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Astron. Astrophys. 320, 568-574 (1997)

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2. Observation and data reduction

2.1. Imaging

Images of the field around HR Car have been taken with a CCD camera on the 0.9 m telescope at the Cerro Tololo Inter-American Observatory in March 1996. The seeing was between 1 [FORMULA] 4 and [FORMULA] during the observations. An H [FORMULA] filter and Strömgren y filter were used. The H [FORMULA] filter, having a central wavelength of 6563 Å and a filter width of 75 Å included the [NII ] lines at [FORMULA] 6548 Å and [FORMULA] 6583 Å. The Strömgren y filter was used to obtain continuum images to facilitate the continuum subtraction from the H [FORMULA] images. The [FORMULA] Tek2K3 CCD was used, and the pixel size was approximately 0 [FORMULA] 4.

To avoid saturation of the bright star HR Car itself, we secured multiple short exposures. A total of 10 frames in the y filter and 60 frames in the H [FORMULA] filter were taken, each having 30 s exposure. To speed up the readout, only the central [FORMULA] pixels were read, hence the field of view was 6 [FORMULA] 75. The combined H [FORMULA] image centered on HR Car is shown in Fig. 1.

[FIGURE] Fig. 1. H [FORMULA] image centered on HR Car. The field of view is [FORMULA]. North is up and east is to the left.

A funnel-shaped nebulosity is detected to the northwest of HR Car in Fig. 1. To investigate the spatial extent of this nebulosity, a second set of 5 H [FORMULA] and 5 y frames of 300 s exposure each were taken of the adjacent field. The combined H [FORMULA] image of the second field is displayed in Fig. 2. Note that the faint oval halo, [FORMULA], around HR Car in Fig. 1 is not present in Fig. 2, indicating that this halo is probably caused by the internal scattering inside the telescope optics rather than being real emission.

[FIGURE] Fig. 2. H [FORMULA] image centered at northwest of HR Car. The field of view is [FORMULA]. North is up and east is to the left. HR Car is visible at the southeastern edge of the frame.

HR Car, the star itself, is so much brighter than the surrounding nebula that it is necessary to subtract the continuum image from the H [FORMULA] image to obtain a better view of the nebula. We have subtracted the scaled, combined y image from the combined H [FORMULA] image. The scaling factor is estimated using the neighboring stars. HR Car is a strong H [FORMULA] emitter and hence cannot be removed completely in the continuum-subtracted H [FORMULA] image. The central [FORMULA] of the resultant H [FORMULA] image is displayed in Fig. 3. The y filter and the H [FORMULA] filter have quite a large difference in their central wavelengths. Thus stars with extreme red or blue colors will be either under- or over-subtracted, and appear dark or white in Fig. 3. The white arc to the north of HR Car is caused by an over-subtraction of the continuum caused by a low-intensity ghost in the y-filter images.

[FIGURE] Fig. 3. H [FORMULA] image of the nebula around HR Car. The field of view is [FORMULA] by [FORMULA]. North is up and east is to the left. The continuum is subtracted to our best effort. The over- and under-subtracted stars are the effect of their extreme colors. HR Car has a strong stellar H [FORMULA] emission and hence remains bright in the continuum-subtracted image. The inset at the lower right corner shows HR Car and its visual companion at the same plate scale as the main image in this figure.

2.2. Echelle spectroscopy

We obtained high-dispersion spectroscopic observations of the nebula around HR Carinae with the echelle spectrograph on the 4 m telescope at Cerro Tololo Inter-American Observatory in January 1996. We used the long-slit mode, inserting a post-slit H [FORMULA] filter (6563/75 Å) and replacing the cross-disperser with a flat mirror. A 79 l mm-1 echelle grating was used. The data were recorded with the long focus red camera and the [FORMULA] Tek2K4 CCD. The pixel size was 0.08 Å pixel-1 along the dispersion, and 0 [FORMULA] 26 pixel-1 perpendicular to the dispersion. The slit length was effectively limited by vignetting to [FORMULA]. Both H [FORMULA] 6563 Å and the [N II ] 6548 Å, 6583 Å lines were covered in the setup. The slit-width was 250 µm ([FORMULA]) and the instrumental FWHM was about 14 km s-1 at the H [FORMULA] line. The seeing was [FORMULA] during the observations. Thorium-Argon comparison lamp frames were taken for wavelength calibration and geometric distortion correction.

Two slit positions were observed. One was offset by [FORMULA] to the north of HR Car, and the other [FORMULA] to the south of HR Car. For both positions the slit was rotated to a position angle of [FORMULA]. The slit positions are marked in Fig.3. The exposure time was 600 s for the [FORMULA] S position and 300 s for the [FORMULA] N position. The echelle images of the H [FORMULA] +[N II ] lines are presented in Fig. 4. Unfortunately, the echelle observations were made before our discovery of the funnel-shaped nebulosity to the northeast of HR Car, so no echelle observations of this nebulosity are available.

[FIGURE] Fig. 4. Echellograms of the HR Car nebula: a the H [FORMULA] line of the northwestern lobe, b the [N II ] [FORMULA] 6583 line of the northwestern lobe, c the H [FORMULA] line of the southeastern lobe, and d the [N II ] [FORMULA] 6583 line of the southeastern lobe. The horizontal axis is the position along the slit and covers [FORMULA]. Northeast is to the left and southwest is to the right. The vertical axis is along the spectral dispersion and covers 13 Å, or 600 km s-1. The wavelength (or velocity) increases upward. The background H II component has [FORMULA] km s-1.
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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998