ± 0.014[5] R☉
Luminosity4.70+0.49
−0.44[3] L☉
Surface gravity (log g)3.996 ± 0.011[3] cgs
Temperature6,310 ± 150[3] K
Rotational velocity (v sin i)4 ± 1[6] km/s
Other designations
AI Phe, CD−46°322, HD 6980, HIP 5438, SAO 215389[7]
Database references
SIMBADdata

The primary star is a K-type subgiant with a spectral type of K0IV and an effective temperature of 5,000 K, while the secondary is an F-type main sequence star with a spectral type of F7V and a temperature of 6,300 K. The primary component, while visually fainter, is slightly more luminous than the secondary due to its higher infrared output.[3] The primary is at the end of its main sequence life and is likely in the short contraction phase known as a hook, where core hydrogen fusion has ceased but shell burning has not yet started, before ascending towards the red giant branch.[5] Photometric and spectroscopic observations have allowed the direct determination of the parameters of the stars with extreme precision, and this system is frequently used to test stellar evolution models.[6][3][5][9] The masses of the stars, 1.247 M☉ for the primary and 1.197 M☉ for the secondary, are known to a precision of just 0.3%, while the radii of 2.91 R☉ and 1.84 R☉ have uncertainties of 0.8% and 0.5% respectively.[5] Stellar evolution models show the stars have a common age of about 4.4 billion years.[5]

The orbit of AI Phoenicis has a period of 24.59248 days and a moderate eccentricity of 0.1821 ± 0.0051. The observation of eclipses is allowed by its 88.5° inclination to the plane of the sky. Times of minimum light show the orbital period of the system is not constant,[5] which can be caused by a third star in the system. An analysis of the alignment of the system by the Rossiter–McLaughlin effect suggests that the secondary star rotation axis is not aligned with the orbital axis, with an angle of 87 ± 17° between them, which also indicates interactions with a third star.[10]

Investigations continue with the TESS observatory in 2020. See Arxiv astro-ph.SR/ 2003.09295

References
  1. 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.
  2. Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  3. Torres, G.; Andersen, J.; Giménez, A. (2010). "Accurate masses and radii of normal stars: Modern results and applications". Astronomy and Astrophysics Review. 18 (1–2): 67–126. arXiv:0908.2624. Bibcode:2010A&ARv..18...67T. doi:10.1007/s00159-009-0025-1. S2CID 14006009.
  4. Hełminiak, K. G.; Konacki, M.; Ratajczak, M.; Muterspaugh, M. W. (2009). "Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue - I. A sample of systems with components' masses between 1 and 2 Msolar". Monthly Notices of the Royal Astronomical Society. 400 (2): 969. arXiv:0908.3471. Bibcode:2009MNRAS.400..969H. doi:10.1111/j.1365-2966.2009.15513.x. S2CID 16668225.
  5. Kirkby-Kent, J. A.; Maxted, P. F. L.; Serenelli, A. M.; Turner, O. D.; Evans, D. F.; Anderson, D. R.; Hellier, C.; West, R. G. (2016). "Absolute parameters for AI Phoenicis using WASP photometry". Astronomy and Astrophysics. 591: A124. arXiv:1605.07059. Bibcode:2016A&A...591A.124K. doi:10.1051/0004-6361/201628581. S2CID 56113989.
  6. Andersen, J.; Clausen, J. V.; Nordstrom, B.; Gustafsson, B.; Vandenberg, D. A. (1988). "Absolute dimensions of eclipsing binaries. XIII. AI Phoenicis : A casestudy in stellar evolution". Astronomy and Astrophysics. 196: 128. Bibcode:1988A&A...196..128A.
  7. "AI Phe". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 17 February 2019.
  8. Strohmeier, W. (1972). "Three New Bright Eclipsing Binaries". Information Bulletin on Variable Stars. 665: 1. Bibcode:1972IBVS..665....1S.
  9. Higl, J.; Weiss, A. (2017). "Testing stellar evolution models with detached eclipsing binaries". Astronomy and Astrophysics. 608: A62. Bibcode:2017A&A...608A..62H. doi:10.1051/0004-6361/201731008.
  10. Sybilski, P.; Pawłaszek, R. K.; Sybilska, A.; Konacki, M.; Hełminiak, K. G.; Kozłowski, S. K.; Ratajczak, M. (2018). "Tracking spin-axis orbital alignment in selected binary systems: The Torun Rossiter-McLaughlin effect survey". Monthly Notices of the Royal Astronomical Society. 478 (2): 1942. arXiv:1805.00520. Bibcode:2018MNRAS.478.1942S. doi:10.1093/mnras/sty1135. S2CID 119008317.
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