木星族彗星 73P/Schwassmann-Wachmann 3 及歐特雲族彗星 C/2007 W1 Boattini 之毫米波段觀測

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(1)國立臺灣師範大學地球科學研究所碩士論文. 木星族彗星 73P/Schwassmann-Wachmann 3 及歐特雲族彗星 C/2007 W1 Boattini 之毫米波段觀測 Millimeterwave Observations of Jupiter-Family Comet 73P/Schwassmann-Wachmann 3 and Oort-Cloud Comet C/2007 W1 Boattini. 研究生：潘韋翔指導教授：管一政. 博士. 中華民國一百年十二月.

(2) Millimeterwave Observations of Jupiter-Family Comet 73P/Schwassmann-Wachmann 3 and Oort-Cloud Comet C/2007 W1 Boattini. Wei-Hsiang Pan Supervisor：Prof. KUAN, Yi-Jehng. A thesis submitted in conformity with the requirements For the degree of Master of Science Department of Earth Sciences National Taiwan Normal University.

(3) Abstract Comets, the most pristine deposits of ice, are thought to preserve molecules produced during the formation of early Solar System. Thus, knowledge of solar-type low-mass star formation and observations of cometary molecules are both important to our understanding of Solar System formation. To reveal the chemical evolution of Solar Nebula, we observed the break-up of Jupiter Family comet (JFCs) 73P/Schwassmann- Wachmann fragments B (73P-B) and C (73P-C) in 2006 May, and the Oort Cloud comet (OCCs) C/2007 W1 (Boattini) in 2008 June, by using the Kitt Peak 12m telescope (KP12M) and the Submillimeter Telescope (SMT) of Arizona Radio Observatory. We searched for cometary molecular species CS, HCN, H2CO, c-C3H2, CH3OH and some deuterated molecules toward 73P-B and 73P-C. We have HCN clearly detected with production rates of 1.92×1025 sec-1 for 73P-B and 1.40–4.26×1025 sec-1 for 73P-C. The simplest ring molecule cyclopropenylidene, c-C3H2, which is widely distributed in the interstellar medium was tentatively detected in 73P-C. We also looked for CS, HCN, H2CO and HDCO toward Comet C/2007 W1 (Boattini) and had a clear detection of CS at a production rate of 4.30×1025 sec-1, plus a tentative detection of HCN. Compared to other known comets, 73P-B and 73P-C showed similar HCN abundances of 0.10% and 0.11%, typical to JFCs, to each other. With no detection of CS in 73P, and with HCN the only molecule detected securely of similar abundances in both Fragments B and C of 73P, we conclude that these two cometary fragments are of similar chemical compositions and have gone through similar chemical evolution since their breakup; our results may simply imply that most JFCs were formed in regions at similar distances from the Sun. Comet C/2007 W1 (Boattini) was observed to have a large quantity of CS molecules presented but with very few HCN molecules. Furthermore, the observed CS mixing ratio of 0.35% relative to water was found close to that of Comet Hale–Bopp, 0.40%; our finding made Boattini a very special comet among all comets observed to date. Keywords: Jupiter Family comet、Oort Cloud comet、Comet 73P、Comet C/2007 W1 (Boattini). I.

(4) 摘要彗星，保存最原始的物質，也被認為是保留早期太陽系形成過程中產生的分子。因此，對於我們對太陽系形成的理解，包括太陽型的低質量恆星的形成和觀測彗星的分子都相當重要。我們在 2006 年 5 月利用兩座位於亞利桑那州的電波天文台: 基特峰 12 米望遠鏡（KP12M）和次毫米波望遠鏡（SMT），來觀測木星族彗星 73P/Schwassmann-Wachmann（73P-B）和 C（73P-C），和 2008 年 6 月歐特雲族彗星（OCCs）C/2007 W1（Boattini），。我們尋找彗星的 CS，氰化氫，H2CO 分子，c-C3H2，甲醇和一些氘分子的分子以及最簡單的環分子 cyclopropenylidene，c-C3H2，這是一種廣泛分佈在星際介質中的分子。我們也期待觀測到彗星 C/2007 W1（Boattini）中的 CS、HCN、H2CO 與 HDCO。和其他已知的彗星相比，73P-B、73P-C 的發現 HCN 相對於水的比值為 0.10％和 0.11％。我們得出這樣的結論：這兩個彗星碎片是類似的化學成分和他們分裂以來，已通過了類似的化學演化，這樣的結果可能暗示，木星族彗星形成類似太陽的距離。彗星 C/2007 W1（Boattini）被觀察到有大量的 CS，但很少 HCN。此外，觀測到的 CS 為 0.35％，和海爾－波普彗星相比(0.40％);我們認為 Boattini 為迄今觀察到彗星中非常特殊的一顆。關鍵字: 木星族彗星、歐特雲族彗星、73P 彗星、波特妮彗星. II.

(5) Contents. ABSTRACT .................................................................................................................. I CONTENTS............................................................................................................... III LIST OF FIGURES .................................................................................................... V LIST OF TABLES ...................................................................................................VII CHAPTER 1 INTRODUCTION ................................................................................1 1.1. THE ORIGIN OF COMETS .......................................................................................... 1 1.2. VOLATILE MOLECULES IN COMETS..................................................................... 1 1.3. CHEMICAL DIVERSITY IN COMETS ....................................................................... 2 1.4. COMETS 73P/SCHWASSMANN–WACHMANN 3 AND C/2007 W1 (BOATTINI) ....................................................................................................................................... 7. CHAPTER 2 OBSERVATIONS ............................................................................. 11 2.1. SMT AND KP12M.......................................................................................................11 2.2. JUPITER–FAMILY COMET 73P/SCHWASSMANN–WACHMANN 3..................14 2.3. OORT–CLOUD COMET C/2007 W1 (BOATTINI) ..................................................15 2.4. DATA REDUCTION ...................................................................................................19. CHAPTER 3 RESULTS ........................................................................................... 21 3.1. CARBON MONOSULFIDE (CS) ...............................................................................21 3.2. HYDROGEN CYANIDE AND ITS 15N ISOTOPOMER ...........................................21 3.3. FORMALDEHYDE AND DEUTERATED FORMALDEHYDE ..............................23 3.4. DEUTERIUM WATE AND HYDROGEN CYANIDE ..............................................24 III.

(6) 3.5. CYCLOPROPENYLIDENE (c-C3H2) .........................................................................25 3.6. METHANOL (CH3OH) ...............................................................................................26. CHAPTER 4 ANALYSES........................................................................................ 38 4.1. ROTATIONAL TEMPERATURE AND MOLECULAR COLUMN DENSITY ......38 4.2. GAS PRODUCTION RATES ......................................................................................40. CHAPTER 5 DISCUSSIONS AND SUMMARY .................................................. 45 5.1. HCN IN COMET 73P/SCHWASSMANN–WACHMANN 3 ....................................45 5.2. CS IN COMET C/2007 W1 (BOATTINI) ...................................................................47 5.3. COMPARISONS TO OTHER COMETS ....................................................................47 5.4. SUMMARY .................................................................................................................51. BIBLIOGRAPHY ..................................................................................................... 56. IV.

(7) List of Figures FIGURE 1.1. A SCHEMATIC VIEW OF LOW-MASS STAR FORMATION ................... 3 FIGURE 1.2. THE SNOW LINES FOR VARIOUS COMETARY VOLATILE ................... 4 FIGURE 1.3. RELATIVE PRODUCTION RATES OF COMETARY VOLATILES AND THEIR COMET-TO-COMET VARIATIONS ....................................................... 5 FIGURE 1.4. NICE MODEL IN WHICH THE ARCHITECTURE OF THE SOLAR SYSTEM ......................................................................................................................... 6 FIGURE 1.5. COMET 73P/SCHWASSMANN-WACHMANN 3 APPROACHED THE RING NEBULA M57 ON 2006 MAY 8 TAKEN BY STEFAN SEIP AT STUTTGART, GERMANY. .................................................................................................................... 8 FIGURE 1.6. COMET 73/SCHWASSMANN-WACHMANN 3 SPLITS INTO FRAGMENTS, THE BRIGHTEST AT UPPER RIGHT IS FRAGMENT C ................. 8 FIGURE 1.7. COMET C/2007 W1 (BOATTINI) WITH ITS MAGNITUDE ~5 OBSERVED ON 2008 JUNE 28, TAKEN BY JOHN DRUMMOND IN NEW ZEALAND. ............. 9 FIGURE 2.1. SUBMILLIMETER TELESCOPE (SMT) NEAR SAFFORD, ARIZONA, USA. .............................................................................................................................. 12 FIGURE 2.2. THE 12M TELESCOPE (KP12M) LOCATED NEAR TUCSON IN ARIZONA, USA. .......................................................................................................... 13 FIGURE 2.3. SMT MAIN BEAM EFFICIENCIES ............................................................ 20 FIGURE 3.1. THE CS J = 3–2 TRANSITION OBSERVED WITH THE KP12M TELESCOPE TOWARD THE COMET C/2007 W1 (BOATTINI), ON 2008 JUNE 14 ....................................................................................................................................... 27 FIGURE 3.2. THE HCN SPECTRUM OF THE J = 1–0 TRANSITION OBSERVED TOWARD THE COMET 73P-B ON 2006 MAY 13 WITH THE KP12M TELESCOPE. ....................................................................................................................................... 28 FIGURE 3.3. HCN J = 1–0 SPECTRA OBSERVED TOWARD COMET 73P-C ON 2006 MAY 09, 10 AND 13 (TOP TO BOTTOM). ................................................................. 29 FIGURE 3.4. HCN J = 3–2 SPECTRA OBSERVED TOWARD 73P-C ON 2006 MAY 5, 7 AND 8. .......................................................................................................................... 30 FIGURE 3.5. HDO 21,1–11,0 SPECTRA OBSERVED TOWARD COMET C/2007 W1 (BOATTINI) .................................................................................................................. 31 FIGURE 3.6. HDO 42,2–42,3 SPECTRA OBSERVED TOWARD COMET 73P-C.............. 32 FIGURE 3.7. THE c-C3H2 SPECTRUM IN COMET 73P-C TAKEN IN THREE CONSECUTIVE 18-MINUTE INTERVALS ON 2006 MAY 6.47 .............................. 33 FIGURE 4.1. HCN ROTATIONAL DIAGRAM OF COMET 73P-C ................................. 39 V.

(8) FIGURE 5.1. THE ABUNDANCES (OR MIXING RATIOS) OF HCN ............................ 54 FIGURE 5.2. THE ABUNDANCES (OR MIXING RATIOS) OF CS ................................ 55. VI.

(9) List of Tables. TABLE 2.1. SMT BACKEND SPECTROMETERS ............................................................. 12 TABLE 2.2. KP12M BACKEND SPECTROMETERS......................................................... 14 TABLE 2.3. JPL ALTERNATE ORBITS USED FOR COMET 73P-B AND C .................... 14 TABLE 2.4. MOLECULES OBSERVED TOWARD COMET 73P-B .................................. 15 TABLE 2.5. MOLECULES OBSERVED TOWARD COMET 73P-C .................................. 16 TABLE 2.6. JPL ORBITAL SOLUTIONS FOR COMET BOATTINI .................................. 17 TABLE 2.7. OBSERVED MOLECULE SPICES TOWARD COMET C/2007 W1 ............. 18 TABLE 2.8. KP12M TELESCOPE CORRECTED MAIN BEAM EFFICIENCIES. ........... 20 TABLE 3.1. OBSERVED MOLECULAR SPICES RESULTS TOWARD COMET 73P-B BY USING KP12M ............................................................................................................... 34 TABLE 3.2. OBSERVED MOLECULAR SPICES RESULTS TOWARD COMET 73P-C BY USING KP12M OR SMT ............................................................................. 35 TABLE 3.3. OBSERVED MOLECULAR SPICES RESULTS TOWARD COMET BOATTINI BY USING KP12M ..................................................................................... 37 TABLE 4.1. PHYSICAL PARAMETERS AND ROTATIONAL CONSTANTS USED TO DERIVE COLUMN DENSITIES................................................................. 43 TABLE 4.2. MOLECULAR COLUMN DENSITIES AND GAS PRODUCTION RATES IN COMET 73P-B, C AND COMET BOATTINI ............................................ 44 TABLE 5.1. HCN PRODUCTION RATES IN COMET 73P-B COMPARED TO OTHER STUDIES DURING 2006 APPARITION ........................................................ 48 TABLE 5.2. HCN PRODUCTION RATES IN COMET 73P-C COMPARED TO OTHER STUDIES DURING 2006 APPARITION ........................................................ 49 TABLE 5.3. GAS PRODUCTION RATES IN COMET 73P-B, C AND BOATTINI COMPARED TO OTHER STUDIES DURING APPARITION .................................... 53. VII.

(10) Chapter 1 Introduction 1.1. The Origin of Comets Comets are thought to have been formed during the formation of the Solar System, and thus preserve the physical and chemical conditions of the solar nebula. Based on their inclinations and orbital characteristics, comets are divided into two main categories: 1) nearly isotropic orbits of comets with random inclinations, and 2) ecliptic comets with small orbital inclinations. These two classes of comets each have their own reservoirs. The nearly isotropic comets come from the Oort cloud, which is a spherical shell of comets lying at a distance ranging from 103 to 105 AU from the Sun (Stern 2003). The ecliptic comets were once thought to have come from the Kuiper belt, a ring-shaped disk outside the orbit of Neptune, 30 to 1000 AU away from the Sun. The former group is comprised of Oort cloud comets (OCCs) with long orbital periods (> 200 years) and Halley-type comets (HTCs) with short periods (20–200 years), while the latter consists of mainly Jupiter-family comets (JFCs) with even shorter periods (≦ 20 years), which are bound by the gravity of Jupiter (Levison 1996). Recent studies suggest that JFCs, instead of coming from the Kuiper belt itself, may in fact come from a sub-class of the Kuiper belt, i.e., the trans-Neptunian scattered disk (Duncan & Levison 1997, Duncan et al. 2004). A new class of comets, which are objects in the asteroid belt showing comet-like features, was discovered in 2006 and subsequently labeled as main-belt comets (Hsieh & Jewitt 2006). However, detailed chemical and physical properties of main-belt comets are still waiting to be disclosed.. 1.2. Volatile Molecules in Comets Molecular clouds are regions in space with dense quantities of hydrogen gas. When a cold molecular cloud begins to collapse, most volatile molecules in the gas phase are condensed onto the surfaces of grains. When the central star is formed, volatile 1.

(11) molecular species in the surrounding cloud will be evaporated from the grain mantles, and become more complex molecules via gas-phase reactions (van Dishoek & Blake 1998). Shown in Figure 1.1 is one possible star-forming scenario of a young low-mass stellar object. Our Solar System may have undergone a similar process, with orbiting planets eventually formed. While preserving the pristine chemical compositions of the primordial solar nebula, comets were affected by the gravitational influence of the Jovian planets and disposed to the Oort cloud or the Kuiper belt. Volatile species in comets were preserved according to their condensation temperatures and their distances to the Sun (Figure 1.2). Once comets were heated by solar radiation, their volatile molecules were sublimated into space. To date, there have been many volatiles observed in comets. Figure 1.3 summarizes the molecules detected: nitrogen-bearing molecules, such as HCN, HNCO, HNC, and CH3CN; oxygen-bearing molecules, like CH3OH, H2CO, HOCH2CH2OH, and HCOOH; and sulfur-bearing molecules, with H2S, OCS, SO2, CS2 and H2CS. The most complex molecule detected by spectroscopy in comets is ethylene glycol (HOCH2CH2OH) (Crovisier et al. 2004). Complex molecules may have been important sources for life in the early Earth.. 1.3. Chemical Diversity in Comets Numerical simulations (Levison and Duncan 1997, Levison et al. 2008) indicated that nearly isotropic comets were formed in the giant planets region (~5–30 AU), and were then expelled to outside the Solar System, in contrast to the JFCs that originated in the outer region (> 30 AU). Hence, we can ideally discriminate between these two different origins of comets via their distinct chemical compositions, as the JFCs would have been formed in a warmer environment and the OCCs in colder locations. Recent observations, however, have shown no clear correlation between comets, even in different wavelengths. (A'Hearn et al. 1995, Biver 2002, Mumma et al. 2003, DiSanti & Mumma 2008). There was also no correlation found between comets’ dynamical classes and their chemical compositions (Figure 4). Gomes et al. (2005) proposed that JFCs and OCCs were both formed in the outer proto-planetary disk and were then ejected to their current places. Following this model (the so-called Nice model), the chemical differences in JFCs and OCCs are not distinct. Thus, establishing taxonomy of comets to test the Nice model is an effective approach to 2.

(12) Figure 1.1. A schematic view of low-mass star formation. (a) Dark cloud cores, roughly 1 pc in size, gradually contract until (b) magnetic support is overcome and inside-out collapse begins at t = 0. (c) For ~104–105 years, a phase of both high accretion and supersonic outflow occurs in deeply embedded protostars (young stellar objects or YSOs). (d) Gradual clearing by the outflow leaves only the young T Tauri star and a residual protoplanetary accretion disk, which, on time scales of 106–107 years, leads to the formation of a mature planetary system (e). Characteristic molecules at each of these stages are indicated (Adopted from Hogerheijde, after Shu et al. 1987).. 3.

(13) Figure 1.2. The snow lines for various cometary volatiles. The sublimation/condensation temperatures of Yamamoto, 1985, and a temperature profile T = 273 rh −0.5 are assumed. It must be noted that this law and the place of the planets, as represented in the figure, pertain to the present Solar System and may greatly differ for comets formed in the early Solar System (Crovisier 2007).. 4.

(14) Figure 1.3. Cometary volatiles detected in spectroscopic surveys. Most listed species are regarded as primary, except for HNC, which is in large part a product species. Others may be both primary and product in origin (e.g., H2CO, CO). For each molecular species, the number of comets in which it has been detected is shown on the right margin, and the range of values found among those detections is shown as a color bar (light green). The six species designated “1” on the right margin were detected only in comet Hale-Bopp, the brightest comet of the past several decades. Adapted from Crovisier (2006), with updates for CO2 and NH3. See also Bockelée-Morvan et al. (2004). Adopted from Mumma et al. (2011).. 5.

(15) Figure 1.4. The Nice model in which the architecture of the Solar System is set by the clearing of a massive (30 M⊕) Kuiper belt (stippled green region) when planets are thrown outwards by strong interactions between Jupiter (red) and Saturn (pink) at the 2:1 mean-motion resonance, shown at: (a) the initial configuration with the giant planets at 5.5, 8.2, 11.5 and 14.2 AU; (b) just before the 2:1 resonance crossing, timed to occur near 880 Myr from the start; (c) at 3 Myr after resonance crossing (note the large eccentricity of Uranus (purple) at this time and the placement of Neptune (blue) in the Kuiper belt); and (d) 200 Myr later, by which time the planetary orbits have assumed nearly their current properties. These are adapted with permission from Gomes et al. 2005 (Jewitt et al., 2009).. 6.

(16) understanding the early phases of our solar system... 1.4. Comet 73P/Schwassmann–Wachmann 3 and C/2007 W1 Boattini The short-period comet 73P/Schwassmann–Wachmann 3 (hereafter 73P) with its 5.4 year returning period, was first discovered in 1930 by two astronomers, Carl Arnold Schwassmann and Arno Arthur Wachmann, at Hamburg, Germany. Due to poor observation conditions, 73P was not observed again for almost 40 years, until 1979, and it was lost again during its subsequent return to perihelion. In 1990, 73P reappeared and become a noticeable comet in 1995 because of outburst events. In its 1995 apparition, 73P underwent three outbursts and reached a brightness of 6.3 in visual magnitude. Multiple nuclei within the 73P coma were later found, and were labeled as fragments A, B, C and D (Boehnhardt & Kaufl 1995). In 2001, B and C (hereafter referred to as 73P-B and 73P-C) were recovered, along with a new fragment, E. In its 2006 apparition, not only were 73P-B and 73P-C recovered, but new and larger components G and R combined with more than 60 smaller fragments were also found. The breakup of 73P released internal primitive materials from the cometary nucleus, providing us with an opportunity to study the physical conditions of the early formation of the Solar System. Compared to OOCs, JFCs are often fainter. Nevertheless, when 73P made a surprisingly close approach to the Earth on May 12, 2006, only 0.08 AU away, it made both 73P-B and 73P-C naked-eye visible, with visual magnitudes up to ~5. However, their nucleus sizes were not large, estimated to be > 0.2 and ~0.5 km in radius, respectively (Howell et al. 2007). 73P is also a perfect target for single-dish telescopes to measure its chemical composition in detail. We thus observed 73P-C in 2006, over May 5–8, 9–10, and 13–14, with the Heinrich Hertz Submillimeter Telescope (SMT), and observed 73P-B and 73-C from May 13 to 14, 2006, with the Kitt Peak 12M (KP12M) radio telescope at the Arizona Radio Observatory. The comet C/2007 W1 (Boattini) was discovered in November, 2007, in a plan by the Mount Lemmon Survey to search for near-Earth objects. It was classified as an OOC, and with its parabolic, long-period orbit, it was labeled as a dynamical comet. This was the first time the comet had come into the inner Solar System. In June, 2008, 7.

(17) Figure 1.5. Comet 73P/Schwassmann-Wachmann 3 approaching the ring nebula M57 on May 8, 2006. This picture was taken by Stefan Seip at Stuttgart, Germany.. Figure 1.6. Comet 73/Schwassmann-Wachmann 3 splits into fragments; the brightest in the upper right is Fragment C, and lower left is Fragment B. The picture was taken by the Spitzer Space Telescope over May 4 to 6, 2006, with 21 hours exposure time.. 8.

(18) Figure 1.7. Comet C/2007 W1 (Boattini) with magnitude ~5, observed on June 28, 2008. This picture was taken by John Drummond in New Zealand.. 9.

(19) the long-period comet C/2007 W1 (Boattini), with an orbital period of ~63,000 years, was at perihelion, with a geocentric distance at closest approach of 0.21 AU. C/2007 W1 (Boattini) reached a visual magnitude of ~5, and also visible with the naked eye, during May–July, 2008. To study the chemical compositions of OOCs as compared to JFCs, we have chosen comets 73P-B, 73P-C, and C/2007 W1 (Boattini) as our targets. Our observations toward comet C/2007 W1 (Boattini) were performed on June 14, 17, 19, 20 and 22 with KP12M.. 10.

(20) Chapter 2 Observations 2.1. SMT and KP12M Comets which are bright in visible and are observable with optical telescopes may not be bright enough for radio telescopes very often, even when comets are at perihelion. Therefore high sensitivity instruments and excellent observing facilities are essential for successful radio observations. When compared to interferometer arrays, higher detection rates are generally achieved via single-dish observations. For our target comets JFC 73P (including fragments B and C) and the long-period OCC C/2007 W1 (Boattini), both comets reached the perigee at a relatively low brightness with a visual magnitude ~5. In order to obtain molecular spectral data from these two dim comets, two world-class millimeter-wave single-element telescopes were thus used for our study. Built in 1990 and maintained by the Arizona Radio Observatory of University of Arizona, the Heinrich Hertz Submillimeter Telescope (SMT; Figure 2.1) is a bent Cassegrain focus 10–meter-wide telescope located on Mt. Graham near Safford, Arizona, USA. Four types of heterodyne receivers are mounted on the SMT: 0.4 mm (600–720 GHz), 0.8 mm (315–365 GHz), 1.3 mm (211–275 GHz; ALMA Band-6), and 2 mm (133–180 GHz); however, currently the 2 mm receiver is only available for very long baseline interferometry (VLBI) observations. For our SMT observations, the backend spectrometers employed were Forbes filter banks (FFB) and high-resolution filter banks (FB2), with a spectral resolution of 1 MHz ch-1 and 250 kHz ch-1, respectively, in parallel mode. A single-channel chirp transform spectrometer (CTS), with a resolution of 47 kHz ch-1, and dual-channel Acousto-Optical-Spectrometers (AOS), with ~1 MHz ch-1 resolution, were also applied. The characteristics of all the spectrometers onboard the SMT are summarized in Table 2.1.. 11.

(21) Table 2.1. SMT Backend Spectrometers. Spectrometers FFB-A/B FB2-A/B CTS-A AOS-A AOS-B AOS-C. Resolution -1 (kHz ch ) 1000.0 250.0 46.8 478.2 a / 1011.5 b 480.7 a / 1084.9 b 121.1 a / 392.4 b. Bandwidth (MHz) 1024.0 64.0 215.3 1024.0 1024.0 250.0. a. Frequency sampling interval, which covered the channel spacing of the central one-third of channels and was measured on March 22, 2005. b Effective FWHM resolution of the central one-third or channels or effective channel width, measured on March 22, 2005.. Figure 2.1. Submillimeter Telescope (SMT) near Safford, Arizona, USA. (Taken from ARO: http://aro.as.arizona.edu/images/smt/smt_at_night_med.jpg). 12.

(22) Constructed in 1967, the Kitt Peak 12M telescope (KP12M; Figure 2.2) on Kitt Peak at Tucson, Arizona, USA, is a 12-meter-diameter telescope. It was originally governed by the National Radio Astronomy Observatory (NRAO) and control was transferred to the University of Arizona in 2000. For KP12M, the observed frequencies covered a range from 2 to 3 mm and is good for studying molecular vib-rotational transitions. KP12M receivers contain 2 mm (133–180 GHz), 3 mm-low (68–90 GHz), 3 mm-high (90–116 GHz) and the newly mounted ALMA Band-3 receiver (83–116 GHz) in May 2008. Table 2.2 summarizes the KP12M spectrometers adopted for the backend. These were two filter-bank (FB) systems at 100 kHz ch-1 and 250 kHz ch-1 spectral resolution, respectively, in parallel mode for dual polarization, and the dual-channel millimeter autocorrelator (MAC) at 196 kHz ch-1 resolution.. Figure 2.2. The 12M telescope (KP12M) located near Tucson in Arizona, USA. (Taken from NRAO: http://aro.as.arizona.edu/images/12_meter/12meter_dish.jpg). 13.

(23) Table 2.2. KP12M Backend Spectrometers Spectrometers FB1-1/2 FB2-1/2 MAC. Resolution -1 (kHz ch ) 100.0 250.0 97.6 a / 195.3 b. Bandwidth (MHz) 12.8 32.0 300.0 c. a. Frequency sampling interval. FWHM channel width, which is half of the frequency sampling interval. c Usable bandwidth, which is at 75% efficiency of the total bandwidth. b. 2.2. Jupiter-Family Comet 73P/SchwassmannWachmann 3 By using the SMT, we focused on the largest fragment C of Comet 73P, 73P-C, over 2006 May 5–8, and combined this with KP12M observations over May 9–10 and 13–14. On 2006 May 13, an outburst event occurred which made the other fragment 73P-B increase its brightness from apparent magnitude 6 to 4.5; 73P-B and 73P-C were thus simultaneously observed in May 13–14. During our observations, the bright planets Jupiter or Venus and the massive star-forming region DR21 were selected as our pointing and focusing targets. Position switching (PS mode) in Az. 30′ west was used during observations toward both 73P-B and 73P-C. To track the two fragments of Comet 73P, orbital solutions calculated by the JPL HORIZONS online Solar System data service, which are summarized in Table 2.3, were employed to make ephemerides for SMT and KP12M observing. For 73P-B, the orbital solution K061-13 was used on May 13, 2006, and then updated to K061-14 on the following day. For 73P-C, we applied the solution K061-13 during 2006 May 5–8, and updated to K061-14 for observations in 2006 May 9–10 and 13–14.. Table 2.3. Orbital solutions (JPL/Horizons) employed for observations of comet 73P.* Observation Date (Day) 2006 May 05-08 2006 May 09-10 2006 May 13 2006 May 14. 73P-B (Orbital solution) -a K061-13 K061-14. a. 73P-C (Orbital solution) K061-13 K061-14 K061-14 K061-14. no observations toward this fragment. * For 73P-B, the perihelion occurred on 2006 June 08; for 73P-C, June 07. 14.

(24) With their distances from the Earth ranging from 0.06 AU to 0.10 AU, we observed many molecular transitions toward both B and C fragments of Comet 73P. N-bearing (HCN, and its. 15. N isotopomer HC15N), S-bearing (CS), and deuterated. molecules (HDO, DCN, and HDCO) were searched for. Other larger important organic molecules, such as CH3OH and c-C3H2, were also looked for in fragment C, which was the largest fragment after 73P’s breakup. Table 2.4 lists the molecules observed toward 73P-B, and Table 2.5 lists those for 73P-C.. 2.3. Oort-Cloud Comet C/2007 W1 (Boattini) In June 2008, the brightness of Comet C/2007 W1 (Boattini) reached 5 in visual magnitude, which made it a good target for study. Bottini was therefore observed with KP12M on 2008 June 14, 17, 19–20, and 22, before its perigee on 2008 June 24. Pointing and focus calibration were performed by observing Uranus, Mars, and Saturn, depending on the elevation and azimuth of the comet. Position switching (PS) mode with OFF position in Az. 30′ west was also applied when observing Boattini. Similarly, for tracking Comet C/2007 W1 (Boattini), orbital solutions obtained from the JPL HORIZONS online Solar System website were employed and are summarized in Table 2.6. The orbital solution JPL #29 was only used on 2008 June 14, and was then updated to JPL #30 for the following observations on June 17, 19 and 20. On 2008 June 22, cometary ephemeris was updated again with JPL #31 orbital solution for better tracking.. Table 2.4. JPL Orbital solutions employed for Comet C/2007 W1 (Boattini).* Observation Date (Day) 2008 Jun 14 2008 Jun 17 2008 Jun 22. C/2007 W1 (Boattini) (Orbital solution) JPL #29 JPL #30 JPL #31. * Comet Boattini was at perihelion on 2008 June 24.. The molecules observed toward C/2007 W1 (Boattini) are listed in Table 2.7, sorted by number of atoms. On 2008 June 14, two days after C/2007 W1 (Boattini) perigee at 0.21 AU, we searched for N-bearing (HCN) and S-bearing (CS) molecules. To derive the D/H ratio, we observed H2CO and the deuterated formaldehyde HDCO on 2008 June 17, 19–20 and 22. 15.

(25) Table 2.5. Molecular transitions observed toward Comet 73P-B Molecule CS HCN HC15N. Transition J→J’ 2–1 1–0 F=2–1 1–0 F=1–1 1–0 F=0–1 1–0. Frequency (MHz) 97980.9 88631.8 88630.4 88633.9 86055.0. a. b. c. Date (UT) 2006 May 14.31. r (AU) 1.006. Δ (AU) 0.067. Eu (K) 7.1. 2006 May 13.76. 1.009. 0.067. 4.3. KP12M. 2006 May 13.33. 1.011. 0.067. 4.1. KP12M. a. Heliocentric distance. Geocentric distance. c Upper-state energy level. b. 16. Telescope KP12M.

(26) Table 2.6. Molecular transitions observed toward Comet 73P-C Molecule CS. Transition J→J’ 3–2. Frequency (MHz) 146969.0. 1–0*. 88630. 3–2. 265886.4. 1–0 3–2 21,1–11,0 21,2–11,1 31,2–21,1 30,3–20,2 21,1–21,2 42,2–42,3 21,1–11,0 41,4–30,3. 86055.0 217238.6 150498.3 140839.5 225697.8 218222.2 241561.6 143727.2 134284.8 150851.9. 52,3–43,2. 249054.4. 62,5–51,4. 251527.3. 70,7–61,6 53,3–42,2 50,5–5-1,5. 251314.3 254987.6 157179.0. HCN. HC15N DCN H2CO HDO HDCO. c-C3H2. CH3OH. a. Date (UT) 2006 May 14.75 2006 May 09.66 2006 May 10.65 2006 May 13.72 2006 May 05.56 2006 May 07.51 2006 May 08.65 2006 May 13.48 2006 May 06.62 2006 May 09.33 2006 May 14.61 2006 May 05.29 2006 May 06.28 2006 May 08.26 2006 May 10.53 2006 May 14.41 2006 May 09.52 2006 May 06.47 2006 May 09.50 2006 May 06.63 2006 May 07.26 2006 May 07.56 2006 May 06.53 2006 May 10.34. r (AU) 0.999 1.026 1.021 1.004 1.051 1.038 1.032 1.005 1.044 1.028 1.000 1.053 1.046 1.034 1.021 1.001 1.027 1.045 1.027 1.044 1.040 1.039 1.045 1.022. a. b. Δ (AU) 0.081 0.082 0.080 0.079 0.098 0.089 0.085 0.079 0.093 0.083 0.081 0.099 0.095 0.086 0.080 0.080 0.082 0.094 0.083 0.093 0.090 0.089 0.093 0.081. c. Eu (K) 14.1. 17. KP12M. 4.3. KP12M. 25.5. SMT. 4.1 20.9 22.6 21.9 33.5 21.0 95.3 319.2 17.6 19.3. KP12M SMT KP12M KP12M SMT SMT SMT KP12M KP12M KP12M. 41.1. SMT. 47.5. SMT. 50.7 41.1 48.0. SMT SMT KP12M. Heliocentric distance. Geocentric distance. c Upper-state energy level. * The HCN 1–0 line includes three hyperfine structure transitions: F=2–1 at 88631.8 MHz, F=1–1 at 88630.4 MHz, and F=0–1 at 88633.9 MHz. b. Telescope.

(27) Table 2.7. Molecular transitions observed toward Comet C/2007 W1 (Boattini). Molecule CS HCN. Transition J→J’ 3–2 1–0 F=2–1 1–0 F=1–1 1–0 F=0–1. Frequency (MHz) 146969.0 88631.8 88630.4 88633.9. H2CO. 21,1–11,0. 150498.3. HDCO. 21,1–11,0. 134284.8. a. b. c. Date (UT) 2008 June 14.75. r (AU) 0.870. Δ (AU) 0.211. Eu (K) 14.1. 2008 June 14.66. 0.871. 0.211. 4.3. KP12M. 2008 June 17.65 2008 June 19.89 2008 June 20.64 2008 June 22.81 2008 June 19.69 2008 June 22.65. 0.860 0.855 0.853 0.851 0.855 0.851. 0.217 0.223 0.226 0.236 0.223 0.235. 22.6. KP12M. 17.6. KP12M. a. Heliocentric distance. Geocentric distance. c Upper-state energy level. b. 18. Telescope KP12M.

(28) 2.4. Data Reduction The 1.3-, 2-, and 3-mm observations were performed using the SMT and KP12M dual-polarization SIS mixers operating in single-sideband mode. System temperatures ranged from 100–500 K with typical image sideband rejections greater than 20 dB. For all measurements, the chopper-wheel method (Penzias and Burrus 1973) was introduced, which is a way to measure ambient temperature toward the sky using a chopper or a vane absorber as the calibration signal. The temperature scale achieved by the SMT is the observed source antenna temperature, TA*, which is corrected for atmospheric attenuation, radiative loss, rearward scattering and spillover. For column density calculation, in which we need to know the source radiation temperature (TR) or the main-beam brightness temperature (Tmb), one can use the formula TR = TA*/ ηb, where ηb is the main beam efficiency; according to the SMT website, the average value of ηb is 0.74 over the 1-mm band (Figure 2.3). The KP12M intensity scale is the observed source antenna temperature, TR*, which is again corrected for atmospheric attenuation, radiative loss, rearward and forward scattering, and spillover. Compared to the TA* used at the SMT, TR* includes in it forward scattering losses. To derive the radiation temperature, TR* was converted using the formula TR = TR*/ ηc, where ηc is the corrected main beam efficiency, which is available in the KP12M user manual (Table 2.8). Data reduction was carried out using the Continuum and Line Analysis Single-dish Software (CLASS) package, which was developed at IRAM. For a given molecular spectral line, we first added all scans that were collected, and then removed continuum baselines. Compared to rms noises, spectral features with intensities greater than 3σ were identified as firm detections, while no-detections correspond to those lower than 3σ.. 19.

(29) Figure 2.3. The SMT main beam efficiencies by measuring Mars and Saturn were found in fall 2007–spring 2008 across 1 mm, and the average main beam efficiency is 0.74. (Taken from ARO website: http://aro.as.arizona.edu/smt_docs/smt_beam_eff.htm.) This value is in agreement with the Ruze formula, which is related to the gain of an antenna and the rms of the random surface errors, and is applied to calculate telescope main beam efficiencies here.. Table 2.8. KP12M telescope corrected main beam efficiencies. Frequency (GHz) 70 90 115 145. Beam width (arcsec) 90 70 55 43. a. ηc. a. 0.98 0.95 0.85 0.80. Corrected main beam efficiency (percentage of power in the main diffraction beam relative to the outlying error beam).. 20.

(30) Chapter 3 Results 3.1. Carbon Monosulfide Carbon monosulfide (CS) was first detected in the comet 1976 VI (West) in rocket ultraviolet spectrum. (Smith et al. 1980). Since then, thanks to the work of the IUE satellite, CS at (0,0), (1,0), and (0,1) bands have been detected in many other comets (Weaver et al. 1981). Observations toward Comet 1979 X (Bradfield) suggested that CS was not released from the nucleus itself, but rather from the dissociation of other bigger parent molecules, such as carbon sulfide (CS2) (Jackson et al. 1982). However, the very short lifetime of CS2 makes the detection of this molecule less likely. Therefore, like other radio astronomers, our observations toward 73P-B, 73P-C, and C/2007 W1 (Boattini) focused on the CS lines. CS J = 2–1 and J = 3–2 transitions were observed on 2006 May 14, toward 73P-B and 73P-C, respectively (Tables 3.1 & 3.2). CS J = 2–1 was searched for toward 73P-B earlier in the day of May 14, but we did not detect CS at this transition. We then tuned to a higher frequency for the J = 3–2 transition and changed our target to the larger component, 73P-C. As 73P-C is the main component of Comet 73P after its fragmentation in 1995, we expected a higher possibility of detection of CS; however, we did not find any toward 73-P. CS J = 3–2 was also searched for on 2008 June 14 in the long-period comet C/2007 W1 (Boattini), and CS was clearly detected this time (Figure 3.1; Table 3.3). CS has also been detected in several other comets, such as Comet Hale–Bopp (Biver et al. 1999), Comet Hyakutake (Biver et al. 1997) and Comet Lee (Biver et al. 2000). Our detection of CS in Comet Boattini can be used to compare chemical compositions and abundances in OCCs, JFCs, and in other orbital groups.. 3.2. Hydrogen Cyanide and its 15N Isotopomer 21.

(31) HCN has been widely observed in many OCCs; in fact, hydrogen cyanide is the best studied cometary molecule. HCN is an abundant cometary parent molecule; more importantly, HCN/H2O ratios are nearly constant around ~0.1% in most comets observed including JFCs, hence HCN has been used as an indicator of the gas production rate of a comet (Bockelée-Morvan et al. 2004). The HCN J = 1–0 transition at 88.63 GHz was looked for with the KP12M on 2006 May 13 toward 73P-B, and on May 9, 10, and 13 toward 73P-C (Tables 3.1 & 3.2). The HCN J = 1–0 line was clearly detected In both fragments. In 73-B, a slightly blue-shifted (0.1 km s-1) line profile was revealed (Figure 3.2), which could be due to small fragmentation events that were still active in the 73-B component (Vincent et al. 2009). Toward 73P-C, the line intensity illustrated a trend of weakness from observations on May 9 and 10 to May 13 (Figure 3.3). During these three dates, 73P was moving away from the Sun while closer to the Earth. Since heating from the Sun governs cometary activities dominantly, the increasing heliocentric distance may be a plausible cause of the diminishing line intensity observed. Because of the nitrogen atom in the molecule, the HCN J = 1–0 ―line‖ actually includes three transitions of hyperfine structure with F = 0–1, F = 2–1 and F = 1–1 which are discernible at high enough spectral resolution (Figure 3.2 and 3.3). In an optically thin case, the expected line intensity ratio between these three hyperfine components of F = 0–1, 2–1 and 1–1 would be about 1:5:3 accordingly in the local thermodynamic equilibrium (LTE) condition; however, due to the weakness of the HCN emission and high noise levels of the observed spectra, except the strongest hyperfine transition at F = 2–1, the remaining two hyperfine components at F = 1–1 and 0–1 were not visible in the HCN spectrum taken toward 73P-B. Likewise, the line intensity ratio of the hyperfine components of HCN toward 73P-C was not apparent either, even though the F = 1–1 transition was revealed marginally on May 9.7 and was securely detected on May 10.7. The HCN emission appeared to be fading during the time of our observations and disappeared completely on May 13.7. On the other hand, the HCN J = 3–2 line at 265.8 GHz was clearly detected toward 73P-C sometime earlier on 2006 May 5, 7 and 8 (Figure 3.4). There was no obvious temporal variation in the observed HCN line intensity for the duration in early May; the primary beam of the SMT was of 28˝ or ~1,800 km in linear size at the time, with 1˝ corresponding to a linear scale of ~65 km when the comet was ~0.09 AU away. The nearly constant HCN 3–2 intensity indicates that our beam is smaller than the gas outflow shell of HCN and we were looking into the inner coma of the comet. 22.

(32) HCN is thought to be a parent molecule and is released from comet nucleus directly into its expanding atmosphere (Bockelée-Morvan et al. 1984). The double-peak line profile of HCN (visible in Figure 3.4) may imply an expanding inner coma with a shell-like structure. The stronger red-shifted line component of the HCN spectral profile, when compared to the blue-shifted one, seen on 2006 May 5.56 may suggest that some additional HCN molecules could have been evaporated directly from the red-shifted dust tail. The detection of HCN in the J = 3–2 transition in 73P-C inspired us to observe its isotopomer, HC15N. We would be able to derive the 14N to 15N isotope ratio if we had HC15N detected. The cometary. 14. N/15N ratio can be a useful tool to understand the. physical conditions in the early Solar System (Hutsemekérs et al. 2009); a. 14. N/15N. ratio of about 330 was derived in the long-period comet Hale-Bopp (Jewitt et al. 1997; Ziurys et al. 1999). However, we did not detect HC15N in both 73P-B and 73P-C on 2006 May 13, and only upper limits were obtained (Tables 3.1 & 3.2). The HCN J = 1–0 transition was also observed toward Comet C/2007 W1 (Boattini) with the KP12M on 2008 June 14 (Table 3.3); however, we did not detect HCN in Boattini during this period of time. The strong HCN J = 3–2 line detected in 73P encouraged us to observe this higher transition of HCN in Boattini. Unfortunately, due to an instrumental failure of the SMT, we were not able to observe the HCN 3–2 line in Comet Boattini. Observations of the HC15N isotope of HCN were also attempted yet were unsuccessful. The non-detection of HCN 1–0 emission in Boattini is kind of unusual as HCN has been found in abundance in most comets. The non-detection of the three hyperfine components of HCN 1–0 transition may be mainly due to the bad weather experienced. During the HCN observation, the only available planet then, Uranus, was not bright enough in a poor weather condition, therefore good focus and pointing were not attainable. Another factor causing the HCN non-detection may be instrumental. Channel-1 receiver was very unstable and jumpy during the run so channel-1 data are not useable through out the run which reduced our integration time to half equivalently hence made HCN data noiser.. 3.3. Formaldehyde and Deuterated Formaldehyde Formaldehyde, H2CO, and its deuterated isotopomer HDCO were searched for in both 73P and Boattini without success. We looked for formaldehyde emission at different H2CO transitions in 73P-C on 2006 May 5, 6, 9 and 14. Cometary formaldehyde was 23.

(33) first identified in Comet Halley and its spatial distribution implies the presence of an extended source of H2CO, e.g. native polymerized H2CO or POM (polyoxymethylene) in the coma (Bockelée-Morvan et al. 2004). Although H2CO has often been seen in many comets, we did not detect H2CO in 73P-C (Table 3.2). The non-detection could be due to instrumental limitations or simply because 73P-C was too small and too faint and contained very little H2CO. Therefore it was no surprise that we did not detect the deuterated H2CO isotope, HDCO, at the same 21,1–11,0 transition at 134,284 MHz in 73P-C either on 2006 May 14 (Table 3.2). The H2CO 21,1–11,0 transition at 150,498 MHz was also searched for in comet C/2007 W1 (Boattini) during 2008 June 17, 19, 20 and 22. Despite our long-hour integration, no H2CO emission was obvious at this transition (Table 3.3). We also observed HDCO emission in Boattini at the same 21,1–11,0 transition on 2008 June 19 and 22 (Table 3.3). On June 19, a slightly blue-shifted (Figure 3.5), likely spectral feature of HDCO at a cometocentric velocity of -1.2 km s-1 was marginally detected but faded away over time. As mentioned previously, comet C/2007 W1 (Boattini) was rather active still which could explain the marginal detection of HDCO; on June 22, there was no more HDCO line profile visible.. 3.4. Deuterated Water and Hydrogen Cyanide In addition to HDCO (the deuterated formaldehyde, see Section 3.3), deuterated hydrogen cyanide (DCN or deuterium cyanide) was also searched for in 73P-C without success on 2006 May 6 in an attempt to derive the cometary D/H ratio of JFCs. Deuterium has been detected in only a few comets, and D/H ratios have only been derived in several others — Comet 1P/Halley (Balsiger et al. 1995), Comet C/1995 O1 Hale–Bopp (Meier et al. 1998), and Comet C/2006 B2 Hyakutake (Bockelee-Morvan et al. 1998) — and none of them is a Jupiter-family member. In fact, even isotope ratios in JFCs are poorly known due to their weak activities. We expect that, however, more advanced instruments (like the ALMA array), which have higher sensitivities, will be much more efficient and effective for observing isotopes in JFCs. Deuterated water, HDO, was also searched for in 73P-C on 2006 May 8 and 10. The 1.3-mm 21,1–21,2 and 2-mm 42,2–42,3 transitions of HDO were observed with the SMT and KP12M, respectively. On 2006 May 8, observations of the 21,1–21,2 24.

(34) transition of HDO was carried out toward 73P-C with no luck; however, a 3-σ upper limit of line intensity was determined. On 2006 May 10.5, more observations of the HDO 42,2–42,3 transition at 143,727 MHz toward 73P-C resulted in, unfortunately, a 2-σ blue-shifted spectral feature (Figure 3.6). Obviously deeper observations with much longer integration time should have been contributed for a firm detection.. 3.5. Cyclopropenylidene (c-C3H2) With its ring structure and many rotational transitions in radio, cyclopropenylidene (c-C3H2) has been observed already in many star-forming regions in our galaxy, such as in the TMC-1 dark cloud (Matthews and Irvine, 1985). However, c-C3H2 has never been detected in any comets to date. Complex molecules with large structure are not often seen in comets, and the existence of complex organic molecules in comets may provide new evidence for an entirely different scenario for the chemical evolution of comets which is important for astrobiology study. As discussed in Section 3.3, for instance, the spatial distribution of H2CO disclosed so far indicates formaldehyde may not be a parent molecule, but rather a daughter molecule coming from an extended source of H2CO in the coma which may be either (native) polymerized H2CO, POM (polyoxymethylene), or even POM-like polymers (Cottini et al. 2004). Likewise it seems likely that cometary c-C3H2 would be produced through the photolytic decomposition of hydrocarbon polymers or aromatic compounds, as this has been suggested as a possible origin for c-C3H2 in UV-irradiated interstellar sources (e.g. Pety et al. 2005). Therefore, cometary c-C3H2 can be a good tracer for studying its precursor hydrocarbon polymers or aromatic compounds in comets. We observed multiple transitions of c-C3H2 on 2006 May 6, 7 and 9 toward 73P-C. The c-C3H2 line of the 52,3–43,2 transition was tentatively detected on May 6.47 in an 18-minute observation (Figure 3.7). Shown in Figure 3.6 are the c-C3H2 spectra taken at 18-minute interval. c-C3H2 was clearly detected in the 1st 18-minute interval; and noticeably the c-C3H2 intensity dropped with time, and the c-C3H2 emission was no longer visible after 36 minutes and could not be further detected in the following days. Evidently the intensity of c-C3H2 was a function of time and dropped as the time went by. Since the linear scale of our beam size was only ~1,700 km in diameter at the 25.

(35) time of the c-C3H2 detection, a gas outburst at ~1 km s-1 would escape from our beam within ~20 minutes. Therefore, it is very likely that we happened to catch the c-C3H2 gas outburst activity in 73P-C in time.. 3.6. Methanol (CH3OH) Methanol, CH3OH, was first reported in observations of Comet 1P/Halley, in its low-resolution spectra (Knacke et al. 1986). Further observations of other comets have also identified spectral features at 3.52 µm as CH3OH line (Hoban et al. 1991). By using the IRAM 30-m telescope, Bockelée-Morvan et al. (1991, 1994) detected several CH3OH rotational lines toward Comets C/1989 X1 (Austin) and C/1990 K1 (Levy) in the radio spectrum as well. Cometary methanol was searched for at a favorable 50,5–5-1,5 transition at 157,179 MHz with an upper energy level (Eu) of 48 K toward 73P-C on 2006 May 10. No CH3OH detection was found. We then checked the wideband receivers MAC of the KP12M and AOS of the SMT for possible chance interlopers of methanol while observing other molecular lines. After careful checking the likely favored CH3OH transitions with their rest frequencies by chance also included in these wideband spectral windows, we found no methanol lines at all in either fragments of 73P or Boattini. It is obvious now that both comets 73P (with a diameter of the nucleus less than 0.5 km) and Boattini were too small thus too faint to be good targets for radio observations even though they were extremely close to the Earth (within 0.2 AU).. 26.

(36) Figure 3.1. The CS J = 3–2 transition observed with the KP12M telescope toward the comet C/2007 W1 (Boattini), on 2008 June 14. The rms noise level is of 31 mK in the TR* scale at a spectral resolution of 250 kHz ch-1. CS was detected only in Comet Boattini, but not in both components B or C of the comet 73P.. 27.

(37) Figure 3.2. The HCN spectrum of the J = 1–0 transition observed toward the comet 73P-B on 2006 May 13 with the KP12M telescope, a slightly blue-shifted (0.1 km s-1) line profile was revealed. The spectral resolution is at 100 kHz ch-1 and the rms noise level is of 33 mK. The three transitions of the hyperfine structure of HCN due to nuclear spin of nitrogen atom are denoted by the fiducial marks, from the left to right, at F = 0–1, 2–1 and 1–1.. 28.

(38) Figure 3.3. HCN J = 1–0 spectra observed toward Comet 73P-C on 2006 May 09, 10 and 13 (top to bottom). The three transitions of the hyperfine structure of HCN due to nuclear spin of nitrogen atom are denoted by the fiducial marks, from the left to right, at F = 0–1, 2–1 and 1–1 in each panel. The spectral resolution is 100 kHz ch-1 for all spectra, with noise levels in the TR* scale at 17, 14 and 19 mK in the top, middle and the bottom panels, respectively. 29.

(39) Figure 3.4. HCN J = 3–2 spectra observed toward 73P-C on 2006 May 5, 7 and 8. The double-peak HCN line profiles are apparent which suggest an expanding shell-like structure of HCN emission. The spectral resolution is of 93.6 kHz ch-1 (smoothed) for all spectra, and the rms noise levels in TA* scales are 59, 67 and 61 mK of the spectra in the top, middle and bottom panels, respectively.. 30.

(40) Figure 3.5. HDCO 21,1–11,0 spectrum of comet C/2007 W1 (Boattini) taken on 2008 June 19.69. A marginal 2-σ detection of a slightly blue-shifted spectral feature at V = -1.2 km s-1 is visible. The spectral resolution is of 100 kHz ch-1 and the rms noise is at 25 mK in T*R scale.. 31.

(41) Figure 3.6. HDO 42,2–42,3 spectrum of 73P-C taken on 2006 May 10.5. A 2-σ marginal detection of a slightly blue-shifted spectral feature at V = -1.3 km s-1 is visible. The spectral resolution is of 100 kHz ch-1 and the rms noise is at 11 mK in T*R scale.. 32.

(42) Figure 3.7. The c-C3H2 spectra of 73P-C taken in three consecutive 18-minute intervals on 2006 May 6.47. (a) A clear detection of c-C3H2 during the 1st 18-minute interval; (b) the of c-C3H2 signal was fading away in the 2nd 18-minute interval, and (c) non-detection of c-C3H2 in the last 18-minute interval. 33.

(43) Table 3.1: Spectral parameters measured of the molecular transitions observed toward comet 73P-B with the KP12M. Molecules CS HCN HC15N. Transition J→J’ 2–1 F=2–1 1–0 F=1–1 F=1–0 1–0. Frequency (MHz) 97980.9 88631.8 88630.4 88633.9 86055.0. Date (UT) 2006 May 14.31. θba (˝) 64. Db (km) 3100. 2006 May 13.76. 71. 3450. 2006 May 13.66. 73. 3500. a. TR* c (K) < 0.054 0.110 ± 0.033 < 0.099 < 0.099 < 0.030. ηc d 0.95 0.95 0.95. Tmb e (K) < 0.057 0.116 ± 0.035 < 0.104 < 0.104 < 0.032. ΔVFWHM f (km s-1) 1.0 0.98 ± 0.32 1.0 1.0 1.0. Wg (K km s-1) < 0.06 0.09 ± 0.03 < 0.10 < 0.10 < 0.03. The half-power beam width (HPBW) of the primary beam. The linear scale of the primary beam of the KP12M at the comet. c The line intensity shown in TR* for KP12M data with the FB1 receiver at 100 kHz ch-1 resolution; if no detection, adopted a 3-σ upper limit for intensity. d The corrected main-beam efficiency. e The main-beam brightness temperature. f Gaussian-fitted spectral line width (FWHM) if there is a detection; otherwise, a linewidth of 1.0 km s-1 is assumed for upper limit calculations. g The integrated line intensity. Values listed are corrected for the main-beam efficiency. b. 34.

(44) Table 3.2: Spectral parameters measured of the molecular transitions observed toward comet 73P-C with the KP12M or SMT. Molecules. Transition J→J’ 3–2 F=2–1 1–0 F=1–1 F=1–0 F=2–1 1–0 F=1–1 F=1–0 F=2–1 1–0 F=1–1 F=1–0. Frequency (MHz) 146969.0 88631.8 88630.4 88633.9 88631.8 88630.4 88633.9 88631.8 88630.4 88633.9. HCN. 3–2. 265884.4. HC15N DCN. 1–0 3–2 21,1–11,0 21,2–11,1 30,3–20,2 31,2–21,1. 86055.0 217238.6 150498.3 140839.5 218222.2 225697.8. CS. HCN. H2CO. Date (UT) 2006 May 14.75. θba (˝) 43. Db (km) 2500. 2006 May 09.66. 71. 4250. 2006 May 10.65. 71. 4150. 2006 May 13.72. 71. 4100. 2006 May 05.56 2006 May 07.51 2006 May 08.65 2006 May 13.81 2006 May 06.62 2006 May 09.33 2006 May 14.61 2006 May 06.28 2006 May 05.29. 28 73 35 42 45 35 33. 2000 1850 1750 4200 2350 2500 2650 2400 2400. TR* or TA* c (K) < 0.099 0.084 ± 0.017 < 0.051 <0.051 0.047 ± 0.014 0.053 ± 0.014 < 0.042 < 0.057 < 0.057 < 0.057 0.695 ± 0.059 0.634 ± 0.067 0.578 ± 0.061 < 0.024 < 0.054 < 0.033 < 0.045 < 0.057 < 0.030. a. ηc d 0.80 0.95. 0.95. 0.95. 0.74 0.95 0.74 0.80 0.80 0.74 0.74. Tmbe (K) < 0.124 0.088 ± 0.018 < 0.054 < 0.054 0.049 ± 0.015 0.056 ± 0.015 < 0.045. ΔVFWHM f (km s-1) 1.0 0.60 ± 0.20 1.0 1.0 1.20 ± 0.39 1.00 ± 0.28 1.0. Wg (K km s-1) < 0.12 0.05 ± 0.01 < 0.05 < 0.05 0.05 ± 0.02 0.05 ± 0.01 < 0.05. < 0.060. 1.0. < 0.06. KP12M. 0.939 ± 0.080 0.857 ± 0.091 0.781 ± 0.082 < 0.032 < 0.073 < 0.041 < 0.056 < 0.077 < 0.041. 1.45 ± 0.07 1.49 ± 0.07 1.48 ± 0.08 1.0 1.0 1.0 1.0 1.0 1.0. 1.08 ± 0.07 1.16 ± 0.07 0.99 ± 0.08 < 0.03 < 0.07 < 0.04 < 0.06 < 0.08 < 0.04. SMT SMT SMT KP12M SMT KP12M KP12M SMT SMT. Telescope KP12M KP12M. KP12M. The half-power beam width (HPBW) of the primary beam. The linear scale of the primary beam of the KP12M or the SMT at the comet. c The line intensity shown in TR* for KP12M data with the FB1 receiver at 100 kHz ch-1 resolution, or in TA* for SMT data with the FB2 receiver at 250 kHz ch-1 resolution, except for the HCN J = 3–2 transition which was measured with the Chirp Transform Spectrometer (CTS) of the SMT at 46.8 kHz ch-1 resolution; if no detection, adopted a 3-σ upper limit for intensity. d The corrected main-beam efficiency. e The main-beam brightness temperature. f Gaussian-fitted spectral line width (FWHM) if there is a detection; otherwise, a linewidth of 1.0 km s-1 is assumed for upper limit calculations. g The integrated line intensity. Values listed are corrected for the main-beam efficiency. b. 35.

(45) Table 3.2 (continued): Spectral parameters measured of the molecular transitions observed toward comet 73P-C with the KP12M or SMT. Molecules HDO HDCO. c-C3H2. CH3OH. Transition J→J’ 21,1–21,2 42,2–42,3 21,1–11,0 41,4–30,3. Frequency (MHz) 241561.6 143727.2 134284.8 150851.9. 52,3–43,2. 249054.4. 62,5–51,4. 251527.3. 70,7–61,6 53,3–42,2 50,5–5-1,5. 251314.3 254987.6 157179.0. Date (UT) 2006 May 08.26 2006 May 10.53 2006 May 14.41 2006 May 09.52 2006 May 06.47 2006 May 09.50 2006 May 06.63 2006 May 07.26 2006 May 07.56 2006 May 06.53 2006 May 10.34. θba (˝) 31 44 47 42 30 30 30 30 40. Db (km) 1950 2550 2750 2500 2100 1850 2050 1950 1950 2000 2350. TR* or TA* c (K) < 0.063 < 0.033 < 0.060 < 0.048 < 0.048 < 0.036 < 0.066 < 0.039 < 0.042 < 0.048 < 0.036. a. ηc d 0.74 0.80 0.80 0.80 0.74 0.74 0.74 0.74 0.80. Tmb e (K) < 0.085 < 0.042 < 0.075 < 0.060 < 0.065 < 0.049 < 0.089 < 0.053 < 0.057 < 0.065 < 0.045. ΔVFWHM f (km s-1) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0. Wg (K km s-1) < 0.09 < 0.04 < 0.08 < 0.06 < 0.07 < 0.05 < 0.09 < 0.05 < 0.06 < 0.07 < 0.05. Telescope SMT KP12M KP12M KP12M SMT SMT SMT SMT SMT SMT KP12M. The half-power beam width (HPBW) of the primary beam. The linear scale of the primary beam of the KP12M or the SMT at the comet. c The line intensity shown in TR* for KP12M data with the FB1 receiver at 100 kHz ch-1 resolution, or in TA* for SMT data with the FB2 receiver at 250 kHz ch-1 resolution, except for the HCN J = 3–2 transition which was measured with the Chirp Transform Spectrometer (CTS) of the SMT at 46.8 kHz ch-1 resolution; if no detection, adopted a 3-σ upper limit for intensity. d The corrected main-beam efficiency. e The main-beam brightness temperature. f Gaussian-fitted spectral line width (FWHM) if there is a detection; otherwise, a linewidth of 1.0 km s-1 is assumed for upper limit calculations. g The integrated line intensity. Values listed are corrected for the main-beam efficiency. b. 36.

(46) Table 3.3: Spectral parameters measured of the molecular transitions observed toward comet C/2007 W1 (Boattini) with the KP12M. Molecules CS HCN. Transition J→J’ 3–2 1–0 F=2–1 1–0 F=1–1 1–0 F=0–1. Frequency (MHz) 146969.0 88631.8 88630.4 88633.9. H2CO. 21,1–11,0. 150498.3. HDCO. 21,1–11,0. 134284.8. Date (UT) 2008 June 14.75. θba (˝) 43. Db (km) 6600. TR* c (K) 0.095 ± 0.031. 2008 June 14.66. 71. 10900. < 0.063. 6650 6800 6900 7200 7600 13000. < 0.117 < 0.069 < 0.039 < 0.102 < 0.036 < 0.051. 2008 June 17.65 2008 June 19.89 2008 June 20.64 2008 June 22.81 2008 June 19.69 2008 June 22.65. 42. 47. a. ηc d 0.80. Tmbe (K) 1.188 ± 0.039. ΔVFWHM f (km s-1) 1.05 ± 0.31. Wg (K km s-1) 1.08 ± 0.03. 0.95. < 0.066. 1.0. < 0.07. < 0.146 < 0.086 < 0.049 < 0.128 < 0.045 < 0.064. 1.0 1.0 1.0 1.0 1.0 1.0. < 0.15 <0.09 < 0.05 < 0.13 < 0.05 < 0.06. 0.80. 0.80. The half-power beam width (HPBW) of the primary beam. The linear scale of the primary beam of the KP12M at the comet. c The line intensity shown in TR* for KP12M data with the FB1 receiver at 100 kHz ch-1 resolution; if no detection, adopted a 3-σ upper limit for intensity. d The corrected main-beam efficiency. e The main-beam brightness temperature. f Gaussian-fitted spectral line width (FWHM). g The integrated line intensity. Values listed are corrected for the main-beam efficiency. b. 37.

(47) Chapter 4 Analysis 4.1. Rotational Temperature and Molecular Column Density Rotational excitation temperature (Trot) is measured from multiple transitions of one molecule, which is an indicator of the physical conditions, such as the (kinetic) temperature and density, of the gas in the inner coma region (Bockelée-Morvan et al. 1994). Thus, Trot can represent kinetic environments in comets and is also an important physical parameter for deriving the column density. In an ideal case, different transitions of one molecule would be observed simultaneously with the same telescope and receiver. However, during our observations, the HCN J = 1–0 and J = 3–2 transitions were observed in comet 73P-C on 2006 May 5, 7 and 8 with the SMT, and on May 9, 10, and 13 with the KP12M, respectively. Thus, to minimize the extent of possible variations of the physical and chemical environments of the comet caused by its evolution during the perihelion, we have chosen the measurements of HCN J = 1–0 transition conducted on 2006 May 8.65 and the J = 3–2 line on May 9.66 when 73P-C was at a distance 1.032 and 1.026 AU, respectively, from the Sun for the derivation of Trot. For a given molecule, by assuming the LTE, which is optically thin for all transition lines, and making the excitation temperature of all transitions equal to Trot, the background temperature is much smaller than Trot and all transitions fall in the Rayleigh-Jeans region. We then followed the work of Turner (1991), by using a rotational diagram to derive Trot, as shown below:. log. 3kW N Eu log e = log − , 2 8π ν S μ g I g k Qrot k Trot 3. (4.1). where W = ∫Tmb dν is the integrated line intensity corrected for the main-beam efficiency (as shown in Tables 3.1, 3.2 and 3.3), S is the line strength, μ is the dipole moment, gI is the reduced nuclear spin weight, gk is the K-level degeneracy, Eu is the. 38.

(48) upper-state energy level of the transition, Qrot is the rotational partition function, k is the Boltzmann’s constant, and N is the total column density. The rotational partition function, Qrot, can be computed differently according to various molecular structures. For linear species, such as CS and HCN, the partition function can be approximated as (Turner 1991): Qrot = σ. kTrot , hB. (4.2). where σ is the multiplicity, h is the Planck’s constant and B is the rotational constant. We note that the left-hand side of Equation 4.1, log (3kW / 8π3νSμ2 gI gk), if plotted on a log–log scale diagram (e.g. Figure 4.1), is a 1st-order linear function of the right-hand side term, (Eu / k), with a negative slope of – [(log e)/Trot] and an intercept of [log (N/Qrot)]. Derivation of the rotational excitation temperature by using Equation 4.1 and plotted on a log–log diagram is called the rotational diagram method.. Figure 4.1. The HCN rotational diagram of Comet 73P-C, based on observations conducted on 2006 May 9 and 10 where goodness of fit was applied to calculate the Trot upper and lower limits. Trot = 71 +−72 24 was derived and was also applied to Comet 73P-B for further calculations.. 39.

(49) By plotting the rotational diagram (Figure 4.1), we measured Trot = 71+−72 24 for. HCN excitation in 73P-C when the comet was at 1.026–1.032 AU from the Sun; the same rotational temperature of 71 K derived from 73P-C is also applied to 73P-B when calculating the total column density of HCN gas in the comet coma. The goodness-of-fit method was applied in order to estimate the error of the Trot derived based on merely two data points. For comet C/2007 W1 (Boattini), we adopted a rotational temperature of Trot = 78 ± 3 K (Villanueva et al. 2011) for further calculations. For single-dish observations, as discussed in the previous section, column densities can be derived from the rotational diagram method. With the same argument and assumption, the total column density of an observed molecule can also be obtained from a derivative of Equation 4.1 in a slightly different format by rearranging Equation (4.1). We have. N=. 3kWQrot E exp( u ) . 2 8π ν S μ g I g k kTrot 3. (4.3). We thus applied the derived Trot = 71 +−72 24 K of 73P-C to all transitions of various molecules observed in both 73P-B and 73P-C. Again, for Boattini, we adopted Trot = 78 ± 3 K for all column density estimations. Table 4.1 lists important molecular and physical parameters of the detected cometary molecules CS and HCN. Table 4.2, meanwhile, lists the column densities in comet 73P and comet Boattini.. 4.2. Gas Production Rates Molecules which are evaporated directly from cometary nuclei are called parent molecules. Here we will apply the Haser model for parent molecular species (Haser 1957) to calculate gas production rates for cometary molecules we detected. Even though CS is known to be a daughter molecule of CS2, due to the very short lifetime of CS2, (~500 sec at 1 AU), we will still treat CS as a parent molecule and apply the Haser model for parent molecules to calculate the CS production rate. Assuming that the parent molecules were sublimated from the nucleus directly outward to the coma, we have the averaged production rate, Q:. 40.

(50) Q = 4π rn2 E ,. (4.5). where E is the evaporation rate (cm-2 s-1) and rn is the radius of cometary nucleus. If the gas expands at a constant speed, Vexp, then the number density, n, is a function of the distance to the nuclear surface, namely, rn. The spherical shell can be presented as: Q . 4π rn2Vexp. n(rn ) =. (4.6). As these molecules are moving outward, their number densities are also decayed exponentially to their original abundances and form a new generation of daughter molecules. Thus, Equation 4.6 becomes: n(rc ) =. Q e − ( rc −rn ) L , (4.7) 2 4π rc Vexp. where L is the scale length of parent molecules and rc is the distance from the nuclear center to the edge of the coma. Here the scale length is defined as L = Vexp τ rh2,. (4.8). where τ is the molecule lifetime which is equal to the reciprocal of the molecular photodissociation rate at a distance 1 AU from the quiet Sun (listed in Table 4.2), and rh is the heliocentric distance (in AU). However, in our case, in which we observed comets 73P and Boattini close to the Earth (~0.08 and ~0.21 AU, respectively), the beam sizes (< 103 and < 104 km) of the telescopes are much smaller than the observed molecular scale lengths (typically ~105 km). Thus, the average column density of a particular molecule can be approximated in the following form (Bockelée-Morvan 2005): N =. Q Vexp d. ,. (4.9). where d is the primary beam diameter in linear scale. With the derived total column densities, we can simply apply Equation (4.9) to obtain Q. All of the calculated results are summarized in Table 4.2. Water is known to be the most abundant molecule in comets. When comparing chemical abundances of various molecules in a comet or chemical compositions 41.

(51) between different comets, we usually normalize the gas production rate of a certain molecule measured with water production rate first. To increase the accuracy and minimize possible uncertainties, we normally assume the values of water production rate measured at the time closest to our observations. Thus, for Comet 73P-C, the water production rates adopted for calculations are 1.06 × 1028 sec-1 and 1.26 × 1028 sec-1 (Dello Russo et al. 2007) for May 5, 7 and 9, accordingly, and 1.65 × 1028 sec-1 and 1.43 × 1028 sec-1 (Schleicher et al. 2011) for May 8 and 10, respectively. For comets 73P-B and Boattini, water production rates of 1.9 × 1028 sec-1 (Kobayashi et al. 2007) and 1.22 × 1028 sec-1 (Villanueva et al. 2011), respectively, were employed. The gas production rates relative to water (in percentage) in 73P and Boattini are listed in the last column of Table 4.2.. 42.

(52) Table 4.1 Molecular and physical parameters of the detected cometary molecular species. Molecules. CS HCN. Dipole Moments a μa (Debye) 1.957 2.984. A -. Rotational Constants a B (MHz) 24495.562 44315.975. C -. Photodissociation Rate c. Lifetime f. (sec-1) 1.0 × 10-5 d 1.3 × 10-5 e. (sec) 1.00 × 105 7.69 × 104. Taken from the JPL molecular database. At 1 AU from the quiet Sun. The reciprocal of the molecular photodissociation rate is the lifetime of the molecule. d Biver et al. (1999). e Jackson et al. (1982). f The duration in which the number of certain molecular species is reduced to a factor of e-1 of its original quantity after being released from cometary nucleus.. a c. 43.

(53) Table 4.2 Molecular column densities and gas production rates in comet 73P-B, 73P-C and comet Boattini. Molecules . Transition J→J’ . Date (UT). r a (AU). L c D b 3 (×10 km) (×104 km) Comet 73P-B. N d (×1012 cm‐2). Q(X) e (×1025 sec‐1). Q(X)/QH2O h (%) [range]. HCN. 1–0. 2006 May 13.76. 1.010. 3.45 4.99 Comet 73P-C. 1.135 +−0.425 0.401. 1.92 +−1.58 1.08. 0.10 +−0.08 0.05. 2006 May 05.56 2006 May 07.51 2006 May 08.65 2006 May 09.66 2006 May 10.65. 1.051 1.038 1.032 1.026 1.021. 2.00 8.01 1.85 8.02 1.75 7.88 4.25 3.16 4.15 6.25 Comet Boattini. 0.589 +−0.169 0.135 0.656 +−0.0.186 154 1.096 +−0.0.327 252 +0.327 1.096 −0.252 0.833 +−0.0.181 172. 0.85 +−0.30 0.23 0.90 +−0.31 0.25 1.42 +−0.52 0.39 +1.02 1.40 −0.68 2.07 +−1.27 0.96. 0.10 +−0.04 0.03 0.09 +−0.03 0.02 0.09 +−0.03 0.02 +0.19 0.11 −0.56 0.15 +−0.09 0.07. 2008 June 14.75. 0.860. 6.60. 1.294 +−0.385 0.356. 4.48 +−3.05 2.19. 0.35 +−0.27 0.18. 3–2 HCN 1–0. CS. 3–2. 3.06. Half-power beam-width (HPBW). The linear scale of the primary beam of KP12M at the comet. c Scale length of molecules when comets are at 1 AU from the Sun. Values listed were derived using Equation (4.8). d Column density; Trot = 71 K derived from 73P-C is also adopted for 73P-B, and Trot = 78 K (Villanueva et al. 2011) is assumed for Boattini. e Gas production rate. h The water production rates adopted for calculations are: a) for 73P-C, 1.06 × 1028 sec-1 on May 5 and 7, and 1.26 × 1028 sec-1 (Dello Russo et al. 2007) on May 9, and 1.65 × 1028 sec-1 and 1.43 × 1028 sec-1 (Schleicher et al. 2011) for May 8 and 10, respectively. b) for 73P-B and Boattini, water production rates of 1.98 × 1028 sec -1 (Kobayashi et al. 2007) and 1.16 × 1028 sec-1 (Lippi et al. 2010), on 2006 May 12 and 2008 May 30, respectively, were applied. a. b. 44.

(54) Chapter 5 Discussions and Summary 5.1. HCN in Comet 73P/Schwassmann-Wachmann 3 Our pre-perihelion observations of comets 73P-B and 73P-C covering a heliocentric distance from 0.974 to 1.210 AU in early May, 2006 had HCN emission detected. HCN has been widely seen in JFCs and has been found in more than twenty comets previously regardless which orbital family they belong to. In this study, we report an 25 HCN production rate of 1.92 +−1.58 sec-1 in 73P-B on 2006 May 13.76. 1.08 ×10 Listed in Table 5.1 are the published HCN production rates of fragment B from other studies taken on various dates during the 2006 apparition of Comet 73P. We found in general, together with our data, the HCN production rate of 73P-B did show a clear trend of decrease during 2006 May 09–15 when the comet was moving from a distance 1.033 AU from the Sun to 1.000 AU. The reducing HCN gas production while the comet was getting closer to the Sun appears to be counterintuitive. On the other hand, during 2006 May 8–9, 73P-B was reported to experience a sudden gas outburst (Lara et al. 2006b, Bertini 2009). However, this outburst event did not last long and the cease of the outburst was noticeable at different wavelengths across most of the EM spectrum, and was also reflected by the sudden plunge of HCN production rates from 6.60×1025 sec-1 on May 10 to 3.23×1025 sec-1 the next day (Table 5.1). Thus it becomes apparent that the decreasing HCN gas production from 2006 May 09 to 16 was largely due to the momentary event of outburst occurred on May 8–9. If we now consider the HCN gas production rate with respect to water, we find the Q(HCN)/Q(H2O) ratio also decreased during the time right after the outburst event from May 10 to 13, but starting from May 14 the ratio soon rose back up. The gas production rates relative to water, Q(X)/QH2O, are often called mixing ratios or, sometimes, simply abundances in cometary study. The nontrivial inconsistency noticed between HCN production rate and HCN mixing ratio suggests HCN molecules may not be well mixed with water ice over the surface layers on the cometary nucleus of 73P-B. 45 .

(55) For Comet 73P-C, the HCN production rate was relatively more stable during pre-perihelion if compared to 73P-B (Table 5.2). The HCN gas production rate of 73P-C was increased by a factor of ~2 from the early April, 2006, to the early May when the heliocentric distance, rh, of 73P-C shortened from 1.27 AU to 1.04 AU. In 2006 May, 73P-C was about 1.0 AU from the Sun basically and the HCN production rate had been rather steady around 2×1025 sec-1 during the period from 2006 May 05 to May 20, except a couple of irregularities occurred with a factor of 2 surge up to ~4×1025 sec-1 around 2006 May 09. The apparent rising of HCN production rate seen near 2006 May 8 and 9 seems real (Table 5.2). If we consider our own results only (Table 5.2), we would see a stable value, ~0.10%, of the measured HCN production rate relative to water, i.e., the abundance or mixing ratio, in 73P-C between 2006 May 5.56 and 8.65. However, it is not apparent in the results obtained by Paganini et al. (2010) who also used the SMT to observe 73P but assumed constant water production rates of 1.9×1028 sec-1 and 1.14×1028 sec-1 for comets 73P-B and 73P-C, respectively. In contrast, we adopted the day-to-day water production rates collected from the literature, as shown in Table 5.2, for HCN mixing ratio computation. For the KP12M observations of 73P-C on 2006 May 9.66 and 10.65, the HCN mixing ratios were found to be 0.11% and 0.15%, respectively, which are, again, relative stable during our observation. Our HCN measurements are consistent with the study done by Bockelée-Morvan et al. (2004) who concluded that HCN abundance is nearly constant around ~0.1%, in most comets – including JFCs. Table 5.3 gives the observed abundances of CS and HCN relative to water of some bright comets in different dynamical groups. Comet 73P broke up further into several more pieces of fragments in its 2006 return and revealed fresh materials once buried deep within the nuclear mantle or beneath the crust. It appears that the HCN mixing ratios of both Fragments B and C of Comet 73P are pretty much consistent with each other. For 73P-B, the HCN mixing ratio is 0.10 with respect to water (H2O = 100), and for the largest fragment C of 73P, an averaged abundance of 0.11 is derived. The similarity in chemical abundance between these two fragments has also been confirmed by IR observations; Dello Russo (2007) suggested high degree of homogeneity exists among 73P-B and 73P-C. With no detection of CS in 73P and with HCN the only molecule detected securely with similar abundances in 73P Fragments B and C, we conclude that 73P-B and C are of similar chemical composition and have gone through similar chemical evolution since their breakup. 46 .