Of the 40 objects listed in Table 1 (click here), only 13 have previously been detected in the 21cm HI line (see also Table 3 (click here)). Four galaxies (Kar 1N, A952+69, Kar 61, and Garland), as well as 8 of the peculiar low-surface brightness objects first noted by Börngen et al. (1984) have never before been observed in the 21cm line. These 4 galaxies, as well as the four brightest objects of unknown nature, i.e. Kar 8N, and Anon 5, 6 and 7, were selected for our deep HI search.
Four objects (HolmbergI, Kar 52 (= M 81 dwarf A), Kar 73 and Kar 3N) were mapped in HI with the VLA (Westpfahl & Prugniel 1994). The first two look like rather face-on incomplete rings with evidence for slow rotation, while the latter two resemble discs with a central hole seen edge-on and complex or confused velocity fields without clear signs of systematic rotation in the dwarf systems. No HI profile parameters are given in this reference - note, that neither Kar 73 nor Kar 3N has been reported as detected in any single-dish study, including ours.
Fifteen of these galaxies have previously been searched for with the 90 m Green Bank (Schneider et al. 1992) and the 100 m Effelsberg dish (Huchtmeier & Skillman 1994, 1997), with an rms noise varying from 7 to 15 mJy, and 4 with an rms noise of 18 mJy only for earlier work by Fisher & Tully (1981) at Green Bank and Effelsberg. We reobserved these galaxies at Nançay with considerably higher sensitivity ( rms).
The total sample of 23 dwarf galaxy candidates selected for observation in HI at Nançay are marked in the last column of Table 1 (click here). The searches for 21cm HI line emission were made with the Nançay decimetric radio telescope in the period December 1995 - September 1996. The telescope is a meridian transit-type instrument, which permits the tracking of such high-declination galaxies for about 3 hours per day. The telescope has the equivalent collecting surface of a 94 m diameter round dish, but its HPBW is about 4' 22' (), due to its elongated geometry. Most objects were observed for about 4 hours each, while the 3 low-surface brightness Anonymous objects were observed for about 8 hours each. It should be noted that the telescope is somewhat less sensitive at high declinations, like those observed for the present survey (), then at lower declinations, due to its geometry.
The 1024 channel correlator set-up used permitted an HI line search in both H and V polarisation in the radial velocity range of -529 to 1826 , with a 190 overlap between the filter banks, from 548 to 747 , at a resolution of about 6 .
After averaging the individual spectra, the data was smoothed to a velocity resolution of 12.7 , and third-order baselines were fit. For the conversion of antenna temperature to flux density in mJy we used the standard declination-dependent calibration relation established by the Nançay staff through regular monitoring of strong continuum sources, and our observations of a sample strong late-type galaxies (Matthews et al. 1997) observed earlier at Nançay as well as with other telescopes.