RADIO FREQUENCY SPECTRAL LINES ASSOCIATED WITH INFRARED OBJECTS by PHILIP RAYMOND SCHWARTZ S.B., Massachusetts Institute of Technology (1966) Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy at the Massachusetts Institute of Technology May, 1971 Signature of Author Veparlment of Physics, May 7, 1971 Certified by Thesis Supervisor Accepted by Chal-rmanrDepart1mental Committee on Archives Graduate Students MAY 24 1971 'LIBRRIESE - 2 - RADIO FREQUENCY SPECTRAL LINES ASSOCIATED WITH INFRARED OBJECTS by PHILIP RAYMOND SCHWARTZ Submitted to the Department of Physics on May 7, 1971, in partial fulfillment of the requirements for the degree of Doctor of Philosophy. ABSTRACT This thesis describes observations of radio frequency spectral lines, particularly the 616-523 H 2 0 rotational transition at 1.35 cm, in a number of galactic objects in- cluding HII regions and late type stars. H20 emission has been found to be definitely a maser type process originating from sources with typical dimensions of the order of a few A.U. The emission is highly variable in time and is associ- ated with OH emission both in position and radial velocity. In many cases, H 20 emission is found to occur in objects which are strong infrared emitters and a survey of late type stars has revealed that a number of otherwise normal M type variable stars are sources. Emission from M stars occurs at velocities of a few km/sec with respect to the star and varies in intensity in phase with the infrared variations possibly indicating that the H2 0 maser is pumped by infra- red radiation from the star. Stars with H 20 emission are usually also OH sources but at the main lines rather than the 1612 MHz transition usually associated with infrared star/OH sources demonstrating an intimate connection between the two masering phenomena. An analysis of the conditions required to produce H20 masering produces the result that the emission can be pumped by the 2V continuum from a star and that the maser is probably located in the circumstellar region of a star undergoing mass loss. The discovery of H20 and OH emission from certain late type stars represents the identification of a previously unknown process in ap- parently normal stars which can be studied at radio, infra- red and optical wavelengths. Thesis Supervisor: Alan H. Barrett Professor of Physics - 3 - ACKNOWLEDGMENTS During the nearly three years of work reported in this thesis, I have had the good fortune to be associated with a number of other individuals connected with radio astronomy whose assistance, advice and friendship I value. Portions of the work on H20 emission from HII regions was done in cooperation with David Buhl, Lewis E. Snyder, M. L. Meeks, Joseph Waters, Barry E. Turner and Robert Rubin. I would like to thank them for their efforts and, in some cases, for the use of their data prior to publication. The VLBI observations of H20 sources were performed by a group com- posed of individuals connected with MIT, the U.S. Naval Re- search Laboratory and the Smithsonian Astrophysical Obser- vatory including James Moran, B. F. Burke, D. C. Papa, George Papadopoulos, Kenneth Johnston, S. H. Knowles and W. T. Sullivan. Finally, I am indebted to Joseph Carter and D. L. Thacker for the work that they have done on both the VLBI project and the other observations reported here. Mr. Car- ter's technical expertise and understanding of the opera- tional aspects of experimental design made working at Hay- stack possible and his ideas are incorporated in nearly every result in this thesis. Mr. Thacker has been both a friend and an invaluable asset to most of the work done at NRAO where his experience and tireless efforts have saved more than one experiment from technical or political disaster. - 4- Radio emission from late type stars was discovered by William J. Wilson and so many of his theories and ob- servations are contained in my work that I consider him a coauthor of much of it. For the support, encouragement, and knowledge that my advisor, Prof. Alan Barrett, has given me throughout my years at MIT I can only say "thank you" and hope that the pupil can some day deserve his tea- cher. My work at MIT was supported in part by the National Science Foundation (Grant GP-13056) and by the National Aeronautics and Space Administration (Grant NGL-22-009-016) through the MIT Research Laboratory of Electronics. Tech- nical and observing assistance was supplied by the MIT Haystack observatory and by the National Radio Astronomy Observatory which is operated by Associated Universities Inc. for the NSF. - 5- TABLE OF CONTENTS Page List of Figures 8 List of Tables 10 I. Microwave Spectroscopy of the Interstellar Medium 11 IA. History 11 IB. Physics of Molecular Lines 15 IB1. Microwave Spectral Lines and the Interstel- lar Medium 15 IB2. Microwave Molecular Transitions 18 IB3. Examples of Molecular Lines 21 IB3a. Water Vapor 21 IB3b. OH Lambda Doubling 25 IC. Astronomical Masers 28 IC1. Characteristics of Maser Emission 31 IC2. Evidence of Maser Emission 35 II. Studies of Water Vapor Emission from HII Regions 38 IIA. Early Observations 38 IIB. Observations of HII Regions 43 IIBl. Sources Observed at NRAO: April-May 1969 44 IIB2. Sources Observed at Haystack or NRAO 62 IIC. Generalizations Concerning H 20 Emission from HII Regions 71 IIC1. H2 0 and HII Regions 71 IIC2. H2 0 and OH Emission 80 -6- Page IIC3. Other Molecular Lines 85 III. Studies of Water Vapor Emission from Infrared Stars 87 IIIA. Survey and Results 88 IIIB. Stars with Water Vapor Emission 92 IIIB1. Peculiar Infrared Stars with Water Vapor Emission 92 IIIB2. Long Period Variables with Water Vapor Emission 112 IIIC. Time Variations 126 IIID. Generalizations Concerning Water Vapor Emission from Stars 130 IV. Studies of Water Vapor Emission with Interfero- metric Techniques 139 IVA. Experimental Considerations 142 IVB. History of Observations 150 IVC. Results 153 IVC1. Angular Sizes 153 IVC2. Angular Structure 156 IVC3. Positions 159 IVD. Interpretations of the Spatial Structure of H20 Sources 162 IVD1. Interpretation of Interferometer Angu- lar Sizes 162 IVD2. Spatial Structure and Position 167 - 7- Page V. Studies of Other Molecular Lines 169 VA. Observations of OH Excited States 169 VA1. Observations of the 2 W½ J=3/2 State 170 VA2. Observations of the 2f½ J=5/2 State 173 VB. Observations of CH 20 Near Carbon Stars 178 VI. The Water Vapor Maser 186 VIA. General Model 187 VIB. Geometric and Kinematic Considerations 190 VIC. Pumping Models 195 VID. H20 Emission from Late Type Stars 197 VII. Appendices 202 VIIA. Radiometric Systems 202 VIIA1. Radiometers 202 VIIA2. Spectrometers 208 VIIB. Antennae 209 VIIBl. Antenna Performance 210 VIIB2. Antenna Pointing 211 VIIC. Observing Techniques 215 VIIC1. Total Power Spectroscopy 217 VIIC2. Strong Spectral Lines 218 Bibliography 220 Biographical Note 226 - 8 - LIST OF FIGURES Page I-i Rotational states connected by electronic and vibration-rotation transition in OH (a) and H 20 (b). 22 I-2 Geometry and vibrational modes of the H20 molecule. 22 I-3 Energy levels of the H 20 and OH molecules. 24 II-1 Haystack spectrum of Orion A. 41 II-2 Spectra of H20 sources, April 1969. 47 II-3 W3 Spectrum, June 1970. 48 II-4 W30H spectrum, June 1970. 50 11-5 Time variations in Orion A, April-May 1969. 51 II-6 Orion A spectrum, June 1970. 52 II-7 Time variations of main W49 features, April- May 1969. 56 II-8 W49 main features, June 1970. 57 11-9 Wide band spectrum of W49, April 1969. 59 II-10 W51 spectrum, June 1970. 61 II-11 Time variations in W24B2. 64 II-12 NGC 6334 spectrum. 65 11-13 W31 (G10.6) spectrum. 66 II-14 W44 (G35.8) spectrum. 68 II-15 Time Variations in ON-I. 69 II-16 H94a line in W31. 75 III-1 Time variation of intensity and radial ve- locity in VY CMa. 105 III-2 Line velocities in VY CMa and VX Sgr. 107 III-3 Spectra of RX Boo and VX Sgr. 109 - 9- Page III-4 Spectrum of NML Cyg. 113 III-5 Temperature vs spectral type for M stars. 115 III-6 Spectra of U Ori and S CrB. 120 III-7 Time variations in W Hya. 121 III-8 Time variations in U Her. 123 III-9 Time variations in R Aql. 125 III-10 Light curves of the microwave variation of W Hya, U Her and R. Aql. 129 III-11 Light curves of the microwave variation of U Ori, RX Boo and S CrB. 131 III-12a Infrared and microwave variation of R Aql. 136 III-12b Infrared and microwave variation of NML Cyg. 137 IV-1 VLBI recording system. 144 IV-2 Fringe frequency, phase and amplitude on W49. 147 IV-3 Local oscillator stability with two masers. 149 IV-4 Fringe visibility of Orion A. 157 IV-5 Fringe rate map of W49. 160 IV-6 Relative phase vs L.H.A. in W49. 161 V-1 W30H at 8135 MHz. 176 V-2 W30H CH20 spectrum. 181 VI-1 Geometry of H20 emission from a late type star. 193 VII-1 8.1 GHz system at Haystack. 205 VII-2 H20/VLBI system for the NRAO 140'. 207 VII-3a Gain vs elevation for Haystack 213 VII-3b Gain vs L.H.A. for the NRAO 140'. 214 VII-4 NRAO 140' pointing curves. 216 - 10 - LIST OF TABLES Page I-1 616-523 Hyperfine Multiplet of Water 26 I-2 Frequencies of OH Transitions 29 II-1 Orion A Source Positions 54 11-2 H20 Emission from HII Regions 70 II-3 Radio Recombination Line Data 75 II-4 Microwave Lines from H20 Sources 78 II-5 OH Velocities in HII Regions 82 III-1 Stars Surveyed for H20 Emission 93 III-2 Stars with H20 Emission 117 III-3 Isotropic Intensity of H 20 Sources 133 IV-1 H 20 VLBI Baselines 154 IV-2 "Spot" Sizes of H20 Sources 158 IV-3 Positions of H20 Sources 163 V-1 OH Excited State Frequencies 171 V-2 2w½r J=3/2 OH Line Search Results 172 V-3 2 9 J=5/2 OH Line Search Results 175 V-4a Carbon Stars Searched for CH20 183 V-4b Other Stars Searched for CH20 184 V-5 Molecular Abundances in Stars 185 VII-1 Radiometric Systems 203 VII-2 Haystack and NRAO 140' Parameters 212 - 11 - I.