scientific abstract the present proposal concerns a large area survey for low-mass, young and embedded stars in several well-known, nearby star-formation regions: taurus, perseus, rho ophiucus, orion, l1641, l1630, rcra, serpens, chameleon, monoceros and cepheus. the total area coverage of the survey is approximately 2.5j sq. deg. the proposed survey is 10-50 times more sensitive to point sources than iras and will be conducted with two isocam filters, lw2 (5-8.5 microns) and lw3 (12-17 microns). the proposed pixel field of view is 6, resulting in a more than tenfold increase in spatial resolution compared to iras. the observations will yield a rather complete sample of the stellar population in the selected dark clouds for luminosities larger than a few x 0.001lsun. as a result of the proposed survey any sufficiently luminuous matter around the embedded objects will be detected if extended on a scale > 5 arcsec., which corresponds to linear scales of >1000au at a distance of 150 pc. observation summary the goal is to cover large areas of known star-forming regions and to get as much overlap as possible with ism and other star formation proposals without introducing unwanted bias effects. for a region like rho oph the ism program will actually add area to the survey proposed here. to keep the total observing time within reasonable limits the integration time per frame has been kept short (effectively 40 sec is spent on each sky bin). according to the time calculator the corresponding flux limit for point sources (s/n = 10) are 0.8 mjy and 1.5 mjy for lw2 and lw3 repectively. the reason for proposing a survey in two filters, lw2 and lw3 , is that it will help significantly in characterizing the energy distributions, in particular as 2.2 micron data will be obtained for the same regions by means of ground-based observations. the selected filters allow sensitive measurements to be made of objects with a wide range of spectral energy distributions, and to cover important spectral regions for which ground-based observations are impossible and interstellar/circumstellar dust is rather transparent. both filters lie outside the silicate absorption feature at 9.7 micron but lw2 covers the spectral region where several strong infrared emission band features occur. to minimize the problem with background stars all but three regions have galactic latitudes in the interval b_abs = 15 - 20 degr. to save observing time it is proposed to use a pixel field of view of 6 for both filters. this means that the lw3 observations will be diffraction limited, while the psf will be under-sampled for lw2. the most effective observing scheme is provided by the aot 1 general observations. each region will then obviously be completed in one filter before the second one is used. the spacecraft time has been calculated assuming the following observation scheme: 1. move to the target (180 sec.) 2. make 4x5 sec integrations (20 sec) 3. move 1.5 arcmin (half-frame) in ra (10sec) 4. make 4x5 sec integrations (20sec) etc. the next row of raster positions is shifted by 2.6 arcmin (this slew takes 11 sec.), which means that there will be no gap between the rows, regardless of the array orientation. the fact that the scan direction normally differs from the x- and y-axes of the array means that the maps will contain pieces that are exposed three times instead of twice. this can be avoided using the space-craft axes, but as our regions (in some cases) are quite elongated, this solution would not be practical. and after all, this extra coverage is not useless. in our source list we include the map size (arcmin(ra) x arcmin(dec)) in the object name slot as well as the filter. some of the regions have in the target list been split into sub-regions to keep the time per raster map within reasonable limits. normally there is an overlap of 3 arcmin between two such sub-regions. for the smaller maps we propose concatenation when changing to the other filter. the only reason for this is to save observing time.
Instrument
CAM01 , PHT22
Temporal Coverage
1996-02-04T04:20:52Z/1998-01-29T11:40:26Z
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, Nordh et al., 1999, 'A survey for young comma low-mass stars in nearby molecular clouds. ', 1.0, European Space Agency, https://doi.org/10.5270/esa-x4uqbth
