X Sagittarii

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X Sagittarii
Sagittarius constellation map.svg
Red circle.svg
Location of X Sagittarii (circled)
Observation data
Epoch J2000       Equinox J2000
Constellation Sagittarius
Right ascension 17h 47m 33.62410s [1]
Declination −27° 49′ 50.8490″ [1]
Apparent magnitude  (V)4.54 [2]
Characteristics
Spectral type F7II [3]
U−B color index +0.50 [2]
B−V color index +0.80 [2]
Variable type Cepheid [4]
Astrometry
Radial velocity (Rv)−10.10 [5]  km/s
Proper motion (μ)RA: −5.097 [1]   mas/yr
Dec.: −9.722 [1]   mas/yr
Parallax (π)3.4314 ± 0.2020  mas [1]
Distance 950 ± 60  ly
(290 ± 20  pc)
Absolute magnitude  (MV)−2.85 [6]
Details
Mass 6.31 [7]   M☉
Radius 53±3 [8]   R☉
Luminosity 2,647 [7]   L☉
Surface gravity (log g)1.77 [9]   cgs
Temperature 6,305 [7]   K
Metallicity [Fe/H]−0.01 [6]   dex
Rotational velocity (v sin i)27.1 [10]  km/s
Other designations
3 Sagittarii, X Sgr, CD−27°11930, FK5  1464, GC  24135, HD  161592, HIP  87072, HR  6616, SAO  185755, GSC  06836-00118 [11]
Database references
SIMBAD data

X Sagittarii is a variable star and candidate binary star system in the southern constellation of Sagittarius, near the western constellation boundary with Ophiuchus. It has a yellow-white hue and is visible to the naked eye with an apparent visual magnitude that fluctuates around 4.54. [2] The star is located at a distance of approximately 950  light years from the Sun based on parallax, [1] and is drifting closer with a radial velocity of −10 km/s. [5] The star has an absolute magnitude of around −2.85. [6]

A visual band light curve for X Sagittarii, plotted from ASAS data XSgrLightCurve.png
A visual band light curve for X Sagittarii, plotted from ASAS data

This is an F-type bright giant with a stellar classification of F7II. [3] It is a Classical Cepheid variable that ranges in apparent magnitude from 4.20 down to 4.90 with a period of 7.01283 days. [13] Its variation in brightness is accompanied by a change in spectral classification, from G2 to F5. [4] The amplitude of each pulsation causes the stellar radius to vary by ~9%. [14] Analysis of the spectra suggest there are two shock waves per pulsation period, with complicated patterns appearing in the metallic lines. [15] The star is surrounded by an optically-thin circumstellar envelope at 15–20 stellar radii, which appears as an infrared excess of 13.3%. [16] This may be composed of amorphous carbon. [14]

László Szabados suggested in 1990 that this might be a binary system with a period of 507 days. A detection of this projected companion was reported in 2013 using the VLTI/AMBER instrument. However, the object was at the detection limit of the instrument, showing an angular separation of 10.7  mas from the primary and a magnitude difference of 5.6 in the K-band. [8] A subsequent optical search reported a failure to detect the companion in 2014, excluding companions brighter than a A-type main-sequence star class of A9V. [17] The estimated mass of this object is 0.2–0.3  M☉ . [15]

Related Research Articles

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<span class="mw-page-title-main">43 Sagittarii</span> Star in the constellation of Sagittarius

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<span class="mw-page-title-main">R Muscae</span> Variable star in the constellation Musca

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<span class="mw-page-title-main">U Sagittarii</span> Star in the constellation Sagittarius

U Sagittarii is a variable star in the southern constellation of Sagittarius, abbreviated U Sgr. It is a classical Cepheid variable that ranges in brightness from an apparent visual magnitude of 6.28 down to 7.15, with a pulsation period of 6.745226 days. At its brightest, this star is dimly visible to the naked eye. The distance to this star is approximately 2,080 light years based on parallax measurements, and it is drifting further away with a radial velocity of 2 km/s.

References

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  2. 1 2 3 4 Ducati, J. R. (2002). "Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. 1 2 Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1982mcts.book.....H
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  5. 1 2 Kharchenko, N. V.; et al. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv: 0705.0878 . Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. S2CID   119323941.
  6. 1 2 3 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. Vizier catalog entry
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  8. 1 2 Li Causi, G.; et al. (January 2013). "On the binarity of the classical Cepheid X Sagittarii from interferometric observations". Astronomy & Astrophysics. 549: 5. arXiv: 1211.4698 . Bibcode:2013A&A...549A..64L. doi:10.1051/0004-6361/201220207. S2CID   54805744. A64.
  9. ↑ Soubiran, Caroline; Le Campion, Jean-François; Brouillet, Nathalie; Chemin, Laurent (2016). "The PASTEL catalogue: 2016 version". Astronomy & Astrophysics. 591: A118. arXiv: 1605.07384 . Bibcode:2016A&A...591A.118S. doi:10.1051/0004-6361/201628497. S2CID   119258214.
  10. ↑ De Medeiros, J. R.; Mayor, M. (1999). "A catalog of rotational and radial velocities for evolved stars". Astronomy and Astrophysics Supplement Series. 139 (3): 433. arXiv: astro-ph/0608248 . Bibcode:1999A&AS..139..433D. doi:10.1051/aas:1999401. Vizier catalog entry
  11. ↑ "X Sgr". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2020-12-01.
  12. ↑ "ASAS All Star Catalogue". The All Sky Automated Survey. Retrieved 8 December 2021.
  13. ↑ Samus, N. N.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID   125853869.
  14. 1 2 Gallenne, A.; et al. (February 2012). "Thermal infrared properties of classical and type II Cepheids. Diffraction limited 10 μm imaging with VLT/VISIR". Astronomy & Astrophysics. 538: 16. arXiv: 1111.7215 . Bibcode:2012A&A...538A..24G. doi:10.1051/0004-6361/201117307. S2CID   118585523. A24.
  15. 1 2 Mathias, P.; et al. (October 2006). "Multiple shock waves in the atmosphere of the Cepheid X Sagittarii?". Astronomy and Astrophysics. 457 (2): 575–579. Bibcode:2006A&A...457..575M. doi: 10.1051/0004-6361:20065299 .
  16. ↑ Gallenne, A.; et al. (October 2013). "Extended envelopes around Galactic Cepheids. IV. T Monocerotis and X Sagittarii from mid-infrared interferometry with VLTI/MIDI". Astronomy & Astrophysics. 558: 9. arXiv: 1309.0854 . Bibcode:2013A&A...558A.140G. doi:10.1051/0004-6361/201322257. S2CID   118837854. A140.
  17. ↑ Gallenne, A.; et al. (July 2014). "Searching for visual companions of close Cepheids. VLT/NACO lucky imaging of Y Oph, FF Aql, X Sgr, W Sgr, and η Aql". Astronomy & Astrophysics. 567: 8. arXiv: 1406.0493 . Bibcode:2014A&A...567A..60G. doi:10.1051/0004-6361/201423872. S2CID   55702630. A60.
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