V1494 Aquilae or Nova Aquilae 1999 b was a nova which occurred during 1999 in the constellationAquila 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 × 10−10M☉ 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]
^ abDrake, Jeremy J.; Wagner, R. Mark; Starrfield, Sumner; Butt, Yousaf; Krautter, Joachim; Bond, H. E.; Della Valle, M.; Gehrz, R. D.; Woodward, Charles E.; Evans, A.; Orio, M.; Hauschildt, P.; Hernanz, M.; Mukai, K.; Truran, J. W. (2003). "The Extraordinary X-ray Light Curve of the Classical Nova V1494 Aquilae (1999 No. 2) in Outburst: The Discovery of Pulsations and a "Burst"". The Astrophysical Journal. 584 (1): 448–452. arXiv:astro-ph/0210072. Bibcode:2003ApJ...584..448D. doi:10.1086/345534. S2CID14866037.
^ abcBarsukova, E. A.; Valeev, A. F.; Goranskij, V. P.; Zharova, A. V. (October 2013). "Spectroscopic detection of resolved ejecta of nova V1494 Aql". The Astronomer's Telegram. 5454 (5454): 1. Bibcode:2013ATel.5454....1B.
