LL Aquarii
Binary star in the constellation Aquarius
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LL Aquarii is an eclipsing binary star system in the equatorial constellation of Aquarius, abbreviated LL Aqr. At peak brightness it has a combined apparent visual magnitude of 9.23,[1] which is too dim to be visible to the naked eye. Based on parallax measurements, it is located at a distance of approximately 447 light years from the Sun.[2] The system is drifting closer with a heliocentric radial velocity of about −10 km/s.[7]
Min I: 9.86
Min II: 9.59[3]
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Aquarius[1] |
| Right ascension | 22h 34m 42.153s[2] |
| Declination | −03° 35′ 58.17″[2] |
| Apparent magnitude (V) | 9.23[1] Min I: 9.86 Min II: 9.59[3] |
| Characteristics | |
| Evolutionary stage | main sequence[4] |
| Spectral type | F9 V + G3 V[5] |
| U−B color index | 0.029[6] |
| B−V color index | 0.601±0.037[1] |
| Variable type | Algol[3] |
| Astrometry | |
| Radial velocity (Rv) | −9.59±0.46[7] km/s |
| Proper motion (μ) | RA: 73.192 mas/yr[2] Dec.: −21.545 mas/yr[2] |
| Parallax (π) | 7.297±0.0219 mas[2] |
| Distance | 447 ± 1 ly (137.0 ± 0.4 pc) |
| Absolute magnitude (MV) | 3.95[1] |
| Orbit[4] | |
| Period (P) | 20.178322(1) days |
| Semi-major axis (a) | 40.744±0.007 R☉[5] |
| Eccentricity (e) | 0.3163±0.0003 |
| Inclination (i) | 89.545±0.003° |
| Longitude of the node (Ω) | 32.11±0.14[5]° |
| Periastron epoch (T) | 2460223.84444(1) BJD |
| Argument of periastron (ω) (secondary) | 155.69±0.12° |
| Semi-amplitude (K1) (primary) | 49.948±0.013[5] km/s |
| Semi-amplitude (K2) (secondary) | 57.736±0.014[5] km/s |
| Details[4] | |
| Primary | |
| Mass | 1.1947(9) M☉ |
| Radius | 1.3180(13) R☉ |
| Luminosity | 2.377 L☉ |
| Surface gravity (log g) | 4.2755(9) cgs |
| Temperature | 6,242±50 K |
| Metallicity [Fe/H] | 0.075±0.030 dex |
| Rotation | 19.1±3.2 days |
| Rotational velocity (v sin i) | 3.5±0.5[5] km/s |
| Age | 3.01±0.12 Gyr |
| Secondary | |
| Mass | 1.0334(6) M☉ |
| Radius | 0.9927(8) R☉ |
| Luminosity | 1.030 L☉ |
| Surface gravity (log g) | 4.4587(8) cgs |
| Temperature | 5,839±44 K |
| Metallicity [Fe/H] | 0.052±0.027 dex |
| Rotation | 14.0±1.7 days |
| Rotational velocity (v sin i) | 3.6±0.4[5] km/s |
| Age | 2.67±0.12 Gyr |
| Other designations | |
| LL Aqr, BD−04°5706, HD 213896, HIP 111454, SAO 146171, PPM 206522[8] | |
| Database references | |
| SIMBAD | data |
Observations
In 1996, this star was found to be an Algol-type eclipsing binary based on photometric observations made with the Hipparcos space observatory. It was assigned the variable-star designation LL Aqr in 1999.[10] This is a detached system forming a double-lined spectroscopic binary. In 2004, a more extensive light curve showed an eccentric orbit with a period of 20.1784 days. During the primary eclipse, the system dropped to magnitude 9.86, while the secondary eclipse showed a magnitude of 9.59.[11] The first orbital elements were published in 2008, showing an orbital eccentricity of 0.3095 with a mass ratio of 0.86. Stellar models indicated the stars are near the mid point of their main sequence lifetimes.[7]
The more massive member of the system, the primary component, has a stellar classification of F9 V,[5] matching an F-type main-sequence star. It has 19.5% more mass than the Sun and a 32% greater girth. This star is radiating 2.15 times the luminosity of the Sun from its photosphere at an effective temperature of around 6,080 K. It is spinning with a projected rotational velocity of 3.5±0.5 km/s. The metallicity, or abundance of elements with mass greater than helium, is very nearly Sun-like.[5]
The secondary component is considered a solar twin, which means its properties are close to Sun-like. It is a G-type main-sequence star with a class of G3 V.[5] Neither member of the system shows signs of stellar activity, being slowly rotating and not emitting X-rays. Tidal effects between the two stars is negligible;[12] they have an orbital separation of 40.7 times the radius of the Sun.[5]