1,656 research outputs found
The Position of High Frequency Waves with Respect to the Granulation Pattern
High frequency velocity oscillations were observed in the spectral lines Fe I
543.45nm and 543.29nm, using 2D spectroscopy with a Fabry- Perot and speckle
reconstruction, at the VTT in Tenerife. We investigate the radial component of
waves with frequencies in the range 8 - 22mHz in the internetwork, network and
a pore. We find that the occurrence of waves do not show any preference on
location and are equally distributed over down-flows and up-flows, regardless
of the activity of the observed area in the line of Fe I 543.45nm. The waves
observed in the lower formed line of Fe I 543.29nm seem to appear
preferentially over down-flows.Comment: Article has 12 pages and 7 images. It is accepted in Solar Physics
Journa
A tilted interference filter in a converging beam
Context. Narrow-band interference filters can be tuned toward shorter
wavelengths by tilting them from the perpendicular to the optical axis. This
can be used as a cheap alternative to real tunable filters, such as
Fabry-P\'erot interferometers and Lyot filters. At the Swedish 1-m Solar
Telescope, such a setup is used to scan through the blue wing of the Ca II H
line. Because the filter is mounted in a converging beam, the incident angle
varies over the pupil, which causes a variation of the transmission over the
pupil, different for each wavelength within the passband. This causes
broadening of the filter transmission profile and degradation of the image
quality. Aims. We want to characterize the properties of our filter, at normal
incidence as well as at different tilt angles. Knowing the broadened profile is
important for the interpretation of the solar images. Compensating the images
for the degrading effects will improve the resolution and remove one source of
image contrast degradation. In particular, we need to solve the latter problem
for images that are also compensated for blurring caused by atmospheric
turbulence. Methods. We simulate the process of image formation through a
tilted interference filter in order to understand the effects. We test the
hypothesis that they are separable from the effects of wavefront aberrations
for the purpose of image deconvolution. We measure the filter transmission
profile and the degrading PSF from calibration data. Results. We find that the
filter transmission profile differs significantly from the specifications.We
demonstrate how to compensate for the image-degrading effects. Because the
filter tilt effects indeed appear to be separable from wavefront aberrations in
a useful way, this can be done in a final deconvolution, after standard image
restoration with MFBD/Phase Diversity based methods. We illustrate the
technique with real data
Velocities measured in small scale solar magnetic elements
We have obtained high resolution spectrograms of small scale magnetic structures with the Swedish 1-m Solar Telescope. We present Doppler measurements at 0\farcs{2} spatial resolution of bright points, ribbons and flowers and their immediate surroundings, in the C {\small{I}} 5380.3 {\AA} line (formed in the deep photosphere) and the two Fe {\small{I}} lines at 5379.6 {\AA} and 5386.3 {\AA}. The velocity inside the flowers and ribbons are measured to be almost zero, while we observe downflows at the edges. These downflows are increasing with decreasing height. We also analyze realistic magneto-convective simulations to obtain a better understanding of the interpretation of the observed signal. We calculate how the Doppler signal depends on the velocity field in various structures. Both the smearing effect of the non-negligible width of this velocity response function along the line of sight and of the smearing from the telescope and atmospheric point spread function are discussed. These studies lead us to the conclusion that the velocity inside the magnetic elements are really upflow of the order 1--2 km s while the downflows at the edges really are much stronger than observed, of the order 1.5--3.3 km s
Dynamics of Magnetic Flux Elements in the Solar Photosphere
The interaction of magnetic fields and convection is investigated in the
context of the coronal heating problem. We study the motions of photospheric
magnetic elements using filtergrams obtained at the Swedish Vacuum Solar
Telescope at La Palma. We use potential-field modeling to extrapolate the
magnetic and velocity fields to larger height. We find that the velocity in the
chromosphere can be locally enhanced at the separatrix surfaces between
neighboring flux tubes. The predicted velocities are several km/s,
significantly larger than those of the photospheric flux tubes, which may have
important implications for coronal heating. sComment: submitted to ApJ, 21 pages, 10 figure
GDPR in research - what does it mean for research institutions?
Collection of materials from the event "GDPR in research - what does it mean for research institutions?" which was hosted by TU Delft Library on 30 August 2018. The collection includes the following materials: The programme of the event The welcome slide All presentations from the event All authors and event organisers are listed in alphabetical order. Any questions about these materials should be addressed to [email protected]
High-Frequency Oscillations in a Solar Active Region observed with the Rapid Dual Imager
High-cadence, synchronized, multiwavelength optical observations of a solar
active region (NOAA 10794) are presented. The data were obtained with the Dunn
Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly
developed camera system : the Rapid Dual Imager. Wavelet analysis is undertaken
to search for intensity related oscillatory signatures, and periodicities
ranging from 20 to 370 s are found with significance levels exceeding 95%.
Observations in the H-alpha blue wing show more penumbral oscillatory phenomena
when compared to simultaneous G-band observations. The H-alpha oscillations are
interpreted as the signatures of plasma motions with a mean velocity of 20
km/s. The strong oscillatory power over H-alpha blue-wing and G-band penumbral
bright grains is an indication of the Evershed flow with frequencies higher
than previously reported.Comment: 9 pages, 9 figure
On the continuum intensity distribution of the solar photosphere
We present a detailed comparison between simulations and seeing-free
observations that takes into account the crucial influence of instrumental
image degradation. We use images of quiet Sun granulation taken in the blue,
green and red continuum bands of the Broadband Filter Imager of the Solar
Optical Telescope (SOT) onboard Hinode. The images are deconvolved with Point
Spread Functions (PSF) that account for non-ideal contributions due to
instrumental stray-light and imperfections. In addition, synthetic intensity
images are degraded with the corresponding PSFs. ... Removing the influence of
the PSF unveils much broader intensity distributions with a secondary component
that is otherwise only visible as an asymmetry between the darker and brighter
than average part of the distribution. The contrast values increase to (26.7
+/- 1.3) %, (19.4 +/- 1.4) %, and (16.6 +/- 0.7) % for blue, green, and red
continuum, respectively. The power spectral density of the images exhibits a
pronounced peak at spatial scales characteristic for the granulation pattern
and a steep decrease towards smaller scales. The observational findings like
the absolute values and centre-to-limb variation of the intensity contrast,
intensity histograms, and power spectral density are well matched with
corresponding synthetic observables from three-dimensional radiation
(magneto-)hydrodynamic simulations. We conclude that the intensity contrast of
the solar continuum intensity is higher than usually derived from ground-based
observations and is well reproduced by modern radiation (magneto-)hydrodynamic
models. Properly accounting for image degradation effects is of crucial
importance for comparisons between observations and numerical models.Comment: 15 pages, 10 figures; A&A, in pres
Do mixed histological features affect survival benefit from neoadjuvant platinumâbased combination chemotherapy in patients with locally advanced bladder cancer? A secondary analysis of Southwest Oncology GroupâDirected Intergroup Study (S8710)
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86993/1/j.1464-410X.2010.09900.x.pd
High Resolution Observations using Adaptive Optics: Achievements and Future Needs
Over the last few years, several interesting observations were obtained with
the help of solar Adaptive Optics (AO). In this paper, few observations made
using the solar AO are enlightened and briefly discussed. A list of
disadvantages with the current AO system are presented. With telescopes larger
than 1.5m are expected during the next decade, there is a need to develop the
existing AO technologies for large aperture telescopes. Some aspects of this
development are highlighted. Finally, the recent AO developments in India are
also presented
- âŠ