The Coolest X-ray Emitting White DwarfsquestionMark

Among the virgul6000 new white dwarfs (WDs) spectroscopically confirmed by the SloanDigital Sky Survey (SDSS) are three cool DAs and two cool DBs within 1. ofsupersoft ROSAT All Sky Survey (RASS) sources. WDs at these relatively lowtemperatures (<23,000K) are not expected to be Xray emitters, but the SDSSphotometric and spectroscopic data fail to identify any other obvious opticalcounterparts to the RASS sources to the SDSS limits (gvirgul23 mag in photometry). Wepropose 5 ksec XMMNewton observations of these five SDSS WDs to obtain pinpointXray positions and improved flux measures for these objects. If XMM dataconfirm that the five WDs are Xray sources, they will be of great interest; inparticular, theoretical work will be required to explain how such cool WDs can emit X rays. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]