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ψ Phoenicis
	Location of ψ Phoenicis (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Phoenix
Right ascension	01h 53m 38.74103s
Declination	−46° 18′ 09.6048″
Apparent magnitude (V)	4.41 (4.3 - 4.5)
Characteristics
Evolutionary stage	asymptotic giant branch
Spectral type	M4III
U−B color index	+1.71
B−V color index	+1.59
Variable type	SR
Astrometry
Radial velocity (Rv)	+2.90 km/s
Proper motion (μ)	RA: -93.16 mas/yr ; Dec.: -91.17 mas/yr
Parallax (π)	9.54 ± 0.19 mas
Distance	342 ± 7 ly ; (105 ± 2 pc)
Absolute magnitude (MV)	−0.71
Details
Mass	1.3 ± 0.2 M☉
Radius	86 ± 3 R☉
Luminosity	1050+150; −140 L☉
Surface gravity (log g)	0.68+0.10; −0.11 cgs
Temperature	3,586 K
Metallicity [Fe/H]	−1.24 ± 0.39 dex
Rotational velocity (v sin i)	3.9 ± 0.9 km/s
Age	4.9 Gyr
Other designations
	CD−46°552, FK5 67, GC 2303, HIP 8837, HR 555, HD 11695, SAO 215696
Database references
SIMBAD	data

Psi Phoenicis (ψ Phoenicis) is a star in the constellation Phoenix. Its apparent magnitude varies from 4.3 to 4.5 with a period of about 30 days.^[3] It is visible to the naked eye. It is approximately 342 light years away based on parallax.^[1]

A light curve for Psi Phoenicis, plotted from *Hipparcos* data^[11]

Psi Phoenicis is a red giant in the asymptotic branch with a spectral type of M4III,^[4] indicating it is an evolved star in the last evolutionary stage before becoming a white dwarf. In 1973 astronomer Olin J. Eggen discovered it is a variable star, varying in magnitude between 4.3 and 4.5 with an approximate period of 30 days.^[12] A more recent study identified two possible periods of 43.7 and 48.1 days, with amplitudes of 0.038 and 0.023 magnitudes.^[13] The star is classified as a semiregular variable, of no specific subtype.^[3]

In 2001, Psi Phoenicis was observed by the VLT Interferometer with the test instrument VINCI. The observations, in combination with stellar atmospheric models, detected the limb darkening effect on the star's disk and found an angular diameter of 8.13±0.2 mas, corresponding to a stellar radius of 86±3 solar radii. From the radius and estimating an effective temperature of 3,550 K, a luminosity of 1,000 times the solar luminosity was calculated.^[7] A 2008 study reanalyzed the interferometric data with a new atmospheric model, finding an angular diameter of 10.15±0.15 mas and a radius of 85±1.6 R_☉.^[14]

By having directly measured distance, radius and luminosity, Psi Phoenicis was included in a list of 34 well characterized stars to be used as a reference. This program made the first measurement of the metallicity of Psi Phoenicis, showing it is a metal-poor star with only 5% the amount of iron of the Sun ([Fe/H] = −1.24±0.39). This value has a large uncertainty due to the difficulties in modeling the spectra of cool stars, which have strong molecular absorption. The evolutionary state and poorly constrained metallicity result in an uncertain mass of 1.0±0.4 M_☉.^[9]^[15] Assuming a metallicity closer to solar, a mass of 1.3±0.2 M_☉ is derived.^[7]

Psi Phoenicis is considered a single star, and has no known companions.^[7]^[16] It has been considered a possible spectroscopic binary, including in the Hipparcos Catalogue, which stems from spectroscopic observations in 1919 which showed a possibly variable radial velocity. More recent data, however, showed the velocity to be constant.^[7]

References

^ ^a ^b ^c ^d ^e ^f 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
^ ^a ^b ^c 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.
^ ^a ^b ^c ^d 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.
^ ^a ^b Eggen, Olin J. (July 1992), "Asymptotic giant branch stars near the sun", Astronomical Journal, 104 (1): 275–313, Bibcode:1992AJ....104..275E, doi:10.1086/116239.
^ ^a ^b Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644. Vizier catalog entry
^ Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
^ ^a ^b ^c ^d ^e ^f ^g ^h Wittkowski, M.; Aufdenberg, J. P.; Kervella, P. (2004). "Tests of stellar model atmospheres by optical interferometry. VLTI/VINCI limb-darkening measurements of the M4 giant ψ Phe". Astronomy and Astrophysics. 413 (2): 711–723. arXiv:astro-ph/0310128. Bibcode:2004A&A...413..711W. doi:10.1051/0004-6361:20034149. S2CID 18340833.
^ ^a ^b Schonrich, R.; Bergemann, M. (2014). "Fundamental stellar parameters and metallicities from Bayesian spectroscopy: Application to low- and high-resolution spectra". Monthly Notices of the Royal Astronomical Society. 443 (1): 698. arXiv:1311.5558. Bibcode:2014MNRAS.443..698S. doi:10.1093/mnras/stu1072. S2CID 118335709.
^ ^a ^b Jofré, P.; Heiter, U.; Soubiran, C.; Blanco-Cuaresma, S.; Worley, C. C.; Pancino, E.; Cantat-Gaudin, T.; Magrini, L.; Bergemann, M.; González Hernández, J. I.; Hill, V.; Lardo, C.; De Laverny, P.; Lind, K.; Masseron, T.; Montes, D.; Mucciarelli, A.; Nordlander, T.; Recio Blanco, A.; Sobeck, J.; Sordo, R.; Sousa, S. G.; Tabernero, H.; Vallenari, A.; Van Eck, S. (2014). "Gaia FGK benchmark stars: Metallicity". Astronomy and Astrophysics. 564: A133. arXiv:1309.1099. Bibcode:2014A&A...564A.133J. doi:10.1051/0004-6361/201322440. S2CID 119241541.
^ Zamanov, R. K.; et al. (October 2008), "Rotational velocities of the giants in symbiotic stars - III. Evidence of fast rotation in S-type symbiotics", Monthly Notices of the Royal Astronomical Society, 390 (1): 377–382, arXiv:0807.3817, Bibcode:2008MNRAS.390..377Z, doi:10.1111/j.1365-2966.2008.13751.x, S2CID 118697261.
^ "/ftp/cats/more/HIP/cdroms/cats". Centre de Données astronomiques de Strasbourg. Strasbourg astronomical Data Center. Retrieved 15 October 2022.
^ Eggen, O. J. (1973), "The classification of intrinsic variables. IV. Very-small-amplitude, very-short-period red variables", Astrophysical Journal, 184: 793, Bibcode:1973ApJ...184..793E, doi:10.1086/152371.
^ Tabur, V.; et al. (December 2009), "Long-term photometry and periods for 261 nearby pulsating M giants", Monthly Notices of the Royal Astronomical Society, 400 (4): 1945–1961, arXiv:0908.3228, Bibcode:2009MNRAS.400.1945T, doi:10.1111/j.1365-2966.2009.15588.x, S2CID 15358380.
^ Neilson, Hilding R.; Lester, John B. (2008). "Determining parameters of cool giant stars by modeling spectrophotometric and interferometric observations using the SAtlas program". Astronomy and Astrophysics. 490 (2): 807–10. arXiv:0809.1875. Bibcode:2008A&A...490..807N. doi:10.1051/0004-6361:200810627. S2CID 1586125.
^ Heiter, U.; Jofré, P.; Gustafsson, B.; Korn, A. J.; Soubiran, C.; Thévenin, F. (2015), "Gaia FGK benchmark stars: Effective temperatures and surface gravities", Astronomy & Astrophysics, 582: A49, arXiv:1506.06095, Bibcode:2015A&A...582A..49H, doi:10.1051/0004-6361/201526319, S2CID 53391939.
^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.