# 13 Sagittae

13 Sagittae
Observation data
Epoch J2000      Equinox J2000
Constellation Sagitta
Right ascension 20h 00m 03.30846s[1]
Declination +17° 30′ 59.4373″[1]
5.33[2]
Characteristics
Spectral type M4 III[2]
B−V color index 1.576±0.010[3]
Variable type semiregular[4]
Astrometry
Proper motion (μ) RA: +49.424[1] mas/yr
Dec.: +2.738[1] mas/yr
Parallax (π)5.94 ± 0.36[1] mas
Distance550 ± 30 ly
(170 ± 10 pc)
Absolute magnitude (MV)−2.12[3]
Details
Luminosity2173.57[3] L
Surface gravity (log g)3.00[7] cgs
Temperature3,844±251[8] K
Other designations
13 Sge, VZ Sge, BD+17° 4183, HD 189577, HIP 98438, HR 7645, SAO 105522, WDS J20001+1731C[9]
Database references

13 Sagittae is a single[10] star in the northern constellation of Sagitta. The designation comes from the star catalogue of John Flamsteed, first published in 1712. It can be viewed with the naked eye, having an apparent visual magnitude of 5.33.[2] Based upon an annual parallax shift of 5.94 mas as seen from Earth's orbit, it is located at a distance of around 170 parsecs (550 ly). It is moving closer to the Sun with a heliocentric radial velocity of −17.56 km/s.[5]

Pulsation Cycles[2]
Period
(days)
Amplitude
(magnitude)
36.5 0.082
39.2 0.043
51.4 0.031
65.2 0.030

This is an evolved red giant with a stellar classification of M4 III[2] – a star that has used up its core hydrogen and has expanded – and is currently on the asymptotic giant branch.[7] Classified as a semiregular variable and given the variable star designation VZ Sagittae, it varies between apparent magnitudes 5.27 and 5.57.[4] The measured angular diameter, after correction for limb darkening, is 3.3±1.1 mas.[11] At its estimated distance, this yields a physical size of about 60 times the radius of the Sun.[6]

There is a magnitude 9.96 companion located at an angular separation of 112.6 arcseconds along a position angle of 297°, as of 2013.[12] Designated HD 351107, this is a class F0 star.[13]

## References

1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
2. 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:. Bibcode:2009MNRAS.400.1945T. doi:10.1111/j.1365-2966.2009.15588.x.
3. ^ a b c Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
4. ^ a b VSX (25 August 2009). "VZ Sagittae". AAVSO Website. American Association of Variable Star Observers. Retrieved 4 January 2015.
5. ^ a b Famaey, B.; et al. (January 2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters". Astronomy and Astrophysics. 430: 165–186. arXiv:. Bibcode:2005A&A...430..165F. doi:10.1051/0004-6361:20041272.
6. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
{\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(168.4\cdot 3.3\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 119.5\cdot R_{\bigodot }\end{aligned}}}
7. ^ a b Ortiz, Roberto; Guerrero, Martín A. (2016). "Ultraviolet emission from main-sequence companions of AGB stars". Monthly Notices of the Royal Astronomical Society. 461 (3): 3036. arXiv:. Bibcode:2016MNRAS.461.3036O. doi:10.1093/mnras/stw1547.
8. ^ Soubiran, C.; et al. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247
9. ^ "13 Sge". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-02-28.
10. ^ 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:. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
11. ^ 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
12. ^ Mason, B. D.; et al. (2014), The Washington Visual Double Star Catalog, Bibcode:2001AJ....122.3466M, doi:10.1086/323920
13. ^ Nesterov, V. V.; et al. (1995). "The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars". Astronomy and Astrophysics. 110. Bibcode:1995A&AS..110..367N.