Phi Phoenicis,Latinized from φ Phoenicis, is abinary star[3] system in the southernconstellation ofPhoenix. It is faintly visible to the naked eye with anapparent visual magnitude of 5.1.[2] Based upon an annualparallax shift of10.185 mas as seen from Earth,[1] it is located approximately 320 light years from theSun. It is moving away with a heliocentricradial velocity of10.4 km/s.[5]
The primary component is aB-type main-sequence star with astellar classification of B9 V.[4] It is a type ofchemically peculiar star known as anHgMn star, which means it shows surface overabundances of certain elements including mercury and manganese, and deficiencies in others including helium, cobalt.[8] The star has about three[3] times themass of the Sun and is radiating 87[6] times theSun's luminosity from itsphotosphere at aneffective temperature of about10,500 K.[6]
The reconstruction of the surface of Phi Phoenicis byDoppler imaging showed it to be heterogeneous with regions of different elemental abundances. In particular, the star formsspots with high or low abundances of yttrium, strontium, titanium, and chromium. The comparison of the abundance maps in different epochs revealed that the spot configurations vary on monthly or yearly time scales.[8][5] The spectral lines of the irregularly distributed elements show variations that allowed a precise rotation period of 9.53 days to be determined, and also show evidence of long term abundance changes. The analysis of the spots suggests that the rotation axis is inclined to the line of sight by an angle of about 53°, and shows evidence of very weakdifferential rotation.[5] The starspots probably cause milimagnitude variations in the brightness of Phi Phoenicis, even though there are no precise observations to confirm this.[9]
The origin of the starspots and chemical anomalies in HgMn stars is uncertain and has generated controversy. Typically, such as forAp and Bp stars, inhomogeneously distributed elements are attributed to be large-scale organizedmagnetic fields, but there are not conclusive detection of magnetic fields in HgMn stars. In 2012, a study claimed to have detected a weak magnetic field in Phi Phoenicis correlated with the spots,[4] but this has been contested.[6][10] It is believed that diffusion processes in the atmosphere may be related to the chemical anomalies, but this does not explain quantitatively the observed variations.[6]
Phi Phoenicis is a single-linedspectroscopic binary with aperiod of 1126 days and aneccentricity of 0.59. There is no evidence for additional stars in the system, but in the past this has been considered a triple system, due to the detection of the wrong spectroscopic period.[3]
The variability of theradial velocity of Phi Phoenicis was discovered in the first spectroscopic observations of the star in 1911,[11] and was confirmed in 1982, but the data were still inclusive and no orbit was determined.[12] The first orbital solution was finally published in 1999, yielding a period of 41.4 days.[13] At the same time, in 1997, theHipparcos Catalogue was published revealing Phi Phoenicis to be anastrometric binary with an estimated period of 878 days (circular orbit solution). Thus Phi Phoenicis became a triple star system, with a visible star, a spectroscopic companion, and an astrometric companion.[14] A 2013 study, with new high-resolution radial velocity data from the FEROS,HARPS andCORALIE spectrographs, showed that the period of the spectroscopic orbit is actually closer to 1126 days, and not 41.4 days;[5] this indicates that the spectroscopic companion is the same one that the astrometric data detected. In the same year another study fitted the astrometric data to the spectroscopic orbit, revealing the orbitalinclination of the system and allowing to estimate the properties of the secondary star.[3]
The orbit of the system is highly eccentricity and is seen almost side-on, with an inclination of 93 ± 4.7°. The high uncertainty means that the occurrence ofeclipses is possible, despite being unlikely. From this inclination and assuming a mass of 3.0 M☉ for the primary, thebinary mass function can be used to calculate a mass of 0.91 M☉ for the secondary. The secondary star is assumed to be ayellow dwarf with an effective temperature around5,500 K, and is 5.7 visual magnitudes fainter than the primary. The average separation between the two star is estimated at around3.4 AU.[3]
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