| Description |
scientific abstract recent high-resolution radio mapping observations have revealed the presence of the high-density cores in molecular clouds. these are the most likely places for star-formation. in fact, iras has found a good correlation between the far-infrared point sources and the cores. the iras sources associated with the cores (class i sources) are believed to be in a very early stage of star-formation, i.e., candidate protostars. these are considered to evolve to low-mass main-sequence stars via t tauri phases. however, not all of the radio cores are associated with the iras sources and the nature of the cores without the iras sources are not well known. one explanation is that the core source is still too cold to be detected by iras. if the sensitivity is high enough, even such cold sources will be detected and we can distinguish between the cold cores without any far-infrared sources and the cold cores with faint far-infrared sources. if detected, the faint far-infrared sources are likely to be the precursor of class i sources. another explanation is that the cores without iras sources are actually in a stage before forming stars. we propose to make deep far-infrared survey of the radio-selected sample of high-density molecular cores in taurus or ophiuchus depending on the launch season. the targets are selected based on the nobeyama radio observatory c18o maps and univ. nagoya surveys. observation summary photometry and imaging of the compact continuum emission in 103 high-density cores either in the taurus or ophiuchus dark clouds (comprising of 90 sources detected with the nro 45m telescope and 13 sources selected by the nagoya group) will be made with pht-c in 3 filters (60, 100, and 180 microns), and with pht-p in 2 filters (11.5 and 25 microns) using an aperture of 52 arcsec. the large aperture for pht-p is used for matching the pixels scale of pht-c. these cores are identified with a small beam of the nobeyama telescope, therefore serving as a unique and complete list of the high density cores. most of their positions have been measured with an accuracy better than 18 arcsec. the observations will enable us to detect faint, compact far-ir sources undetected by iras (presumably very low-luminosity or cold sources) and determine the spectral energy distribution of the detected sources between 10 and 200 microns. even if no fir emission is detected in each core, we can set an upper limit for the total luminosity from the core more than one order of magnitudes lower than the iras limit. to complete the 60-180 micron photometry of the nobeyama sources, we will divide the 90 sources into 5 groups, and 18 sources plus 2 off positions in each group will be observed in a sparse mapping mode as follows: a) starting with 60 and 100 micron filters, we observe an off-position (pht37), then object1 (pht38), object2,.., object18, and the off-position (pht39). b) subsequently, changing to 180 micron filter, we measure the off-position (pht37), then object1 (pht38), object2,.., object18, and the off-position (pht39). we employ an integration time of 64 sec for 60, 100, and 180 micron filters, which will ensure the s/n ratio of 3-20 (depending on the wavelengths and regions) for a source with 0.1 jy flux. it will take 27615 sec to finish the 60-180 micron observations. these observations correspond to part 1-5 of our proposal. photometry at 11.5 and 25 microns (pht03) will be made with the rectangular chopping in a concatenated mode. 18 sources are observed in one concatenated observation. we employ an integration time of 32 sec. it will take 23303 sec to finish the short wavelength observations. these observations correspond to part 6-10 of our proposal. 13 nagoya sources will be separately observed with pht03 and pht22 with a rectangular chopping and an integration time of 16 sec for all filters (8671 sec in total). the 60-180 micron and 10-25 micron observations will be concatenated in each source. this corresponds to part 11 of our proposal. |
