379 research outputs found

    Spectroscopic Observations of Fe XVIII in Solar Active Regions

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    The large uncertainties associated with measuring the amount of high temperature emission in solar active regions represents a significant impediment to making progress on the coronal heating problem. Most current observations at temperatures of 3 MK and above are taken with broad band soft X-ray instruments. Such measurements have proven difficult to interpret unambiguously. Here we present the first spectroscopic observations of the Fe XVIII 974.86 AA emission line in an on-disk active region taken with then SUMER instrument on SOHO. Fe XVIII has a peak formation temperature of 7.1 MK and provides important constraints on the amount of impulsive heating in the corona. Detailed evaluation of the spectra and comparison of the SUMER data with soft X-ray images from the XRT on Hinode confirm that this line is unblended. We also compare the spectroscopic data with observations from the AIA 94 AA channel on SDO. The AIA 94 AA channel also contains Fe XVIII, but is blended with emission formed at lower temperatures. We find that is possible to remove the contaminating blends and form relatively pure Fe XVIII images that are consistent with the spectroscopic observations from SUMER. The observed spectra also contain the Ca XIV 943.63 AA line that, although a factor 2 to 6 weaker than the Fe XVIII 974.86 AA line, allows us to probe the plasma around 3.5 MK. The observed ratio between the two lines indicates (isothermal approximation) that most of the plasma in the brighter Fe XVIII active region loops is at temperatures between 3.5 and 4 MK.Comment: 12 pages, 5 figures. Submitted as letter to Ap

    Evidence for Steady Heating: Observations of an Active Region Core with Hinode and TRACE

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    Previous observations have not been able to exclude the possibility that high temperature active region loops are actually composed of many small scale threads that are in various stages of heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer (EIS) and X-ray Telescope (XRT) on \textit{Hinode} we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for steady heating. We find that the emission observed in XRT is generally steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive heating events are observed, but they appear to be unrelated to the steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlated with the hot emission, as would be expected if the high temperature loops are the result of impulsive heating. Finally, we also find that intensities in the "moss", the footpoints of high temperature loops, are consistent with steady heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the heating in the core of an active region is effectively steady, that is, the time between heating events is short relative to the relevant radiative and conductive cooling times.Comment: Minor changes based on the final report from the referee; Movies are available from the first autho

    The Heating of the Solar Atmosphere: from the Bottom Up?

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    The heating of the solar atmosphere remains a mystery. Over the past several decades, scientists have examined the observational properties of structures in the solar atmosphere, notably their temperature, density, lifetime, and geometry, to determine the location, frequency, and duration of heating. In this talk, I will review these observational results, focusing on the wealth of information stored in the light curve of structures in different spectral lines or channels available in the Solar Dynamic Observatory's Atmospheric Imaging Assembly, Hinode's X-ray Telescope and Extreme-ultraviolet Imaging Spectrometer, and the Interface Region Imaging Spectrograph. I will discuss some recent results from combined data sets that support the heating of the solar atmosphere may be dominated by low, near-constant heating events

    Institutions, Developmental Alliances, and Economic Development in Korea and Brazil (1950-1985)

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    This paper compares the development of Korea and Brazil, 1950-85. These newly industrialized countries developed at above-average rates among less developed countries. Korea developed more rapidly than Brazil. The paper contends that institutions, interest groups (especially firms) and the state, enter into developmental alliances. Alliances affect policies. Policies, then, affect development. Findings reveal interesting trends in the 1950s\u27 democracies of the cases. Both countries had semi-autonomous states, equivocally committed to industrialization. Industry was the growth point in each. Korea used local firms to industrialize; Brazil used foreign firms. In both cases, the state allied itself with firms. Policy mostly favored industrialization. Both countries experienced comparable rates of industrialization. Findings of the 1960s-1980s\u27 bureaucratic-authoritarianisms (B-A) of the cases also reveal interesting trends. While the state became more autonomous with B-A in both cases, the Korean state became more autonomous. Korea developed an unequivocal commitment to industrialization; Brazil retained its lukewarm industrial commitment. Brazil formed an alliance with public firms to modernize in the 1970s; Korea turned to large local capital. Korea\u27s policy was myopically pro-industrial; Brazil\u27s policy was not as narrowly pro-industrial. Korea displayed phenomenally higher rates of development during B-A than it exhibited in democracy. Brazil continued at a pace comparable to the democratic period. The paper finds the following conclusions. Autonomous states with high commitment to economic development maximize development. Firm types that optimize economic development are local. Primary developmental alliances of state with fins augment development. Pervasive, pro-industrial policies expand development. To the extent that both cases possessed these characteristics, they developed rapidly. Since Korea possessed these qualities to a greater extent than Brazil, Korea developed more rapidly

    Coronal Heating Observed with Hi-C

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    The recent launch of the HighResolution Coronal Imager (HiC) as a sounding rocket has offered a new, different view of the Sun. With approx 0.3" resolution and 5 second cadence, HiC reveals dynamic, smallscale structure within a complicated active region, including coronal braiding, reconnection regions, Alfven waves, and flows along active region fans. By combining the HiC data with other available data, we have compiled a rich data set that can be used to address many outstanding questions in solar physics. Though the HiC rocket flight was short (only 5 minutes), the added insight of the smallscale structure gained from the HiC data allows us to look at this active region and other active regions with new understanding. In this talk, I will review the first results from the HiC sounding rocket and discuss the impact of these results on the coronal heating problem
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