Spitzer Space Telescope - Archive Research Proposal #50156


The Mid-Infrared Cepheid Distance Scale: A Reconnaissance Program of Cepheids in
the Local Group

Principal Investigator: Barry Madore
           Institution: Carnegie Institution of Washington

     Technical Contact: Barry Madore, Carnegie Institution of Washington

Co-Investigators: 
Wendy Freedman, Carnegie Observatories                                
Violet Mager, Carnegie Observatories                                  
Jane Rigby, Carnegie Observatories                                    

Science Category: local group galaxies 
Dollars Approved: 25000 

Abstract:
We request archival funding to search for serendipitous IRAC detections of known
Cepheids in Local Group galaxies. This archival proposal is a parallel study in
support of a Cycle 5 GO proposal (PI: Freedman) to re-calibrate the Cepheid
distance scale from the ground up using new IRAC photometry of ten Galactic
Cepheids having HST trigonometric parallaxes (Benedict et al. 2007), in
combination with eighty LMC Cepheids (from Persson et al. 2004), to establish
the slope and secure the zero point of the Cepheid Period-Luminosity Relation at
3.6 and 4.5 micron. Here we intend to characterize the mid-infrared
detectability of Cepheids in Local Group galaxies, by examining upwards of 8,000
archival images containing cataloged Cepheids with known periods and predicted
luminosities. The Cepheids in these images exhibit a wide range of background
intensity, often have complex crowding, and have a wide range of apparent
magnitudes. From this reconnaissance survey we will be able to directly assess
the ability of Spitzer to obtain high signal-to-noise observations of Cepheids
in individual Local Group galaxies, and we will select the least crowded and
least confused of the serendipitously--obserserved Cepheids. We plan to target
this sample in the Warm Mission, with the goal of putting the Local Group
securely onto the mid-infrared Cepheid distance scale.