77
€3 systems have recently been discovered with
binary periods
<10 min (600 sec)! Small enough to fit within Jupiter
<10 min (600 sec)! Small enough to fit within Jupiter
RXJ1914.4+2457 
9.5
minCropper et al (1998)
(V407 Vul)
9.5
minCropper et al (1998)(V407 Vul)RXJ0806.3+15275.4
minRamsay,
Hakala & Cropper (2002) Israel
et al (2002)
5.4
minRamsay,
Hakala & Cropper (2002) Israel
et al (2002)KUV01584–093910.3
minWarner & Woudt (2002)
(ES Cet)
10.3
minWarner & Woudt (2002)(ES Cet)Ultra-short
period Binaries