Impulsively generated short-period fast magneto-acoustic wave trains, guided by solar and stellar coronal loops, are numerically modelled. In the developed stage of the evolution, the wave trains ...have a characteristic quasi-periodic signature. The quasi-periodicity results from the geometrical dispersion of the guided fast modes, determined by the transverse profile of the loop. A typical feature of the signature is a tadpole wavelet spectrum: a narrow-spectrum tail precedes a broad-band head. The instantaneous period of the oscillations in the wave train decreases gradually with time. The period and the spectral amplitude evolution are shown to be determined by the steepness of the transverse density profile and the density contrast ratio in the loop. The propagating wave trains recently discovered with the Solar Eclipse Coronal Imaging System (SECIS) instrument are noted to have similar wavelet spectral features, which strengthens the interpretation of SECIS results as guided fast wave trains.
The large and small-scale (pc) structure of the Galactic interstellar medium can be investigated by utilizing spectra of early-type stellar probes of known distances in the same region of the sky. ...This paper determines the variation in line strength of Call at 3933.661 Aring as a function of probe separation for a large sample of stars, including a number of sight-lines in the Magellanic Clouds. FLAMES-GIRAFFE data taken with the Very Large Telescope towards early-type stars in 3 Galactic and 4 Magellanic open clusters in Call are used to obtain the velocity, equivalent width, column density, and line width of interstellar Galactic calcium for a total of 657 stars, of which 443 are Magellanic Cloud sight-lines. In each cluster there are between 43 and 111 stars observed. For the four Magellanic clusters studied with FLAMES, the strength of the Galactic interstellar Call K equivalent width on transverse scales from ~O.O5-9 pc is found to vary by factors of ~1.8-3.0, corresponding to column density variations of ~0.3-O.5 dex in the optically-thin approximation.
Some of the first results are reported from RISE – a new fast camera mounted on the Liverpool Telescope primarily designed to obtain high time-resolution light curves of transiting extrasolar planets ...for the purpose of transit timing. A full and partial transit of WASP-3 are presented, and a Markov-Chain Monte Carlo analysis is used to update the parameters from the discovery paper. This results in a planetary radius of $1.29^{\rm +0.05}_{-0.12}$ RJ and therefore a density of $0.82^{+0.14}_{-0.09}~{\rho}_J$, consistent with previous results. The inclination is $85.06^{\rm +0.16}_{-0.15}$ deg, in agreement (but with a significant improvement in the precision) with the previously determined value. Central transit times are found to be consistent with the ephemeris given in the discovery paper; however, a new ephemeris calculated using the longer baseline results in Tc(0) = 2 454 605.55915 ± 0.00023 HJD and P = 1.846835 ± 0.000002 days.
We present the discovery of WASP-39b, a highly inflated transiting Saturn-mass planet orbiting a late G-type dwarf star with a period of 4.055259 ± 0.000008 d, Transit Epoch T0 = 2 455 ... 342.9688 ± 0.0002 (HJD), of duration 0.1168 ± 0.0008 d. A combined analysis of the WASP photometry, high-precision follow-up transit photometry, and radial velocities yield a planetary mass of Mpl = 0.28 ± 0.03 MJ and a radius of Rpl = 1.27 ± 0.04 RJ, resulting in a mean density of 0.14 ± 0.02 ρJ. The stellar parameters are mass M⋆ = 0.93 ± 0.03 M⊙, radius R⋆ = 0.895 ± 0.23 R⊙, and age \hbox{$9^{+3}_{-4}$}9-4+3 Gyr. Only WASP-17b and WASP-31b have lower densities than WASP-39b, although they are slightly more massive and highly irradiated planets. From our spectral analysis, the metallicity of WASP-39 is measured to be Fe/H = −0.12 ± 0.1 dex, and we find the planet to have an equilibrium temperature of \hbox{$1116^{+33}_{-32}$}1116-32+33 K. Both values strengthen the observed empirical correlation between these parameters and the planetary radius for the known transiting Saturn-mass planets.
Aims. In this paper we aim to investigate the evolution of plasma properties and Stokes parameters in photospheric magnetic bright points using 3D magneto-hydrodynamical simulations and radiative ...diagnostics of solar granulation. Methods. Simulated time-dependent radiation parameters and plasma properties were investigated throughout the evolution of a bright point. Synthetic Stokes profiles for the FeI 630.25 nm line were calculated, which also allowed the evolution of the Stokes-I line strength and Stokes-V area and amplitude asymmetries to be investigated. Results. Our results are consistent with theoretical predictions and published observations describing convective collapse, and confirm this as the bright point formation process. Through degradation of the simulated data to match the spatial resolution of SOT, we show that high spatial resolution is crucial for the detection of changing spectro-polarimetric signatures throughout a magnetic bright point’s lifetime. We also show that the signature downflow associated with the convective collapse process tends towards zero as the radiation intensity in the bright point peaks, because of the magnetic forces present restricting the flow of material in the flux tube.
Simultaneous observations of explosive chromospheric evaporation are presented using data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and the Coronal Diagnostic ...Spectrometer (CDS) on board the Solar and Heliospheric Observatory. For the first time, cospatial imaging and spectroscopy have been used to observe explosive evaporation within a hard X-ray emitting region. RHESSI X-ray images and spectra were used to determine the flux of nonthermal electrons accelerated during the impulsive phase of an M2.2 flare. When we assumed a thick-target model, the injected electron spectrum was found to have a spectral index of 67.3, a low-energy cutoff of 620 keV, and a resulting flux of .4 x 10 super(10) ergs cm super(-2) s super(-1). The dynamic response of the atmosphere was determined using CDS spectra; we found a mean upflow velocity of 230 c 38 km s super(-1) in Fe XIX (592.23 AA) and associated downflows of 36 c 16 and 43 c 22 km s super(-1) at chromospheric and transition region temperatures, respectively, relative to an averaged quiet-Sun spectra. The errors represent a 1 s dispersion. The properties of the accelerated electron spectrum and the corresponding evaporative velocities were found to be consistent with the predictions of theory.
We report on a search for short-period intensity variations in the green-line (Fe
xiv
530.3 nm) emission from the solar corona during the 21 August 2017 total eclipse viewed from Idaho in the United ...States. Our experiment was performed with a much more sensitive detection system, and with better spatial resolution, than on previous occasions (1999 and 2001 eclipses), allowing fine details of quiet coronal loops and an active-region loop system to be seen. A guided 200-mm-aperture Schmidt–Cassegrain telescope was used with a state-of-the-art CCD camera having 16-bit intensity discrimination and a field-of-view (
0.43
∘
×
0.43
∘
) that encompassed approximately one third of the visible corona. The camera pixel size was 1.55 arcseconds, while the seeing during the eclipse enabled features of
≈
2
arcseconds (1450 km on the Sun) to be resolved. A total of 429 images were recorded during a 122.9 second portion of the totality at a frame rate of
3.49
s
−
1
. In the analysis, we searched particularly for short-period intensity oscillations and travelling waves, since theory predicts fast-mode magneto-hydrodynamic (MHD) waves with short periods may be important in quiet coronal and active-region heating. Allowing first for various instrumental and photometric effects, we used a wavelet technique to search for periodicities in some
404
,
000
pixels in the frequency range
0.5
–
1.6
Hz
(periods 2 seconds to 0.6 seconds). We also searched for travelling waves along some 65 coronal structures. However, we found no statistically significant evidence in either. This negative result considerably refines the limit that we obtained from our previous analyses, and it indicates that future searches for short-period coronal waves may be better directed towards Doppler shifts as well as intensity oscillations.
We use high spatial resolution observations and numerical simulations to study the velocity distribution of solar photospheric magnetic bright points. The observations were obtained with the Rapid ...Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope, while the numerical simulations were undertaken with the MURaM code for average magnetic fields of 200 G and 400 G. We implemented an automated bright point detection and tracking algorithm on the data set and studied the subsequent velocity characteristics of over 6000 structures, finding an average velocity of approximately 1 km s--1, with maximum values of 7 km s--1. Furthermore, merging magnetic bright points were found to have considerably higher velocities, and significantly longer lifetimes, than isolated structures. By implementing a new and novel technique, we were able to estimate the background magnetic flux of our observational data, which is consistent with a field strength of 400 G.
We have employed the VULCAN laser facility to generate a laser plasma X-ray source for use in photoionization experiments. A nanosecond laser pulse with an intensity of order 1015 Wcm−2 was used to ...irradiate thin Ag or Sn foil targets coated onto a parylene substrate, and the L-shell emission in the 3.3–4.4 keV range was recorded for both the laser-irradiated and nonirradiated sides. Both the experimental and simulation results show higher laser to X-ray conversion yields for Ag compared with Sn, with our simulations indicating yields approximately a factor of two higher than those found in the experiments. Although detailed angular data were not available experimentally, the simulations indicate that the emission is quite isotropic on the laser-irradiated side but shows close to a cosine variation on the nonirradiated side of the target as seen experimentally in the previous work.
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