Astron. Astrophys. 319, 788-795 (1997)

2. Observations and results

The H observations of the region l = , b =  have been made with a 36 cm telescope equipped with a focal reducer and a scanning Fabry-Perot interferometer. This equipment installed at La Silla, of Chile, is devoted to an H survey of our Galaxy. A complete description of this equipment and of the reduction techniques can be found in le Coarer et al. (1992). Each observation is a data cube (x, y, ) covering a 38' x 38' field, with a 9" x 9" spatial resolution. The Fabry-Perot, with interference order 2604, allows a velocity sampling of 5 km  and a free spectral range of 115 km  .

The wavelength calibration is supplied by an H lamp and the shape of the instrumental line profile is given by a neon lamp (since it provides a narrow line at 6598.9 Å compared with H lamp). This last profile helps us to map the center to edge widening correction. Some night sky lines (geocoronal H and OH 6568.8 Å) are also transmitted through the interference filter used. These lines, which were fitted with an instrumental profile, show an intensity varying with time and from one sky region to another. For each observation, an estimation of their intensity is made independently in order to subtract them, from the observed profile.

The data cube reduction method used is described in Georgelin et al. (1994). Table 1 gives the coordinates of the center of each observed field together with the date of observations and mean sky night line intensities. Figure 1 summarizes the results; it shows the map of the ionized gas obtained when adding wavelength channels centered on the H emission with positive velocities (V = +25 to + 35 km  ) for Fig. 1a and negative velocities (V = -25 to -40 km  ) for Fig. 1b. In addition in Fig. 1c we present the Caswell & Haynes continuum radio map of the same region.

Table 1. Observations

Fig. 1a-c. Monochromatic images (bandwith 0.3 Å) of the H emission at positive a and negative b velocities. In addition the 5GHz radio continuum map of Caswell & Haynes (1987) is presented c (contours levels 0.4, 1, 2 and 8 K). Let us note from b that the H emission around 11 39 is a part of the large HII region RCW62

2.1. The HII regions

Most of the HII regions detected in the area studied exhibit a relatively small size. The H profile of each HII region is added over its total surface and then fitted with a gaussian profile convolved with the instrumental profile. This H profile can then be used to determine the systemic velocity and the doppler width of each discrete HII region.

Table 2. Integrated H velocities and FWHM of discrete HII region. In parallel, H109 , H₂ CO and OH velocities are shown

For each detected HII region we give, in Table 2, the H velocity and the FWHM of the deconvolved gaussian together with radial velocities at other wavelength:

• Column 1: Galactic coordinates of the 5GHz continuum radiosources catalogued by Caswell & Haynes (1987).
• Column 2: Equatorial coordinates of the H sources.
• Column 3: Estimated H diameter.
• Column 4: H velocity and width measured in this study.
• Column 5: H109 velocity (Caswell & Haynes 1987).
• Column 6: H₂ CO velocity (Whiteoak & Gardner 1974).
• Column 7: CO velocity (Whiteoak et al. 1982; Brand 1986).
• Column 8: OH velocity (Caswell & Robinson 1974).

Two velocity groups are easily identified in this area: the HII region RCW 64 which exhibits a negative velocity and the other ones which exhibit positive velocities placing them beyond the solar circle.

Let us note the case of the H emission having apparently no radio nor infrared counterpart. It is well identified on Fig. 1a at coordinates 12 04 and (l = 297:O93, b = -1:O75). With such a positive velocity this region is far away in spite of its appearance.

2.2. The diffuse emission

A diffuse H emission is widely distributed all around the discrete HII regions of the area studied. In order to increase the signal/noise ratio, the profiles were added over extended zones. The obtained profiles were then fitted in the same manner as for discrete HII regions.

The profile decompositions reveal 3 components with negative velocities. The most intense (mean intensity 0.9 counts/px/h) is relatively uniform all over the whole area, its mean velocity is -2.6 km  . The mean velocities of the two fainter components are -41 km  (varying between -44.3 and -36.8) and -25 km  (varying between -21.5 and -29.5). The -25 km  component is detected all over the studied area, its mean intensity is 0.4 counts pixel hr but it can increase twofold inside the same 38' x 38' elementary field; such an increase sometimes significantly changes the profile shape of the observed line. For example we can see from Fig. 1b that the emission is reinforced at 12 08   , 12 13   and 11 51   .

The mean intensity of the weakest component is 0.26 counts pixel hr and in some elementary fields it is not detected at all.

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998
helpdesk.link@springer.de