Orange-hued giant star in the constellation Sagittarius
τ Sagittarii Location of τ Sagittarii (circled)
Observation dataEpoch J2000.0 Equinox J2000.0 Constellation Sagittarius Right ascension 19h 06m 56.40897s [ 1] Declination −27° 40′ 13.5189″[ 1] Apparent magnitude (V)+3.326[ 2] Characteristics Evolutionary stage red clump [ 3] Spectral type K1 III[ 4] U−Bcolor index +1.185[ 2] B−Vcolor index +1.170[ 2] Astrometry Radial velocity (Rv )+45.4[ 5] km/s Proper motion (μ)RA: −50.61[ 1] mas /yr Dec.: −249.80[ 1] mas /yr Parallax (π)28.3195± 0.3134 mas [ 6] Distance 115 ± 1 ly pc ) Absolute magnitude (MV )0.48[ 7] Details[ 8] Mass 1.25 M ☉ Radius 15.71 R ☉ Luminosity 87.6 L ☉ Surface gravity (log g )2.15 cgs Temperature 4,459 K Metallicity [Fe/H] −0.27 dex Rotational velocity (v sin i )1.04[ 9] Age 7.91 Gyr Other designations Namalsadirah 2, Rabi al Sadira, τ Sagittarii, τ Sgr, Tau Sgr, 40 Sagittarii,CPD −27°6617,FK5 1496,GC 26291,HD 177716,HIP 93864,HR 7234,PPM 269078,SAO 187683 Database references SIMBAD data
Tau Sagittarii (Tau Sgr ,τ Sagittarii ,τ Sgr ) is astar in the southernzodiac constellation ofSagittarius .
With anapparent visual magnitude of +3.3,[ 2] light-years (37parsecs ), based uponparallax measurements.[ 1]
This is aspectral type K1giant star with about 1.25 M ☉ . The stellar envelope is slightly cooler than the Sun with aneffective temperature of 4,459 K, giving the star a light orange color. Theinterferometry -measuredangular diameter of this star, after correcting forlimb darkening , is3.93 ± 0.04mas ,[ 10] radius of the Sun .[ 11]
τ Sagittarii is a suspected double star although no companion has been confirmed yet. A lower metal content (Fe to H ratio is 54% lower than the sun's) and a highpeculiar velocity (64 km/s, four times the local average) relative to the Sun suggest the star is a visitor from a different part of the Galaxy.[ 12]
τ Sagittarii is ared clump giant, a star with a similar mass to the sun which has exhausted its core hydrogen, passed through thered giant branch , and started helium fusion in its core.[ 3]
τ Sagittarii is the closest constellational star (a star that is part of the traditional outline of a constellation) to the origin of the 1977Wow! signal .[ 13]
The star forms part of simpleasterisms :γ Sgr ,τ Sgr ,δ Sgr ,ε Sgr ,ζ Sgr ,λ Sgr ,σ Sgr andφ Sgr — theTeapot [ 14] φ Sgr ,τ Sgr ,ζ Sgr ,χ Sgr (double) andσ Sgr —the Returning Ostriches ; in ArabicAl Naʽām al Ṣādirah often transliterated asNamalsadirah (النعم السادرة).[ 15] ν Sgr ,τ Sgr ,ψ Sgr ,ω Sgr ,60 Sgr andζ Sgr ,Al Udḥiyy —the Ostrich's Nest .[ 15] In the entirely separateChinese tradition —斗 Dǒu Dipper φ Sgr ,λ Sgr ,μ Sgr ,σ Sgr andζ Sgr . The star itself is斗宿五 Dǒu Xiù wǔ the Dipper's fifth star ).[ 17] ^a b c d e van Leeuwen, F. (November 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 ^a b c d Celis S., L. (October 1975), "Photoelectric photometry of late-type variable stars",Astronomy and Astrophysics Supplement Series ,22 :9– 17,Bibcode :1975A&AS...22....9C ^a b Alves, David R. (2000). "K-Band Calibration of the Red Clump Luminosity".The Astrophysical Journal .539 (2):732– 741.arXiv :astro-ph/0003329 Bibcode :2000ApJ...539..732A .doi :10.1086/309278 .S2CID 16673121 . ^ Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample",The Astronomical Journal 132 (1):161– 170,arXiv :astro-ph/0603770 Bibcode :2006AJ....132..161G ,doi :10.1086/504637 ,S2CID 119476992 ^ Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities".Carnegie Institute Washington D.C. Publication . Carnegie Institute of Washington D.C.Bibcode :1953GCRV..C......0W . ^ Brown, A. G. A. ; et al. (Gaia collaboration) (2021)."Gaia Early Data Release 3: Summary of the contents and survey properties" .Astronomy & Astrophysics 649 : A1.arXiv :2012.01533 Bibcode :2021A&A...649A...1G .doi :10.1051/0004-6361/202039657 S2CID 227254300 . (Erratum: doi :10.1051/0004-6361/202039657e ) . Gaia EDR3 record for this source atVizieR .^ Cardini, D. (January 2005), "Mg II chromospheric radiative loss rates in cool active and quiet stars",Astronomy and Astrophysics ,430 :303– 311,arXiv :astro-ph/0409683 Bibcode :2005A&A...430..303C ,doi :10.1051/0004-6361:20041440 ,S2CID 12136256 . ^ Reffert, Sabine; et al. (2015). "Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity".Astronomy & Astrophysics .574 : A116.arXiv :1412.4634 Bibcode :2015A&A...574A.116R .doi :10.1051/0004-6361/201322360 .hdl :10722/215277 .S2CID 59334290 . ^ Hekker, S.; Meléndez, J. (2007). "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters".Astronomy and Astrophysics .475 (3): 1003.arXiv :0709.1145 Bibcode :2007A&A...475.1003H .doi :10.1051/0004-6361:20078233 .S2CID 10436552 . ^ Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements",Astronomy and Astrophysics ,431 (2):773– 777,Bibcode :2005A&A...431..773R ,doi :10.1051/0004-6361:20042039 ^ Lang, Kenneth R. (2006),Astrophysical formulae Birkhäuser ,ISBN 3-540-29692-1 * ) is given by:2 ⋅ R ∗ = ( 10 − 3 ⋅ 37 ⋅ 3.93 ) AU 0.0046491 AU / R ⨀ ≈ 31.3 ⋅ R ⨀ {\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(10^{-3}\cdot 37\cdot 3.93)\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 31.3\cdot R_{\bigodot }\end{aligned}}} ^ "The Teapot: A Guide to Deep Sky Objects in Sagittarius – Constellation Guide" .www.constellation-guide.com . Retrieved2023-02-09 .^ "The world's biggest mysteries scientists still can't solve" . 2 September 2014. Archived fromthe original on 8 November 2015. Retrieved11 September 2015 .^ "Teapot" . constellation-guide.com. Retrieved2017-05-13 .^a b Allen, R. H. (1963).Star Names: Their Lore and Meaning 355 .ISBN 0-486-21079-0 . Retrieved2012-09-04 .{{cite book }}:ISBN / Date incompatibility (help ) ^ Jack W. Rhoads -Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars , Jet Propulsion Laboratory, California Institute of Technology; November 15, 1971 ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日 Archived 2011-05-22 at theWayback Machine
