Post-perihelion activity of comet C/2022 E3 (ZTF)

It is believed that small celestial bodies contain primordial material from the Solar System formation epoch. Long-period comets that due to their dynamical characteristics spend mostly of time far from the Sun consist of mater barely differentiated by the Solar radiation. Moreover, comets that coming into the inner part of the Solar System at the first time are the most prominent objects for study from this point of view. Comet C/2022 E3 (ZTF) is a hyperbolic comet was discovered on March 2, 2022, with the 48-inch Schmidt-type telescope of the Zwicky Transient Facility (ZTF), as an object of approximately 17.3^m at a heliocentric distance of r_h = 4.3 au (Bolin et al. 2022). C/2022 E3 (ZTF) reached a perihelion distance of 1.112 au on January 12, 2023. We present the results of observations obtained after the perihelion passage using broad- and narrowband photometrical, and long-slit spectral methods. Such complex analysis allows us to study more precisely the dust and gas components of the comet.

Observations. The observations of comet C/2022 E3 (ZTF) were carried out from January 23 to February 20, 2023, right after the perihelion passage when the heliocentric and geocentric distances of the comet changed from 1.127 to 1.276 au and from 0.402 to 0.684 au, respectively. It worth be noted that during our observation the comet made its closest approach to the Earth on January 31, 2023.

Photometrical observations were performed at 61-cm telescope of Skalnaté Pleso observatory (Slovakia). We used the CCD chip SBIG ST-10 Dual with 1092px×736 px after applying 2×2 binning. The pixel’s size was 13.6×13.6 μm corresponding to 1.07ʺ/px on the sky plane after binning. We used broadband B, V, R Johnson-Causins filter and narrowband cometray filters BC, C₂, RC.

We provided spectral observations of the comet on 40ʺ Zeiss telescope of Vainu Bappu Observatory (Kavalur, India) and 2.0-m Himalyan Chandra Telescope of the Indian Astronomical Observatory. The long-slit spectra were obtained using several grisms as a disperser. The slit size was 2ʺ ×11ʹ was placed on the nucleus position in the sky. The obtained spectra covered the wavelength range 4000–7800 Å.

Results. Photometry. We estimated the dust productivity using the Afρ parameter. It was about 2500 cm in red domain. The comet also demonstrated typical red colour, based on V-R and BC-RC calculated values. To reveal the low-contrast structures in the dust coma, we constructed an intensity map of comet C/2022 E3 (ZTF) using digital filters. Based on the distribution map of intensity, we derived the radial profiles of the surface brightness for observed structures to describe the dust brightness as a function of the distance from the optocenter. The profiles demonstrate slopes differed from the value -1, which corresponds to the case of a steady and isotropic emission of long-lived grains.

Spectroscopy. We analyzed cometary spectra in the wavelength region of 4000–7800 Å. Significant gas emission lines were detected in the spectra. The strongest features belong to molecules of C₂, C₃, and NH₂. Gas production ratios were calculated for all detected molecules using the Haser model [2]. Also, we estimated the gas contribution in wavelength regions corresponding to broadband filters used for photometric studies. To compare with photometrical results, we also computed a colour slope value based on the spectral data. The results from both methods are in good agreement.

Acknowledgments. The research is supported by the Government Office of the Slovak Republic within NextGenerationEU programme under project No. 09I03-03-V01-00001, the Slovak Academy of Sciences (grant Vega 2/0059/22), the Slovak Research and Development Agency under the Contract no. APVV-19-0072, the DST, Government of India, under the Women Scientist Scheme (PH) project reference number SR/WOS-A/PM-17/2019.

References

[1] Bolin, B. T., Masci, F. J., Ip, W.-H., et al. (2022), MPEC (USA: IAU), 2022-F13

[2] Haser L. (1957) Bull. Soc. R. Sci. Liege, 43, pp. 740-750