* Astronomy

Title: New Evidence for Mass Loss from delta Cephei from HI 21-cm Line Observations
Authors: L. D. Matthews (MIT Haystack), M. Marengo (Iowa State), N. R. Evans (Harvard-Smithsonian CfA), G. Bono (University of Rome)

Recently published Spitzer observations of the classical Cepheid archetype delta Cephei revealed an extended dusty nebula surrounding this star and its hot companion. The infrared emission resembles a bow shock aligned with the direction of space motion of the star, indicating that delta Cep is undergoing mass-loss through a stellar wind. Here we report HI 21-cm line observations with the VLA to search for neutral atomic hydrogen associated with this wind. Our VLA data reveal a spatially extended HI nebula (~13' or 1 pc across) surrounding the position of delta Cep. The nebula has a head-tail morphology, consistent with circumstellar ejecta shaped by the interaction between a stellar wind and the ISM. We directly measure a mass of circumstellar hydrogen M_HI ~0.07 solar masses, although the total HI mass may be larger. The HI data imply a stellar wind with an outflow velocity V_o=35.6 ±1.2 km/s and a mass-loss rate of solar masses=(1.0 ±0.8)x10**-6 solar masses/yr. We have computed theoretical evolutionary tracks that include mass loss across the instability strip and show that a mass-loss rate of this magnitude, sustained over the preceding Cepheid lifetime of delta Cep, could be sufficient to resolve a significant fraction of the discrepancy between the pulsation and evolutionary masses for this star.

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Maxima of the variable star Delta Cephei on the 17th November, 2011.

Maximum of Delta Cephei variable star at 05:25 UT, 21st October, 2011.

Maximum of the variable star Delta Cephei at 18:10 UT, 29th September, 2011.