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Narrow band filter photometry of Comet Kohoutek
ICARUS 24,
116--119 (1975)
Narrow Band Filter Photometry of Comet Kohoutek R O N A L D J. A N G I O N E A~trono~ny Department, San Diego State University, San Diego, California 92115
R O B E R T G. R O O S E N N A S A , Goddard Space Flight Center, New Mexico Station, Albuquerque, New Mexico 87104 AND
H O W A R D LA_NNING Astronomy Department, San Diego State University, San Diego, California 92115
Received June 4, 1974; revised August 7, 1974 Narrow band photoelectric measurements of CN(3870), CO+(4250), C2(4700), and C2(5120) were made on twelve nights in December and January of comet Kohoutek. CN and C2 appear to be stronger after perihelion, and CO+ showed a strong post perihelion increase coincident with the first appearance of a s~rong gas tail and then decreased to a fairly constant level. INTRODUCTION
This p a p e r reports t h e observational results o f photoelectric n a r r o w b a n d measu r e m e n t s of emission line features of comet K o h o u t e k (1973f). B r o a d b a n d measurem e n t s were also m a d e and are contained in the p a p e r b y Angione et al. (1975). T h e photoelectric observations were m a d e at b o t h Mr. L a g u n a O b s e r v a t o r y and t h e J o i n t O b s e r v a t o r y for Comet Research (hereafter called JOCR). Mr. L a g u n a O b s e r v a t o r y is located 40 miles east of San Diego, California (latitude = 32°50'24 ", longitude = 116°25'33 ", altitude = 6100ft) a n d is o p e r a t e d b y San Diego State University. J O C R is located on S o u t h B a l d y p e a k just west of Socorro, N e w Mexico (latitude = 33°59'05 ", longitude = 107°11' 19 ", altitude = 10 615ft) and is o p e r a t e d j o i n t l y b y N A S A / G o d d a r d Space Flight Center and New Mexico I n s t i t u t e o f Mining and Technology. EQUIPMENT AND OBSERVATIONS The photoelectric measurements were o b t a i n e d with Boller and Chivens 16-in. telescopes located a t b o t h J O C R and Mt. Copyright ~) 1975 by Academic Press, Inc. All rights of reproduction in any form reserved. Printed in Great Britain
Laguna. The L a g u n a p h o t o m e t e r consisted of a 1P21 d e t e c t o r and a digitized W e i t b r e c h t charge integrating system. T h e o u t p u t of the amplifier was fed to a digital v o l t m e t e r , and this, along with the digital clock, gain setting, filter position, integration time, etc., was r e a d b y a serializer and t h e n fed to a teletype. T y p i c a l l y two 30-sec integration intervals were used for each filter m e a s u r e m e n t . After a complete filter sequence on the comet, the sequence was r e p e a t e d on the sky, and the sky was s u b t r a c t e d from each corresponding comet m e a s u r e m e n t . E a c h r e p o r t e d m e a s u r e m e n t in Table I I is the average of two or more such individual measurements. The J O C R m e a s u r e m e n t s were m a d e with a digitized single channel pulse counter p r o v i d e d b y San Diego State University. This consisted o f an E M I 6256B photomultiplier f e e d i n g an SSR 1120 p r e a m p - d i s c r i m i n a t o r and a Monsanto 101C counter. The o u t p u t o f the counter and other r e l e v a n t i n f o r m a t i o n was recorded on p u n c h e d t a p e in a m a n n e r similar to the L a g u n a setup. The measurem e n t sequence was also similar, e x c e p t pairs of ten-second c o u n t intervals were 116
NARROW BAND PHOTOMETRY OF KOHOUTEK
maximum (FWHM), and the maximum transmission. These quantities were determined from transmission tracing curves of each filter. The parameters were found to be identical for the filter sets used at both observatories, which is to be expected since the filters were from the same batch. These narrow band filters and tracings were supplied by NASA/Goddard Space Flight Center.
TABLE I FILTER SPECIFICATIONS
Band C N wide CN narrow CO + Continuum C2 Continuum C2 Continuum
Effective wavelength FW~tM 3867A 3873 4251 4299 4713 4843 5125 5292
65A 34 56 48 73 64 82 71
117
Maximum trans mission 31% 31 39 43 49 39 49 50
RESULTS
The narrow band photometry is summarized in Table II, giving the Julian date, heliocentric distance of the comet (Yeomans, 1973), aperture in arc seconds, and the relative emission band strengths for CN(3870), C0+(4250), C2(4720), and C2(5120 ). Inspection of Table I shows t h a t for C0* and the two C2 features we have a filter on the adjacent continuum. Of course, this is not strictly true because what we are calling "continuum"does contain some lines, notably the 4843/~ filter, which includes H a . However, none of these lines are prominent in cometary or solar
found to be sufficient for each filter measurement. Due to the motion of the comet, the telescope had to be repositioned after each filter reading. The specifications of the narrow band filters (manufactured by Ditric Optics) are given in Table I. Reading from left to right the columns list the spectral feature, effective wavelength, full width at half TABLE
II
N A R R O W B A N D PHOTOMETRY Relative band strength
(UT)
J.D. 2,400,000
AAU
Location
Aperture
CN
CO +
C2(4720)
1973 Dec. 9 Dec. 12
42026.04 42039.05
0.667 0.586
Laguna Laguna
73.0" 37.8 73.0
--1.61 -0.82 -0.95
-0.27 -0.37 -0.24
--1.36 -1.10 --0.77
1974 Jan. 5 Jan. 9 J a n . 12
42052.57 42056.56 42059.58
0.340 0.464 0.551
JOCR JOCR JOCR
J a n . 13
42060.58
0.579
JOCR
J a n . 15 J a n . 16
42062.63 42063.61
0.635 0.661
Laguna Laguna
42070.61
0.838
Laguna
J a n . 25 J a n . 28 J a n . 31
42072.61 42075.62 42078.61
0.886 0.956 1.024
Laguna Laguna Laguna
--2.22 --1.88 --1.96 --2.18 --2.04 --2.19 --2.08 --2.15
--0.10 --0.49 --0.20 --0.49 --0.15 --0.30 --0.09 +0.06 --0.09 --0.25 --0.12 --0.12 --0.06 --0.13
--1.60 --2.12 --2.34 --2.41 --2.22 --2.37 --2.47 --2.40 --2.45
J a n . 23
92.4 32.4 32.4 92.4 32.4 92.4 73.0 37.8 73.0 37.8 73.0 73.0 73.0 73.0
Date
--2.30 --2.54 --2.42 --2.22
C2(5120)
--1.81 --2.40 --2.58 --2.71 --2.52 --2.64 --2.75 --2.84
118
~GIONE~ ROOSEI~ AND LAI~NIlqG
spectra, and it would be worse to place the reference c o n t i n u u m f a r t h e r away. We define t h e relative emission b a n d s t r e n g t h as - 2 . 5 log ( F J F c ) , where F~ a n d F¢ are the measured intensities t h r o u g h the emission-centered a n d continuum-centered filters, respectively. Thus the more negative the emission strength, t h e stronger the emission feature. I n the case of CN t h e r e is no suitable adjacent continuum, so we call F= the i n t e n s i t y measured t h r o u g h the n a r r o w filter and Fw t h a t t h r o u g h the wide filter. T h e relative b a n d s t r e n g t h for CN is t h e n defined as - 2 . 5 log [F=/(Fw -- F=)], which is convenient because the wide filter is n e a r l y twice the w i d t h of t h e n a r r o w filter. The observing procedure called for a m e a s u r e m e n t t h r o u g h the filter centered on the emission b a n d followed i m m e d i a t e l y b y a m e a s u r e m e n t on the corresponding continuum. Thus the differential n a r r o w b a n d m e a s u r e m e n t s F~ and F~ are separa t e d b y only seconds in time. Inspection o f the internal scatter shows it to be always less t h a n 0.02 magnitudes, so we will assign an e s t i m a t e d error of 0.05 magnit u d e s t o the relative b a n d strengths in Table II, making allowance for other possible sources of error. The filter selection a n d reduction proeedure follows t h a t contained in the r e p o r t edited b y Rahe, Vanysek, and B r a n d t (1973). W e h a v e chosen to present our n a r r o w b a n d d a t a in a fairly raw form. The purpose is to allow users o f this d a t a to a p p l y corrections (based on the filter transmissions, t u b e sensitivities, etc.) in t h e m a n n e r each reader determines to be most suitable for his purpose. I n principle if one observes a source of the same spectral i n t e n s i t y distribution as the comet, one can s u b t r a c t out t h e effects of spectral gradient and t u b e a n d filter sensitivities from the comet measurements. W e did take n a r r o w b a n d observations of close b y comparison stars. H o w e v e r , none o f these stars m a t c h e d t h e i n t e n s i t y distribution of the c o m e t v e r y well. F u r t h e r m o r e , even t h o u g h the comet a n d comparison star were usually separated b y only a b o u t one degree, for the large airmass a t which we were forced to work
|
4
CN ( 3 8 7 0 }
+ 5 8 Arcsec • 73
0
2 e
O
'
~,5 -, +
,I D. 2 4 4 2 0 0 0 +
FIG. 1. The time variation of the relative strength of the CN(3870) band as measured at ~¢[$. Laguna Observatory. The arrow a~ J. I). 2442045 indicates time of Perihelion passage. the airmasses of the objects differed substantially requiring r a t h e r large extinction corrections (from 0.1 to 0.2 magnitudes). All things considered, in our j u d g e m e n t the circumstances and q u a l i t y of t h e observations do n o t justify att e m p t i n g such corrections. Inspection of Table I I shows t h a t t h e CN B a n d remained fairly c o n s t a n t b u t stronger after perihelion passage. B o t h C 2 Swan bands a p p e a r to b e h a v e similarly as e x p e c t e d (e.g. M a y e r and O'Dell, 1968). Figures 1, 2, and 3 present t h e relative b a n d strengths o f selected apertures o f CN, CO +, a n d C2(4720 ) during D e c e m b e r '
•
CO ÷
• 32 Arcsec • 73 • 92
A
O $
= i "1
OO A
J 0. 2 4 4 2 0 0 0 +
FIG. 2. The time variation of the relative band strength of the CO+ emission. Measurements with the 32 and 92arc second aperbures are from the JOCR, and the 73are second measurements are from Mr. Laguna. The arrow at J. D. 2442045 indicates the time of perihelion passage.
NARROW BAND PHOTOMETRY OF KOHOUTEK
119
• 32 Arcse¢ • 73 •92
C4 (4720)
=
==-I @
~o ~
~ J.D 2 4 4 2 0 0 0
+
FIG. 3. The time variation of the relative band strength of the 02(4720) emission feature• The 32 and 92arc second measurements are from the JOCR, and the 73arc second measurements are from Mr. Laguna. The arrow at J. D. 2442045 indicates the time of perihelion passage.
and January. The CO + band showed more activity, including a sharp rise in strength from J a n u a r y 5 to 9, and then a drop to a fairly constant level from J a n u a r y 15 to 31. The C2(4720) band shows a strong rise in strength during approximately the same time period as the CO + band. These increases in emission band strengths coincide with the post perihelion appearance of pronounced gas tail. ACKNOWLEDGMENTS R. J. A. acknowledges supporb from NASA contract NAS5-23249.
REFERENCES A~GIO~E, R., GATES, B., ItEmiZE, K., AND ROOSEN, R. (1975). The light curve of comet Kohoutek (1973f). Icarus 24, 111-115. MAYER, I)., ~ O'DELL, C. R. (1968). Emissionband ratios in comet Rudnicki (1966e). Astrophys. J . 153, 951-962. RAHE, J. VANYSEK, V., AND BRANDT, J., Eds. (1973)• Report on planned observing programs for comet Kohoutek (1973f). NASA]Goddard
Space Flight Center. ¥EO~ANS, D. K. (1973). Velocity ephemeris for comet Kohoutek (1973f). Operation Kohoutek Special Office, Code 683, NASA/Goddard Space Flight Center.
116--119 (1975)
Narrow Band Filter Photometry of Comet Kohoutek R O N A L D J. A N G I O N E A~trono~ny Department, San Diego State University, San Diego, California 92115
R O B E R T G. R O O S E N N A S A , Goddard Space Flight Center, New Mexico Station, Albuquerque, New Mexico 87104 AND
H O W A R D LA_NNING Astronomy Department, San Diego State University, San Diego, California 92115
Received June 4, 1974; revised August 7, 1974 Narrow band photoelectric measurements of CN(3870), CO+(4250), C2(4700), and C2(5120) were made on twelve nights in December and January of comet Kohoutek. CN and C2 appear to be stronger after perihelion, and CO+ showed a strong post perihelion increase coincident with the first appearance of a s~rong gas tail and then decreased to a fairly constant level. INTRODUCTION
This p a p e r reports t h e observational results o f photoelectric n a r r o w b a n d measu r e m e n t s of emission line features of comet K o h o u t e k (1973f). B r o a d b a n d measurem e n t s were also m a d e and are contained in the p a p e r b y Angione et al. (1975). T h e photoelectric observations were m a d e at b o t h Mr. L a g u n a O b s e r v a t o r y and t h e J o i n t O b s e r v a t o r y for Comet Research (hereafter called JOCR). Mr. L a g u n a O b s e r v a t o r y is located 40 miles east of San Diego, California (latitude = 32°50'24 ", longitude = 116°25'33 ", altitude = 6100ft) a n d is o p e r a t e d b y San Diego State University. J O C R is located on S o u t h B a l d y p e a k just west of Socorro, N e w Mexico (latitude = 33°59'05 ", longitude = 107°11' 19 ", altitude = 10 615ft) and is o p e r a t e d j o i n t l y b y N A S A / G o d d a r d Space Flight Center and New Mexico I n s t i t u t e o f Mining and Technology. EQUIPMENT AND OBSERVATIONS The photoelectric measurements were o b t a i n e d with Boller and Chivens 16-in. telescopes located a t b o t h J O C R and Mt. Copyright ~) 1975 by Academic Press, Inc. All rights of reproduction in any form reserved. Printed in Great Britain
Laguna. The L a g u n a p h o t o m e t e r consisted of a 1P21 d e t e c t o r and a digitized W e i t b r e c h t charge integrating system. T h e o u t p u t of the amplifier was fed to a digital v o l t m e t e r , and this, along with the digital clock, gain setting, filter position, integration time, etc., was r e a d b y a serializer and t h e n fed to a teletype. T y p i c a l l y two 30-sec integration intervals were used for each filter m e a s u r e m e n t . After a complete filter sequence on the comet, the sequence was r e p e a t e d on the sky, and the sky was s u b t r a c t e d from each corresponding comet m e a s u r e m e n t . E a c h r e p o r t e d m e a s u r e m e n t in Table I I is the average of two or more such individual measurements. The J O C R m e a s u r e m e n t s were m a d e with a digitized single channel pulse counter p r o v i d e d b y San Diego State University. This consisted o f an E M I 6256B photomultiplier f e e d i n g an SSR 1120 p r e a m p - d i s c r i m i n a t o r and a Monsanto 101C counter. The o u t p u t o f the counter and other r e l e v a n t i n f o r m a t i o n was recorded on p u n c h e d t a p e in a m a n n e r similar to the L a g u n a setup. The measurem e n t sequence was also similar, e x c e p t pairs of ten-second c o u n t intervals were 116
NARROW BAND PHOTOMETRY OF KOHOUTEK
maximum (FWHM), and the maximum transmission. These quantities were determined from transmission tracing curves of each filter. The parameters were found to be identical for the filter sets used at both observatories, which is to be expected since the filters were from the same batch. These narrow band filters and tracings were supplied by NASA/Goddard Space Flight Center.
TABLE I FILTER SPECIFICATIONS
Band C N wide CN narrow CO + Continuum C2 Continuum C2 Continuum
Effective wavelength FW~tM 3867A 3873 4251 4299 4713 4843 5125 5292
65A 34 56 48 73 64 82 71
117
Maximum trans mission 31% 31 39 43 49 39 49 50
RESULTS
The narrow band photometry is summarized in Table II, giving the Julian date, heliocentric distance of the comet (Yeomans, 1973), aperture in arc seconds, and the relative emission band strengths for CN(3870), C0+(4250), C2(4720), and C2(5120 ). Inspection of Table I shows t h a t for C0* and the two C2 features we have a filter on the adjacent continuum. Of course, this is not strictly true because what we are calling "continuum"does contain some lines, notably the 4843/~ filter, which includes H a . However, none of these lines are prominent in cometary or solar
found to be sufficient for each filter measurement. Due to the motion of the comet, the telescope had to be repositioned after each filter reading. The specifications of the narrow band filters (manufactured by Ditric Optics) are given in Table I. Reading from left to right the columns list the spectral feature, effective wavelength, full width at half TABLE
II
N A R R O W B A N D PHOTOMETRY Relative band strength
(UT)
J.D. 2,400,000
AAU
Location
Aperture
CN
CO +
C2(4720)
1973 Dec. 9 Dec. 12
42026.04 42039.05
0.667 0.586
Laguna Laguna
73.0" 37.8 73.0
--1.61 -0.82 -0.95
-0.27 -0.37 -0.24
--1.36 -1.10 --0.77
1974 Jan. 5 Jan. 9 J a n . 12
42052.57 42056.56 42059.58
0.340 0.464 0.551
JOCR JOCR JOCR
J a n . 13
42060.58
0.579
JOCR
J a n . 15 J a n . 16
42062.63 42063.61
0.635 0.661
Laguna Laguna
42070.61
0.838
Laguna
J a n . 25 J a n . 28 J a n . 31
42072.61 42075.62 42078.61
0.886 0.956 1.024
Laguna Laguna Laguna
--2.22 --1.88 --1.96 --2.18 --2.04 --2.19 --2.08 --2.15
--0.10 --0.49 --0.20 --0.49 --0.15 --0.30 --0.09 +0.06 --0.09 --0.25 --0.12 --0.12 --0.06 --0.13
--1.60 --2.12 --2.34 --2.41 --2.22 --2.37 --2.47 --2.40 --2.45
J a n . 23
92.4 32.4 32.4 92.4 32.4 92.4 73.0 37.8 73.0 37.8 73.0 73.0 73.0 73.0
Date
--2.30 --2.54 --2.42 --2.22
C2(5120)
--1.81 --2.40 --2.58 --2.71 --2.52 --2.64 --2.75 --2.84
118
~GIONE~ ROOSEI~ AND LAI~NIlqG
spectra, and it would be worse to place the reference c o n t i n u u m f a r t h e r away. We define t h e relative emission b a n d s t r e n g t h as - 2 . 5 log ( F J F c ) , where F~ a n d F¢ are the measured intensities t h r o u g h the emission-centered a n d continuum-centered filters, respectively. Thus the more negative the emission strength, t h e stronger the emission feature. I n the case of CN t h e r e is no suitable adjacent continuum, so we call F= the i n t e n s i t y measured t h r o u g h the n a r r o w filter and Fw t h a t t h r o u g h the wide filter. T h e relative b a n d s t r e n g t h for CN is t h e n defined as - 2 . 5 log [F=/(Fw -- F=)], which is convenient because the wide filter is n e a r l y twice the w i d t h of t h e n a r r o w filter. The observing procedure called for a m e a s u r e m e n t t h r o u g h the filter centered on the emission b a n d followed i m m e d i a t e l y b y a m e a s u r e m e n t on the corresponding continuum. Thus the differential n a r r o w b a n d m e a s u r e m e n t s F~ and F~ are separa t e d b y only seconds in time. Inspection o f the internal scatter shows it to be always less t h a n 0.02 magnitudes, so we will assign an e s t i m a t e d error of 0.05 magnit u d e s t o the relative b a n d strengths in Table II, making allowance for other possible sources of error. The filter selection a n d reduction proeedure follows t h a t contained in the r e p o r t edited b y Rahe, Vanysek, and B r a n d t (1973). W e h a v e chosen to present our n a r r o w b a n d d a t a in a fairly raw form. The purpose is to allow users o f this d a t a to a p p l y corrections (based on the filter transmissions, t u b e sensitivities, etc.) in t h e m a n n e r each reader determines to be most suitable for his purpose. I n principle if one observes a source of the same spectral i n t e n s i t y distribution as the comet, one can s u b t r a c t out t h e effects of spectral gradient and t u b e a n d filter sensitivities from the comet measurements. W e did take n a r r o w b a n d observations of close b y comparison stars. H o w e v e r , none o f these stars m a t c h e d t h e i n t e n s i t y distribution of the c o m e t v e r y well. F u r t h e r m o r e , even t h o u g h the comet a n d comparison star were usually separated b y only a b o u t one degree, for the large airmass a t which we were forced to work
|
4
CN ( 3 8 7 0 }
+ 5 8 Arcsec • 73
0
2 e
O
'
~,5 -, +
,I D. 2 4 4 2 0 0 0 +
FIG. 1. The time variation of the relative strength of the CN(3870) band as measured at ~¢[$. Laguna Observatory. The arrow a~ J. I). 2442045 indicates time of Perihelion passage. the airmasses of the objects differed substantially requiring r a t h e r large extinction corrections (from 0.1 to 0.2 magnitudes). All things considered, in our j u d g e m e n t the circumstances and q u a l i t y of t h e observations do n o t justify att e m p t i n g such corrections. Inspection of Table I I shows t h a t t h e CN B a n d remained fairly c o n s t a n t b u t stronger after perihelion passage. B o t h C 2 Swan bands a p p e a r to b e h a v e similarly as e x p e c t e d (e.g. M a y e r and O'Dell, 1968). Figures 1, 2, and 3 present t h e relative b a n d strengths o f selected apertures o f CN, CO +, a n d C2(4720 ) during D e c e m b e r '
•
CO ÷
• 32 Arcsec • 73 • 92
A
O $
= i "1
OO A
J 0. 2 4 4 2 0 0 0 +
FIG. 2. The time variation of the relative band strength of the CO+ emission. Measurements with the 32 and 92arc second aperbures are from the JOCR, and the 73are second measurements are from Mr. Laguna. The arrow at J. D. 2442045 indicates the time of perihelion passage.
NARROW BAND PHOTOMETRY OF KOHOUTEK
119
• 32 Arcse¢ • 73 •92
C4 (4720)
=
==-I @
~o ~
~ J.D 2 4 4 2 0 0 0
+
FIG. 3. The time variation of the relative band strength of the 02(4720) emission feature• The 32 and 92arc second measurements are from the JOCR, and the 73arc second measurements are from Mr. Laguna. The arrow at J. D. 2442045 indicates the time of perihelion passage.
and January. The CO + band showed more activity, including a sharp rise in strength from J a n u a r y 5 to 9, and then a drop to a fairly constant level from J a n u a r y 15 to 31. The C2(4720) band shows a strong rise in strength during approximately the same time period as the CO + band. These increases in emission band strengths coincide with the post perihelion appearance of pronounced gas tail. ACKNOWLEDGMENTS R. J. A. acknowledges supporb from NASA contract NAS5-23249.
REFERENCES A~GIO~E, R., GATES, B., ItEmiZE, K., AND ROOSEN, R. (1975). The light curve of comet Kohoutek (1973f). Icarus 24, 111-115. MAYER, I)., ~ O'DELL, C. R. (1968). Emissionband ratios in comet Rudnicki (1966e). Astrophys. J . 153, 951-962. RAHE, J. VANYSEK, V., AND BRANDT, J., Eds. (1973)• Report on planned observing programs for comet Kohoutek (1973f). NASA]Goddard
Space Flight Center. ¥EO~ANS, D. K. (1973). Velocity ephemeris for comet Kohoutek (1973f). Operation Kohoutek Special Office, Code 683, NASA/Goddard Space Flight Center.