Ea. Ajhar et al., CALIBRATION OF THE SURFACE BRIGHTNESS FLUCTUATION METHOD FOR USE WITHTHE HUBBLE-SPACE-TELESCOPE, The Astronomical journal, 114(2), 1997, pp. 626-634
This paper presents the calibration of the surface brightness fluctuat
ion (SBF) technique for use with the Wide Field and Planetary Camera-2
(WFPC-2) on the Hubble Space Telescope (HST), The calibration has a c
olor term and zero point significantly different from the Kron-Cousins
I-band SBF technique developed for ground-based observations. It is a
required first step for using SBF at the larger distances now made po
ssible with HST. WFPC-2 observations of 16 nearby galaxies through the
F555W and F814W filters were tied to the V and I photometry of the gr
ound-based SBF Survey (Tonry ct al. 1997, ApJ, 475. 399), The calibrat
ion of the photometry agrees with that of Holtzman et al. (1995, PASP,
107, 1065) to within a few percent. We used a composite WFPC-2 point
spread function (PSF) to measure (m) over bar, and we found that SBF m
easurements are relatively insensitive to small variations in the PSF,
The identification of globular clusters and dust is much easier with
HSTs high spatial resolution, We computed (M) over bar(1F814W) for th
e sample from the measured (I) over bar(F814W) and the ground-based SB
F Survey distance modulus, The best fitting calibration has (M) over b
ar(1F814W) = (-1.73 +/- 0.07) + (6.5 +/- 0.7)[(V - I)(0) - 1.15], This
color dependence is significantly steeper than the one for I-KC used
on the ground, The total rms about this fit is 0.16 mag, reflecting no
t only the error in WFPC-2 measurements presented here but also the er
rors in the ground-based distance moduli, After accounting for additio
nal sources of error of similar to 0.05-0.10 mag, the HST observations
and ground-based observations are seen to contribute roughly equally
to the residual error. We measured (I) over bar(F814W) for NGC 3379 fr
om the ground to check this calibration, The distance obtained using t
he F814W filter and the HST calibration agreed well with that obtained
in the SBF Survey. For NGC 3379 we also compared the difference in fl
uctuation magnitudes Delta (m) over bar between the I-KC and I-F814W f
ilters to theoretical predictions for a typical old, metal rich popula
tion of a giant elliptical galaxy and found excellent agree mont. (C)
1997 American Astronomical Society.