SDSS 1355 + 0856 was identified as a hot white dwarf ( WD ) with a binary companion from time-resolved SDSS spectroscopy as part of the ongoing SWARMS survey .
Follow-up observations with the ARC 3.5m telescope and the MMT revealed weak emission lines in the central cores of the Balmer absorption lines during some phases of the orbit , but no line emission during other phases .
This can be explained if SDSS 1355 + 0856 is a detached WD+M dwarf binary similar to GD 448 , where one of the hemispheres of the low-mass companion is irradiated by the proximity of the hot white dwarf .
Based on the available data , we derive a period of 0.11438 \pm 0.00006 days , a primary mass of 0.46 \pm 0.01 M _ { \odot } , a secondary mass between 0.083 and 0.097 M _ { \odot } , and an inclination larger than 57 ^ { \circ } .
This makes SDSS 1355 + 0856 one of the shortest period post-common envelope WD+M dwarf binaries known , and one of only a few where the primary is likely a He-core white dwarf , which has interesting implications for our understanding of common envelope evolution and the phenomenology of cataclysmic variables .
The short cooling time of the WD ( 25 Myr ) implies that the system emerged from the common envelope phase with a period very similar to what we observe today , and was born in the period gap of cataclysmic variables .