AAS 207th Meeting, 8-12 January 2006
Session 170 Cosmology, Early Universe, Cosmic Distance Scale
Poster, Thursday, 9:20am-4:00pm, January 12, 2006, Exhibit Hall

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[170.03] Searching for Long-period Cepheids in NGC 4258 with Gemini

C.E. Smith (Indiana U.), L.M. Macri (NOAO)

We present preliminary results of a survey for long-period (P>20d) Cepheids in NGC 4258 using the Gemini North telescope.

NGC 4258 is a key galaxy for the absolute calbration of the Extragalactic Distance Scale, given its precise (3%) geometric distance obtained through VLBI observations of water masers. A recent survey of two fields in this galaxy using HST+ACS yielded over 300 Cepheids, most of which had periods below 10 days. Given the importance of long-period Cepheids for the extragalactic distance scale, we aimed to enlarge the sample of these variables in NGC 4258 through ground-based observations.

Queue-scheduled observations of the ACS fields were carried out at Gemini North using GMOS on ten nights spread over two observing seasons. Data analysis was carried out using both PSF and DIA techniques. We present light curves of the newly-discovered Cepheids and preliminary P-L relations.

This research has been funded in part by NASA grants HST-GO-09810.01-A and HST-HF-01153.01-A. C.E.S. was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program, which is funded by the National Science Foundation through Scientific Program Order No. 3 (AST-0243875) of the Cooperative Agreement No. AST-0132798 between the Association of Universities for Research in Astronomy (AURA) and the NSF.

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