U Sagittarii information

U Sagittarii
	; U Sagittarii (center) is the brightest star in the open cluster Messier 25.
Observation data; Epoch J2000 Equinox J2000
Constellation	Sagittarius
Right ascension	18h 31m 53.332s
Declination	−19° 07′ 30.26″
Apparent magnitude (V)	6.28 to 7.15
Characteristics
Evolutionary stage	Supergiant
Spectral type	G1Ib
U−B color index	+0.85
B−V color index	+1.06
Variable type	δ Cep
Astrometry
Radial velocity (Rv)	2.2±0.3 km/s
Proper motion (μ)	RA: −1.795 mas/yr ; Dec.: −6.127 mas/yr
Parallax (π)	1.5693 ± 0.0224 mas
Distance	2,080 ± 30 ly ; (637 ± 9 pc)
Absolute magnitude (MV)	−3.86 to −3.10
Details
Mass	6.54 to 6.64 M☉
Radius	55.5 to 56.3 R☉
Luminosity	4,370 to 4,650 L☉
Surface gravity (log g)	0.99 cgs
Temperature	5,802 K
Metallicity [Fe/H]	0.17 dex
Rotational velocity (v sin i)	15.4 km/s
Age	91 Myr
Other designations
	U Sgr, BD−19°5047, GC 25287, HD 170764, HIP 90836, HR 6947, SAO 161571, WDS J18319-1908A
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]

A light curve for U Sagittarii, plotted from ASAS data^[12]

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]

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[Majaess_et_al_2013-17] Cite error: The named reference Majaess_et_al_2013 was invoked but never defined (see the help page).

Observation data Epoch J2000 Equinox J2000
U Sagittarii (center) is the brightest star in the open cluster Messier 25.^[1]
Constellation	Sagittarius
Right ascension	18^h 31^m 53.332^s^[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 (R_v)	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 (M_V)	−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
U Sgr, BD−19°5047, GC 25287, HD 170764, HIP 90836, HR 6947, SAO 161571, WDS J18319-1908A^[11]
Database references
SIMBAD	data

U Sagittarii information

and 28 Related for: U Sagittarii information

U Sagittarii

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Mu Sagittarii

Open cluster

Zeta Sagittarii

Sigma Sagittarii

Tau Sagittarii

Gamma2 Sagittarii

Chi Sagittarii

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Omega Sagittarii

Lambda Sagittarii

Theta Sagittarii

Delta Sagittarii

V356 Sagittarii

Ross 154

Phi Sagittarii

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Xi Sagittarii

Mounted archery

VX Sagittarii

UY Scuti

Beta Sagittarii

Beta2 Sagittarii

KW Sagittarii

Pi Sagittarii