2. Observations and results
2.1. (sub)millimetre observations
Submillimetre and millimetre continuum observations at 800, 1100, 1300 and 2000 µm of the source NGC 7129 FIRS 2 were carried out using the James Clerk Maxwell Telescope (JCMT) on Mauna Kea, Hawaii, on May, 1990. and the bolometer UKT14 (Duncan et al. 1990). Beam sizes were FWHM for 800, 1100 and 1300 µm, and for 2000 µm. The signal from FIRS 2 was peaked up before commencing integration. Absolute calibration was achieved using Mars and Uranus assuming the brightness temperature of Griffin et al. (1986) and Orton et al. (1986), and filter passbands correct for 1 mm of water vapour. The likely uncertainty in the absolute flux of these calibrators is 5-10%. The consistency of the photometry was checked by observing other sources from the same observing run (Casali et al. 1993). Measured flux values are given in Table 1.
Table 1. IRAS and submillimetre fluxes of FIRS 2.
2.2. IRAS data
At SRON (Groningen, The Netherlands) we used the high-resolution image reconstruction algorithm (HIRAS) to produce IRAS 12, 25, 60 and 100 µm images of NGC 7129. HIRAS is a maximum entropy image restoration technique, which uses an interactive procedure giving a significant gain in spatial resolution and can approach the difraction limit of the IRAS telescope, which ranges from to . at 12 and 100 µm, respectively. A detailed description of the whole procedure is given by Bontekoe et al. (1994). In the final NGC 7129 HIRAS maps, positions of point-like sources differ randomly by 15"-20", which is of the order of the default pixel-size, 15", used in the reconstructed HIRAS images. Therefore, the differences in positions are not meaningful within the spatial resolution. Fluxes have been estimated after removing the residual background, which remains left in the reconstructed images after applying the reconstruction procedure (see Bontekoe et al. 1994); in our case, it was practically zero at 12 µm and small values at other wavelengths.
Fig. 1 shows the HIRAS maps at 12, 25, 60 and 100 µm. Common to all wavelengths is the presence of a far-IR peak, FIRS 1, at the position of LkH 234 and extended diffuse emission. A second prominent peak located southwards of the former is seen at 25, 60 and 100 µm. IRAS fluxes are given in Table 1. This peak coincides with the source FIRS 2 detected by Bechis et al. (1978) and Harvey et al. (1984). At 12 µm it seems to be a weak source close to this position; the angular distance from the 12 µm peak to any of the flux maxima at the other IRAS wavelengths is on average . This is twice as large as the offset in position found among the peaks of the IRAS bands for any other source in the maps. Thus, an association of the 12 µm souce with FIRS 2 is doubtful. In addition, since the flux from the 12 µm source is very low ( 0.2 Jy, background sustraction uncertain), the properties of FIRS 2 we deduce below and its nature are not significantly affected if such an association were real (for instance, the change of luminosity would be 3%). Therefore, we do not consider the 12 µm source in the following, although the emission of FIRS 2 at 12 µm should be clarified in the future. A pair of weak, secondary peaks are also seen in the shortest IRAS wavelengths. One of them, FIRS 3, coincides with the T Tauri star V 350Cep (see Miranda et al. 1994); the second one, FIRS 4, seems to be extended and is likely related to the reflection nebulosity GM 1-53 (Magakian 1983), which is illuminated by the near-infrared source SVS 10, a B8-A0 star close to the main sequence (Strom et al. 1976, Magakian & Movsesian 1997). Table 2 gives 1950.0 coordinates, as measured at 25 µm, and fluxes of FIRS 3 and FIRS 4.
Table 2. 25 µm positions and fluxes in Jy of FIRS 3 and FIRS 4 in NGC 7129
© European Southern Observatory (ESO) 1998
Online publication: June 12, 1998