Radio Emission from delta Cephei: Evidence of Mass Loss Via an Ionized Wind?

Mass loss during the Cepheid evolutionary phase has long been suspected as a means of accounting for the so-called Cepheid mass discrepancy — i.e., the persistent 10-15% disagreement between stellar masses derived from stellar evolution models versus those derived from the Period-Luminosity relation or orbital dynamics. Recently, the Cepheid archetype delta Cephei was found to exhibit sharp, periodic increases in X-ray emission during the stellar pulsation phase associated with maximum radius. These X-rays are thought to originate either from flare-like coronal emission or pulsationally-driven shocks and may be linked with mass loss. Such processes are predicted to result in partial ionization of the stellar atmosphere. To search for evidence of such ionized gas, we recently used the Karl G. Jansky Very Large Array (VLA) to search for radio continuum emission from delta Cephei during epochs near maximum radius. Here we report a detection of the star at 15 GHz (~6 sigma). To our knowledge, this is the first reported detection of radio emission from a Cepheid. Implications for the origin of the periodic X-ray emission and the possible presence of ongoing mass loss will be discussed.