Proposal #599

Proposer	(37223) Andre Kovacs (andre.kovacs@gmail.com) obscode: KADB
Assigned To	(3663) Dirk Terrell
Date Submitted	Feb. 10, 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-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 a par of photometric filters B and V (faint targets) or R and I (bright targets), 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
EPIC 212822491	13.738733	-4.82750	11.03–11.05	—	—	—	No
HD 4875	0.844442	-18.50592	9.12–8.98	—	—	—	No

Comments

(3663) Dirk Terrell — Feb. 12, 2025, 4:10 p.m.

The TAC is inclined to look at these targets to check the feasibility of achieving the project's goals. First would be to take images of each field and see if the desired S/N can be reached and if the small FOV of OC61 can provide a good comp star. If we then proceed, you would need to provide a list of observing times for the eclipses that you want to cover. Looking at the TESS data, I see that the secondary eclipses are complete (total), so with good data you could achieve the goals of the project. HD 4875 is pretty quiet outside the eclipses, so it provides the best chance of success. The other two have large variations outside eclipse but maybe they're gradual enough that you can get a good flux ratio.

(37223) Andre Kovacs — Feb. 12, 2025, 10:33 p.m.

Dear Dirk,

Indeed, the small FOV of OC61 makes the data reduction very chalenging, but we only need a single usable comp for this project, even using magnitudes from the Tycho2 catalog that we've already done before except for HD 4875.

According to the latest test observations on 2025-02-11, I managed to check that an SNR~1000 is achievable in the SI filter with integration times ranging from 5s up to 20s for these targets.

Unfortunately, we still haven't been able to observe the secondary eclipses from MJUO, only primary eclipses so far for EPIC 212822491, TYC 8547-22-1 and CD-31 3271.

Cordially,
Andre

(37223) Andre Kovacs — Feb. 13, 2025, 11:57 a.m.

Dear Dirk,

Here are the upcoming eclipses visible from MJUO for the targets:

The following list of predicted eclipse observations are suggested for the next 180 days for TYC 8547-22-1 (OC61 - pre/post-baseline(s) already considered):
- 2025-02-23 8:40 (Session start time in UTC) to 12:32 (Session end time in UTC): primary eclipse with 24% Moon illumination at 94˚ distance;
- 2025-02-25 10:00 (Session start time in UTC) to 15:26 (Session end time in UTC): secondary eclipse with 8% Moon illumination at 96˚ distance;
- 2025-02-27 12:54 (Session start time in UTC) to 15:42 (Session end time in UTC): primary eclipse with 0% Moon illumination at 96˚ distance;
- 2025-03-29 7:36 (Session start time in UTC) to 10:59 (Session end time in UTC): primary eclipse with 0% Moon illumination at 96˚ distance;
- 2025-03-31 8:26 (Session start time in UTC) to 13:35 (Session end time in UTC): secondary eclipse with 6% Moon illumination at 93˚ distance;
- 2025-05-02 6:43 (Session start time in UTC) to 9:25 (Session end time in UTC): primary eclipse with 26% Moon illumination at 87˚ distance;

The following list of predicted eclipse observations are suggested for the next 180 days for CD-31 3271 (OC61 - pre/post-baseline(s) already considered):
- 2025-02-24 10:05 (Session start time in UTC) to 13:55 (Session end time in UTC): primary eclipse with 15% Moon illumination at 120˚ distance;
- 2025-03-27 8:36 (Session start time in UTC) to 11:53 (Session end time in UTC): secondary eclipse with 6% Moon illumination at 106˚ distance;

The following list of predicted eclipse observations are suggested for the next 180 days for EPIC 212822491 (OC61 - pre/post-baseline(s) already considered):
- 2025-04-05 9:59 (Session start time in UTC) to 13:00 (Session end time in UTC): secondary eclipse with 53% Moon illumination at 96˚ distance;
- 2025-05-18 7:48 (Session start time in UTC) to 12:06 (Session end time in UTC): secondary eclipse with 71% Moon illumination at 97˚ distance;

The following list of predicted eclipse observations are suggested for the next 180 days for HD 4875 (OC61 - pre/post-baseline(s) already considered):
- 2025-06-04 16:14 (Session start time in UTC) to 18:15 (Session end time in UTC): secondary eclipse with 64% Moon illumination at 157˚ distance;

Cordially,
Andre

(37223) Andre Kovacs — Feb. 14, 2025, 11:06 a.m.

Hello Dirk,

Regarding the existing TESS data, we need additional observations in a different passband to complement the TESS observations with color information to improve the stellar atmospheric model.
Unfortunately, we tried observing in B and V using smaller telescopes to see if it would work with the TESS passband, but we had to switch, instead, to the infrared band to have better defined secondary eclipses, requiring larger telescopes like the OC61.
Hope this helps to clarify our intent with this proposal.
Dr. Pierre Maxted can provide further details on that subject during his webinar on March 1st.

Cordially,
Andre

(3663) Dirk Terrell — Feb. 14, 2025, 4:12 p.m.

Yes, I understand that you need other bands because the flux ratios will be different in each band if the stars have different temperatures, as is obviously the case here. I was just pointing out that the TESS data demonstrate that the eclipses are complete, so it is straightforward in that case to get the flux ratio. It is the ratio of the eclipse depth divided by the observed flux that remains. If the eclipses were partial, then the flux ratio is indeterminate and you have to get that information from spectra. So, you'll get the deepest eclipse in the I band (thus a better determination of the eclipse depth) and you should probably work in that filter primarily. You mention BV observations. Is that because you want to measure the flux ratios in those bands also for some reason?

(37223) Andre Kovacs — Feb. 14, 2025, 8:43 p.m.

Hello Dirk,

Please ignore the paragraph about the BV observations, since our previous tests from OC61 and the BSMs in Australia showed that secondary eclipses in those two filters were not sufficiently defined to fit the eclipse model having only a parcial secondary eclipse.

So, instead, we had now to switch to the observations only in the Sloan I filter, and use both the TESS and Sloan I bands for the flux ratio.

I'm very sorry for the confusion.

Cordially,
Andre

(4726) Kenneth Menzies — Feb. 17, 2025, 1:02 a.m.

Andre:

Send me an email at kenmenstar@gmail.com and I will send you a plan template to fill in with target name, RA/DEC and start and end time for each eclipse.

Ken

Comments on this proposal are closed.