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Observations of the NI 5200 Å auroral doublet at Byrd Station, Antarctica
p&mu. m
86.. 1963,Vol. 11.pp. 1375to 1376 --Ltd.
PdllldinN-hdUld
RESEARCH NOTE
OBSERVATIONS OF THE NI 5200 A AURORAL DOUBLET AT BYRD STATION, ANTARCTICA (Rceckrcd20 Aqput 1963) During the past three years, LarserP and MulyamhW have published their interferometric work on the auroral nitrogen doublet at 5200 A in whichtheygivesomeestimates of the waveleng& of the two lines. Recently, Larsen(*) has revised his 6gums and now gives 5199-85 f O-1A and 520229 f O-1A asnewwave+ lengths for the lines. The large estimated error is, as Larsen states, due mostly to the fact that the fringe pictums were not sut8ciently sharp. According to Lafaen, the @omucal vahre for the ratio Is/Z1 of the intensities of the two lines is 144 where Z, mpresents the intensity of the shorter wavelengtb and Zl is that of the longer. Larsen’s observed vahre for the ratio is Is/Z1 = l-27 f 0.08. Mulyarchik does not mention any accurate values for the wavele@s; however, he does give an observed value of II/Z, = l-7 f O-1for the intensity ratio, both Zl and Z, repmsenting the same quantities as before. Thus according to Mulyarchik, the longer wav&ngth line of the doublet is the stronger whereas Larsen reports the shorterwavele@ tobethestronger. SomeintelferometJicmeas urements of the nitrogen doublet were made by the author at Byrd Station, Antarctica during the 1962 austral winter. The instrument used was a low order photographic Fabry-Perot interferometer designed by Dr. R. V. KammWar and constructed at Air Force Cambridge Reseamh Laboratories. The two 4 in. dia. fused quartz etalon plates used in the instrument wem Sat to about n/l5 and they were coated with a five layer dielectric coating. Four sets of invar spacers were available, the lengths of which had been cakxdated using the wavelengths rZ, = 519994 and ill = 5202-10 given by Larsen”’ in 1960. The resulting central orders and the central order di&ences for each of the four sets of spacers are as follows:
229 344 4.58 s-21
Central order 1, 11 8807.793 8804.137 13230.921 13225.428 17615587 17608.274 20038692 20030.372
central order dilTemllce 3-656 s-493 7.313 8.320
The rest of the optical system consisted of an f 0.7 70 mm Simlarlenssndaninterferentx A. Kodak 103a-J plates were filter having a passband with a half-width of three angstroms 54.00A. The whole system usedbecauseoftheirpeaksensitivitynears2~Aand was housed in an insulated box in which the temperature was thermostatically controlIed. The instrument, mounted vertically under a plexiglass dome, had a field of about 12“ in diameter centered on the zenith. Before each auroral exposure was made, calibration exposures were made using di!Temnt spectral souses with interference filters to isolate certain accurately known wavelengths. These fring systems were sllbsequently used in calculating the unknown wavek@hs. During 1962, am-oral displays were visible at Byrd Station on almost every clear night. For the most part, they were of the greenkh white type, but on particularly disturbed nights there would often be some red type B displays. There were, however, no red type A aurorae in which the forbidden lines are usually enhanced. Because of this, the 5200/02 lines were quite weak and very long exposures wete v. The longest exposures lasted 40-50 hr and had to be accumulated over 4 or 5 nights. During these lcng exposures, accurate temperature control was very difficult to maintain and some change in the spacer lengths ma have occuned. On a few plates, however, a comparison of interference fringes of the same soul-W maJ e before and after the aurora1 exposure indicated that no signiScant change in the spacer length had occuned, and from these plates accurate measurements were possible. A careful study of all the interferograms was made, but two separate frmge systems corresponding to the two wavelengths could not be detected on any of the plates. The fringes were sut8ciently sharp, and the resolution was such that, had the lines been separated, they would certainly have been vrsible. From 0
1375
1376
&search note
this it can be conch&d that, for the spacers used, the fringe systems due to the two lines must either have completaly overlapped or else have very nearly done so. Two of the beat latas, each taken with an etalon separation of 229 mm, have been mcasumi. Using then&hodofexact i!kction@, the wavekngth for the only visible line was calculated to be 519992 f O-01k the wavekngth of the line, it is possible to set an approximate value for the other values by LarserP are masonably correct. If the two fringe systems were completely di&ence in the observed central ~rdem would have bean sn intagur. The observed central 5199.92 line is 8804.68. This 5gure was then changad by integral steps until the calculated wavekngth was closest to Larsen’svalue. The integral change was minus 4 orders. Therefore, for a central order of 8800.68, the resultingwavelength was 520229 A. From an examination of the plates and an e&mate oftheaccumcyofthemaas urements, it was concluded that the resulting wavekngth may be given as 5202.29 f 0.06 A. Thusthevaluefor the wavekngths of the nitrogen doublet obtained ip this study am: rzI= 5199.92 zt o-01 A il. - 5202.29 & O-06A Atthepreaenttimanewinstruma3ltandanotheraetofdifferents~arebejngpreparedanditis hopedthatsomemoreconclusivadatacanbeobtained. The author wishes to thank Dr. R. V. Karandiksr and Mr. Norman J. Oliver of AF ACk?lOWltSt&~ CambridaeRaaaamhLaboratoriesfor their advice and assistance in makine this stndv uossible. The author is also h&b&d to Mr. R. Erikson of AFCRL. who built the instrument t&d in the*piqmm. Tbe~repartedinthisnotswassupportedbyaNati~ScisDceFoundationgranttotheArctic Institute of North America. Arctic Znstituteof North America W-ton, 0.6.
JOHNP. TURTLE
IuzmRENw 1. S. H. H. LAR88N et al., Studies of AuroraISpcctmscopy, and of the Rapid Pluctuatiotuin the Geomqnetic &Id d&g Distrabanccs. Technical report under Contract No. AF 61(514)-1123 Oslo, January 15 (1960). 2. T. M. M~L.YAWHIK, Bull. (Zzv.) Geophys. Ser. Akud. Sci. USSR No. 3,297 (1960). 3. S. H. H. LARW, Planet. Space Sci. 9,811 (1962). 4. F. H. HOLTand H. BARREL& Pm. Roy. Sot. A122,122 (1928).
Cd 5085.822
52
Cd
hr
A
auroral
5085.822
A
calibration
5200A
calibration
exposure
exposure
exposure
THE FK. I. A SERIES OF TYPICAL INTERFERENCE FRINGES ~ROMONEOFTHEMEASUR~DPLAIES. CEN'I ‘RAL 52 hr AURORAL EXPOSURE WAS ACCUMULATED OVER THE NIGHTS OF AUGUST 1,2,3, 4, 5, 1962. THE CD CALIBRATION EXPOSURES WERE TAKEN ONE BEFORE AND ONE AFTER THE AuR( >RAL EXPOSURE AND SHOW THAT NO CHANGE IN THE SPACERS'LENGTHOCCURREDI,URIN(i THE 52 hr.
86.. 1963,Vol. 11.pp. 1375to 1376 --Ltd.
PdllldinN-hdUld
RESEARCH NOTE
OBSERVATIONS OF THE NI 5200 A AURORAL DOUBLET AT BYRD STATION, ANTARCTICA (Rceckrcd20 Aqput 1963) During the past three years, LarserP and MulyamhW have published their interferometric work on the auroral nitrogen doublet at 5200 A in whichtheygivesomeestimates of the waveleng& of the two lines. Recently, Larsen(*) has revised his 6gums and now gives 5199-85 f O-1A and 520229 f O-1A asnewwave+ lengths for the lines. The large estimated error is, as Larsen states, due mostly to the fact that the fringe pictums were not sut8ciently sharp. According to Lafaen, the @omucal vahre for the ratio Is/Z1 of the intensities of the two lines is 144 where Z, mpresents the intensity of the shorter wavelengtb and Zl is that of the longer. Larsen’s observed vahre for the ratio is Is/Z1 = l-27 f 0.08. Mulyarchik does not mention any accurate values for the wavele@s; however, he does give an observed value of II/Z, = l-7 f O-1for the intensity ratio, both Zl and Z, repmsenting the same quantities as before. Thus according to Mulyarchik, the longer wav&ngth line of the doublet is the stronger whereas Larsen reports the shorterwavele@ tobethestronger. SomeintelferometJicmeas urements of the nitrogen doublet were made by the author at Byrd Station, Antarctica during the 1962 austral winter. The instrument used was a low order photographic Fabry-Perot interferometer designed by Dr. R. V. KammWar and constructed at Air Force Cambridge Reseamh Laboratories. The two 4 in. dia. fused quartz etalon plates used in the instrument wem Sat to about n/l5 and they were coated with a five layer dielectric coating. Four sets of invar spacers were available, the lengths of which had been cakxdated using the wavelengths rZ, = 519994 and ill = 5202-10 given by Larsen”’ in 1960. The resulting central orders and the central order di&ences for each of the four sets of spacers are as follows:
229 344 4.58 s-21
Central order 1, 11 8807.793 8804.137 13230.921 13225.428 17615587 17608.274 20038692 20030.372
central order dilTemllce 3-656 s-493 7.313 8.320
The rest of the optical system consisted of an f 0.7 70 mm Simlarlenssndaninterferentx A. Kodak 103a-J plates were filter having a passband with a half-width of three angstroms 54.00A. The whole system usedbecauseoftheirpeaksensitivitynears2~Aand was housed in an insulated box in which the temperature was thermostatically controlIed. The instrument, mounted vertically under a plexiglass dome, had a field of about 12“ in diameter centered on the zenith. Before each auroral exposure was made, calibration exposures were made using di!Temnt spectral souses with interference filters to isolate certain accurately known wavelengths. These fring systems were sllbsequently used in calculating the unknown wavek@hs. During 1962, am-oral displays were visible at Byrd Station on almost every clear night. For the most part, they were of the greenkh white type, but on particularly disturbed nights there would often be some red type B displays. There were, however, no red type A aurorae in which the forbidden lines are usually enhanced. Because of this, the 5200/02 lines were quite weak and very long exposures wete v. The longest exposures lasted 40-50 hr and had to be accumulated over 4 or 5 nights. During these lcng exposures, accurate temperature control was very difficult to maintain and some change in the spacer lengths ma have occuned. On a few plates, however, a comparison of interference fringes of the same soul-W maJ e before and after the aurora1 exposure indicated that no signiScant change in the spacer length had occuned, and from these plates accurate measurements were possible. A careful study of all the interferograms was made, but two separate frmge systems corresponding to the two wavelengths could not be detected on any of the plates. The fringes were sut8ciently sharp, and the resolution was such that, had the lines been separated, they would certainly have been vrsible. From 0
1375
1376
&search note
this it can be conch&d that, for the spacers used, the fringe systems due to the two lines must either have completaly overlapped or else have very nearly done so. Two of the beat latas, each taken with an etalon separation of 229 mm, have been mcasumi. Using then&hodofexact i!kction@, the wavekngth for the only visible line was calculated to be 519992 f O-01k the wavekngth of the line, it is possible to set an approximate value for the other values by LarserP are masonably correct. If the two fringe systems were completely di&ence in the observed central ~rdem would have bean sn intagur. The observed central 5199.92 line is 8804.68. This 5gure was then changad by integral steps until the calculated wavekngth was closest to Larsen’svalue. The integral change was minus 4 orders. Therefore, for a central order of 8800.68, the resultingwavelength was 520229 A. From an examination of the plates and an e&mate oftheaccumcyofthemaas urements, it was concluded that the resulting wavekngth may be given as 5202.29 f 0.06 A. Thusthevaluefor the wavekngths of the nitrogen doublet obtained ip this study am: rzI= 5199.92 zt o-01 A il. - 5202.29 & O-06A Atthepreaenttimanewinstruma3ltandanotheraetofdifferents~arebejngpreparedanditis hopedthatsomemoreconclusivadatacanbeobtained. The author wishes to thank Dr. R. V. Karandiksr and Mr. Norman J. Oliver of AF ACk?lOWltSt&~ CambridaeRaaaamhLaboratoriesfor their advice and assistance in makine this stndv uossible. The author is also h&b&d to Mr. R. Erikson of AFCRL. who built the instrument t&d in the*piqmm. Tbe~repartedinthisnotswassupportedbyaNati~ScisDceFoundationgranttotheArctic Institute of North America. Arctic Znstituteof North America W-ton, 0.6.
JOHNP. TURTLE
IuzmRENw 1. S. H. H. LAR88N et al., Studies of AuroraISpcctmscopy, and of the Rapid Pluctuatiotuin the Geomqnetic &Id d&g Distrabanccs. Technical report under Contract No. AF 61(514)-1123 Oslo, January 15 (1960). 2. T. M. M~L.YAWHIK, Bull. (Zzv.) Geophys. Ser. Akud. Sci. USSR No. 3,297 (1960). 3. S. H. H. LARW, Planet. Space Sci. 9,811 (1962). 4. F. H. HOLTand H. BARREL& Pm. Roy. Sot. A122,122 (1928).
Cd 5085.822
52
Cd
hr
A
auroral
5085.822
A
calibration
5200A
calibration
exposure
exposure
exposure
THE FK. I. A SERIES OF TYPICAL INTERFERENCE FRINGES ~ROMONEOFTHEMEASUR~DPLAIES. CEN'I ‘RAL 52 hr AURORAL EXPOSURE WAS ACCUMULATED OVER THE NIGHTS OF AUGUST 1,2,3, 4, 5, 1962. THE CD CALIBRATION EXPOSURES WERE TAKEN ONE BEFORE AND ONE AFTER THE AuR( >RAL EXPOSURE AND SHOW THAT NO CHANGE IN THE SPACERS'LENGTHOCCURREDI,URIN(i THE 52 hr.