- Ramadurai for a thorough reading of the manuscript. - Vivek Vengurlekar in the preparation of the manuscript is highly appreciated. - Temperature and velocity of the coma gas. - Origin of the Oort Cloud. - In other words, (1/a) gives a measure of the comet’s age.. - In fact, the existence of the solar wind, i.e. - study of the ion tails of comets. - n covering the whole range of the Sun-comet distance. - (1.4) as a function of the time from the perihelion passage. - The various fragments of the comet can clearly be seen. - This is called the anti-tail of the comet. - But this is not so in the case of the plasma tail. - 1977, Proceedings of the Robert A. - The rotation of the nucleus of Comet Halley was also confirmed.. - The shapes and sizes of the cometary. - This gives rise to the observed curved nature of the dust tail. - a = length of the semi major axis;. - Ω = longitude of the ascending node. - (2.1) and (2.4), the expression for the orbital speed of the particle can be obtained and it is given by. - P = Area of the ellipse areal velocity. - The geometrical position of the earth can be obtained from the. - What is the nature of the orbit?. - Find the elements of the orbit of the comet. - The solutions of the equations of Sec. - The gaseous material of a comet is immersed in the radiation field of the Sun. - Figure 3.1 shows a plot of the Eq. - From the measurement of the shift of the lines using Eq. - (3.9), it is possible to determine the velocity of the source.. - Most of the lines of the Balmer series lie in the visible spectral region. - The vibrational energy of the molecule can be represented as. - where w e , w e x e and w e y e are the spectroscopic constants of the molecule.. - I is the moment of inertia of the molecule. - B is known as the rotational constant of the molecule. - (B 2 Σ − X 2 Σ) of the CN system and (A 2 Π − X 2 Σ) of the CO + system and so on.. - Here µ denotes the reduced mass of the molecule. - The minimum of the curve corresponds to the equilibrium position.. - The energy level diagram of the hydroxyl radical,. - Table 3.1 Radio lines of the OH molecule.. - The surface temperature of the Sun is about 6000 ◦ K. - (3.1)] most of the energy is concentrated in the visible region of the spectrum. - This is due to the reflection of the solar radiation by the nucleus. - Since the Swan bands of the C 2. - The wavelength of the (0, 0) band of CN + arising out of ( 1 Σ − 1 Σ) transition is at 3185 ˚ A. - Table 4.1 Some of the observed spectroscopic features of molecules.. - Most of the observed features are attributed to methanol (CH 3 OH).. - J Reproduced by permission of the AAS).. - A compilation of some of the observed atomic and molecular species. - Table 4.2 Some of the observed species in comets.. - A good account of the spectra of comets can be found in the following:. - A discussion of the observations in the Ultraviolet (5), Visible (5,6), In- frared (7,8) and Radio (8,9) region can be found in. - 3) of the comet through the relation. - For the vibrational levels of the lower electronic state. - 7) and for the vibrational levels of the upper electronic state. - where µ 1 is the coefficient of the linear term in the dipole moment expansion and. - 5.5 Comparison of the observed R-branch lines of (0,0) band of (B 2 Σ. - In addition, it is necessary to consider the velocity of the gas in the coma. - vibrational temperature of the C 2 molecule. - 5.8 the vibrational levels of the electronic states a 3 Π u. - and b 3 Σ − g of the triplet states are also shown. - The singlet electronic state is the ground state of the molecule. - flux ratios for the Mulliken system of the C 2 molecule. - in contrast to the case of the C 2 molecule which arise from the triplet states (d 3 Π g - a 3 Π u. - 5.11 Comparison of the calculated (continuous) and observed (dashed) spectra of. - ∆v = +1 sequence of the C 2 Swan system for Comet West. - The intensities of the lines decrease downwords from the rotational quantum. - Many of the lines marked B in the spectra are the prompt emission lines of OH. - From the energy level diagram of the oxygen atom (Fig. - the P, Q and R branches of the band. - where B is the rotational constant of the molecule (Chap. - From the slope of the line the rotational temperature can be evaluated.. - G(v) represents the energy of the vibrational level v . - This is of the same order as the rotational temperature.. - where χ is the excitation potential of the line and θ = (5040/T. - Therefore a comparison of the isotopic ratios of. - Consider the (B−X) transitions of the molecular hydrogen. - the first singlet (A 1 II ) and the triplet (a 3 II ) electronic states of the CO molecule. - of the comet.. - where Q i is the production rate of the species. - This has to be taken into account in the analysis of the observations. - 6.9) also enters in the lifetime of the molecules. - The resulting expression is of the form. - hν abs m ρ ν (r) P M (ρ) (6.29) where L(ρ) is the observed luminosity in the emission line and M (ρ) is the total number of the species in the field of view. - of the lines in the ultraviolet region. - of the lambda doublet (Fig. - 5.14) and ∆ is the geocentric distance of the comet.. - (6.42) where n(OH) is the density of the OH molecule. - v OH is the radial velocity of the OH molecule. - Ap.J Reproduced by permission of the AAS).. - Therefore CO 2 is also a trace constituent of the nucleus.. - Therefore, CS 2 is also a trace constituent of the nucleus.. - kT ) of the Planck function.. - In general, the abundance of most of the molecules. - The observed intensity of the line is therefore given by. - N is the column density of the parents and τ P. - For the calculation of the produc-. - 6.9 The observation of the cometary [OI] 6300 ˚ A line. - Hence, in the case of the Sun, gravity essentially prevents hy-. - Since the lifetime for the ionization of the molecule is. - sion of the hydrogen atoms has to be calculated. - This is borne out by the shape of the isophotes in the visible region