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Alert Notice 525: Observing Campaign on KIC 02856960

July 31, 2015: The AAVSO requests time-series observations of the eclipsing binary system KIC 02856960 beginning immediately, with intensive coverage urgently requested during the window of 2015 August 8.0 through August 12.0.  Observations are requested on behalf of an international campaign coordinated by Dr. Thomas Marsh (University of Warwick) who is attempting to explain the enigmatic behavior of this possible triple system.  CCD observers around the world are encouraged to participate, since the observing program requires as complete temporal coverage as can possibly be obtained.  Observers in continental Asia and the Pacific are especially encouraged to participate.

The object is located at the following (J2000) coordinates:

RA: 19 29 31.52 , Dec: +38 04 35.9

The star has an approximate V magnitude of around 16.0 (B-V ~ 0.85).  The short-period component of the system has regular eclipses with a period of 0.2585082 days, and an eclipse depth of less than 0.015 magnitudes in V.  This campaign is focused on the longer-period eclipses which occur approximately every 204 days, with a depth of about 0.07 magnitudes.  The properties of this system have not been successfully modeled, and observations of this eclipse are strongly desired to provide additional constraints for the modeling efforts.  This is a challenging campaign due to the small amplitudes involved (less than 0.1 magnitude) and the relative faintness of the target (V=16.0), but our calculations suggest that the required precision should be achievable by many AAVSO observers using CCD cameras and typical telescopes of 20cm and larger.

Observers are asked to obtain photometry at the level of 1-2 percent (0.01 to 0.02 magnitudes) or better, using net exposure times less than 600 seconds (10 minutes) total.  For observers with larger apertures, the use of filters is encouraged if the net exposure time per measurement can be kept below 600 seconds, with the Ic and V filters preferred in that order. Only one filter is needed, and observers may take clear or unfiltered data if needed to reach the required S/N in sufficient time.  Exposures of 60 seconds are ideal, however, *please note the following*: if you would otherwise combine multiple exposures to create a stacked image with the requisite S/N within 600 seconds, the researchers have asked that you submit measurements from the individual frames instead.  This will give the researchers additional flexibility in averaging your observations together, even though your S/N per measure might be lower than ideal.

Marsh and collaborators request as intense coverage as possible between 2015 August 8.0 (JD 2457242.5) and 2015 August 11.0 (2457245.5); the eclipse event is currently predicted to begin around 2015 August 9.5 (JD 2457244.0) and to end around 2015 August 10.4 (2457244.9), and the researchers would like at least a day's intensive coverage on either side to better determine each observer's out-of-eclipse mean magnitude.  If possible, we strongly encourage additional time-series outside this window, beginning as early as August 1, and continuing to at least August 14 to provide additional information about the background variations and mean light.

Charts for this object are available via AAVSO VSP:

https://www.aavso.org/vsp

The AAVSO Sequence Team has assigned a subset of Dr. Marsh's suggested near-field comparison stars for this target that provide a reasonable match to the variable's (g-r) color.  Observers should use these comparisons if at all possible; please clearly identify any and all comparisons used in your report.

Observers are asked to promptly process their photometry and submit their observations as normal via the WebObs feature on the AAVSO website; please clearly indicate which comparison(s) were used and the filter(s) used for the observation.  Please use the name "KIC 02856960" when submitting observations, including the leading zero ("0") in the KIC identifier.

For more information and scientific background on this campaign, please refer to the researchers' website at the following URL:

http://deneb.astro.warwick.ac.uk/phsaap/kic2856960/

This AAVSO Alert Notice was prepared by M. Templeton.

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