Delta1 Lyrae
Binary star system in the constellation of Lyra
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Delta1 Lyrae, its name Latinized from δ1 Lyrae, is a binary star system in the northern constellation of Lyra. It is dimly visible to the naked eye at night with a combined apparent visual magnitude of 5.56.[2] The system is located at a distance of approximately 1,160 light years from the Sun based on parallax,[1] but is drifting closer with a radial velocity of −26 km/s.[5] O. J. Eggen originally included this as a candidate member of the proposed Delta Lyrae cluster.[12]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Lyra |
| Right ascension | 18h 53m 43.55924s[1] |
| Declination | +36° 58′ 18.1891″[1] |
| Apparent magnitude (V) | 5.56[2] |
| Characteristics | |
| Spectral type | B2.5V[3][4] |
| U−B color index | −0.67[2] |
| B−V color index | −0.15[2] |
| Astrometry | |
| Radial velocity (Rv) | −25.8[5] km/s |
| Proper motion (μ) | RA: +1.350[1] mas/yr Dec.: −2.985[1] mas/yr |
| Parallax (π) | 2.8072±0.1334 mas[1] |
| Distance | 1,160 ± 60 ly (360 ± 20 pc) |
| Absolute magnitude (MV) | −1.55[6] |
| Orbit[7] | |
| Period (P) | 88.352 days |
| Semi-major axis (a) | ≥46.8 Gm (0.313 AU) |
| Eccentricity (e) | 0.37±0.03 |
| Periastron epoch (T) | 2428406.613±0.500 JD |
| Argument of periastron (ω) (secondary) | 191.3±0.1° |
| Semi-amplitude (K1) (primary) | 39.7±1.8 km/s |
| Details | |
| δ1 Lyr A | |
| Mass | 7.9±0.1 M☉[4] 7.75±0.50 M☉[8] 6.6+0.68 −0.61[9] M☉ |
| Luminosity | 838[6] L☉ |
| Luminosity (bolometric) | 3,620[8] L☉ |
| Surface gravity (log g) | 3.764±0.032 (3.848 polar)[10] cgs |
| Temperature | 20,350[8] K |
| Metallicity [Fe/H] | −0.05[6] dex |
| Rotational velocity (v sin i) | 86±10[10] km/s |
| Age | 21.1±2.2 Myr[4] 9+9 −4[9] Myr |
| Other designations | |
| Delta1 Lyr, 11 Lyrae, NSV 11504, BD+36°3307, GC 25934, HD 175426, HIP 92728, HR 7131, SAO 67537, WDS J18537+3658A, GSC 02650-02146[11] | |
| Database references | |
| SIMBAD | data |
The variable radial velocity of this star was discovered from photographic plates taken at the Yerkes Observatory in 1904.[13] The first set of orbital elements was computed by Frank Craig Jordan in 1916.[14] It is a single-lined spectroscopic binary with an orbital period of 88.4 days and an eccentricity (ovalness) of 0.37.[7]
The visible component of the pair has a blue-white hue with a stellar classification of B2.5V,[3][4] indicating that it is a B-type main-sequence star undergoing core hydrogen fusion. It is a few million years old with a relatively high rotation rate and around 7–8 times the mass of the Sun. The star is radiating about 3,620[8] times the Sun's luminosity from its photosphere at an effective temperature of 20,350 K.[8]
There is a magnitude 9.93 visual companion at an angular separation of 175.30 arcseconds along a position angle of 20°, as of 2012. This component was discovered by William Herschel.[15] It is an evolved giant star with a class of K2III at a distance of around 1,760 light years.[16]