- ID:
- ivo://CDS.VizieR/J/ApJ/854/78
- Title:
- Magnetohydrodynamic (MHD) simulations. II.
- Short Name:
- J/ApJ/854/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During the lifetime of Sun-like or low-mass stars a significant amount of angular momentum is removed through magnetized stellar winds. This process is often assumed to be governed by the dipolar component of the magnetic field. However, observed magnetic fields can host strong quadrupolar and/or octupolar components, which may influence the resulting spin-down torque on the star. In Paper I (Finley & Matt 2017ApJ...845...46F), we used the magnetohydrodynamic (MHD) code PLUTO Mignone+ 2007ApJS..170..228M ; Mignone 2009MSAIS..13...67M) to compute steady-state solutions for stellar winds containing a mixture of dipole and quadrupole geometries. We showed the combined winds to be more complex than a simple sum of winds with these individual components. This work follows the same method as Paper I, including the octupole geometry, which not only increases the field complexity but also, more fundamentally, looks for the first time at combining the same symmetry family of fields, with the field polarity of the dipole and octupole geometries reversing over the equator (unlike the symmetric quadrupole). We show, as in Paper I, that the lowest-order component typically dominates the spin-down torque. Specifically, the dipole component is the most significant in governing the spin-down torque for mixed geometries and under most conditions for real stars. We present a general torque formulation that includes the effects of complex, mixed fields, which predicts the torque for all the simulations to within 20% precision, and the majority to within ~5%. This can be used as an input for rotational evolution calculations in cases where the individual magnetic components are known.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/410/735
- Title:
- MAG waves in magnetic and rotating stars
- Short Name:
- J/MNRAS/410/735
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The expression for the energy flux of magnetoacoustic-gravity-inertial (MAGI) waves derived in the Part I (Campos, 2011MNRAS.410..717C) of the present paper is applied to the luminosity of stars, leading to more than 60 relations between observable stellar quantities. Three of these relations are compared with empirical data, viz. concerning stellar luminosity or brightness compared with (i) magnetic field strength for strong magnetic stars, (ii) rotation period for fast rotating stars and (iii) mass and temperature for stars in general.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/74.66
- Title:
- Main sequence magnetic stars properties
- Short Name:
- J/other/AstBu/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We reconsidered the previous studies of properties of magnetic stars based on the latest data on average surface magnetic fields of 177 stars. New, corrected results have been obtained that allow a better understanding of the phenomenon of magnetic chemically peculiar stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/2157
- Title:
- Main-sequence star chromospheres
- Short Name:
- J/MNRAS/403/2157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on high-resolution observations of two dM1 stars: Gl 867A, an active dM1e star, and Gl 205, a less active dM1 star. The wavelength coverage is from 3890 to 6820{AA} with a resolving power of about 45000. The difference spectrum of these two stars allows us to make a survey of spectral lines sensitive to magnetic activity.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A116
- Title:
- Maps and datacubes of NGC 7538 IRS 1
- Short Name:
- J/A+A/567/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 7538 IRS 1-3 is a high-mass star-forming cluster with several detected dust cores, infrared sources, (ultra)compact HII regions, molecular outflows, and masers. In such a complex environment, interactions and feedback among the embedded objects are expected to play a major role in the evolution of the region. We study the dust, kinematic, and polarimetric properties of the NGC 7538 IRS 1-3 region to investigate the role of the different forces in the formation and evolution of high-mass star-forming clusters. Methods: We performed SMA high angular resolution observations at 880um with the compact configuration. We developed the RATPACKS code to generate synthetic velocity cubes from models of choice to be compared to the observational data. To quantify the stability against gravitational collapse we developed the "mass balance" analysis that accounts for all the energetics on core scales. We detect 14 dust cores from 3.5M_{sun}_ to 37M_{sun}_ arranged in two larger scale structures: a central bar and a filamentary spiral arm. The spiral arm presents large-scale velocity gradients in H^13^CO^+^ 4-3 and C^17^O 3-2, and magnetic field segments aligned well to the dust main axis. The velocity gradient is reproduced well by a spiral arm expanding at 9km/s with respect to the central core MM1, which is known to power a large precessing outflow. The energy of the outflow is comparable to the spiral-arm kinetic energy, which dominates gravitational and magnetic energies. In addition, the dynamical ages of the outflow and spiral arm are comparable. On core scales, those embedded in the central bar seem to be unstable against gravitational collapse and prone to forming high-mass stars, while those in the spiral arm have lower masses that seem to be supported by non-thermal motions and magnetic fields. The NGC 7538 IRS 1-3 cluster seems to be dominated by protostellar feedback. The dusty spiral arm appears to be formed in a snowplow fashion owing to the outflow from the MM1 core. We speculate that the external pressure from the redshifted lobe of the outflow could trigger star formation in the spiral arm cores. This scenario would form a small cluster with a few central high-mass stars, surrounded by a number of low-mass stars formed through protostellar feedback.
- ID:
- ivo://CDS.VizieR/J/A+A/555/A23
- Title:
- M82-A radio continuum and polarisation study I.
- Short Name:
- J/A+A/555/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to study the cosmic ray propagation and determine the magnetic field strength and dominant loss processes in the nearby prototypical starbursting galaxy M82, a multi-frequency analysis at four radio wavelengths is presented. Archival data from the Westerbork Synthesis Radio Telescope (WSRT) was reduced and a new calibration technique introduced to reach the high dynamic ranges needed for the complex source morphology. These data were combined with archival Very Large Array (VLA) data, yielding total power maps at {lambda}3cm, {lambda}6cm, {lambda}22cm, and {lambda}92cm. The data show a confinement of the emission at wavelengths of {lambda}3/{lambda}6cm to the core region and a largely extended halo reaching up to 4kpc away from the galaxy midplane at wavelengths of {lambda}22/{lambda}92cm up to a sensitivity limit of 90uJy and 1.8mJy respectively indicating different physical processes in the core and halo regions. The results are used to calculate the magnetic field strength to 98uG in the core region and to 24uG in the halo regions. From the observation of ionisation losses, the filling factor of the ionised medium could be estimated to 2%. This leads to a revised view of the magnetic field distribution in the core region and the propagation processes from the core into the halo regions.
- ID:
- ivo://CDS.VizieR/J/A+AS/123/353
- Title:
- Mean magnetic field modulus of Ap stars
- Short Name:
- J/A+AS/123/353
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper reports about a systematic study of the mean magnetic field modulus of Ap stars with magnetically resolved split lines. Tables 2a and 2b present the main properties of all such stars presently known. The results about their mean magnetic field modulus derived in this study are summarized in Table 3, while the individual field measurements are given in Table 4.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/2432
- Title:
- MiMeS magnetic analysis of O-type stars
- Short Name:
- J/MNRAS/465/2432
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis performed on spectropolarimetric data of 97 O-type targets included in the framework of the Magnetism in Massive Stars (MiMeS) Survey. Mean least-squares deconvolved Stokes I and V line profiles were extracted for each observation, from which we measured the radial velocity, rotational and non-rotational broadening velocities, and longitudinal magnetic field B_l_. The investigation of the Stokes I profiles led to the discovery of two new multiline spectroscopic systems (HD 46106, HD 204827) and confirmed the presence of a suspected companion in HD 37041. We present a modified strategy of the least-squares deconvolution technique aimed at optimizing the detection of magnetic signatures while minimizing the detection of spurious signatures in Stokes V. Using this analysis, we confirm the detection of a magnetic field in six targets previously reported as magnetic by the MiMeS collaboration (HD 108, HD 47129A2, HD 57682, HD 148937, CPD-28 2561, and NGC 1624-2), as well as report the presence of signal in Stokes V in three new magnetic candidates (HD 36486, HD 162978, and HD 199579). Overall, we find a magnetic incidence rate of 7+/-3 per cent, for 108 individual O stars (including all O-type components part of multiline systems), with a median uncertainty of the B_l_ measurements of about 50G. An inspection of the data reveals no obvious biases affecting the incidence rate or the preference for detecting magnetic signatures in the magnetic stars. Similar to A- and B-type stars, we find no link between the stars' physical properties (e.g. T_eff_, mass, and age) and the presence of a magnetic field. However, the Of?p stars represent a distinct class of magnetic O-type stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/456/2
- Title:
- MiMeS survey of magnetism in massive stars
- Short Name:
- J/MNRAS/456/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation of the magnetic properties of O- and early B-type stars. Initiated in 2008 and completed in 2013, the project was supported by three Large Program allocations, as well as various programmes initiated by independent principal investigators, and archival resources. Ultimately, over 4800 circularly polarized spectra of 560 O and B stars were collected with the instruments ESPaDOnS (Echelle SpectroPolarimetric Device for the Observation of Stars) at the Canada-France-Hawaii Telescope, Narval at the Telescope Bernard Lyot and HARPSpol at the European Southern Observatory La Silla 3.6m telescope, making MiMeS by far the largest systematic investigation of massive star magnetism ever undertaken. In this paper, the first in a series reporting the general results of the survey, we introduce the scientific motivation and goals, describe the sample of targets, review the instrumentation and observational techniques used, explain the exposure time calculation designed to provide sensitivity to surface dipole fields above approximately 100G, discuss the polarimetric performance, stability and uncertainty of the instrumentation, and summarize the previous and forthcoming publications.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A21
- Title:
- M83 magnetic and gaseous spiral arms images
- Short Name:
- J/A+A/585/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The magnetic field configurations in several nearby spiral galaxies contain magnetic arms that are sometimes located between the material arms. The nearby barred galaxy M83 provides an outstanding example of a spiral pattern seen in tracers of gas and magnetic field. We analyse the spatial distribution of magnetic fields in M83 and their relation to the material spiral arms. Isotropic and anisotropic wavelet transforms are used to decompose the images of M83 in various tracers to quantify structures in a range of scales from 0.2 to 10kpc. We used radio polarization observations at {lambda}6.2cm and {lambda}13cm obtained with the VLA, Effelsberg and ATCA telescopes and APEX sub-mm observations at 870{mu}m, which are first published here, together with maps of the emission of warm dust, ionized gas, molecular gas, and atomic gas. The spatial power spectra are similar for the tracers of dust, gas, and total magnetic field, while the spectra of the ordered magnetic field are significantly different. As a consequence, the wavelet cross-correlation between all material tracers and total magnetic field is high, while the structures of the ordered magnetic field are poorly correlated with those of other tracers. The magnetic field configuration in M83 contains pronounced magnetic arms. Some of them are displaced from the corresponding material arms, while others overlap with the material arms. The pitch angles of the magnetic and material spiral structures are generally similar. The magnetic field vectors at {lambda}6.2cm are aligned with the outer material arms, while significant deviations occur in the inner arms and, in particular, in the bar region, possibly due to non-axisymmetric gas flows. Outside the bar region, the typical pitch angles of the material and magnetic spiral arms are very close to each other at about 10{deg}. The typical pitch angle of the magnetic field vectors is about 20{deg} larger than that of the material spiral arms. One of the main magnetic arms in M83 is displaced from the gaseous arms similarly to the galaxy NGC6946, while the other main arm overlaps a gaseous arm, similar to what is observed in M51. We propose that a regular spiral magnetic field generated by a mean-field dynamo is compressed in material arms and partly aligned with them. The interaction of galactic dynamo action with a transient spiral pattern is a promising mechanism for producing such complicated spiral patterns as in M83.
