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We present the results of a long-term search (25 yrs) for radial velocity variability in a sample of seven bright proto-planetary nebulae showing axial symmetry. They all vary in velocity due to periodic pulsations. However, only marginal evidence is found for multi-year variations that might be due to a binary companion.
Construction of Canada's Dominion Astrophysical Observatory (DAO) commenced in 1914 with first light on 6 May 1918. As distinct from the contemporaneous development with private funding of major observatories in the western United States, DAO was (and remains) funded by the federal government. Canada's initial foray into ‘big science’, creation of DAO during the First World War was driven by Canada's desire to contribute significantly to the international rise of observational astrophysics enabled by photographic spectroscopy. In 2009 the Observatory was designated a National Historic Site. DAO's varied, rich contributions to the astronomical heritage of the 20th century continue in the 21st century, with particularly strong ties to Maunakea.
The spectropolarimeter dimaPol measures circular polarization in spectral lines of stellar objects. The instrument is used to simultaneously detect polarization signals in the hydrogen Hβ line as well as nearby metallic lines. A fast switching ferro-electric liquid crystal waveplate synchronized with charge shuffling on the CCD is employed to greatly reduce instrumental systematics. dimaPol has been in use on the DAO 1.8-m Plaskett telescope since 2007. In this presentation we show the capabilities of the instrument as well as some of the main results obtained with it to date.
The Magnetism in Massive Stars (MiMeS) project represents the largest systematic survey of stellar magnetism ever undertaken. Based on a sample of over 550 Galactic B and O-type stars, the MiMeS project has derived the basic characteristics of magnetism in hot, massive stars. Herein we report preliminary results.
In this paper we present a few results from the first three years of an ongoing survey of globally-ordered magnetic fields in relatively faint (down to V ≈ 9) upper main sequence peculiar stars that we are conducting on the Dominion Astrophysical Observatory (DAO) Plaskett telescope. The DMFS uses the inexpensive DAO polarimeter module, dimaPol, mounted at the Cassegrain focus of the 1.8 m telescope to detect new magnetic stars and determine rotation periods and longitudinal magnetic field curves using medium-resolution (R ≈ 10,000) circular spectropolarimetry of both the Hβ line and metal lines in an approximately 280 Å wide wavelength region centered on Hβ. By concentrating on the mid-B to A-type peculiar stars, the DMFS provides an extension to the ‘Magnetism in Massive Stars’ (MIMES) Large Program which concentrated on similar field detections in more massive stars.
Commission 29 consists of members of the International Astronomical Union carrying out theoretical and observational studies of stars using spectroscopy, developing instrumentation for spectroscopy and producing and collecting data for interpretation of spectra.
The Magnetism in Massive Stars (MiMeS) Project is a consensus collaboration among many of the foremost international researchers of the physics of hot, massive stars, with the basic aim of understanding the origin, evolution and impact of magnetic fields in these objects. At the time of writing, MiMeS Large Programs have acquired over 950 high-resolution polarised spectra of about 150 individual stars with spectral types from B5-O4, discovering new magnetic fields in a dozen hot, massive stars. The quality of this spectral and magnetic matériel is very high, and the Collaboration is keen to connect with colleagues capable of exploiting the data in new or unforeseen ways. In this paper we review the structure of the MiMeS observing programs and report the status of observations, data modeling and development of related theory.
The nature of the light variations of chemically peculiar stars was studied in detail only in a very few cases. To better understand the mechanisms of light variability of these stars, we study the light variations of the well-known magnetic chemically peculiar star CU Vir and one of the least amplitude variable stars HD 64740. We show that the light variability of these stars is induced by flux redistribution in spots of enhanced abundance of chemical elements (e.g., helium, silicon, iron or chromium), and by the stellar rotation. We conclude that this is a promising model for the explanation of the light variability of most chemically peculiar stars.
We review the status of a long-term program to search for stellar magnetospheres in Bp stars. A few new σOri E analogues discovered during the course of this investigation are briefly discussed and other stars that may be worthy of further study are noted.
We report on the detection of a strong, organized magnetic field in the helium-variable early B-type star HR 7355 using spectropolarimetric data obtained with ESPaDOnS on CFHT by the MiMeS large program. We also present results from new V-band differential photometry obtained with the CTIO 0.9m telescope. We investigate the longitudinal field, using a technique called Least-Squares Deconvolution (LSD), and the rotational period of HR 7355. These new observations strongly support the proposal that HR 7355 harbors a structured magnetosphere similar to that in the prototypical helium-strong star, σ Ori E.
The business meeting was attended by 23 members of the Commission. The meeting started at 16:00 a short report of the activities during the triennium 2006-2009. The focus of the activities was the sharing of expertise between spectroscopic techniques in various areas of astronomical research. In particular, the progress in instrumentation, detectors, data reduction, data analysis and archiving. The second activity was the analysis of to IAU meeting proposals followed by recommendations for improvements and eventually support. The sponsored symposia included Sponsoring symposia The Ages of Stars and The Disk Galaxy Evolution in the Cosmological Context. The Commission was also disseminating information about the Commission activities and relevant meetings to the Commission members. In this respect the Commission web page is playing a crucial role.
Evidence suggesting an observable magnetic interaction between a star and its hot Jupiter (Porb < 7 days, a < 0.1 AU, Mpsini > 0.2 MJ) appears as a cyclic variation of stellar activity synchronized to the planet's orbit. HD 179949 has been observed almost every year since 2001. Synchronicity of the Ca II H & K emission with the orbit is clearly seen in four out of six epochs, while rotational modulation with Prot=7 days is apparent in the other two seasons. We observe a similar phenomenon on υ And, which displays rotational modulation (Prot=12 days) in September 2005, while in 2002 and 2003 variations appear to correlate with the planet's orbital period. This on/off nature of star-planet interaction (SPI) in the two systems is likely a function of the changing stellar magnetic field structure throughout its activity cycle. The tentative correlation between this activity in the 13 stars we have observed to date and the ratio of Mpsini to the planet's rotation period, a quantity proportional to the hot Jupiter's magnetic moment, first presented in Shkolnik et al. (2005) remains viable. This work furthers the characterization of SPI, improving its potential as a probe of extrasolar planetary magnetic fields.
Globally ordered magnetic fields are known to exist in non-degenerate stars with spectral types between approximately F0 and B2. Among the B stars, and in order of increasing effective temperature, these include the Bp Si stars, helium-weak stars, and the helium-strong stars. These rather remarkable objects present us with an excellent opportunity to quantitatively examine the possible effects of magnetic fields on the photospheres, winds, and circumstellar environments of hot stars. In this paper we review some of the observations of the magnetic fields and field geometries of magnetic B stars, and also briefly discuss the success of attempts to measure magnetic fields in hotter OB and Be stars. We point out some of the interesting observational similarities of the helium-weak and helium-strong stars to Be and other hot stars, including their spectroscopic and photometric variability, variable winds as demonstrated by the UV resonance lines of C IV and Si IV, and their non-thermal radio emission. Continuing work also suggests that a considerable fraction of the rapidly rotating magnetic helium-peculiar stars are in fact variable Be and Be shell stars.
The helium-weak and helium-strong stars are main sequence stars with anomalously weak and strong helium lines for their spectral types respectively. Many members of the two classes have strong, globally ordered magnetic fields (Thompson and Landstreet 1985; Bohlender et al. 1987) and are currently thought to represent high temperature extensions of the Ap stars. In collaboration with C. T. Bolton (U. of Toronto), we have obtained high S/N phase resolved spectra of several stars using the coudé reticon detector at CFHT. One of the principle goals of this work is to determine abundance and surface magnetic field geometries of several helium peculiar stars with large, well-determined effective fields. We employ a line synthesis program (Landstreet 1987) that incorporates the effects of surface magnetic fields and non-uniform abundances on the observed line profiles of a star. Since these stars are rapid rotators the surface magnetic field strength must be inferred from differential magnetic intensification of lines with different magnetic sensitivities. Of the few lines with suitable strengths in these hot stars we have decided that the Si III multiplet 2 lines are best suited for this aspect of our investigation. We have also modelled the unblended He I line λ4437, ignoring magnetic effects for the time being. Individual results are discussed below.
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