Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Sagittarius |
Right ascension | 18h 31m 53.332s [2] |
Declination | −19° 07′ 30.26″ [2] |
Apparent magnitude (V) | 6.28 to 7.15 [3] |
Characteristics | |
Evolutionary stage | Supergiant |
Spectral type | G1Ib [4] |
U−B color index | +0.85 [5] |
B−V color index | +1.06 [5] |
Variable type | δ Cep [3] |
Astrometry | |
Radial velocity (Rv) | 2.2±0.3 [6] km/s |
Proper motion (μ) |
RA: −1.795
mas/
yr
[2] Dec.: −6.127 mas/ yr [2] |
Parallax (π) | 1.5693 ± 0.0224 mas [2] |
Distance | 2,080 ± 30
ly (637 ± 9 pc) |
Absolute magnitude (MV) | −3.86 to −3.10 [5] |
Details | |
Mass | 6.54 to 6.64 [7] M☉ |
Radius | 55.5 to 56.3 [7] R☉ |
Luminosity | 4,370 to 4,650 [7] L☉ |
Surface gravity (log g) | 0.99 [8] cgs |
Temperature | 5,802 [8] K |
Metallicity [Fe/H] | 0.17 [8] dex |
Rotational velocity (v sin i) | 15.4 [9] km/s |
Age | 91 [10] Myr |
Other designations | |
Database references | |
SIMBAD | data |
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. [3] 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, [2] and it is drifting further away with a radial velocity of 2 km/s. [6]
The variability of this star was announced by J. Schmidt in 1866, who found a preliminary period of 6.74784 days. [13] It was later determined to be a variable of the Cepheid type. [14] In 1925, P. Doig assumed that the star is a member of the open cluster Messier 25 (M25), but actual evidence of its membership would not be available until 1932 when P. Hayford made radial velocity measurements of the cluster. [15] Membership in this cluster is now reasonably established, [16] and as such this Cepheid serves as one of the anchors for the cosmic distance scale since the distance to the cluster can be determined independently from the star. [17]
This is an evolved G-type supergiant star with a typical stellar classification of G1Ib. [4] It appears to be making its third traversal of the instability strip with its period changing at the rate of +0.073±0.010 s·yr−1. Elemental abundances are similar to those in the Sun. [17] It has an estimated 6.6 times the mass of the Sun and 56 times the Sun's radius. The star is radiating over 4,000 [7] times the Sun's luminosity from its photosphere at an effective temperature of 5,802 K. [8]
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Sagittarius |
Right ascension | 18h 31m 53.332s [2] |
Declination | −19° 07′ 30.26″ [2] |
Apparent magnitude (V) | 6.28 to 7.15 [3] |
Characteristics | |
Evolutionary stage | Supergiant |
Spectral type | G1Ib [4] |
U−B color index | +0.85 [5] |
B−V color index | +1.06 [5] |
Variable type | δ Cep [3] |
Astrometry | |
Radial velocity (Rv) | 2.2±0.3 [6] km/s |
Proper motion (μ) |
RA: −1.795
mas/
yr
[2] Dec.: −6.127 mas/ yr [2] |
Parallax (π) | 1.5693 ± 0.0224 mas [2] |
Distance | 2,080 ± 30
ly (637 ± 9 pc) |
Absolute magnitude (MV) | −3.86 to −3.10 [5] |
Details | |
Mass | 6.54 to 6.64 [7] M☉ |
Radius | 55.5 to 56.3 [7] R☉ |
Luminosity | 4,370 to 4,650 [7] L☉ |
Surface gravity (log g) | 0.99 [8] cgs |
Temperature | 5,802 [8] K |
Metallicity [Fe/H] | 0.17 [8] dex |
Rotational velocity (v sin i) | 15.4 [9] km/s |
Age | 91 [10] Myr |
Other designations | |
Database references | |
SIMBAD | data |
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. [3] 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, [2] and it is drifting further away with a radial velocity of 2 km/s. [6]
The variability of this star was announced by J. Schmidt in 1866, who found a preliminary period of 6.74784 days. [13] It was later determined to be a variable of the Cepheid type. [14] In 1925, P. Doig assumed that the star is a member of the open cluster Messier 25 (M25), but actual evidence of its membership would not be available until 1932 when P. Hayford made radial velocity measurements of the cluster. [15] Membership in this cluster is now reasonably established, [16] and as such this Cepheid serves as one of the anchors for the cosmic distance scale since the distance to the cluster can be determined independently from the star. [17]
This is an evolved G-type supergiant star with a typical stellar classification of G1Ib. [4] It appears to be making its third traversal of the instability strip with its period changing at the rate of +0.073±0.010 s·yr−1. Elemental abundances are similar to those in the Sun. [17] It has an estimated 6.6 times the mass of the Sun and 56 times the Sun's radius. The star is radiating over 4,000 [7] times the Sun's luminosity from its photosphere at an effective temperature of 5,802 K. [8]