The Palomar twilight survey of 'Ayló'chaxnim, Atiras, and comets

TL;DR

The paper addresses the challenge of detecting near-Sun asteroids and comets, including Aylo ($Q<0.718$ au) and Atira ($0.718$ au$<Q<0.983$ au) populations, using a twilight survey strategy. It details a dedicated P48/ZTF twilight program that exploits brief, shallow r-band exposures during evening and morning twilight, supported by a fast-moving-object pipeline (ZMODE Lite) and Tails for comet detection, plus a broad follow-up network to secure orbits. The study reports 1 Aylo, 3 Atiras, and 8 comets discovered, with additional serendipitous recoveries and substantial recoveries of known MBAs and NEOs, and it characterizes the orbital element distributions and limiting-magnitude behavior, comparing to NEOMOD population models. The results demonstrate the feasibility and value of near-Sun twilight surveys and outline how upcoming surveys like LSST/Rubin can optimize cadence and sky coverage to maximize inner-Solar-System discoveries, informing population models and search strategies.

Abstract

Near-sun sky twilight observations allow for the detection of asteroid interior to the orbit of Venus (Aylos), the Earth (Atiras), and comets. We present the results of observations with the Palomar 48-inch telescope (P48)/Zwicky Transient Facility (ZTF) camera in 30 s r-band exposures taken during evening astronomical twilight from 2019 Sep 20 to 2022 March 7 and during morning astronomical twilight sky from 2019 Sep 21 to 2022 Sep 29. More than 46,000 exposures were taken in evening and morning astronomical twilight within 31 to 66 degrees from the Sun with an r-band limiting magnitude between 18.1 and 20.9. The twilight pointings show a slight seasonal dependence in limiting magnitude and ability to point closer towards the Sun, with limiting magnitude slightly improving during summer. In total, the one Aylo, (594913) 'Ayló'chaxnim, and 4 Atiras, 2020 OV1, 2021 BS1, 2021 PB2, and 2021 VR3, were discovered in evening and morning twilight observations. Additional twilight survey discoveries also include 6 long-period comets: C/2020 T2, C/2020 V2, C/2021 D2, C/2021 E3, C/2022 E3, and C/2022 P3, and two short-period comets: P/2021 N1 and P/2022 P2 using deep learning comet detection pipelines. The P48/ZTF twilight survey also recovered 11 known Atiras, one Aylo, three short-period comes, two long-period comets, and one interstellar object. Lastly, the Vera Rubin Observatory will conduct a twilight survey starting in its first year of operations and will cover the sky within 45 degrees of the Sun. Twilight surveys such as those by ZTF and future surveys will provide opportunities for discovering asteroids inside the orbits of Earth and Venus.

Figures (13)

• Figure 1: Duration of twilight and 5.5$\%$ of twilight + night survey time. The blue line shows the time between nautical and astronomical twilight (-12$^{\circ}$ to -18$^{\circ}$ Sun altitude) as a function of the day of the year. The orange line shows the time corresponding to 5.5$\%$ of the total survey time including evening/morning nautical twilight and total night time.
• Figure 2: Sky coverage of the ZTF twilight survey between 2019 September and 2022 September.Top panel: the Sun-centric ecliptic sky-plane distribution of ZTF twilight survey fields taken between 2019 September and 2021 April. Center panel: the skyplane distribution of ZTF twilight survey fields taken between 2021 April and 2022 March for the evening portion and 2021 April and 2022 September for the morning portion. Bottom panel: the skyplane distribution of ZTF twilight survey fields taken between 2019 September and 2022 March for the evening portion and 2019 September and 2022 September for the morning portion. The Sun-centric sky plane position of Aylo and Atira asteroids and long and short-period comets are indicated by crosses, x's, circles, and stars. These symbols are filled in for ZTF discoveries and outlined for recoveries. The color bar indicates the number of visits per sq.deg. covered by the twilight survey. The position of the Sun is indicated by a yellow starburst.
• Figure 3: Sun-centric angular distance and 5-$\sigma$ limiting magnitude distributions of twilight survey fields taken between 2019 September and 2022 September.Top left panel: the Sun-centric angular distance distribution of evening twilight survey fields taken between 2021 April and 2022 March for the evening portion and 2021 April and 2022 September for the morning potion. Top right panel: the cummulative Sun-centric angular distance distribution of evening twilight survey fields taken between 2021 April and 2022 March for the evening portion and 2021 April and 2022 September for the morning potion. Center left panel: the cumulative Sun-centric angular distance distribution of evening twilight survey fields taken between 2019 September and 2022 March. Center right panel: the cumulative Sun-centric angular distance distribution of morning twilight survey fields taken between 2019 September and 2022 September. Bottom left panel: the cumulative Sun-centric angular distance distribution of evening and morning twilight survey fields taken between 2019 September and 2022 March for the evening portion and 2019 September and 2022 September for the morning portion. Bottom right panel: the cumulative 5-$\sigma$ limiting r magnitude distribution of evening and morning twilight survey fields taken between 2019 September and 2022 March for the evening portion and 2019 September and 2022 September for the morning portion. Orange lines are indicated for ' Ayló' chaxnim discovery and recoveries. Blue lines are indicated for Atira discovery and recoveries. Both long and short-period comets are indicated by grey lines. The lines will be solid for ZTF discoveries and dashed for recoveries.
• Figure 4: Time after sunset/before sunrise and limiting magnitude distributions of twilight survey fields taken between 2019 September and 2022 September.Top panel: the time after sunset vs limiting magnitude distribution of evening twilight survey fields taken between 2019 September and 2022 March. Middle panel: the time before sunset vs limiting magnitude distribution of evening twilight survey fields taken between 2019 September and 2022 September. Bottom panel: the time after sunset vs limiting magnitude distribution of evening twilight survey fields taken between 2019 September and 2022 March and time before sunrise 2019 September and 2022 September for the morning portion. Orange lines are indicated for ' Ayló' chaxnim discovery and recoveries. Blue lines are indicated for Atira discovery and recoveries. Grey lines indicate both long and short-period comets. The lines will be solid for discoveries and dashed for recoveries. The filled-in plus symbols show the limiting magnitude of the image in which a discovery or recovery was made. The filled-in black circle shows the magnitude of the asteroid or comet discovery or recovery. The bin size after sunset/before sunrise was 0.3 minutes, and the bin size in the magnitude direction was 0.06125 mags. The color scale indicates the Log number of visits per 2D bin +1. The green error bar line indicates the running mean of the limiting magnitude in increments of 2.4 minutes after/before Sunset with error bars corresponding to the per bin 1-$\sigma$ standard deviation value.
• Figure 5: Sun altitude and limiting magnitude distributions of twilight survey fields taken between 2019 September and 2022 September.Top panel: the Sun altitude vs limiting magnitude distribution of evening twilight survey fields taken between 2019 September and 2022 March. Middle panel: the Sun altitude vs limiting magnitude distribution of evening twilight survey fields taken between 2019 September and 2022 September. Bottom panel: the Sun altitude vs limiting magnitude distribution of evening twilight survey fields taken between 2019 September and 2022 March for the evening portion and 2019 September and 2022 September for the morning portion. Orange lines are indicated for ' Ayló' chaxnim discovery and recoveries. Blue lines are indicated for Atira discovery and recoveries. Both long and short-period comets are indicated by grey lines. The lines will be solid for discoveries and dashed for recoveries. Orange lines are indicated for ' Ayló' chaxnim discovery and recoveries. Blue lines are indicated for Atira discovery and recoveries. Grey lines indicate both long and short-period comets. The lines will be solid for ZTF discoveries and dashed for recoveries. The filled-in plus symbols show the limiting magnitude of the image in which a discovery or recovery was made. The filled-in black circle shows the magnitude of the asteroid or comet discovery or recovery. The bin size in the Sun altitude direction is 0.06125$^{\circ}$, and the bin size in the magnitude direction was 0.06125 mags. The color scale indicates the Log number of visits per 2D bin +1. The green error bar line indicates the running mean of the limiting magnitude in increments of 0.5$^{\circ}$ Sun altitude with error bars corresponding to the per bin 1-$\sigma$ standard deviation value.