June 30, 2017: Dr. Octavi Fors (University of North Carolina at Chapel Hill) and colleagues have requested AAVSO observers' assistance in following up on some targets from the Evryscope survey.
Dr. Fors writes: "The Evryscope team is running a survey of transiting planetesimals around white dwarfs (WDs). To date, WD1145+017, discovered by Kepler, is the only WD found to have disintegrating transiting Ceres-mass objects. The debris/planetesimals transits candidates found by Evryscope need to be confirmed with V or R Johnson filtered, higher SNR (~50) and faster (~25-60s) cadence photometry than Evryscope. We encourage AAVSO observers to follow up these debris/planetesimals transits candidates.
"As a by-product of this survey, Evryscope is also detecting WDs and hot sub dwarfs which show variability of all kinds which we encourage to follow up too."
The first set of targets in this Evryscope-AAVSO follow-up collaboration is given in the list below. The targets will become increasingly observable over the coming weeks and months. Please add them to your programs if possible as soon as they become observable from your location.
|EC 01541-1409||01 56 31.90||-13 54 26.4||12.29-12.33V||4-5 (u)||V361HYA (very rapidly pulsating hot sub-dwarf B star)|
|GD 1068||02 00 13.26||-17 28 43.8||11.95-12.13V||5-6||High proper motion star**; R (close binary with strong reflection)|
|HE 0218-4447||02 20 24.49||-44 33 28.5||12.89-?V||2 runs x 5||Variability type unknown|
|HE 0218-3437||02 20 59.77||-34 23 35.3||13.39-13.40V||2 runs x 5||ELL (rotating ellipsoidal close binary)|
|2MASS J05144393-0848064||05 14 43.93||-08 48 06.4||11.21-?V||4-5 (u)||Hot subdwarf|
|ASAS J102322-3737.0||10 23 21.89||-37 36 59.9||11.61-11.83V||4||EA+R|
|JL 94||22 01 52.22||-75 52 04.4||13.03-?V||2 runs x 6||Hot subdwarf|
|EC 23073-6905||23 10 35.60||-68 49 30.5||12.59-?V||4-5 (u)||Variability type unknown|
*Number of hours each target should be observed in a single night. (u) means debris-like targets which need uninterrupted photometry for 4-5 hrs.
**GD 1068 proper motion values (mas/yr) are RA -20.7, Dec -40.5
Dr. Fors adds that "Transits/dips due to debris-like/planetesimal eclipses around WDs have periods of 4-5hrs (at least in the case of WD1145+017). Thus, we would like to obtain uninterrupted (except for readout time) photometry runs of 4-5hrs imaging the same candidate. If target visibility prevents doing so, at least 2.5hr-runs would be valuable; 2 or 3 runs of 2.5 hrs each would be great."
Johnson V photometry is preferred; if V is not possible, R is okay. Remember that when you are submitting your data to the AAVSO, the letter 'R' stands for Cousins R; 'RJ' stands for Johnson R.
Cadences of 25-60 sec should allow resolution of a debris disk or period determination for the variables on the list. A SNR>50 or higher is requested for all targets.
Charts: Finder charts with comparison star sequences may be created using the AAVSO Variable Star Plotter (VSP). For GD 1068, a 'D' or 'E' scale chart will need to be created to see the comp stars. Also, observers are reminded that GD 1068 is a high proper motion star so it may not be located in the crosshairs.
Submit observations: Please submit observations to the AAVSO International Database using the names given in the target list, making sure to include spaces between parts of a name as given.
This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.
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