WD 1302+597
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."
Basic Information

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

Finder Image

FOV = 18.6 x 12.4 'arc, north up, east left.

Spectral Energy Distribution

According to the SED analysis B-band should produce the highest SNR.

Related Links



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 page 

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, 692-699.

Pereira, C., P. Bergeron and F. Wesemael, 2005, "Discovery of Spectroscopic Variations in the DAB White Dwarf GD 323," AJ, 623, 1076-1082..

B. Gary.  This site opened:  2013.05.12.