AAS 207th Meeting, 8-12 January 2006
Session 105 M31, Galaxy Kinematics and the Distance Scale
Oral, Tuesday, 2:00-3:30pm, January 10, 2006, Balcony C/D

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[105.06] HST Observations of Cepheid Variables in NGC 4258

L.M. Macri (NOAO), K.Z. Stanek (OSU), D.F. Bersier (Liverpool JMU), L.J. Greenhill, M.J. Reid (CfA)

We present the results of an HST/ACS survey for Cepheid variables in the spiral galaxy NGC 4258, a key galaxy for the absolute calibration of the Extragalactic Distance Scale.

We obtained BVI observations of two fields in NGC 4258 using the ACS Wide Field Camera on twelve epochs over a time interval of 46 days. We discovered over 300 Cepheids with periods ranging from 3 to 45 days, a major improvement over the previous sample of 15 Cepheids discovered with HST/WFPC2.

We present the final ACS sample of Cepheids, tentative distance estimates based on the ACS BVI data, and preliminary results of follow-up observations of a sub-sample of the Cepheids using HST/NICMOS. We also discuss preliminary results from additional observations acquired with Gemini North/GMOS to extend the sample of long-period Cepheids.

This research has been funded in part by NASA grants HST-GO-09810.01-A, HST-GO-10399.01-A and HST-HF-01153.01-A.

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