Photometry and spectroscopy of distant comet C/2014 N3 (NEOWISE)

Context. We analyzed spectral and photometric data of comet C/2014 N3 (NEOWISE) to investigate its physical properties and activity at a heliocentric distance of 4.51 au. Aims. The aim of the analysis was to detect gas emissions and determine the dust characteristics in the coma and nucleus regions. We also sought to estimate the comet’s dust production rate and infer the size of its nucleus based on photometric data and Monte Carlo dust-tail modeling. Methods. Two-dimensional long-slit spectra and photometric images were obtained using the multimode focal reducer SCORPIO-2 installed on the 6 m telescope BTA of the Special Astrophysical Observatory. The spectral range covered λ4000–7200 Å. The analysis focuses on the detection of gas emissions, continuum reddening effects, and the determination of the color and production rate of dust. Results. No gas emissions above level 3σ were detected. The continuum shows a reddening effect with a normalized gradient of reflectivity along a dispersion of (8 ± 1)% per 1000 Å. The dust color (g–r) of the comet is predominantly red (0.69 ± 0.06)m for an aperture size of about 20 000 km. The A f ρ value varied from 830 ± 70 to 900 ± 80 cm in the r-sdss filter and from 715 ± 65 to 780 ± 70 cm in the g-sdss filter across aperture radii from 5000 to 11 000 km. According to NEOWISE data, the Af ρ parameter changed from 370 ± 88 cm in 2014 to 421 ± 98 cm in 2016. The peak of dust production occurred approximately 300 days before perihelion, with a maximum mass-loss rate of about 700 kg s−1 according to Monte Carlo simulations. The total dust mass loss is estimated to be around 4.5–4.9 × 1010 kg. For particles with a radius of 1 μm, the ejection velocity was about 100 m s−1, while for 1 cm particles, the velocity was ~1 m s−1 at perihelion. Based on NEOWISE data, the upper limit of the gas production rate of CO2 changed from (3.0 ± 0.4) × 1026 mol s−1 at r = 3.96 au to (1.6 ± 0.4) × 1026 mol s−1 at r = 4.68 au (i.e., before and after perihelion passage, respectively).