We have observed the whole sample of 114 galaxies in B, R, and in the light of H during a total of 11 observing runs between June 2001 and July 2002. Nine of the observing runs were carried out at the Palomar Observatory 60-inch telescope using CCD Camera with the 2048 × 2048 pixel CCD#13 attached. The pixel scale was 0.378 arcsec/pixel. Two additional observing runs were carried out at the du Pont 100-inch telescope in Las Campanas Observatory (Chile) between February 8-9 2002 and March 5-9 2002. We used the Direct CCD with the 2048 × 2048 pixel Tek5 CCD attached, which, placed at the Cassegrain focus of the telescope, gives a scale of 0.260 arcsec/pixel. In Table 2 we give a summary of the observing runs and the properties of the detectors used (gain, readout noise, etc).
Note. - Columns stand for: (1) Observing run. (2) Nights observed. (3) Observatory. (4) Telescope. (5) Detector. (6) Spatial scale at the detector in arcsec/pixel. (8) Gain of the detector in e-/ADU. (9) Readout noise of the detector in e-. Note that two different gain settings were used during the Las Campanas observing runs.
Typical exposure times in B, R, and H were, respectively, 15, 45, and 90 min at Palomar Observatory and 15, 15, and 30 min at Las Campanas. A total of 86 galaxies were observed at Palomar Observatory and 28 at Las Campanas. The seeing (FWHM) in the images ranged from 0.6 arcsec (Tol 002 in R) to 4.3arcsec (Haro 14 in B). The median seeing values in B, R, and H were 1.8, 1.6, and 1.5 arcsec, with 80 per cent of the galaxies having seeing better than 2.5, 2.0, and 1.9 arcsec, respectively. The image quality at Las Campanas Observatory was significantly better than at Palomar Observatory. In this sense, the median seeing of the B, R, and H images taken at Las Campanas were 1.1, 0.9, and 0.9 arcsec, respectively, whereas at Palomar Observatory the median seeing values achieved were 2.0, 1.7, and 1.6 arcsec. In Table 3 we give a summary of the characteristics of some of the images contained in this Atlas, including observatory, telescope, date, exposure time, number of frames, airmass, and FWHM (the complete table is available in the electronic version of the paper). The date of observation given in this table corresponds to the civil date at the start of the observing night.
Note. - Columns stand for: (1) Galaxy name. (2) Observatory and telescope (P60: Palomar Observatory 60-inch; C100: Las Campanas observatory du Pont 100-inch). (3) Date of observation for the B-band image. (4) Number of frames and exposure time per frame for the B-band in seconds. (5) Mean airmass of the B-band exposure. (6) Seeing (FWHM) of the B-band image in arcsec. (7-10) The same as (3-6) for the R-band exposure. (11-14) The same as (3-6) for the H exposure.
In Figure 2 we give the spectral response functions of the filters used in this Atlas as provided by the manufacturers. Thin continuous-lines correspond to the filters used at the Palomar Observatory 60-inch telescope and broad-lines to those used at Las Campanas 100-inch telescope. This figure clearly shows that the Johnson-B and Cousins-R filters used in this Atlas are very similar to those used by Landolt (1992a) to build his list of standard stars (dotted-line) and also similar to those originally used to define the Johnson-Cousins system (dashed-line; B-band: Azusienis & Straizys 1969; R-band: Bessell 1990). It is worth noting that our filters as plotted have been convolved with the spectral response functions of the corresponding detectors. This could be, in part, the reason for the apparently-poorer spectral response of our filters to wavelengths longer than ~ 6500Å compared to those used by Landolt (1992a) and Bessell (1990). Narrow-band filters used at Palomar and Las Campanas were 20Å and 65Å wide, respectively. The use of narrower H filters at Palomar Observatory reduced the contribution of the continuum to the photon noise of the H images, partially compensating for both the poorer image quality of the H images obtained at Palomar Observatory and the smaller collecting area of the 60-inch telescope.
Figure 2. a) Spectral response function of the B and R broad-band filters used at the Palomar Observatory 60-inch telescope (solid-thin line) and at the Las Campanas Observatory du Pont 100-inch telescope (solid-thick line) convolved with the quantum efficiency of the detector. The response function of the filters used by Landolt (1992a; dotted-line) to construct his list of secondary standards and those originally used to define the Johnson-Cousins system (dashed-line; B-band: Azusienis & Straizys 1969; R-band: Bessell 1990). b) Spectral response function of the narrow-band H filters used in the Las Campanas Observatory 100-inch telescope (from left to right: LC 6570, LC 6600, LC 6630). c) The same as b) for the Palomar Observatory 60-inch telescope (from left to right: PO 6563, PO 6570, PO 6584, PO 6593, PO 6601, PO 6614, PO 6624, PO 6640). Vertical marks indicate the range in wavelength covered by the redshifted H line for the galaxies in our sample.