NOAO >   Observing Info >   Approved Programs >   2004B-0048

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Proposal Information for 2004B-0048


PI: Thomas E. Harrison, New Mexico State Universtiy, tharriso@nmsu.edu
Address: Astronomy Department, Box 30001/MSC4500, Las Cruces, New Mexico 88003, USA

CoI: G. Fritz Benedict, University of Texas, Austin
CoI: Barbara McArthur, University of Texas, Austin
CoI: Ryan Campbell, New Mexico State University
CoI: Richard Patterson, University of Virginia
CoI: Thomas Barnes III, University of Texas, Austin
CoI: Wendy Freedman, Carnegie Institution of Washington
CoI: Michael Feast, University of Cape Town

Title: An Astrometric Calibration of the Cepheid Period-Luminosity Relation

Abstract: We have a large (110 orbit) \it HST project in Cycles 12 & 13 to astrometrically calibrate the Cepheid Period-Luminosity (PL) relation. The main result of this program will be a calibration of the PL relation zero point to +/- 3%. This improvement will reinstate Galactic Cepheids as the fundamental rung in the extragalactic distance scale ladder. In addition, we will be able to refine the distance modulus to the LMC. To produce high-precision parallaxes with the Fine Guidance Sensors on the \it HST requires us to estimate the parallaxes of the reference frame stars. We do this by determining the spectral type of each reference star, and then using \it UBVRIJHK photometry to estimate A_\rm V and M_\rm V. We request three nights on the KPNO 4m with the RC spectrograph, and three nights on the 2.1m with the GoldCam spectrograph, to obtain moderate resolution spectroscopy of the 34 reference stars to perform MK classification.


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