Helium line formation and abundance during a C-class flare

During a coordinated campaign which took place in May 2001, a C-class flare was observed both with SOHO instruments and with the Dunn Solar Telescope of the National Solar Observatory at Sacramento Peak. In two previous papers we have described the observations and discussed some dynamical aspects of the earlier phases of the flare, as well as the helium line formation in the active region prior to the event. Here we extend the analysis of the helium line formation to the later phases of the flare in two different locations of the flaring area. We have devised a new technique, exploiting all available information from various SOHO instruments, to determine the spectral distribution of the photoionizing EUV radiation produced by the corona overlying the two target regions. In order to find semiempirical models matching all of our observables, we analyzed the effect on the calculated helium spectrum both of A(He) (the He abundance) and of the uncertainties in the incident EUV radiation (level and spectral distribution). We found that the abundance has in most cases (but not in all) a larger effect than the coronal back-radiation. The result of our analysis is that, considering the error of the measured lines, and adopting our best estimate for the coronal EUV illumination, the value A(He)=0.075 +/- 0.010 in the chromosphere (for T>6300 K) and transition region yields reasonably good matches for all the observed lines. This value is marginally consistent with the most commonly accepted photospheric value: A(He)=0.085.Comment: 34 pages + 13 figures; to be published in Ap

Dynamics of the chromospheric flares

In this paper, I describe how chromospheric observations of a flare are used to locate the footpoints of the flaring loops and to analyse the response to the energy release during a flare. In particular, a red asymmetry in chromospheric lines is often observed during the impulsive phase of flares and is explained as due to Doppler-shifted emission of downward-moving chromospheric plasma. Using flare dynamic models that simulate in detail the physical conditions within the chromosphere, observables such as the response time, the duration and the peak value of the downflow velocity can yield information on the flare energetics. Moreover, this downward velocity is a chromospheric signature present in major events as well as in micro-flares, and seems to be a very distinctive characteristics of the flare process, more than the increasing intensity itself

CO2-Enriched atmosphere on the microscope stage

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TRACE and ground-based observations of microflares

We present high temporal and spatial resolution, multiwavelength observations of small-scale activity phenomena. The data were obtained during a coordinated campaign between ground-based and space observatories. Our analysis supports the concept that small flares are just miniature flares, i.e. that the same physical processes are at work, but that it is mandatory to have an excellent resolution in order to clearly identify them. In particular, we find that chromospheric downward motions are a very distinctive characteristic of the flare phenomenon even in tiny events

Flare model sensitivity of the Balmer spectrum

Careful studies of various chromospheric spectral signatures are very important in order to explore their possible sensitivity to the modifications of the thermodynamic quantities produced by the flare occurrence. Pioneer work of Canfield and co-workers have shown how the H alpha behavior is able to indicate different changes in the atmospheric parameters structure associated to the flare event. It was decided to study the behavior of the highest Balmer lines and of the Balmer continuum in different solar flare model atmospheres. These spectral features, originating in the deep photosphere in a quiet area, may have a sensitivity different from H alpha to the modification of a flare atmosphere. The details of the method used to compute the Stark profile of the higher Balmer line (n is greater than or equal to 6) and their merging were extensively given elsewhere (Donati-Falchi et al., 1985; Falchi et al., 1989). The models used were developed by Ricchiazzi in his thesis (1982) evaluating the chromospheric response to both the nonthermal electron flux, for energy greater than 20 kev, (F sub 20) and to the thermal conduction, (F sub c). The effect of the coronal pressure values (P sub O) at the apex of the flare loop is also included

Modelos atmosféricos de una fulguración estelar

Se presentan modelos semi-empíricos de la atmósfera de la estrella dMe AD-Leo, calculados para ajustar las observaciones de la fulguración del 12 de abril de 1985, una de las mayores fulguraciones estelares que hayan sido observados. La comparación de las observaciones con los modelos, calculados para distintos valores del área de la fulguración, permiten estimar dicha área. Asimismo, se presenta una estimación de la energía necesaria para producir la fulguración, y se compara con las fulguraciones en luz blanca observadas en el Sol.Asociación Argentina de Astronomí

Proteostasis Regulators in Cystic Fibrosis: Current Development and Future Perspectives

In cystic fibrosis (CF), the deletion of phenylalanine 508 (F508del) in the CF transmembrane conductance regulator (CFTR) leads to misfolding and premature degradation of the mutant protein. These defects can be targeted with pharmacological agents named potentiators and correctors. During the past years, several efforts have been devoted to develop and approve new effective molecules. However, their clinical use remains limited, as they fail to fully restore F508del-CFTR biological function. Indeed, the search for CFTR correctors with different and additive mechanisms has recently increased. Among them, drugs that modulate the CFTR proteostasis environment are particularly attractive to enhance therapy effectiveness further. This Perspective focuses on reviewing the recent progress in discovering CFTR proteostasis regulators, mainly describing the design, chemical structure, and structure-activity relationships. The opportunities, challenges, and future directions in this emerging and promising field of research are discussed, as well