21
61 A which includes the N II lines. For HoII, a correction for this contribution
to the H ux is made by assuming f H f H + f N II
0
:
88, based
on spectral observations of H II regions by Hunter & Gallagher 1985. This cor-
rection is applied while calibrating the image using the technique of Waller 1990
and observations of the H standard star BD +8 2015 Stone 1977. Attempt-
ing to reproduce the irregular apertures de ned by Hodge, Strobel, & Kennicutt
1994 for H II regions in HoII provides a check for the H calibration constant.
Our photometry of these regions agree within
9 . Deviations may be caused
by failure to reproduce the irregular apertures exactly. Since an H standard
was not observed for the IC2574 image, it is calibrated using uxes of 20 clearly
de ned HII regions provided by Miller & Hodge 1994. The small dispersion,
= 0
:
29, about the mean indicates that this is a robust estimate of the calibra-
tion constant. The H used at LCO has a centroid wavelength 6563 A and width
73 A. The image is calibrated using uxes from 5 compact HII regions given by
Hodge
et
al.
1994. The estimated calibration constant has a small dispersion
about the mean, = 0
:
22. An H emission image is produced for each galaxy
by scaling stars in the H image with those in the R-band image and subtracting
the stellar continuum component.
2.3
HI
Observ
ations
The 21 cm images used in this study were observed with the Very Large Array
VLA of the National Radio Astronomy Observatory and are kindly provided by
David Westpfahl. The HI emission of HoII was observed with the VLA B, C, and
D arrays. The uniformly weighted column density map has a spatial resolution of
4
00
4
:
00
5, corresponding to a spatial resolution of 60 pc at the distance of HoII.
This image is used in the Puche
et
al.
1992 study of the galaxy where a complete
