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Register a new userThe magnetic field of the hot spectroscopic binary HD5550
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HD5550 is a spectroscopic binary composed of two A stars observed with Narval at TBL in the frame of the BinaMIcS (Binarity and Magnetic Interactions in various classes of Stars) Large Program. One component of the system is found to be an Ap star with a surprisingly weak dipolar field of ~65 G. The companion is an Am star for which no magnetic field is detected, with a detection threshold on the dipolar field of ~40 G. The system is tidally locked, the primary component is synchronised with the orbit, but the system is probably not completely circularised yet. This work is only the second detailed study of magnetic fields in a hot short-period spectroscopic binary. More systems are currently being observed with both Narval at TBL and ESPaDOnS at CFHT within the BinaMIcS project, with the goal of understanding how magnetism can impact binary evolution and vice versa.
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About 10% of hot stars host a fossil magnetic field on the pre-main sequence and main sequence. However, the first magnetic evolved hot stars have been discovered only recently. An observing program has been set up to find more such objects. This will allow us to test how fossil fields evolve, and the impact of magnetism on stellar evolution. Already 7 evolved magnetic hot stars are now known and the rate of magnetic discoveries in the survey suggests that they host dynamo fields in addition to fossil fields. Finally, the weakness of the measured fields is compatible at first order with simple magnetic flux conservation, although the current statistics cannot exclude intrinsic decay or enhancement during stellar evolution.
Massive stars play a significant role in the chemical and dynamical evolution of galaxies. However, much of their variability, particularly during their evolved supergiant stage, is poorly understood. To understand the variability of evolved massive stars in more detail, we present a study of the O9.2Ib supergiant $zeta$ Ori Aa, the only currently confirmed supergiant to host a magnetic field. We have obtained two-color space-based BRIght Target Explorer photometry (BRITE) for $zeta$ Ori Aa during two observing campaigns, as well as simultaneous ground-based, high-resolution optical CHIRON spectroscopy. We perform a detailed frequency analysis to detect and characterize the stars periodic variability. We detect two significant, independent frequencies, their higher harmonics, and combination frequencies: the stellar rotation period $P_{mathrm{rot}} = 6.82pm0.18$ d, most likely related to the presence of the stable magnetic poles, and a variation with a period of $10.0pm0.3$ d attributed to circumstellar environment, also detected in the H$alpha$ and several He I lines, yet absent in the purely photospheric lines. We confirm the variability with $P_{mathrm{rot}}$/4, likely caused by surface inhomogeneities, being the possible photospheric drivers of the discrete absorption components. No stellar pulsations were detected in the data. The level of circumstellar activity clearly differs between the two BRITE observing campaigns. We demonstrate that $zeta$ Ori Aa is a highly variable star with both periodic and non-periodic variations, as well as episodic events. The rotation period we determined agrees well with the spectropolarimetric value from the literature. The changing activity level observed with BRITE could explain why the rotational modulation of the magnetic measurements was not clearly detected at all epochs.
YY Gem is a short-period eclipsing binary system containing two nearly identical, rapidly rotating, very active early-M dwarfs. This binary represents an important benchmark system for calibrating empirical relations between fundamental properties of low-mass stars and for testing theories of interior structure and evolution of these objects. Both components of YY Gem exhibit inflated radii, which has been attributed to poorly understood magnetic activity effects. Despite a long history of magnetic activity studies of this system no direct magnetic field measurements have been made for it. Here we present a comprehensive characterisation of the surface magnetic field in both components of YY Gem. We reconstructed the global field topologies with the help of a tomographic inversion technique applied to high-resolution spectropolarimetric data. This analysis revealed moderately complex global fields with a typical strength of 200-300 G and anti-aligned dipolar components. A complementary Zeeman intensification analysis of the disentangled intensity spectra showed that the total mean field strength reaches 3.2-3.4 kG in both components of YY Gem. We used these results together with other recent magnetic field measurements of M dwarfs to investigate the relation between the global and small-scale fields in these stars. We also assessed predictions of competing magnetoconvection interior structure models developed for YY Gem, finding that only one of them anticipated the surface field strength compatible with our observations. Results of our star spot mapping of YY Gem do not support the alternative family of theoretical stellar models which attempts to explain the radii inflation by postulating a large spot filling factor.
The survey of radial velocity orbits for short period (P < 1 day), bright (V < 10, with a few fainter stars) conducted at the David Dunlap Observatory in the last 9 years before its closure in 2008 included 162 binaries and resulted in 150 SB2 orbits and 5 SB1 spectroscopic orbits thus becoming one of the main legacies of DDO. The paper summarizes the main results from the survey.
We present the results of a study of the star HD 34736. The spectropolarimetric observations carried out at the 6-m telescope showed the presence of a strong variable longitudinal magnetic field, exceeding -4500 G. The analysis of the HIPPARCOS photometry gives a set of possible periods of the brightness variability of the star, of which 0.3603 days is preferred. The variable radial velocity of spectral lines of the star and some signatures of lines of at least one other component show that HD 34736 is a double short-period system. Modeling of the spectra allowed us to estimate the effective temperature $T_{eff}$ of the stars (13 700 and 11 500 K) and their projected rotational velocities $vsin i$ (73 and $geq90$ km s$^{-1}$). The analysis of all the available information about the star allows us to hypothesize that the object of study is a close, possibly interacting binary system.
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