Bruce L. Gary, Hereford
Arizona Observatory, Last updated 2013.08.14
This web page describes a white dwarf
star whose variations were discovered by amateur observers
as part of the PAWM2 project. The semi-amplitude (~6 mmag)
and period (~3.5 hours) could
be produced by 1) a star spot, or 2) an exoplanet
reflecting WD star light.
Update: 2013 Aug 13, Pierre Bergeron (WD expert in Canada)
reviewed this web page and will keep it in mind for anyone
interested in what we found, and wrote "I will let you know if I
ever go back to study this star in the future."
WD 1302+597 (hereafter referred to as "1302") is located at
13:04:32.04 +59:27:33.6 (J2000). The observing season is centered on
April 7. V-mag = 14.4, B-V = -0.160 and J-K = -0.135. These two
colors are "compatible" in the sense that this color combination is
found at the blue end of a color/color distribution of main sequence
stars without binary companions. The spectral energy distribution
(SED) is also consistent with there not being a cool binary.
The optical spectrum shows both hydrogen and helium abasorption
lines, so the spectral type is DBA. Aliases for 1302 include EG 235,
LP 96-040, GD 323, LB 2539.
Review of Previous Publications
One of the first publication about 1302 was by Liebert et al (1984).
They concluded that it had "an optically thin hydrogen layer
overlying a helium envelope..." Koester et al (1994) ruled out
spectroscopic variability on timescales of hours to a decade, which
was used as evidence that star spots are not present. Pereira et al
(2005) discovered 3.5 hour variability in spectral line widths, with
H and He varying in an opposite manner. They attributed the 3.5-hour
periodicity to rotation of a star with an inhomogeneous surface
distribution of H and He.
Variability Discovery Story
The evidence for 1302's variability began with two LCs by Joe
Garlitz (2013.05.09 and .10, C-band), because the two LC shapes
differed in a way that could be explained by a variation
superimposed on a large air mass curvature. This was confirmed
by a follow-up observation by Bruce Gary (2013.05.12, g'-band),
where the AMC was much less. The variability resembles that for WD
2359-434, which has been described by Gary (2013). Whereas WD
2359-434 could not be observed by most northern hemisphere
observers, 1302 is located at a northern declination within reach of
more amateur observers.
Sample Light Curve
FOV = 18.6 x 12.4 'arc, north up, east left.
According to the SED analysis B-band should produce the highest SNR.
Gary, Bruce L., T. G. Tan, Ivan
Curtis, Paul J. Tristram and Akihhiko Fukui, 2013, "Searching for
White Dwarf Exoplanets: WD 2359-434 Case Study", Society for
Astronomical Sciences 2013 Conference Proceedings, 1st
Koester, D., James Liebert and Rex A. Safer, 1994, "GD
323: New Observations and Analysis of the Prototype DAB White
Dwarf," AJ, 422, 783-790.
Liebert, James, F. Wesemael, E. M. Sion and G. Wegener, 1984,
"GD 323: A White Dwarf with a Stratified H/He Atmosphere?" AJ, 277,
Pereira, C., P. Bergeron and F. Wesemael, 2005, "Discovery of
Spectroscopic Variations in the DAB White Dwarf GD 323," AJ,
WebMaster: B. Gary. This site opened: 2013.05.12.