Observations of Cepheid and Mira Variables in M101

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Session 24 -- The Distance Scale
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

[24.08] Observations of Cepheid and Mira Variables in M101

D.R.Alves (UCD/LLNL), K.H.Cook (LLNL)

KPNO 4m BVRI CCD images of an outer field in M101 have been searched for variable stars. We have identified 4 Cepheids and 6 Miras by the morphology of their phased lightcurves and their color information. The Cepheid and Mira periods range from 30 to 60 days and 350 to 800 days, respectively. We will present Cepheid and Mira distance moduli determinations that agree within experimental uncertainties. We estimate an approximate modulus of 29.25.

We have derived multi-wavelength period-luminosity relations for our Cepheids. This allows the simultaneous determination of distance modulus and reddening. The analysis suggests negligible reddening for these stars. A preliminary analysis shows no dependence of the Cepheid P-L relation on the M101 abundance gradient across this field.

We have used our multi-wavelength data to determine bolometric corrections for the Miras. Two of the Miras appear to be Asymptotic Giant Branch members. We employed a P-L relation for long period AGB Miras to derive an M101 distance modulus independent of the Cepheid distance scale.

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