19h23m05.38s, +04° 57′ 20.1″
| |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Aquila |
| Right ascension | 19h23m 05.30s[1] |
| Declination | 04° 57′ 19.1″[1] |
| Apparent magnitude (V) | 3.9 Max. 17.1 Min.[2][3] |
| Characteristics | |
| Variable type | Classical Nova[3], eclipsing binary[4] |
| Astrometry | |
| Parallax (π) | 0.5615 ± 0.1281 mas[5] |
| Distance | 1,239+422 −127[3] pc |
| Absolute magnitude (MV) | −8.2 Max. 4.8 Min.[2][3] |
| Orbit[6] | |
| Period (P) | 0.1346 days |
| Semi-major axis (a) | 1.17 - 1.24 R☉ |
| Inclination (i) | 78.5[7]° |
| Details | |
| white dwarf | |
| Mass | 0.92 - 1.13[6] M☉ |
| Luminosity | 750 - 3,000[7] L☉ |
| Temperature | >100,000 (2000)[8] K |
| donor | |
| Mass | 0.28[6] M☉ |
| Temperature | 3,000[7] K |
| Other designations | |
Nova Aquilae 1999 b, AAVSO 1918+04 | |
| Database references | |
| SIMBAD | data |
V1494 AquilaeorNova Aquilae 1999 b was a nova which occurred during 1999 in the constellation Aquila and reached a brightness of magnitude 3.9 on 2 December 1999.[2] making it easily visible to the naked eye.[9] The nova was discovered with 14×100 binoculars by Alfredo Pereira of Cabo da Roca, Portugal at 18:50 UT on 1 December 1999, when it had a visual magnitude of 6.0.[10]
V1494 Aquilae is classified as a fast nova, meaning it faded from peak brightness by more than 3 magnitudes in less than 100 days.[11] During its decline, V1494 Aql produced unusual variations in its x-ray radiation, including a bright burst lasting several minutes. During 2000, the x-ray spectrum developed from a hard (high energy) emission-line spectrum to a spectrum typical of a super soft X-ray source. The x-ray intensity varied with a period of about 40 minutes, probably due to pulsations induced in the white dwarf by its re-kindled hydrogen fusion.[8]
All novae are binary systems with two stars orbiting so close to each other that one star, the "donor" star transfers matter to the other star which is a white dwarf. In the case of V1494 the white dwarf has a mass of 1.20M☉, and it is accreting mass from the donor star at a rate of 2.1 × 10−10 M☉yr−1.[12] The stars' orbital period is 3.23 hours,[11] and the system is an eclipsing binary with two brightness minima each orbit, one 0.5 and one 0.1 magnitudes deep.[2][4] This apparently is a measurement of two stars of approximately equal brightness, the nova and a companion 1.4″ to the south east. Measuring only the brightness of the nova, the eclipses are about two magnitudes deep.[13] The white dwarf is probably an oxygen-neon-magnesium type.[6]
Unlike some novae, the material ejected from V1494 Aquilae has not formed a visible nebula around the star.[14] However, a shell approximately 6.5″ across has been detected spectroscopically in H-alpha emission.[13]
The distance to V1494 Aquilae has been estimated by different methods. Early estimates were based on assumptions about the luminosity of the nova and gave distances around 1.2 kpc.[7] Later models assumed distances of up to 2.2 kpc.[6] Comparison of the measured shell size with the observed expansion velocity give a distance of 1.2±0.2 kpc.[13] Gaia DR2 published a parallax of 0.8394±0.1415 mas, corresponding to a distance of 1,239+422
−127 kpc.[3] Gaia EDR3 published a parallax of 0.5615±0.1281 mas, corresponding to a distance around 1,800 kpc.[5]
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