X Sagittarii

X Sagittarii
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]
Distance950 ± 60 ly
(290 ± 20 pc)
Absolute magnitude (MV)−2.85[6]
Details
Mass6.31[7] M☉
Radius53±3[8] R☉
Luminosity2,647[7] L☉
Surface gravity (log g)1.77[9] cgs
Temperature6,305[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
SIMBADdata

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[12]

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]

References

  1. ^ a b c d e f Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. ^ a b c d 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. ^ a b 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
  4. ^ a b Samus, N. N.; Durlevich, O. V.; et al. (2009). "General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  5. ^ a b 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. ^ a b c 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
  7. ^ a b c Hohle, M. M.; et al. (2010). "Masses and luminosities of O- and B-type stars and red supergiants". Astronomische Nachrichten. 331 (4): 349. arXiv:1003.2335. Bibcode:2010AN....331..349H. doi:10.1002/asna.200911355. S2CID 111387483. Vizier catalog entry
  8. ^ a b 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. ^ a b 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. ^ a b 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.