July 21, 2017: The following request for AAVSO assistance has been received from Denis Denisenko (Sternberg Astronomical Institute, Moscow State University) to help characterize "...the cataclysmic variable DDE 48 in Vulpecula. This CV belongs to the rare ER UMa subtype of dwarf novae, with only 6 other stars in VSX being classified as UGER. According to 2016-2017 observations by Nikolay Mishevskiy (MNIC) and Denis Denisenko (DDE), this variable is very active, with superoutbursts to magnitude V=15.4 occurring approximately once a month. There are several normal outbursts between the superoutbursts.
"The campaign has two goals: 1) to study the long-term behaviour (that is, determine the supercycle length and the exact number of normal outbursts per supercycle); 2) to measure the orbital period and to follow the evolution of superhumps period during the superoutbursts.
"Snapshot photometry (preferrably 2-3 times per night) is requested beginning now until the next superoutburst, which is about to start within the next 2-3 days. Observations from different longitudes are essential since the variable is changing very rapidly. When DDE 48 brightens to magnitude V=16, continuous time series are requested for as long as possible while the object is above 30 deg elevation." DDE 48 is V=19.0-19.5 at minimum.
"Unfiltered observations are OK when the variable is below magnitude V=16. Use V filter only if you can reach S/N ratio of at least 50 in 60-sec or 90-sec exposures.
"Charts with a comparison star sequence for DDE 48 may be created using the AAVSO Variable Star Plotter (VSP). The recommended comparison star is the 146 on the AAVSO chart (V=14.573) and is located 3 arc min east of DDE 48, and the check star is the 156 (V=15.605), which is 2 arc min east of DDE 48."
DDE 48 entry in AAVSO VSX: https://www.aavso.org/vsx/index.php?view=detail.top&oid=473984
Coordinates: 20 46 11.80 +24 20 57.2 (J2000.0)
"Note: DDE 48 is located only 4 arc minutes west of another dwarf nova, MASTER OT J204627.96+242218.0, which has outbursts to V=15.5. Please take the opportunity to investigate these two poorly studied cataclysmic variables in one CCD field of view. The same comparison stars can be used for both CVs.
"A color-combined DSS finder chart showing the position of DDE 48 and MASTER OT J204627.96+242218.0 (10'x10' FOV) may be seen at: http://scan.sai.msu.ru/~denis/DDE48-BRIR.jpg "
Please report your observations to AAVSO International Database using the name DDE 48.
This campaign, which will run through October 2017, is being monitored on the AAVSO Observing Campaigns webpage and is being followed on the Campaigns and Observation Reports Forum at https://www.aavso.org/dde-48-observing-campaign.
This AAVSO Alert Notice was compiled by Elizabeth O. Waagen from text supplied by Denis Denisenko.
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