SUMER Data Research Articles

Empirical relations between the intensities of Lyman lines of H and He+

Context.Empirical relations between major UV and extreme UV spectral lines are one of the inputs for models of chromospheric and coronal spectral radiances and irradiances. They are also needed for the interpretation of some of the observations of the Solar Orbiter mission.Aims.We aim to determine an empirical relation between the intensities of the H I121.6 nm and He II30.4 nm Ly-αlines.Methods.Images at 121.6 nm from the Chromospheric Lyman-Alpha Spectro Polarimeter (CLASP) and Multiple XUV Imager (MXUVI) sounding rockets were co-registered with simultaneous images at 30.4 nm from the EIT and AIA orbital telescopes in order to derive a spatially resolved relationship between the intensities.Results.We have obtained a relationship between the H I121.6 nm and He II30.4 nm intensities that is valid for a wide range of solar features, intensities, and activity levels. Additional SUMER data have allowed the derivation of another relation between the H I102.5 nm (Ly-β) and He II30.4 nm lines for quiet-Sun regions. We combined these two relationships to obtain a Ly-α/Ly-βintensity ratio that is comparable to the few previously published results.Conclusions.The relationship between the H I121.6 nm and He II30.4 nm lines is consistent with the one previously obtained using irradiance data. We have also observed that this relation is stable in time but that its accuracy depends on the spatial resolution of the observations. The derived Ly-α/Ly-βintensity ratio is also compatible with previous results.

Prospective associations of psychosocial work exposures with mortality in France: STRESSJEM study protocol

IntroductionAlthough evidence has been provided on the associations between psychosocial work exposures and morbidity outcomes in the literature, knowledge appears much more sparse on mortality outcomes. The objective of STRESSJEM...

A coronal wave and an asymmetric eruptive filament in SUMER, CDS, EIT, and TRACE co-observations

The objectives of the present study is to provide a better physical understanding of the complex inter-relation and evolution of several solar coronal features comprising a double-peak flare, a coronal dimming caused by a CME, a CME-driven compression, and a fast-mode wave. For the first time, the evolution of an asymmetric eruptive filament is analysed in simultaneous SUMER spectroscopic and TRACE and EIT imaging data. We use imaging observations from EIT and TRACE in the 195A channel and spectroscopic observations from the CDS in a rastering and SUMER in a sit-and-stare observing mode. The SUMER spectra cover spectral lines with formation temperatures from logT(K) ~ 4.0 to 6.1. Although the event was already analysed in two previous studies, our analysis brings a wealth of new information on the dynamics and physical properties of the observed phenomena. We found that the dynamic event is related to a complex flare with two distinct impulsive peaks, one according to the GOES classification as C1.1 and the second - C1.9. The first energy release triggers a fast-mode wave and a CME with a clear CME driven compression ahead of it. This activity is related to, or possibly caused, by an asymmetric filament eruption. The filament is observed to rise with its leading edge moving at a speed of ~300 km/s detected both in the SUMER and CDS data. The rest of the filament body moves at only ~150 km/s while untwisting. No signature is found of the fast-mode wave in the SUMER data, suggesting that the plasma disturbed by the wave had temperatures above 600 000 K. The erupting filament material is found to emit only in spectral lines at transition region temperatures. Earlier identification of a coronal response detected in the Mg X 609.79 A line is found to be caused by a blend from the O IV 609.83 A line.

SPECTROSCOPIC OBSERVATIONS OF Fe XVIII IN SOLAR ACTIVE REGIONS

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.

Distribution of jets and magnetic fields in a coronal hole

Context. Recent observations of ubiquitous jets in coronal holes suggest that they play an important role in coronal heating and solar wind acceleration. Aims. The aim of our study is to understand the magnetic connectivity and the formation of jets in coronal holes. The study of jets also helps to understand the magnetic field configuration in the coronal hole. Methods. A coordinated observation between EIS and SUMER was carried out in a polar coronal hole to investigate both the transition region and the corona. Spectropolarimeter (SP) data allowed us to examine the relationship between the distribution of jets and magnetic fields in the photosphere. Results. Coronal jets as well as explosive events and cool upflows were identified from EIS and SUMER data. The location of these events are correlated with network fields in the photosphere. Conclusions. Footpoints of coronal jets are connected to patches of vertical kG fields in the photosphere, which are thought to anchor open fields in the upper corona. Explosive events and cool upflows occur in network regions which harbor low-lying fields in the transition region.

Can the solar wind originate from a quiet Sun region?

Context. It is well known that the fast solar wind originates from coronal holes (CHs). However, the question whether it can also originate from quiet Sun regions has not yet been answered. Aims. To study this problem we analyze SOHO data obtained from observations made in a quiet Sun area. The data set includes far-ultraviolet data from SUMER, magnetic field data from MDI, and extreme-ultraviolet data from EIT. Methods. We make a potential-field extrapolation of the coronal magnetic field and calculate the field lines from the photosphere up to 80 Mm height. Those field lines which can be traced from the bottom to the top of the extrapolation box are called (locally) open field lines. By a combined analysis of the coronal magnetic field structures inferred from MDI data, the flows indicated by the Ne viii Doppler shifts in the SUMER data, and the Fe xii radiance images from EIT, it is possible to study this problem in depth. Results. We find that most of the sites with plasma outflow, which can be recognized by the Ne viii blue shift, are not located in regions with an open magnetic field. Most likely, these outflows just correspond to plasma being delivered to magnetic loops. It is further found that, in a cross-section plane located at a height of 25 Mm, the pattern of open field lines intersecting that plane is consistent with the dark pattern of low radiance in the image of the Fe xii 19.5 nm line. Usually, small dark regions are considered to represent small CHs, and thus are assumed to be sources of the solar wind. However, since here the source of the low emission appears to be located at a height of only 25 Mm, it seems more likely that this radiation originates near the foot points of large coronal loops. Conclusions. Previous results obtained at middle latitudes on the quiet Sun indicated that sizable outflow velocities occur at the intersections of the network boundaries. This finding is also confirmed here. However, we could not identify most of these intersections as sources of the solar wind. Only a few small outflow regions might be sources. Yet, one dark area that we found on the EIT map seems to be connected with open field lines, and therefore it could be a source of the solar wind.

Line broadening of EUV lines across the solar limb observed by SUMER/SOHO

We analyze time series scans of the solar limb performed by the spectrometer SUMER on-board the SoHO satellite. The analyzed dataset consists of observations obtained in the C III 977 Å line. After applying the standard SUMER data reduction procedure, we perform a one line Gaussian fit to the profiles to obtain different parameters for each pixel within the scans. Studying the variations of the line width from the disk to the limb and off-limb we find that it increases off-limb and shows a peak at $\sim15\prime\prime above the limb. We suggest that this increase is due to the random directions of several spicules found along the line of sight.

Comparison of blinkers and explosive events: A case study

Blinkers are brightenings at network cell junctions that are traditionally identified with SOHO/CDS and explosive events or high velocity events are identified in high resolution UV spectra obtained from HRTS and SOHO/SUMER. Criteria are determined to facilitate objective automatic identification of both blinkers and explosive events in both SOHO/CDS and SOHO/SUMER data. Blinkers are identified in SUMER data, if the temporal resolution of the data is reduced to that of CDS. Otherwise short lived, localised intensity enhancements that make up the blinker are identified. Explosive events are identified in CDS data when the line width is significantly increased, and occasionally if there is an enhancement in the wing of the line profile. A theoretical statistical model is presented which hypothesises that blinkers and explosive events are random and not connected in any way. The results given in this paper suggest that this hypothesis can not be rejected and our probability interpretation of the recent results of Brkovic & Peter (2004, A&A, 422, 709) are inconclusive.

THE PROMINENCE – CORONA AND THE FILAMENT – CORONA TRANSITION REGION: IS THERE ANY DIFFERENCE?

The ratio between the Extreme Ultraviolet emission of the prominence–corona transition region and that of the quiet Sun (QS) transition region is measured using observations from the CDS and SUMER instruments on board the SOHO Satellite. These results are compared with those obtained in an earlier paper, analysing the same prominence as a filament on the disk. Theoretical models predict a difference in the emission of the prominence–corona transition region when it is observed at the limb and on the disk as a filament; the aim of the present work is to provide an observational check of this difference. SUMER and CDS data provide fairly good agreement if the prominence intensity measured by SUMER is compared with the average quiet-Sun intensity, measured near the disk center; the prominence intensity relative to the average quiet-Sun level measured on the same rasters results in disagreement with CDS, due to the smaller size of the disk portion and to the very strong limb brightening present in SUMER rasters. The relative prominence to quiet-Sun intensity ratio varies from 0.2 to 0.4, depending on the line formation temperature. This value leads to a discrepancy with the results obtained in a previous study when the same prominence was observed as a filament. This discrepancy indicates that the prominence–corona transition region emission is different when emitted by different sides of the prominence.

SOHO/SUMER observations and analysis of the hydrogen Lyman spectrum in solar prominences

The complete hydrogen Lyman spectrum in several prominences has been observed with the UV spectrometer SUMER on-board the SOHO, during the Joint Observing Programme 107, together with other space and ground-based observatories. Based on these observations, we are able to demonstrate, for the first time, that there exists a large variety of intensities and shapes of Lyman lines in different prominences and in various parts thereof. Therefore, no canonicalLyman spectrum can be considered for modelling purposes. However, we have identified at least two representative properties of the observed spectra: in one case (May 28, 1999 prominence) we detected high integrated intensities and no reversals in lines higher than Lα . Another prominence (June 2, 1999) exhibited quite similar integrated intensities, but all lines have rather strongly reversed profiles. This behaviour cannot be explained in terms of standard isothermal-isobaric models and we thus consider more general models which are in pressure equilibrium with the magnetic field and which have significant prominence-corona transition region (PCTR) temperature gradients. This type of model, recently suggested by Anzer & Heinzel ([CITE]), is capable of explaining strong emission profiles without reversal. Based on extended non-LTE computations, we suggest that quite different Lyman spectra mentioned above may correspond to two types of PCTRs, one seen along the magnetic-field lines (unreversed profiles) and the other one seen across the field lines (reversed profiles). Finally, we again confirm the importance of partial-redistribution (PRD) scattering processes for Lyman lines in prominences. However, our analysis of new SUMER data also points to a critical role of the PCTR in radiative transport in these lines.

SimultaneousSOHOandYohkohObservations of a Small Solar Active Region

We present new results from observations of a small active region taken with the SUMER spectrograph and Extreme Ultraviolet Imaging Telescope (EIT) on SOHO and with the Soft X-Ray Telescope (SXT) on Yohkoh. The SUMER study features line and continuum emission covering a wide range of temperatures and includes the density-sensitive O IV] λ1400 multiplet. A more extensive analysis of quiet Sun data presented in a previous paper is also included. The presence of a power-law relationship between emission-line power and electron density is confirmed, although the exponents in the active region are slightly higher than those found in the quiet Sun. These power-law relationships suggest that the volume filling factor decreases with increasing density and indicate possible differences between emitting material in active regions and the quiet Sun. We study active-region emission measures from both the SUMER and SXT data sets. For the active region as a whole, SXT temperatures and emission measures appear to fit smoothly onto the emission-measure distribution determined from cooler transition region and coronal lines in the SUMER spectra. We find no significant variation in the shape of the lower transition region emission-measure distribution for different subregions of the data set. This reinforces the conclusion from the original quiet Sun paper that ensembles of cool loops are unlikely to be the source of this emission unless the structures are considerably smaller than the 1'' spatial resolution of SUMER.

Analysis of Transition‐Region Emission‐Line Profiles from Full‐Disk Scans of the Sun Using the SUMER Instrument onSOHO

We examine statistical properties of line profiles seen in full-disk observations with the UV spectrograph SUMER on board SOHO. In the SUMER data archive, full-disk data with complete spectral information are available only for wavelength regions including the He I (584 A), Ne VIII (770 A), C III (977 A) and C IV (1548 A) emission lines. In this paper we will concentrate on C IV and Ne VIII. Collectively these data provide us with the unique opportunity to study the properties of line profiles in the lower and upper solar transition-region beyond what could be achieved with earlier instruments. In particular, these data reveal the center-to-limb behavior of line shifts and line widths for the first time in a statistically meaningful way. For C IV these data show the well-known redshift of the transition-region lines in the quiet Sun and a clear correlation of the Doppler shift and the nonthermal broadening to the intensity as a characteristic of the network structure. This correlation is not found in the coronal holes. No indications for the network can be found in Ne VIII. For Ne VIII we find a center-to-limb variation of the line shift opposite to C IV, which leads to the conclusion that Ne VIII must be blueshifted at disk center. This also shows the need for a remeasurement of the wavelength of Ne VIII in the laboratory. The center-to-limb variation of the line width leads to the conclusion that the nonresolved motions are not isotropic with a preference for the vertical component. Both lines show a clear signal for an outflow in the polar coronal holes. We discuss the implications of these and other observations for models of the transition-region and corona. The line shift behavior of Ne VIII and other lines from the upper transition-region deserves deeper investigation and probably has pivotal importance in our understanding of the solar transition-region. We are pursuing such work.

Evidence in Support of the “Nanoflare” Picture of Coronal Heating from SUMER Data

We study high signal-to-noise profiles of O IV emission lines obtained using the SUMER instrument on SOHO. Data for the quiet Sun obtained close to the disk center and at the solar limb were acquired. After careful data processing in which disk data were analyzed differentially against limb data, we find a systematic correlation between a density-sensitive emission-line ratio and Doppler shift across the same emission-line profiles. While unidentified blended lines cannot be completely discounted, the data suggest that the effects of such blends are small. Based on theoretical results in an earlier paper, we argue that if wave motions are responsible for the observed behavior, then the data reveal evidence for compressive waves propagating downward from the corona to the chromosphere. This analysis naturally lends support to the dominance of the nanoflare mechanism for coronal heating over other theories that invoke upward wave propagation, but other mechanisms capable of generating downward-propagating waves cannot be discounted. If, instead, steady flows are the cause of the observed behavior, such as return flows from spicules, then they must be such that the density is higher in the downflowing plasma. While these particular data do not allow us to discriminate between waves or steady flows, additional data from SOHO should be able to address this problem. This work required and achieved very accurate wavelength calibrations (better than 1/5 of a pixel on the detectors), taking SUMER close to its observational capabilities. We therefore present the elements of the analysis and calibration of SUMER data that may be of interest to other users.

Signatures of Acoustic and Magnetic Waves in Solar and Stellar Coronae

Time-dependent dynamical calculations of the radiating gas in solar coronal flux tubes are used to identify features of UV spectral-line profiles that can reveal the direction in which wave energy flows through the solar transition region. The profile features survive spatial and temporal averaging through nonlinear dependencies of line emission coefficients on thermal properties of the plasma that are correlated with fluid velocities. This approach can be applied to stellar and other unresolved sources, as well as the solar atmosphere. It can be regarded as a new angle of attack on the long-standing problem of determining coronal heating mechanisms. The approach requires low noise data of high spectral resolution. Therefore, it can take advantage of some unique properties of the SUMER instrument on SOHO. We make specific predictions for SUMER data that, in principle, can test whether energy propagates upward or downward in coronal flux tubes, thus allowing one to discriminate between competing theories of coronal heating. We are acquiring SUMER data in an attempt to do this.