scientific abstract the iso lws gives the opportunity to perform ir spectroscopic observations of extended, weak sources like the cirrus, evidenced by iras at high galactic latitude. it allows to study gas properties through fine structure emission lines and to correlate these emission with the dust spectrum observed simultaneously. in particular the cii 158 um line is believed to be the more effective coolant for the considered diffuse regions so these observations should give information on the role of dust and small particles in the heating of the gas. observation summary we will observe a small number of diffuse clouds, with several positions presenting different characteristics within the cloud (transition regions from atomic to molecular gas or regions presenting ir colour spatial variations). the cii 158 um line is expected to be the dominant emission line. following the uv-absorption derived c+ cooling rate (gry et al., 1992, a&a 266, 457) and the estimation of the fir emission (boulanger and perault, 1988, apj 330, 964) we expect a contrast between the cii line and the adjacent continuum around 4. a recent analysis of the cobe data (benett et al., 1993, cobe preprint) finds this contrast to be only 1 in the galactic plane and 0.5 at b=50. however these values show that grating spectra should be sufficient for accurate cii line measurements. other lines could be of interest in the lws range, like oi 63.18 um, oi 145.53 um, oiii 51.82 um, oiii 88.36 um, feii 51.30 um, feii 87.38 um, nii 121.89 um, feiii 51.7 um, feiii 105.4 um and niii 57.33 um. however they are expected to be much weaker than the cii line and their detection could only be marginal. the strategy will thus be to take a full grating spectrum for each position. the exposure times are calculated with aot lws01 (full grating scan) with 2 samples per resolution element, on the basis of a s/n around 10 for the continuum at 100 um. they should unfortunately only give a s/n of the order of 3 at 60 um for our objects, but a confortable s/n of 15 at 158 um. the iras fluxes considered have previously been corrected for the revised calibration of iras fluxes with cobe data. off-source positions are required for extracting the background emission. for each object, we will observe one position close to the cloud, with the longest exposure time used for the object.
Instrument
LWS01
Temporal Coverage
1996-04-11T00:47:05Z/1997-09-01T08:04:13Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, Gry et al., 1999, 'STUDY OF THE LOW DENSITY COMPONENTS OF THE ISM THE INTERSTELLAR CIRRUS ', 1.0, European Space Agency, https://doi.org/10.5270/esa-2s7939u
