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Astron. Astrophys. 336, 1024-1028 (1998)

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2. Observations and data reduction

The [FORMULA]-band and 11.2µm direct images of NGC 6334 F were obtained with UKIRT and CFHT on Mauna Kea on February and July 1996, respectively.

For the [FORMULA]-band IRCAM3 mounted on UKIRT was used, equipped with a 256[FORMULA]256 InSb array and with a scale of [FORMULA]/pix. The observation was made at dawn with no secondary mirror chopping. To achieve rapid sky subtraction, the telescope was nodded with an amplitude of [FORMULA] after each 6.5 sec integration, achieving a total on-source integration time of 468 sec. No standard stars were observed to calibrate the image. A rough calibration was obtained using the [FORMULA]-band photometry of IRS-I 1 taken with an aperture of [FORMULA] by Becklin & Neugebauer (1974).

The narrow-band image at 11.2µm ([FORMULA] = 0.44µm) was obtained with the mid-IR camera CAMIRAS developed at the Service d'Astrophysique at Saclay (Lagage et al.  1992), equipped with a 192[FORMULA]128 Si:Ga/DVR detector array, and mounted at CFHT(Canadian-French-Hawaii Telescope). We used a scale of [FORMULA]/pix and the measured point-spread function was of [FORMULA]. The observations were made in chopping and nodding mode in order to subtract the sky and the telescope emissions. The standard stars [FORMULA] Aql and [FORMULA] Sgr were observed at approximately the same air mass to calibrate the image of NGC 6334 F. The astrometry of the 11.2µm image was made comparing it with the K image with similar spatial resolution obtained by Persi et al.  (1996). Figs. 1 and 2 show the [FORMULA]-band and the 11.2 µm images of NGC 6334 F.

[FIGURE] Fig. 1. [FORMULA]-band image of NGC 6334 F. The area imaged is 19.7[FORMULA]19.7 square arcsec. The cross indicates the position of IRS-I 2.

[FIGURE] Fig. 2. 11.2µm image of NGC 6334 F. The area imaged is 59.5[FORMULA]39.7 square arcsec. The cross indicates the position of IRS-I 2.

Given the low sensitivity of the [FORMULA]-band image, only IRS-I 1 was observed, though with a "cometary" shape (Fig. 1), while in the 11.2µm image (Fig. 2) this source (here named MIR 2) and other two point-like sources (all found in the near-IR by Tapia et al.  1996) as well as diffuse emission extending west of IRS-I 1 were detected. The estimated flux density at 11.2µm for the diffuse emission is [FORMULA] 14 Jy.

In Table 1 we report the positions and the flux densities at 11.2µm of the detected sources. The flux density of MIR 2 (IRS-I 1) is relative to an aperture of [FORMULA] in radius.


Table 1. Positions and flux densities of the small diameter 11.2µm sources observed in NGC 6334 F
References: a) Tapia et al.  (1996), b) Harvey & Gatley (1983).

In order to study in detail the morphology of this source we have applied to the 11.2µm image, the Lucy-Richardson spatial enhancement algorithm developed by Richardson (1972) and Lucy (1974). This treatment is based on a good spatial sampling of the point-spread-function and the high signal-to-noise ratio of the raw data. Both requirements are satisfied for our image. With this algorithm, we can obtain a resolution of [FORMULA]. The contour map of the deconvolved 11.2µm image of NGC 6334 F is reported in Fig. 3. MIR 2 (IRS-I 1) appears to be resolved with an effective FWHM size of [FORMULA] (2090 AU, [FORMULA] 3 1016 cm at d = 1.74 Kpc) and contains approximately 80% of the total flux reported in Table 1.

[FIGURE] Fig. 3. Contour levels of the deconvolved 11.2µm image of NGC 6334 F. The origin of the coordinates is at [FORMULA](1950) = 17h 17m 32.3s; [FORMULA](1950) = [FORMULA]

Finally, the images of Figs. 1 and 2 do not show any mid-IR source at the position of IRS-I 2 (indicated with a cross in the figures). The upper limits for a point source are 0.08 and 1.2 Jy (1 [FORMULA]) at 3.8 and 11.2µm, respectively. Although the sensitivity at 11.2µm is high ([FORMULA]25 mJy/arcsec2), the rather large value of the upper limit is due to the fact that IRS-I 2 is located within the diffuse emission (see Fig. 2).

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© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998