We present new measurements of the mean magnetic field modulus a sample Ap stars with spectral lines resolved into magnetically split components. report discovery 16 having this property. This brings total number such known to 42. have performed more than 750 40 these 42 stars, between May 1988 and August 1995. The best them an estimated accuracy . availability large allows us discuss for first time distribution intensities. A most intriguing result is apparent existence sharp cutoff at low...

Within the context of collaboration "B fields in OB stars (BOB)", we used FORS2 low-resolution spectropolarimeter to search for a magnetic field 50 massive stars, including two reference stars. Because many controversies detections obtained with FORS instruments, derived values completely independent reduction and analysis pipelines. We compare discuss results from general good agreement, indicating that most discrepancies on reported literature are caused by interpretation significance...

The Herbig Ae/Be star HD,190073 is one of the very few magnetic stars for which close low-mass companions have been reported. Previously published field measurements indicated an annual change in configuration. We aim to study detail spectral and variability this characterise its magnetosphere first time. Newly acquired archival spectropolarimetric observations are combined determine a more precise period constrain geometry field. hydrogen line profiles studied using dynamical spectra....

We present a high resolution spectral atlas of the HgMn star HD 175640 covering 3040-10 000 Å region. UVES spectra observed with 90 000-110 resolving power and signal to noise ratio ranging from 200 400 are compared synthetic spectrum computed SYNTHE code (Kurucz [CITE]). The model atmosphere is an ATLAS12 [CITE]) parameters = 12 K, 3.95, ξ 0 km s-1. stellar individual abundances in were derived iterative procedure. starting atomic line lists downloaded Kurucz website have been improved...

The evolutionary state of magnetic Ap stars is rediscussed using the recently released Hipparcos data. distribution mass below 3 M☉ in H-R diagram differs from that normal same temperature range at a high level significance. Magnetic are concentrated toward center main-sequence band. This shown two forms diagram: one where log L plotted against Teff and version more directly tied to observed quantities, showing astrometry-based luminosity (Arenou & Luri) (B2-G)0 index Geneva photometry. In...

New determinations of the mean longitudinal magnetic field, crossover, and quadratic field Ap stars are presented. They based on spectra recorded simultaneously in both circular polarizations at ESO with CASPEC spectrograph fed by 3.6 m telescope. This paper discusses 95 observations 44 stars. A major result this study is discovery that HD 137509 has a predominantly quadrupolar strucuture previously found only couple Improvement or revision determination rotation period been achieved for 3...

Evolutionary models for massive stars, accounting rotational mixing effects, do not predict any core-processed material at the surface of B dwarfs with low velocities. Contrary to theoretical expectations, we present a detailed and fully-homogeneous, NLTE abundance analysis 20 early B-type (sub)giants that reveals existence population nitrogen-rich boron-depleted, yet intrinsically slowly-rotating objects. The low-rotation rate several these stars is firmly established, either from...

We present the results of a magnetic survey sample eight beta Cephei stars and 26 Slowly Pulsating B with FORS1 at VLT. A weak mean longitudinal field order few hundred Gauss is detected in star xi^1 CMa 13 SPB stars. The becomes third among Before our study, zeta Cas was only known star. All for which we gathered several measurements show that varies time. do not find relation between evolution stellar age small sample. Our observations imply SPBs can no longer be considered as classes...

The "B fields in OB stars" (BOB) collaboration is based on an ESO Large Programme, to study the occurrence rate, properties, and ultimately origin of magnetic massive stars. In framework this programme, we carried out low-resolution spectropolarimetric observations a large sample stars using FORS2 installed at VLT 8-m telescope. We determined field values with two completely independent reduction analysis pipelines. Our in-depth measurements shows that differences between our pipelines are...

Aims. The determination of effective temperature for chemically peculiar (CP) stars by means photometry is a sophisticated task due to their abnormal colours. Standard calibrations normal lead erroneous results and, in most cases corrections are necessary.

With FORS 1 at the VLT we have tried for first time to measure magnetic field variation over pulsation cycle in six roAp stars begin study of how and interact. For star HD 101065, which has one highest photometric amplitudes any star, found a signal known frequency 3σ level data set; however this could not be confirmed by later observations. A preliminary simple calculation expected variations suggests that they are same order as our current noise levels, leading us expect further...

Among the 21 Herbig Ae/Be stars studied, new detections of a magnetic field were achieved in six stars. For three stars, we confirm previous detections. The largest longitudinal field, <B_z> = -454+-42G, was detected star HD101412 using hydrogen lines. No detection at significance level 3sigma with debris disks. Our study does not indicate any correlation strength disk orientation, geometry, or presence companion. We also do see simple dependence on mass-accretion rate. However, it is likely...

Context. The presence of magnetic fields in O-type stars has been suspected for a long time. discovery these would explain wide range well documented enigmatic phenomena massive stars, particular cyclical wind variability, Hα emission variations, chemical peculiarity, narrow X-ray lines, and non-thermal radio/X-ray emission.

To investigate statistically whether magnetic fields in massive stars are ubiquitous or appear with specific spectral classification, certain ages, a special environment, we acquired 41 new spectropolarimetric observations for 36 stars. Among the observed sample roughly half of probable members clusters at different whereas remaining field not known to belong any cluster association. Spectropolarimetric were obtained during three nights using low-resolution mode FORS2 (FOcal Reducer low...

Within the context of "B fields in OB stars (BOB)" collaboration, we used HARPSpol spectropolarimeter to observe early B-type beta CMa (HD44743; B1 II/III) and epsilon (HD52089; B1.5 II). For both stars, consistently detected signature a weak (<30 G absolute value) longitudinal magnetic field. We determined physical parameters characterise their X-ray spectrum. CMa, our mode identification analysis led determining rotation period 13.6+/-1.2 days an inclination angle axis 57.6+/-1.7 degrees,...

We present the results of an extensive all-sky survey nearby stars spectral type F8 or later in a systematic search young (zero-age main sequence) objects. Our sample has been derived by cross-correlating ROSAT All-Sky Survey and TYCHO catalogue, yielding total 754 candidates distributed more less randomly over sky. Follow-up spectroscopy these candidate objects performed on 748 them. have discovered tight kinematic group ten with extremely high lithium equivalent widths that are presumably...

Magnetic fields play a key role in the pulsations of rapidly oscillating Ap (roAp) stars since they are necessary ingredient all pulsation excitation mechanisms proposed so far. This implies that proper understanding seismological behaviour roAp requires knowledge their magnetic fields. However, not well studied. Here we present new results measurements mean longitudinal field 14 obtained from low resolution spectropolarimetry with FORS 1 at VLT.

We have discovered an extraordinarily large mean longitudinal magnetic field of 7.5 kG in the ultra-cool low mass Ap star HD 154708 using FORS 1 spectropolarimetric mode. From UVES spectra, we measured a modulus 24.5 kG. This is second-largest ever star. Furthermore, it very likely that this one coolest and least massive among stars located H-R diagram same region which rapidly oscillating been detected. note all known roAp much smaller fields, by at factor three.

HD 154708 has an extraordinarily strong magnetic field of 24.5 kG. Using 2.5 h high time resolution Ultraviolet and Visual Echelle Spectrograph (UVES) spectra we have discovered this star to be roAp with a pulsation period 8 min. The radial velocity amplitudes in the rare earth element lines Nd ii, iii Pr are unusually low –∼60 m s−1– for star. Some evidence suggests that stars stronger fields lower amplitudes. Given central role plays oblique pulsator model stars, extensive study relation...

Abstract Our knowledge of the presence and strength magnetic fields in intermediate‐mass pre‐main‐sequence stars remains very poor. We present new field measurements six Herbig Ae/Be observed with HARPS spectropolarimetric mode. downloaded from European Southern Observatory (ESO) archive publically available spectra for stars. Wavelength shifts between right‐ left‐hand side circularly polarised were interpreted terms a longitudinal 〈 B z 〉, using moment technique introduced by Mathys. The...

Herbig Ae stars are young A-type in the pre-main sequence evolutionary phase with masses of ~1.5–3 . They show rather intense surface activity (Dunkin et al. [CITE], MNRAS, 290, 165) and infrared excess related to presence circumstellar disks. Because their youth, primordial magnetic fields inherited from parent molecular cloud may be expected, but no direct evidence for on surface, except one case (Donati 291, 658), has been found until now. Here we report observations optical circular...

We obtained accurate circular spectropolarimetric observations of a sample Vega-like and Herbig Ae/Be stars with FORS 1 at the VLT in an attempt to detect their magnetic fields. No field could be diagnosed any star. The most determination field, 2.6 σ level, was performed for star ι Cen, which we measured G. In prototype stars, β Pictoris, shows conspicuous signs chromospheric activity, longitudinal is only ~1.5 level. first time level higher than 3 two Ae HD 31648 144432 confirm existence...

We re-discuss the evolutionary state of upper main sequence magnetic stars using a sample Ap and Bp with accurate Hipparcos parallaxes definitely determined longitudinal fields. confirm our previous results obtained from study measurements mean field modulus quadratic fields that mass M < 3 M_sun are concentrated towards centre main-sequence band. In contrast, masses > seem to be closer ZAMS. The few known members nearby open clusters confirms these conclusions. Stronger tend found in...

We present the results of continuation our magnetic survey with FORS1 at VLT a sample B-type stars consisting confirmed or candidate beta Cephei and Slowly Pulsating B (hereafter SPB) stars, along small number normal stars. A weak mean longitudinal field order few hundred Gauss was detected in three two suspected to be five SPB eight Additionally, level larger than 3sigma has been diagnosed nitrogen-rich early star HD52089 B5 IV HD153716. Roughly one third have fields: Out 13 studied date...