Iota Sagittarii

ι Sagittarii

Location of ι Sagittarii (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Sagittarius
Right ascension	19^h 55^m 15.69691^s[1]
Declination	−41° 52′ 05.8388″[1]
Apparent magnitude (V)	+4.118[2]
Characteristics
Spectral type	K0 II-III[3]
U−B color index	+0.911[2]
B−V color index	+1.084[2]
Astrometry
Radial velocity (Rv)	+35.8[3] km/s
Proper motion (μ)	RA: +22.61[1] mas/yr Dec.: +51.40[1] mas/yr
Parallax (π)	17.94 ± 0.21 mas[1]
Distance	182 ± 2 ly (55.7 ± 0.7 pc)
Absolute magnitude (MV)	+0.39[4]
Details
Mass	1.40[3] M☉
Radius	14[5] R☉
Luminosity	87[3] L☉
Surface gravity (log g)	1.89[6] cgs
Temperature	4,594±41[3] K
Metallicity [Fe/H]	−0.26[6] dex
Age	4.74[3] Gyr
Other designations
ι Sgr, CPD−42° 8944, FK5 1520, HD 188114, HIP 98032, HR 7581, SAO 229927[7]
Database references
SIMBAD	data

Iota Sagittarii (Iota Sgr, ι Sagittarii, ι Sgr) is a star in the zodiac constellation of Sagittarius. With an apparent visual magnitude of +4.118, it is bright enough to be viewed with the naked eye.[2] Based upon an annual parallax shift of 17.94 mas as seen from Earth,[1] this star is located 182 light years from the Sun. It is moving away from the Earth with a radial velocity of +35.8 km/s.[3]

This is a probable astrometric binary,[8] based upon proper motion data collected during the Hipparcos mission.[9] The visible component shows the spectrum of an evolved K-type giant or bright giant star with a stellar classification of K0 II-III.[3] The measured angular diameter, after correction for limb darkening, is 2.32±0.02 mas.[10] At an estimated distance of this star, this yields a physical size of about 14 times the radius of the Sun.[5] It has 1.4[3] times the mass of the Sun and is radiating 87[3] times the Sun's luminosity from its photosphere at an effective temperature of about 4,594 K.[3]

References

1. 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.
2. Cousins, A. W. J. (1973), "Revised zero points and UBV photometry of stars in the Harvard E and F regions", Memoirs of the Royal Astronomical Society, 77: 223–236, Bibcode:1973MmRAS..77..223C.
3. Luck, R. Earle (2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 88, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, S2CID 118505114.
4. 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.
5. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R_*) is given by:

   ${\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(55.7\cdot 2.32\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 27.8\cdot R_{\bigodot }\end{aligned}}}$

6. Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247, S2CID 118362423.
7. "iot Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-07.
8. 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.
9. Frankowski, A.; et al. (March 2007), "Proper-motion binaries in the Hipparcos catalogue. Comparison with radial velocity data", Astronomy and Astrophysics, 464 (1): 377–392, arXiv:astro-ph/0612449, Bibcode:2007A&A...464..377F, doi:10.1051/0004-6361:20065526, S2CID 14010423.
10. 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.