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Front. Astron. Space Sci. | doi: 10.3389/fspas.2019.00065

Prospects for X-Ray and FUV Observations to Provide Insight into the ``Cepheid Mass Problem"

  • 1Smithsonian Astrophysical Observatory, Center for Astrophysics, Harvard University, United States
  • 2Department of Astrophysics & Planetary Science, Villanova University, United States

The classical Cepheid Leavitt Law (Period-Luminosity relation) has been known for
100 years, and used as in extragalactic distance determination for nearly as
long. However, Cepheids still present us with surprises. Recent results about X-ray
behavior is just one example. Around minimum radius the pulsation wave from the
envelope creates a disruption in the photosphere and chromosphere. X-ray activity,
on the other hand remains constant at a low level at this phase. Just after maximum radius, however,
X-ray flux increases sharply (four fold in the case of $\delta$ Cep). We summarize here
the observational program to explore parameters involved and theoretical investigations
searching for a basic understanding of this upper atmosphere phenomena.

Keywords: Cepheids, Variable - stars, Luminosity, distance scale, X-Rays

Received: 07 Feb 2019; Accepted: 24 Sep 2019.

Copyright: © 2019 Evans and Engle. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Nancy R. Evans, Smithsonian Astrophysical Observatory, Center for Astrophysics, Harvard University, Cambridge, United States, nevans@cfa.harvard.edu