Cometary ion tail observations using commercial CN narrowband UV 387nm/11nm filter
Abstract
Cometary CN jets with a corkscrew effect can be observed using a commercially available narrowband UV filter having a 11nm bandwidth centered near the CN (0,0) emission line at 3883Å with amateur size telescopes [1]. The commercial CN filter Semrock Brightline 387BW11 (387nm center with a measured bandpass from 380nm to 395nm [2]) includes also cometary ion emission lines of N2+ (0,0) at 3914Å and partly CO+ (4,0) red end 3800Å line.
Comet C/2022 E3 (ZTF) and comet 12P/Pons-Brooks have been observed, both showing ion tail signal, using this commercial CN bandwidth filter. Bright comet C/2023 A3 (Tsuchinshan-ATLAS) was also observed with CN and a wide band red filter for comparison.
1. Introduction
The commercial CN filter’s (Semrock Brightline 387/11nm) actual bandpass has been measured earlier with a high resolution spectrometer [2]. Figure 1 shows the CN emission spectra and two ionic emission lines marked, N2+ and CO+ (4,0). The N2+ band is fully inside the filter’s bandpass and should be detected if it exists in a comet’s coma or tail. CO+ red end is also inside the bandpass.
2. Observations
2.1 Comet C/2022 E3 (ZTF)
Comet C/2022 E3 (ZTF) was observed on 21.2.2023 with the CN 387/11nm filter and the 0.3m telescope at observatory M00 Viestikallio Finland. The image (Figure 2) shows a large CN coma but also a 30’ long ion tail. The ion tail was changing it’s structure during blinking of 30x60s exposures. The filter bandpass area make it possible that the observed ion tails are either from N2+ or CO+ emission. A wide band Red filter (660nm center, and 60nm bandpass) was used to detect dust emissions, a probable H2O+ and possible red leak. The R band tail PA’s were different than the CN band ion tails. (Figure 2).
2.2 Comet 12P/Pons-Brooks
The 12P/Pons-Brooks observation with CN filter on 17.11.2023 shows a possible wide structured ion tail at solar wind direction PA 39°. The red filter image shows a short wide dust tail. (Figure 3). 12P/Pons-Brooks was an active comet having many outbursts during 2023-2024 [6].
2.3 Comet C/2023 A3 (Tsuchinshan-ATLAS)
The C/2023 A3 (Tsuchinshan-ATLAS) observations with the CN and R filter were obtained on 20.10.2024 from observatory Y71 Makroskooppi Spain. They show a dim wide tail at solar wind direction PA 72°. The wide band Red (650 nm center/110nm wide) filter image shows a very bright wide dust tail toward the solar wind direction, (Figure 4). Quite similar dim ion tails in these CN and R filter observations are probably from possible CO+, H2O+ ions and a red leak signal.
3. Equipment and software
3.1 Equipment
The telescope used in observatory M00 Viestikallio Finland was a 305mm aperture and 1205mm focal length f/4 Newtonian with coma corrector. The CCD-camera was a cooled QSI690wsg having a Sony ICX814 CCD-sensor. Filters used were Semrock BrightLine CN 387/11nm (center 387nm, bandpass 11nm) diameter 26mm and 31mm, Astrodon Gen2 R 660/60nm and Antlia Dark series R 650/110nm filter.
The telescope used in observatory Y71 Makroskooppi Spain was a 305mm aperture and 2400mm focal length f/8 corrected Dall-Kirkham telescope. A CMOS-camera was a cooled QHY600M having a Sony IMX455 CMOS-sensor. Filters used were Semrock BrightLine CN 387/11nm diameter 31mm and Antlia Dark series R 650/110nm filter.
3.2 Software
NINA software was used to control observatory, telescope and camera. TychoTracker software was used to image processing, plate solving, astrometric measurement and stacking.
4. Figures
Figure 1: Semrock Brightline “CN” filter 387/11nm measured bandpass ([2]) with CN 3883Å, N2+ (0,0) at 3914Å, CO+ (4,0) 3780Å & 3800Å emission lines marked.
Figure 2: C/2022 E3 (ZTF) with filters CN and R, 2023-01-21. Left/CN image possible CO+ ion tail in PA’s marked as Tail 1 PA 285°, Tail 2 PA 270°. Right/R image has dust tail PA marked, also possible H2O+ ion tail at PA 290°.
Figure 3: 12P/Pons-Brooks with filters CN and R, 2023-11-17. Left/CN image possible N2+ and/or CO+ ion tail in PA’s marked as Tail 1 PA 25°, Tail 2 60°. Right R image has wide dust Tail 1 at PA 40°.
Figure 4: C/2023 A3 (Tsuchinshan-ATLAS) with filters CN and R, 2024-10-20. Left CN filter tail signal probably from CO+ and red leak. Right R filter image shows strong dust tail and possible H2O+ ion tail.
5. Summary and Conclusions
These comets observed with the commercial CN filter with bandwidth 380nm – 395nm make it possible that there are ionic tail signals from N2+ and/or CO+. This will need more observations with future medium bright comets together with high resolution spectrographic observations to confirm what are the specific ions. Observations made by amateur/pro-am resources and telescopes can be used as an “observation alarm” trigger, i.e when N2+/ CO+ ionic signals are observed, high resolution spectrograph observations can be considered.
Acknowledgements
Special thanks to Anita Cochran /University of Texas at Austin, Tony Farnham /University of Maryland, Emmanuel Jehin /Université de Liège, Matthew Knight /United States Naval Academy of analyzing and giving feedback of observations and to this abstract.
References
[1] EPSC-DPS 2019: Cometary CN cyanogen jet observations using small telescopes with narrowband UV filter, J. Ryske, https://meetingorganizer.copernicus.org/EPSC-DPS2019/EPSC-DPS2019-1980-1.pdf
[2] CN Filter Tests, M. Knight, University of Maryland 2018, https://wirtanen.astro.umd.edu/46P/CN_filter_test.shtml
[3] Spectroscopic Investigations of Fragment Species in the Coma, Comets II, P. Feldman, A. Cochran, M. Combi.
[4] Strong CO+ and N2+ Emission in Comet C/2016 R2 (Pan-STARRS), A. Cochran, A. McKay, https://doi.org/10.3847/2041-8213/aaab57
[5] MNRAS 2024: An updated fluorescence emission model of CO+ for cometary science, S. Bromley, J. Noonan, A. Cochran, https://doi.org/10.1093/mnras/stae456
[6] MNRAS 2025: Mass of particles released by comet 12P/Pons–Brooks during 2023–2024 outbursts, M. Gritsevich, M. Wesołowski, A. Castro-Tirado https://doi.org/10.1093/mnras/staf219
