2. Observations and data reduction

The observations were done in 1984 with the WSRT (Högbom & Brouw 1974). Each pointing was observed for 12 hours, with a total bandwidth of 10 MHz and 31 frequency channels, resulting in a channel spacing of . The velocity resolution is 1.2 times the velocity spacing between adjacent channels. The calibration was done according to the standard WSRT procedures, described by van Someren-Greve (1974). The observational parameters are shown in Table 1 (click here).

   

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Field Beam size Bandwidth Central vel. rms mJy-K conv.

(h m s) (hrs.) (MHz) (km s^-1) (km s^-1) mJy/beam mJy/beam

1 1 45 00.0 36 00 00.0 12 10 4700 68.1 0.89 0.37

2 1 47 00.0 35 05 00.0 12 10 4750 68.1 0.95 0.52

3 1 49 30.0 35 50 00.0 12 10 5400 68.1 1.04 0.53

4 1 51 00.0 36 25 00.0 12 10 5100 68.1 0.93 0.36

5 1 53 00.0 35 50 00.0 12 10 5000 68.1 0.86 0.48

Column 1: Field number.
Columns 2 and 3: R.A. and Dec. (1950) of each pointing.
Column 4: Integration time.
Column 5: Minor and major axes of the synthesized beams, in seconds of arc.
Column 6: Total observed bandwidth in MHz.
Column 7: Heliocentric velocity of the central channel.
Column 8: Channel separation in km s^-1. The velocity resolution is equivalent to 1.2 times this velocity spacing.
Column 9: rms noise per channel after continuum subtraction, in mJy/beam.
Column 10: The flux density per beam area (in mJy/beam) equivalent to 1.0 K in the channel maps.

For the observed fields the synthesized beam is about . Our final sample consists of ten spirals and one irregular out of nearly 30 candidates. Only two of the detected galaxies (NGC 710 and CGCG 522-049) are slightly HI deficient.

The WSRT data reduction program NEWSTAR was used to transform the UV data to () cubes. Further data reduction was done with the Groningen Image Processing System (GIPSY). First a continuum map was constructed by averaging channels at the high and low end of the passband; first and last channels were always excluded because of their higher noise levels. This continuum map was then subtracted and the channel maps were inspected for 21 cm line emission. A new continuum map was made for each detected galaxy using only line-free channels, and it was subtracted from the original cube. After the continuum subtraction, maps were CLEANed and restored with a Gaussian beam with the same FWHM as the original beam, in order to remove instrumental effects. The CLEAN procedure was done to a depth of , the rms noise in the cubes. The maps were then smoothed spatially, in order to improve the signal-to-noise ratio of extended emission. The beam size typically used was , except for NGC 710, where a beam was used. In order to make the total HI maps,
velocity fields and position-velocity plots, shown in the next section, line emission was isolated using the mask (or conditional transfer) procedure. The main parameters of the eleven detected galaxies are listed in Table 2 (click here).

   

(1) (2) (3) (4) (5) (6) (7) (8) (9) 10

Name Type mag i PA HI Def

(1) NGC 668 1 43 27.2 36 12 40 Sb 12.64 50¹ 33¹ 0.77 0.03

(2) UGC 1257 1 45 11.3 36 12 13 Sab 14.59 64² 107² 0.57 0.11

(3) UGC 1277 1 46 30.7 35 12 14 S0a 14.03 62² 75² 0.55 0.22

(4) UGC 1299 1 47 37.6 35 06 39 Im 15.69 65² 85² 0.53 -0.17

(5) NGC 688 1 47 48.8 35 02 13 SBb(rs)p 12.43 55¹ 146¹ 0.56 0.10

(6) NGC 710 1 49 57.5 35 48 26 Scd 13.79 19² 51⁴ 0.06 0.38

(7) UGC 1347 1 49 49.0 36 22 21 SABc(rs) 13.23 30¹ 18¹ 0.26 -0.07

(8) CGCG 522-049 1 50 53.7 36 19 07 SBd¹ 15.10 45² 149³ 0.26 0.33

(9) UGC 1361 1 50 56.2¹ 36 20 27¹ Scd 15.43 73² 131³ 0.27 0.12

(10) UGC 1387 1 52 13.8 36 01 00 Sdm 15.37 48² 175² 0.27 -0.06

(11) NGC 753 1 54 45.4 35 40 22 SABbc(rs) 11.66 50¹ 128¹ 0.58 -0.15

Column 1: Galaxy identification.
Columns 2 and 3: 1950 R.A. and Dec. from RC3 except for (1), taken from Paturel et al. (1989).
Column 4: Morphological type from RC3 except for (1), taken from the LEDA data base.
Column 5: Blue magnitude after corrections for redshift, galactic and internal extinction (Wegner et al. 1993).
Column 6: Optical major and minor axis in minutes of arc, from the UGC when available, else from Wegner et al. (1993).
Column 7: Inclination angle; from Amram et al. (1994) (1), and the LEDA base data (2).
Column 8: Position angle from Amram et al. (1994) (1), Nilson (1973) (2), Gavazzi et al. (1995) (3), and Scodeggio et al. (1992) (4).
Column 9: Distance from the cluster center in units of Abell radii ( for A 262).
Column 10: The HI deficiency is defined as the difference between the observed HI mass and that expected for an isolated galaxy of the same optical linear diameter and morphological type (Giovanelli & Haynes 1985).

 

(1) (2) (3) (4) (5)

Name W₂₀ HI flux

km s^-1 km s^-1 Jy km s^-1 (mJy)

(1) NGC 668 4533 318

(2) UGC 1257 4667 417

(3) UGC 1277 4128 617

(4) UGC 1299 5498 235

(5) NGC 688 4166 455

(6) NGC 710 6111 316

(7) UGC 1347 5551 183

(8) CGCG 522-049 4691 244

(9) UGC 1361 5749 291

(10) UGC 1387 4548 265

(11) NGC 753 4890 468

 

Column 1: Galaxy name.
Column 2: Heliocentric velocity, derived from the HI profile. The uncertainty is of the order of half the velocity resolution, i.e. .
Column 3: 21 cm profile width, at a level of 20% of the peak value. Uncertainty in the widths are of the order of the velocity resolution.
Column 4: 21 cm total line flux and the corresponding error.
Column 5: 21 cm continuum flux. Uncertainty is equal to in the continuum map.