The first observations of the J = 16 to J = 15, 162.8 microns transition of CO from an astronomical source are reported. Measurements were carried out on the Kleinmann-Low Nebula. The intensity observed is in good agreement with predictions from previous spectroscopic work carried out in the far infrared. The observation strengthens the previous claim that approximately 1.5 solar mass of molecular hydrogen is heated to a temperature above 750 K within the shocked region in the Nebula. Upper limits to he OH intensity in the F2 (2Pi 1/2) transitions J = 3/2 to J = 1/2 which fall into two groups centered respectively at 163.12 and 163.40 are presented

Harwit, M.

Kurtz, N. T.

Smyers, S. D.

Stacey, G. J.

English

NASA Technical Reports Server

NASA Techn ical Memorandum 84321 
· - -~~ '--- . -- .. ----~--
Airborne Astronomy Program 
Medium Altitude Missions Branch 
Preprint Series 004 
NASA-TM-84321 19830011389 
Highly Ejected [J = 16 to 15] 
Rotational Transitions of 
CO, at 162.8 Jlm in the 
Orion Cloud 
Gordon J. Stacey, 
Noel T. Kurtz, 
Scott D. Smyers 
and Martin Harwit 
January 1983 
Kuiper Ai rborne Observatory 
NI\S/\ 
National Aeronautics and 
Space Administration 
CD 
I 
- --- - - - _._-- -- ----
____ . _____ J 
https://ntrs.nasa.gov/search.jsp?R=19830011389 2020-03-21T03:53:23+00:00Z
NASA Technical Memorandum 84321 Airborne Astronomy Program 
Medium Altitude Missions Branch 
Preprint Series 004 
Highly Ejected [J = 16 to 15] 
Rotational Transitions of CO, at 
162.8 Ilm in the Orion Cloud 
Gordon J . Stacey 
Noel T. Kurtz 
Scott D. Smyers 
Mart in Harwit, Center for Radiophysics and Space Research , Corne ll University, Ithaca, New York 
NI\S/\ 
National Aeronautics and 
Space Administration 
Ames Research Center 
Moffett Field . California 94035 
HIGHLY EXCITED (J = 16 to 15) ROTATIONAL TRANSITIONS 
OF CO, AT 162.8 um, IN THE ORION CLOUD 
Gordon J. Stacey, Noel T. Kurtz, Scott D. Smyers 
and Martin Harwit 
Astronomy Department 
Center for 2adiopnysics and Space ~esearch 
Cornell University 
Ithaca, New York, 14853-0352 
Subject Headings: Interstellar medium-shocks, cooling; 
CO transitions; submillimeter astronomical 
spectroscopy 
Accepted b y : Monthly Notices of the Royal Astronomical 
Society as a Short Communication. 
2eceived 1982 September 16. 
2 
ABSTRACT 
We present the first observations of the J = 16 to 
J = 15, 162.8~ transition of CO from an as t ronomical 
source. These measurements were carried out on the 
Kleinmann-Low Nebula. The intensi t y observed is in 
good agreement with predictions from previous spectro-
scopic work carried out in the far infrared by the Uni-
versity of California, Berkeley group, and by our group 
at Cornell. The observation strengthens our previous 
claim that ~1.5 ~ of molecular hydrogen is heated to 
a temperature above 750 K within the shocked region in 
the Nebula. We present upper limits to the OH 
intensity in the Fz (Z rr l / 2) transitions J = 3/ 2 to J = 
1 / 2 which fall into two groups centered respectively at 
163.12 and 163.40~. 
,- - - '- - - ,--- -- -~, --- ---- - - - - - ---- - - - -
3 
I. INTRODUCTION 
Two years ago Watson et al., 1980, discovered 
radiation from highly excited CO molecules in the 
Kleinmann-Low Nebula. Rotational transitions from 
upper levels in the range J = 21 to J = 30 were 
studied. This radiation is believed to emanate from 
shocked molecular hydrogen regions and gases left in 
the wake of shocks. The lines observed lie in the 87-
to 124-micron wavelength range. 
By observing at longer wavelengths, our group has 
recently also observed the J = 17 to J = 16 transition 
at 153~ (Stacey et ale 1982). Here we report new 
observations obtained in January 1982 in which we also 
observed the J = 16 to J = 15 line at 162.8lJ (Fig. 1). 
The interesting feature of both transitions is the vir-
tual independence of their strengths from temperature 
and density conditions over a wide range of tempera-
tures above 750 K and molecular hydrogen densities 
above 10 6 cm- 3 (McKee et ale 1982, Stacey et ale 
1982). This enables one to define the mass of CO in 
the Kleinmann-Low Nebula at temperatures above 750 K, 
at least within a factor of two, to be 8 x 1030g , 
corresponding to our observed intensity of 6.4 x 10 - 17 
') 
Watt cm-~ in the line. By assuming cosmic abundance, 
and one-quarter of the carbon to be present in the form 
of CO, as justified by Storey et ale 1981, we then find 
that about 1. 5 Me of molecular hydrogen have been 
heated to these t~~peratures within the nebula. 
- I 
~-- . __ ... ---- -- - - --
4 
Since direct observations of the hydrogen are com-
plicated by enormous near-infrared opacities -- opaci-
ties believed to play a negligible role at 163u -- this 
indirect estimate of the total mass of material 
involved in shocks is significant. 
II. OBSERVATIONS AND RESULTS 
On the morning o f January 1 4 and 15, 1982, we 
observed the Kle i nma nn- Low ( KL )/Beckli n-Neugebauer (BN) 
region of the Or i on Nebul a while f lying aboard the 
Kuiper Airborne Obse rvatory ( RA O) a t an altitude of 
12 .5 km. The instrument used on the 90-cm tel escope 
was our interferometer-grating-spectrometer described 
elsewhere (Harwit et al e 1981). The resolving power of 
this instrument is rough ly A/~A ~ 1000, corresponding 
to a line-of-sight velo c ity spread ~300 km sec- i. The 
bandpass of our ins trument is roughly on~ mic ron 
between half-power points, and the separation between 
independent spec t ral l i ne is 0.13 ~ at 162 .8 ~. Our beam 
is approximately I' square, and we measure an in-flight 
system-noise-equivalent-power (NEP) of 2.9 x 10- 13 ~v 
Hz -1 / 2, as judged through observations of the KL-BN 
continuum spectrum. Two stressed gallium-doped 
ge r manium detectors a r e h oused in our instrument. The 
portions of the spec t rum observed are separated by 
0.7~. While one detector observed a range around 
l62.5~, the other was centered at l 63.2~. 
--- ---- -
r-
5 
Two sets of observations were undertaken: First, 
we sought the intensity of the l62.8~ transition from a 
field of view centered on the Becklin-Neugebauer 
object, but including the Kleinmann-Low Nebula. These 
data were obtained on January 14. The following night 
we attempted to map the region, at lS3.3~, in order 
to assess the size of the emitting region we had 
observed the previous September. Five fields of view 
were observed, the peak emission region and four 
others, respectively displaced by approximately half an 
arc minute to the north, south, east and west. Time 
limitations precluded our taking more than one spectrum 
per region. Within our noise values, which were of the 
order of half the signal strength, we observed no 
de f inite signal outside our main beam, although there 
was a hint of extension toward the northwest. This 
suggests that the dimensions of the region emitting at 
lS3 ~ are not appreciably extended on a scale of one arc 
mi nute, a result consistent with observations of 
Phi l lips et ale 1979 and Storey et ale 1981, respec-
tively, in the J = 3 + 2 and J = 21 + 20 transitions. 
Figure 1 shows the spectrum observed at 162 ~ . The 
flu x observed from the 162.8 ~ line was ca l ibrated 
aga i nst the known continuum emission from the Nebula 
or wh ich we assumed a flux mode led by We rner et al. 
(1976) as that from a 70 K blackbody whose emissivity 
6 
beyond wavelength A = 20~ drops as 20/ A• The flux in 
the line is then calculated to be 6.4 + 1 x 10- 17 W 
cm-
2
• This may be compared to our previously cited 153~ 
flux of 7 x 10- 17 W cm- 2 (Stacey et ale 1982). 
III. DISCUSSION 
It is also worth comparing our result to intensi-
ties seen in other transitions observed from the same 
field of view. These are exhibited in Fig. 2. The 
line intensities observed at high J values are well 
fitted with a curve const ructed by McKee et ale (1982) 
based on a shock model which reaches a peak temperature 
of ~3 x 10 3 K, in the neutral gas. 
At low J-values a magnetohydrodynamic shock model 
due to Draine and Roberge (1982) gives a somewhat 
better fit, since it includ es a range of preshock, 
shock, and post-shock temperatures. The low J-values 
refer to cool gas that exhibits a wide velocity range 
in the "pedestal" spectrum. Evidently there is more 
cool gas than accounted for in the simpl e models. The 
results obtained are consistent with our previous 
( Stacey et ale 1982) claim that the total number of 
molecules i n our beam, in a gas component at tempera-
6 _ 3 · 53 
ture above 750 K and nU2 > 10 em ,1S 10 CO 
molecules. As previously concluded this corresponds to 
- - - --
r--
I 
7 
about 1.5 Me of hydrogen in such a heated cloud. 
As a side product of our CO observations, we also 
observed the part of the spectrum in which OH radicals 
emit around 163.1 and l63.4u. At the longer of these 
two wavelengths, our second detector was used. For OH, 
the Fz(2 IT1 / 2 ) transitions J = 3/2 to J = 1/2, exhibit 
sets of three closely spaced lines clustered 
respectively around 163.12 and 163.40u (Brown et ale 
1982). Our spectral resolution suffices only to 
resolve these six lines into two distinct groups. 
Storey et ale (1981a) previ ously observed companion 
transitions 2 FI ( IT3 / 2) J = 5/2 to J = 3/2, where six 
closely spaced lines again break into two clearly 
separated sets of three, respectively, at 119.23 and 
119.44u. While the Berkeley group clearly observed 
these lines in absorption against the Galactic Center, 
they placed less confidence in an apparent emission 
they saw from the BN region, where each of the two 
small features seen appeared displaced from the 
expected line position by 1/20 micron. At any rate, if 
correct, the line intensity of both these features 
corresponds to 1.6 x 10- 17 W cm- 2 • 
Our own observations of the 163u lines place upper 
limits of 1.5 x 10- 17 W cm- 2 __ one standard deviation 
from the mean--on each of these features. For a 
hydrogen density nH = 106 cm_ 3 , Flower et ale 2 
8 
(1982) calculate a cooling rate for OH, through all 
transitions, of ~5 x 10- 18 erg sec- 1 per OH molecule. 
In order to observe OH emission from BN at the level 'of 
sensitivity cited by either the Berkeley group or given 
by our upper limits, one would require a column density 
"3.6 x 10 15 crn- Z as noted by the Berkeley group. 
This must be compared to a column density NCO "9 x 
10 17 cm- Z obtained by averaging the total number of CO 
molecules observed over the area of our beam. If one.-
quarter of the carbon is in the form of CO, and cosmic 
abundance of carbon is assumed, we have nCO/ nH2 
.. 1.7 x 10- 4 • In that case the mean OH density along 
the line of sight would give nOH/ nH2 < 7 x 10- 7 
for the shocked region. 
This is important for the following reason. The 
oxygen abundance should be roughly twice the carbon 
abundance if normal cosmic abundances hold in the 
nebula. As summarized by Stacey et al., however, 
observations by a variety of different workers and 
techniques have shown that there is little oxygen in 
atomic form, or in the form of H20, in the Kleinmann-
Low Nebula. Since the OH abundance also appears to be 
low, oxygen, if as abundant as expected, would have to 
be in the form of 0z- That would be consistent with 
models for cool dense molecular clouds produced by 
9 
Iglesias (1977) but less readily reconciled with the 
shock models of Igle'sias and Silk (1978) which suggest 
that much of the molecular oxygen is destroyed in hot 
shocks. It is interesting, nevertheless, that observa-
tions of this kind are able to lead us to a juncture 
where chemical reaction schemes in interstellar space 
can now be subjected to detailed analysis. 
ACKNOWLEDGEMENTS 
The work reported here was supported through NASA 
Grant NSG-2347. We thank the staff of the RAO for 
their whole-hearted support throughout our observing 
run. Bruce Draine kindly sent us a preprint of his 
article with Wayne Roberge, prior to publication. Dan 
Watson very kindly discussed some of the Berkeley 
group's results with us before publication, and 
permitted us to cite them. Jim Houck gave us the use 
of his excellent offset guider for the observations we 
report. 
10 
REFERENCES 
Brown, J. M., Schubert, J. E., Evenson, K. M. and 
Radford, H. E., 1982, Astrophys. J. ~, 899. 
Draine, B. T. and Roberge, W., 1982, Astrophys. J., 
259, L91. 
Flower, D. R., Guil1oteau, S. and Hartquist, T. W., 
1982, Mon. Not. R. astr. Soc., 200, SSP. 
Goldsmi th, P., Erickson, N. R., Fetterman, H. R. 
Clifton, B. J., Peck, D. D., Tannenwald, P. E., 
Koepf, G. A., Buhl, D. and McAvoy , N., 1981 
Astroohys. J., 243, L79. 
Harwit, M., Kurtz, N. T., Russell, R. W. and Smyers, 
S. D., 1981, Appl. Optics, 20, 7792. 
Iglesias, E. 1977, Ap. J., 218, 697. 
Iglesias, E. and Silk, J., 1978, Ap. J., 226,851. 
McKee, C. F., Storey, J. W. V. and vlatson, D. M., 1982, 
Ap. J., 259, 647. 
Phillips, T. G., Huggins, P. J., Neugebauer, G. and 
Werner, M. W., 1977, Astrophys. J., 217, L161. 
Stacey, G, Kurtz, N, Smyers, S., Harwi t, M., 
Russell, R, and Melnick, G., 1982, Astrophys. J ., 
257, L3 7 . 
Storey, J. W .. V., vlatson, D. M., Townes, C. H., 
Haller, E. E., and Hansen, W. L., 1981, 
Astrophys. J., 247, 136. 
11 
Storey, J. W. V., Watson, D. M. and Townes, C. H., 
1981a, Astrophys. J., 244, L27. 
Watson, D. M., Storey J. W. V., Townes, C. H., Haller, 
E. E. and Hansen, W. L., 1980, Astrophys. J., 
239, L129. 
Watson, D., 1982, private communication. 
Werner, M. W., Gatley, 1., Harper, D. A., Becklin, E. 
E., Lowevnstein, R. F., Telesco, C. M., and 
Thronson, H. A., 1976, Ap. J., 204,420. 
12 
FIGURE CAPTIONS 
Figure 1 - The spectrum of the Kleinmann-Low Nebula at 
162.5~. Our instrumental profile predicts a 
triangular spectral response for the contin-
uum emission from the Nebula--dashed lines. 
Below 162.l~ and above 163.l~ we expect to 
observe no signal. The noise in these por-
tions of the spectrum is a measure of our 
overall uncertainty. The Fourier trans-
formed spectrum is a power spectrum so that 
all values shown are positive. Error bars 
are one standard deviation from the mean for 
the three spectral runs represented here. A 
triangular apodization was used in the 
Fourier reduction. The CO line is not 
resolved with our instrument. 
Figure 2 - Intensities in the CO transitions J to J-l 
observed by different groups for an aproxi -
~ately 40 n to l' beam centered on the Klein -
mann-Low Nebula. Symbols have the following 
meanings: 
!Phillips et al. 1977, 'Goldsmith et al. 
1981, tStacey et ale 1982, V'Storey et 
a1. 1981, Watson et ale 1980, Watson 
1982; cresu1ts presented in this paper . 
--- ---- -
--- - -- --
13 
Filled symbols ground-based; open symbols 
airborne observations. The solid curve is 
drawn for a 103 K gas with density nH2 = 
10 6 cm- 3 as given by McKee et al. (1982). 
The dashed curve, at low J-values was 
obtained by Draine and Roberge (1982) for a 
comprehensive magnetohydrodynamic shock 
model. 
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KLEINMANN - LOW 
Continuum Convolved 
With Spectrom~tcr 
Sl i t Function 
111 
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Expected i62 .8fLCO Line Po'sition 
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161.0 161.5 162.0 162.5 1630 163.5 
Wavelength (microns) 
1640 164.5 165.0 
Figure 1 
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Figure 2 
1. Report No. 2. Government Accession No. 3. Reci pient 's Cata log No. 
NASA TM-84321 
4. Ti t le and Subtitle 5. Report Date 
HIGHLY EXCITED (J = 16 TO 15) ROTATIONAL TRANSI- Januarv 1983 
TIONS OF CO , AT 162 . 8 )lm, IN THE ORION CLOUD 6. Perform ing Organ ization Code 
7. Author(s) 8 . Performing Organ ization Report No. 
Gordon J . Stacey, Noel T. Kurtz, Scott D. Smyers, A- 9214 
and Martin Harwit 10. Work Unit No. 
9. Performiny Organization Name and Address 352-02-03 
Center for Radiophysics and Space Research " . Contract or Grant No. 
Cornell University , Ithaca, New York 
13. Type of Report and Period Covered 
12. Sponsoring Agency Name and Address 
National Aeronautics and Space Administration Technical Memorandum 
Washington, D.C . 20546 
14. Sponsor ing Agency Code 
15. Supplementary Notes Preprint Series 004 - Supported by NASA grants . Point of 
Contact : L. c. Haughney , Ames Research Center, MiS 211- 12, Moffett Field, 
Calif . 94035, (415) 965- 5339, FTS 448-5339 . 
16. Abstra ct 
We present the first observations of the J = 16 t o J = 15, 162.8 )1 
transition of CO from an astronomical source . These measurements were 
carried out on the Kleinmann- Low Nebula . The intensity observed is in 
good agreement with predictions from previous spectroscopic work carried 
out in the far infrared by the University of California, Berkeley group , 
and by our gr oup at Cornell. The observation strengthens our previous 
c laim tha t "'='1 . 5 M8 of molecular hydrogen is heated t o a t emper at ure a bove 
750 K within the shocked region in the Nebula. We present upper limits 
t o the OH intensit y in the F2 ( 27T 1/2 ) transitions J = 3/2 to J = 1/2 
whi ch fall int o two groups cen t ered respective l y a t 163 . 12 and 163.40 IJ • 
17 . Key Words (Suggested by Author (s)) 18. Distri but ion Statement 
Astronomy Unlimited 
Interstellar medium shocks 
CO transitions 
Submillimeter astronomical STAR Category 89 -
soectroscoov 
19. Secur ity Classif . (of this report) 20. Security Classif . (of t his page) 21. No . of Pages 22. Price . 
Unclassified Unclassified 17 A02 
• For sale by the National Technical Information Se rvice , Springfield , Virginia 221 61 


Highly ejected J = 16 to 15 rotational transitions of CO at 162.8 mirons in the Orion cloud

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