Alpha Tucanae

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<tr><th style="background-color: #FFFFC0; text-align: center;" colspan="2">Astrometry</th></tr></th></tr><tr><th colspan="2" style="text-align: center"></tr><tr style="vertical-align:top;"><td>Radial velocity (Rv)</td><td>+45.8[4] km/s</td></tr><tr style="vertical-align:top;"><td>Proper motion (μ)</td><td> RA: −70.72[1] mas/yr
Dec.: −39.44[1] mas/yr </td></tr><tr style="vertical-align:top;"><td>Parallax (π)</td><td>16.33 ± 0.59[1]mas</td></tr><tr style="vertical-align:top;"><td>Distance</td><td>200 ± 7 ly
(61 ± 2 pc)</td></tr><tr><th colspan="2" style="text-align: center"></th></tr> <tr><td style="background-color: #FFFFC0;" colspan="2" align=center>Orbit[5]</td></tr><tr valign=baseline><td>Period (P)</td><td>4197.7 days</td></tr><tr valign=baseline><td>Eccentricity (e)</td><td>0.39</td></tr><tr valign=baseline><td>Periastron epoch (T)</td><td>18666.4</td></tr><tr valign=baseline><td>Argument of periastron (ω)
(secondary)</td><td>48.5°</td></tr><tr valign=baseline><td>Semi-amplitude(K1)
(primary)</td><td>7.2 km/s</tr> <tr><th style="background-color: #FFFFC0; text-align: center;" colspan="2">Other designations</th></tr><tr><td colspan="2">
CP−60 7561, FK5 841, HD 211416, HIP 110130, HR 8502, SAO 255193.[6]
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Alpha Tucanae <tr><td colspan="2" style="text-align:center;">

Location of α Tucanae (circled)
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Observation data
Epoch J2000      Equinox J2000
Constellation Tucana
Right ascension 22h 18m 30.09478s[1]
Declination –60° 15′ 34.5263″[1]
Apparent magnitude (V) 2.86[2]
Characteristics
Spectral type K3 III[3]
U−B color index +1.54[2]
B−V color index +1.39[2]

Alpha Tucanae (α Tuc, α Tucanae) is a binary star system in the southern circumpolar constellation of Tucana. With an apparent visual magnitude of 2.86,[2] it can be seen with the naked eye from the southern hemisphere. Using parallax measurements, the distance to this system can be estimated as 200 light-years (61 parsecs).[1] A cool star with a surface temperature of 4300 K, it is 424 times as luminous as the sun and 37 times its diameter. It is 2.5 to 3 times as massive. It is unclear what stage of evolution the star is in.[7]

This is a spectroscopic binary, which means that the two stars have not been individually resolved using a telescope, but the presence of the companion has been inferred from measuring changes in the spectrum of the primary. The orbital period of the binary system is 4197.7 days (11.5 years).[5] The primary component has a stellar classification of K3 III,[3] which indicates it is a giant star that has exhausted the supply of hydrogen at its core and evolved away from the main sequence. It has the characteristic orange hue of a K-type star.

References

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