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]

  1. ^ a b c d e f Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference Ducati2002 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference houk1979 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference gcvs was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Kharchenko2007 was invoked but never defined (see the help page).
  6. ^ a b c Cite error: The named reference XHIP was invoked but never defined (see the help page).
  7. ^ a b c Cite error: The named reference Hohle2010 was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference LiCausi_et_al_2013 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Soubiran2016 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference deMedeiros1999 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference ASASServer was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Samus_et_al_2017 was invoked but never defined (see the help page).
  14. ^ a b Cite error: The named reference Gallenne2012 was invoked but never defined (see the help page).
  15. ^ a b Cite error: The named reference Mathias2006 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference Gallenne_et_al_2013 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference Gallenne_et_al_2014 was invoked but never defined (see the help page).