The main focus of this thesis is in performing abundance analyses of magnetic Bp stars using the fortran program zeeman. In chapters 2 and 3, detailed models of the magnetic Bp stars
HD 133880 and HD 147010 are described, which include models of their magnetic field ge- ometries and chemical abundance distributions based on spectropolarimetric observations from the Canada-France-Hawaii Telescope’s (CFHT) ESPaDOnS spectropolarimeter. Chapter 4 in- vestigates the discrepancy between abundances derived from Siiiand Siiiiin late B-type stars.
We report abundances derived from the two ionisation states of silicon for normal, HgMn and magnetic Bp stars ranging in effective temperature from about 10500 to 15000 K in an effort to determine regularities in the phenomenon. We attempt to explain this discordance in terms of vertical stratification in the atmospheres of these stars. In chapter 5, we present a compre- hensive study of the atmospheric chemical abundances of a sample of 15 magnetic Bp stars, with mass 3.5±0.5 M⊙, that are members of open clusters, and thus have well-known ages. We
characterise trends with stellar age in the atmospheric abundances of these stars, providing the first observational constraints to diffusion theory on how these abundances evolve during the main sequence lifetime of these stars. Finally, chapter 6 summarises the work presented and suggests future avenues to expand upon this research.
Bibliography
Abt H. A. & Levy S. G., 1985, ApJS, 59, 229
Abt, H. A., Levato, H., & Grosso, M. 2002, ApJ, 573, 359
Alecian E. et al., 2009, in EAS Publications Series, Vol. 39, EAS Publications Series, C. Neiner & J.-P. Zahn, ed., pp. 121–132
Alecian G., Stift M. J., Dorfi E. A. 2011, MNRAS, 418, 997 Babcock H. W., 1947, ApJ, 105, 105B
Babcock H. W., 1960, ApJ, 132, 521
Bagnulo S., Szeifert T., Wade G. A., Landstreet J. D., Mathys G., 2002, A&A, 389, 191 Bagnulo S., Landstreet J. D., Mason E., Andretta V., Silaj J., Wade G. A., 2006, A&A, 450,
777
Bailey J. D., Landstreet J. D., Bagnulo S., Fossati L., Kochukhov O., Paladini C., Silvester J., Wade G., 2011, A&A, 535, A25
Bailey, J. D. & Landstreet, J. D. 2013b, A&A, 551, A30
Donati J.-F., Semel M., Carter B. D., Rees D. E., Collier Cameron A., 1997, MNRAS, 291, 658
Fossati, L., Bagnulo, S., Monier, R. et al. 2007, A&A, 476, 921
Kupka, F., Piskunov, N. E., Ryabchikova, T. A., Stempels, N. C., & Weiss, W. W. 1999, A&A, 138, 119
Landstreet J. D., 1982, ApJ, 258, 639 Landstreet J. D., 1988, ApJ, 326, 967
BIBLIOGRAPHY 23
Landstreet, J. D., Barker, P. K., Bohlender, D. A., & Jewison, M. S. 1989, ApJ, 344, 876 Landstreet, J. D. (2004). A stars as physics laboratories. In J. Zverko, J. Ziznovsky, S. J. Adel-
man, & W. W. Weiss, editor, The A-Star Puzzle, volume 224 of IAU Symposium, pages 423–432
Landstreet J. D., Bagnulo S., Andretta V., Fossati L., Mason E., Silaj J., Wade G. A., 2007, A&A, 470, 685
Landstreet, J. D., Silaj, J., Andretta, V., et al. 2008, A&A, 481, 465
Landstreet, J. D. (2009). Observing and Modelling Stellar Magnetic Fields 2. Models. In C. Neiner & J. -P. Zahn, editor, Stellar Magnetism, volume 39 of EAS Publication Series, pages 21–37
Landstreet, J. D. 2011, A&A, 528, A132
Mestel, L., & Landstreet, J. D. 2005, in Lecture Notes in Physics vol. 664, Cosmic Magnetic Fields, ed. R. Wielebinski, R. Beck, 183
Michaud, G. 1970, ApJ, 160, 641M
Michaud, G., Charland, Y., Vauclair, S., & Vauclair, G. 1976, ApJ, 210, 447 Martin, B. & Wickramasinghe, D. T. 1979, MNRAS, 189, 883
Mathys, G. & Hubrig, S. 1997, A&AS, 124, 475
Piskunov, N. E., Kupka, F., Ryabchikova, T. A., Weiss, W. W., & Jeffery, C. S. 1995, A&A, 112, 525
Preston, G. W. 1974, ARA&A, 12, 257
Richard, O., Talon, S., & Michaud, G. 2004, in IAU Symp. 224, The A-Star Puzzle, ed. J. Zverko, J. Ziznovsky, S. J. Adelman, & W. W. Weiss (Cambridge: Cambridge Univ. Press), 215
Ryabchikova T. A., 1991, in IAU Symposium, Vol. 145, Evolution of Stars: the Photospheric Abundance Connection, G. Michaud & A. V. Tutukov, ed., pp. 149–+
Ryabchikova, T. A., Piskunov, N. E., Kupka, F., & Weiss, W. W. 1997, Baltic Astronomy, 6, 244
24 BIBLIOGRAPHY
Ryabchikova, T. A., Savanov, I. S., Malanushenko, V. P., & Kudryavtsev, D. O. 2001, Astron- omy Reports, 45, 382
Schaller, G., Schaerer, D., Meynet, G., & Maeder, A. 1992, A&A, 96, 269
Stenflo, J.-O. 1994, Solar Magnetic Fields: Polarized Radiation Diagnostics (Berlin: Springer) Stepien, K. 2000, A&A, 353, 227
Wade, G. A., Donati, J. F., Landstreet, J. D., Shorlin, S. L. S. 2000, MNRAS, 313, 851
Wade G. A., Bagnulo S., Kochukhov O., Landstreet J. D., Piskunov N., Stift M. J. 2001, A&A, 374, 265
Wade G. A., Drouin D., Bagnulo S., Landstreet J. D., Mason E., Silvester J., Alecian E., B¨ohm T., Bouret J.-C., Catala C., & Donati J.-F. 2005, A&A, 442, L31
Chapter 2
The rapidly rotating magnetic Bp star
HD 133880
2.1
Introduction
HD 133880 (=HR 5624) is a rapidly rotating late B-type chemically peculiar (Bp) star with the Si λ4200 peculiarity. It exhibits an unusual magnetic field. The mean line-of-sight mag- netic fieldhBziis very strong and observed to vary from about -4 to+2 kG (Landstreet, 1990). Unlike most chemically peculiar stars, HD 133880 has a field that is predominantly quadrupo- lar as opposed to dipolar. HD 133880 is a photometric variable with variations on the order of 0.15 mag in the U-band, which may be the result of the large magnetic field (Waelkens, 1985). The magnetic field serves to create a “patchy” distribution of elements on the surface of the star. This non-uniform abundance distribution, and its associated line blocking and back- warming, may explain the photometric variations (Ryabchikova, 1991). Specifically, several elements are distributed non-uniformly over the stellar surface in a non-axisymmetric pattern about the rotation axis. As the star rotates, the observed magnetic field strengthhBzivaries and over/underabundances of elements are detected. The most striking anomalous abundances in Bp stars are often found for Cr and rare-earth elements, which can be as much as 102and 104−5
overabundant compared to the Sun, respectively (Ryabchikova, 1991). The resultant variability is explained by the oblique rotator model: the rotation and magnetic field axes are at angles i andβto the line-of-sight and rotation axis, respectively.
Landstreet (1990) used longitudinal magnetic field measurements obtained from Hβ, in conjunction with photometric data reported by Waelkens (1985), to deduce a period of P =
0.877485 ± 0.00002 days for HD 133880. Lim, Drake & Linsky (1996) did a preliminary 1A version of this chapter is published as Bailey, J.D. et al. 2012, MNRAS, 423, 328.
26 Chapter2. The rapidly rotating magneticBp starHD 133880
analysis of the rotational modulation of 3 cm and 6 cm radio emission from HD 133880. The radio emission variation had both broad and narrow peaks that correlated with the maximum extrema of the dipolar, Bd, and quadrupolar, Bq, contributions to the magnetic field reported by Landstreet (1990), respectively.
Landstreet et al. (2007) confirmed HD 133880 as a member of the Upper Cen Lup associ- ation and thus it is a star with a well known age of log t = 7.20 ± 0.10 (yrs). HD 133880 is a very young star, having completed only about 5% of its main sequence lifetime (Landstreet et al., 2007, 2008). Their preliminary analysis of many physical characteristics concluded that
Teff =12000±500 K, log L/L⊙ =2.10±0.1, and M/M⊙=3.20±0.15. Note that our analysis
(see below) has shown that the Teffis likely closer to 13000 K. Table 1 summarises the physical
properties of HD 133880.
There are few hot chemically peculiar stars with broad spectral features for which abun- dance analyses have been carried out. Because of the very complex, strong and unusual mag- netic field, HD 133880 is a worthwhile candidate to study in detail. It is also interesting from the fact that it is a star with a well known age. HD 133880 is one in a large sample of cluster Ap/Bp stars first compiled by Bagnulo et al. (2006) and Landstreet et al. (2007, 2008) to study the time evolution of magnetic fields in Ap stars. The current study is part of an effort to under- stand empirically how chemical abundances evolve with time and stellar age in the magnetic chemically peculiar stars. Recently Bailey et al. (2011) characterised one star in this sample, the Ap star HD 318107 (=NGC 6405 77). HD 133880 is a second star of great interest from that sample.
This chapter will discuss the efforts to characterise the magnetic field and abundance distri- butions of several elements for HD 133880. The following section discusses the polarimetric and spectroscopic observations used as well as the deduced longitudinal fields; Sect. 2.3 dis- cusses improvement of the rotational period ; Sect. 2.4 describes the determination of physical parameters; Sect. 2.5 addresses the observed line profile variations; Sect. 2.6 & 2.7 discuss the magnetic field and abundance models; Sect. 2.8 reports the abundances obtained; Sect. 2.9 discusses the Hαand radio magnetosphere; and Sect. 2.10 summarises the presented work.