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A Spectroscopic Study Into Accretion In Herbig Ae/Be Stars. John Robert Fairlamb School of Physics and Astronomy University of Leeds Submitted in accordance with the requirements for the degree of Doctor of Philosophy March 2015 ii The candidate confirms that the work submitted is his own, except where work which has formed part of jointly authored publications has been included. The contribution of the candidate and the other authors of this work has been explicitly indicated. The candidate confirms that appropriate credit has been given within this thesis where reference has been made to the work of others. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. c 2015 The University of Leeds and John Robert Fairlamb. Preface Within this thesis, some of the chapters contain work presented in the following jointly authored publications: I. “Spectroscopy and linear spectropolarimetry of the early Herbig Be stars PDS 27 and PDS 37” – K. M. Ababakr, J. R. Fair- lamb, R. D. Oudmaijer, M. E. van den Ancker, 2015, MNRAS, submitted. II. “X-Shooter spectroscopic survey of Herbig Ae/Be stars I: Stellar parameters and accretion rates” – J. R. Fairlamb, R. D. Oud- maijer, I. Mendigut´ıa, J. D. Ilee, M. E. van den Ancker, 2015, MNRAS, submitted. III. “ Stellar Parameters and Accretion Rate of the Transition Disk Star HD 142527 from X-Shooter ” – I. Mendigut´ıa, J. R. Fair- lamb, B. Montesinos, R. D. Oudmaijer, J. Najita, S. D. Brittain, M. E. van den Ancker, 2014, ApJ, 790, 21. IV. “Investigating the inner discs of Herbig Ae/Be stars with CO bandhead and Brγ emission” – J. D. Ilee, J. R. Fairlamb, R. D. Oudmaijer, I. Mendigut´ıa, M. E. van den Ancker, S. Kraus, H. E. Wheelright, 2015, MNRAS, 445, 3723. Paper I is included in a small section in Chapter 2. The paper in- volves a dedicated procedure for obtaining stellar parameters in the stars PDS 27 and PDS 37. The methods and work presented in these sections of the paper were performed and written by the second au- thor J. R. Fairlamb. Other sections of the paper were either jointly written between the primary author, K. M. Ababakr, and the sec- ondary author, or they were the sole work of K. M. Ababakr; as such, these particular sections are not included in this thesis. Paper II forms the basis of Chapter 2 and 3. The paper details the derivation of stellar parameters for a large sample of HAeBe stars, and it analyses the mass accretion rate using the UV-excess. The work was carried out by the primary author, J. R. Fairlamb, and the text was also written by the primary author. The co-authors provided comments on various drafts of the paper which the primary author has incorporated in the final paper. Paper III is a dedicated study of the Herbig Ae star HD 142527. The secondary author, J. R. Fairlamb, wrote the section involving accretion derived from the Balmer excess and performed the relevant work behind the values listed. The techniques in this paper are similar to the ones presented in Chapter 3, but the methodology and stellar parameters used are slightly different. Paper IV contains Brγ line strengths and luminosities. These values are also present in Chapter 4. Their determinations involved some of the stellar parameter given in Chapter 2. All of these values were determined by the second author, J. R. Fairlamb, with the relevant sections in the paper regarding the values also written by the sec- ond author. The remainder of the paper was written by the primary author, J. D. Ilee, and is not included in this thesis. Acknowledgements Firstly, my thanks go out to my supervisor Ren´eOudmaijer, whose knowledge has helped me immensely, but perhaps more importantly his constant enthusiasm has kept me motivated throughout. My thanks are extended to the rest of my academic peers here in Leeds for providing valuable insights and discussions. In particular, thanks go to Ignacio Mendigutia and John Ilee who have greatly helped in my studies, both academically in the office, and non-academically in the “executive office”. Next, thanks are required for all of my fellow PhD students, every one of whom have provided great conversation and good times over the many years. Special thanks go to my office mates Nichol Cunning- ham and Tom Douglas for all the chin-wag sessions, and of course for putting up with me during these final months. Special thanks are due for Jacob Close and Karim Ababakr for including me in their en- tertaining and constant bickering (and also for being great climbing buddies). Outside of the office my thanks go to my friends, both near and far, for always having encouraged me and being there for me when I need to chill out. Special thanks go to my fellow monster hunters, and beer hunters, James Banning and Oscar Shefik for forcing me to play so many videogames and boardgames in my free time here in Leeds. Super special thanks go to my wonderful fianc´ee Gemma, who has al- lowed me to drag her away from Scotland to keep me company here. My thanks are for you always being there to talk to and laugh with at any hour, I couldn’t ask for a more wonderful partner. Lastly, important extra special thanks go to my parents who have provided me with support both emotionally and financially, not just throughout my PhD but throughout the whole of my life too. Without your never-ending encouragement and support I wouldn’t be where I am today. Thanks. Abstract This thesis presents a spectroscopic study of the stellar properties, accretion rates, and emission lines of 91 Herbig Ae/Be stars. Medium resolution spectra and optical photometry are used to spec- trally type a sample of 91 Herbig Ae/Be stars in a homogeneous fash- ion. Stellar parameters of temperature, surface gravity, mass, radius, luminosity, distance, age, and reddening are determined using the above in combination with pre-main sequence tracks. The tempera- tures are in agreement with previous assessments, while new distance and mass estimates for some objects constitute a large improvement. Measurements of the UV-excess across the Balmer jump region are made, and they are modelled within the context of magnetospheric accretion. Accretion rates are derived from the fitting. Seven Herbig Be stars could not be fitted within this context, suggesting a possi- ble breakdown of magnetospheric accretion towards the higher mass Herbig Ae/Be stars. Different relationships between accretion rate and age are observed for the cases of Herbig Ae stars and Herbig Be stars; this is suspected to be an evolutionary effect of both the star approaching the main sequence and the pre-main sequence lifetime of the star itself. Line luminosities are measured for 32 different emission lines ranging from ∼ 4000–21700 A.˚ All lines are observed to be correlated with the accretion luminosity, providing multiple new accretion diagnos- tics. The mean power-law relationship between accretion luminosity and line luminosity is observed to be the same between HAeBes and CTTs, within the errors. However, a line by line comparison between the two, demonstrates deviation in 80% of comparable lines. This deviation appears greatest in the Herbig Be regime. Further investi- gation is required into the line profiles and current scatter observed in relationships for different classes of pre-main sequence stars. Abbreviations BL Boundary Layer CMF Core Mass Function CTTs Classical T Tauri stars ESO European Southern Observatory EW Equivalent Width GMC Giant Molecular Cloud HAe Herbig Ae HAeBe Herbig Ae/Be HBe Herbig Be HR Hertzsprung-Russell IMF Initial Mass Function IR Infrared ISM Interstellar Medium KH Kelvin-Helmholtz MA Magnetospheric Accretion MYSO Massive Young Stellar Object NIR Near Infrared PAH Polycyclic Aromatic Hydrocarbon PDS Pico dos Dias Survey PMS Pre-Main Sequence SED Spectral Energy Distribution x SNR Singal-to-Noise Ratio TTs T Tauri stars UVB Ultra-Violet and Blue UV Ultra-Violet VIS Visible YSO Young Stellar Object ZAMS Zero Age Main Sequence 2MASS 2 Micron All Sky Survey Contents 1 Introduction 1 1.1 Clouds,Filaments,andCores . 1 1.1.1 GiantMolecularClouds . 2 1.1.2 Filaments ........................... 4 1.1.3 Cores.............................. 6 1.1.4 CoreCollapse ......................... 8 1.2 YoungStellarObjects . .. .. 12 1.2.1 TTauriStars ......................... 14 1.2.2 MassiveYoungStellarObjects. 16 1.2.3 HerbigAe/BeStars. 18 1.3 ThesisIntentions ........................... 22 2 Spectral Typing of Herbig Ae/Be Stars 25 2.1 Introduction.............................. 25 2.2 ObservationsandDataReduction . 27 2.2.1 X-Shooter Spectrograph and Target Selection . 35 2.2.2 DataReduction........................ 37 2.3 Distance and Stellar Parameters Determinations . .... 40 xii CONTENTS 2.3.1 Temperature and Surface Gravity Determination . 42 2.3.2 PhotometryFitting. 43 2.3.3 Mass, Age, Radius, and log(g) Determination . 47 2.4 LiteratureComparisons. 50 2.5 ExceptionalStars ........................... 62 2.5.1 PDS27&PDS37 ...................... 65 2.6 HR-diagram Location and Evolutionary Discussion . ... 70 2.6.1 HR-diagramLocation. 70 2.6.2 Age .............................. 73 2.7 Conclusions .............................. 75 3 Accretion Rate Determinations From UV-Excess Measurements 77 3.1 Introduction.............................. 77 3.2 BalmerExcess............................. 80 3.2.1 Method 1 – SED Matching: Single Point Measurement . 81 3.2.2 Method 2 – B-Band Normalised, Multi-point Measurements 84 3.2.3 ComparisonsandChecks. 87 3.3 AccretionRates............................ 93 3.3.1 Magnetospheric Modelling . 93 3.3.2 LiteratureComparisons . 102 3.4 Discussion ............................... 106 3.4.1 OverallResults . 106 3.4.2 Age .............................. 108 3.4.3 Accretion Rate vs. Stellar Parameters . 110 3.5 Conclusions .............................
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  • –1– 1. the Salpeter Initial Mass Function the Initial Mass Function Is

    –1– 1. the Salpeter Initial Mass Function the Initial Mass Function Is

    –1– 1. The Salpeter Initial Mass Function The initial mass function is a function describing the distribution of stellar masses in a newly formed population (i.e. none of the stars have had a chance to loose mass or undergo supernova). The initial mass function, IMF, was first derived by Ed Salpeter in 1955, who found that: dN ξ(logM)= = k M −Γ = k M −1.35 (1) dlog(M) 1 1 A similar function is the mass spectrum dN = k M −α = k M −2.35 (2) dM 2 2 where α =Γ+1. The total mass is then the integral of this: Mmax −2.35 k2 −0.35 −0.35 Mtot = Mk2M dM = (Mmin − Mmax ) (3) ZMmin 0.35 This shows that most of the stellar mass is in low mass stars. On the other hand, if we calculate the total luminosity (and assuming L ∝ M 3), then Mmax 3 −2.35 k2k3 1.65 1.65 Ltot = k3M k2M dM = (Mmax − Mmin ) (4) ZMmin 1.65 which shows that the total luminosity is driven by the most massive stars. We know now that the IMF is not a strict power law, and we will examine the variations. –2– 2. The Field Star IMF One way of deriving the IMF is to use field stars. To show how this is done, we follow the seminal work of Miller & Scalo (1979). This goes in two steps. First, a present day mass function, PDMF or φ(logM) for main sequence stars is found. This is the number of stars per mass per unit area in the galaxy; it is integrated over the ”vertical” dimension of the disk.