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31. Polarisation and magnetic fields in Ap stars
ID:
ivo://CDS.VizieR/J/MNRAS/426/1003
Title:
Polarisation and magnetic fields in Ap stars
Short Name:
J/MNRAS/426/1003
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper we describe and evaluate new spectral line polarization observations obtained with the goal of mapping the surfaces of magnetic Ap stars in great detail. One hundred complete or partial Stokes IQUV sequences, corresponding to 297 individual polarized spectra, have been obtained for seven bright Ap stars using the Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) and NARVAL high-resolution spectropolarimeters. The targets span a range of masses from approximately 1.8 to 3.4M_{sun}_, a range of rotation periods from 2.56 to 6.80d and a range of maximum longitudinal magnetic field strengths from 0.3 to over 4kG. For three of the seven stars, we have obtained dense phase coverage sampling the entire rotational cycle.
32. Radial velocities of magnetic Ap stars
ID:
ivo://CDS.VizieR/J/A+A/601/A14
Title:
Radial velocities of magnetic Ap stars
Short Name:
J/A+A/601/A14
Date:
21 Oct 2021
Publisher:
CDS
Description:
Some Ap stars that have a strong enough magnetic field and a sufficiently low v sin i show spectral lines resolved into their magnetically split components. We present the results of a systematic study of the magnetic fields and other properties of those stars. Methods. This study is based on 271 new measurements of the mean magnetic field modulus <B> of 43 stars, 231 determinations of the mean longitudinal magnetic field <Bz> and of the crossover <Xz> of 34 stars, and 229 determinations of the mean quadratic magnetic field <Bq> of 33 stars. Those data were used to derive new values or meaningful lower limits of the rotation periods Prot of 21 stars. Variation curves of the mean field modulus were characterised for 25 stars, the variations of the longitudinal field were characterised for 16 stars, and the variations of the crossover and of the quadratic field were characterised for 8 stars. Our data are complemented by magnetic measurements from the literature for 41 additional stars with magnetically resolved lines. Phase coverage is sufficient to define the curve of variation of Hm for 2 of these stars. Published data were also used to characterise the Hz curves of variation for 10 more stars. Furthermore, we present 1297 radial velocity measurements of the 43 Ap stars in our sample that have magnetically resolved lines. Nine of these stars are spectroscopic binaries for which new orbital elements were derived. The existence of a cut-off at the low end of the distribution of the phase-averaged mean magnetic field moduli <B>av of the Ap stars with resolved magnetically split lines, at about 2.8kG, is confirmed. This reflects the probable existence of a gap in the distribution of the magnetic field strengths in slowly rotating Ap stars, below which there is a separate population of stars with fields weaker than ~2kG. In more than half of the stars with magnetically resolved lines that have a rotation period shorter than 150 days, <B>av>7.5kG, while those stars with a longer period all have <B>av<7.5kG. The difference between the two groups is significant at the 100.0% confidence level. The relative amplitudes of variation of the mean field modulus may tend to be greater in stars with Prot>100d than in shorter period stars. The root-mean-square longitudinal fields of all the studied stars but one is less than one-third of their phase-averaged mean field moduli, which is consistent with the expected behaviour for fields whose geometrical structure resembles a centred dipole. However, moderate but significant departures from the latter are frequent. Crossover resulting from the correlation between the Zeeman effect and the rotation-induced Doppler effect across the stellar surface is definitely detected in stars with rotation periods of up to 130 days and possibly even up to 500 days. Weak, but formally significant crossover of constant sign, has also been observed in a number of longer period stars, which could potentially be caused by pulsation velocity gradients across the depth of the photosphere. The quadratic field is in average ~1.3 times greater than the mean field modulus and both of those moments vary with similar relative amplitudes and almost in phase in most stars. Rare exceptions almost certainly have unusual field structures. The distribution of the known values and lower limits of the rotation periods of the Ap stars with magnetically resolved lines indicates that for some of them, Prot must almost certainly reach 300 years or possibly even much higher values. Of the 43 Ap stars that we studied in detail, 22 are in binary systems. The shortest orbital period P_orb of those systems is 27 days. For those non-synchronised Ap binaries for which both the rotation period and the orbital period, or meaningful lower limits thereof, are reliably determined, the distribution of the orbital periods of the systems in which the Ap star has a rotation period that is shorter than 50 days is different from its distribution for those systems in which the rotation period of the Ap star is longer, at a confidence level of 99.6%. The shortest rotation and orbital periods are mutually exclusive: all but one of the non-synchronised systems that contain an Ap component with Prot<50d, have Porb>1000d. Stars with resolved magnetically split lines represent a significant fraction, of the order of several percent, of the whole population of Ap stars. Most of these stars are genuine slow rotators, whose consideration provides new insight into the long-period tail of the distribution of the periods of Ap stars. Emerging correlations between rotation periods and magnetic properties provide important clues for the understanding of the braking mechanisms that have been at play in the early stages of stellar evolution. The geometrical structures of the magnetic fields of Ap stars with magnetically resolved lines appear in general to depart slightly, but not extremely, from centred dipoles. However, there are a few remarkable exceptions, which deserve further consideration. Confirmation that pulsational crossover is indeed occurring at a detectable level would open the door to the study of non-radial pulsation modes of degree l, which is too high for photometric or spectroscopic observations. How the lack of short orbital periods among binaries containing an Ap component with magnetically resolved lines is related to their (extremely) slow rotation remains to be fully understood, but the very existence of a correlation between the two periods lends support to the merger scenario for the origin of Ap stars.
33. Speckle interferometry of Ap stars
ID:
ivo://CDS.VizieR/J/other/AstBu/67.44
Title:
Speckle interferometry of Ap stars
Short Name:
J/other/AstBu/67
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of speckle interferometry of a sample of 117 chemically peculiar stars with global magnetic fields. The observations were made in December 2009 at the BTA with a spatial resolution of about 0.02 arcseconds in the visual spectral region. Twenty-nine stars were resolved into individual components, 14 of them for the first time (HD965, HD5797, HD8855, HD10783, HD16605, HD21699, HD35502, HD51418, HD64486, HD79158, HD103498, HD108651, HD213918, HD293764). In twelve cases a companion turned out to be 2-4 magnitudes fainter than the main component - a magnetic star. Young hot Bp stars HD35502 and HD213918 are exceptions, since their companions are fainter by about 1 magnitude. In all cases, the linear distance from a star to its companion at the epoch of observations in the picture plane exceeded 10^9^km. Eighty-eight magnetic CP stars revealed no secondary components within our study. Thus, the fraction of speckle interferometric binaries in our sample amounts to 25%.
34. Speckle interferometry of Ap stars. II.
ID:
ivo://CDS.VizieR/J/other/AstBu/69.296
Title:
Speckle interferometry of Ap stars. II.
Short Name:
J/other/AstBu/69
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of speckle interferometric observations of 156 stars possessing global magnetic fields, carried out with the 6-m BTA telescope of the Special Astrophysical Observatory. Virtually all stars were observed between 2010 and 2012. Thirty-four stars were resolved into individual components (31 double and 3 triple), of which 14 binary systems (BD+41 43, HD2887, HD30466, HD36540, HD36955, HD37479, HD61045, HD89069, HD144334, HD164258, HD349321, HD343872, HD184471, HD196691) and 2 triple systems (HD37140, HD338226) were for the first time resolved by the astrometric method.
35. ubvy Photometry of magnetic CP stars
ID:
ivo://CDS.VizieR/J/A+AS/103/1
Title:
ubvy Photometry of magnetic CP stars
Short Name:
J/A+AS/103/1
Date:
21 Oct 2021
Publisher:
CDS
Description:
Differential Stroemgren uvby photometric observations from the Four College Automated Photoelectric Telescope of four magnetic Chemically Peculiar stars are presented. We refined the period of 63 And to 4.1890 days. The period of the sharp-lined Si star HD 192913 is 16.840 days, a value close to, but slightly different from published values. HR 8240, a sharp-lined Si star, is found not to be a photometric variable. Comparison of four color photometry of 108 Aqr by Morrison and Wolff and from the Four College APT indicates that subtle changes in the shapes of the light curves, especially that for u, have occurred suggesting that this star may be precessing.
36. Variations of Ap stars in the Geneva system
ID:
ivo://CDS.VizieR/J/A+AS/127/201
Title:
Variations of Ap stars in the Geneva system
Short Name:
J/A+AS/127/201
Date:
21 Oct 2021
Publisher:
CDS
Description:
The photometric behaviour of 21 Ap stars has been analyzed from observations obtained in the Geneva system. Variability has been detected for 9 Ap stars, as well as for a star which initially was a comparison star. Preliminary values for the periods are presented as well as an analytical description of the light curves. The material has been collected during a 23-night observing run at La Silla with the 70cm telescope of the Geneva Observatory equipped with the standard Geneva photometer. The parameters of a second-order cosine fit to the lightcurves are stored in the accompanying table. Time origin is JD 2450000.0. The 17 phase diagrams for each of the 9 stars are presented in 9 postscript files. The observational data are superimposed on the Fourier fit. Data are differential, except for HD 191439 and HD 192674 which had no suitable comparisons.