O. I. Pintado

Multisite spectroscopic seismic study of the β Cep star V2052 Ophiuchi: inhibition of mixing by its magnetic field

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic β Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f1 = 7.148 46 d−1) and by rotational modulation (Prot = 3.638 833 d). Two non-radial low-amplitude modes (f2 = 7.756 03 d−1 and f3 = 6.823 08 d−1) are also detected. The four periodicities that we found are the same as the ones discovered from a companion multisite photometric campaign and known in the literature. Using the photometric constraints on the degrees l of the pulsation modes, we show that both f2 and f3 are prograde modes with (l, m) = (4, 2) or (4, 3). These results allowed us to deduce ranges for the mass (M ∈ [8.2, 9.6] M⊙) and central hydrogen abundance (Xc ∈ [0.25, 0.32]) of V2052 Oph, to identify the radial orders n1 = 1, n2 = −3 and n3 = −2, and to derive an equatorial rotation velocity veq ∈ [71, 75] km s−1. The model parameters are in full agreement with the effective temperature and surface gravity deduced from spectroscopy. Only models with no or mild core overshooting (αov ∈ [0, 0.15] local pressure scale heights) can account for the observed properties. Such a low overshooting is opposite to our previous modelling results for the non-magnetic β Cep star θ Oph having very similar parameters, except for a slower surface rotation rate. We discuss whether this result can be explained by the presence of a magnetic field in V2052 Oph that inhibits mixing in its interior.

Angle-dependent radiative grain alignment Confirmation of a magnetic field - radiation anisotropy angle dependence on the efficiency of interstellar grain alignment

Context. Interstellar grain alignment studies are currently experiencing a renaissance due to the development of a new quantitative theory based on radiative alignment torques (RAT). One of the distinguishing predictions of this theory is a dependence of the grain alignment efficiency on the relative angle (Ψ) between the magnetic field and the anisotropy direction of the radiation field. In an earlier study we found observational evidence for such an effect from observations of the polarization around the star HD 97300 in the Chamaeleon I cloud. However, due to the large uncertainties in the measured visual extinctions, the result was uncertain. Aims. By acquiring explicit spectral classification of the polarization targets, we have sought to perform a more precise reanalysis of the existing polarimetry data. Methods. We have obtained new spectral types for the stars in our for our polarization sample, which we combine with photometric data from the literature to derive accurate visual extinctions for our sample of background field stars. This allows a high accuracy test of the grain alignment efficiency as a function of Ψ. Results. We confirm and improve the measured accuracy of the variability of the grain alignment efficiency with Ψ, seen in the earlier study. We note that the grain temperature (heating) also shows a dependence on Ψ which we interpret as a natural effect of the projection of the grain surface to the illuminating radiation source. This dependence also allows us to derive an estimate of the fraction of aligned grains in the cloud.

On the effective temperatures and surface gravities of superficially normal main sequence band B and A stars

Eective temperatures and surface gravities for 48 main sequence band B and A stars were found by matching optical region spectrophotometry and H profiles with the predictions of ATLAS9 solar composition model atmospheres. When these values were compared with those found using Stromgren uvby photometry based on ATLAS6 model atmospheres, we found a dierence (photometry-spectrophotometry) of 25118 K for 29 stars with 8000 K Te 10 050 K compared to 76 105 K for 14 stars with 10 050 K Te 17 000 K. The surface gravity scales are in agreement. These stars are suciently hot that their eective temperatures and surface gravity determinations are unaected by discrepancies due to the choice of Mixing-Length or Canuto-Mazzitelli convection theories.

Elemental abundance studies of CP stars - III. The magnetic CP stars

Fine analyses of the magnetic CP stars α Scl and HD 170973 are presented using ATLAS9 model atmospheres which have same bulk metallicity as the deduced abundances. The light elements are mostly solar except for silicon, and all the heavier elements except nickel in HD 170973, which is solar, are greatly overabundant. The iron peak elements are typically 10 times overabundant, Sr is of order of 1000 times solar, Y and Zr are of order of 100 times solar. The rare earths are 1000 or more times overabundant.

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In a sample of six young open clusters (NGC 1502, NGC 3105, Stock 16, NGC 6268, NGC 7235, and NGC 7510) we investigated 1753 objects using the narrow band, three filter ∆a photometric system resulting in the detection of eleven bona-fide magnetic chemically peculiar (CP) stars and five Be or metal-weak stars. The results for the distant cluster NGC 3105 is most important because of the still unknown influence of the global metallicity gradient of the Milky Way. These findings confirm that CP stars are present in open clusters of very young ages (log t ≥ 6.90) at galactocentric distances up to 11.4 kpc. For all programme clusters the age, reddening, and distance modulus were derived using the corresponding isochrones. Some additional variable stars within Stock 16 could be identified by comparing different photometric studies.

Scl and HD 170973

We report on the detection of the first extragalactic, classical chemically peculiar (CP) stars more than 100 years after the discovery of this group. Using the tool of CCD

CCD photometric search for peculiar stars in open clusters - VI. NGC 1502, NGC 3105, Stock 16, NGC 6268, NGC 7235 and NGC 7510

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On the detection of the first extragalactic classical chemically peculiar stars

-photometry, eight definite positive detections in the globular-like stellar cluster NGC 1866 and its surrounding in the Large Magellanic Cloud were made. More than 1950 objects within a radius of 9.5′ of the cluster center down to 20.5 magnitude were observed in this three filter, narrow band photometric system. Averaging more than 70 individual frames for all three filters yielded a 3 σ detection limit of 0.015 mag for stars with

Eclipsing Am binary systems in the SuperWASP survey

V=20

CCD photometric search for peculiar stars in open clusters - VIII. King 21, NGC 3293, NGC 5999, NGC 6802, NGC 6830, Ruprecht 44, Ruprecht 115, and Ruprecht 120

mag. Furthermore we found three objects with significantly negative