The asymmetries observed in the line profiles of solar flares can provide important diagnostics of the properties and dynamics of the flaring atmosphere. In this paper the evolution of the Ha and Ca ...ii lambda8542 lines are studied using high spatial, temporal, and spectral resolution ground-based observations of an M 1.1 flare obtained with the Swedish 1 m Solar Telescope. The temporal evolution of the Ha line profiles from the flare kernel shows excess emission in the red wing (red asymmetry) before flare maximum and excess in the blue wing (blue asymmetry) after maximum. However, the Ca ii lambda8542 line does not follow the same pattern, showing only a weak red asymmetry during the flare. RADYN simulations are used to synthesize spectral line profiles for the flaring atmosphere, and good agreement is found with the observations. We show that the red asymmetry observed in H alpha is not necessarily associated with plasma downflows, and the blue asymmetry may not be related to plasma upflows. Indeed, we conclude that the steep velocity gradients in the flaring chromosphere modify the wavelength of the central reversal in the H alpha line profile. The shift in the wavelength of maximum opacity to shorter and longer wavelengths generates the red and blue asymmetries, respectively.
The WASP Project and the SuperWASP Cameras Pollacco, D. L.; Skillen, I.; Cameron, A. Collier ...
Publications of the Astronomical Society of the Pacific,
10/2006, Letnik:
118, Številka:
848
Journal Article
Recenzirano
Odprti dostop
The SuperWASP cameras are wide‐field imaging systems at the Observatorio del Roque de los Muchachos on the island of La Palma in the Canary Islands, and at the Sutherland Station of the South African ...Astronomical Observatory. Each instrument has a field of view of some 482 deg2with an angular scale of 13
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7 pixel−1, and is capable of delivering photometry with accuracy better than 1% for objects having
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. Lower quality data for objects brighter than
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are stored in the project archive. The systems, while designed to monitor fields with high cadence, are capable of surveying the entire visible sky every 40 minutes. Depending on the observational strategy, the data rate can be up to 100 Gbytes per night. We have produced a robust, largely automatic reduction pipeline and advanced archive, which are used to serve the data products to the consortium members. The main science aim of these systems is to search for bright transiting exoplanet systems suitable for spectroscopic follow‐up observations. The first 6 month season of SuperWASP‐North observations produced light curves of ∼6.7 million objects with 12.9 billion data points.
The hot-Jupiter WASP-10b was reported by Maciejewski et al. to show transit timing variations (TTVs) with an amplitude of ∼3.5 min. These authors proposed that the observed TTVs were caused by a 0.1M
...Jup perturbing companion with an orbital period of ∼5.23 d, and hence, close to the outer 5:3 mean-motion resonance with WASP-10b. To test this scenario, we present eight new transit light curves of WASP-10b obtained with the Faulkes Telescope North and the Liverpool Telescope. The new light curves, together with 22 previously published ones, were modelled with a Markov Chain Monte Carlo transit fitting code. Transit depth differences reported for WASP-10b are thought to be due to starspot-induced brightness modulation of the host star. Assuming the star is brighter at the activity minimum, we favour a small planetary radius. We find
in agreement with Johnson et al. and Maciejewski et al. Recent studies find no evidence for a significant eccentricity in this system. We present consistent system parameters for a circular orbit and refine the orbital ephemeris of WASP-10b. Our homogeneously derived transit times do not support the previous claimed TTV signal, which was strongly dependent on two previously published transits that have been incorrectly normalized. Nevertheless, a linear ephemeris is not a statistically good fit to the transit times of WASP-10b. We show that the observed transit time variations are due to spot occultation features or systematics. We discuss and exemplify the effects of occultation spot features in the measured transit times and show that despite spot occultation during egress and ingress being difficult to distinguish in the transit light curves, they have a significant effect in the measured transit times. We conclude that if we account for spot features, the transit times of WASP-10b are consistent with a linear ephemeris with the exception of one transit (epoch 143) which is a partial transit. Therefore, there is currently no evidence for the existence of a companion to WASP-10b. Our results support the lack of TTVs of hot-Jupiters reported for the Kepler sample.
Abstract
Understanding the Fe
II
emission from active galactic nuclei (AGNs) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving ...both quasar classification schemes such as “Eigenvector 1” and tracing the chemical evolution of the cosmos. Recently, three large Fe
II
atomic data sets with radiative and electron collisional rates have become available. We have incorporated these into the spectral synthesis code
Cloudy
and examined predictions using a new generation of AGN spectral energy distribution (SED), which indicates that the ultraviolet (UV) emission can be quite different depending on the data set utilized. The Smyth et al. data set better reproduces the observed Fe
II
template of the I ZW 1 Seyfert galaxy in the UV and optical regions, and we adopt these data. We consider both thermal and microturbulent clouds and show that a microturbulence of ≈100 km s
−1
reproduces the observed shape and strength of the so-called Fe
II
“UV bump.” Comparing our predictions to the observed Fe
II
template, we derive a typical cloud density of 10
11
cm
−3
and photon flux of 10
20
cm
−2
s
−1
, and show that these largely reproduce the observed Fe
II
emission in the UV and optical. We calculate the
I
(Fe
II
)/
I
(Mg
II
) emission-line intensity ratio using our best-fitting model and obtain log(
I
(Fe
II
)/
I
(Mg
II
)) ∼ 0.7, suggesting many AGNs have a roughly solar Fe/Mg abundance ratio. Finally, we vary the Eddington ratio and SED shape as a step in understanding the Eigenvector 1 correlation.
Solar spectra of ultraviolet bursts and flare ribbons from the Interface Region Imaging Spectrograph (IRIS) have suggested high electron densities of > 10 12 cm−3 at transition region temperatures of ...0.1 MK, based on large intensity ratios of Si iv λ1402.77 to O iv λ1401.16. In this work, a rare observation of the weak O iv λ1343.51 line is reported from an X-class flare that peaked at 21:41 UT on 2014 October 24. This line is used to develop a theoretical prediction of the Si iv λ1402.77 to O iv λ1401.16 ratio as a function of density that is recommended to be used in the high-density regime. The method makes use of new pressure-dependent ionization fractions that take account of the suppression of dielectronic recombination at high densities. It is applied to two sequences of flare kernel observations from the October 24 flare. The first shows densities that vary between 3 × 10 12 and 3 × 10 13 cm−3 over a seven-minute period, while the second location shows stable density values of around 2 × 10 12 cm−3 over a three-minute period.
Vorticity in the solar photosphere Shelyag, S.; Keys, P.; Mathioudakis, M. ...
Astronomy and astrophysics (Berlin),
02/2011, Letnik:
526
Journal Article
Recenzirano
Odprti dostop
Aims. We use magnetic and non-magnetic 3D numerical simulations of solar granulation and G-band radiative diagnostics from the resulting models to analyse the generation of small-scale vortex motions ...in the solar photosphere. Methods. Radiative MHD simulations of magnetoconvection are used to produce photospheric models. Our starting point is a non-magnetic model of solar convection, where we introduce a uniform magnetic field and follow the evolution of the field in the simulated photosphere. We find two different types of photospheric vortices, and provide a link between the vorticity generation and the presence of the intergranular magnetic field. A detailed analysis of the vorticity equation, combined with the G-band radiative diagnostics, allows us to identify the sources and observational signatures of photospheric vorticity in the simulated photosphere. Results. Two different types of photospheric vorticity, magnetic and non-magnetic, are generated in the domain. Non-magnetic vortices are generated by the baroclinic motions of the plasma in the photosphere, while magnetic vortices are produced by the magnetic tension in the intergranular magnetic flux concentrations. The two types of vortices have different shapes. We find that the vorticity is generated more efficiently in the magnetised model. Simulated G-band images show a direct connection between magnetic vortices and rotary motions of photospheric bright points, and suggest that there may be a connection between the magnetic bright point rotation and small-scale swirl motions observed higher in the atmosphere.
We study the C8.4-class solar flare SOL2016-05-14T11:34 UT using high-resolution spectral imaging in the Ca ii 8542 line obtained with the CRISP imaging spectropolarimeter on the Swedish 1 m Solar ...Telescope. Spectroscopic inversions of the Ca ii 8542 line using the non-LTE code NICOLE are used to investigate the evolution of the temperature and velocity structure in the flaring chromosphere. A comparison of the temperature stratification in flaring and non-flaring areas reveals strong footpoint heating during the flare peak in the lower atmosphere. The temperature of the flaring footpoints between log τ 500 − 2.5 and − 3.5 , where τ500 is the continuum optical depth at 500 nm, is ∼ 5 - 6.5 kK close to the flare peak, reducing gradually to ∼ 5 kK . The temperature in the middle and upper chromosphere, between log τ 500 − 3.5 and −5.5, is estimated to be ∼6.5-20 kK, decreasing to preflare temperatures, ∼5-10 kK, after approximately 15 minutes. However, the temperature stratification of the non-flaring areas is unchanged. The inverted velocity fields show that the flaring chromosphere is dominated by weak downflowing condensations at the formation height of Ca ii 8542 .
Effective collision strengths for forbidden transitions among the five energetically lowest fine-structure levels of O ii are calculated in the Breit–Pauli approximation using the R-matrix method. ...Results are presented for the electron temperature range 100–100 000 K. The accuracy of the calculations is evaluated via the use of different types of radial orbital sets and a different configuration expansion basis for the target wavefunctions. A detailed assessment of previous available data is given, and erroneous results are highlighted. Our results reconfirm the validity of the original Seaton and Osterbrock scaling for the optical O ii ratio, a matter of some recent controversy. Finally, we present plasma diagnostic diagrams using the best collision strengths and transition probabilities.
Context. Sunspot atmospheres have been shown to be highly inhomogeneous hosting both quasi-stable and transient features, such as small-scale umbral brightenings (previously named “umbral ...micro-jets”) and dark fibril-like events. Aims. We seek to understand the morphological properties and formation mechanisms of small-scale umbral brightenings (analogous to umbral micro-jets). In addition, we aim to understand whether links between these events and short dynamic fibrils, umbral flashes, and umbral dots can be established. Methods. A Swedish 1 m Solar Telescope (SST) filtergram time-series sampling the Ca ii H line and a CRisp Imaging Spectro-Polarimeter (SST/CRISP) full-Stokes 15-point Ca ii 8542 Å line scan dataset were used. The spatial resolutions of these datasets are close to 0.1′′ and 0.18′′ with cadences of 1.4 s and 29 s, respectively. These data allowed us to construct light-curves, plot line profiles, and to perform a weak-field approximation in order to infer the magnetic field strength. Results. The average lifetime and lengths of the 54 small-scale brightenings identified in the sunspot umbra are found to be 44.2 s (σ = 20 s) and 0.56′′ (σ = 0.14′′), respectively. The spatial positioning and morphological evolution of these events in Ca ii H filtergrams was investigated finding no evidence of parabolic or ballistic profiles nor a preference for co-spatial formation with umbral flashes. Line scans in Ca ii 8542 Å and the presence of Stokes V profile reversals provided evidence that these events could form in a similar manner to umbral flashes in the chromosphere (i.e. through the formation of shocks either due to the steepening of localised wavefronts or due to the impact of returning material from short dynamic fibrils, a scenario we find evidence for). The application of the weak-field approximation indicated that changes in the line-of-sight magnetic field were not responsible for the modifications to the line profile and suggested that thermodynamic effects are, in fact, the actual cause of the increased emission. Finally, a sub-set of small-scale brightenings were observed to form at the foot-points of short dynamic fibrils. Conclusions. The small-scale umbral brightenings studied here do not appear to be jet-like in nature. Instead they appear to be evidence of shock formation in the lower solar atmosphere. We found no correlation between the spatial locations where these events were observed and the occurrence of umbral dots and umbral flashes. These events have lifetimes and spectral signatures comparable to umbral flashes and are located at the footpoints of short dynamic fibrils, during or at the end of the red-shifted stage. It is possible that these features form due to the shocking of fibrilar material in the lower atmosphere upon its return under gravity.
Abstract
Using high-cadence observations from the Hydrogen-alpha Rapid Dynamics camera imaging system on the Dunn Solar Telescope, we present an investigation of the statistical properties of ...transverse oscillations in spicules captured above the solar limb. At five equally separated atmospheric heights, spanning approximately 4900–7500 km, we have detected a total of 15,959 individual wave events, with a mean displacement amplitude of 151 ± 124 km, a mean period of 54 ± 45 s, and a mean projected velocity amplitude of 21 ± 13 km s
−1
. We find that both the displacement and velocity amplitudes increase with height above the solar limb, ranging from 132 ± 111 km and 17.7 ± 10.6 km s
−1
at ≈4900 km, and 168 ± 125 km and 26.3 ± 14.1 km s
−1
at ≈7500 km, respectively. Following the examination of neighboring oscillations in time and space, we find 45% of the waves to be upwardly propagating, 49% to be downwardly propagating, and 6% to be standing, with mean absolute phase velocities for the propagating waves on the order of 75–150 km s
−1
. While the energy flux of the waves propagating downwards does not appear to depend on height, we find the energy flux of the upwardly propagating waves decreases with atmospheric height at a rate of −13,200 ± 6500 W m
−2
/Mm. As a result, this decrease in energy flux as the waves propagate upwards may provide significant thermal input into the local plasma.
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