157 research outputs found
Transition region features observed with Hinode/EIS
Two types of active region feature prominent at transition region
temperatures are identified in Hinode/EIS data of AR 10938 taken on 2007
January 20. The footpoints of 1 MK TRACE loops are shown to emit strongly in
emission lines formed at log T=5.4-5.8, allowing the temperature increase along
the footpoints to be clearly seen. A density diagnostic of Mg VII yields the
density in the footpoints, with one loop showing a decrease from 3x10^9 cm^-3
at the base to 1.5x10^9 cm^-3 at a projected height of 20 Mm. The second
feature is a compact active region transition region brightening which is
particularly intense in O V emission (log T=5.4) but also has a signature at
temperatures up to log T=6.3. The Mg VII diagnostic gives a density of 4x10^10
cm^-3, and emission lines of Mg VI and Mg VII show line profiles broadened by
50 km/s and wings extending beyond 200 km/s. Continuum emission in the short
wavelength band is also found to be enhanced, and is suggested to be free-bound
emission from recombination onto He^+.Comment: 11 pages, 9 figures, submitted to PASJ Hinode first results issu
Chromospheric explosions
Three issues relative to chromospheric explosions were debated. (1) Resolved: The blue-shifted components of x-ray spectral lines are signatures of chromospheric evaporation. It was concluded that the plasma rising with the corona is indeed the primary source of thermal plasma observed in the corona during flares. (2) Resolved: The excess line broading of UV and X-ray lines is accounted for by a convective velocity distribution in evaporation. It is concluded that the hypothesis that convective evaporation produces the observed X-ray line widths in flares is no more than a hypothesis. It is not supported by any self-consistent physical theory. (3) Resolved: Most chromospheric heating is driven by electron beams. Although it is possible to cast doubt on many lines of evidence for electron beams in the chromosphere, a balanced view that debaters on both sides of the question might agree to is that electron beams probably heat the low corona and upper chromosphere, but their direct impact on evaporating the chromosphere is energetically unimportant when compared to conduction. This represents a major departure from the thick-target flare models that were popular before the Workshop
Strongly Blueshifted Phenomena Observed with {\it Hinode}/EIS in the 2006 December 13 Solar Flare
We present a detailed examination of strongly blueshifted emission lines
observed with the EUV Imaging Spectrometer on board the {\it Hinode} satellite.
We found two kinds of blueshifted phenomenon associated with the X3.4 flare
that occurred on 2006 December 13. One was related to a plasmoid ejection seen
in soft X-rays. It was very bright in all the lines used for the observations.
The other was associated with the faint arc-shaped ejection seen in soft
X-rays. The soft X-ray ejection is thought to be an MHD fast-mode shock wave.
This is therefore the first spectroscopic observation of an MHD fast-mode shock
wave associated with a flare.Comment: 18 pages, 1 table, 6 figures. ApJ, accepte
Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
The extreme ultraviolet portion of the solar spectrum contains a wealth of
diagnostic tools for probing the lower solar atmosphere in response to an
injection of energy, particularly during the impulsive phase of solar flares.
These include temperature and density sensitive line ratios, Doppler shifted
emission lines and nonthermal broadening, abundance measurements, differential
emission measure profiles, and continuum temperatures and energetics, among
others. In this paper I shall review some of the advances made in recent years
using these techniques, focusing primarily on studies that have utilized data
from Hinode/EIS and SDO/EVE, while also providing some historical background
and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the
Topical Issue on Solar and Stellar Flare
LEMUR: Large European Module for solar Ultraviolet Research. European contribution to JAXA's Solar-C mission
Understanding the solar outer atmosphere requires concerted, simultaneous
solar observations from the visible to the vacuum ultraviolet (VUV) and soft
X-rays, at high spatial resolution (between 0.1" and 0.3"), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK, from the
chromosphere to the flaring corona), and the capability of measuring magnetic
fields through spectropolarimetry at visible and near-infrared wavelengths.
Simultaneous spectroscopic measurements sampling the entire temperature range
are particularly important.
These requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload providing a
significant improvement of imaging and spectropolarimetric capabilities in the
UV, visible, and near-infrared with respect to what is available today and
foreseen in the near future.
The Large European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload of
high-resolution imaging spectrographs and cameras. LEMUR consists of two major
components: a VUV solar telescope with a 30 cm diameter mirror and a focal
length of 3.6 m, and a focal-plane package composed of VUV spectrometers
covering six carefully chosen wavelength ranges between 17 and 127 nm. The
LEMUR slit covers 280" on the Sun with 0.14" per pixel sampling. In addition,
LEMUR is capable of measuring mass flows velocities (line shifts) down to 2
km/s or better.
LEMUR has been proposed to ESA as the European contribution to the Solar C
mission.Comment: 35 pages, 14 figures. To appear on Experimental Astronom
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