High-Resolution Magnetic Field Measurements of RR Lyrae Stars with SemPol

2009 ◽  
Author(s):  
E. Guggenberger ◽  
K. Kolenberg ◽  
S. C. Marsden ◽  
I. A. Waite ◽  
H. F. Henrichs ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Field Measurements ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Magnetic Field Measurements ◽  
Lyrae Stars

scholarly journals Magnetic Models Can Not Explain The Blazhko Effect in RR Lyrae Stars

2004 ◽  
Vol 193 ◽  
pp. 535-538
Author(s):  
M. Chadid ◽  
S.L.S. Shorlin ◽  
J.D. Landstreet
Keyword(s):  
Magnetic Field ◽  
Longitudinal Magnetic Field ◽  
Field Measurements ◽  
Magnetic Star ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Magnetic Field Measurements ◽  
Blazhko Effect ◽  
Bona Fide ◽  
Lyrae Stars

AbstractWe report a new series of high-precision Stokes V profiles and longitudinal magnetic field measurements of RR Lyrae, obtained with the MuSiCoS spectropolarimeter over a period of four years. These data provide no evidence whatsoever for a strong magnetic field in the photosphere of RRLyrae, which is consistent with Preston’s (1967) results, but inconsistent with apparent magnetic field detections by Babcock (1958) and Romanov et al. (1987, 1994). Following discussion of these disparate results, we conclude that RR Lyrae is a bona fide non-magnetic star, a conclusion which leads to the general falsification of models of the Blazkho effect requiring strong photospheric magnetic fields.

scholarly journals High resolution magnetic field measurements in high-mass star-forming regions using masers

2016 ◽  
Author(s):  
Gabriele Surcis ◽  
Wouter H.T. Vlemmings ◽  
Huib Jan van Langevelde ◽  
Busaba Hutawarakorn Kramer
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Field Measurements ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Magnetic Field Measurements

scholarly journals Magnetohydrostatic modeling of AR11768 based on a SUNRISE/IMaX vector magnetogram

2020 ◽  
Vol 640 ◽  
pp. A103 ◽  
Author(s):  
X. Zhu ◽  
T. Wiegelmann ◽  
S K. Solanki
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Field Measurements ◽  
Plasma Pressure ◽  
Photospheric Magnetic Field ◽  
Solar Photosphere ◽  
Free Layer ◽  
Lower Boundary Condition ◽  
Magnetic Field Measurements ◽  
The Magnetic Field

Context. High-resolution magnetic field measurements are routinely only done in the solar photosphere. Higher layers, such as the chromosphere and corona, can be modeled by extrapolating these photospheric magnetic field vectors upward. In the solar corona, plasma forces can be neglected and the Lorentz force vanishes. This is not the case in the upper photosphere and chromosphere where magnetic and nonmagnetic forces are equally important. One way to deal with this problem is to compute the plasma and magnetic field self-consistently, in lowest order with a magnetohydrostatic (MHS) model. The non-force-free layer is rather thin and MHS models require high-resolution photospheric magnetic field measurements as the lower boundary condition. Aims. We aim to derive the magnetic field, plasma pressure, and density of AR11768 by applying the newly developed extrapolation technique to the SUNRISE/IMaX data embedded in SDO/HMI magnetogram. Methods. We used an optimization method for the MHS modeling. The initial conditions consist of a nonlinear force-free field (NLFFF) and a gravity-stratified atmosphere. During the optimization procedure, the magnetic field, plasma pressure, and density are computed self-consistently. Results. In the non-force-free layer, which is spatially resolved by the new code, Lorentz forces are effectively balanced by the gas pressure gradient force and gravity force. The pressure and density are depleted in strong field regions, which is consistent with observations. Denser plasma, however, is also observed at some parts of the active region edges. In the chromosphere, the fibril-like plasma structures trace the magnetic field nicely. Bright points in SUNRISE/SuFI 3000 Å images are often accompanied by the plasma pressure and electric current concentrations. In addition, the average of angle between MHS field lines and the selected chromospheric fibrils is 11.8°, which is smaller than those computed from the NLFFF model (15.7°) and linear MHS model (20.9°). This indicates that the MHS solution provides a better representation of the magnetic field in the chromosphere.

scholarly journals High Resolution Magnetic Field Measurements in the Sunspot Photosphere

1993 ◽  
Vol 141 ◽  
pp. 11-19
Author(s):  
Axel Hofmann ◽  
Wolfgang Schmidt ◽  
Horst Balthasar ◽  
Theodore T. Tarbell ◽  
Zoe A. Frank
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Field Strength ◽  
Spectral Resolution ◽  
Field Measurements ◽  
Brightness Variation ◽  
Longitudinal Component ◽  
Azimuthal Variation ◽  
Magnetic Field Measurements ◽  
The Magnetic Field

AbstractWe analysed calibrated Stokes V magnetograms and simultaneously measured Stokes I spectra of high spatial and spectral resolution taken in a medium sized sunspot. We found a clear (anti-) correlation between the brightness variation of penumbral structures and the longitudinal component (B*cosγ) of the magnetic field. No azimuthal variation of the amount of the magnetic field strength (B) was observed across dark and bright structures. There the field is more vertical in bright filaments compared to dark ones.

scholarly journals The Oblique Pulsator Model for the Blazhko Effect in RR Lyrae Stars. Theory of Amplitude Modulation I

2000 ◽  
Vol 176 ◽  
pp. 299-306 ◽  
Author(s):  
Hiromoto Shibahashi
Keyword(s):  
Magnetic Field ◽  
Symmetry Axis ◽  
Rotation Axis ◽  
Oscillation Mode ◽  
Stellar Rotation ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Quadrupole Component ◽  
Blazhko Effect ◽  
Lyrae Stars

AbstractBy assuming that RR Lyrae stars have fairly strong dipole magnetic fields with symmetry axis oblique to the rotation axis of the star, I show that the oscillation mode which would be a pure radial oscillation in absence of the magnetic field has a quadrupole component, whose symmetry axis coincides with the magnetic axis. The aspect angle of the quadrupole component changes due to the stellar rotation, and this apparent amplitude variation is interpreted as the Blazhko effect in RR Lyrae stars. It is shown that, in the case of off-axis magnetic field, phase modulation is expected. I list up some theoretical predictions based on this model, which would observationally examine this hypothesis.

scholarly journals New results on field and cluster RR Lyraes

1993 ◽  
Vol 139 ◽  
pp. 335-336
Author(s):  
G. Clementini ◽  
R. Merighi ◽  
M. Tosi ◽  
R. Gratton ◽  
E. Carretta
Keyword(s):  
High Resolution ◽  
Horizontal Branch ◽  
Chemical Abundance ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Horizontal Branch Stars ◽  
The Galaxy ◽  
Metal Abundance ◽  
Lyrae Stars ◽  
Good Agreement

AbstractRR Lyrae stars both in the field and in clusters can be used to derive the metal abundance of the regions and systems where they are found.(1) New data have been collected on a sample of field ab-type RR Lyraes with the aim of studying the composition of the halo and the disk of the galaxy, (Clementini et al. 1992a, in preparation), using the relation found by Clementini et al. (1991), (hereafter CTM91), between [Fe/H] and the equivalent width of the Ca II K-line W‘(K). (2) A quantitative chemical abundance analysis of the ab type RR Lyrae (V29) in the globular cluster M4 has been performed using high resolution, high S/N spectroscopy. We obtain [Fe/H]=–1.3 ± 0.2 and the α– elements (Mg and Ti) are overabundant by 0.6 dex. These results are in good agreement with determinations from high resolution spectra of giants and blue horizontal branch stars (Clementini et al. 1992b, in preparation).

scholarly journals Metallicities from high-resolution spectra of 49 RR Lyrae variables

2021 ◽  
Vol 503 (4) ◽  
pp. 4719-4733
Author(s):  
Christina K Gilligan ◽  
Brian Chaboyer ◽  
Massimo Marengo ◽  
Joseph P Mullen ◽  
Giuseppe Bono ◽  
...  
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Large Telescope ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Lyrae Stars

ABSTRACT Accurate metallicities of RR Lyrae are extremely important in constraining period–luminosity–metallicity (PLZ) relationships, particularly in the near-infrared. We analyse 69 high-resolution spectra of Galactic RR Lyrae stars from the Southern African Large Telescope. We measure metallicities of 58 of these RR Lyrae stars with typical uncertainties of 0.15 dex. All but one RR Lyrae in this sample has accurate ($\sigma _{\varpi }\lesssim 10{{\ \rm per\ cent}}$) parallax from Gaia. Combining these new high-resolution spectroscopic abundances with similar determinations from the literature for 93 stars, we present new PLZ relationships in WISE W1 and W2 magnitudes, and the Wesenheit magnitudes W(W1, V − W1) and W(W2, V − W2).

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