Proposal #665

Proposer	(37223) Andre Kovacs (andre.kovacs@gmail.com) obscode: KADB
Assigned To	(3663) Dirk Terrell
Date Submitted	Nov. 22, 2025
Status	Accepted
Priority	Normal
Proposal	Dear AAVSONet Telescope Allocation Committee, As part of the PLATO benchmark eclipsing binaries initiative and also member of AAVSO, I would like to propose the observation of eclipses for the detached eclipsing binaries HD 4875, TYC 8547-22-1, CD-27 2812, CD-31 3271, and EPIC 212822491, using the Optical Craftsman 0.61m Telescope (OC61), located at the Mount John University Observatory (MJUO), via the AAVSONet. The PLATO (PLAnetary Transits and Oscillations of stars) is the third medium-class mission in ESA's Cosmic Vision program. PLATO was adopted by ESA Science Programme Committee in June 2017 and is due to be launched in 2026. Its objective is to find and study a large number of extrasolar planetary systems, with emphasis on the properties of terrestrial planets in the habitable zone around Sun like stars. PLATO has also been designed to investigate seismic activity in stars, enabling the precise characterization of the planet host stars, including its age. The PLATO benchmark eclipsing binaries initiative, conducted by the PLATO Benchmark stars work package (WP 125 500) of the Determination of Stellar Parameters work package (WP 125 000), as part of the Stellar Science work package (WP12) (https://warwick.ac.uk/fac/sci/physics/research/astro/plato-science/resources/psmdocuments/plato-uwa-psm-wbs-0013_i4.0_wp120000_stellar_science_structure.pdf), has as one of its main objetives the coordination of benchmark observations for testing stellar models used by the PLATO mission, and for validation of the stellar parameters that will be provided in the PLATO mission data products (Gent et al. 2022). The 20 detached eclipsing binary stars (DEBS) selected as targets for the benchmark show a total secondary eclipse with depths around 1 per cent and narrow eclipses (Maxted et al. 2023). Observations preferably in the Sloan i' filter of the secondary eclipse are needed to measure the flux ratio, in order to help improve the the accuracy and reliability of the effective temperature measurements for the two stars in the binary system. However, observations of the primary eclipse should also be useful for the analysis. The observations of each eclipse must be conducted in high cadence using, using the Johnson V photometric filter, in order to cover a complete ingress and/or egress of an eclipse plus some data before and after (~20 minutes) to measure the out-of-eclipse level and eclipse depth. In addition, the 24" OC61 telescope is particularly useful for these observations due to the following factors: - The 24" OC61 telescope is well suited for these targets in order to achieve the photometric precision required for HD 4875 at 11.08 ppt depth of the secondary eclipse and 8.97 V-mag star; - The observability from the southern celestial hemisphere at the Mount John University Observatory is favorable for all these targets below +35° in declination, and its elevation at 1029 meters and Class 2 Bortle scale sky should be also helpful; - The necessity for only ingress or egress observations of the eclipses, plus the required baseline observation of 20 minutes pre-ingress or post-egress, leads to minimum duration of 1.82 hours for the observing session of CD-31 3271 at best case. According to the Dr Karen Pollard (Director UC Mt John Observatory), this should provide a good match for the climate variations at the New Zealand site, and should also help minimize the conflict with other observation activities currently in place. Finally, the observations would require a high cadence in the Sloan i' filter, and having the integration time adjusted accordingly in order to achieve a SNR~500 (or ~2 ppt RMS), not to exceed an interval of 2 minutes between exposures and also having the minimum dead time between them as low as possible, in order not to impact the precision of the eclipse model fit to the data. Cordially, Andre Kovacs

Targets
Target	RA (H.HH)	Dec (D.DD)	Magnitude	Telescope	Observation Frequency	Expiration Date	Proprietary Term
TYC 8547-22-1	18.680319	34.55958	10.26–10.09	—	—	—	No
CD-31 3271	6.413592	-31.86450	10.17–9.94	—	—	—	No
CD-27 2812	6.216572	-27.88039	9.84–9.73	—	—	—	No
HD 4875	0.844442	-18.50592	9.12–8.98	—	—	—	No
EPIC 212822491	13.738733	-4.82750	11.03–11.05	—	—	—	No

Comments

(3663) Dirk Terrell — Nov. 23, 2025, 2:42 a.m.

Is this not just an extension of proposal #599?

(37223) Andre Kovacs — Nov. 23, 2025, 11:16 a.m.

Hello Dirk,

Sort of, I had to add CD-27 2812 to the target list and also to focus only on observing in the V filter, but the strategy is pretty much the same.

PS: I can provide an observing plan for ACP, based on the observing plan from the previous proposal.

Regards,
Andre

(3663) Dirk Terrell — Nov. 25, 2025, 3:55 p.m.

We are inclined to approve this but one member of the TAC has concerns about HD 4875:
"I have concerns over using OC61 for all of the stars in this project. For example, HD 4875 has no reasonable comp stars in the small 8x14arcmin field of view. I'm not sure how millimag precision on the secondary eclipse will be achievable without a good comp star. The other 3 targets seem to have bright stars that could be included in the field. The longish periods mean timing to catch primary/secondary eclipses will be difficult, and the weather at Mt. John has been particularly poor this summer season."

(37223) Andre Kovacs — Nov. 25, 2025, 9:51 p.m.

Hello Dirk,

Thank you very much for the feedback.

From our previous run, we already have successful observations of the ingress/egress of the eclipses in SI for CD-31 3271 and TYC 8547-22-1 from MJUO, but additional observations in V and of the secondary eclipse would be very helpful.
For this work, we don't need comps from AAVSO finder charts, and we've been using comps detected by relative brightness to the target and magnitudes directly from the cataloges, when necessary.

For HD 4875 in particular, we already have an egress of the primary eclipse observed in V using the BSM_S station in Australia, but an observation of the secondary eclipse would be very helpful.
Unfortunately, I only have test images from before the QHY600 upgrade, but a single comp should be sufficient. However, I checked VSP for stars within 20" and only a couple of stars having magnitude ~12 should be available.
Maybe, this target would be better suited for one of the BSM stations in Australia?

In general, except for EPIC 212822491 (11.05 mag), I believe all the other targets could be observed from the BSM stations in Australia, if necessary.

Regards,
Andre

(3663) Dirk Terrell — Nov. 27, 2025, 7:23 p.m.

Do you have any results from the previous allocation of time that shows you can reached the needed precision for the secondary eclipses?

(37223) Andre Kovacs — Nov. 28, 2025, 6:18 p.m.

Hello Dirk,

As I said before, from our previous run, we already have successful observations of the ingress/egress of the eclipses in SI for CD-31 3271 and TYC 8547-22-1 from MJUO.
For instance, the photometric precision has usually been up to 3.7 ppt, and we also managed to almost observe a complete ingress (13.7 ppt depth eclipse, 9.54 V-mag target) for TYC 8547-22-1 on 2025-02-25 with the SI filter, but the pre-ingress baseline was too short in this particular occasion.
For the primary eclipses, for instance, we have a complete egress (120.9 ppt depth eclipse) for TYC 8547-22-1 on 2025-02-23 with the SI filter, having a photometric precision of 4.6 ppt.

Alternatively, for the BSM stations in Australia, we also managed to observe an ingress of the secondary eclipse for TYC 8547-22-1 on 2024-10-29 with the V filter, having a photometric precision of 3.6 ppt.

From all the targets, the secondary eclipses for CD-27 2812 and HD 4875 would be the most challenging ones, having depths of only 12.1 and 11.1 ppt, respectively. Unfortunately, the necessary photometric precision for these secondary eclipses seem to be out of reach for the BSM stations in Australia.

In essence, from both MJUO and BSM, the main issue has been the changing weather conditions during the observing session, preventing us from to have as many complete datasets as necessary.

Regards,
Andre

(3663) Dirk Terrell — Nov. 28, 2025, 6:28 p.m.

Ok, thank you. I will pass this along to the TAC.

Comments on this proposal are closed.