I. Ilyin

Doppler Imaging of stellar magnetic fields. III. Abundance distribution and magnetic field geometry of alpha 2 CVn

We used the new magnetic Doppler Imaging code to reconstruct the magnetic eld geometry and surface abundance distributions for the classical magnetic CP star 2 CVn. High-resolution spectropolarimetric observations in the Stokes I and V parameters were collected with the SOFIN echelle spectrograph at the Nordic Optical Telescope. This superb observational material in combination with the advanced modelling technique allowed to achieve the rst simultaneous self-consistent mapping of the vector magnetic eld and the abundance distributions of six chemical elements. In recovering the stellar magnetic distribution no prior assumptions about the eld geometry or strength were made. Instead, we restricted possible solutions of the inverse problem by means of the multipolar regularization method which searches for the eld map close to a general non-axisymmetric multipolar conguration but allows departures from this geometry if that is required by the observational data. We found that the magnetic eld of 2 CVn is dominated by a dipolar component and has a minor quadrupole contribution. The surface distributions of the chemical species form symmetric patterns which closely follow the magnetic geometry. This discovery constitutes one of the rst direct observational constraints on the horizontal diusion processes acting in the upper envelope of a strongly magnetized stellar atmosphere. In addition to the extensive magnetic Doppler Imaging analysis, we derived new accurate estimates of the atmospheric parameters and basic physical properties of 2 CVn using the energy distribution, hydrogen line proles and the recent

Non-axisymmetric accretion on the classical TTS RW Aur A

(Abridged) High-resolution spectroscopic monitoring of RW Aur A was carried out in 1996, 1998 and 1999 with simultaneous B, V photometry. A multicomponent spectrum is revealed with a veiled photospheric spectrum, broad emissions, narrow emission lines of helium, and accretion, wind and shell features. Periodic modulations in many spectral features were found. The photospheric absorption lines show sinusoidal variations in radial velocity with an amplitude of +-6 km/s and a period of about 2.77 days. The radial velocities of the narrow emission lines of He vary with the same period but in anti-phase to the photospheric lines. The equivalent widths of the narrow emissions vary with a phase-shift with respect to the velocity curve. The strength of the red-shifted accretion components of Na D and other lines is also modulated with the same period. The broad emission lines of metals vary mostly with the double period of about 5.5 days. One unexpected result is that no correlation was found between the veiling and the brightness, although both varied in wide ranges. This is partly due to a contribution of the shell absorption to the photospheric line profiles, which make them vary in width and depth thus simulating lower veiling. Most of the observed features can be interpreted in the framework of non-axisymmetric magnetospheric accretion. We consider two possible models. In the first the asymmetry is induced by orbital motion of an invisible, low mass secondary, which also influences the gasflows around the star, the second considers rotational modulation of a single star with an inclined or asymmetric magnetosphere.High{resolution spectroscopic monitoring of the exceptionally active classical T Tauri star (CTTS) RW Aur A was carried out in three seasons of 1996, 1998 and 1999 with simultaneous B, V photometry. The high quality spectra revealed a multicomponent structure of the spectrum, which includes: 1) a veiled photospheric spectrum of a K1{K4 star, 2) broad emission lines of neutrals and ions, 3) narrow emission lines of He i and He ii, 4) red{shifted accretion features of many lines, 5) shell lines at about the stellar velocity, 6) blue{shifted wind features and 7) forbidden lines. Periodic modulations in many spectral features were found. The photospheric absorption lines show sinusoidal variations in radial velocity with an amplitude of 6k m s 1 and a period of about 2: 77. The radial velocities of the narrow emission lines of He vary with the same period but in anti{phase to the photospheric lines. The equivalent widths of the narrow emissions vary with a phase{shift with respect to the velocity curve. The strength of the red{shifted accretion components of Na D and other lines is also modulated with the same period. The broad emission lines of metals vary mostly with the double period of about 5: d 5. One unexpected result is that no correlation was found between the veiling and the brightness, although both parameters varied in wide ranges. This is partly due to a contribution of the shell absorption to the photospheric line proles, which make them vary in width and depth thus simulating lower veiling. The spectral lines of the accreting gas show two distinct components: one is formed at low velocity at the beginning of the accretion column, and the other at high velocity near the stellar surface. The low velocity components are strong in low excitation lines of neutrals, while the high velocity components are strong in high excitation lines of ions, thus showing the gradients of temperature and density along the accretion column. Most of the observed features can be interpreted in the framework of non{axisymmetric magnetospheric accretion, but the origin of this asymmetry can be explained in dierent ways. We consider two possible models. The rst model suggests that RW Aur A is a binary with a brown dwarf secondary in a nearly circular orbit with a period of 2: d 77. The orbiting secondary generates a moving stream of enhanced accretion from one side of the disk towards the primary. The other model assumes that RW Aur A is a single star with a rotational period of 5: d 5a nd with two footpoints of channeled accretion streams within a global magnetosphere which is tilted relative to the rotational axis or otherwise non{axisymmetric. Both models can explain qualitatively and quantitatively most of the observed variations, but there are some details which are less well accounted for.

Magnetic Doppler imaging of the roAp star HD 24712

Aims. We present the first magnetic Doppler images of a rapidly oscillating Ap (roAp) star. Methods. We deduce information about magnetic field geometry and abundance distributions of a number of chemical elements on the surface of the hitherto best studied roAp star, HD 24712, using the magnetic Doppler imaging (MDI) code, invers10, which allows us to reconstruct simultaneously and consistently the magnetic field geometry and elemental abundance distributions on a stellar surface. For this purpose we analyse time series spectra obtained in Stokes I and V parameters with the SOFIN polarimeter at the Nordic Optical Telescope and recover surface abundance structures of sixteen different chemical elements, respectively ions, including Mg, Ca, Sc, Ti, Cr, Fe, Co, Ni, Y, La, Ce, Pr, Nd, Gd, Tb, and Dy. For the rare earth elements (REE) Pr and Nd separate maps were obtained using lines of the first and the second ionization stage. Results. We find and confirm a clear dipolar structure of the surface magnetic field and an unexpected correlation of elemental abundance with respect to this field: one group of elements accumulates solely where the positive magnetic pole is visible, whereas the other group avoids this region and is enhanced where the magnetic equatorial region dominates the visible stellar surface. We also observe relative shifts of abundance enhancement- or depletion regions between the various elements exhibiting otherwise similar behaviour.

An asteroseismic study of the β Cephei star 12 Lacertae: multisite spectroscopic observations, mode identification and seismic modelling

We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the slowly pulsating B-stars (SPB)-like g-mode with frequency 0.3428 d −1 reported before is detected in our spectroscopy. We identify the four main modes as (� 1, m1) = (1, 1), (� 2, m2) = (0, 0), (� 3, m3) = (1, 0) and (� 4, m4) = (2, 1) for f 1 = 5.178 964 d −1 , f 2 = 5.334 224 d −1 , f 3 = 5.066 316 d −1 and f 4 = 5.490 133 d −1 , respectively. Our seismic modelling shows that f 2 is likely the radial first overtone and that the core overshooting parameter αov is lower than 0.4 local pressure scale heights.

Optical spectra of five UX Orionis-type stars

We present in this paper several high resolution (R = 27 000) spectra of ve UXORs (UX Ori, CQ Tau, BF Ori, RR Tau, WW Vul), which cover the entire visual range, from 3900 to about 8700 A. There are between 4 and 7 spectra per star, obtained over a time interval of two years. Simultaneous or quasi-simultaneous photometric observations were also obtained at the Crimean Astrophysical Observatory. The complete, reduced and normalized spectra are available in electronic form. We show for each star a selection of the most interesting lines, and the full spectrum of UX Ori computed by averaging the spectra obtained when the star was at maximum light. For UX Ori we show also the synthetic spectrum and provide an identication of most of the lines. The spectra are too sparse to form true time sequences; however, they provide an extremely useful database for studies of UX Ori-type stars. We discuss briefly the main features of the spectra. We show that they contain many time-stable photospheric lines that can be described to a good approximation by the synthetic spectra of normal A stars with log g =3 :5 4 and we derive for each star eective temperature, gravity and rotational velocity. We examine the time variability of selected lines and study their connection with the photometric activity of the stars. Two dierent types of spectral variability are identied. One is common to all stars with circumstellar (CS) gas and is caused by perturbations of the physical and kinematic conditions of the emitting region. There is no correlation between this type of activity and the brightness variations of the star. On the contrary, a second type of spectral variability correlates well with the brightness variations and is very likely connected with the screening eect of an opaque dust cloud which sporadically intersects the line of sight. This type of variability has been observed in its simplest form in one of the RR Tau spectra, where the equivalent width of the forbidden line (O i) 6364 A increased by a factor of about three as the star faded by approximately the same amount.

Exploring the origin of magnetic fields in massive stars: II. New magnetic field measurements in cluster and field stars

Context. Theories on the origin of magnetic fields in massive stars remain poorly developed, because the properties of their magnetic field as function of stellar parameters could not yet be investigated. Additional observations are of utmost importance to constrain the conditions that are conducive to magnetic fields and to determine first trends about their occurrence rate and field strength distribution. Aims. To investigate whether magnetic fields in massive stars are ubiquitous or appear only in stars with a specific spectral classification, certain ages, or in a special environment, we acquired 67 new spectropolarimetric observations for 30 massive stars. Among the observed sample, roughly one third of the stars are probable members of clusters at different ages, whereas the remaining stars are field stars not known to belong to any cluster or association. Methods. Spectropolarimetric observations were obtained during four different nights using the low-resolution spectropolarimetric mode of FORS2 (FOcal Reducer low dispersion Spectrograph) mounted on the 8-m Antu telescope of the VLT. Furthermore, we present a number of follow-up observations carried out with the high-resolution spectropolarimeters SOFIN mounted at the Nordic Optical Telescope (NOT) and HARPS mounted at the ESO 3.6m between 2008 and 2011. To assess the membership in open clusters and associations, we used astrometric catalogues with the highest quality kinematic and photometric data currently available. Results. The presence of a magnetic field is confirmed in nine stars previously observed with FORS1/2: HD36879, HD47839, CPD−282561, CPD−472963, HD93843, HD148937, HD149757, HD328856, and HD164794. New magnetic field detections at a significance level of at least 3� were achieved in five stars: HD92206c, HD93521, HD93632, CPD−468221, and HD157857. Among the stars with a detected magnetic field, five stars belong to open clusters with high membership probability. According to previous kinematic studies, five magnetic O-type stars in our sample are candidate runaway stars.

Pulsation in the atmosphere of the roAp star HD 24712 - I. Spectroscopic observations and radial velocity measurements

Aims.We have investigated the structure of the pulsating atmosphere of one of the best studied rapidly oscillating Ap stars, HD 24712.Methods.For this purpose we analyzed spectra collected during ...

Study of FK Comae Berenices V. Spot evolution and detection of surface differential rotation

Aims. We investigate the spot evolution and the surface differential rotation of the single late-type giant FK Com. Methods. A total of 18 new surface temperature maps of FK Com are calculated with the Doppler imaging technique for the years 1993–2003. Photometric observations from 2002–2004 are also given. The new and previously published spectroscopic and photometric observations are used to study the spot locations and lifetimes, and to estimate the value of the surface differential rotation. Results. The phases of the active regions determined from the Doppler images follow closely the active longitudes determined earlier from the long-term photometric observations. One active longitude can remain active for several years, but the exact spot configuration within the active longitude changes on much shorter time scales, indicating that the spot lifetime is months instead of years. There are periods during which the spot configuration changes even within days. Measurements using spot latitudes from the Doppler images and spot rotation periods from the photometric observations yield a surface differential rotation law of Ω= (151.30 ◦ /day ± 0.09 ◦ /day) − (1.78 ◦ /day ± 0.12 ◦ /day) sin 2 ψ and the relative differential rotation coefficient α = 0.012 ± 0.002 for FK Comae.

HARPS spectropolarimetry of Herbig Ae/Be stars

Our knowledge of the presence and the strength of magnetic fields in intermediate-mass pre-main-sequence stars remains very poor. We present new magnetic field measurements in six Herbig Ae/Be stars observed with HARPS in spectropolarimetric mode. We downloaded from the European Southern Observatory (ESO) archive the publically available HARPS spectra for six Herbig Ae/Be stars. Wavelength shifts between right- and left-hand side circularly polarised spectra were interpreted in terms of a longitudinal magnetic field , using the moment technique introduced by Mathys. The application of the moment technique to the HARPS spectra allowed us in addition to study the presence of the crossover effect and quadratic magnetic fields. Our search for longitudinal magnetic fields resulted in first detections of weak magnetic fields in the Herbig Ae/Be stars HD58647 and HD98922. Further, we confirm the previous tentative detection of a weak magnetic field in HD104237 by Donati et al. and confirm the previous detection of a magnetic field in the Herbig Ae star HD190073. Surprisingly, the measured longitudinal magnetic field of HD190073, =91+-18G at a significance level of 5sigma is not in agreement with the measurement results of Alecian et al. (2013), =-10+-20G, who applied the LSD method to exactly the same data. No crossover effect was detected for any star in the sample. Only for HD98922 the crossover effect was found to be close to 3sigma with a measured value of -4228+-1443 km/s G. A quadratic magnetic field of the order of 10kG was detected in HD98922, and of ~3.5kG in HD104237.

Magnetic fields of HgMn stars

Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of magnetic fields in these stars using the least-squares deconvolution (LSD) technique have failed to detect magnetic fields, indicating an upper limit on the longitudinal field between 8 and 15 G. In these LSD studies, assumptions were made that all spectral lines are identical in shape and can be described by a scaled mean profile. Aims. We re-analyse the available spectropolarimetric material by applying the moment technique on spectral lines of inhomogeneously distributed elements separately. Furthermore, we present new determinations of the mean longitudinal magnetic field for the HgMn star HD 65949 and the hotter analog of HgMn stars, the PGa star HD 19400, using FORS 2 installed at the VLT. We also give new measurements of the eclipsing system AR Aur with a primary star of HgMn peculiarity, which were obtained with the SOFIN spectropolarimeter installed at the Nordic Optical Telescope. Methods. We downloaded from the European Southern Observatory (ESO) archive the publically available HARPS spectra for eight HgMn stars and one normal and one superficially normal B-type star obtained in 2010. Out of this sample, three HgMn stars belong to spectroscopic double-lined systems. The application of the moment technique to the HARPS and SOFIN spectra allowed us to study the presence of the longitudinal magnetic field, the crossover effect, and quadratic magnetic fields. Results for the HgMn star HD 65949 and the PGa star HD 19400 are based on a linear regression analysis of low-resolution spectra obtained with FORS 2 in spectropolarimetric mode. Results. Our measurements of the magnetic field with the moment technique using spectral lines of several elements separately reveal the presence of a weak longitudinal magnetic field, a quadratic magnetic field, and the crossover effect on the surface of several HgMn stars as well as normal and superficially normal B-type stars. Furthermore, our analysis suggests the existence of intriguing correlations between the strength of the magnetic field, abundance anomalies, and binary properties. The results are discussed in the context of possible mechanisms responsible for the development of the element patches and complex magnetic fields on the surface of late B-type stars.