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Carbon stars (with C/O> 1) were long assumed to all be giants, because onlyAGB stars dredge up significant carbon into their atmospheres. The case isnearly iron-clad now that the formerly mysterious dwarf carbon (dC) stars areactually far more common than C giants, and have accreted carbon-rich materialfrom a former AGB companion, yielding a white dwarf and a dC star that hasgained both significant mass and angular momentum. Some such dC systems haveundergone a planetary nebula phase, and some may evolve to become CH, CEMP, orBa giants. Recent studies indicate that most dCs are likely from older,metal-poor kinematic populations. Given the well-known anti-correlation of ageand activity, dCs would not be expected to show significant X-ray emissionrelated to coronal activity. However, accretion spin-up might be expected torejuvenate magnetic dynamos in these post mass-transfer binary systems. Wedescribe our Chandra pilot study of six dCs selected from the SDSS for Halphaemission and/or a hot white dwarf companion, to test whether their X-rayemission strength and spectral properties are consistent with a rejuvenateddynamo. We detect all 6 dCs in the sample, which have X-ray luminositiesranging from logLx= 28.5 - 29.7, preliminary evidence that dCs may be active ata level consistent with stars that have short rotation periods of several daysor less. More definitive results require a sample of typical dCs with deeperX-ray observations to better constrain their plasma temperatures.

A Chandra Study: Are Dwarf Carbon Stars Spun Up and Rejuvenated by Mass Transfer?