scientific abstract we want to investigate the ir properties of the diffuse infrared emission of the galaxy using pht and cam. different programs are proposed depending on the accessible sky with iso. if the galactic centre is visible, pht-s spectra are measured at selected positions along and near the galactic plane between l=-60 and l=60 degrees. an important objective for this program is to measure intensities of the uir emission features in different parts of the galaxy as the sightlines are sufficiently bright for good pht-s spectra. the positions are representative for the galactic radiation away from bright discrete sources. the pht-s spectra will be complemented by pht-p measurements. as an additional program, linked observations with isocam are proposed. these observations are described in part 2 of this proposal. the cam data are coordinated with the cp proposal selected area galactic survey with isocam (price et al.) and are shared between the consortia of this and price.s proposal. in case orion is visible we study the (weaker) emission of the galactic anti-centre region. we will perform raster scans in the c_200 and c_120 micron bands along selected pieces of the accessible galactic equator from l=67 to l=331. in addition, raster scans perpendicular to the galactic plane will be performed centered at the same fields and reaching from b = -0.8 to b = 2.3 degrees. these data will be utilized to investigate the distribution of cold interstellar dust and the isrf throughout the outer galaxy and to search for small scale structures of the very cold dust emission. the spatial changes in dust grain populations is one central open problem. with its 3. wide beam (1.5.x 1.5. pixels) isophot-c200 is ideally suited for the kind of studies suggested here. the smaller beam as compared to cobe provides the advantage to avoid discrete sources and to see the truly diffuse component of the background radiation. observation summary in case of an autumn launch (hole in orion) we want to take pht-s spectra with aot p40 at regularly spaced positions along the galactic plane at b=0.0, b=+/-1 (=on-positions), and at b=+/-5 degrees. (=off-positions). at each on-position a raster of 2x2 positions with 64sec integration time for each raster position will be observed. the sensitivity of pht-s is sufficient to achieve a signal (zodiacal background subtracted) r.m.s. of 0.8 and 1.5 mjy/sr per pixel for ss and sl, respectivel, for the co-added signal from the four raster positions. the observations at b=+/-5 degrees are off-positions; therefore an 1x2 point raster map will be performed at each off-position with 64 sec integration time per raster point. the combined pht-s exposure time at these two off-positions will therefore be equal to the pht-s exposure time spent at each one of the on-positions. aot p03 measurements of 32 seconds in p_3.6 and p_7.3 will be performed to calibrate the ss and sl spectra. for b=0, p03 observations in the filterbands p_25, p_60 and p100 to determine the emission in a 99 aperture. these data will be compared and cross calibrated with both the lws (cf iso proposal by caux et al.) and iras data. the p_3.6 and p_7.3 measurements will be obtained in a 50 aperture to obtain an s/n of at least 20 and to ensure comparison with the longer wavelength data. in case of a spring launch the camera c200 and aot p22 configured in two filters - c_200 and c_120 - are used to scan selected pieces of 4.5 deg length at or near the galactic equator in the raster scan mode. in addition, we perform also a raster scan perpendicular to the galactic plane from -0.8 deg to +2.3 deg latitude at the central point of each galactic equator scan. the galactic coordinates of the central positions of these cross scans are: l / 67.0 90.0 118.0 165.0 240.0 275.0 301.0 degrees. b / 0.3 0.5 0.5 0.0 -0.5 -0.5 -0.2 degrees these positions have been selected in such a way that they avoid the bright hot dust areas around hii regions. the positions are not exactly at the galactic equator but follow the ridge of maximum fir emission as determined from the iras 100 micron data. this optimizes the detection possibilities of very cold dust. each set of measurements consists of ten concatenated linear raster scans - five in each of the two filters - of 32 positions with 180 spacing. the integration time is 10 sec per raster position. for a typical brightness in the outer galactic plane of 50 mjy/sr we reach a s/n of better than 500, i.e. features as weak as 0.5 can be measured with s/n = 5 in the single-pixel mode.
Instrument
PHT03 , PHT40
Temporal Coverage
1996-02-06T12:01:37Z/1996-10-01T17:10:26Z
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, Mattila et al., 1999, 'Diffuse infrared emission of the Galaxy comma Part 1 ', 1.0, European Space Agency, https://doi.org/10.5270/esa-eldv49k
