多極行星狀星雲NGC 2440和NGC 6302的分子分佈

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(1)國立台灣師範大學理學院地球科學所碩士論文 Institute of Earth Sciences College of Science National Taiwan Normal University Master thesis. 多極行星狀星雲 NGC 2440 和 NGC 6302 的分子分佈 Molecular Distributions in the Multipolar Planetary Nebulae NGC 2440 and NGC 6302. 研究生：王美雁 (Wang, Mei-Yan). 指導教授：管一政教授 (Prof. Kuan, Yi-Jehng) 共同指導：長谷川辰彥. 博士 (Dr. Hasegawa, Tatsuhiko). 中華民國九十八年六月 June 2009.

(2) Molecular Distributions in the Multipolar Planetary Nebulae NGC 2440 and NGC 6302 Wang, Mei-Yan June 30, 2009.

(3) Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. iii. List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . .. iv. List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii 1 INTRODUCTION. 1. 1.1. Origin and Evolution of Planetary Nebulae . . . . . . . . . . .. 1. 1.2. Molecular Distributions in Planetary Nebulae . . . . . . . . .. 9. 1.3. Multipolar Planetary Nebulae . . . . . . . . . . . . . . . . . . 16 1.3.1. NGC 2440 . . . . . . . . . . . . . . . . . . . . . . . . . 16. 1.3.2. NGC 6302 . . . . . . . . . . . . . . . . . . . . . . . . . 23. 2 OBSERVATIONS AND DATA REDUCTION. 28. 2.1. NGC 2440 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29. 2.2. NGC 6302 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30. 3 MOLECULAR DISTRIBUTIONS IN NGC 2440. 32. 3.1. The central torus . . . . . . . . . . . . . . . . . . . . . . . . . 32. 3.2. The extended components with the systemic velocity . . . . . 37. 3.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39. i.

(4) 3.3.1. Remnants from the CSE ejected during the AGB phase 43. 3.3.2. Swept-up molecular materials from the AGB CSE . . . 43. 3.3.3. Fragments of a blown out torus . . . . . . . . . . . . . 44. 4 MOLECULAR DISTRIBUTIONS IN NGC 6302. 45. 4.1. The central torus . . . . . . . . . . . . . . . . . . . . . . . . . 45. 4.2. The extended components with the systemic velocity . . . . . 51. 4.3. The extended components E1, W1, and W2 . . . . . . . . . . 55. 4.4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61. 5 FUTURE WORK 5.1. 5.2. 65. NGC 2440 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 5.1.1. Extended CO search . . . . . . . . . . . . . . . . . . . 65. 5.1.2. High spatial and high spectral resolution observations . 66. NGC 6302 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 5.2.1. Extended CO search . . . . . . . . . . . . . . . . . . . 67. 5.2.2. H2 observation . . . . . . . . . . . . . . . . . . . . . . 67. 6 CONCLUSIONS. 69. A The detection of a molecular bipolar flow in the multipolar planetary nebula NGC 2440. 76. ii.

(5) Abstract The CO(3−2) distributions in the optical multipolar planetary nebulae NGC 2440 and NGC 6302 are presented in this thesis. The observed CO J = 3 − 2 emission in NGC 2440 shows two major velocity components near the central region which are blue- and red-shifted by 18 km s−1 relative to the systemic velocity of VLSR = 43 km s−1 . The spatial distribution of CO emission shows two emission peaks at the systemic velocity which coincide well with the emission knots in the optical, suggesting that the CO outflow corresponds to one pair of the multiple optical bipolar lobes of the nebula. This particular pair of bipolar lobes seem distinctly rich in heavy molecules compared with the other optical bipolar lobes. The observed CO J = 3 − 2 emission in NGC 6302 also shows two major velocity components at the center which are blueand red-shifted by 8 km s−1 with respect to the systemic velocity of VLSR = 30 km s−1 . The spatial distribution of CO emission shows three extended components at the systemic velocity, an extended component blueshifted by 12−46 km s−1 with respect to the systemic velocity, an extended component redshifted by 30 km s−1 , and an extended component redshifted by 36−56 km s−1 . These extended components give us important insight into the interaction between the multiple flows and the AGB CSE. iii.

(6) List of Figures 1.1. Stellar evolutionary track for a 1 M¯ star . . . . . . . . . . . .. 4. 1.2. The ISW model . . . . . . . . . . . . . . . . . . . . . . . . . .. 5. 1.3. Round, elliptical, & bipolar PNe . . . . . . . . . . . . . . . . .. 7. 1.4. Multipolar & point-symmetric PN . . . . . . . . . . . . . . . .. 8. 1.5. NGC 7027 − channel map of CO(1−0) emission at the systemic velocity (26 km s−1 ) . . . . . . . . . . . . . . . . . . . . 11. 1.6. NGC 7027 − comparison of the CO(1−0) emission and the H2 v=1−0 S(1) emission . . . . . . . . . . . . . . . . . . . . . . . 12. 1.7. NGC 7027 − comparison of the H2 v=1−0 S(1) emission and the Brγ emission . . . . . . . . . . . . . . . . . . . . . . . . . 13. 1.8. BD+30◦ 3639 − CO(2−1) emission & millimeter continuum . . 14. 1.9. He 3−1475 − CO(2−1) contours overlaid with the HST image 15. 1.10 Helix nebula − composite image of the CTIO and HST observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.11 Cometary globules in Helix nebula − mosaic image taken with the HST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.12 Cometary globules in Helix nebula − small area samples . . . 19. iv.

(7) 1.13 Cometary globules in Helix nebula − molecular distribution of a single globule . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.14 NGC 2440 − an optical image . . . . . . . . . . . . . . . . . . 21 1.15 NGC 2440 − an illustration of the multiple lobes in the optical image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 1.16 NGC 2440 − CO(2−1) and CO(1−0) spectra . . . . . . . . . 24 1.17 NGC 2440 − H2 image . . . . . . . . . . . . . . . . . . . . . . 25 1.18 NGC 6302 − the evident butterfly shape in the optical image . 26 1.19 NGC 6302 − CO spectra . . . . . . . . . . . . . . . . . . . . . 27 3.1. NGC 2440 − CO(3−2) spectra . . . . . . . . . . . . . . . . . 33. 3.2. NGC 2440 − channel maps of CO(3−2) . . . . . . . . . . . . 36. 3.3. NGC 2440 − CO(3−2) emission in contours overlaid with an optical image . . . . . . . . . . . . . . . . . . . . . . . . . . . 40. 3.4. NGC 2440 − CO(3−2) emission in contours overlaid with an optical image . . . . . . . . . . . . . . . . . . . . . . . . . . . 41. 3.5. NGC 2440 − CO(3−2) emission in contours overlaid with the molecular hydrogen image . . . . . . . . . . . . . . . . . . . . 42. 4.1. NGC 6302 − channel maps of CO(3−2) . . . . . . . . . . . . 46. 4.2. NGC 6302 − CO(3−2) spectra (1) . . . . . . . . . . . . . . . 48. 4.3. NGC 6302 − sketch of the spatial distribution of the central torus along the line-of-sight direction . . . . . . . . . . . . . . 50. 4.4. NGC 6302 − CO(3−2) emission at lower contour levels of the northeast extended components NE overlaid with an optical image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52. v.

(8) 4.5. NGC 6302 − CO(3−2) emission of the northeast extended components NE overlaid with the HST image . . . . . . . . . 53. 4.6. NGC 6302 − sketch of the spatial distribution of the extended components with the systemic velocity along the line-of-sight direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54. 4.7. NGC 6302 − CO(3−2) spectra (2) . . . . . . . . . . . . . . . 57. 4.8. NGC 6302 − CO(3−2) emission of the extended components E1, W1, and W2 overlaid with an optical image . . . . . . . . 58. 4.9. NGC 6302 − CO(3−2) emission of the extended east component (E1) with a HST image . . . . . . . . . . . . . . . . . . . 59. 4.10 NGC 6302 − long-slit line profiles compared with the optical image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 5.1. NGC 6302 − the H2 v=1−0 S(1) image . . . . . . . . . . . . . 68. vi.

(9) List of Tables 3.1. NGC 2440 − intensity and column density of CO . . . . . . . 34. 4.1. NGC 6302 − positions selected for obtaining spectra at Center, NE, SE, SE, and non-detection region . . . . . . . . . . . 49. 4.2. NGC 6302 − positions selected for obtaining spectra at E1, W1, and W2. . . . . . . . . . . . . . . . . . . . . . . . . . . . 56. vii.

(10) Chapter 1 INTRODUCTION 1.1. Origin and Evolution of Planetary Nebulae. Although planetary nebulae (PNe) has been observed for more than two centuries, basic concepts of their origin and evolution are still uncertain and debated. Our theoretical understanding of the origin of PNe came from Shklovsky (1956), who proposed that PNe are descendants of red giants and progenitors of white dwarfs. The point of view was supported by Abell & Goldrich (1966) who suggested that PNe are the ejected atmospheres of red giants since the expansion velocities of PNe are equal to that of red giants. The evolutionary track of PNe in the late stages of stellar evolution was established by Paczy` nski (1971) and confirmed by further calculations by Schönberner (1979), Iben (1984), and Wood & Faulkner (1986). It is a more. 1.

(11) luminous and even redder type of star, the asymptotic giant branch (AGB) stars, but not normal red giants to be PNe progenitors. After exhausting the supply of hydrogen, a star terminates its core hydrogen burning. Subsequently the core of the star contracts and heats the outer hydrogen layers to expand and cool. As a result the star becomes a red giant with increasing luminosity, following a track along the red-giant branch to the upper right corner of the H-R diagram (Figure 1.1). The helium-rich core of the star continues to shrink and heat the outer layers until helium burning begins. During core helium burning, the star moves along the horizontal branch (for population II stars) or red clump (for population I stars) to the left-hand side of the H-R diagram. At the end of helium burning in the core, the star follows a track along the asymptotic giant branch, which is nearly aligned with the red-giant branch, to the right and upwards on the H-R diagram once more. Stars in this stage are called AGB stars. The star is considered to eject ∼ 50% of its mass during the AGB phase (Wallerstein & Knapp 1998). After that the central star evolves to high temperature with almost constant luminosity, and then turns to the white dwarf cooling track (Bloecker 1995). When the extensive mass loss on the AGB has ceased, and the central star is still too cool to produce enough ultraviolet radiation to ionize the surrounding gases ejected during the preceding AGB phase, it is defined to be the protoplanetary nebula (PPN) (Kwok). When the surface temperature of the central star reaches ∼ 30, 000K, the photo-ionization suddenly commences, and a PN is born. Moreover, only the stars with initial masses between 0.8 M¯ and 8 M¯ are believed to become PNe (Iben & Renzini 1983). During the AGB phase, the large-scale mass loss forms the circumstellar envelopes. 2.

(12) (CSE) which contains lately-produced elements originating from nucleosynthesis within the central stars (Busso et al. 1999). Accordingly, the AGB stars contribute new elements such as crucial biogenic elements, C and O, and return a great quantity of material ( ∼ 50% of the mass from evolved stars) to the interstellar medium (ISM). Therefore, investigating the process going through the AGB - PNe pathway is important to understand their influence on solar system composition and formation, as well as on galactic chemical history. While the nature of the central stars were understood, detailed scenario for ejected CSE of AGB stars evolving into PNe remained a mystery. A different mechanism was required to explain why PNe show definite morphologies, and have higher densities and expansion velocities than the CSE of AGB stars. The breakthrough started with the interacting stellar winds (ISW) model on PNe formation introduced by Kwok, Purton & FitzGerald (1978) and Kwok (1982). The ISW model suggests that the shell-like structures of PNe result from a snow-plow effect in which the slower and denser CSE of AGB stars are compressed and accelerated by later-developed fast stellar winds. Furthermore, the ISW model predicts the existence of a low-density halo standing for the un-shocked AGB CSE, and a high-temperature bubble defining the shocked fast wind (Figure 1.2). However, only the spherical PNe can be ideally explained by the ISW model. Even though PNe evolve from the spherically symmetric CSE surrounding AGB stars, many PNe appear elliptical or bipolar rather than round (Figure 1.3). The generalized interacting stellar winds (GISW) model expands on the ISW model to have an aspherical AGB CSE which forms an. 3.

(13) Figure 1.1 The illustration of stellar evolutionary track for a 1 M¯ star clarifies where each phase is located on the H-R diagram. From: http://iapetus.phy.umist.ac.uk/Teaching/IntroAstro/StellarEvolution.html. 4.

(14) Figure 1.2 A schematic diagram of the structure of a PN according to the ISW model. From Kwok (1994).. 5.

(15) equatorially enhanced region. The fast, radiatively-driven, isotropic stellar winds are hydrodynamically collimated by the equatorial torus (Balick 1987). When we observe the PNe along their symmetric axes, elliptical and bipolar PNe appear to be round PNe (Frank et al. 1993). It seemed promising that all morphological types of PNe known could be reproduced through the interacting winds process by GISW. Shortly afterwards the Hubble Space Telescope (HST) with penetrating spatial resolution (∼ 0.100 ) revealed an unexpected variety of morphologies which could not be accounted for by the models in existence (Balick & Frank 2002). A morphologically unbiased survey of young PNe with the HST showed that most objects have more than one polar axis (often with highly point symmetry) (Sahai & Trauger 1998) (Figure 1.4), and that some PNe with apparently typical bipolar structures actually have multiple outflow axes. The discovery of these structures calls for an even more elaborate scenario. Both magnitude and direction of the mass loss rate and the fast wind velocity may change with time (Kwok 2004). One the other hand, jets or fast collimated outflows have been introduced as the primary agent for breaking spherical symmetry (Sahai & Trauger 1998). Concerning the origin of the anisotropy, binary interaction/rotation (Morris 1987, Soker & Livio 1994, & Livio & Pringle 1997) and magnetic fields (Garc´ıa-Segura et al. 1999, & Blackman et al. 2001) were proposed as essential factors in generating the axial- or point-symmetric structures. Even both of the above types of models are correct (Balick & Frank 2002), no consensus has been reached yet.. 6.

(16) Figure 1.3 Illustrations of morphological types of PNe. (Left) IC 3568 (Bond & NASA), (Upper right) NGC 3132 (Sahai & NASA), (Lower right) M 2−9 (Balick & NASA).. 7.

(17) Figure 1.4 Illustrations of multipolar & point-symmetric PN (Sahai 2000). (Left) Hα image of M 1−37 taken with the WFPC2 on the HST. (Right) False-color image processed from the data in the left panel to enhance sharp structures. The multiple lobes and point-symmetric features are labeled. The symmetric center at the waist region is marked with a cross. The dashed line shows the minor axis. The bright curved edges of lobes N1 and S4 are located point-symmetrically around the waist’s geometric center.. 8.

(18) 1.2. Molecular Distributions in Planetary Nebulae. The dense circumstellar envelopes (CSE) are the direct outcome of intense AGB mass loss. Hence the mass distribution of residual neutral gas in PNe is significant for investigating the formation and following evolution of the nebulae. While the distribution of the ionized gas (through optical and radio imaging) is well determined, the distribution of the neutral gas is still poorly known. The neutral gas component can be studied in CO (e.g., Huggins et al. 1996, 2005), H2 (e.g., Kastner et al. 1996), OH (e.g., Zijlstra et al. 2001), and other molecular species (e.g., Hasegawa 2005, & Ziurys 2006), as well as neutral atoms, H I , C I , O I , etc (e.g., Rodriguez et al. 2002, Bachiller et al. 1994, Liu et al. 2001, & Dinerstein et al. 1995). The infrared lines of H2 merely trace highly excited (by collision at a few 1,000 K or UV radiation) molecular regions. The millimeter lines of CO has turned out to be especially practical probes of the dense and cold (10 to 1,000 K) molecular gas in PNe because CO is relatively abundant and its low-lying rotational lines are easily excited. The expanding molecular envelope has been observed as a bright CO shell in the young PN NGC 7027 (Figure 1.5) (Fong et al. 2006). The systemic velocity (26 km s−1 ) of the channel maps points up the spherical symmetry of the CSE (Fong et al. 2006). The CO emission is depressed toward the core, and shows two openings to the northwest and southeast along a symmetric axis. This feature of CO emission cavity at the central region is coincident. 9.

(19) with the four-lobed clover shape of H2 emission (Figure 1.6) (Cox et al. 2002). Both the morphological and the kinematic structures of the H2 emission reveal a series of holes which are point-symmetric about the center (Cox et al. 2002). These H2 observations demonstrate action of multiple pairs of jets/outflows. In addition, the cavity in H2 emission is filled with the ionized gas (Figure 1.7) (Cox et al. 2002). The molecular hydrogen emission is consequently suggested to trace the photodissociation region (PDR) between the ionized nebula and the surrounding molecular envelope. The molecular component can exhibit distinct feature from the ionized nebula. Take the young elliptical PN BD+30◦ 3639 for example. The ionized nebula displays a ring morphology with millimeter continuum observations which represent free-free emission (Figure 1.8) (Bachiller et al. 2000). However, the CO emission reveals two molecular bullets which are symmetric in position (±300 at P.A. ∼22◦ ) and velocity (±50 km s−1 ) about the central star (Bachiller et al. 2000). The high velocity molecular structures indicate invisible bipolar jets/outflows from the central stellar system that compress the neutral gas into discrete knots. In addition to the jets/outflows, the torus, equatorial enhancement, is also a prominent molecular characteristic of PNe. The region of equatorially enhanced mass loss can be seen as a dark lane oriented perpendicular to the nebular axis in optical images. The comparison of the CO map and the HST image for the young PN He 3−1475 (Figure 1.9) shows that the molecular emission covers the central dark lane (Huggins et al. 2004). On the other hand, the molecular gas can be associated with the small scale structure of PNe such as cometary globules. The globules are dense. 10.

(20) Figure 1.5 NGC 7027 − channel map of CO(1−0) emission at the systemic velocity (26 km s−1 ). The channel widths are 2 km s−1 . The contour levels are in increments of 6 σ (σ = 0.17 Jy beam−1 ). (Fong et al. 2006). 11.

(21) Figure 1.6 NGC 7027 − comparison of the channel map at the systemic velocity (25 km s−1 ) in the CO(1−0) line (from Graham et al. 1993) (grey scale) with that in the H2 v=1−0 S(1) line (contours). The channel widths are 5 km s−1 . The offsets are given with respect to the central star (represented as a filled star symbol). (Cox et al. 2002). 12.

(22) Figure 1.7 NGC 7027 − comparison of the velocity integrated H2 v=1−0 S(1) line emission (grey scale) with the Brγ emission (contours). The offsets are given with respect to the central star (represented as a filled star symbol). (Cox et al. 2002). 13.

(23) Figure 1.8 Millimeter observations of the young PN BD+30◦ 3639. (Top) CO(2−1) emission in integrated intensity. (Bottom) The millimeter continuum. Data from the IRAM interferometer. (Bachiller et al. 2000). 14.

(24) Figure 1.9 He 3−1475 − comparison of the CO(2−1) emission in integrated intensity (contours) with the HST image in Hα+[N II] (grey scale). CO data were taken from the IRAM interferometer. (Huggins et al. 2004). 15.

(25) condensations of molecular gas embedded in the ionized nebula. These structures are best seen in the nearest PN (D∼200 pc) NGC 7293 (Helix Nebula). See Figure 1.10, Figure 1.11 ,& Figure 1.12 (O’Dell et al. 2004). The molecular component of a single globule in NGC 7293 has been resolved in CO and H2 (Figure 1.13) (Huggins et al. 2002). The molecules exist not only in the globule heads but also in the tails. Furthermore, the CO observations demonstrate the molecular gas is quiescent (Huggins et al. 1992, 2002).. 1.3. Multipolar Planetary Nebulae. PNe with more than one polar axis indicate episodic changes in bipolar jet/outflow direction or the operation of multiple jets/outflows with various orientations. The multipolar structures are more eminent in younger PNe, and in general slightly smoothed out in evolved PNe. The molecular distributions at the periphery of the elongated shell of ionized gas in the young PN NGC 7027 prove the early development of the multipolar structure. Accordingly, studying the molecular distributions in a fully developed multipolar PN contributes to a complete picture of the subsequent shaping process and gives us important insight into the kinematical and physical states of the PN. In this thesis, molecular distributions in multipolar PNe NGC 2440 and NGC 6302 are reported.. 1.3.1. NGC 2440. NGC 2440 was ever classified as a simple bipolar PN, but is now regarded as a representative multipolar PN (Cuesta & Phillips 2000, López et al. 16.

(26) Figure 1.10 Helix nebula − composite image of the CTIO and HST observations made with Hα+[N. and [O. III]. II]. as red, an average of Hα+[N II] and [O. III]. as green,. as blue. In each color the image was made by combining the. ACS observations of the inner nebula with the MOSAIC images of the outer nebula. (O’Dell et al. 2004). 17.

(27) Figure 1.11 Helix nebula − the Hα+[N II] mosaic image taken with the ACS on the HST. Sample one is 10200 ×10200 . Samples two, three, and five are 5100 ×5100 . Sample four is 5100 ×10200 . (O’Dell et al. 2004). 18.

(28) Figure 1.12 Cometary globules in Helix nebula − the first three samples of Figure 1.11 was shown in series of negative images. (O’Dell et al. 2004). 19.

(29) Figure 1.13 A cometary globule in the Helix Nebula. (Right) dust absorption, seen against the nebula emission in [O. (Center right) Hα+[N II] 6584 ˚ A. (Center left) H2 v=1−0 S(1). (Left) CO(1−0) central channel. Data from the NTT and IRAM interferometer. (Huggins et al. 2002). 20. III]. 5007 ˚ A..

(30) Figure 1.14 NGC 2440 − the [N II] image obtained with the CFHT (Kwok 2004). 1998). The multipolar lobes have been identified in the optical (Figure 1.14 & Figure 1.15) (López et al. 1998, Cuesta & Phillips 2000). NGC 2440 is one of representative extreme type I planetary nebulae (Kingsburgh & Barlow 1994, & Perinotto 1991). This PN is characterized by an N/O ratio greater than 1 (Kingsburgh & Barlow 1994, & Zuckerman & Aller 1986), a hot central star with Tef f = 170,000 to 200,000 K (Shields et al. 1981, Kwitter & Henry 1996, & Heap & Hintzen 1990), and high expansion velocities up to 200 km s−1 of the ionized gas (Lopez et al. 1998).. 21.

(31) Figure 1.15 NGC 2440 − an illustration of the morphological components of NGC 2440 and their sizes (López et al. 1998). The central bright knots labeled A and B represent the expanding equatorial torus. The symmetric knots marked C and D correspond to the opposite side of the bipolar structure labeled as P.A. = 60◦ . The main bipolar lobe to the northeast and southeast are indicated by a dashed line labeled as P.A. = 35◦ . Another pair of diffuse bipolar lobes with the axis labeled as P.A. = 85◦ is shown as dashed curves.. 22.

(32) The optical studies of NGC 2440 with dramatic improvements in sensitivity and angular resolution have not been matched by molecular studies. CO was first detected in this source by Huggins et al. (1996) and by Dayal & Bieging (1996) (Figure 1.16). The CO(2−1) spectra observed by the two groups consistently show a double peak shape. The CO observations have been limited to seven points, even though the optical size of NGC 2440 is about 8000 and H2 observations imply a widespread, if fragmented, presence of molecular gas in this PN (Figure 1.17) (Latter & Hora 1997). Cold molecular gas in the CO(J = 3 − 2) line has been searched for over a 6000 × 7000 area with a fine sampling interval (600 ) in NGC 2440. The uniform and fine spatial sampling over the optical nebula region allowed us to constrain the extent of CO emission and to detect a bipolar molecular structure associated with one optical bipolar flow.. 1.3.2. NGC 6302. NGC 6302 displays an extreme butterfly shape with two evident lobes separated by an equatorial dark lane in optical images (Figure 1.18). However, the kinematic observation revealed multipolar outflows which emanate from the central region of this PN (Meaburn et al. 1980, 2005). The northwestern lobe of NGC 6302 is measured to be expanding at ≥ 600 km s−1 (Meaburn et al. 2005). NGC 6302 has also been classified as a type I planetary nebula (Perinotto 1991). The elemental abundances are [C/H] = 1 × 10−4 , [N/H] = 8.5 × 10−4 , & [O/H] = 5 × 10−4 (Perinotto 1991). The obscured central star of NGC 6302 was suggested to be a white dwarf or approaching a white dwarf which 23.

(33) Figure 1.16 NGC 2440 − CO(2−1) and CO(1−0) spectra obtained with the IRAM 30 m telescope (Huggins et al. 1996).. 24.

(34) Figure 1.17 NGC 2440 − the H2 image taken with the University of Hawaii 2.2m telescope and the ”QUIRC” 102400 × 102400 array camera (Latter & Hora 1997).. 25.

(35) Figure 1.18 NGC 6302 − the evident butterfly shape in the optical [N II] image (Hua 1997). has a G−type companion (Feibelman 2001), and its excitation temperature is extremely high, ∼ 380, 000 K (Pottasch et al. 1996). The strong CO rotational lines in NGC 6302 indicate the existence of a massive molecular envelope (Huggins et al. 1996, Hasegawa & Kwok 2003). The CO spectra show not only a double-peak profile but also extended wings (Figure 1.19) (Hasegawa & Kwok 2003). The wings extend ∼40 km s−1 from the systemic velocity, and indicate the asymmetric structure of the molecular envelope or the presence of a fast molecular outflow. The CO(J = 3 − 2) emission of NGC 6302 has been searched for over a 8500 × 3000 area with a fine sampling interval (600 ). The scope of CO emission and the molecular components responsible for the extended wings shown in the CO spectra can be investigated through the uniform and appropriate spatial sampling over the optical nebula region. 26.

(36) Figure 1.19 NGC 6302 − C I (3 P1 −3 P0 ), CO(2−1), and obtained with the JCMT (Hasegawa & Kwok 2003).. 27. 13. CO(2−1) spectra.

(37) Chapter 2 OBSERVATIONS AND DATA REDUCTION The CO J = 3 − 2 observations of NGC 2440 and NGC 6302 were both made with the James Clark Maxwell Telescope (JCMT). The JCMT has a half-power beam width (HPBW) of 14” at the frequency of CO(3 − 2), 345.7960 GHz. The receiver was RxB3, a single sideband, dual polarization channel receiver with a typical receiver temperature of about 230 K at 345 GHz. The spectrometer was DAS (Dutch Autocorrelator Spectrometer), a standard spectrometer for common use on the JCMT. The original CO(3−2) spectra were obtained with a frequency resolution of 378 kHz (a channel interval of 312.5 kHz) and an instantaneous band width of 250 MHz. The data were processed with the spectral line data reduction package SPECX.. 28.

(38) 2.1. NGC 2440. The CO(3 − 2) observations of NGC 2440 were made in 2000 October, 2001 October, and 2003 October. The JCMT program ID was M00BC06, M01BC07, and M03BC13. Totally 121 positions were observed, covering a region of about 6000 × 7000 centered at (α, δ) = (07h 41m 55.41s , −18◦ 120 30.700 ) (J2000.0). The sky subtraction was made in a beam switching mode with an azimuth beam throw of 12000 and at a cycle of 1 Hz. Each position was observed as a part of a gridmap of a typical size of 5 × 5 or 3 × 9 grid points with a common grid interval of 600 . The integration time was 30 or 60 seconds at a time for each position. The grid mapping was repeated 5−12 times, hence the total integration time for each position was about 6 minutes for each polarization channel. Pointing was checked every 60−90 minutes with OH231.8 in a continuum five-point mode with RxB3. The pointing uncertainties were about 200 . According to the JCMT SCUBA calibration and imaging document1 , OH231.8 is not resolved at 850 µm or 450 µm with the SCUBA on the JCMT. Therefore, OH231.8 can be regarded as a point-like source for pointing calibration at 345 GHz for the JCMT. We adopt a main beam efficiency ηB of 0.63, which was a JCMT standard facility value at 345 GHz (Matthews, Leech, & Friberg 2004). The intensities of NGC 2440 are expressed in main beam temperature TMB = TA∗ /ηB in this thesis. During data reduction, the spectra from the two polarization channels were averaged, and eight channels were binned. The frequency resolution 1. http://www.jach.hawaii.edu/JCMT/continuum/calibration/sens/oh231.8 2004.html. 29.

(39) of the CO(3 − 2) spectra presented here is 2.5 MHz (2.17 km s−1 ). Only linear baselines were removed from the individual spectra, where the adopted baseline regions were (1) VLSR = −60−0 km s−1 , and (2) VLSR = 80−140 km s−1 . The rms noise levels σMB of the individual spectra presented in the present work are typically about 0.048 K (0.03 K in TA∗ ) at the frequency resolution of 2.5 MHz.. 2.2. NGC 6302. The CO J = 3 − 2 emissions of NGC 6302 were observed in 2000 July and 2002 June. The JCMT program ID was M00AC20 and CANSERV02A05. The observations included a total of 255 positions which covered a region of about 8500 × 3000 . The central position was at (α, δ) = (17h 10m 21.58s , −37◦ 020 46.3900 ) (J2000.0). The observations were made in a raster mode (also called ’on-the-fly mapping mode’). The adopted OFF position was (∆α, ∆δ) = (−18000 , 000 ) for all CO(3 − 2) observations of NGC 6302. In the raster mode, the observing sequence is off-position, on-position-1, on-position-2, on-position-3, ..., to on-position-N. This is a variation of absolute position switching mode. Once the sequence (one row) is over, (on-position-1 − offposition), (on-position-2 − off-position), ..., to (on-position-N − off-position) are recorded as sky-subtracted spectra. Then there will be N spectra. The integration time for each on-position observation is only 6 seconds. On the other hand, the integration time for an OFF position observation was 6 √ seconds × N. Typically N = 9 was used. The sampling interval was 600 (in ∆α and in ∆δ). The same positions were observed repeatedly. (i.e., The. 30.

(40) same area was mapped usually five times and the maps were averaged.) The typical integration time for each position was about 5 × 6 seconds (on) + 5 × 6 seconds (off) = 60 seconds (on+off). During data reduction, only linear baselines were removed from the individual spectra, where the adopted baseline regions were (1) VLSR = −130−−80 km s−1 , and (2) VLSR = 20−70 km s−1 .. 31.

(41) Chapter 3 MOLECULAR DISTRIBUTIONS IN NGC 2440 The CO(3−2) emission was detected at about 45 positions, where the peak intensities are 0.16 to 0.65 K in TMB . Representative spectra are shown in Figure 3.1 for positions (∆α, ∆δ) = (0, 0), (+1800 , +2400 ), (−1800 , −2400 ), (+1200 , +600 ), and (−1200 , −600 ). The peak intensities, noise levels (σMB in TMB ), and integrated intensities are given in Table 3.1 for the five positions.. 3.1. The central torus. The strongest CO(3−2) emission comes from the (0, 0) position. The spectrum at the center has (1) a full width at zero intensity (FWZI) of 75 km s−1 , (2) a line center velocity of 43 km s−1 in VLSR , and (3) two narrow com32.

(42) Figure 3.1 Representative CO(3−2) spectra in NGC 2440. Position offsets (∆α, ∆δ) (arcseconds) are indicated to the left of individual spectra. The spectra have been offset by (from bottom to top) 0, 0.4, 0.8, 1.2, and 1.6 K.. 33.

(43) Table 3.1. NGC 2440 − intensity and column density of CO R. (∆α, ∆δ). TMB (peak). σMB. TMB dV. N (CO). (arcsec). (K). (K). (K km s−1 ). (1015 cm−2 ). 17.19. 7.52. (0, 0). 0.653. 0.054. (−12, −6). 0.291. 0.048 5.02. 2.19. (+12, +6). 0.212. 0.052. 3.21. 1.40. (−18, −24) 0.281. 0.041. 3.16. 1.38. (+18, +24). 0.046. 2.90. 1.27. 0.307. ponents at VLSR = 26 and 61 km s−1 . In addition, the line profile shows two weaker but distinct narrow components at 42 and 51 km s−1 . These features are consistent with the previously reported observations by Huggins et al. (1996) and by Dayal & Bieging (1996). The systemic velocity for the molecular component from the present observation is thus VLSR = 43 km s−1 . The 26 and 61 km s−1 components in Figure 3.1 are blue- and red-shifted by 18 km s−1 from the systemic velocity. The double-horn profile at the central position is indicative of an unresolved, expanding torus or ring. Very similar double-horn CO profiles have been observed in NGC 6072, NGC 6563, and IC 4406, where the dark lanes (likely molecular regions) in optical images show obvious torus morphologies (Cox et al. 1991). As for examples of model double-horn spectra of an unresolved ring, see Ford et al. (2003). Based on these empirical relations. 34.

(44) between the CO profiles and the morphologies, we assume an unresolved, expanding molecular torus for the CO emitting region in NGC 2440. The supposed central torus is probably highly fragmented and the torus morphology may not be readily recognizable. No existing optical image of NGC 2440 reveals a dark lane indicative of a torus. Although a torus morphology is barely distinguishable in any optical (line or continuum) image, López et al. (1998) made a similar suggestion for the central ionized gas of NGC 2440. Another similar suggestion of a torus morphology has been made from H2 observations by Latter et al. (1995) and Kastner et al. (1996). According to the assumption of an expanding molecular torus at the central region of NGC 2440, the velocity shifts of 18 km s−1 of the two prominent spike-like features from the systemic velocity can be interpreted as the expansion velocity Ve of the bulk molecular gas in the central region. The expansion velocity likely reflects the mass loss rate during the late AGB phase. The expansion velocity could be as large as 21 km s−1 , if the expansion velocity is estimated from the full width at half maximum of the CO spectrum at the central position in Figure 3.1. The ionized part of the central, probably toroidal, structure is expanding at 22 km s−1 (López et al. 1998). Consequently, the molecular gas in the central region is expanding at almost the same velocity as the ionized gas in the central region. Figure 3.2 shows the spatial distribution of integrated intensity over a 9 km s−1 interval centered at different velocities (channel maps). The spatial distributions of the 26 and 61 km s−1 components appear in the 24 and 60 km s−1 maps, respectively, in Figure 3.2. These prominent velocity components are concentrated in the central region with a size of about 2400 , although no. 35.

(45) Figure 3.2 Channel maps of CO(3−2). The central velocity in VLSR is indicated at the top left corner in each frame. Each map covers a velocity interval of 9 km s−1 . Both contours and gray scale show the integrated TMB . The lowest contour is 0.4 K km s−1 , and the contour interval is 0.4 K km s−1 , corresponding to a 2σ level for the velocity interval. Position offsets are from (α, δ) = (07h 41m 55.41s , −18◦ 120 30.700 [J2000.0]) ((α, δ) = (07h 39m 41.50s , −18◦ 050 24.000 [J1950])).. detailed structures are resolved in the present observation. Beyond the expansion velocity, fast moving CO emission is apparently recognizable in the spectrum at the central position. The fast blue component is shifted by 20 to 40 km s−1 with respect to the systemic velocity. The fast red component is shifted by 20 to 30 km s−1 relative to the systemic velocity. The fast blue component (0 < VLSR < 20 km s−1 ) is detected only at the central 9 positions with confidence. Likewise, the fast red component (65 < VLSR < 75 km s−1 ) is detected only at several positions near and at the center.. 36.

(46) The distribution of the fast blue emission can be seen in the 6 and 15 km s−1 maps in Figure 3.2. The distribution of the fast red component can be seen in the 69 km s−1 map in Figure 3.2. The fast components are concentrated in the central region that is bright in optical and H2 observations. The presence of the fast CO components are in line with the often suggested idea that the neutral, dense central torus (still containing significant molecular material) is being blown away by very fast outflowing winds. With the angular resolution and S/N levels in the present observation, the details of the fast molecular components are not well constrained.. 3.2. The extended components with the systemic velocity. Near the systemic velocity, the CO emission has an elongated distribution which can be seen in the 33 and 42 km s−1 channel maps in Figure 3.2. The extent of the CO emission near the systemic velocity is about 2000 (northeastsouthwest) by 7000 (northwest-southeast) in the 42 km s−1 map. The emission distribution is nearly point symmetric about the central position, and shows a bipolar morphology. The northeast and southwest emission peaks (hereafter the NE and SW peaks, respectively) are 3000 away from the central position. There is no detectable velocity difference between the NE and SW emission peaks [see the spectra at positions (+1800 , +2400 ) and (−1800 , −2400 ) in Figure 3.1]. The locations of the two CO emission peaks coincide well with those of the optical emission knots NK and SK described by López et al. (1998). (See 37.

(47) Figure 1.15 by López et al. [1998] for NK and SK.) The distribution of the CO emission near the systemic velocity is overlaid with the Digitized Sky Survey (red ) and Canada-France-Hawaii Telescope (CFHT) [N II] images of NGC 2440 in Figure 3.3 and Figure 3.4, respectively. The velocity range for CO contours in Figure 3.3 and Figure 3.4 are both from 35 to 55 km s−1 . (The velocity range for the 42 km s−1 map in Figure 3.2 is from 38 to 47 km s−1 .) The overall distributions of CO emission in Figure 3.2 and Figure 3.3 are very similar to each other, and are not affected by the choice of velocity interval. Low-level emission of CO(3−2) is detected above a 3σ-level in the regions between the central peak and the NE and SW peaks [for example, at positions (+1200 , +1200 ), (+600 , +1800 ), (−600 , −1800 ), and (−1800 , −1200 )]. The CO emission in Figures 3 and 4 (and in the 42 km s−1 map in Figure 3.2) roughly traces the well-collimated optical bipolar lobes, one extending from the center to the northeast and the other extending from the center to the southwest, with a position angle (P.A.) of 35◦ (hereafter the P.A. = 35◦ bilobal structure following the notation by López et al. 1998). Up to the present, at least two bilobal structures (with P.A. = 85◦ and P.A. = 35◦ ) and a possible third one (P.A. = 60◦ ) have been identified from nebular line observations (López et al. 1998). The P.A. = 35◦ bilobal structure is the brightest of the three, and is often referred to as the main lobes. Even though the P.A. = 35◦ bilobal structure is identified based on intensity distribution and velocity, it does not show any distinct nature from the rest of the optical nebula in electron temperature or electron density (Figure 3.3 in Cuesta & Phillips 2000). The detection of CO in the P.A. = 35◦ bipolar lobes (other than the central region) apparently points out that this. 38.

(48) bilobal structure is rich in heavy molecules. The molecular rich property makes the P.A. = 35◦ bipolar lobes distinct from the rest of the extended optical structures of NGC 2440. The lack of a velocity gradient along the P.A. = 35◦ bilobal structure in CO(3−2) is consistent with the optical line observations by López et al. (1998). The lack of a velocity gradient is explained as the bipolar axis being nearly perpendicular to the line of sight (López et al. 1998). The NK and SK optical emission knots are interpreted as working interfaces (shocked regions) between a fast outflowing medium and a slow-moving dense gas by López et al. (1998). The H2 images (Figure 3.5 and Figure 1.17 by Latter & Hora [1997]) show two bright spots to the northeast and southwest coincident with the CO emission peaks and with the optical knots NK and SK. Additional H2 emission features extend to north-northwest, northwest, south-southeast, and southeast. In the present search, CO was not detected with confidence in these extended, fragmental H2 emission regions.. 3.3. Discussion. The origins of CO in the optical NK and SK regions are not clear. Although a formation of CO through shock- or photo-chemistry on a timescale of order 10 to 100 years cannot be ruled out, more conservative scenarios should be considered first. Accordingly, the question reduces to how original CO molecules in a spherically symmetric CSE ejected during the AGB phase survived and reached where it is detected in the present observation. There are three possible scenarios listed below to explain the presence of. 39.

(49) 11m30.0s. NGC 2440 CO(3-2). DEC(2000). -18d12m00.0s. 30.0s. N. 13m00.0s E. 7h41m59.0s. 7h41m55.0s RA(2000). 52.0s. Figure 3.3 CO(3−2) emission in contours is overlaid with the Digitized Sky Survey image (gray scale) of NGC 2440. The VLSR interval for CO emission is 35−55 km s−1 . The lowest contour and the contour interval are both 0.63 K km s−1 , which corresponds to about 2σ.. 40.

(50) N E. Figure 3.4 CO(3−2) emission in contours is overlaid with the [N II] image (gray scale) of NGC 2440 obtained with the CFHT (Kwok 2004). North is to the top, and east is to the left. The VLSR interval for CO emission is 35 to 55 km s−1 . The lowest contour and the contour interval are both 0.63 K km s−1 , which corresponds to about 2σ.. 41.

(51) N E. Figure 3.5 CO(3−2) emission in contours is overlaid with the H2 [v = 1 − 0 S(1)] image (gray scale) of NGC 2440 obtained with the CFHT (C. M. Mariappan et al. 2007, in preparation). North is to the top, and east is to the left. The VLSR interval for CO emission is 35 to 55 km s−1 . The lowest contour and the contour interval are both 0.63 K km s−1 , which corresponds to about 2σ.. 42.

(52) CO detected in the NK and SK regions.. 3.3.1. Remnants from the CSE ejected during the AGB phase. The CO gas traveled with the constant expansion velocity Ve (= 18 km s−1 ). Fast multiple bipolar flows may have evacuated significant volume of the spherical CSE ejected during the AGB phase. Subsequently, low density parts of the originally molecular volume would be photodissociated. Local density enhancements in the CSE (dust and H2 shielding) such as the NK and SK regions could prolong the lifetime of CO. The evident CO(3−2) emission in the NK and SK regions is excited by an impinging fast, collimated wind.. 3.3.2. Swept-up molecular materials from the AGB CSE. The formerly spherical AGB CSE was carried by later developed multiple collimated fast flows. The molecular gas was swept up or pushed aside. The swept up gas was accelerated and compressed. Small-scale condensations may have generated in this process. The swept up gas resulted in a bilobal (hollow) morphology. The P.A. = 85◦ bilobal structure (López et al. 1998) may have been formed this way. The P.A. = 35◦ may be a later (but before ionization) development. The swept up molecular material at the both ends are the CO gas associated with NK and SK optical knots. The CO gas between the central star and the NK and SK knots was originally AGB CSE, but was swept or pushed aside (in the lateral direction) to form a surrounding shell. Because the P.A. = 85◦ bilobal structure was old, the molecular gas. 43.

(53) was dispersed and subsequently photodissociated. The P.A. = 35◦ bilobal structure is younger, and the swept up molecular gas was denser. As a result, the CO gas associated with P.A. = 35◦ bilobal structure has not been photodissociated.. 3.3.3. Fragments of a blown out torus. Initially, the system might have developed a normal bipolar structure with a central torus and a bipolar nebula. The P.A. = 85◦ bilobal structure might have been the early bipolar lobes. Most of the molecules in the early bilobal structure have already been photodissociated. Later, a strong and highly collimated bipolar wind (corresponding to the present P.A. = 35◦ bilobal structure) developed with an axis almost intersecting the early toroidal structure. The new flow was sufficiently strong that parts of the still-molecular torus was blown away in dense fragments. The molecular material near the flow axis was blown to the current locations of the NK and SK. The original dense molecular fragments were accelerated on the way. In this scenario, the weak CO emission between the central region and the NK and SK peaks represents possible fragments of blown apart molecular gas off the flow axis. The fastblue and fast-red emission, seen in the CO spectrum at the central position in the present work, are shifted by only 20−40 km s−1 from the systemic velocity. If the assumed expansion velocity of 18 km s−1 of the postulated torus is taken into account, the extra velocity of the supposedly blown away fast CO gas is at most 20 km s−1 near the central position. If the acceleration of the dense molecular gas by the fast wind is gradual, then the molecules may survive for a few 1000 yrs. 44.

(54) Chapter 4 MOLECULAR DISTRIBUTIONS IN NGC 6302 4.1. The central torus. The spatial distribution of the CO J = 3 − 2 emission in NGC 6302 is shown as a function of velocity (channel maps) in Figure 4.1. The CO(3−2) emission comes principally from the central region within an area of 4000 × 4000 . The emission peak of the central component slightly shifts from west to east in the panels as the velocity increases from −47.5 km s−1 to −17.5 km s−1 . The representative spectrum for the central component (Figure 4.2) has an evident double-peak profile with a total velocity extent (FWZI) of 60 km s−1 . The positions selected for obtaining this spectrum is listed in Table 4.1. The systemic velocity for the molecular component from the line center is 45.

(55) Figure 4.1 Channel maps of CO(3−2) in NGC 6302. The central velocity in VLSR is indicated at the top left corner in each frame. Each map covers a velocity interval of 15 km s−1 . Both contours and gray scale show the integrated TA∗ . The lowest contour is 0.96 K km s−1 , corresponding to about 3 σ level. The contour interval is 1.92 K km s−1 .. 46.

(56) VLSR = −30 km s−1 . The double-peak profile of the spectrum obtained at the center and the shift of emission peak from west to east with the increase of VLSR suggest an unresolved, expanding torus which has an axis in the east-west direction. The high angular resolution interferometric observations of CO J = 2 − 1 emission with the SMA resolved the expanding torus with a size of 3000 × 1000 and demonstrated that the torus axis is in the east-west direction (Trung et al. 2008). The optical image of NGC 6302 (Figure 1.18) which exhibits an equatorial dark lane supports the presence of a molecular torus oriented in the north-south direction as well. The presumed central torus will then be expanding at ∼8 km s−1 which corresponds to the velocity shifts of the two peak features from the systemic velocity. The expansion velocity estimated from our observation is consistent with that obtained by Peretto et al. (2007). The spatial distribution of the molecular torus and the ionized gas along the line-of-sight direction of NGC 6302 is illustrated in the sketch (Figure 4.3). The inclination angle of 15◦ of the torus axis with respect to the plane of the sky is inferred from radiative transfer modeling (Trung et al. 2008). The conical shell is seen to tilt at the same degree as the torus. The northwestern lobe axis is 12.8◦ to the plane of the sky, which is measured from spectroscopic observations of nebular lines (Meaburn et al. 2005).. 47.

(57) Figure 4.2 Representative CO(3−2) spectra for the central component and the northeast extended component (NE) in NGC 6302. The spectra have been offset by (from bottom to top) 0, 0.4, 0.8, 1.2, and 1.6 K.. 48.

(58) Table 4.1. NGC 6302 − positions selected for obtaining spectra at Center, NE, SE, SE, and non-detection region. Component. (∆α, ∆δ) (arcsec). Center. (−600 , 0), (0, 0), (+600 , 0), (0, −600 ), & (0, +600 ), (−600 , −600 ), (+600 , −600 ). NE. (+1200 , +1800 ), (+1800 , +600 ), (+1800 , +1200 ), & (+1800 , +1800 ), (+3000 , +1200 ), (+3000 , +1800 ), & (+2400 , +600 ), (+2400 , +1200 ), (+2400 , +1800 ). SW. (−2400 , 0), (−2400 , −600 ), (−2400 , −1200 ), & (−1800 , −1800 ), (−1200 , −1800 ). SE. (−600 , −1800 ), (0, −1800 ), (+600 , −1800 ), & (+1200 , −1200 ), (+1200 , −1800 ), (+1800 , −1800 ). No detection (−7200 , −1800 ), (−6000 , +1800 ), (−4200 , −1800 ), & (+4800 , +1800 ), (+6600 , +600 ), (+7200 , +600 ). 49.

(59) Figure 4.3 NGC 6302 − sketch of the spatial distribution of the central torus and the ionized gas along the line-of-sight direction.. 50.

(60) 4.2. The extended components with the systemic velocity. The channel map of the CO(3−2) emission near the systemic velocity (−32.5 km s−1 ) shows extended distributions to the northeast, to the southwest, and to the southeast. Representative spectra for the northeast component, the southwest component, and the southeast component (hereafter the NE, SW, and SE components, respectively) are shown in Figure 4.2. The positions selected for obtaining each spectrum in Figure 4.2 are listed in Table 4.1. The spatial relations to the optical nebula of the NE component, the SW component, and the SE component can be seen in the plots of the CO(3 − 2) emission overlaid on the [N II] images of NGC 6302 in Figure 4.4 and Figure 4.5. The velocity range for CO(3 − 2) contours in Figure 4.4 and Figure 4.5 are from −35 to −20 km s−1 which is selected to achieve an clearer representation for the NE component and the SW component. The CO J = 3 − 2 line profile for the NE component is centered at −32 km s−1 , near the systemic velocity. The emission peak of the NE component is about 2500 away from the center. The extent of the NE component is about 2200 (east-west) by 2000 (north-south). The upper flat contours in Figure 4.4 and Figure 4.5 are due to the boundary of the observed area. The location of the NE component is right outside the optical structure (possibly an outflow) extending to the north east (Figure 4.4 and Figure 4.5), and is at the north of the southeast lobe. The spatial distribution of the NE component with respect to the optical northeast flow and the molecular torus along the lineof-sight direction of NGC 6302 is illustrated in the sketch (Figure 4.6).. 51.

(61) Figure 4.4 CO(3−2) emission of the northeast extended components NE1 in contours is overlaid with an [N II] image (gray scale) of NGC 6302 (Hua 1997).. The lowest contour is 1.02 K km s−1 , corresponding to about 3 σ. The contour interval is 0.34 K km s−1 for contour levels from 1.02 K km s−1 to 2.38 K km s−1 .. 52.

(62) Figure 4.5 CO(3−2) emission of the northeast extended components NE1 in contours is overlaid with the HST WFPC2 image (gray scale) of NGC 6302. The F658N image (λ0 = 6590˚ A, ∆λ0 = 28.5˚ A) is used as an 6584˚ A [N II] image. The. lowest contour is 1.02 K km s−1 , corresponding to about 3 σ. The contour interval is 0.34 K km s−1 for contour levels from 1.02 K km s−1 to 2.38 K km s−1 .. 53.

(63) Figure 4.6 NGC 6302 − sketch of the spatial distribution of the extended components with the systemic velocity along the line-of-sight direction.. 54.

(64) The SE component extends out to ∼ 3200 (at 3σ level) from the center, along the southern wall of the conical-like shell of the ionized gas (Figure 4.5). The CO J = 3−2 line for the SW component shows a profile with a double peak. The left peak of the profile is blueshifted by 8 km s−1 relative to the systemic velocity, corresponding to the blueshifted velocity of the molecular torus. Moreover, the SW component is located near the central region. The emission of the left peak of the profile consequently comes from the central molecular torus. The right peak of the profile is centered at about −30 km s−1 , corresponding to the systemic velocity. The spatial distribution of the SW component along the line-of-sight direction of NGC 6302 is illustrated in the sketch (Figure 4.6). Figure 4.4 displays the spatial distribution of the SW component projected to the plane of the sky. The SW component appears to be located at the south of the prominent northwest lobe.. 4.3. The extended components E1, W1, and W2. In addition to the extended components with the systemic velocity, the channel maps of the CO(3 − 2) emission (Figure 4.1) reveal three extended components which are the east component (hereafter the E1 component) at a blueshifted velocity (−62.5 km s−1 ), the west component one (hereafter the W1 component) at a redshifted velocity (12.5 km s−1 ), and the west component two (hereafter the W2 component) at a redshifted velocity (−2.5 km s−1 ). Figure 4.7 shows the representative spectra for the extended emission components E1, W1, and W2. The positions selected for obtaining each 55.

(65) Table 4.2. NGC 6302 − positions selected for obtaining spectra at E1, W1, and W2. Component. (∆α, ∆δ) (arcsec). E1. (+4200 , +600 ), (+3600 , +600 ), (+3600 , 0), & (+3000 , +600 ), (+3000 , 0), (+3000 , −600 ). W1. (−2400 , 0) & (−1800 , +600 ). W2. (−6000 , +600 ), (−6000 , 0), (−6000 , −600 ), & (−5400 , −600 ), (−6600 , 0), (−6600 , −600 ). spectrum in Figure 4.7 are listed in Table 4.2. The spatial distribution of the E1 component, the W1 component, and the W2 component is illustrated in the plots of the CO(3 − 2) emission overlaid on the [N II] images of NGC 6302 in Figure 4.8 and Figure 4.9. The velocity range for CO(3 − 2) contours of the E1 component is from −70 to −50 km s−1 , for the W1 component is from 5 to 20 km s−1 , and for the W2 component is from −10 to 3 km s−1 . The E1 component is blueshifted by 12−46 km s−1 with respect to the systemic velocity. The emission peak of the E1 component is about 3200 away from the center. The extent of the E1 component is about 2000 × 2000 . The E1 component appears to be located at the eastern side of the wall-like clumps of the ionized gas (Figure 4.9). The wall-like clumps and the knots with the wind-tail structures which point away from the center suggest that the. 56.

(66) Figure 4.7 Representative CO(3−2) spectra for the central component and the extended components E1, W1, and W2 in NGC 6302. The spectra have been offset by (from bottom to top) 0, 0.4, 0.8, 1.2, and 1.6 K.. 57.

(67) Figure 4.8 CO(3−2) emission in contours is overlaid with a [N II] image (gray scale) of NGC 6302 (Hua 1997). The extended emission peaks are labeled E1, W1, and W2. The lowest contour for E1 is 1.2 K km s−1 , corresponding to about 3 σ. The contour interval for E1 is 0.4 K km s−1 . The lowest contour for W1 is 1.02 K km s−1 , corresponding to about 3 σ. The lowest contour for W2 is 0.96 K km s−1 , corresponding to about 3 σ. The contour interval for W2 is 0.32 K km s−1 .. 58.

(68) Figure 4.9 CO(3−2) emission of the northeast extended east components (E1) in contours is overlaid with the HST WFPC2 image (gray scale) of NGC 6302. The F658N image (λ0 = 6590˚ A, ∆λ0 = 28.5˚ A) is used as an 6584˚ A [N II] image. The. lowest contour is 1.2 K km s−1 , corresponding to about 3 σ. The contour interval is 0.4 K km s−1 .. 59.

(69) gas is compressed by the fast wind from the west. The CO(3 − 2) emission of the E1 component demonstrates the presence of the molecular gas in the eastern region of the wall-like clumps. The spatial distribution of the E1 component along the line-of-sight direction of NGC 6302 is illustrated in the sketch (Figure 4.6). The emission peak of the W1 component is about 2200 away from the center. The extent of the W1 component is about 1700 (northeast-southwest) by 800 (northwest-southeast). The CO J = 3 − 2 line profile for the W1 component exhibits two velocity components. One is redshifted by 36−56 km s−1 relative to the systemic velocity; the other is blueshifted by 2−22 km s−1 with respect to the systemic velocity. The W1 component can be identified obviously in the channel map at redshifted velocity (12.5 km s−1 ). On the other hand, the position, (−2400 , 0), used to obtain the spectrum for the W1 component belongs to the SW component in the channel map near the systemic velocity (−32.5 km s−1 ); the position, (−1800 , +600 ), used to obtain the spectrum for the W1 component belongs to the central torus in the channel map at blueshifted velocity (−47.5 km s−1 ). Therefore, only the redshifted velocity component, W1 component, will be further discussed. The spatial distribution of the W1 component and the ionized gas is shown in Figure 4.8. The radial velocities of the ionized gas at the location of the W1 component along the line of sight can be estimated from the PV array of [N II] λ6584 profiles (Figure 4.10) (Meaburn et al. 2005). The PV arrays for different slit positions across the northwest lobe of NGC 6302 show the radial expansion of this optical lobe (Meaburn et al. 2005). The ionized gas of the northwest lobe at the location of the W1 component along the line of. 60.

(70) sight appears to be redshifted by ∼ 30 to 50 km s−1 relative to the systemic velocity. Based on an assumption of similar kinematics of the molecular gas and the ionized gas at the location of the W1 component along the line of sight, the W1 component is inferred to be located at the periphery of the northwest lobe. The spatial distribution of the W1 component along the line-of-sight direction of NGC 6302 is illustrated in the sketch (Figure 4.6). The peak of the CO J = 3−2 line profile for the W2 component is centered at about −2 km s−1 , which is redshifted by 30 km s−1 with respect to the systemic velocity. The extent of the W2 component is about 2000 × 2000 . The emission peak of the W2 component is about 6200 away from the center, and is located at the border of the ionized gas (Figure 4.8). The W2 component does not show a clear relation to any component of NGC 6302. The spatial distribution of the W2 component along the line-of-sight direction of NGC 6302 is uncertain. The sketch illustrates only one possibility (Figure 4.6).. 4.4. Discussion. The expanding torus which is coincident with the obvious dark lane in the optical image of NGC 6302 is nearly edge-on and extending from north to south. The spatial distributions of the extended NE, SE, SW, E1, W1, and W2 components along the line-of-sight direction demonstrate that they are not perpendicular to the torus axis. Hence the extended molecular components revealed in our observation are not part or extension of a torus. According to Figure 4.4 and Figure 4.6, the NE, SW, E1, and W1 components are located within the overall conical-shape/butterfly-shape struc-. 61.

(71) Figure 4.10 (Top) PV array of [N II] λ6584 profiles for the east-west slit position shown in the bottom panel. The green line indicates the systemic heliocentric radial velocity of V sys = −29.8 ± 1 km s−1 . The red line indicates the redshifted velocity of the ionized gas. (Bottom) The Hα+[N II] image of NGC 6302. The orange line indicates the location of the west component one (W1). (Meaburn et al. 2005). 62.

(72) ture, and the SE component distributes along the southeast edge of the conical structure.. Hence the formation activities of the overall conical-. shape/butterfly-shape morphology did not wipe out the molecular gas within the overall conical structure. The CO gas close to the southeast border of the shell may be entrained by the southeast-direction flow which is well collimated. The NE component lies in the north of the southeast optical lobe (Figure 4.4); the SW component lies in the south of the northwest optical lobe. The NE component lies to the end of the northeast flow which appears collimated in the optical image of NGC 6302. The location of the NE component relative to the optical flow in NGC 6302 resembles that of the NK and SK knots relative to the optical flow in NGC 2440. On the basis of the discussion of the CO gas associated with the NK and SK optical knots in NGC 2440, the NE component located at the end of the northeast flow in NGC 6302 probably originates from the remnant from CSE ejected during the AGB phase or the swept-up molecular material from the AGB CSE. The E1 component is located between the conical-shape/butterfly-shape shell and the periphery of the southeast lobe (Figure 4.6); the W1 component is located between the overall conical shell and the periphery of the northwest lobe. Furthermore, the E1 component is blueshifted by 12−46 km s−1 with respect to the systemic velocity; the W1 component is redshifted by 36−56 km s−1 . The actual velocities for the E1 and W1 components are expected to be greater than or equal to the blue- and red-shifted velocities. The E1 and W1 components exhibit higher velocities than the expansion velocity Ve (= 8 km s−1 ) of the dense molecular torus in NGC 6302. Therefore, these extended. 63.

(73) molecular components are not simply remnants from the CSE ejected during the AGB phase. No molecular component is inferred to be located within the northwest lobe and the southeast lobe in our observation (Figure 4.6). The collimated fast flows swept up or pushed aside the molecular gas. The blue- and redshifted velocities of the E1 and W1 components demonstrate that the CO gas is accelerated when swept up or pushed aside by the fast flows.. 64.

(74) Chapter 5 FUTURE WORK 5.1 5.1.1. NGC 2440 Extended CO search. The H2 images (Figure 3.5 and Figure 1.17 by Latter & Hora [1997]) in this thesis both show an extended spherical distribution with a radius of 3000 to 4000 surrounding the optical nebula. However, the present CO observation does not cover the ring-like structure of the H2 emission. On the other hand, if the origin of the CO gas in the NK and SK regions is remnant from the AGB CSE, some CO may still exist at many locations with similar distances (∼ 3000 ) from the central star. An extended CO search with a better angular resolution and a better sensitivity may reveal extended but fragmentary CO gas. Moreover, the IRAM 30 m telescope (CO 2−1) and the JCMT (CO 3−2) are now equipped with multi-beam receivers. Such an extended CO search is feasible with these telescopes at present.. 65.

(75) 5.1.2. High spatial and high spectral resolution observations. In order to confirm whether the CO detected at the NK and SK peaks represents possible fragments of a blown out torus, it is essential to study the spatial distribution of the residual molecular gas of the torus and the direction of the flow which blow away the molecular gas from the torus. Although the equatorial torus can be easily recognized as a dark lane in images of NGC 6302, NGC 7027, etc., it is difficult to identify the torus structure and its orientation with respect to the bipolar flows in images of NGC 2440. The CO(3 − 2) observations show a double-horn profile at the center and indicate the presence of a molecular torus expanding at 18 km s−1 . However, the single dish CO observations have too poor angular resolution to clarify the torus structure. A CO observation with a velocity resolution of 1 km s−1 and an angular resolution of 100 may detect a pattern of (probably fragmented) expanding ring with a likely diameter of 1000 to point out the direction of the powerful collimated flow. Such a spatio-kinematic observation should be possible with the currently existing telescopes such as the Plateau de Bure Interferometer (PdBI) (CO 2 − 1) and the Submillimeter Array (SMA) (CO 2 − 1 or 3 − 2). However, the required observing time will be several nights to attain a satisfactory sensitivity. High spatial (0.500 ) and high spectral (8.7 km s−1 ) resolution near-infrared spectro-imaging of NGC 7027 reveals the detailed morphology and kinematics of the H2 emission (Cox et al. 2002). The spatio-kinematic observation of H2 in NGC 2440 whose velocity resolution is about 2 km s−1 will allow us to 66.

(76) isolate the torus. Furthermore, the orientation of the torus will be determined by mapping P-V maps at various position angles.. 5.2 5.2.1. NGC 6302 Extended CO search. The present CO(3 − 2) observations of NGC 6302 do not extend to the tip of the prominent northwest lobe, the southeast lobe, and the southwest lobe in optical images. An extended CO search covered the whole extent of the nebula will contribute to a complete picture of the extent of CO emission and the interaction between the multiple flows and the AGB CSE.. 5.2.2. H2 observation. The previous H2 observation of NGC 6302 (Figure 5.1) did not reveal any distinct component due to the lack of spatial resolution (Kastner et al. 1996). Higher resolution deep images of the H2 emission in NGC 6302 will allow us to resolve finer structures of the shocked gas at the interface where the highvelocity outflows interact with the slower AGB CSE.. 67.

(77) Figure 5.1 NGC 6302 − the H2 v=1−0 S(1) image. North is up, and east is to the left. (Kastner et al. 1996). 68.

(78) Chapter 6 CONCLUSIONS The CO(J = 3 − 2) line emission was searched for over a 6000 × 7000 region in the multipolar planetary nebula NGC 2440. CO was detected in the central 2400 × 2400 region. In addition, the CO line emission extends to the northeast and southwest, tracing the optical bilobal structure with a position angle of 35◦ . The P.A. = 35◦ bilobal structure is distinct from the rest of the extended ionized lobes in that it is rich in heavy molecules. The observations of CO(3 − 2) emission covered a region of about 8500 × 3000 in the multipolar planetary nebula NGC 6302. In addition to the well-studied central torus region, the CO (3 − 2) emission with the systemic velocity shows extended distributions to the northeast, to the southwest, and to the southeast. The CO (3−2) emission at a blueshifted velocity (−62.5 km s−1 ) exhibits an extended component in the east, and the CO (3−2) emission at redshifted velocities (12.5 km s−1 and −2.5 km s−1 ) reveal tow extended components in the west. The molecular components detected within the overall conical-shape structure cannot be explained by the interacting stellar 69.

(79) winds (ISW) or generalized interacting stellar winds (GISW) models. The operation of jets/collimated outflows with various orientations can explain the existence of residual molecular gas between jets/collimated outflows. The extended components located close to the northwest and southeast lobes suggest the molecular gas to be entrained or accelerated by the jets/collimated outflows.. 70.

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(85) Appendix A The detection of a molecular bipolar flow in the multipolar planetary nebula NGC 2440. 76.