The results of a systematic magnetic survey of the brightest northern MS stars are presented. A homogeneous and representative sample of 30 upper MS stars was observed. Both fast and slow rotating normal and CP stars have been investigated by the same technique. A limit in accuracy of magnetic field measurements at a level of 10 G was reached for the stars with sharp lines in spectra. A statistical analysis of the magnetic field strength distribution of MS stars have been made. In the surface magnetic field range, BS = 0.1 ÷ 100 kG, the distribution cannot be represented by a single power relation. There is a real break at BS ≈ 3 - 5 kG earlier suspected, and which cannot be explained by observational selections only. We discuss a possible mechanism of the break. The distribution of highly magnetic stars is represented by a power law. It was shown that normalization of the high-field part of the distribution could be obtained in the study of the low-field part where the probabilities of finding are much higher. The distribution of weakly magnetic stars is It is very similar to that of magnetic white dwarfs. It has been determined that there are 7.2÷8.7% of MS stars with surface magnetic fields higher than 1 kG among MS stars of B8÷F9 spectral classes.

Abstract 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.

AbstractIn 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.

A new polarimeter module has been built for the Dominion Astrophysical Observatory's (DAO) 1.8 m Plaskett telescope for a hardware cost, including spare components, of approximately CDN$5,000. Implemented as a plug-in addition to the telescope's existing Cassegrain spectrograph, the device is being used to obtain medium resolution (R approximate to 10,000) circular spectropolarimetry of stars in an approximately 280 angstrom wide wavelength region centered on the H beta line. The intermediate resolution of the spectrograph permits stellar longitudinal magnetic field measurements to be made with both single or multiple strong metallic lines as well as the H beta line. The instrument's dual-beam design together with fast switching of the liquid crystal wave plate (up to 100 Hz) synchronized with charge shuffling on the CCD is used to significantly reduce instrumental effects and achieve high precision polarimetric measurements. In this paper we present the first new science results obtained with the instrument. These include the discovery of a strong magnetic field and co-rotating magnetosphere in the helium-weak star HD 176582, the detection of several new magnetic stars, and a study of the observed (and occasionally very large) differences in stellar longitudinal magnetic fields as measured with the H beta line and metallic lines.

AbstractWe 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.

The fast-switching DAO spectropolarimeter mounted on the 1.8-m Plaskett telescope started operation in 2007. Almost 14,000 medium-resolution (R=15,000) polarimetric spectra of 65 O - F type stars have been obtained since then in the course of three ongoing projects: the DAO Magnetic Field Survey, supporting observations for the CFHT MiMeS survey, and an investigation of the systematic differences between the observed longitudinal field measured with the Hbeta line and metallic lines. The projects are briefly described here. The current status as well as some results are presented.

We report the detection of a strong, reversing magnetic field and variable Ha emission in the bright helium-weak star HD 176582 (HR 7185). Spectrum, magnetic, and photometric variability of the star are all consistent with a precisely determined period of 1.5819840 +/- 0.0000030 days which we assume to be the rotation period of the star. From the magnetic field curve, and assuming a simple dipolar field geometry, we derive a polar field strength of approximately 7 kG and a lower limit of 52 degrees for the inclination of the rotation axis. However, based on the behavior of the Ha emission, we adopt a large inclination angle of 85 degrees and this leads to a large magnetic obliquity of 77 degrees. The Ha emission arises from two distinct regions located at the intersections of the magnetic and rotation equators and which corotate with the star at a distance of about 3.5 R(*) above its surface. We estimate that the emitting regions have radial and meridional sizes on the order of 2 R(*) and azimuthal extents ( perpendicular to the magnetic equator) of less than approximately 0.6 R(*). HD 176582 therefore appears to show many of the cool magnetospheric phenomena as that displayed by other magnetic helium-weak and helium-strong stars such as the prototypical helium-strong star sigma Ori E. The observations are consistent with current models of magnetically confined winds and rigidly rotating magnetospheres for magnetic Bp stars.

We describe an ongoing programme using the FORS1 spectropolarimeter on the ESO-VLT to search for magnetic fields in Herbig Ae/Be stars. Our aim is to identify the pre-Main Sequence progenitors of magnetic Ap stars, and to trace the evolution of their magnetic fields at the earliest possible stages.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

High-S/N, phase-distributed circular polarisation spectra of the variable HgMn star α And provide no evidence of any photospheric magnetic field, with an upper limit for oblique dipolar fields of 280 G (approximately the equipartition field at log τ5000 = 0.0). We therefore propose that the variability of the Hg λ3984 line and the inferred nonuniform distribution of Hg (reported by Adelman et al. 2002) most plausibly result from a separation mechanism unrelated to the presence of a magnetic field.

A program of the search for and analysis of profile variability in the spectra of bright O supergiants with a time resolution of 5–30 min is described. Preliminary results of the spectroscopic observations of the stars λ Ori, α Cam, and 19 Cep with the 1-m Special Astrophysical Observatory telescope in 2001 are presented. Line-profile variability was detected in the spectra of all the stars studied; variability in the Hα and C III λ5696 Å lines in the spectrum of λ Ori has been found for the first time. The variability amplitude is 4–5% for 19 Cep and 1–2% for α Cam and λ Ori on time scales from several hours to 3 or 4 days, and the width of the variable features reaches 2 Å (100 km s−1). We detected cyclical variations in the He II λ4686 and C III λ5696 line profiles in the spectrum of λ Ori on time scales of 1.3–1.6 days. Rapid profile variations on time scales of 3.5–7 h were found in the violet parts of the Hα and He I λ4715 line profiles in the spectrum of λ Ori A.

Two newly identified Ae stars, ν Cyg and κ UMa, were discovered in the course of the Magnetic Survey of Bright main sequence stars (Monin et al. 2002). We present their Hα profiles along with measurements of their equivalent width and parameters of emission features. Emission in the Hα line of ν Cyg is variable on a time scale of 3 years. κ UMa exhibits weak emission which is rather stable. The emission is thought to arise from a circumstellar disk, and we have estimated the size of that disk.Both new emission stars are IRAS sources. Their IR color excesses are consistent with those of classical Ae stars. Thus, ν Cyg and κ UMa appear not to belong to the class of Herbig Ae/Be stars. We argue that the frequency of Ae stars may be underestimated due to the difficulty of detection of weak emission in some A stars.

A study of the structure of hot stars and the nature of their variability is presented. We propose a three-phase model for hot-star winds and calculate the X-ray line emission of the hot component of the wind in comparison with the XMM Newton X-ray spectrum of O4f star κ Puppis. The results of high-resolution spectroscopy for some bright O stars are also presented. The line profile variability of bright O stars 19 Cep and λ Ori A is detected.

We report on the development of a fast crossed-dispersion spectrograph (CRAB) mounted at the Nasmyth focus of the 6-m telescope. The spectrograph is designed for visible and near-infrared (3800–10 500 Å) CCD observations with the spectral resolution R=4000. We give the basic parameters of the optical scheme and the parameters of the echelle frame. We determined the gain involved in putting the spectrograph into observational practice and discuss the possible range of spectroscopic problems for which the instrument is optimal.

The first results of a systematic search for magnetic fields in the brightest upper main sequence ( MS) stars are presented. The main goal is to survey the stars with about the same detection limit and to improve existing statistics of their magnetism. The target list contains 57 upper MS stars and represents well B0.5-F9 stars. High-resolution Zeeman spectra were obtained for 30 stars of the list. The accuracy of the magnetic field measurements ranges from 20 to 300G depending mainly on spectral class. In the majority of studied stars we did not detect magnetic fields. In some stars we suspect the presence of a weak magnetic field. These are the best candidates for more extensive studies. A particular case is the star chiDra where we probably detected the global magnetic field. The longitudinal field strength is B-1 = -54 +/- 12G. Further observations of this star are needed to confirm the detection and to ascertain if the magnetic field is variable with the period of rotation.

The results of photometric CCD monitoring and spectral observations of the black hole binary and microquasar V4641 Sgr in the quiet state are presented. The ellipsoidal light curve with large amplitude of 0.36^m in R band suggests the influence of a massive object orbiting around a normal B9 star. In the spectra taken with the 6-m telescope one hour before black hole inferior conjunction, an absorption component in the red wing of Halpha line is visible. It is formed by gaseous stream moving in the direction to the normal star. That suggests the grazing conjunction in this system. Maximum velocity of the stream is of 650 km/s. Assuming that the stream is moving through the circular Keplerian orbit around black hole, the mass of the black hole is determined to be M_{BH}=7.1-9.5Msun, what confirms the model by Orosz et al.

We present, a comparison of observed and calculated Stokes IQUV spectra of two well-known magnetic chemically peculiar stars, beta Coronae Borealis and 53 Camelopardalis. The observed Stokes spectra were recently described by Wade et al. (2000a), and have been complemented with additional circularly polarized spectra obtained at the Special Astrophysical Observatory. The calculated spectra represent the predictions of new and previously published magnetic field models derived from the analysis of some surface averaged field estimates (e.g., longitudinal field, magnetic field modulus, etc.). We find that these magnetic models are not sufficient to account fully for the observed Stokes profiles particularly remarkable is the disagreement between the predicted and observed Stokes Q and U profiles of 53 Cam. We suggest that this should be interpreted in terms of magnetic morphologies which are significantly more complex than the second-order multipolar expansions assumed in the models. However, it is clear that some of our inability to reproduce the detailed shapes of the Stokes IQUV profiles is unrelated to the magnetic models. For many metallic ions, for both stars, we found it impossible to account for the strengths and shapes of the observed spectral line profiles when we adopted a unique value for the individual ion abundance. We suggest that this results from strongly non-uniform distributions of these ions as a function of optical depth (i.e., chemical stratification), a hypothesis that is supported by comparison with simple chemically stratified models.