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A1619 2002-Feb-01 15:02:16
Technical Page
Proposal Type: Regular
General Category: Astronomy
Sub-Category: Spectroscopy
Observation Category:
Total Time Requested: 51 Hours
Proposal Title: Probing Low Temperature and High Density Clouds via 6 cm Formaldehyde
Absorption of the CBR
ABSTRACT:
The lowest transition of ortho-formaldehyde (H2CO) is seen in absorption against the cosmic background radiation
in molecular clouds. The reason for this peculiar behavior is that the excitation temperature of these levels is
lowered by collisional pumping. As the density rises, however, the level populations are forced toward equilibrium
at the kinetic temperature, and the line goes into emission. Since these levels lie very low in energy, they provide a
probe of high density material at low temperature. A previous proposal was assigned observing time in
December 2001. Considerable time was required to develop the optimum observing strategy for this type of
observation at Arecibo, and we determined that total power \on source" observations were ideal for these very
narrow lines, and yielded baseline noise consistent with radiometric uctuations, once a low{order polynomial was
removed. With the improvement in sensitivity resulting from elimination of switching, we were able to obtain
limited measurements of three pre{protostellar clouds. The formaldehyde absorption is clearly mappable, and we
have achieved unparalleled resolution of the hyperne components of the 6cm inversion doublet. We are here
proposing to extend the observations to fully dene the extent of the absorption in these clouds. We are also
proposing to expand our source list to include other protostellar clouds which may be dense enough in their central
regions to drive this transition into emission.
Name Institution E-mail Phone Student
Neal J. Evans University of Texas nje@astro.as.utexas.edu 512 471 4396 no
Service Observing Request Remot e Observing Request
X None No
All of the observing run. X Maybe
Part of the observing run. Yes
Queue Observing
Instrument Setup
C
Atmospheric Observation Instruments:
1

Special Equipment or setup: none
RFI Considerations
Frequency Ranges Planned
2