Some photometric observations of auroral spectra

Journal of Atmoapherlc and Terre&M

Physics, 1953, Vol. 7, pp. 141 to 151.

Pergamon Press Ltd., London

Some photometric observations of aurora1spectra* D. M. HUNTEN University

of Saskatchewan,

Ssskatoon

(Received 7 March 1955) ABSTRACT These A variety of measurements of aurora1 spectra has been made with a photoelectric spectrometer. include relative and absolute intensity measurements of the more prominent features, and a verification of SEATON’S absolute intensity scale. Observations of HP seem to indicate more erratic behaviour than has been assumed. The intensity of the N II lines 5001-5 A shows little or no excitation by helium ions. A very intense feature observed in Type B red aurora appears to be due to sodium. The vibrational development of the N,+ first negative system indicates electron excitation from the ground state of N, at e temperature of O-700°K. The results show the spectrometer to be useful for intensity measurement and the observation of short-lived effects. It is, however, limited to the brighter forms of aurora. 1.

INTRODUCTION

A photoelectric spectrometer capable of producing a tracing of an aurora1 spectrum in ten seconds with 10-A resolution has been described in another paper (HUNTEN, 1953). When this instrument was first put into operation (the spring of 1952), a large number of spectra were taken with the main object of testing its performance. Since that time, the aurora has been considerably fainter; consequently all the spectra taken have covered a very restricted range of wavelength, so that The original spectra covered a range of about the sensitivity could be increased. 2500 A, and since they were the only ones of this type available, they were examined and found to contain a good deal of interesting information. This information is the subject of the present paper. Many of the features could well be studied in more detail when bright aurora is again available in sufficient quantity. The resolution used was sometimes 10 A, sometimes 20. On some of the nights, spectra were also taken of a secondary standard low-brightness source which gives a continuous spectrum. This source has recently been provided with an absolute calibration against a black body at a known temperature by G. G. SHEPHERD (1954). Absolute intensities could therefore be found from some of the aurora1 spectra. Another group gave relative but not absolute intensities. We have found it convenient to express the emission rates in quanta per second per unit solid angle from a square centimetre in the line of sight. The emission rate at wavelength 1 will be written &(A) and the units understood to be 10’ quanta/cm2 set ateradian. Besides measuring intensities, we have been able to identify a few new minor features, to study the spectrum of Type B red aurora, to make some observations on forbidden transitions, and to estimate the vibrational temperature given by the N,+ first negative system. * The research reported in this paper has been sponsored by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, under Contract AF 19 (122)-152.

141

D. M. HUIWEN

2. LINES AND BANDS IDENTIFIED In general, the features observed were the strong ones; however, some could not be resolved from neighbouring ones of greater intensity. A few bands could be identified with some certainty’by their correlation with known ones of the same system. These are: N,

second positive

2-7 3-8

4490 A 4417

N,+

first negative

O-4 l-5

5865 5755

N,+

Meinel

4-O 5-l

6130 6270

(probable) (probable)

(probable) (possible, but badly blended) The last four are further discussed in Section 3. A fairly prominent feature appears at about 5000 A. The two multiplets of N II to which it might belong are shown in Table l> which is taken mostly from Miss MOORE’S multiplet table (1945)_ PETRIE and SMALL (1952) ident’ify the feature with the first three lines of multiplet 19, but say that t’he intensity distribution in the multiplet is anomalous, presumably because the lines at 5016 A and 5026 A are weaker than expected from the intensities given by Miss MOORE. These may, however, have been merely eye estimates; we have therefore calculated the expected intensities from the tables of RUSSELL (1936), and found them to be much lower for these two lines. CHAMBERLAIN and OLIVER (1953) prefer to Table 1. The two multiplets (both X II) that have linesnear 5001 a, as listed in Miss MOOHE’S table (1945). The last two columns give the intensities from this table and those calculated from the tables of RUSSELL (1936).

Multiplet

and h’o.

J

A

IM

IR

I

383P-3JJ3As 4 3p3D-3d3Fo 19

2-l l-l O-l

5045.1 5010.6 5002.7

8

3-4 2-3 l-2 2-2 3-3 3-2

5005.1 5001.5 5001.1 5016.4 5025.7 5040.8

10 8 7 5 6 0

6 2

5 3 1 100 69 47 8.7 8.7 0.25

assign the 5000-A feature to multiplet 4, but Table 1 immediately shows t’hat this is incorrect, since the line at 5003 A is the weakest of the multiplet. The objections to the identification of multiplet 19 seem to have been removed, and the feature may be called N II 5001-5 A. The same conclusion appears to have been reached by CHAMBERLAINand MEINEL (1954). 142

Some photometric

observations

of aurora1 spectra

3. RED AURORA OP TYPE B This is the name given to aurora with a red lower border. It is usually bright, but lasts only a short time; conventional spectrographs are thus not well suited to its st,udy. It has already been report’ed (DAHLSTROM and HUSTEN. 1951) that bands of the O,+ first negative system are responsible for the red colour. Further observations have shown that these are usually, if not always, accompanied by N, first positive bands. Both systems make an important contribution to the red sensation. A typical spect,rum is shown in Fig. 1. A sequence of N, first posit’ive bands shows from 6500 to 7000 A; the bump at 6400 A and the large peak at 6000 A are produced by O,, bands. While t,here are more first positive bands between

\

\

\\\\\\\\\\\\\\\\\\\\\\\ 5000

boo0

7000

Fig. 1. A spectrum of Type B aurora taken on March 31, 1952, with 20 A resolution. Wavelengt,hs of band maxlma for several systems are shown; the lengths of the lines for t’he N, fist positive bands indicate either observed or expected intensities. It should be noted that the sensitivity decreases by a factor of 10 for each 650 A beyond 5500 A. (The same spectrum has been reproduced by CHAMBERLAIN and MEINEL, 1954, Fig. 10a.)

5700 and 6200 A, it does not appear that they could account for t’he features at 5750, 5870, and 6130 A. The contribution of first positive bands was estimat’ed by the following procedure: (1) The intensities of the bands from 4-l to 8-5 were measured. (2) The intensities of the corresponding bands from 5-l to 8-4 were then found from these by means of the intensity ratios measured by TURNER and NICHOLLS (1954); for the 4-O band the intensity ratio was found from the relative transition probabilities calculated by JARMAIN and NICHOLLS (1954). The bands from 9-5 to 11-7, and 9-6 to 11-8, were estimated relative to (3) 8-4 and 8-5 by means of the aurora1 intensities given by PETRIE and SMALL (1953). The resulting intensities, corrected for the response of the spectrometer, are shown in Fig. 1 by means of vertical lines at the wavelengths of the band maxima (PEARSE and GAYDON, 1950). It seems probable that first positive bands cannot entirely account for the features observed. It is natural first of all to see whether the N,+ first negative bands O-4 (5865 A) and l-5 (5754 A) are capable of accounting for the features at 5870 and 5750 is. The expected intensity of the O-4 band can be found from the observed intensity 143

D. M. HUNTEN

of the O-3 band, if the relative intensities are known. Unfortunately, HERZBERG (1928) was unable to measure the O-4 band, because it was obscured by N, first but his results suggest that an intensity ratio of about O-2 is positive bands; reasonable. The relative transition probabilities calculated by JARMAIN, FRASER, and NICHOLLS (1953) are very uncertain for these two bands, but give an intensity ratio of 0.25. Using the last figure, the expected intensity of the O-4 band is about one-third of the intensity of the 5870-A feature. It appears t,hat the O-4 band may give the inflection on the short-wavelength side, but cannot account for the whole feature. The identification of the 5750-A feature with the l-5 band appears satisfactory. It is difficult to avoid the conclusion that the sodium D lines are responsible for most of the intensity at 5570 A. The wavelength match with the red side of the feature is excellent, and the D lines are by far the strongest to be seen in this region of the spectra of PETRIE and SMALL (1952), on tracings reproduced by CHAMBERLAIN and MEINEL (1954). It is known from twilight observations (HUNTEN and SHEPHERD, 1954) that the density of sodium atoms follows approximately that of the atmosphere as a whole from 85 to at least 110 km. Since t’he Type B aurora observed was presumably at a lower-than-average altitude, a very strong radiation from sodium is perhaps not so strange as might appear at first sight. It is interesting to estimate the maximum observed emission rate and to compare it wit,h that observed in the twilight. The bright,est spectrum recorded on March 3, 1952, gave Q(5893) = 130, after allowing for the first positive bands. The twilight scattering gives Q(5893) = 30 on the average at this season, and may give as much as 45 (HUNTEN and SHEPHERD, unpublished). All the observations of Type B aurora were made with 20-A resolution. Higher resolution studies will be necessary before theeidentification of such a strong feature with the sodium lines is established with certainty. A search was made for the second principal doublet of sodium at 3303 A on some of the brightest spectra. If present, it was masked by ultraviolet1 radiations of second order or red ones of first order. The feature at 6130 w may most naturally be assigned to the 4-O band of the On some spectra there is an inflection corresponding MEINEL system of N,+. to the 5-l band at 6270 A, but the identification is very uncertain. It is noteworthy that the red lines of oxygen, normally much stronger than anything else in their region, are not visible at all in Fig. 1 and many other spectra of Type B aurora. Emission rates for some of the principal features were measured from the same spectrum used for the sodium, and are given in Table 2. Since the 3914-A band and the green line went off scale, their emission rates had to be estimated. The ratio &(3914)/&(5228) is 110, according to the calculations of JARMAIN, FRASER, and NICHOLLS (1953). Q(3914) is then 19,000. This may be checked by means of the ratio &(3805)/&(3914) + 0.06 given in Section 4; t,he result is Q(3914) = 4000. A rough average of these two was adopted for Table 2. Since the green line is normally only a little stronger than the 3914-A band (Section 4), the value Q(5577) + 10,000 was assumed. This, of course, is rather uncertain. since there is no assurance that the green line is not relatively weaker in Type B 144

$ome

photometric observations of euroral spectra

&Ul?W&. The relative weakness of the red lines could be taken as evidence of this, and the cause could be assumed to be the scarcity of atomic oxygen at lower levels. However, since the red lines are weakened by collisional de-excitation at lower levels, it is impossible to be sure. Table 2.

Emission rates in units of 10’ quanta cm2 set sterad. for the strongest spectrwn of March 3, 1952. 3914 end 5577 went off scale and were estimated by the method given in the text.

1

IdentiJication

5893

NaI? o,+ O-0, l-l MEINELPO N,+ O-3 2PG O-2 Na+ O-O @I)

6000 6130 5228 3805 3914 5577

130 270 210 170 250 (10,000) (10,000)

1

Identi,ficution

6875 6789 6705 6624 6545 6469

IPG 3-O 4-l 5-2 6-3 7-4 8-5

Q(R) 2000 2300 1850 1500 900 860

4. EMISSION RATES IN NORMAL AURORA

The emission rates of the green line in aurorae estimated to be of brightness coefficient II and III on the international scale, were found to be about Q(5577) = 80 and 800. If these are multiplied by 471they agree perfectly with the omnidirectional emission rates lOlo and loll quanta/see cm2 estimated by SEATON (1954). The Type B aurora reported in Table 2 must have been of brightness IV; the emission rate for it is a little over 1012 quanta/see cm2, rather lower than SEATON’S figure. For photometric work it would be convenient to standardize the values log, lOlo, loll, 1012 quanta/set cm2 (Q(5577) = 8, 80, 800, 8000) for brightness coefficients I, II, III, and IV.* Relative emission rates for various pairs of the strongest or most interesting radiations were measured; the results are given in Table 3. The usual custom is to measure all radiations relative to the green line, but this has the disadvantages (1) that it is not always possible in practice, because the ratio may be very small, and (2) that some other pair of radiations may be associated with each other but not with the green line. (Possible examples are the various emissions of nitrogen.) The pairs chosen were usually close together in wavelength, so that uncertainties in the correction for atmospheric extinction would give small errors. All the spectra measured were taken at a zenith distance near 45’, so that the corrections were small. The extinction coefficients given by VAN DE HULST (1952) were used. l Note added in proof: J. W. CHAMBERLAIN, in a recent discussion with the writer, has pointed out that SEATON’S estimates are probably of surface brightness rather than omnidirectional emission rate. The conversion factor & should then be replaced by one approaching 2rr (depending on the angular dependence of intensity). The agreement, while no longer perfect, is still good. A great advantep;e of the “Q” scale used here is that it is free of any such ambiguity, being directly related to an observed quant,ity. The proposed photometric scale should be established in “Q” units for this reason.

145

D. M. HUNTEN

Many of the intensity variations shown in Table 3 are probably real, especially since some of the values given are the average from several successive spectra. Table 3.

Ratios

of the emission

rates for several prominent

aurora1 features.

Values in italics are averages from several successiva spectra; values bracketed together are from individual successive spectra. Intensity ratios by VEGARD and KVIFTE (1945) have been converted to emission-rate ratios, and are given when available.

Ratio

QW'WQWl4)

Q(5001-6)/Q(5577) Q(5001-5)/&(4709)

Values found

Averages

9.42, 0.56, 041, 1.28, (0.20, 0.17, 0.18), (0.42, 0.37, 0.38) 0.027 to 0.144 0.0041 to 0.0086 0.16 to 0.30

VEUARDKVIFTE

0.77 0.29

0.33 0.57

0.046 to 0.066 0.074 0.22

0.10

Remurlcs

Lab. value 0.29

Assumes Q(5001-5)/Q(5228) &W/W&(4709)

1.3 0.02 to 0.10 0.02 to 0.04

1.0 to 1.8 0.01 to 0.15 0.01 to 0.09 (110, 130, 260) (24,67)

Q‘(4709)/Q(5228)=6.1 normal aurora Type B flickering vary active rays

The ratio &(4278)/&(3914) is of course a constant of the N,+ ion, so that the variations shown for it are certainly false. The average for the six spectra, however, agrees very well with the laboratory value. (That this is not so for the measurements of VEC+ARDand KVIFTE has already been pointed out by SEATON, 1954.) The agreement gives a useful check on the other measurements. The ratio of N, second positive to N 2+ first negative is usually constant to &20 per cent, but sometimes varies a good deal more. The N II lines 5001-5 A have been studied in the laboratory by FAN and MEINEL (1953). They found that the ratio of intensity of these lines to that of the N,+ band 5228 A depended on the type of ion exciting the spectrum. For hydrogen ions the ratio was 1.3, and for helium ions it was 10. We were able to measure &(5001-5)/&(4709) on a few spectra, and converted this to the desired ratio by means of the known value of &(4709)/&(5228). The result, &(5001-5)/ Q(5228) = 1.3, shown in Table 3, indicates excitation by protons. (Because of the small difference in wavelength the Q ratio and the intensity ratio do not differ appreciably.) The only hydrogen line which is far enough from other features to be observable is Hp. The spectra studied showed large and often sudden variations in the intensity of HP, and it was never possible to predict when it would be present. No spectra were obtained in the earliest stages of a display, when hydrogen lines are usually strongest (MEINEL, 1952; PETRIE and SMALL, 1952). H/l was observed with remarkably high relative intensity (though the absolute intensity 146

Some photometric observations of aurora1spectra

was normal) on two occasions in the faint, very active aurora which is usually seen just after a big display. These spectra were examined carefully to make sure that the feature was indeed HP, and not the 2-15 band of the Vegard-Kaplan system. Though one might doubt that a scanning spectrometer could get reliable spectra from this type of aurora, experience has shown that it can, since successive spectra are found to be very similar. An estimate of the absolute emission rate of H,4 is of interest, since CHAMBERLAIN (1954) has shown how a value of the proton flux can be found from it. Only a rough absolute calibration of the spectrometer was available for the observations of H/l reported in Table 4, but it is felt that the results should be correct within a factor of 2. According to CHAMBERLAIN, one proton gives about eleven quanta of H/3; thus a flux of 10’ protons/cm2 set gives &(Hb) = l.* The flux estimated by Table 4.

Absolute

emission

rates of HP for the same spectra as in Table 3.

Correspondin.g proton fluxes were deduced from the work of CHAMBERLAIN (1954). Aurora

Proton flux (protons/cm2 set)

Q(W)

Normal


Type B Flickering Very active rays

<2 to 16 (7, 12, 6)

7 x

(3, 6) I

<107 to 108 <2 x 10’ to-l.6 x lo8 lo’, 1.2 x lo*, 6 x 10’ 3 x lo’, 6 x 10’

,

CHAMBERLAIN for an arc, 6 x 10’ protons/cm2 see, is seen to be of the same order as the values in Table 4. Another observation was made on the “afterglow” type of aurora when studying the Au = 2 sequence of the N, second positive system. Fig. 2 shows one of three almost identical successive spectra taken on September 25, 1952, with 10-A resolution; a normal spectrum is superposed in dotted lines. It is

Fig. 2. An aurora1 spectrum covering the wavelengths from 3650 to 3850 A with 10-A resolution. In addition to the usual N, second positive bands shown with dotted lines, there are two strong Vegard-Kaplan bands. The aurora was of the very active “afterglow” type, in which radiation continues for some time after a bright outburst.

2-4 1-3 o-2

LLic iv*-r 2PC.

;’ ..

3700

immediately

that

the relative

intensity

3000

of the Vegard-Kaplan bands than normal; they are almost as strong as the l-3 band of the second positive system. This suggests that a large concentration of excited molecules was built up during the bright display, 1-11

evident

: ; :.,:

(3684 A) and 2-12 (3768 A) is much greater

* Note added in proof: This is strictly true only if the observation is made along the path of the protons, as pointed out by CHAMBERLAINin a discussion. The observations quoted were made at zenith engles of 45’ or less; the error introduced should be small.

147

D. M. HUNTEN and that, when the source of excitation disappeared, these molecules continued to radiate for some time. If this is so, the radiative mean life for the A3Z excited state which leads to the Vegard-Kaplan bands must be at least twenty or thirty seconds. Indirect evidence has been found that the forbidden line [NI] at 5199 ip On photographic spectra this line is nearly as strong as the behaves similarly. O-4 band of the N,+ negative system at 5228 A (PETRIE and SMALL, 1952). The photoelectric spectra, on the other hand, have never shown any sign of it; it would probably be visible if it were one-tenth as strong as the band. If the intensity of the [N I] line is smaller, it must be present for a much larger fraction of the time than the other radiations. 5. VIBRATIONAL TEMPERATURE FROM N,+ BANDS The relative intensities in several band systems were discussed some years ago in a well-known paper by BATES (1949). He showed for the N,+ negative system how observations could give information about the method of excitation and the vibrational temperature existing before the excitation. The mechanisms considered were: electron excitation from (1) the ground state of N,; (2) the ground state of Nzf; and (3) electron and photon excitation as in (2) but with the vibrational distribution determined, not by thermal equilibrium, but by Table 5. Relative intetity of the 1-2 Nz+ band expressed a.a a percentage of the intensity of the O-l band, and relative population rata for the v’ = 0 and 1 levels. Set No.

Relutive

1 2 3 4 5 6

Average

int.

Population

15.5 13.7 10.3 11.3 13.1 12-o

rates

100 : 13.3 100 : 11.8 100 : 8.9 100 : 9.7 100 : 11.3 100 : 10.3

I

I

100 : 10.9

I equilibrium between excitation and emission, For high-latitude aurora he concluded that the measurements available favoured mechanism (1) but required that this state have a vibrational temperature around 2000°K. It was suggested that excitation by heavy particles might be important. There were, however, serious uncertainties in the measurements. More recently, PETRIE and SMALL (1953) made some further observations at Saskatoon, and found a vibrational temperature near 1000°K; the same excitation mechanism was indicated. (Comparison of their figures for relative population rates with Table 5 suggests a temperature a little higher than 1000’K.) 148

Some photometric

observations

of aurora1 spectra

Several of the negative group bands showed up well on the spectrometer tracings. Relative intensity measurements were made only on one sequence at a time in order to eliminate the need for extinction corrections, The Au = -1 sequence was not resolved from strong second positive bands. The intensit’ies in the Au = 0 sequence fall off much too rapidly for it to be useful. Measurements were therefore confined to the Au = 1 and 2 sequences. It was found that the l-3 band (4652 A) always gave high results; this was attributed to the presence of a strong 0 II line at 4639 A (PETRIE and SMALL, 1953). Finally, the 2-3 band (4199 A) could not be measured because of the 2-6 band (4200 A) of the second positive system. This left only the O-l (4278 A) and l-2 (4236 A); however, a large number of independent measurements were possible. These were averaged the results are given in Table 4. To compare them with in suitable groups; theory, it is convenient to find the relative population rates for the levels with v’ = 0 and 1. This is done by means of BATES’S equation (10) : g(v’)

p(vI,

Q(v’, v”) vzjqq~

; P(V’,v11)v3(v’, 0.

Here g(v’) is the population rate for the level v’, v is the frequency of the radiation, and p is the relative transition probability for the band. The calculated values of the p’s by JARMAIN, FRASER, and NICHOLLS (1953) were used, giving

The relative population rates resulting are given in the last column of Table 4. The corresponding vibrational temperature may be found by comparison with Table 5, adapted from BATES’S paper with an added entry for 0°K. The average Table 0. Relative population rates for the vibrational levele of the Nz+ ion resultingfrom electron impact with the N, molecule in the ground state. Calculations

Vibrational temperature (“K)

v’ = 0 1 2

by

BATES(1949). 0

500

100 11 0

100 11 0

1000

100 13 1

I-

2000

100 26 7

result g(1) = 10.9 is seen to indicate a temperature in the range 0 to perhaps 700°K. This is consistent with the expected temperature of about 300°K. The only excitation mechanism giving any agreement with observation is electron impact with the N, molecule in the ground state, as was found by other workers already mentioned. 6.

CONCLUSIONS

The variety of results obtained in this paper shows that the photoelect’ric spectrometer is useful for certain types of aurora1 studies. These are the quick, 149

D. M. HUNTEN

easy, and fairly accurate measurement of absolute and relative intensities. and the Measurements are usually limited to the observation of short-lived effects. brighter aurora1 forms, and seldom extend much to the red of 6200 A. Results from aurora whose intensity is changing rapidly must be interpreted with caution, but can still be useful. The main conclusions of this paper are the following: (1) A few new bands of well-known nitrogen systems have been observed. (2) The identification of the atomic feature near 5000 A has been discussed. There seems little doubt that it is the three strongest lines of t,he multiplet 3~30 - 3d3F0 of N II, with wavelengths 5001-5 A. (3) The red colour of Type B aurora has been found due to O,+ first negat’ive and N, first positive bands in about equal proportions. (4) A strong feat’ure observed in Type B aurora seems to be the sodium D lines. An intensity has been observed three times as great as that found in the twilight. (5) Absolute intensities have been estimated for the strongest features in a bright spectrum of Type B aurora. (6) The absolute intensity of the green line has been measured for aurorae of international brightness coefficient II, III, and IV, and found to agree well with the estimates of SEATON. A photometric scale has been suggested in which

each

unit increase

in the brightness

coefficient

corresponds

to a factor

of 10 in intensity. (7) Relative

emission

as would agrees

with

indicates (8) The

that

little

relative

emission

(10)

Measurements show

that

state

at

Many

measured

FAN

and

for several

MEINEL

from

for

helium

rat’e leads

of radiations;

One

proton

of the

excitation.

ratios and

ions.

H#l has been found

of

emission

pairs

of variations.

to show

to proton

large fluxes

and sudden up to about

sec. found

for a very

slow

decay

in int,ensity

of t’he Vegard-

and the [N I] line at 5199 A. of the vibrational

a vibrational

excitation

by electron temperature

of the temperature

of the results

be repeated

by

rate

it’ is produced

specification should

is evidence

absolute

has been bands

been

or no contribution

lo8 protons/cm2 (9) Evidence

have t’here

found

The

variations.

Kaplan

rates

be expected,

should

when

Acknowledgements-The discussions with Dr.

aurora

writer would A.

VALLANCE

between

appears

be regarded

bright

of the N,+

impact

on N, zero

and

experimentally

as preliminary becomes

more

first negat,ive

molecules

system

in the ground

700°K. almost

A

closer

impossible.

and the measurements plentiful.

like to acknowledge

the value

of

many

JONES.

REFERENCES BATES, D. R. CHAMBERLAIN,J. W. CHAMBERLAIN, J. W., and MEINEL,A. B.

1949 1954 1954

CHAMBERLAIN, J. W., and OLIVER,N. J.

1953 150

Proc. Roy. Sot. A196, 217 Astrophys. J. 120, 360 The earth as a planet (Ed. C. I’. Kuiper) University of Chicago Press J. geophys. Res. 58, 457

Some photometric observations of aurora1spectra

DAHLSTROM, C. E., and HUNTEN, D. M. FAN, C. Y., and MEINEL, A. B. HERZBERG,G. HUNTEN, D. M. HTJNTEN,D. M., and SHEPHERD,G. G. JARMAIN,W. R., and NICHOLLS,R. W. JARMAIN,W. R., FRASER,P. A., and NICHOLLS,R. W. MEINEL, A. B. MOORE,C. E.

1951 1953 1928 1953 1954 1954

Phys. Rev. 84, 378 Astrophys. J. 118,205 Ann. Phys. 86, 189 Car&. J. l’hys. 31, 681 J. Atnwsph. Terr. Phys. 5, 57 Cnnad. J. l’hys. 32, 201

1953 1952 1945

Astrophys.

PEARSI, R. W. B., and GAYDON,A.G.

1950

PETRIE,W., and SMALL,R. G.

1952 1953 1936 1954 1954

RUSSELL,H. N. SEATON,M. J. SHEPHERD,G. G.

TURNER,R. G., and NICHOLLS,R. VAN DE HULST, H. C.

VEOARD,L., and KVIFTE, G.

W.

1954 1952

1945

151

J. 118,1228 .X&t. Sot. Roy. ,!!cici.Liege 12, 203

A multiplet table of astrophysical interest, Princeton University Observatory The identification of molecular spectra, 2nd ed., Chapman and Hall Astrophys. J. 116, 433 Canad. J. Phys. 31, 911 Astrophys. J. 83, 129 J. Atmosph. Terr. Phys. 4, 285 Scientific Report No. AR-l% Contract AF19(122)-152, University of Saskatchewan Can&. J. Whys. 32,468 The atmospheres of the earth and planets (Ed. G. P. Kuiper), 2nd ed., University of Chicago Press Beofys. Publ. 16, No. 7