[en] We have observed weak upper-chromospheric and transition region (TR) emission from two dM stars (G1784 and G1825) using deep IUE SWP exposures. In addition to the usual TR lines, Lyα fluxes for the two stars were also determined for the first time. In this paper we discuss the relative importance of Lyα and MgII as chromospheric coolants in the M dwarfs and the status of the X-ray/Hell (1640A) relationship in the light of these results

[en] A wavelength list is presented for the solar flare of 7 September, 1973 in the spectral range 1335 A-380 A. The ions observed suggest a range of temperatures in the flare plasma from 8 x 10³ K to 10⁷ K. This wavelength range contains many of the important electron density diagnostics lines for the solar transition zone and corona. The line list should also be of potential use in the identification and comparison with stellar spectra. (orig.)

[en] Mg II h and k fluxes are given for late-type dwarfs whose rotation periods are known. A good correlation between an activity parameter Rsub(hk) (represented by the ratio of Mg II h and k luminosity to bolometric luminosity) versus the Rossby-number is found for main-sequence stars F to late M. Both single and binary stars are found to follow the same relation. A saturation of Rsub(hk) occurs at rotation periods of approximately 4 day, it is suggested that stars whose rotation period is close to or shorter than this value are completely covered by active plage regions, although an alternative explanation may be saturation of the dynamo itself. (author)

[en] IUE observations of the RS CVn star II Peg in the upper chromospheric and transition regions lines MgIIk, CIV and HeII in February 1983 shows evidence for flare activity. The electron pressure derived from the mean of two different line ratios produce good agreement between the allowed and intersystem lines in the differential emission measure curves. The total radiative losses from the chromosphere and transition region for the first flare on Feb. 2 is 2.46 10³⁵ erg and at least 1.91 10³⁴ erg for the flare on Feb. 4

[en] The authors correlate Einstein observations of the X-ray flux of quiescent dMe stars with the time-averaged energy emitted by flares in the Johnson-U band, showing that the X-ray energy emitted by the coronae of these stars is about an order of magnitude greater than the U-band flare energy. From the estimate of the ratio of the total radiation emitted to the U-band flux, it is possible that, if a similar amount of energy were dissipated in the stellar atmosphere, then the observed flare events could heat the coronae of these stars. (author)

[en] Einstein observations of the X-ray flux of quiescent dwarf Me stars are correlated with the time-averaged energy emitted by flares in the Johnson U band. It is shown that the energy emitted by the coronae of these stars in X-rays is about an order of magnitude greater than the U band flare energy. From an estimate of the ratio of the total radiation emitted to the U band flux, it seems possible that if a similar amount of mechanical energy was dissipated in the stellar atmosphere, then the observed flare events can provide sufficient energy to heat the coronae of these stars. (orig.)

[en] In this paper we construct emission measure curves for average coronal hole and quiet-Sun spectra taken during the Skylab mission with the Harvard College Observatory spectroheliometer. These curves are then used to discuss the implications for the energy balance in each region. We find that the coronal hole spectrum shows a smaller slope in the emission measure distribution, consistent with the expected expect effects of outflows. Models of constant cross section coronal loops with radiative losses balanced by the divergence of the thermal conduction flux predict an emission measure rise between 10⁵ K and 10⁶ K, consistent with the average quiet-Sun observations, but not with the cell center or network emission measure distributions

[en] Proton excitation cross sections and rate coefficients are given for the fine-structure transitions in the (2s2p)³P state in the Be-like ions C III, N IV, O V, F VI, Ne VII, Mg IX, Si XI, S XIII, Ar XV, Ca XVII, and Fe XXIII. In the low-energy region we used the semiclassical Coulomb excitation method, while for the intermediate-energy range, we used a close-coupling impact parameter method. For the temperatures tabulated here, the rate coefficients for all the transitions are better than 5%. copyright 1987 Academic Press, Inc

[en] The extreme ultraviolet emission-line spectrum of very intense sunspot plumes is analyzed. Several of the standard density diagnostics suggest a constant density, rather than constant pressure, emitting region. Temperature diagnostic line ratios of several ions yield temperatures below those expected in ionization equilibrium (and observed in the quiet Sun). This provides strong evidence for the suggestion that the internal energy of cooling, falling gas accounts for the observed radiation. The lack of such departures from equilibrium in the quiet Sun demonstrates that downflows are not the dominant source of energy at transition region temperatures. We assess the accuracy of several atomic rate coefficients

[en] Optical and infrared photometry plus spectroscopic data is present for two new flare stars, GI 375 and GI 431. Both of these stars have the hydrogen Balmer lines strongly in emission. Several flares were detected on GI 375 implying a high level of flare activity. The Hα surface flux of 1.0 x 10⁶ erg cm^-2s^-1 for both stars is similar to that of other active flare stars. Fluxes are given for several of the higher Balmer lines