59,234 research outputs found
Atomic physics and modern solar spectro-polarimetry
Observational solar physics is entering a new era with the advent of new 1.5
m class telescopes with adaptive optics, as well as the Daniel K. Inouye 4 m
telescope which will become operational in 2019. Major outstanding problems in
solar physics all relate to the solar magnetic field. Spectropolarimetry offers
the best, and sometimes only, method for accurate measurements of the magnetic
field. In this paper we highlight how certain atomic transitions can help us
provide both calibration data, as well as diagnostic information on solar
magnetic fields, in the presence of residual image distortions through the
atmosphere close to, but not at the diffraction limits of large and polarizing
telescopes. Particularly useful are spectral lines of neutrals and singly
charged ions of iron and other complex atoms. As a proof-of-concept, we explore
atomic transitions that might be used to study magnetic fields without the need
for an explicit calibration sequence, offering practical solutions to the
difficult challenges of calibrating the next generation of solar
spectropolarimetric telescopes. Suggestions for additional work on atomic
theory and measurements, particularly at infrared wavelengths, are given. There
is some promise for continued symbiotic advances between solar physics and
atomic physics.Comment: Can. J. Phys., in pres
Instrument and data analysis challenges for imaging spectropolarimetry
The next generation of solar telescopes will enable us to resolve the
fundamental scales of the solar atmosphere, i.e., the pressure scale height and
the photon mean free path. High-resolution observations of small-scale
structures with sizes down to 50 km require complex post-focus instruments,
which employ adaptive optics (AO) and benefit from advanced image restoration
techniques. The GREGOR Fabry-Perot Interferometer (GFPI) will serve as an
example of such an instrument to illustrate the challenges that are to be
expected in instrumentation and data analysis with the next generation of solar
telescopes.Comment: 4 pages, 1 figure, accepted for publication in Astronomische
Nachrichten/AN, special issue of the 1st EAST-ATST Workshop: "Science with
large solar telescopes" in Freiburg, Germany, October 14-16, 200
Was the GLE on May 17, 2012 linked with the M5.1-class flare the first in the 24th solar cycle?
On May 17, 2012 an M5.1-class flare exploded from the sun. An O-type coronal
mass ejection (CME) was also associated with this flare. There was an instant
increase in proton flux with peak at MeV, leading to S2 solar
radiation storm level. In about 20 minutes after the X-ray emission, the solar
particles reached the Earth.It was the source of the first (since December
2006) ground level enhancement (GLE) of the current solar cycle 24. The GLE was
detected by neutron monitors (NM) and other ground based detectors. Here we
present an observation by the Tupi muon telescopes (Niteroi, Brazil, , , 3 m above sea level) of the enhancement of muons at ground
level associated with this M5.1-class solar flare. The Tupi telescopes
registered a muon excess over background in the 5-min binning time
profile. The Tupi signal is studied in correlation with data obtained by
space-borne detectors (GOES, ACE), ground based neutron monitors (Oulu) and air
shower detectors (the IceTop surface component of the IceCube neutrino
observatory). We also report the observation of the muon signal possibly
associated with the CME/sheath striking the Earth magnetosphere on May 20,
2012. We show that the observed temporal correlation of the muon excess
observed by the Tupi muon telescopes with solar transient events suggests a
real physical connection between them. Our observation indicates that
combination of two factors, the low energy threshold of the Tupi muon
telescopes and the location of the Tupi experiment in the South Atlantic
Anomaly region, can be favorable in the study and detection of the solar
transient events. Our experiment provides new data complementary to other
techniques (space and ground based) in the study of solar physics.Comment: 9 pages, 10 figure
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
IR spectroscopy of COmosphere dynamics with the CO first overtone band
We discuss observations of the weak first overtone CO absorption band near
2300 nm with the U.S. National Solar Observatory Array Camera (NAC), a modern
mid-infrared detector. This molecular band provides a thermal diagnostic that
forms lower in the atmosphere than the stronger fundamental band near 4600 nm.
The observed center-to-limb increase in CO line width qualitatively agrees with
the proposed higher temperature shocks or faster plasma motions higher in the
COmosphere. The spatial extent of chromospheric shock waves is currently at or
below the diffraction limit of the available C0 lines at existing telescopes.
Five minute period oscillations in line strength and measured Doppler shifts
are consistent with the p-mode excitation of the photospheric gas. We also show
recent efforts at direct imaging at 4600 nm. We stress that future
large-aperture solar telescopes must be teamed with improved, dynamic
mid-infrared instruments, like the NAC, to capitalize on the features that
motivate such facilities.Comment: 4 pages, 3 figures, Published in Astronomische Nachrichten on behalf
of the 1st EAST-ATST Workshop: "Science with Large Solar Telescopes
Telescopes and space exploration
The necessity for different types of telescopes for astronomical investigations is discussed. Major findings in modern astronomy by ground-based and spaceborne telescopes are presented. Observations of the Crab Nebula, solar flares, interstellar gas, and the Black Hole are described. The theory of the oscillating universe is explored. Operating and planned telescopes are described
Correcting for the solar wind in pulsar timing observations: the role of simultaneous a nd l ow-frequency observations
The primary goal of the pulsar timing array projects is to detect
ultra-low-frequency gravitational waves. The pulsar data sets are affected by
numerous noise processes including varying dispersive delays in the
interstellar medium and from the solar wind. The solar wind can lead to rapidly
changing variations that, with existing telescopes, can be hard to measure and
then remove. In this paper we study the possibility of using a low frequency
telescope to aid in such correction for the Parkes Pulsar Timing Array (PPTA)
and also discuss whether the ultra-wide-bandwidth receiver for the FAST
telescope is sufficient to model the solar wind variations. Our key result is
that a single wide-bandwidth receiver can be used to model and remove the
effect of the solar wind. However, for pulsars that pass close to the Sun such
as PSR J1022+1022, the solar wind is so variable that observations at two
telescopes separated by a day are insufficient to correct the solar wind
effect.Comment: accepted by RA
Future prospects for gamma-ray
Astrophysical phenomena discussed are: the very energetic and nuclear processes associated with compact objects; astrophysical nucleo-synthesis; solar particle acceleration; the chemical composition of the planets and other bodies of the solar system; the structure of our galaxy; the origin and dynamic pressure effects of the cosmic rays; the high energy particles and energetic processes in other galaxies, especially active ones; and the degree of matter antimater symmetry of the universe. The gamma ray results of GAMMA-I, the gamma ray observatory, the gamma ray burst network, solar polar, and very high energy gamma ray telescopes on the ground provide justification for more sophisticated telescopes
JPEG2000 Image Compression on Solar EUV Images
For future solar missions as well as ground-based telescopes, efficient ways
to return and process data have become increasingly important. Solar Orbiter,
e.g., which is the next ESA/NASA mission to explore the Sun and the
heliosphere, is a deep-space mission, which implies a limited telemetry rate
that makes efficient onboard data compression a necessity to achieve the
mission science goals. Missions like the Solar Dynamics Observatory (SDO) and
future ground-based telescopes such as the Daniel K. Inouye Solar Telescope, on
the other hand, face the challenge of making petabyte-sized solar data archives
accessible to the solar community. New image compression standards address
these challenges by implementing efficient and flexible compression algorithms
that can be tailored to user requirements. We analyse solar images from the
Atmospheric Imaging Assembly (AIA) instrument onboard SDO to study the effect
of lossy JPEG2000 (from the Joint Photographic Experts Group 2000) image
compression at different bit rates. To assess the quality of compressed images,
we use the mean structural similarity (MSSIM) index as well as the widely used
peak signal-to-noise ratio (PSNR) as metrics and compare the two in the context
of solar EUV images. In addition, we perform tests to validate the scientific
use of the lossily compressed images by analysing examples of an on-disk and
off-limb coronal-loop oscillation time-series observed by AIA/SDO.Comment: 25 pages, published in Solar Physic
Helioseismology, solar models and solar neutrinos
We review recent advances concerning helioseismology, solar models and solar
neutrinos. Particularly we shall address the following points: i) helioseismic
tests of recent SSMs; ii)the accuracy of the helioseismic determination of the
sound speed near the solar center; iii)predictions of neutrino fluxes based on
helioseismology, (almost) independent of SSMs; iv)helioseismic tests of exotic
solar models.Comment: 11 pages with 6 ps figures included, procsla style, based on the
talks presented at Neutrino Telescopes '99, Venice, February 1999, and at
Valencia '99, Valencia, May 1999, to appear in the proceeding
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