3. Identification and description
From an earlier photometric study (Malfait et al. 1998a), it is known that the infrared spectrum of HD 142527 is characterized by a warm and a cold component, intersecting at 20 µm. On top of that warm continuum ( 20 µm) a silicate bump is clearly visible. Evidence for the 3.3 µm and 6.2 µm UIR bands, usually attributed to PAHs is present as well, though the previously mentioned 3.5 µm band (Waelkens et al. 1996) cannot be confirmed using the latest calibration files (Van Kerckhoven, in prep.). The scientific relevance of the features seen longwards of the silicate emission (between 11 and 16 µm), is questionable. A detailed study of similar features shortward of the 6.2 µm PAH, showed that not all 12 detectors observed the features in both up and down scans, thus one can conclude that these features are spurious. For the features between 11 and 16 µm, a more detailed study should be done to discriminate whether they are real, since also severe memory effects take place in the relevant detectors. This will be done when the PAHs will be discussed in more detail (Van Kerckhoven, in prep.).
In the longer wavelength part of the spectrum, sharp solid state peaks at 43, 47, 50 and the 158 µm-line attributed to forbidden are visible on top of the very strong continuum flux. A broad feature at 55-75 µm is visible as well.
The sharp peak at 43 µm in combination with the broad band centered at 63 µm, is a characteristic for crystalline -ice, which seems to be quite common in the environment of young stars and post-AGB stars (Waters et al. 1996; Barlow 1998; Malfait et al. 1998b). If we compare the features of HD 100546 (Malfait et al. 1998b) with those of HD 142527, the strength ratio is drastically higher for the latter. The dust temperature found from continuum modelling is higher for HD 100546 ( 40-210 K) than for HD 142527 ( 30-90 K). This shifts the far infrared dust emission to shorter wavelengths, attenuating the 43 µm peak relatively to the 63 µm peak, and explaining the different band strength ratio.
Table 1. Reference list of optical properties used.
© European Southern Observatory (ESO) 1999
Online publication: April 12, 1999