SPECTROPHOTOMETRIC
STUDY OF P/HALLEY
POST PERIHELION
DURING
PASSAGE
P. S. GORAYA Department of Astronomy
and Space Sciences, Punjabi University,
B. S. RAUTELA, Uttar Pradesh State Observatory,
Patiala, India
B. B. SANWAL Manora Peak, Nainital
(U.P.),
India
H. K. DUGGAL Department of Astronomy
and Space Sciences, Punjabi University,
Patiala, India
and NARENDER Department
K. CHANDEL
of Physics, Punjabi University,
Patiala, India
(Received 9 January. 1991) Spectrophotometric observations of P/Halley are presented for four nights in the optical region (hh3200-7000 A) during post-perihelion period. Emission features due to CN, CH, Cs and Cz molecules are identified and the total apparent fluxes in each emission band are measured. It is found that the comet display large variations in the emission bands as well as continuum.
Abstract.
1. Introduction Comet P/Halley was recovered on 16 October, 1982 (Ye = 11.04 AU; V = 24.2) by Jewitt and Danielson (1982). Since its recovery, a large number of professional and amateur astronomers observed this most fascinating object with a variety of sophisticated instruments. Because of the favourable conditions the comet was observed from a large number of places and has resulted in a large amount of different types of data. We hope that it will help us to understand the mysteries of P/Halley in particular and comets in general. 2. Observations The observations of Comet P/Halley were made on four nights during the month of April, 1986 at the Cassegrain focus (f/13) of the 104-cm reflector of Uttar Pradesh State Observatory, Nainital. The instrumentation is same as described earlier (Goraya et al., 1982, 1984). The Hilger and Watts spectrum scanning giving a dispersion of 70 A mm-’ in the first order was used. A circular diaphragm of 3 mm corresponding to 45 arc set as projected on the head of the comet was adopted for obtaining the spectral scans of the comet. An exit slit of 0.7 mm corresponding to 50 A band pass was used for admitting the spectrum to fall on Earth, Moon, and Planets 54: 13-17, 1991. 0 1991 Kluwer Academic Publishers. Printed in the Netherlands.
14
P. S. GORAYA
ET AL.
the photomultiplier tube. The cooled (-20 “C) EM1 9658 B photomultiplier tube and standard d.c. techniques were employed for detecting and recording the signal. The observational procedures are the same as described earlier (Goraya et al., 1982, 1984). Three spectral scans of the comet were obtained every night and were reduced to instrumental magnitudes individually at a step of 2.5A. Finally, the mean instrumental magnitudes of the scans were adopted. Scans of the neighbouring sky were also taken before and after each comet scan to eliminate the contribution due to the background sky. Along with Comet P/Halley the standard star a,Leo was observed for evaluating atmospheric extinction correction and to convert instrumental magnitudes of Comet P/Halley into standard magnitudes. The instrumental magnitudes of the comet were converted to absolute values with the help of the standard star. The absolute values of magnitudes thus obtained correspond to the calibration of standard stars given by Taylor (1984). The standard monochromatic magnitudes (mh) were converted into fluxes (FV) by using the relation log F, = -19.447 - 0.4m,, .
(1)
3. Strength of Different Emission Bands The spectral scans of Comet P/Halley reduced to absolute fluxes are shown in Figure 1. The,different emission features are indicated by vertical arrows pointing downwards. This figure obviously shows the emission due to CN(O-0) A3883A, CH(O-0) + C3 h4050A and Swan Band Sequence &(1-O) h4734 A, &(0-O) A.5165pi, &(0-l.) A5635A. For deriving the emission strength of different species we measured the total area under different emission bands relative to the continuum. The continuum in the spectrum was drawn by selecting wavelength regions free of emission lines. The area of different emission bands was converted into flux. The total apparent fluxes measured in different emission bands are listed in Table I. It is clear from Figure 1 that the emission bands as well as the continuum level exhibited large variations. The continuum was very strong on April 8.91, but was found very weak on April 18.67. The CN(O-0) band which was quite prominent on April 8.91 was found very weak on April 23.64.
4. Number of CN and C2 Molecules The total number of molecules (N) of CN and C2 contained in a cylinder of diameter 45 arc set in the line of sight and extending through the head of the comet are derived from the total energy emitted in the CN and C, emission bands. A gross estimate of the total number of molecules of different species is made by using the well-known relation (O’Dell and Osterbrock, 1962) recently used by
SPBCTROPHOTOMETRIC
1 -
80.0
STIJDY
OF
P/HALLEY
15
’ Cd,-&,
COMET
c* (0-I)
P/HALLEY
CH(O-0)
60.0 APR.8.91
P
CN (O-O,)
40.0
TN
I -
I
-
30.0
20.0
IO.0
30.0
Pd
--
20.0
-
IO.0
/
I.-
/ -I--l 9.0
- - I-
8.0
7.0 7.0
.._I..._l.I
FREQUENCY Fig. 1.
6.0
5.0
(X Id4Hd
Emission features in Comet P/Halley.
4.0
3.0
0.0
16
P. S. GORAYA
ET AL.
TABLE I Observed emission band fluxes Date U.T. April, 8.91 14.75 18.67 23.64
r
A
(AU)
(AU)
Total apparent flux
1986 1.29 1.38 1.44 1.51
0.43 0.43 0.48 0.59
CN(O-0) (h3883)
CH(O-0) + C&4050)
Cdl-O) (h4734)
2.9 x lo-lo 1.01 x 10-‘O 0.128 x 10-l’ -
6.42 x 10-l’ 1.43 x 10-l” 0.636x10-” 1.62 x 10-l”
3.98 1.52 1.36 1.64
x x x x
lo-” lo-lo lo-” IO-”
C,(O, 0) (h5165)
G(O> 1) (~5635)
7.12 2.48 1.70 1.96
3.54 x lo-lo 0.964 x 10-l’ 0.964 x lo-‘O 1.21 x lo-lo
x x x x
10-l’ lo-” lo-lo 10-l’
TABLE II Values of various parameters Band
f
P
p( v, r) erg cm-3
CN(O-0) G?(l-0)
0.0342” 0.0089b 0.0239” 0.0071b
0.9200b 0.2409b 0.7335b 0.2142b
4.214 x 7.140 X 6.445 x 8.390 x
C2WO)
wo-1)
10-20r-2 b 10e2’rb2 b 10-20r-2 b 10-20r-2 b
a Lambert (1978). b Goraya et al. (1986). TABLE III Number of CN and C2 molecules Date U.T. April, 1986
Number of molecules CN(O-0)
c2u-0)
c2w9
8.91 14.75 18.67 23.64
2.4 x 1O29 0.9 x lo29 0.2 x ld9 -
2.84 x 1030 1.24 x 103’ 1.5 x Id0 3.0 x 1030
7.4 x 2.8 x 2.5 x 4.8 x
C2(0-1)
lozg 1029 102’ lo29
3.02 x 0.95 x 1.27 x 2.66 x
103’ 1030 103’ 103’
many authors (Sivaraman et aE., 1979; Goraya et al., 1982, 1984, 1986), of the form
*=
=me e’rfpP(V, f-1’
where L = luminosity of the respective band; m, = mass of an electron; e = charge of an electron; p = the vibrational transition probability; f = the oscillator strength; and p(~, r) = the solar radiation density at frequency v at a heliocentric distance The values off, p and p( v’,r) used in our caclulations are adopted from Lambert (1978) and Goraya et al. (1986) and are listed in Table II. The total number of molecules estimated by us are tabulated in Table III.
SPECTROPHOTOMETRIC
STUDY
OF
P/HALLEY
17
References Goraya, P. S., Singh, B. K., Chaubey, U. S., and Sanwal, B. B.: 1982, The Moon and the Planets 26, 3. Goraya, P. S., Rautela, B. S., and Sanwal, B. B.: 1984, Earth, Moon and Planets 30, 63. Goraya, P. S., Rautela, B. S., and Sanwal, B. B.: 1986, Earth, Moon and Planets 34, 77. Jewitt, D. C. and Danielson, G. E.: 1982, IHW Newsletter No. 2, p. 2. Lambert, D.: 1978, Mon. Not. R. Astr. Sot. 182, 249. O’Dell, C. R. and Osterbrock, D. E.: 1962, Astrophys. J. 136, 559. Sivaraman, K. R., Babu, G. S. D., Bappu, M. K. V., and Parthasarathy, M.: 1979, Mon. Not. R. Astr. Sot. 189, 897.
Taylor, B. J.: 1984, Astrophys. J. Suppl. 54, 259.
