scientific abstract we propose to observe the hd j=1-0 112 mu line in a dozen interstellar clouds to determine the deuterium abundance in the solar neighborhood, and to search for any possible gradients across the galaxy. in two clouds, the hd j=2-1 56 mu line will be observed as well. the results will form important tests of cosmology and astration models. the total amount of time including overheads is 5.5 hours. the deuterium abundance is one of the most sensitive probes of the baryon density in the early universe. however, attempts to measure the d/h ratio in stellar or interstellar sources have been plagued by a multitude of problems. radio searches for the 92 cm line of d i in emission in interstellar clouds are still unsuccessful, whereas the recent possible detection of the line in absorption against cas a has taken several months of integration time and is difficult to interpret. observations of the lyman lines of h and d toward early type stars suffer from confusion by stellar lines and possible stellar variability, whereas the use of deuterated molecules is hampered by chemical fractionation effects. the best estimates from the ultraviolet absorption line measurements give 5e-65000 jy) (autumn osns 1, 3, 4, and 5; spring osns 1, 2 and 3), the line/continuum ratio is estimated to be about 0.03-0.05. thus a high s/n>100 on the continuum is required for adequate discrimination of the line, resulting in an integration time of 600 seconds per source. for the weaker sources, the estimated line/continuum ratio is 0.05-0.1. for a s/n=30-60, this leads to integration times of 1000-2000 s. the expected strength of the hd line in the outer galaxy sources is particularly uncertain. for the 56 mu, a s/n on the continuum of 50-100 is needed to obtain a detection or a meaningful upper limit. this results in integration times per source ranging from 1200 to 4000 seconds.
Instrument
LWS01 , LWS02 , LWS04
Temporal Coverage
1996-08-05T21:09:21Z/1998-03-27T15:22:50Z
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, van Dishoeck et al., 1999, 'DEUTERIUM IN THE GALAXY: THE HD ABUNDANCE AS A FUNCTION OF GALACTOCENTRIC DISTANCE ', 1.0, European Space Agency, https://doi.org/10.5270/esa-pnml19p
