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Near-UV observations of the planet host star WASP-12 uncovered the apparentabsence of the normally conspicuous core emission of the Mg2 h&k resonancelines. This anomaly could be due either to (1) a lack of stellar activity,which would be unprecedented for a solar-like star of the imputed age ofWASP-12; or (2) extrinsic absorption, from the intervening interstellar medium(ISM) or from material within the WASP-12 system itself, presumably ablatedfrom the extreme hot Jupiter WASP-12b. HIRES archival spectra of the Ca2 H&Klines of WASP-12 show broad depressions in the line cores, deeper than those ofother inactive and similarly distant stars and similar to WASP-12's Mg2 h&kline profiles. We took high resolution ESPADONS and FIES spectra of threeearly-type stars within 20' of WASP-12 and at similar distances, which show theISM column is insufficient to produce the broad Ca2 depression observed inWASP-12. The EBHIS H1 column density map supports and strengthens thisconclusion. Extrinsic absorption by material local to the WASP-12 system istherefore the most likely cause of the line core anomalies. Gas escaping fromthe heavily irradiated planet could form a stable and thick circumstellardisk/cloud. The anomalously low stellar activity index (logR'HK) of WASP-12 isevidently a direct consequence of the extra core absorption, so similar HKindex deficiencies might signal the presence of translucent circumstellar gasaround other stars hosting evaporating planets.

Absorbing gas around the WASP-12 planetary system