Alert Notice 710: Monitoring requested for UXOR ASASSN-V J181654.06-202117.6

Note: This campaign has been concluded as of 28 October 2020, BUT a new campaign from the SAME ASTRONOMER requesting coverage of the SAME TARGET is announced in AAVSO Alert Notice 723.  -  Elizabeth O. Waagen, 28 October 2020

July 14, 2020

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Dirk van Dam (Leiden Observatory) and Dr. Matthew Kenworthy (Leiden Observatory) request AAVSO observer assistance in monitoring the UXOR ASASSN-V J181654.06-202117.6 in an exoplanet/planetary system study.

van Dam writes: "This system is a recently discovered system by ASAS-SN, which shows a very deep eclipse (0.8 mag ~ 50%), that is not only asymmetric (indicative of a circumplanetary disk), but also exhibits substructure (could possibly be rings, or indicative of moon formation). The whole could also be an eclipsing dust cloud or other options, but only further analysis will reveal what this particular occultation is. The AAVSO observations would be helpful to fill out the eclipse and add more detail to the full transit to explore the possibility of rings, or to better constrain the modeling of the eclipse. The potential follow-up campaign would be to catch the whole eclipse and constrain the period of the system."

Observations are currently being made at Las Cumbres Observatory in Chile. AAVSO observers are requested to being monitoring the target now and continue for 10 days after the target has returned to its quiescent level (V~13.3).

CCD photometry is requested (filters in order of priority: Sloan g, V, B, Rc, Ic). If observing with multiple filters, alternating filters is preferred. Filtered photometry is preferred, but if unfiltered observations are made, they should be reduced to a V filter (CV). Visual observations are also welcome.

Re the cadence of CCD observations, van Dam says: "There seems to be at least nightly variation of the target, but shorter cadence is preferred to fill out the light curve and see whether there is intranight variance. The shorter the cadence the better, with a minimum of twice per night. Time series would be the best and every hour would be fantastic, with a minimum SNR of 5."

Observers are requested to include the airmass value for each observation. The astronomers also need to know the location of each observer's telescope, so if you have not filled out the AAVSO's Site and Equipment webpages, please be sure to do so before submitting data on this star. You may also access these pages from your My account page.

van Dam communicates that observers providing sufficient and useful data will definitely be considered for co-authorship.

Note that ASASSN-V J181654.06-202117.6 has been the subject of ATel #13818 (Z. Way et al.).

Coordinates (J2000): R.A. 18 16 54.06  Dec. -20 21 17.5  (from VSX entry for target)

Charts with comparison stars for ASASSN-V J181654.06-202117.6 may be created using the AAVSO Variable Star Plotter (VSP).

Please report all observations to the AAVSO International Database using the name ASASSN-V J181654.06-202117.6.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen using material supplied by Dirk van Dam.

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