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We report the results of two XMM-Newton observations of the ultra-compactlow-mass X-ray binary 4U1850-087 located in the galactic globular clusterNGC6712. A broad emission feature at 0.7keV was detected in an earlier ASCAobservation and explained as the result of an unusual Ne/O abundance ratio inthe absorbing material local to the source. We find no evidence for thisfeature and derive Ne/O ratios in the range 0.14-0.21, consistent with that ofthe interstellar medium. During the second observation, when the source was 10%more luminous, there is some evidence for a slightly higher Ne/O ratio andadditional absorption. Changes in the Ne/O abundance ratio have been detectedfrom another ultra-compact binary, 4U1543-624. We propose that these changesresult from an X-ray induced wind which is evaporated from an O and Ne richdegenerate donor. As the source X-ray intensity increases so does the amount ofevaporation and hence the column densities and abundance ratio of Ne and O.Comment: 9 pages, 6 figures, accepted for publication in Astronomy and  Astrophysic

Low-energy absorption towards the ultra-compact X-ray binary 4U 1850-087 located in the globular cluster NGC 6712