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We report the results of a comprehensive study of the spectroscopic binary (SB2) system HD 34736 hosting two chemically peculiar (CP) late B-type stars. Using new and archival observational data, we characterise the system and its components, including their rotation and magnetic fields. Fitting of the radial velocities yields $P_\mathrm{orb}=83.\!^\mathrm{d}219(3)$ and $e=0.8103(3)$. The primary component is a CP He-wk star with $T_{\mathrm{eff}A}=13000\pm500$ K and $\upsilon_\mathrm{e}\sin i\;=75\pm3$ km/s, while the secondary exhibits variability of Mg and Si lines, and has $T_{\mathrm{eff}B}=11500\pm1000$ K and $\upsilon_\mathrm{e}\sin i=110$-180 km/s. TESS and KELT photometry reveal clear variability of the primary component with a rotational period $P_{\mathrm{rot}A}=1.\!^\mathrm{d}279\,988\,5(11)$, which is lengthening at a rate of $1.26(6)$ s/yr. For the secondary, $P_{\mathrm{rot}B}=0.\!^\mathrm{d}522\,693\,8(5)$, reducing at a rate of $-0.14(3)$ s/yr. The longitudinal component $\langle B_\mathrm{z}\rangle$ of the primary's strongly asymmetric global magnetic field varies from $-6$ to +5 kG. Weak spectropolarimetric evidence of a magnetic field is found for the secondary star. The observed X-ray and radio emission of HD 34736 may equally be linked to a suspected T Tau-like companion or magnetospheric emission from the principal components. Given the presence of a possible third magnetically active body, one can propose that the magnetic characteristics of the protostellar environment may be connected to the formation of such systems., Comment: This preprint has 28 pages, 23 figures, and includes the complete version of Table 1. Published in MNRAS

Numerous magnetic hot stars exhibit gyrosynchrotron radio emission. The source electrons were previously thought to be accelerated to relativistic velocities in the current sheet formed in the middle magnetosphere by the wind opening magnetic field lines. However, a lack of dependence of radio luminosity on the wind power, and a strong dependence on rotation, has recently challenged this paradigm. We have collected all radio measurements of magnetic early-type stars available in the literature. When constraints on the magnetic field and/or the rotational period are not available, we have determined these using previously unpublished spectropolarimetric and photometric data. The result is the largest sample of magnetic stars with radio observations that has yet been analyzed: 131 stars with rotational and magnetic constraints, of which 50 are radio-bright. We confirm an obvious dependence of gyrosynchrotron radiation on rotation, and furthermore find that accounting for rotation neatly separates stars with and without detected radio emission. There is a close correlation between H$\alpha$ emission strength and radio luminosity. These factors suggest that radio emission may be explained by the same mechanism responsible for H$\alpha$ emission from centrifugal magnetospheres, i.e. centrifugal breakout (CBO), however, whereas the H$\alpha$-emitting magnetosphere probes the cool plasma before breakout, radio emission is a consequence of electrons accelerated in centrifugally-driven magnetic reconnection., Comment: 47 pages (16 pages plus appendices), 43 figures, 9 tables, accepted for publication in MNRAS

The rotational and magnetic properties of many magnetic hot stars are poorly characterized, therefore the MiMeS and BinaMIcS collaborations have collected extensive high-dispersion spectropolarimetric datasets of these targets. We present longitudinal magnetic field measurements $\langle B_{\rm z}\rangle$ for 52 early B-type stars (B5 to B0), with which we attempt to determine their rotational periods $P_{\rm rot}$. Supplemented with high-resolution spectroscopy, low-resolution DAO circular spectropolarimetry, and archival Hipparcos photometry, we determined $P_{\rm rot}$ for 10 stars, leaving only 5 stars for which $P_{\rm rot}$ could not be determined. Rotational ephemerides for 14 stars were refined via comparison of new to historical magnetic measurements. The distribution of $P_{\rm rot}$ is very similar to that observed for the cooler Ap/Bp stars. We also measured $v\sin{i}$ and $v_{\rm mac}$ for all stars. Comparison to non-magnetic stars shows that $v\sin{i}$ is much lower for magnetic stars, an expected consequence of magnetic braking. We also find evidence that $v_{\rm mac}$ is lower for magnetic stars. LSD profiles extracted using single-element masks revealed widespread, systematic discrepancies in $\langle B_{\rm z}\rangle$ between different elements: this effect is apparent only for chemically peculiar stars, suggesting it is a consequence of chemical spots. Sinusoidal fits to H line $\langle B_{\rm z}\rangle$ measurements (which should be minimally affected by chemical spots), yielded evidence of surface magnetic fields more complex than simple dipoles in 6 stars for which this has not previously been reported; however, in all 6 cases the second- and third-order amplitudes are small relative to the first-order (dipolar) amplitudes., Comment: 38 pages, 47 figures, accepted for publication in MNRAS

A new time series of high-resolution Stokes I and V spectra of the magnetic B2V star HD 184927 has been obtained in the context of the Magnetism in Massive Stars (MiMeS) Large Program with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope and dimaPol liquid crystal spectropolarimeter at 1.8-m telescope of Dominion Astrophysical Observatory. We model the optical and UV spectrum obtained from the IUE archive to infer the stellar physical parameters. Using magnetic field measurements we derive an improved rotational period of 9.53102+-0.0007d. We infer the longitudinal magnetic field from lines of H, He and various metals, revealing large differences between the apparent field strength variations determined from different elements. Magnetic Doppler Imaging using He and O lines yields strongly nonuniform surface distributions of these elements. We demonstrate that the diversity of longitudinal field variations can be understood as due to the combination of element-specific surface abundance distributions in combination with a surface magnetic field that is comprised of dipolar and quadrupolar components. We have reanalyzed IUE high resolution spectra, confirming strong modulation of wind-sensitive Civ and Siv resonance lines. However, we are unable to detect any modulation of the H$\alpha$ profile attributable to a stellar magnetosphere. We conclude that HD 184927 hosts a centrifugal magnetosphere, albeit one that is undetectable at optical wavelengths. The magnetic braking timescale of HD 184927 is computed to be $\tau_J = 0.96$ or $5.8$ Myr. These values are consistent with the slow rotation and estimated age of the star., Comment: 23 pages, 21 figures. Accepted for publication in MNRAS

gam Peg is a bright B pulsator showing both p and g modes of beta Cep and SPB types. It has also been claimed to be a magnetic star by some authors while others do not detect a magnetic field. We aimed at checking for the presence of a field, characterise it if it exists or provide a firm upper limit of its strength if it is not detected. If gam Peg is magnetic, it would make an ideal asteroseismic target to test various theoretical scenarios. If it is very weakly magnetic, it would be the first observation of an extension of Vega-like fields to early B stars. Finally, if it is not magnetic and we can provide a very low upper limit on its non-detected field, it would make an important result for stellar evolution models. We acquired high resolution, high signal-to-noise spectropolarimetric Narval data at TBL. We also gathered existing dimaPol@DAO and Musicos@TBL spectropolarimetric data. We analysed the Narval and Musicos observations using the LSD technique to derive the longitudinal magnetic field and Zeeman signatures in lines. The longitudinal field strength was also extracted from the Hbeta line observed with the DAO. With a Monte Carlo simulation we derived the maximum strength of the field possibly hosted by gam Peg. We find that no magnetic signatures are visible in the very high quality spectropolarimetric data. The average longitudinal field measured in the Narval data is Bl=-0.1+/-0.4 G. We derive a very strict upper limit of the dipolar field strength of Bpol~40 G. We conclude that gamma Peg is not magnetic: it does not host a strong stable fossil field as observed in a fraction of massive stars, nor a very weak Vega-like field. There is therefore no evidence that Vega-like fields exist in B stars contrary to the predictions by fossil field dichotomy scenarios. These scenarios should thus be revised. Our results also provide strong constraints for stellar evolution models., Comment: 8 pages, accepted in A&A

We have carried out a re-analysis of polarimetric data of central stars of planetary nebulae, hot subdwarfs, and white dwarfs taken with FORS1 (FOcal Reducer and low dispersion Spectrograph) on the VLT (Very Large Telescope), and added a large number of new observations in order to increase the sample. A careful analysis of the observations using only one wavelength calibration for the polarimetrically analysed spectra and for all positions of the retarder plate of the spectrograph is crucial in order to avoid spurious signals. We find that the previous detections of magnetic fields in subdwarfs and central stars could not be confirmed while about 10% of the observed white dwarfs have magnetic fields at the kilogauss level., Comment: 6 pages, Proceedings of the 18th European White Dwarf Workshop, ASP Conference Series

Context: About 10% of white dwarfs have magnetic fields with strength in the range between about 10^5 and 3x10^8 G. It is not known whether the remaining white dwarfs are not magnetic, or if they have a magnetic field too weak to be detected with the techniques adopted in the large surveys. Aims. We describe the results of the first survey specifically devised to clarify the detection frequency of kG-level magnetic fields in cool DA white dwarfs. Methods: Using the FORS1 instrument of the ESO VLT, we have obtained Balmer line circular spectropolarimetric measurements of a small sample of cool (DA6 - DA8) white dwarfs. Using FORS and UVES archive data, we have also revised numerous white dwarf field measurements previously published in the literature. Results: We have discovered an apparently constant longitudinal magnetic field of \sim9.5 kG in the DA6 white dwarf WD2105-820. This star is the first weak-field white dwarf that has been observed sufficiently to roughly determine the characteristics of its field. The available data are consistent with a simple dipolar morphology with magnetic axis nearly parallel to the rotation axis, and a polar strength of \simeq 56 kG. Our re-evaluation of the FORS archive data for white dwarfs indicates that longitudinal magnetic fields weaker than 10 kG had previously been correctly identified in at least three white dwarfs. Conclusions: We find that the probability of detecting a field of kG strength in a DA white dwarf is of the order of 10% for each of the cool and hot DA stars. If there is a lower cutoff to field strength in white dwarfs, or a field below which all white dwarfs are magnetic, the current precision of measurements is not yet sufficient to reveal it., Comment: Accepted for publication in Astronomy & Astrophysics

A new, inexpensive polarimetric unit has been constructed for the Dominion Astrophysical Observatory (DAO) 1.8-m Plaskett telescope. It is implemented as a plug-in module for the telescope's existing Cassegrain spectrograph, and enables medium resolution (R~10,000) circular spectropolarimetry of point sources. A dual-beam design together with fast switching of the wave plate at rates up to 100Hz, and synchronized with charge shuffling on the CCD, is used to significantly reduce instrumental effects and achieve high-precision spectropolarimetric measurements for a very low cost. The instrument is optimized to work in the wavelength range 4700 - 5300A to simultaneously detect polarization signals in the H beta line as well as nearby metallic lines. In this paper we describe the technical details of the instrument, our observing strategy and data reduction techniques, and present tests of its scientific performance., Comment: 32 pages, 15 figures. Accepted for publication in PASP

The origin of magnetic fields in intermediate-mass and high-mass stars is fundamentally a mystery. Clues toward solving this basic astrophysical problem can likely be found at the pre-main sequence (PMS) evolutionary stage. With this work, we perform the largest and most sensitive search for magnetic fields in pre-main sequence Herbig Ae/Be (HAeBe) stars. Sixty-eight observations of 50 HAeBe stars have been obtained in circularly polarised light using the FORS1 spectropolarimeter at the ESO VLT. An analysis of both Balmer and metallic lines reveals the possible presence of weak longitudinal magnetic fields in photospheric lines of two HAeBe stars, HD 101412 and BF Ori. The intensity of the longitudinal fields detected in HD 101412 and BF Ori suggest that they correspond to globally-ordered magnetic fields with surface intensities of order 1 kG. Monte Carlo simulations of the longitudinal field measurements of the undetected stars allow us to place an upper limits of about 300 G on the general presence of aligned magnetic dipole magnetic fields, and of about 500 G on perpendicular dipole fields. We find that the observed bulk incidence of magnetic HAeBe stars in our sample is 8-12%, in good agreement with that of magnetic main sequence stars of similar masses. We also find that the rms longitudinal field intensity of magnetically-detected HAeBe stars is similar to that of Ap stars and consistent with magnetic flux conservation during stellar evolution. These results are all in agreement with the hypothesis that the magnetic fields of main sequence Ap/Bp stars are fossils, which already exist within the stars at the pre-main sequence stage. Finally, we explore the ability of our new magnetic data to constrain magnetospheric accretion in Herbig Ae/Be stars., Comment: Accepted by Monthly Notices of the Royal Astronomical Society, 2007 January 11. Received 2007 January 11; in original form 2006 August 18. The paper contains 18 pages, 11 figures and 2 tables

We present new results of a survey for weak magnetic fields among DA white dwarfs with inclusion of some brighter hot subdwarf stars. We have detected variable circular polarization in the Halpha line of the hot subdwarf star Feige 34 (SP: sdO). From these data, we estimate that the longitudinal magnetic field of this star varies from -1.1 +/- 3.2 kG to +9.6 +/- 2.6 kG, with a mean of about +5 kG and a period longer than 2 h. In this study, we also confirm the magnetic nature of white dwarf WD1105-048 and present upper limits of kilogauss longitudinal magnetic fields of 5 brightest DA white dwarfs. Our data support recent finding that 25% of white dwarfs have kilogauss magnetic fields. This frequency also confirms results of early estimates obtained using the magnetic field function of white dwarfs., Comment: accepted for publication in the Astrphysical Journal

Two newly identified Ae stars, nu Cyg and kappa UMa, were discovered in the course of the Magnetic Survey of Bright MS stars (Monin et al. 2002). We pre sent their Halpha profiles along with measurements of their equivalent width and parameters of emission features. Emission in the Halpha line of nu Cyg is variable on a time scale of 3 years. kappa 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, nu Cyg and kappa 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., Comment: 6 pages,3 figures, submitted to A&A

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., Comment: 3 pages, 2 figures, Proceedings of the 4th Microquasar Workshop, 2002, Eds. Ph.Durouchoux, V.Fuchs, & J.Rodrigues, publ. by the Center for Space Physics, Kolkata

This paper describes results of magnetic field measurements of white dwarfs carried out on the 6-m telescope for the last years. A magnetic field of about Be ~ 28 kG has been discovered in the degenerate star WD 1953-011. A rotational period of WD 0009+501, 1.83 hours, has been discovered, the average magnetic field of the star is = -42.3 +/- 5.4 kG and its semi-amplitude of the rotational variability is 32.0 +/- 6.8 kG. The variable magnetic field of the bright normal (non-magnetic) degenerate star 40 Eridani B was confirmed in January 1999 by Zeeman time-resolved spectroscopy. Both the Halpha and the Hbeta lines give about the same results, we have selected two best periods in the magnetic field variability, 2h25m and 5h17m. The semi-amplitude of the rotational variations B_ max ~ 4000-5000 G and the average field is about zero +/- 500 G. If the magnetic field of 40 Eridani B is a central dipole, then the rotational axis inclination to the line of sight is i ~ 90 DEG, and the magnetic axis inclination to the rotational axis is about the same, beta ~ 90 DEG. For the first time an ultra-high signal-to-noise spectrum of the white dwarf has been obtained (S/N > 1000). We have found in this hydrogen-rich DA white dwarf 40 Eridani B (16500 K) that helium abundance is low (N(He)/N(H) < 10^{-7}), but the spectrum is rich in ultra-weak absorption lines of metals in low ionization states. It was proposed that these lines were produced in both circumstellar and interstellar gas., Comment: 11 pages, 12 figures, "Magnetic fields of chemically peculiar and related stars", eds. Yu. V. Glagolevskij and I.I. Romanyuk, Proceed. of Intern. Meeting, Moscow, 2000 (in press), p.219