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Astron. Astrophys. 332, 849-856 (1998)

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2. Observations and data reduction

2.1. IR spectra

Infrared spectra of the Cha IRN were obtained in April 1994 using the Infrared Spectrometer IRSPEC on ESO's New Technology Telescope (NTT) on La Silla, Chile. A log of all observations is shown in Table 1. IRSPEC is described in Gredel & Weilenmann (1992). Grating 1 was used for all spectra, 2nd order for the 2.3µm range, 1st order for the other ranges. For wavelength calibration, an internal spectral lamp was used. For sky subtraction, a second spectrum of the object shifted a few arc-seconds along the slit was obtained. HR5787 served as the standard star. Data reduction followed the IRSPEC context of ESO's MIDAS data reduction package. Integration times were different for each spectral range and for object and standard star, but always chosen to result in similar count numbers and not to saturate the detector.


[TABLE]

Table 1. Log of observations


2.2. JHK imaging

Imaging of the Cha IRN was performed in November 1995 using IRAC2b on ESO's 2.2 m telescope on La Silla, Chile. The use of objective B of IRAC2b resulted in a scale of [FORMULA] per pixel. For bad pixel correction and sky subtraction, a mosaic mode was chosen. In each wavelength, five integrations were performed, four with the object in a different quadrant of the detector, and one with the object near its centre. A sky image was obtained by taking the median of this cube of five frames. Bad pixels were first corrected by replacing their signal with one from a frame with the object at a different position, then by conventional bad pixel correction using a seek & correct algorithm. This procedure resulted in a total integration time of 10 minutes on the object in each band, with smaller integration times in adjacent areas. Fig. 1 shows a region of the resulting K' mosaic. For flux calibration, similar images of HD18847 were taken. Additionally, we incorporate a K-band high-resolution image obtained by speckle interferometry (Stecklum et al. 1993).

2.3. 10 µm imaging

The 10 µm imaging was performed in 1994 using TIMMI at ESO's 3.6 m telescope on La Silla/Chile (Käufl et al. 1992). The pixel scale is [FORMULA]. The profile shown in Fig. 6 is the result of 750 stacked frames. The detection limit in the image is 0.6 Jy. With this sensitivity, we do not detect any significant deviation from the point spread function, i.e. the source appears unresolved at the nominal resolution of [FORMULA].

2.4. ISO data

These observations were carried out using the spectrophotometer subsystem of ISO's imaging photo-polarimeter ISOPHOT. A detailed description of this instrument can be found in Lemke et al. (1996). The data processing was done using the PHT Interactive Analysis (PIA) software made available by the ISOPHOT Data Centre of the Max Planck Institute for Astronomy, Heidelberg 1. The flux of the ISO spectra differs from the IRSPEC and the IRAS data by a factor of 2.2. Two explanations for this deviation can be thought of: First, the satellite was pointed at the nominal position of IRAS11072-7727. This means, that with the ISOPHOT field of view of [FORMULA], only the eastern half of the source has been measured. Secondly, the absolute photometric calibration of ISOPHOT may not yet be very accurate. In Fig. 5, the ISO data have been multiplied by a factor of 2.2 to match the fluxes of IRAS and IRSPEC data.

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© European Southern Observatory (ESO) 1998

Online publication: March 30, 1998
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