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1.
E. Danezis E. Antonopoulou E. Theodossiou M. Mathioudakis 《Astrophysics and Space Science》1992,187(2):307-318
In this paper we study the far-UV as well as the UV spectrum of the spectroscopic binary system SZ Psc in the wavelength ranges 1235–1950 Å and 2710–3090 Å, respectively, from spectra obtained with the International Ultraviolet Explorer (IUE). The UV spectrum of SZ Psc is mainly an emission spectrum. The short wavelength region includes emission lines formed from the low chromosphere to the transition region (e.g., Siiv,Civ, andNv) and also a deep and broad absorption line of Feii.The Mgii[1] resonance doublet at about 2800 Å presents a P Cygni profile and a multiple structure with two emission and two absorption satellite components. We also present the emission measure diagram in the temperature region 4.4T
e
<53. 相似文献
2.
Keenan F.P. Pinfield D.J. Mathioudakis M. Aggarwal K.M. Thomas R.J. Brosius J.W. 《Solar physics》2000,197(2):253-262
Theoretical electron density sensitive emission line ratios involving a total of eleven 2s
22p
2–2s2p
3 transitions in Sxi between 187 and 292 Å are presented. A comparison of these with solar active region observations obtained during rocket flights by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals generally good agreement between theory and experiment. However, the 186.87 Å line is masked by fairly strong Fexii emission at the same wavelength, while 239.83 Å is blended with an unknown feature, and 285.58 Å is blended with possibly Niv 285.56 Å. In addition, the 191.23 Å line appears to be more seriously blended with an Fexiii feature than previously believed. The presence of several new Sxi lines is confirmed in the SERTS spectra, at wavelengths of 188.66, 247.14 and 291.59 Å, in excellent agreement with laboratory measurements. In particular, the detection of the 2s
22p
2
3
P
1 –2s2p
3
3
P
0,1 transitions at 242.91 Å is the first time (to our knowledge) that this feature has been identified in the solar spectrum. The potential usefulness of the Sxi line ratios as electron density diagnostics for the solar transition region and corona is briefly discussed. 相似文献
3.
Gallagher Peter T. Williams David R. Phillips Kenneth J.H. Mathioudakis Mihalis Smartt Raymond N. Keenan Francis P. 《Solar physics》2000,195(2):367-380
We report on observations of a large eruptive event associated with a flare that occurred on 27 September 1998 made with the Richard B. Dunn Solar Telescope at Sacramento Peak Observatory (several wave bands including off-line-center H), in soft and hard X-rays (GOES and BATSE), and in several TRACE wave bands (including Feix/x 171 Å, Fexii 195 Å, and Civ 1550 Å). The flare initiation is signaled by two H foot-point brightenings which are closely followed by a hard X-ray burst and a subsequent gradual increase in other wavelengths. The flare light curves show a complicated, three-component structure which includes two minor maxima before the main GOES class C5.2 peak after which there is a characteristic exponential decline. During the initial stages, a large spray event is observed within seconds of the hard X-ray burst which can be directly associated with a two-ribbon flare in H. The emission returns to pre-flare levels after about 35 min, by which time a set of bright post-flare loops have begun to form at temperatures of about 1.0–1.5 MK. Part of the flare plasma also intrudes into the penumbra of a large sunspot, generally a characteristic of very powerful flares, but the flare importance in GOES soft X-rays is in fact relatively modest. Much of the energy appears to be in the form of a second ejection which is observed in optical and ultraviolet bands, traveling out via several magnetic flux tubes from the main flare site (about 60° from Sun center) to beyond the limb. 相似文献
4.
5.
R-matrix calculations of electron impact excitation rates in Nixviii are used to derive theoretical electron-temperature-sensitive emission line ratios involving 3s–4p,3p–4d,3p –4s, and 3d–4f transitions in the 41–53 Å wavelength range. A comparison of these with solar flare observations from a rocket-borne X-ray spectrograph (XSST) reveals generally excellent agreement between theory and experiment (within the experimental and theoretical uncertainties), which provides support for the atomic data adopted in the analysis. However the 3s 2S–4p 2P1/2 line of Nixviii at 41.22 Å appears to be blended with the Fexix 13.74 Å feature observed by XSST in third order. In addition, the measured Nixviii intensity ratio I(3p 2P3/2– 4s 2S)/I(3p 2P1/2–4s 2S)=I(51.02 Å)/I(50.26 Å)=0.56, a factor of 3.8 smaller than the theoretical (temperature and density-insensitive) value of 2.1. The reason for this discrepancy is currently unexplained, but is unlikely to be due to blending of the 50.26 Å line, as the intensity of this feature is consistent with that expected from the other Nixviii lines in the XSST spectrum. Future observations of the Nixviii lines by the Advanced X-ray Astrophysics Facility (AXAF) should allow this problem to be resolved, and may also permit the use of the lines as electron-temperature diagnostics. 相似文献
6.
D.R. Williams K.J.H. Phillips P. Rudawy M. Mathioudakis P.T. Gallagher E. O'Shea F.P. Keenan P. Read B. Rompolt 《Monthly notices of the Royal Astronomical Society》2001,326(2):428-436
The Solar Eclipse Corona Imaging System (SECIS) was used to record high-cadence observations of the solar corona during the total solar eclipse of 1999 August 11. During the 2 min 23.5 s of totality, 6364 images were recorded simultaneously in each of the two channels: a white light channel, and the Fe xiv (5303 Å) 'green line' channel ( T ∼2 MK) . Here we report initial results from the SECIS experiment, including the discovery of a 6-s intensity oscillation in an active region coronal loop. 相似文献
7.
Keenan F.P. Katsiyannis A.C. Aggarwal K.M. Mathioudakis M. Brosius J.W. Davila J.M. Thomas R.J. 《Solar physics》2003,212(1):65-79
Theoretical electron-density-sensitive emission line ratios involving 2s 22p 2–2s2p 3 transitions in Si?ix between 223 and 350 Å are presented. A comparison of these with an extensive dataset of solar-active-region, quiet-Sun, subflare and off-limb observations, obtained during rocket flights by the Solar EUV Research Telescope and Spectrograph (SERTS), reveals generally very good agreement between theory and experiment. This provides support for the accuracy of the line-ratio diagnostics, and hence the atomic data on which they are based. In particular, the density-sensitive intensity ratio I(258.10 Å)/I(349.87 Å) offers an especially promising diagnostic for studies of coronal plasmas, as it involves two reasonably strong emission lines and varies by more than an order of magnitude over the useful density range of 109–1011 cm?3. The 2s 22p 2 1 S 0–2s2p 3 1 P 1 transition at 259.77 Å is very marginally identified for the first time in the SERTS database, although it has previously been detected in solar flare observations.
相似文献8.
C. J. Nelson J. G. Doyle R. Erdélyi Z. Huang M. S. Madjarska M. Mathioudakis S. J. Mumford K. Reardon 《Solar physics》2013,283(2):307-323
The properties of Ellerman bombs (EBs), small-scale brightenings in the Hα line wings, have proved difficult to establish because their size is close to the spatial resolution of even the most advanced telescopes. Here, we aim to infer the size and lifetime of EBs using high-resolution data of an emerging active region collected using the Interferometric BIdimensional Spectrometer (IBIS) and Rapid Oscillations of the Solar Atmosphere (ROSA) instruments as well as the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We develop an algorithm to track EBs through their evolution, finding that EBs can often be much smaller (around 0.3″) and shorter-lived (less than one minute) than previous estimates. A correlation between G-band magnetic bright points and EBs is also found. Combining SDO/HMI and G-band data gives a good proxy of the polarity for the vertical magnetic field. It is found that EBs often occur both over regions of opposite polarity flux and strong unipolar fields, possibly hinting at magnetic reconnection as a driver of these events.The energetics of EB events is found to follow a power-law distribution in the range of a nanoflare (1022?25 ergs). 相似文献
9.
F. P. Keenan B. R. Espey M. Mathioudakis K. M. Aggarwal F. L. Crawford W. A. Feibelman F. C. McKenna 《Monthly notices of the Royal Astronomical Society》1999,309(1):195-198
An inspection of a GHRS/ HST spectrum of the symbiotic star RR Telescopii reveals the presence of the [Al ii ] 3s2 1 S – 3s3p 3 P2 line at a vacuum wavelength of 2661.06±0.08 Å, 8.89±0.08 Å away from the Al ii ] 3s2 1 S – 3s3p 3 P1 intercombination transition at 2669.95 Å, in good agreement with the theoretical prediction of Δ λ =8.80 Å. We also find that the Al ii ] line profile is asymmetric, showing a strong low-density component with a weak high-density wing, redshifted by 30 km s−1 , in agreement with the findings of Schild & Schmid, which were based on optical observations. Our measurement of the emission-line ratio R I (2661.06 Å)/ I (2669.95 Å)=0.027±0.003 implies log N e =5.8±0.2, in good agreement with the densities found from other ions, such as Si iii . These results provide strong evidence that we have detected the [Al ii ] line, the first time (to our knowledge) that this feature has been reliably identified in an astrophysical or laboratory spectrum. 相似文献
10.
K.J.H. Phillips M. Mathioudakis D.P. Huenemoerder D.R. Williams M.E. Phillips F.P. Keenan 《Monthly notices of the Royal Astronomical Society》2001,325(4):1500-1510
The primary objective of this work is the analysis and interpretation of coronal observations of Capella obtained in 1999 September with the High Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory and the Extreme Ultraviolet Explorer ( EUVE ). He-like lines of O (O vii ) are used to derive a density of 1.7×1010 cm−3 for the coronae of the binary, consistent with the upper limits derived from Fe xxi , Ne ix and Mg xi line ratios. Previous estimates of the electron density based on Fe xxi should be considered as upper limits. We construct emission measure distributions and compare the theoretical and observed spectra to conclude that the coronal material has a temperature distribution that peaks around 4–6 MK , implying that the coronae of Capella were significantly cooler than in the previous years. In addition, we present an extended line list with over 100 features in the 5–24 Å wavelength range, and find that the X-ray spectrum is very similar to that of a solar flare observed with SMM . The observed to theoretical Fe xvii 15.012-Å line intensity reveals that opacity has no significant effect on the line flux. We derive an upper limit to the optical depth, which we combine with the electron density to derive an upper limit of 3000 km for the size of the Fe xvii emitting region. In the same context, we use the Si iv transition region lines of Capella from HST /Goddard High-Resolution Spectrometer observations to show that opacity can be significant at T =105 K , and derive a path-length of ≈75 km for the transition region. Both the coronal and transition region observations are consistent with very small emitting regions, which could be explained by small loops over the stellar surfaces. 相似文献