How fast is 467 kts

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Some also feature a space where passengers can stow carry-on items inside the cabin. Super Mid Jets The super mid-size jet aircraft is popular among the long-range travel clientele. Get an Instant Quote. Search Monarch. The analysis of the X-ray spectrum of HR also suggests the presence of a non-thermal radiation. Comparison between the spectral index of the power-law X-ray energy distribution with the non-thermal electron energy distribution indicates that the non-thermal X-ray component could be the auroral signature of the non-thermal electrons that impact the stellar surface, the same non-thermal electrons that are responsible for the observed radio emission.

On the basis of our analysis, we suggest a novel model that simultaneously explains the X-ray and the radio features of HR and is likely relevant for magnetospheres of other magnetic early-type stars.

Stellar magnetism at the top of the main sequence is not typical, but neither is it an extremely rare phenomenon. In fact about 10 per cent of the OB-type stars display strong and stable magnetic fields Grunhut et al. The hot magnetic stars are mainly characterized as oblique magnetic rotators OMR : a dipolar magnetic field topology with field axis misaligned with respect to the rotation axis Babcock ; Stibbs The existence of such well-ordered magnetic fields are a cause of inhomogeneous photospheres, giving rise to observable photometric, spectroscopic and magnetic variability that can be explained in the framework of the OMR.

Early-type magnetic stars are sufficiently hot to produce a radiatively driven stellar wind that in the presence of their large-scale magnetic fields may be strongly aspherical.

The wind plasma accumulates at low magnetic latitudes inner magnetosphere , whereas it can freely propagate along directions near the magnetic poles Shore ; Leone The interaction of a radiatively driven wind with the stellar magnetosphere has been well studied.

Evidence of circumstellar matter bound to the strong stellar magnetic field has been reported in a few other cases Leone et al. The stellar rotation plays an important role in establishing the size of the RRM, and the density of the plasma trapped inside. The existence of a CM filled by stellar wind material is a suitable condition to give rise to non-thermal radio continuum emission that was first measured for peculiar magnetic B and A stars Drake et al.

The radio emission features are characterized by a simple dipolar magnetic field topology and have been successfully reproduced using a 3D model that computes the gyro-synchrotron emission Trigilio et al. In this model, the non-thermal electrons responsible for the radio emission originate in magnetospheric regions far from the stellar surface, where the kinetic energy density of the gas is high enough to brake the magnetic field lines forming current sheets.

These regions are the sites where the mildly relativistic electrons originate. Energetic electrons that recirculate through this layer back to the inner magnetosphere radiate radio by the gyro-synchrotron emission mechanism.

The analysis of radio emissions from magnetic early-type stars is a powerful diagnostic tool for the study of the topology of their magnetospheres. The radio radiation at different frequencies probes the physical conditions of the stellar magnetosphere at different depths, even topologies are complex Leto et al.

Hence, the radio emission of the hot magnetic stars provides a favoured window to study the global magnetic field topology, the spatial stratification of the thermal electron density, the non-thermal electron number density and interactions between stellar rotation, wind and magnetic field. In fact, the above physical parameters can be derived by comparing the multiwavelength radio light curves, for the total and circularly polarized flux density, with synthetic light curves using our 3D theoretical model.

It is then possible to study how such stellar properties as rotation, wind, magnetic field geometry affect the efficiency of the electron acceleration mechanism. In particular, it is important to apply the radio diagnostic techniques on a sample of magnetic early-type stars that differ in their stellar rotation periods, magnetic field strengths and field geometries. To this end, we conducted a radio survey of a representative sample of hot magnetic stars using the Karl G.

These stars probe different combinations of source parameters owing to their different physical properties. This paper presents the first results of this extensive study. Here, we present the analysis of the radio emission from the fast rotating, hot magnetic star HR We were able to reproduce multiwavelength radio light curves for the total and the circularly polarized flux density.

The model simulation of the radio light curves, along with a simulation of the X-ray spectrum of HR , are used to significantly constrain the physical parameters of its stellar magnetosphere. On this basis, we suggest a scenario that simultaneously explains the behaviour of HR at both radio and X-ray wavelengths. In Section 2 , we briefly introduce the object of this study, HR The observations used in our analyses are presented in Section 3. The radio properties of HR are discussed in detail in Section 4.

Section 5 describes the model, while stellar magnetosphere is presented in Section 6. Analysis of X-ray emission of HR is provided in Section 6. The considerations on auroral radio emission in HR are given in Section 7 , while Section 8 summarizes the results of our work. This star evidences also a very strong and variable magnetic field Oksala et al. The magnetic curve of HR changes polarity twice per period, and was modelled in the framework of the OMR by a mainly dipolar field, with the magnetic axis significantly misaligned with respect to the rotation axis.

Among the class of the magnetic early-type stars, HR is an extraordinarily fast rotator. Only the B2. The main stellar parameters of HR are listed in Table 1. References: 1 Rivinius et al. HR hosts a strong and steady magnetic field, indicating the existence of a corotating magnetosphere Rivinius et al.

HR has a flux density at 1. Thus, HR is an ideal target to study the effects of fast rotation and the high magnetic field strength for magnetospheric radio emissions. Already the first inspection of the spectra reveals a lack of asymmetric line profiles which would be expected for spectral lines formed in a stellar wind. In fact, Rivinius et al. We attempted to estimate the upper limit for the mass-loss rate that would be still consistent with the IUE observations.

We found that in our models for the stellar parameters given by Rivinius et al. As spherical symmetry is assumed for the powr models while Rivinius et al. For the lower temperature of We also checked for the effect of X-rays via superionization but did not find a major impact on the Si iv resonance line. Broad-band multifrequency observations of HR were carried out using the Karl G. Table 2 reports the instrumental and observational details for each observing epoch.

To maximize the VLA performances, the observations were done using the full array configuration at each observing bands, without splitting the interferometer in sub-arrays. To observe all the selected sky frequencies, the observations were carried out cyclically varying the observing bands. The data were calibrated using the standard calibration pipeline, working on the Common Astronomy Software Applications casa , and imaged using the casa task clean.

Flux densities for the Stokes I and V parameters were obtained by fitting a 2D Gaussian at the source position in the cleaned maps. The size of the Gaussian profile is comparable with the array beam, indicating that HR is unresolved for all the analysed radio frequencies. The minimum array beam size is 0. The errors were computed as the quadratic sum of the flux density error, derived from the bidimensional Gaussian fitting procedure, and the map rms measured in a field area lacking in radio sources.

The data were reduced using the most recent calibration. The background area was chosen to be nearby the star and free of X-ray sources. To analyse the spectra, we used the standard spectral fitting software xspec Arnaud The abundances were set to solar values according to Asplund et al.

Left and right top panels show the magnetic curve of HR and data taken by Oksala et al. The other left-hand panels show the radio light curves for Stokes I obtained at all the observing frequencies.

Right-hand panels display the rotational modulation of the fractional circularly polarized radio emission. The radio light curves for Stokes I are variable at all observed frequencies. The radio data for total intensity seems to show two peaks per cycle that are related to the two extrema of the magnetic field curve. Comparison between the radio and the magnetic curves also indicates a phase lag between the radio light curves and the magnetic one. Furthermore, it appears that the average radio spectrum of HR is relatively flat from 6 to 44 GHz cf.

The error bar of each point shown in the figure is the standard deviation of the measurements performed at a given frequency. Hence, without any information regarding the fraction of the circularly polarized radio emission and its variability, the total radio intensity alone can easily be mistakenly attributed to a bremsstrahlung radiation. Interestingly, a flat radio spectrum has been already detected in some others magnetic chemically peculiar stars Leone et al. Top panel: radio spectrum of HR obtained averaging all the VLA measurements performed at the same observing band.

The error bars are for the standard deviation of the averaged data. Bottom panel: standard deviations of the radio measurements, respectively, for the Stokes I and V. The right-hand panels of Fig. In the top right panel of Fig. It appears that the amplitude of the intensity variation is larger when the circular polarization is smaller. To parametrize the amplitude of the radio light curves for the total and polarized intensity, the bottom panel of Fig. By contrast the standard deviation of the measurements of the circularly polarized flux density increases as the frequency increases.

Considering Fig. When the magnetic poles are close to the direction of the line of sight, we observe most of the radially oriented field lines. In this case, the gyro-synchrotron mechanism gives rise to radio emission that is partially polarized, respectively, right-handed for the north pole and left-handed for the south pole. In previous papers Trigilio et al. In the case of the hot magnetic stars, the scenario attributes the origin of their radio emission as the interaction between the large-scale dipolar magnetic field and the radiatively driven stellar wind.

Following this model, the plasma wind progressively accumulates in the magnetospheric region where the magnetic field lines are closed inner magnetosphere. A fraction of the non-thermal electrons, assumed to have a power-law energy spectrum and an isotropic pitch angle distribution i. This non-thermal electron population has a homogeneous spatial density distribution within the middle magnetosphere, owing to magnetic mirroring. A cross-section of the stellar magnetosphere model is pictured in Fig.

Meridional cross-section of the magnetospheric model for a hot magnetic star, characterized by a simple dipolar magnetic field, and with the dipolar axis misaligned with respect to the rotation axis the misalignment amplitude is arbitrary.

The grey area indicates the thermal plasma trapped within the inner magnetosphere. The magnetic shell, middle-magnetosphere, where the non-thermal electrons indicated by the small vectors propagate towards the stellar surface, radiate by the gyro-synchrotron emission mechanism, is delimited by the two pictured magnetic field lines. The non-thermal electrons moving within the middle magnetosphere radiate at radio wavelengths by the gyro-synchrotron emission mechanism.

To simulate the radio emission arising from these non-thermal electrons, the magnetosphere of the star is sampled in a 3D grid, and the physical parameters needed to compute the gyro-synchrotron emission and absorption coefficients are calculated at each grid point. In the stellar reference frame, assumed with the z -axis coinciding with the magnetic dipole axis, the space surrounding the star is sampled in a 3D Cartesian grid, and the dipolar magnetic field vector components are calculated at each grid point.

In the second step, we locate the magnetospheric subvolume where the unstable electron population propagates. This spatial region is delimited by two magnetic field lines. Within each grid point of the middle magnetosphere, the non-thermal electrons have a constant number density n r. By contrast the inner magnetosphere is filled by a thermal plasma with density and temperature that are functions of the stellar distance as previously described.

We are able to solve numerically the radiative transfer equation along the directions parallel to the line of sight for the Stokes I and V as described in the appendix A of Leto et al. On the basis of the model described in previous section, we seek to reproduce the multiwavelength radio light curves of HR for Stokes I and V.

The already known stellar parameters of HR , needed for the simulations are listed in Table 1. For the sampling step, we adopt a variable grid with a narrow spacing 0. Following results obtained from simulations of radio emissions of other hot magnetic stars Trigilio et al. The temperature of the thermal plasma at the stellar surface has been set equal to the photospheric one given in Table 1 , whereas its density n 0 has been assumed as a free parameter.

The assumed values of the model, free parameters and the corresponding simulation steps are listed in Table 3. Adopting these stellar parameters, we were able to simulate radio light curves for the Stokes I and V that closely resemble the measurement of HR The corresponding ranges of the model parameters are reported in Table 3. The Fig. This envelope was obtained from the simultaneous visualization of the whole set of simulations performed using the combinations of the model-free parameters listed as model solutions in Table 3.

The simulations indicate that gyro-synchrotron emission from a dipole-shaped magnetosphere can closely reproduce the observations of HR The low-frequency Stokes I radio emission shows a clear phase modulation that becomes progressively less evident as the frequency increases. Conversely the simulations of the light curves for the Stokes V indicates that the circularly polarized emission is strongly rotationally modulated, with an amplitude that increases with frequency.

Such behaviour of the simulated radio light curves is consistent with the measurements. The filled circles are the HR observed radio light curves, respectively, of the total intensity Stokes I , and of the circularly polarized flux density Stokes V. The grey areas are the envelope of the modelled light curves obtained by using the combinations of the free parameters able to generate synthetic light curves that close match the observed ones.

The corresponding model solutions are listed in Table 3. To highlight the close match between simulations and observations, we also compared the simulated radio spectra with the observed spectrum.

The synthetic spectra were realized averaging the simulated light curves at each frequency. In the top and middle panels of Fig. In the bottom panel of Fig. In the case of the model simulations, more than one spectrum was produced. The top panel of Fig. Such behaviour is confirmed when looking at the bottom panel of Fig. But we must also take into account that the magnetosphere of this rapidly rotating star could be oblate, whereas our model assumes a simple dipole. The stretching of the magnetosphere could affect the magnetic field topology of the regions where the radio emission at the observed frequencies originate.

The effect of the plasma inertia to the magnetic field configuration is an issue outside the limit of our model. In any case, this mismatch between the dipolar and the true stellar magnetic topology could explain the differences between observations and simulations. The modelling approach followed to simulate the radio light curves of HR does not take into account for the presence of such material.

In any case, the higher dispersion of the simulations with respect to the observations can be explained as a consequence of the coverage for the observed radio light curves not being complete. In fact, we are missing some portions of the light curves that are expected to be highly variable. On the other hand, the frequency dependence of the standard deviations of the simulated Stokes I and V radio light curves are similar to the observed ones see bottom panel of Fig.

This is further evidence of the good fit of our model for describing the radio magnetosphere of HR Top and middle panels: like Fig. The thick lines correspond to the total intensity Stokes I , the thin lines to the circularly polarized flux density Stokes V.

Analysis of model solutions for the observed multiwavelength radio light curves of HR , respectively, for the Stokes I and V, can be used to constrain the physical conditions of the magnetosphere of this hot star.

The thermal electron density at the stellar surface n 0 is well constrained. The other two model-free parameters are degenerate, namely the non-thermal electron density n r and the length of the current sheet l. We found that the column density is a function of R A , the mathematical relationship, obtained by fitting these parameters, is provided in Table 3 , and pictured in Fig. Graphical view of the analytic equation that describes the column density of the non-thermal electrons given in Table 3 , calculated close to the acceleration site, as a function of the values of R A that are able to give simulated radio light curves matching the observed ones.

The grey areas highlight the solution uncertainty. In Trigilio et al. We assume two values of wind terminal velocity that are reasonable for a main-sequence B-type star Prinja ; Oskinova et al. The highest values of R A need a low wind mass-loss rate. The grey area indicates the range of pressures from the thermal plasma trapped within the inner magnetosphere. The model simulation provides an estimate for the density of the thermal plasma trapped within the inner magnetosphere of HR Those solutions that do not satisfy the above equality condition cannot be considered valid.

In the case of a dipolar-shaped magnetosphere see Fig. The fraction of the wind that freely propagates can be estimated from the ratio between the two polar caps area and the whole surface. In fact, the point where the field line, with a given R A , crosses the stellar surface individuates the latitude of the polar cap. The indirect evaluation of the linear extension of the radio emitting region is also useful for estimating the brightness temperature of HR The above estimate reinforces the conclusion that the radio emission from HR has a non-thermal origin.

It is instructive to compare the results obtained from the analysis of radio emission from HR and from the Ap star CU Vir conducted using similar approach Leto et al. Under the reasonable assumption that HR and CU Vir have similar non-thermal acceleration efficiencies, the higher non-thermal electron column density of HR could be explained if it is characterized by a more extended acceleration region as compared to CU Vir.

The above estimation highlights that HR is characterized by a larger magnetospheric volume maintained in rigid corotation compared with that of CU Vir.

The ranges of the allowed R A values, given in units of solar radii, are shown for both stars. The corresponding magnetic field strengths are derived. From a purely qualitative point of view, it is reasonable to assume the non-thermal acceleration process operates within a thicker middle magnetosphere for HR Radial dependence of the magnetic field strength in the equatorial plane of HR continuous line and CU Vir dashed line.

As discussed above, the two stars are characterized by different radio emitting volumes. For HR , the non-thermal electrons also travel within magnetospheric regions at higher magnetic field strength. Using a model for gyro-synchrotron emission, the magnetic field strength directly affects the observed radio flux density level Leto et al.

Taking into account the various physical differences, we are able to explain qualitatively why HR is a brighter radio source as compared to CU Vir. The X-ray flux of HR in the 0. Thus, a cold thermal plasma component responsible for the radio emission alone cannot explain the observed X-rays from HR Weather at epicenter at time of quake: Light Rain Mostrar mapa interactivo. If you felt this quake or if you were near the epicenter , please share your experience and submit a short "I felt it" report!

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