KH 15D obscuration event underway

American Association of Variable Star Observers (AAVSO)
Fri, 11/04/2022 - 20:05

     This binary T Tauri system (V582 Mon), which has a circumbinary disc, is currently undergoing one of its periodic eclipse-like obscuration events.  The mid-time of the eclipse is Nov 16.3 UT, but the sequence of phenomema span a couple of weeks; the precursor dimming started a few days ago.  The AAVSO chart shows the two (only) 'official' comp stars.  Most important is to avoid contamination by the bright B-type star HD 47887, located only 35" SW of the target (it is itself a 13" pair).  What's especially desired is I-filter photometry exposed to avoid scattered light in your set-up from the bright star.  Typically one takes 'many' (like 5 or 10) short exposures and either stack them or take averages.  Using a small measuring aperture in the photometry is critical (something like 8" or 10" _diameter_ at most).  KH 15D drops down to about I mag 17.2 at minimum; there is an intervening asymmetric sub-maximum (the Nov 16 prediction date) before dropping again to mag 17 for a day and then back up.  If you can also get V-filter photometry (minimum brightness about mag 19), that is also useful.

     The purpose of the photometry is to help map out the structure of the the outer periphery of the disc by having the two stars act as flashlights behind the obscuring material.