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Radio Observations As a Tool to Investigate Shocks and Asymmetries in Accreting White Dwarf Binaries

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Radio Observations As a Tool to Investigate Shocks and Asymmetries in Accreting White Dwarf Binaries Radio Observations as a Tool to Investigate Shocks and Asymmetries in Accreting White Dwarf Binaries Jennifer Helen Seng Weston Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences COLUMBIA UNIVERSITY 2016 c 2016 Jennifer Helen Seng Weston All rights reserved ABSTRACT Radio Observations as a Tool to Investigate Shocks and Asymmetries in Accreting White Dwarf Binaries Jennifer Weston This dissertation uses radio observations with the Karl G. Jansky Very Large Array (VLA) to investigate the mechanisms that power and shape accreting white dwarfs (WD) and their ejecta. We test the predictions of both simple spherical and steady-state radio emission models by examining nova V1723 Aql, nova V5589 Sgr, symbiotic CH Cyg, and two small surveys of symbiotic binaries. First, we highlight classical nova V1723 Aql with three years of radio observations alongside optical and X-ray observations. We use these observations to show that multiple outflows from the system collided to create early non-thermal shocks with a brightness temperature of &106 K. While the late-time radio light curve is roughly consistent an 4 expanding thermal shell of mass 2 10− M , resolved images of V1723 Aql show elongated × material that apparently rotates its major axis over the course of 15 months, much like what is seen in γ-ray producing nova V959 Mon, suggesting similar structures in the two systems. Next, we examine nova V5589 Sgr, where we find that the early radio emission is dominated by a shock-powered non-thermal flare that produces strong (kTx > 33 keV) X- 5 rays. We additionally find roughly 10− M of thermal bremsstrahlung emitting material, all at a distance of 4 kpc. The similarities in the evolution of both V1723 Aql and V5589 ∼ Sgr to that of nova V959 Mon suggest that these systems may all have dense equatorial tori shaping faster flows at their poles. Turning our focus to symbiotic binaries, we first use our radio observations of CH Cyg to link the ejection of a collimated jet to a change of state in the accretion disk. 7 We additionally estimate the amount of mass ejected during this period (10− M ), and improve measurements of the period of jet precession (P = 12013 74 day). We then ± use our survey of eleven accretion-driven symbiotic systems to determine that the radio brightness of a symbiotic system could potentially be used as an indicator of whether a symbiotic is powered predominantly by shell burning on the surface of the WD or by accretion. We additionally make the first ever radio detections of seven of the targets in our survey. Our survey of seventeen radio bright symbiotics, comparing observations before and after the upgrades to the VLA, shows the technological feasibility to resolve the nebulae of nearby symbiotic binaries, opening the door for new lines of research. We spatially resolve extended structure in several symbiotic systems in radio for the first time. Additionally, our observations reveal extreme radio variability in symbiotic BF Cyg before and after the production of a jet from the system. Our results from our surveys of symbiotics provide some support for the model of radio emission where the red giant wind is photoionized by the WD, and suggests that there may be a greater population of radio faint, accretion driven symbiotic systems. This work emphasizes the powerful nature of radio observations as a tool for understanding eruptive WD binaries and their outflows. Contents List of Figures iii List of Tables ix Acknowledgements xi 1 Introduction 1 1.1 Accreting, Eruptive White Dwarf Binaries . .1 1.2 Nova Systems and Eruptions . .2 1.2.1 Nova Overview . .2 1.2.2 General Properties of Radio Emission in Novae . .4 1.2.3 The Hubble Flow Model . .8 1.2.4 Variations on the Hubble Flow . 16 1.2.5 Historical Radio Observations of Novae . 19 1.2.6 Structures, Shocks and γ-rays in Novae . 24 1.3 Symbiotic Binary-Star Systems . 31 1.3.1 Symbiotic Stars Overview . 31 1.3.2 Radio Observations of Symbiotics . 33 1.3.3 Radio Emission from Symbiotics . 34 1.3.4 Formation of Jets and Shaping of Nebulae in Symbiotics . 37 1.4 Novae, Symbiotics, and Symbiotic Novae . 40 1.5 Structure of Dissertation . 42 2 Non-Thermal Radio Emission from Colliding Flows in Classical Nova V1723 Aql 45 2.1 Introduction . 45 2.2 Observations and Data Processing . 49 2.3 Data Analysis and Results . 51 2.3.1 Flux density and spectral evolution . 51 2.3.2 Resolved images . 57 2.4 Discussion . 59 2.4.1 Origin of the Late-Time Radio Emission: Expanding thermal shell . 62 2.4.2 Origin of the early time flare: particles accelerated in shocks within the ejecta . 72 2.4.3 Nova Shocks in the context of bipolar flows and γ-rays . 83 2.5 Conclusions . 86 3 Shock-powered radio emission from V5589 Sagittarii (Nova Sgr 2012 #1) 89 3.1 Introduction . 89 3.2 Observations . 93 3.3 Results . 97 3.3.1 Optical emission and estimate of distance . 97 3.3.2 Radio emission . 101 3.3.3 X-ray emission . 106 3.4 Discussion and Interpretation . 108 3.4.1 Evidence for non-thermal emission . 108 3.4.2 Connection to γ-ray producing novae . 113 3.5 Conclusions . 118 4 Radio Observations During a Jet Ejection from CH Cyg 121 4.1 Introduction . 121 i 4.2 Observations . 123 4.3 Results and Analysis . 131 4.3.1 Light curve and spectrum . 131 4.3.2 Images of an expanding, precessing jet . 137 4.4 Conclusions . 140 5 Radio Characteristics of Accretion Driven Symbiotic Systems 142 5.1 Introduction . 142 5.2 Source Selection . 144 5.3 Observations and Data Reduction . 151 5.4 Results and Analysis . 154 5.5 Conclusions . 162 6 Shaping of Nebulae in Symbiotics 164 6.1 Introduction . 164 6.2 Observations and Data reduction . 165 6.3 Results . 168 6.4 Future Work . 172 6.5 Conclusions . 172 7 Conclusion 177 7.1 Overview of Results . 177 7.1.1 Shaping and Non-Thermal Emission from Colliding Flows in the Ejecta of Novae . 177 7.1.2 Accretion and Spatially Resolvable Structures in Symbiotic Binaries . 181 7.2 Greater Context and Future Work . 187 8 Bibliography 190 ii List of Figures 1.1 A Hubble Flow-like nova transitioning from optically thick to optically thin at radio wavelengths. Initially, only optically thick emission is seen, from the surface of the shell (top panel). As the density of the shell decreases, the radio photosphere (at some frequency ν) moves inwards through the shell, and the observer will see a mix of optically thick and optically thin thermal emission (middle panel). Once the radio photosphere has reached the inner edge of the shell, the shell will be optically thin throughout at that frequency. .9 1.2 Below, Figure 5 (left) from Hjellming et al. (1979) shows the radio light curve of FH Ser after eruption in 1970 fit to a linear velocity gradient for a spherical shell. Figure 3 (right) from Kwok (1983) shows the same radio light curve of FH Ser fit to the the steady wind model. 20 1.3 Below, figure 7 (left) from Hjellming et al. (1979) shows the radio light curves of V1500 Cyg after an outburst in 1975 fit to a linear velocity gradient in a spherical shell. Figure 4 (right) from Kwok (1983) shows the same light curves fit to the steady wind model. 21 1.4 Below, figure 5 from Hjellming (1996) shows the radio light curve of V1974 Cyg after a nova eruption in in 1992, fit to a simple linear velocity gradient model with ellipsoidal inner and outer boundaries. 22 1.5 Figure 2 from Taylor et al. (1987) shows the radio map of QU Vul (1984) showing roughly spherical ejecta. It is the first resolved radio image of the ejecta of a nova shortly after eruption. 27 iii 1.6 Figure 3 from Chomiuk et al. (2014) illustrates the development of the ejecta from nova V959 Mon: a slower dense equatorial density enhancement (dark yellow) shaping a faster outflow at the poles (light blue), with shocks (red) forming at the interface between the two outflows. 30 1.7 In Figure 6 from Seaquist et al. (1984) we see the shape of the ionization front for various models compared to predicted spectral behavior. Flux density (on an arbitrary scale) is shown by the solid line, and spectral index α is shown by the dashed line and the right hand scale. An accretion powered system would be expected to follow the uppermost panel, whereas a shell burning powered system would be the bottom-most panel. 36 1.8 In Figure 1 from Corradi (2003) we see two collimated outflows from sym- biotic systems. In the top panel, we see the collimated bipolar jets from R Aqr in [O II]; in the bottom panel, we see the more hour-glass figure from He 2-104 in [N II]................................... 39 1.9 Figure 10 from Chochol et al. (1997) (left panel), obtained with HST using [Ne V] and [O III], shows the presence of a ring in the ejecta from nova V1974 Cyg. In Figure 1 from Hollis et al. (1999) (right panel), we see a ring in [N II] emission in the surrounding nebula of symbiotic R Aqr. The formation of rings and other structures in the ejecta from eruptive WD is not fully understood. 41 2.1 Observed flux densities of V1723 Aql between 2010 September and 2014 March.
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