WD 1639+537
Last Updated:  2013.08.14

This WD is a variable with an amplitude and period that could be explained by a starspot, and probably not an exoplanet. It was discovered to be variable by the PAWM2 group observing project, and noticed as a variable by Joe Garlitz (on June 1). This web page is devoted to light curves of the WD and will serve as a baseline for a later search for changes in either amplitude or phase (which can only occur for the star sot explanation).  [Return to PAWM2 web page]

Update: 2013 Aug 14, Pierre Bergeron (WD expert in Canada) reviewed this web page and wrote "Interesting... This is a magnetic DA white dwarf, therefore it probably has a hydrogen-rich atmosphere rather than a helium-rich composition. Because of the dipole field, it probably has a magnetic spot." He said he'd keep it in mind for others who might be interested in this object's variability.

Basic Data

WD1639+537 (also referred to as GD 356) is currently located at 16:40:56.96 +53:41:06.7 (J2000). It has V-mag = 15.045 and B-V = 0.236 (according to APASS). It has a proper motion of 0.237 "arc/year (to the southwest). The spectral energy distribution (SED) shows it to be a cool white dwarf without evidence for an accretion disk. It has a published temperature of 7510 K (). Its spectrum shows a composition of mostly helium, but hydrogen emission lines are present(). The spectral type is given as DAE.  Spectroscopic line variations imply a rotation period of 0.0803 days (1.927 hours). It has a magnetic field of 13 mega-gauss (). The mass has been estimated to be 0.67(0.07) solar masses. 

Overall Plan

The plan is to establish an accurate phase-folded LC for 2013 June for comparison with a similar analysis using data from the 2014 observing season. If the variation is caused by a starspot there will likely be a change in the amplitude and/or phase. Until I learned that it exhibited spectrum changes with a period essentially the same as that for brightness variations (1.93 vs. 1.927 hrs) I had planned on follow-up observations for the purpose of assessing the idea that an exoplanet was reflecting WD starlight to cause the brightness variations. Because the exoplanet hypothesis is unlikely this target has been abandoned by PAWM2.

Phase Fold Solution


Phase fold solution for 7 useable LCs.

SED


There's no evidence for an IR excess due to accretion disk.


This plot shows the SED in relation to photometry bands. The inset info box gives expected SNR values (ratioed to r'-band).

Finder Images


WD1639+537 (blue star) is now SW of the red star. Since this image was taken the blue star has moved to the lower-right and is very close to the fainter red star.


Thi is an old image, when the WD was NE of a nearby star.


FOV = 18 x 12 'arc, north up, east left. WD1639+537 is indicated by the red lines, and a much fainter nearby star is indicated by blue lines. WD1639+537 is located at 16:40:56.96 +53:41:06.7 (J2000).




Individual Light Curves


References and Relevant 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, PDF link  PPT link 



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WebMaster: B. Gary.  Nothing on this web page is copyrighted. This site opened:  June 8, 2013