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J/A+A/601/A14        Radial velocities of magnetic Ap stars       (Mathys, 2017)

Ap stars with magnetically resolved lines: Magnetic field determinations from Stokes I and V spectra. Mathys G. <Astron. Astrophys. 601, A14 (2017)> =2017A&A...601A..14M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, Ap ; Radial velocities Keywords: stars: chemically peculiar - stars: magnetic field - stars: rotation - binaries: general - stars: oscillations Abstract: 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. Description: Radial velocities measured at multiple epochs for 43 Ap stars with resolved magnetically split lines, from observations of Mathys (1991A&AS...89..121M), Mathys et al. (1997, Cat. J/A+AS/123/353), Mathys & Hubrig (1997A&AS..124..475M), and the present paper. As described in the latter, the adopted value for the measurements uncertainties is 2km/s for those based on spectra recorded in circular polarisation with the ESO CASPEC spectrograph, and 1km/s for all other determinations, from high-resolution spectra recorded in natural light with various combinations of telescopes and instruments. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 107 43 Ap stars with resolved magnetically split lines: stars for which new measurements of the mean magnetic field modulus are presented in this paper apres_rv.dat 28 1297 *Radial velocity measured at multiple epochs for 42 Ap stars
Note on apres_rv.dat: Radial velocities published in Wade et al., 1999, Cat. J/A+A/347/164).
See also: J/A+AS/123/353 : Mean magnetic field modulus of Ap stars (Mathys, 1997) J/A+A/347/164 : HD 59435 Geneva photometry (Wade+, 1999) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 6 I6 --- HD/HDE HD/HDE star number 8- 20 A13 --- OName Other id. 22- 27 F6.3 mag Vmag V magnitude 29- 38 A10 --- SpType MK spectral type 41- 42 A2 --- l_Per [> ] Limit flag on Per 43- 52 F10.5 d Per ? Period 53 A1 --- u_Per [:?] Uncertaitny flag on Per 54 A1 --- x_Per [dy] Unit for Period 56- 61 F6.4 --- Per2 ? Second possible period for HD 70331 62 A1 --- x_Per2 [d] Unit for Period2 70- 71 I2 --- r_Per ? Period reference (1) 73- 83 F11.3 d HJD0 ? Phase origin (Julian Date) 85-104 A20 --- n_HJD0 Phase origin information 106-107 I2 --- r_HJD0 ? Reference for HJD0
Note (1): References as follows: 1 = Romanyuk et al. (2014AstBu..69..427R) 2 = Mathys et al. (1997A&AS..124..475M) 3 = Metlova et al. (2014AstBu..69..315M) 4 = Wade et al. (2000A&A...355.1080W) 5 = Mathys et al. (2016, Cat. J/A+A/586/A85) 6 = Wade et al. (1999, Cat. J/A+A/347/164) 7 = Hill et al. (1998MNRAS.297..236H) 8 = Adelman (1997, Cat. J/PASP/109/9) 9 = Adelman (1981A&AS...44..265A, Cat. III/89) 10 = Preston (1970ApJ...160.1059P) 11 = Kurtz (1989MNRAS.238..261K) 12 = Bailey et al. (2011A&A...535A..25B) 13 = Mathys et al. (2007, Cat. J/A+AS/123/353) 14 = Mathys (1991A&AS...89..121M) 15 = Landstreet (unpublished cited by Mathys 1991A&AS...89..121M) 16 = Wolff (1969ApJ...158.1231W) 17 = Adelman (2006PASP..118...77A) 18 = Wade et al. (1996A&A...313..209W) 19 = Wade et al. (1997MNRAS.292..748W) 20 = Bychkov et al. (2016MNRAS.455.2567B) 21 = Manfroid & Mathys (1997A&A...320..497M)
Byte-by-byte Description of file: apres_rv.dat
Bytes Format Units Label Explanations
1- 6 I6 --- HD/HDE HD/HDE star number 8- 18 F11.3 --- HJD Heliocentric Julian Date of the observation 20- 24 F5.1 km/s HRV Heliocentric radial velocity 26- 28 F3.1 km/s s_HRV Uncertainty of the measured radial velocity
Acknowledgements: Gautier Mathys, gmathys(at)eso.org
(End) Gautier Mathys [JAO/ESO, Chile], Patricia Vannier [CDS] 27-Feb-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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