We use images of high spatial, spectral, and temporal resolution, obtained using both ground- and space-based instrumentation, to investigate the coupling between wave phenomena observed at numerous ...heights in the solar atmosphere. Analysis of 4170 A continuum images reveals small-scale umbral intensity enhancements, with diameters ~0".6, lasting in excess of 30 minutes. We find a maximum waveguide inclination angle of approximately 40degrees between photospheric and chromospheric heights, combined with a radial expansion factor of <76%. Derived kinetic temperature and emission measure time series display prominent out-of-phase characteristics, and when combined with the previously established sub-sonic wave speeds, we conclude that the observed EUV waves are the coronal counterparts of the upwardly propagating magnetoacoustic slow modes detected in the lower solar atmosphere. Thus, for the first time, we reveal how the propagation of 3 minute magnetoacoustic waves in solar coronal structures is a direct result of amplitude enhancements occurring in photospheric UDs.
We present optical spectra of 403 stars and quasi-stellar objects in order to obtain distance limits towards intermediate- and high-velocity clouds (IHVCs), including new Fibre-fed Extended Range ...Optical Spectrograph (FEROS) observations plus archival ELODIE, FEROS, High Resolution Echelle Spectrometer (HIRES) and Ultraviolet and Visual Echelle Spectrograph (UVES) data. The non-detection of Ca ii K interstellar (IS) absorption at a velocity of −130 to −60 km s−1 towards HDE 248894 (d∼ 3 kpc) and HDE 256725 (d∼ 8 kpc) in data at signal-to-noise ratio (S/N) > 450 provides a new firm lower distance limit of 8 kpc for the anti-centre shell HVC. Similarly, the non-detection of Ca ii K IS absorption towards HD 86248 at S/N ∼ 500 places a lower distance limit of 7.6 kpc for Complex EP, unsurprising since this feature is probably related to the Magellanic System. The lack of detection of Na i D at S/N = 35 towards Mrk 595 puts an improved upper limit for the Na i column density of log (N
NaD <) 10.95 cm−2 towards this part of the Cohen Stream where Ca ii was detected by Wakker et al. Absorption at ∼−40 km s−1 is detected in Na i D towards the Galactic star PG 0039+049 at S/N = 75, placing a firm upper distance limit of 1 kpc for the intermediate-velocity cloud south (IVS), where a tentative detection had previously been obtained by Centurión et al. Ca ii K and Na i D absorption is detected at −53 km s−1 towards HD 93521, which confirms the upper distance limit of 2.4 kpc for part of the IV arch complex obtained using the International Ultraviolet Explorer (IUE) data by Danly. Towards HD 216411 in Complex H a non-detection in Na D towards gas with log(
) = 20.69 cm−2 puts a lower distance limit of 6.6 kpc towards this HVC complex. Additionally, Na i D absorption is detected at −43.7 km s−1 in the star HD 218915 at a distance of 5.0 kpc in gas in the same region of the sky as Complex H. Finally, the Na i/Ca ii and Ca ii/H i ratios of the current sample are found to lie in the range observed for previous studies of IHVCs.
We have detected low-amplitude radial-velocity variations in two stars, USNO-B1.0 1219–0005465 (GSC 02265–00107 = WASP–1) and USNO-B1.0 0964–0543604 (GSC 00522–01199 = WASP–2). Both stars were ...identified as being likely host stars of transiting exoplanets in the 2004 SuperWASP wide-field transit survey. Using the newly commissioned radial-velocity spectrograph SOPHIE at the Observatoire de Haute-Provence, we found that both objects exhibit reflex orbital radial-velocity variations with amplitudes characteristic of planetary-mass companions and in-phase with the photometric orbits. Line-bisector studies rule out faint blended binaries as the cause of either the radial-velocity variations or the transits. We perform preliminary spectral analyses of the host stars, which together with their radial-velocity variations and fits to the transit light curves yield estimates of the planetary masses and radii. WASP-1b and WASP-2b have orbital periods of 2.52 and 2.15 d, respectively. Given mass estimates for their F7V and K1V primaries, we derive planet masses 0.80–0.98 and 0.81–0.95 times that of Jupiter, respectively. WASP-1b appears to have an inflated radius of at least 1.33 RJup, whereas WASP-2b has a radius in the range 0.65–1.26 RJup.
The Origin of Type I Spicule Oscillations Jess, D. B; Pascoe, D. J; Christian, D. J ...
Astrophysical journal. Letters,
01/2012, Letnik:
744, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We use images of high spatial and temporal resolution, obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope, to reveal how the generation of transverse ...waves in Type I spicules is a direct result of longitudinal oscillations occurring in the photosphere. Here we show how pressure oscillations, with periodicities in the range of 130-440 s, manifest in small-scale photospheric magnetic bright points, and generate kink waves in the Sun's outer atmosphere with transverse velocities approaching the local sound speed. Through comparison of our observations with advanced two-dimensional magnetohydrodynamic simulations, we provide evidence for how magnetoacoustic oscillations, generated at the solar surface, funnel upward along Type I spicule structures, before undergoing longitudinal-to-transverse mode conversion into waves at twice the initial driving frequency. The resulting kink modes are visible in chromospheric plasma, with periodicities of 65-220 s, and amplitudes often exceeding 400 km. A sausage mode oscillation also arises as a consequence of the photospheric driver, which is visible in both simulated and observational time series. We conclude that the mode conversion and period modification is a direct consequence of the 90degrees phase shift encompassing opposite sides of the photospheric driver. The chromospheric energy flux of these waves are estimated to be approx =3 x 10 super(5) W m super(-2), which indicates that they are sufficiently energetic to accelerate the solar wind and heat the localized corona to its multi-million degree temperatures.
Context. Bright points (BPs) are small-scale, magnetic features ubiquitous across the solar surface. Previously, we have observed and noted their properties for quiet Sun regions. Here, we determine ...the dynamic properties of BPs using simultaneous quiet Sun and active region data. Aims. The aim of this paper is to compare the properties of BPs in both active and quiet Sun regions and to determine any difference in the dynamics and general properties of BPs as a result of the varying magnetic activity within these two regions. Methods. High spatial and temporal resolution G-band observations of active region AR11372 were obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope. Three subfields of varying polarity and magnetic flux density were selected with the aid of magnetograms obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Bright points within these subfields were subsequently tracked and analysed. Results. It is found that BPs within active regions display attenuated velocity distributions with an average horizontal velocity of ~0.6 km s-1, compared to the quiet region which had an average velocity of 0.9 km s-1. Active region BPs are also ~21% larger than quiet region BPs and have longer average lifetimes (~132 s) than their quiet region counterparts (88 s). No preferential flow directions are observed within the active region subfields. The diffusion index (γ) is estimated at ~1.2 for the three regions. Conclusions. We confirm that the dynamic properties of BPs arise predominately from convective motions. The presence of stronger field strengths within active regions is the likely reason behind the varying properties observed. We believe that larger amounts of magnetic flux will attenuate BP velocities by a combination of restricting motion within the intergranular lanes and by increasing the number of stagnation points produced by inhibited convection. Larger BPs are found in regions of higher magnetic flux density and we believe that lifetimes increase in active regions as the magnetic flux stabilises the BPs.
We employ Ca ii K and Na i D interstellar absorption-line spectroscopy of early-type stars in the Large and Small Magellanic Clouds (LMC, SMC) to investigate the large- and small-scale structure in ...foreground intermediate- and high-velocity clouds (I/HVCs). Data include FLAMES-GIRAFFE Ca ii K observations of 403 stars in four open clusters, plus FEROS or UVES spectra of 156 stars in the LMC and SMC. The FLAMES observations are amongst the most extensive probes to date of Ca ii structures on ∼20 arcsec scales in Magellanic I/HVCs. From the FLAMES data within a 0
$_{.}^{\circ}$
5 field of view, the Ca ii K equivalent width in the I/HVC components towards three clusters varies by factors of ≥10. There are no detections of molecular gas in absorption at intermediate or high velocities, although molecular absorption is present at LMC and Galactic velocities towards some sightlines. The FEROS/UVES data show Ca ii K I/HVC absorption in ∼60 per cent of sightlines. The range in the Ca ii/Na i ratio in I/HVCs is from –0.45 to +1.5 dex, similar to previous measurements for I/HVCs. In 10 sightlines we find Ca ii/O i ratios in I/HVC gas ranging from 0.2 to 1.5 dex below the solar value, indicating either dust or ionization effects. In nine sightlines I/HVC gas is detected in both H i and Ca ii at similar velocities, implying that the two elements form part of the same structure.
We investigate the generation mechanisms of MHD Poynting flux in the magnetized solar photosphere. Using radiative MHD modeling of the solar photosphere with initial magnetic configurations that ...differ in their field strength and geometry, we show the presence of two different mechanisms for MHD Poynting flux generation in simulations of solar photospheric magnetoconvection. The weaker mechanism is connected to vertical transport of weak horizontal magnetic fields in the convectively stable layers of the upper photosphere, while the stronger is the production of Poynting flux in strongly magnetized intergranular lanes experiencing horizontal vortex motions. These mechanisms may be responsible for the energy transport from the solar convection zone to the higher layers of the solar atmosphere.
Using direct numerical magneto-hydrodynamic (MHD) simulations, we demonstrate the evidence of two physically different types of vortex motions in the solar photosphere. Baroclinic motions of plasma ...in non-magnetic granules are the primary source of vorticity in granular regions of the solar photosphere, however, there is a significantly more efficient mechanism of vorticity production in strongly magnetised intergranular lanes. These swirly motions of plasma in intergranular magnetic field concentrations could be responsible for the generation of different types of MHD wave modes, for example, kink, sausage and torsional Alfvén waves. These waves could transport a relevant amount of energy from the lower solar atmosphere and contribute to coronal plasma heating.
ABSTRACT We describe a new atomic and molecular database we developed for use in the spectral synthesis code Cloudy. The design of Stout is driven by the data needs of Cloudy, which simulates ...molecular, atomic, and ionized gas with kinetic temperatures and densities spanning the low-to high-density limits. The radiation field between photon energies 10−8 Ry and 100 MeV is considered, along with all atoms and ions of the lightest 30 elements, and ∼102 molecules. For ease of maintenance, the data are stored in a format as close as possible to the original data sources. Few data sources include the full range of data we need. We describe how we fill in the gaps in the data or extrapolate rates beyond their tabulated range. We tabulate data sources both for the atomic spectroscopic parameters and for collision data for the next release of Cloudy. This is not intended as a review of the current status of atomic data, but rather a description of the features of the database which we will build upon.
There have been discussions in the recent literature regarding the accuracy of the available electron impact excitation rates (equivalently effective collision strengths ϒ) for transitions in Be-like ...ions. In the present paper we demonstrate, once again, that earlier results for ϒ are indeed overestimated (by up to four orders of magnitude), for over 40 per cent of transitions and over a wide range of temperatures. To do this we have performed two sets of calculations for N iv, with two different model sizes consisting of 166 and 238 fine-structure energy levels. As in our previous work, for the determination of atomic structure the grasp (General-purpose Relativistic Atomic Structure Package) is adopted and for the scattering calculations (the standard and parallelised versions of) the Dirac Atomic R-matrix Code (darc) are employed. Calculations for collision strengths and effective collision strengths have been performed over a wide range of energy (up to 45 Ryd) and temperature (up to 2.0 × 106 K), useful for applications in a variety of plasmas. Corresponding results for energy levels, lifetimes and A-values for all E1, E2, M1 and M2 transitions among 238 levels of N iv are also reported.
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