Based on a presentation made at the 89th
Annual Meeting of the AAVSO, October 28, 2000
“DE CVn: an Eclipsing Binary with a White Dwarf ?”
DE CVn (RX J1326.9+4532, max. magnitude =
13.68 Rc) is an unusual eclipsing binary. There is currently only one
publication on this star by R. M. Robb and R. Greimel (1997, Inf. Bull. Var.
Stars, No. 4486). These authors suggest that, from their observations, the
primary star is a M0V red dwarf and the secondary component is a white dwarf.
Their initial analysis of the system revealed a 0.18-day period, but was later
doubled to 0.36 day due to unequal maxima in the light curve. Their 1997 data
reflect results from observing in the V and R bands for seven nights, and their
published light curve exhibits two nights’ data.
Due to the brief duration of the primary
minimum, 0.0212 day ± 0.0006, as calculated by Robb and Greimel, data points on
the descending and ascending branches of the primary minimum are few in number.
Gathering more data points for the ascending and descending branches would help
to both determine the degree of totality of the eclipse and refine the
published period of 0.36 day.
We observed DE CVn photometrically in the
UBVRI bands for five nights in June 2000 (JD 2451697 through 2451701) with the
CCD camera of the 31-inch telescope of the Lowell Observatory in Flagstaff,
Arizona. Data in U and I filters were taken during three of the five nights.
Data were reduced using IRAF (version
2.11.3, distributed by NOAO under contract to the NSF) and magnitudes were
extracted using the IRAF Daophot package.
work is in progress, but we would like to present here one result of our CCD
photometry: a strong dependence of the amplitude of variations on the color. An
indication of this effect is found already in the cited paper by Robb and
Greimel: the depth of the eclipse is 0.054 magnitude ± 0.010 in R and
0.128 magnitude ± 0.029 in V. From our current work, we confirm this
trend in all the observed bands:minimum depth is 0.10 magnitude in I, 0.15 in R, 0.30 in V, 0.60 in B,
and 1.00 in U. We suppose that this trend of decreasing minimum depth
with decreasing wavelength is due to the color difference between the white
dwarf and red dwarf stars.
This project has been partially supported
by NSF/REU grant AST-9820555 and grant No. 99-02-16333 from the Russian
Foundation for Basic Research.