Since comet P/Temple-2 is one of the potential targets for the CRAF (Comet Rendezvous Asteroid Flyby) mission, we obtained long slit spectroscopic data with our CCD spectrograph during its 1988 apparition. As the same spectrograph was extensively used for observations of P/Halley, this allowed a direct spectroscopic comparison between the two objects. Furthermore we could choose a P/Halley spectrum which was taken at a heliocentric distance very close to that of P/Temple-2. Finally, we could adjust the integration windows along the slit to compensate for the different geocentric distances, so that roughly the same projected distance of the comets' comae was observed. The parameters for our observations are given

Fink, Uwe

Hicks, Michael

English

NASA Technical Reports Server

Asteroids, Comets, Meteors 1991, pp. 183-186
Lunar and Planetary Institute, Houston, 1992 /_/f_) C_ 2 7 183
Production rates for comet P/Temple 2 from long slit CCD spectroscopy f_ /_"
Uwe Fink and Michael Hicks N 9 3 " 1 9 1 5 G-
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721
Since comet P/Temple 2 is one of the potential targets for the CRAF (Comet Rendezvous Asteroid
Flyby) mission we obtained long slit spectroscopic data with our CCD spectrograph during its 1988 apparition.
As the same spectrograph had been extensively used for observations of P/Halley this-allowed a direct
spectroscopic comparison between the two objects. Furthermore we could choose a P/Halley spectrum which
was taken at a heliocentric distance very close to that of P/Temple 2. Finally, we could adjust the integration
windows along the slit to compensate for the different geocentric distances, so that roughly the same projected
distance of the comets' comae was observed. The parameters for our observations are glven.ln Table 1. _
The spectra of the two comets using .... _-" ......the mtegratton windows m Table 1 were both &wded by a solar
type comparison star. These resulted in a fiat ratio spectrum and required that the absolute flux scale at the left
be given as fractional solar flux. Both comets show emission by the C.z Av = -1 band sequence, a number of
NH 2 bands, the red CN system and the forbidden O 1D lines at 6300A and 6364/_. All of these emission bands
are labelled in the figure. To facilitate visual comparison between the two spectra they were sealed to make the
emission intensities by C.z, NH 2 and CN roughly equal. This immediately points out a major difference in
chemical composition between the two comets. Comet P/Temple 2 exhibits a considerably stronger Ol emission
relative to the other species than comet P/Halley. In addition P/Temple 2 has a lower continuum level.
U
0
b
sn
I
C2 _v = -1
NHZ: 0,t0,0 O,9,O 0,8,0\
I I i
OI ID CN: 2-0 3-1 14) 2-I
P/Temple 2 1988Oct 9.14 r = 1.41 A = L07
P/Harley 1985Dec. 8.13 r = 1.37 b = 0.70
o I I I i
6000 804)0 10000
WavelengthA
Fig. 1. Ratio spectra of comet P/Temple 2 (top) and P/Halley (bottom) with solar type comparison stars
BS 8148 and BS 8931 respectively. The two comets were observed at very similar heliocentric distances. Lack
of a comparison star with close air-mass match leaves some residual telluric bands such as O_ and HzO in the
P/Temple 2 spectrum.
https://ntrs.nasa.gov/search.jsp?R=19930009967 2020-03-17T07:32:32+00:00Z
184 Asteroids, Comets, Meteors 1991
Table 1. Cucumsmaces of _tiom
P/Tcmpk 2 P/u_-y
Perihelion passage:
Observation date:
Sun/Earth distances:
Integration window:.
1988 Sept. 16.73
1988 Oct. 9.14 (1) 20 rain exposure
r = 1A1 AU A = 1.07AU
106" x 2.5" (72,650km x 1,984km)
1986 Feb. 9.45
1985 Dec. 8.13
r = 1.37 AU
151" x 2.5"
(4) 5 rain exIx_ures
A = 0.70 AU
CT7,220kmx l_70km)
Table 2. Flea_ aad pmdw:tioa rates: P/tlaUcy 1985 Dec. &13
Species Flux in slit Band Luminosity
photons s"1 m"2 1028 photons s"1
g-factor
10 3 s-1
Production rate
1026 molecules s-1
Q Adopted
10 _ molecules s"1
H20 (from O1) 1702 1.17 -- 1870
C_ Av=-I 20810 232 30.4 7.0
I_ 0,10,0 4080 6.50 2.82 2.4
0,8,0 .5810 9.2 2.64 3.1
0,7,0 5170 8.2 2.94 2.4
0,6,0 5o3o 8.o 0.gs 7.0
(]H 1-0 14500 436 17.1 4.3
2-1 4480 135 5.4 4.1
2-0 5320 160 5.1 52
3-1 2170 65 2.0 5.5
Coattntmm
$ mZ,_
625O_ 257
1870
7.0
2.6
4.3
P/'reml_e 2 1988 Oct. 9.14
H20 (from O1) 562 0.70 --
C2 Av=-I 2530 58 28.7
1120
1.8
Nil 2 0,10,0 480 1.5 2.66 0.47
0,8,0 700 2.3 2.49 0.76
0,7,0 490 1.9 2.78 0.57
0,6,0 680 2.2 0.92 1.9
O"q' 1-0 2030 116 16.1
2-1 -- -- 5.1
2..0 1060 66 4.9
3-1 530 26 1.9
.... : . :: =
Cominum _-. ii : -_-:!:2:.__
sm-P_
625oA 15.0
1.14
2.1
2.2
1120
1.8
0.60
Asteroids, Comets, Meteors 1991 185
In order to determine the production rates for the observed species we integrated each band over its
spectral extend and along the slit over the integration window given in Table 1. The raw counts were converted
to photons/s mz by observing an absolutely calibrated flux standard, BS 718 and BS 3314 in the case of P/Halley
and BS 718 for P/Temple 2 (Johnson 1980). For these standard stars the slit was opened to 10" yielding
photometric calibrations. After correction to unit airmass the observed fluxes collected by our slit aperture are
listed in column 2. Next the band luminosities were calculated by using a Haser model correction factor and
the appropriate dilution factor (4_rA2) for each comet. These band luminosities are given in column 3. For the
Haser model corrections we employed our recently determined scale lengths (Fink, Combi, and DiSanti 1991
a,b). Since the two comets were observed at nearly identical heliocentric distances, this makes any model
dependent errors in a composition comparison between the two comets quite small. Not considering the
different projected slit widths, the Haser corrections for the slightly larger distance of P/Temple 2 were about
1.16 times higher for all species.
For transitions excited by solar resonance fluorescence such as those of C2, Nil 2 and CN the proper
fluorescence effidendes, or g-factors must be applied to obtain production rates. For the C2 Av = -1 sequence
we used the standard value of Schleicher et al. (1987) for the Av = 0 band sequence, multiplied by 0.50. The
latter number came from measurements of a number of spectra showing both the Av = 0 and Av = -1 C2
emissions (e.g. A'Hearn 1975). For Nil 2 we used the values recently calculated by Tegl_r and Wyckoff (1989).
For the CN red system we used the same numbers as in our analysis of 4 comets some years ago (Johnson, Fink
and Larson 1984). We calculated these values using the average "f' values given in Sneden and Lambert (1982),
Cartwright and Hay (1982), Duric et al. (1978) and Lambert (1968). The g factors listed in Table 2 have been
converted to the appropriate heliocentric distances.
The OI emission is not produced by fluorescence but results from the direct photo-dissociation of H20
to the 1D state. The procedure to obtain H20 production rates follows that given in our recent paper on the
production rate of H20 for comet P/Halley (Fink and DiSanti 1990). The variation in branching ratio for this
process with change in solar activity is discussed in DiSanti and Fink (1991) and concludes that for equal O16300
luminosity the rate of production of water is a factor of 1.23 smaller during periods of active sun. Since this is
not a significant change we did not consider variations in solar activity in this analysis. The production rates for
1-120 and the parents of C2, NH2, and CN for the bands used in our analysis are given in column 5 of Table 2.
Of the four NH 2 bands used the most reliable one is 0,8,0 while 0,6,0 gives a rather deviant production rate
either due to a contamination in that band or to an erroneous g-factor. The production rate adopted (in
column 6) is a weighted average of the other three bands. For CN the most reliable number is that for the 1-0
band which was therefore given most weight for our adopted value.
The comparison of the production rates between P/Halley and P/Temple 2 is illustrated in Table 3.
Since we have recently carried out such a comparison for P/Brorsen-Metcalf (DiSanti and Fink 1991), production
rates for this comet are also included as are nominal values for a number of comets from photometry given by
Schleicher et al. (1987).
Table 3. Productiom rate com_
P/Halley P/'rempl¢ 2 P/Brorsen-Metcalf
1986 Dec. 08 1988 Oct.09 1989 July 13
r=1.37 A=0.70 r=lA1 A =1.07 r=1.36 A--0_9
"Nominal comets"
H20: 1870 a - 100% 1120 - 100% 257 - 100 100
C_ 7.0 - 0.37% 1.8 ~ 0.16% 0.94 - 0.36% 0.20%
NIL2: 2.6 - 0.14% 0.60 - 0.054% 0.15 - 0.06% --
I_1: 4.3 - 0.23% 1.2 - 0.11% 0A7 - 0.18% 0.30%
Cool_,'_ 0.15 O.027
½o
a All production rates are in 1026 molecules/sec.
0.0085
186 Asteroids, Comets, Meteors 1991
We note that the water production rate of P/Temple 2 is actually quite close to that of P/HaUey at a
comparable distance. At first sight this result may appear incongruous since the continuum flux for P/Temple
2 was down by a factor of - 17. However, inspection of Fig. 1 shows that the Ol lines are much stronger relative
to other emissions and the continuum in P/Temple 2. The OI flux gathered by our slit aperture is thus only a
factor of 3.0 lower for P/Temple 2 and after the dilution factor is taken into account the water production rate
is only a factor of 1.7 lower. Our P/Temple 2 water production rate is considerably higher than the IUE values
of -350x1026 reported by Roettger et al. (1990). We offer the following comments on this discrepancy. The
lightcurve of P/Temple 2 (Sekanina, 1991) can allow a factor of -1.75 variation. Changing solar activity yields
a factor of 1.23. The IUE H20 production rates are a factor of 2.6 lower than ground based measurements by
A'Hearn et al. (1989) and are also lower than values of Spinrad (reported in Roettger et al., 1990)
If we compare the production rates of the observed species with that of water (= 100), we find that the
abundance of C2 and Nil 2 is roughly one third that of P/Halley while CN is about one half. For P/Brorsen-
Metcalf on the other hand, C2 and CN are in similar proportion (w.r.t. water) as P/Halley but Nil 2 is down by
a factor of 3 dose to the P/Temple value. The values for nominal comets are reasonably dose for C2 but are
somewhat higher for CN which could come from differences in g values between the CN blue and red system.
The continuum flux compared to water is largest for comet P/Halley, a factor of 5 lower for P/Temple 2 and
another factor of 3 lower for P/Bror_n-Metealf.
We conclude that P/Temple 2 is either enlaanced in H20 over P/Halley if the abundances of C2, CN
and NH 2 are comparable; or if the water abundance in the two comets is equivalent, P/Temple 2 is depleted
in C2, CN and NH 2. The absolute H20 production rate does not give a clue as to which of the above two
scenarios is correct since it depends on the size of the area active in each comet.
This research was supported by NASA grant NAGW 1549.
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Production rates for comet P/Temple 2 from long slit CCD spectroscopy

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