The Southern B Star Spectroscopic Survey

The Southern B Star Spectroscopic Survey Dissertation zur Erlangung des Grades „Doktor der Naturwissenschaften“ an der Fakultät für Physik und Astronomie der Ruhr-Universität Bochum von Thomas Dembsky aus Steinfurt Bochum, 2016 1. Gutachter: Prof. Dr. Rolf Chini Ruhr-Universität Bochum, Bochum, Deutschland 2. Gutachter: Prof. Dr. Stefan Kimeswenger Leopold-Franzens-Universität Innsbruck, Innsbruck, Österreich Universidad Católica del Norte, Antofagasta, Chile Datum der Disputation: 29.06.2016 I To my family II Abstract This work presents the results of the Southern B Star Spectroscopic Survey. From 2008 to 2014, 580 B stars were observed with multi-epoch, high-resolution (λ/∆λ = 48,000) optical spectroscopy at Universitätssternwarte Bochum near Cerro Armazones in Chile. A total of 4019 spectra have been observed by our own spectrograph BESO supple- mented by 818 spectra downloaded from the ESO pipeline-processed data archive of the three high-resolution spectrographs FEROS, HARPS and UVES. Our survey splits up into two subsets limited to V ≤ 8 mag. The first set, comprising 258 B stars, is volume-limited to a distance of 125 parsec (δ < +25◦), while the additional subset of 322 B stars is randomly selected to provide a similar number of stars in each spectral class bin. Hence, this survey seems to be the most comprehensive attempt of a spectroscopic B star survey up until today. The first part of this work analyses the spectroscopic binary fraction statistically to determine possible mass-dependencies. In general, the dimension of previously determined SB fractions could be confirmed. As the spectral type B comprises both, high- and intermediate-mass stars, conclusions about the star formation process with regard to stellar multiplicity could be drawn. A decline of the SB fraction towards late-type B stars has been found for intermediate-mass stars. The observed binary rates are slightly higher than detected in previous studies. An increasing multiplicity rate towards early-type B stars was determined for the volume-limited sample, while the additional subset was biased as discussed in this work. The determined mass-dependency of B stars compared to the previously published O star statistics allows to reasonably assume a correlation between the formation of high-mass stars and stellar multiplicity. Additionally, the decreasing binary frequency towards lower mass ratios, discovered by Wolff [1978], could be confirmed by our findings that the ratio SB1/SB2 stays ≤ 1 for all spectral class bins within our sample. To demonstrate the potential of the collected data, orbital periods of selected stars were determined. After confirmation of a previously known period, the orbital periods of ten stars, preferentially newly-discovered spectroscopic binaries, were calculated. It could be demonstrated that even a low number of spectra is sufficient if the phase coverage is adequate enough. Yet another outcome of this survey is a study of the Be phenomenon. In total, 75 Be stars and 36 supergiant emission-line stars could be identified. Among those stars two candidate Be stars could be confirmed. Additionally, five new Be stars were discovered, although those bright stars had been thoroughly observed within the last decades. The mass-dependent frequencies of all spectral type bins, except for B1, were raised by this study in comparison to collected results of different analyses compiled by Kogure & Hi- rata [1982]. A maximum of the Be star frequency at spectral class B2 could be confirmed. The following variability analysis concentrated on those 69 classical Be stars found in our survey. Within the maximum observation period of six years, two thirds showed variability. More than 20% even showed at least one normal B star phase. Moreover, already known Be stars did not show emission lines in the period of our observations. This all leads to the assumption that many more stars than originally thought pass through at least one Be phase during their lifetime if this does not even happen for all B stars. Large surveys give us the opportunity to reveal a lot about stellar variability: from rare events like outbursts (cf. HD 75860) to long-term variations like the first observed arising of a circumstellar gaseous disc around a certain star (cf. HD 147152). In the framework of our survey, a very rare event could be observed. HD 164284 showed a Balmer line profile of two weak double-peak emissions originating from two indepen- dently rotating gaseous discs in one spectrum. Whether the second, faster rotating disc has been re-accreted on the star, can only be speculated. IV Contents 1 Introduction 1 1.1 Binary Stars . .3 1.1.1 Visual Binaries . .4 1.1.2 Astrometric Binaries . .4 1.1.3 Photometric Binaries . .4 1.1.4 Spectroscopic Binaries . .5 1.2 Be Stars . .6 2 Data 7 2.1 Instruments . .7 2.2 Reduction . .9 2.3 The Survey . 12 2.4 Multiplicity . 13 2.5 Period Determination . 15 3 Results and Discussion 18 3.1 Spectroscopic Multiplicity . 18 3.1.1 Notes on Individual Stars . 19 3.1.2 Statistics of the Complete Sample . 22 3.1.3 The Volume-limited Sample and Comparison . 23 3.1.4 Biases . 24 3.1.5 Discussion . 28 3.2 Orbital Periods . 31 3.2.1 Program testing on HD 35411 . 32 3.2.2 HD 17543 . 35 3.2.3 HD 29763 . 35 3.2.4 HD 37756 . 36 3.2.5 HD 48977 . 36 Contents 3.2.6 HD 83058 . 37 3.2.7 HD 135160 . 37 3.2.8 HD 164402 . 37 3.2.9 HD 178125 . 38 3.2.10 HD 184930 . 38 3.2.11 HD 194739 . 38 3.2.12 Discussion . 38 3.3 Be and Emission-line Stars . 39 3.3.1 Notes on Individual Stars . 43 3.3.2 Apparent Hα Emission due to Binarity . 45 3.3.3 Supergiant Emission-line Stars . 47 3.3.4 The Be Star Frequency . 48 3.3.5 Be Star Variability . 49 3.3.6 Previously Known and Candidate Be Stars . 50 3.3.7 Newly-discovered Be Stars . 52 3.3.8 Discussion . 53 4 Summary and Outlook 56 5 Acknowledgements 59 Bibliography 61 A Tables 66 B Figures 91 B.1 Phase Plots . 91 B.2 Spectra . 100 VI List of Figures 2.1 Distribution of spectra among the stars of the survey . 13 2.2 Time series of HD 74146 . 15 3.1 Multiplicity statistics of the complete sample . 23 3.2 Comparison of the multiplicity statistics of both samples . 24 3.3 Distribution of apparent magnitudes of survey stars . 25 3.4 Multiplicity classification as a function of apparent magnitude . 26 3.5 Distribution of luminosity classes of survey stars . 27 3.6 Multiplicity classification as a function of luminosity class . 27 3.7 Exemplary line fits of HD 35411 . 32 3.8 Phase plot of HD 35411 (sharp-lined component) . 33 3.9 Phase plot of HD 35411 (broad-lined component) . 34 3.10 Phase plot of HD 17543 . 35 3.11 Apparent Hα emission caused by SB2s . 46 3.12 Frequency of Be stars for different spectral types . 49 B.1 Phase plot of HD 29763 (primary component) . 91 B.2 Phase plot of HD 37756 (sharp component, lower period limit of 1 d) . 92 B.3 Phase plot of HD 37756 (broad component, lower period limit of 1 d) . 92 B.4 Phase plot of HD 37756 (sharp component, lower period limit of 0.5 d) . 93 B.5 Phase plot of HD 37756 (broad component, lower period limit of 0.5 d) . 93 B.6 Phase plot of HD 48977 (lower period limit of 1 d) . 94 B.7 Phase plot of HD 48977 (lower period limit of 0.5 d) . 94 B.8 Phase plot of HD 83058 (primary component) . 95 B.9 Phase plot of HD 83058 (secondary component) . 95 B.10 Phase plot of HD 83058 (primary component) . 96 B.11 Phase plot of HD 83058 (secondary component) . 96 B.12 Phase plot of HD 164402 (short period) . 97 B.13 Phase plot of HD 164402 (long period) . 97 List of Figures B.14 Phase plot of HD 178125 . 98 B.15 Phase plot of HD 184930 . 98 B.16 Phase plot of HD 194739 . 99 B.17 Time series of HD 37202 . 100 B.18 Hα line profile of HD 68423 . 101 B.19 Time series of HD 75860 . 101 B.20 Hα line comparison of HD 158220 . 102 B.21 Hα line comparison of HD 219688 . 102 B.22 Hα line comparison of HD 164284 . 103 B.23 Hα line comparison of HD 29365 . 103 B.24 Hα line profile of HD 77907 . 104 B.25 Time series of HD 106955 . 104 B.26 Time series of HD 147152 . 105 B.27 Hα line profile of HD 219188 . 105 B.28 Hα line profile of HD 93540 . 106 B.29 Hα line profile of HD 183144 . 106 B.30 Time series of HD 29335 . 107 B.31 Time series of HD 125104 . 107 B.32 Time series of HD 61330 . 108 VIII List of Tables 2.1 Spectral lines analysed for multiplicity . 14 3.1 Multiplicity of B stars (exemplary) . 19 3.2 Be stars and their characteristics (exemplary) . 41 3.3 Supergiant emission-line stars and their characteristics (exemplary) . 42 3.4 SB2 with separated lines in Hα ....................... 47 A.1 Multiplicity of B stars (complete) . 66 A.2 Be stars and their characteristics (complete) . 85 A.3 Supergiant emission-line stars and their characteristics (complete) . 89 List of Tables X 1 Introduction The Southern B Star Spectroscopic Survey is part of a large observing campaign car- ried out by AIRUB (Astronomisches Institut der Ruhr-Universität Bochum) at Univer- sitätssternwarte Bochum near Cerro Armazones in Chile.

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