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]
  | |
| 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 | |
| Database references | |
| SIMBAD | 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]