Proposal #342

Dear AAVSONet Telescope Allocation Committee,

In support to the PLATO-MERCURY-Test campaign, organized by the PLATO's Citizen Contribution to Photometric Follow-up working group, I would like to propose the observation of a transit for the exoplanet candidate TOI 4600.01, as a workbench for its ground-based follow-up work.
The PLATO-MERCURY-Test campaign aims at building the capabilities using small telescopes to help confirm and decontaminate transits of planets with periods larger than 80 days. Because of longer transit durations of such objects, an international coordination of multiple telescopes is required to observe either the whole length of transit or at least both start and the end of the transit (ingress and egress).
The Citizen Contribution to Photometric Follow-up working group, coordinated by the Ground-based Observation Programme, and has as one of its main objectives conduct photometric follow-up observations in order to discard false positives from future detections of exoplanets by the PLAnetary Transits and Oscillations of stars (PLATO) space telescope, with emphasis on terrestrial planets in the habitable zone of solar-like stars.

The candidate transiting exoplanet TOI 4600.01, detected by the TESS Mission, is a particularly interesting target for test observations for this campaign due to the following factors:
- Having a long orbital period of 82.69 days and a also a long transit duration of 7.2 hours, it almost matches Mercury's orbital period of 80 days, and its long duration transit implies that observations of the full transit will not be possible from a single location;
- Its magnitude of 12.3 in V and transit depth of 6.41 mmag puts this target within reach for observations using small telescopes;
- As a byproduct, the precise photometry could also help the activities of the TESS Follow-up Work Group Support Group 1 (TFOP SG1), for false positive rule out.
- The transit happening on 2023-05-16 UTC will provide a rare opportunity to observe its transit across North America and the North Pacific Ocean;

In addition, both the BSM-Hamren and BSM-NH2 are particularly suitable for these observations due to the following factors:
- Based on previous observations of WASP-148b (12.04 V-mag and 8.79 mmag transit depth, using 55s integration time in V, and achieving SNR~90), the photometric precision required for this 6.41 mmag depth transit and 12.3 V-mag star should be within the capabilities of the 7" E180 telescope and ASI183MM camera setup (assuming longer integration times);
- The new Moon (12% Moon illumination at 98° distance) for the particular night of observations (2023-05-16 UTC) is ideal for high precision exoplanet transit observations;
- The observability from the northern celestial hemisphere at both the BSM-Hamren and BSM-NH2 are extremely favorable for the target at +64.5° in declination;
- From the location of the BSM-Hamren (Hawaii), it would be possible to observe the end of the transit (from mid-transit to post-egress, from 06:21 to 14:03 UTC), occurring around 30˚ above the horizon. Also, its Class 3 Bortle scale sky should be helpful;
- From the location of the BSM-NH2 (New Hampshire), it would be possible to observe the start of the transit (from pre-ingress almost until mid-transit, from 04:41 to 08:11 UTC), occurring around 60° above the horizon. Also, its Class 4 Bortle scale sky should be helpful;
- The observations will be coordinated with other observatories in Texas [from 04:41 to 10:46 UTC] and New Mexico [from 04:41 to 11:02 UTC], that are capable to observe only from pre-ingress to mid-transit;

Finally, the observations of TOI 4600.01 would require a high cadence: having the integration time at the maximum value of 300s and also having the minimum dead time between them as low as possible, in order to achieve SNR~250 (or ~4ppt RMS) and not to impact the precision of the transit model fit to the data.
Also, the specific observations should be scheduled according to the following predicted transit times, and preferably done using a Johnson V filter, to achieve maximum transmission efficiency:
- BSM-Hamren: 2023-05-16, minimum of 2h required from 12:02 (Session start time in UTC) to 14:03 (Session end time in UTC) to capture the transit egress [observability of the transit at the location from 06:21 to 14:03 UTC];
- BSM-NH2: 2023-05-16, minimum of 2h required from 04:41 (Session start time in UTC) to 06:45 (Session end time in UTC) to capture the transit ingress [observability of the transit at the location from 04:41 to 08:11 UTC];

Cordially,
Andre Kovacs