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Exploring the Final Stages of Stars in Our Milky Way Using Large Sky Exploring the final stages of stars in our Milky Way using large sky surveys by Sandra Magdy Kamel Greiss Thesis Submitted to the University of Warwick for the degree of Doctor of Philosophy Department of Physics July 2014 Contents List of Tables iv List of Figures vi Acknowledgments xiv Declarations xvi Abstract xvii Chapter 1 Motivation 1 Chapter 2 Compact stars 5 2.1 TheHertzsprung-Russelldiagram . 5 2.2 Stellar evolution in a nutshell . 5 2.2.1 Nuclearprocesses......................... 5 2.2.2 Shell-hydrogen burning and red-giant phase . 7 2.2.3 Death of stars like the Sun . 9 2.2.4 Death of massive stars . 10 2.3 WhiteDwarfs............................... 11 2.3.1 Spectraltypes .......................... 12 2.3.2 Massdistribution. .. .. .. .. .. .. .. 12 2.3.3 Whyaretheyuseful? ...................... 12 2.3.4 Pulsatingwhitedwarfs. 16 2.3.4.1 Theoretical context . 17 2.4 NeutronStars............................... 23 2.5 Blackholes ................................ 25 2.6 Compactbinarysystems. 25 2.6.1 Cataclysmic variables . 26 2.6.2 Low-massX-raybinaries. 28 Chapter 3 Astronomical tools and methods 30 3.1 Charge-coupleddevices . 30 3.2 Photometry ................................ 30 3.2.1 Colour-colour and colour-magnitude diagrams . 34 3.2.2 Time-series photometry . 34 i 3.3 Spectroscopy ............................... 36 3.3.1 Biasremoval ........................... 36 3.3.2 FlatFielding ........................... 37 3.3.3 Spectrum extraction . 37 3.3.4 Wavelength calibration . 37 3.3.5 Flux calibration . 37 3.4 Summary ................................. 38 Chapter 4 Large Sky Surveys 39 4.1 X-raysurvey ............................... 39 4.1.1 Galactic Bulge Survey (GBS) . 39 4.2 Thenear-infraredsurveys . 41 4.2.1 The Two Micron All Sky Survey (2MASS) . 41 4.2.2 UKIDSS Galactic Plane Survey (GPS) . 42 4.2.3 VISTA Variables in the Via Lactea (VVV) . 43 4.3 Optical survey: The Kepler-INTSurvey ................ 45 4.3.1 Kepler mission .......................... 45 4.3.2 Survey imaging with the Isaac Newton Telescope . 48 4.3.3 INT observations and data . 49 4.3.3.1 Observations . .. .. .. .. .. .. 49 4.3.3.2 Data .......................... 49 4.3.3.3 Quality control flags . 50 4.3.3.4 Photometric calibration . 50 4.3.3.5 Catalogue description . 56 4.4 Summary ................................. 60 Chapter 5 Near-infrared and optical study of the GBS sources 63 5.1 Near-infrared coverage of the Bulge . 63 5.1.1 Coverage ............................. 63 5.1.2 VVVvs2MASS ......................... 64 5.1.3 VVVvsUKIDSSGPS...................... 66 5.2 Extinction................................. 68 5.3 Results................................... 69 5.3.1 Quantifying the false alarm rate . 71 5.3.2 Randommatching ........................ 72 5.3.3 Positional uncertainties . 74 5.3.4 TotalFAP............................. 74 5.3.5 Multiplematches. .. .. .. .. .. .. .. 74 5.3.6 Finaltable ............................ 78 5.3.7 Influence of the hardness of the X-ray sources . 81 5.4 Near-infrared photometry discussion . 81 5.4.1 NIR colours of Hα emission line objects . 81 5.4.2 Towards the identification of key GBS source classes . 83 5.5 VVVVariability ............................. 84 5.6 Mosaicopticaldata............................ 88 ii 5.7 OpticalVariability ............................ 94 5.8 Summary ................................. 96 Chapter 6 White dwarfs in the Kepler field 99 6.1 Searching for white dwarfs in the Kepler field ............. 99 6.2 Spectroscopy ............................... 99 6.3 Ground-based confirmation of pulsators . 107 6.4 Kepler dataoffourZZCetistars . 108 6.4.1 KIC11911480........................... 108 6.4.1.1 Significance threshold . 113 6.4.1.2 Pulsation modes of KIC 11911480 . 113 6.4.1.3 Rotation rate of KIC 11911480 . 116 6.4.2 KIC10132702........................... 118 6.4.2.1 Pulsation modes of KIC 10132702 . 118 6.4.2.2 Rotation rate of KIC 10132702 . 118 6.4.3 KIC04357037........................... 120 6.4.3.1 Pulsation modes of KIC 04357037 . 121 6.4.3.2 Rotation rate of KIC 04357037 . 121 6.4.4 KIC07594781........................... 123 6.4.4.1 Pulsation modes of KIC 07594781 . 123 6.4.4.2 Rotation rate of KIC 07594781 . 124 6.4.5 Summary ............................. 125 6.5 Asteroseismic model of KIC 11911480 . 126 6.5.1 Method .............................. 127 6.5.2 Optimalmodel .......................... 128 6.5.3 Stellar rotation . 128 6.5.4 Nonadiabatic approach . 132 6.5.5 Asteroseismic properties of KIC 11911480 . 133 Chapter 7 Conclusion and future work 135 Abbreviations 139 iii List of Tables 2.1 Stellar evolution end-states as a function of initial masse (Tauris & van den Heuvel, 2006) .......................... 11 2.2 White dwarf spectral types (Koester, 2013). .............. 13 2.3 Observational properties of LMXBs (Tauris & van den Heuvel, 2006) 29 4.1 Exposure times and 5σ limiting magnitudes in all three NIR surveys used in this paper. The GPS integration times are longer than those applied in VVV, allowing for deeper observations of the Bulge than VVV. The magnitude limits given here are for fields that are moder- ately crowded similar to the GBS areas. ................ 45 4.2 Filter parameters of INT observations (Gonz´alez-Solares et al., 2008; Groot et al., 2009) ............................ 48 4.3 Morphological flags ........................... 50 4.4 ∆ filter is the median offset between the KIC and KIS magnitudes { } (see Section 4.3.3.4). The standard deviations of the distributions in each filter are also given here (σ filter ). The distributions are shown in Figure 4.8. ...............................{ } 54 4.5 Description of columns in KIS catalogue ............... 61 4.6 Example of light version of the KIS catalogue ............. 62 5.1 Percentage of total number of GBS X-ray sources with possible coun- terparts found within a 5 arcseconds (upper section) radius and 2.8 arcseconds (lower section) of the X-ray positions, in 2MASS, UKIDSS GPS (DR8) and VVV .......................... 65 5.2 Positions of the 4 closest matches of CX0013 found within R95 in VVV. The red cross indicates the X-ray position and the large dashed green circle indicates the R95 boundary of 2.84 arcseconds in this case. The table below provides information on their magnitudes and false alarm probabilities. ........................... 78 5.3 Four closest VVV matches to CX0013. ................ 78 5.4 Table containing all NIR data and FAP of matches within R95 . 80 6.1 Summary of photometric data of our WD candidates selected for spec- troscopic follow-up. ........................... 102 iv 6.2 Summary of spectroscopic observations and results from model atmo- sphere fits to the spectra. ........................ 106 6.3 Summary of ground-based time-series data of six ZZ Ceti stars con- firmed from our survey. The dominant periods and frequencies found in the amplitude power spectra of each source are given here. 108 6.4 Pulsation frequencies of KIC 11911480 from the Q12 and Q16 data. The uncertainties are given in parentheses. ∆f corresponds to the frequency spacing between two consecutive frequencies in the table . 112 6.5 Pulsation frequencies of KIC 10132702 from the Q15 data. ∆f cor- responds to the frequency spacing between two consecutive frequencies in the table ................................ 119 6.6 Pulsation frequencies of KIC 04357037 from one month of Q16 obser- vations. ∆f corresponds to the frequency spacing between two con- secutive frequencies in the table ..................... 122 6.7 Pulsation frequencies of KIC 07594781 from one month of Q16 obser- vations. ∆f corresponds to the frequency spacing between two con- secutive frequencies in the table ..................... 123 6.8 Identified modes and their periods of optimal model of KIC 11911480. 129 6.9 Pulsation frequencies of KIC 11911480 from the combined Q12 and Q16 data (see Table 6.4). The uncertainties are given in between brackets. ∆f corresponds to the frequency spacing between two con- secutive frequencies in the table. ..................... 131 6.10 Non adiabatic properties of the optimal model of KIC 11911480. 133 v List of Figures 2.1 The Hertzsprung-Russell diagram, showing the locii of the main-sequence where most stars actually lie, as well as other phases. The positions of some specific stars are also included in this sketch. ......... 6 2.2 The H-R diagram with evolutionary tracks of stars with different main-sequence masses. .......................... 8 2.3 Sketch of the stellar composition during different stages of its stellar evolution. ................................. 9 2.4 SDSS DA, DB, DAO and DZ spectra of white dwarf stars (top to bottom). The legend for the lines is the following: cyan H, pink ≡ dashed HeI, blue dotted HeII, yellow CaII. .......... 14 ≡ ≡ ≡ 2.5 Surface gravity and mass distribution of DA WD stars with Teff >13 000 K from the Palomar Green survey (Liebert et al., 2005). The mean values and standard deviations of both distributions are given at the top of each panel. ............................ 15 2.6 A pulsation H-R diagram showing different classes of pulsating stars, taken from Aerts et al. (2010). ..................... 16 2.7 Chemical composition of ZZ Ceti model (taken from Fontaine & Bras- sard 2008). The x-axis corresponds to the logarithm of the fractional mass depth, a scale chosen to emphasize the outer layers of the star, where most of the ‘action’ takes place. ................. 18 2.8 Profiles of the Lamb (dotted) and Brunt-V¨ais¨al¨a(solid) frequencies in a typical ZZ Ceti model (taken from Fontaine & Brassard 2008). 20 2.9 Typical ZZ Ceti model with excited mode l=1, k=1 (taken from Fontaine & Brassard 2008). For the explanation of curves, see Section 2.3.4.1. 22 2.10 Mass-radius diagram for neutron stars, taken from Lattimer & Prakash 2004. The black and green curves are for different equations of state of neutron stars. Regions excluded by general relativity (GR), causal- ity, and rotation constraints are also indicated. ............ 24 2.11 Equipotential lines in a binary system, also indicating the five Lagrangian points of potential equilibrium (Tauris & van den Heuvel, 2006). ..... 27 3.1 Illustration of the concept of a CCD where the ‘raindrops’ are actually the photons.
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