2 Observations

We observed Sextans B (DDO 70, 10h 00m 00s +05d 19m 56s, J2000.0) using the prime focus wide field camera (WFC) of the 2.54 m Isaac Newton Telescope (La Palma, Spain), on February and April 2001. The panoramic detector of the WFC consists of four thinned EEV CCDs of 2048$\times$4096 pixels each, and with a pixel scale of 0$\farcs$33. The $34\arcmin \times34\arcmin$ field of view of the camera covered the entire galaxy. Four narrow-band filters were used, with the following central wavelengths and full widths at half maximum (FWHMs): [O  III] (500.8/10.0 nm), H$\alpha$+ [N  II] (656.8/9.5), He  II (468.6/10.0) and [S  II] (672.5/8.0). A Strömgren y filter, centred at 555.0 nm and with a FWHM of 30.0 nm, was also used to obtain off-band images for continuum subtraction.

Exposure times were 600 s for y, 1200 s for [O  III] and H$\alpha$+ [N  II], and 3600 s for He  II, and [S  II], (split into three sub-exposures). The seeing was 1  through the [O  III], H$\alpha$+ [N  II], [S  II] and y filters, and 15 through the He  II filter. Several observations were made each night of the spectrophotometric standard stars: BD +33 2642, G191-B2B and Feige 34 (Oke 1990).