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- ID:
- ivo://CDS.VizieR/J/A+A/407/631
- Title:
- Catalogue of stellar effective magnetic fields
- Short Name:
- J/A+A/407/631
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the catalogue of averaged quadratic effective magnetic fields <B_e_> for 596 main sequence and giant stars. The catalogue is derived from measurements of the stellar effective magnetic field strengths B_e_, which were compiled from the existing literature.
- ID:
- ivo://CDS.VizieR/J/A+A/636/A45
- Title:
- CEGM03 model and related gravity anomaly data
- Short Name:
- J/A+A/636/A45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chinese lunar missions have grown in number over the last ten years, with an increasing focus on radio science investigations. In previous work, we estimated two lunar gravity field models, CEGM01 and CEGM02. The recently lunar mission, Chang'e 5T1, which had an orbital inclination between 18 and 68 degree, and collected orbital tracking data continually for two years, made an improved gravity field model possible. We aimed to estimate a new lunar gravity field model up to degree and order 100, CEGM03, and a new tidal Love number based on the Chang'e 5T1 tracking data combined with the historical tracking data ever used in the solution of CEGM02. The new model makes use of tracking data with this particular inclination, which has not been used in previous gravity field modeling. The solution for this new model was based on our in-house software, LUGREAS. The gravity spectrum power, postfit residuals after precision orbit determination (POD), lunar surface gravity anomalies, correlations between parameters, admittance/coherence with topography model, and accuracy of POD were analyzed to validate the new CEGM03 model. We analyzed the tracking data of the Chang'e 5T1 mission and estimated the CEGM03 lunar gravity field model. We found that the two-way Doppler measurement accuracy reached the 0.2 mm/s with 10 s integration time. The error spectrum shows that the formal error for CEGM03 was at least reduced by about 2 times below the harmonic degree of 20, when compared to the CEGM02 model. The gravity and topography admittance/correlation was also improved when compared to the correlations for the CEGM02 model. The lunar potential Love number k2 was estimated to be 0.02430+/-0.0001 (ten times the formal error). From the model analysis and comparison of the various models, we identified improvements in the CEGM03 model after introducing Chang'e 5T1 tracking data. Moreover, this study illustrates how the low and middle inclination orbits could contribute better accuracy for a low degree of lunar gravity field.
- ID:
- ivo://CDS.VizieR/J/A+A/629/A83
- Title:
- Complexity of magnetic fields on red dwarfs
- Short Name:
- J/A+A/629/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Generation, amplification, and evolution of magnetic fields in cool stars can be investigated by measuring the Zeeman effect in atomic and molecular lines observed in their spectra. In particular, Zeeman line broadening and polarization have been used for detecting magnetic fields in stellar atmospheres. Similar to the Sun, these fields are complex and height-dependent (i.e., comprise 3D structures) and require advanced diagnostics. Fortunately, many molecular lines dominating M-dwarf spectra, such as FeH, CaH, MgH, and TiO, are temperature- and Zeeman- sensitive and form at different atmospheric heights, which makes them excellent probes of magnetic fields on M dwarfs. Our goal is to analyze the complexity of magnetic fields in M dwarfs. We investigate how magnetic fields vary with the stellar temperature (i.e., mass) and how "surface" inhomogeneities are distributed in height - the dimension that is usually neglected in stellar magnetic studies. This is achieved by including many atomic and molecular species in our study. We have determined effective temperatures of the photosphere and of magnetic features, magnetic field strengths and filling factors for nine M dwarfs (M1-M7). Our chi^2^ analysis is based on a comparison of observed and synthetic intensity and circular polarization profiles (Stokes I and V) of many magnetically sensitive atomic and molecular lines in ten wavelength regions. Stokes profiles were calculated by solving polarized radiative transfer equations under the local thermodynamic equilibrium using model atmospheres. We have found that properties of magnetic structures depend on the analyzed atomic or molecular species and their formation heights within the atmosphere. Two types of magnetic features similar to those on the Sun have been found: one is cooler (starspots), while the other one is hotter (network, small-scale magnetic features). The magnetic field strength in both starspots and network is within 3kG to 6kG, on average it is 5kG for the M1-M7 spectral class range. These fields occupy a large fraction of M dwarf atmospheres at all heights, up to 100%. The plasma beta is less than one throughout the entire M dwarf atmospheres, implying that they are highly magnetized stars. A combination of many molecular and atomic species and a simultaneous analysis of intensity and circular polarization spectra have allowed us to better decipher the complexity of magnetic fields on M dwarfs, including their dependence on the height within the atmosphere. This work provides an opportunity to investigate a larger sample of M dwarfs as well as L-type brown dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/738/119
- Title:
- Conversion from magnetoacoustic to Alfven waves
- Short Name:
- J/ApJ/738/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Alfven waves may be generated via mode conversion from fast magnetoacoustic waves near their reflection level in the solar atmosphere, with implications both for coronal oscillations and for active region helioseismology. In active regions this reflection typically occurs high enough that the Alfven speed a greatly exceeds the sound speed c, well above the a=c level where the fast and slow modes interact. In order to focus on the fundamental characteristics of fast/Alfven conversion, stripped of unnecessary detail, it is therefore useful to freeze out the slow mode by adopting the gravitationally stratified cold magnetohydrodynamic model c->0. This provides a benchmark for fast-to-Alfven mode conversion in more complex atmospheres. Assuming a uniform inclined magnetic field and an exponential Alfven speed profile with density scale height h, the Alfven conversion coefficient depends on three variables only: the dimensionless transverse-to-the-stratification wavenumber {kappa}=kh, the magnetic field inclination from the stratification direction {theta}, and the polarization angle {phi} of the wavevector relative to the plane containing the stratification and magnetic field directions. We present an extensive exploration of mode conversion in this parameter space and conclude that near-total conversion to outward-propagating Alfven waves typically occurs for small {theta} and large {phi} (80-90{deg}), though it is absent entirely when {theta} is exactly zero (vertical field). For wavenumbers of helioseismic interest, the conversion region is broad enough to encompass the whole chromosphere.
- ID:
- ivo://CDS.VizieR/J/other/SoPh/294.144
- Title:
- Coronal hole parameters
- Short Name:
- J/other/SoPh/294
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Coronal holes are usually defined as dark structures seen in the extreme ultraviolet and X-ray spectrum which are generally associated with open magnetic fields. Deriving reliably the coronal hole boundary is of high interest, as its area, underlying magnetic field, and other properties give important hints as regards high speed solar wind acceleration processes and compression regions arriving at Earth. In this study we present a new threshold-based extraction method, which incorporates the intensity gradient along the coronal hole boundary, which is implemented as a user-friendly SSW-IDL GUI. The Collection of Analysis Tools for Coronal Holes (CATCH) enables the user to download data, perform guided coronal hole extraction and analyze the underlying photospheric magnetic field. We use CATCH to analyze non-polar coronal holes during the SDO-era, based on 193{AA} filtergrams taken by the Atmospheric Imaging Assembly (AIA) and magnetograms taken by the Heliospheric and Magnetic Imager (HMI), both on board the Solar Dynamics Observatory (SDO). Between 2010 and 2019 we investigate 707 coronal holes that are located close to the central meridian. We find coronal holes distributed across latitudes of about +/-60{deg}, for which we derive sizes between 1.6x10^9^ and 1.8x10^11^km^2^. The absolute value of the mean signed magnetic field strength tends towards an average of 2.9+/-1.9G. As far as the abundance and size of coronal holes is concerned, we find no distinct trend towards the northern or southern hemisphere. We find that variations in local and global conditions may significantly change the threshold needed for reliable coronal hole extraction and thus, we can highlight the importance of individually assessing and extracting coronal holes.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/72.391
- Title:
- CP stars magnetic fields catalog (2010)
- Short Name:
- J/other/AstBu/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of measuring longitudinal magnetic fields (B_e_), rotation velocities (v_esini_), and radial velocities (V_r_) of 92 stars observed with the Main Stellar Spectrograph (MSS) of the 6-m BTA telescope of the Special Astrophysical Observatory in 2010. Observations of standard stars without magnetic fields confirm the absence of systematic errors capable of introducing distortions into the longitudinal-field measurement results.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/70.444
- Title:
- CP stars magnetic fields catalog (2008)
- Short Name:
- J/other/AstBu/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the magnetic field measurements of 37 chemically peculiar and 4 normal main sequence stars using circularly polarized spectra obtained in 2008 with a Zeeman analyzer on the Main Stellar Spectrograph (MSS) of the Russian 6-m telescope (BTA). Four new magnetic stars have been discovered (HD25999, HD35100, HD96237, and HD279021), the presence of a field was suspected in two stars (HD2887 and BD-12 2366), 16 previously known CP stars were continued to be monitored to study their fields. The results of the longitudinal magnetic field B_e_ measurements show that in stars with narrow spectral lines, systematic errors in B_e_ determination do not exceed 10-20G, which is within the statistical error. Our study of stars with reliable phase curves of the longitudinal field B_e_ show that there are no instrumental effects which can distort the observations.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/71.302
- Title:
- CP stars magnetic fields catalog (2009)
- Short Name:
- J/other/AstBu/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of measuring longitudinal magnetic fields (B_e), rotation velocities (v_e_sini), and radial velocities (V_r_) of 44 stars observed with the Main Stellar Spectrograph (MSS) of the 6-m BTA telescope of the Special Astrophysical Observatory in 2009. Observations of standard stars without magnetic fields confirm the absence of systematic errors capable of introducing distortions into the longitudinal-field measurement results. In this work we comment on the results for each of the stars.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/69.427
- Title:
- CP stars magnetic fields catalog (2007)
- Short Name:
- J/other/AstBu/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog presents the results of magnetic field measurements for 39 chemically peculiar and 3 normal main sequence stars used as standard stars. Observations were carried out with the Main Stellar Spectrograph of the Russian 6-m telescope during 2007. The accuracy analysis for the longitudinal magnetic field measurements of the stars confirms that the systematic errors do not exceed 10-20G and are within the quoted limits. The absence of significant instrumental deviations follows from the measurements of theBD CP stars with well-known B_e_ variation curves.
