The striking case of RX J1856.5-3754
n500 ks DDT Chandra exposure
(i) RX J1856.5-3754 has a featureless  X-ray continuum
(ii) better fit with a simple bb than with more sophisticated atmospheric models (Burwitz et al 2001, Drake et al 2002, Burwitz et al, 2002)
Image generated by Aladdin Ghostscript (device=ppmraw)

CREATOR: XV Version 3.10a  Rev: 12/29/94 (PNG patch 1.2)  Quality = 100, Smoothing = 0
Image generated by Aladdin Ghostscript (device=ppmraw)

CREATOR: XV Version 3.10a  Rev: 12/29/94 (PNG patch 1.2)  Quality = 100, Smoothing = 0
CREATOR: XV Version 3.10a  Rev: 12/29/94 (PNG patch 1.2)  Quality = 100, Smoothing = 0
CREATOR: XV Version 3.10a  Rev: 12/29/94 (PNG patch 1.2)  Quality = 99, Smoothing = 0