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The literature on the $\lambda$ Boo stars has grown to become somewhat heterogenous, as different authors have applied different criteria across the UV, optical and infrared regions to determine the membership status of $\lambda$ Boo candidates. We aim to clear up the confusion by consulting the literature on 212 objects that have been considered as $\lambda$ Boo candidates, and subsequently evaluating the evidence in favour of their admission to the $\lambda$ Boo class. We obtained new spectra of $\sim$90 of these candidates and classified them on the MK system to aid in the membership evaluations. The re-evaluation of the 212 objects resulted in 64 members and 103 non-members of the $\lambda$ Boo class, with a further 45 stars for which membership status is unclear. We suggest observations for each of the stars in the latter category that will allow them to be confidently included or rejected from the class. Our reclassification facilitates homogenous analysis on group members, and represents the largest collection of confirmed $\lambda$ Boo stars known., Comment: 40 pages, 2 tables (spanning 4 pages), 0 figures. Accepted for publication in PASA. (The MN style file was used for convenience in manuscript preparation, only.)

We present measurements of starspot parameters (temperature and filling factor) on five highly active stars, using absorption bands of TiO, from observations made between 1998 March and 2001 December. We determined starspot parameters by fitting TiO bands using spectra of inactive G and K stars as proxies for the unspotted photospheres of the active stars and spectra of M stars as proxies for the spots. For three evolved RS CVn systems, we find spot filling factors between 0.28 and 0.42 for DM UMa, 0.22 and 0.40 for IN Vir, and 0.31 and 0.35 for XX Tri; these values are similar to those found by other investigators using photometry and Doppler imaging. Among active dwarfs, we measured a lower spot temperature (3350 K) for EQ Vir than found in a previous study of TiO bands, and for EK Dra a lower spot temperature (~3800 K) than found through photometry. For all active stars but XX Tri, we achieved good phase coverage through a stellar rotational period. We also present our final, extensive grid of spot and nonspot proxy stars.

The A5 star β Pictoris is a possible young planetary system and has the best-studied circumstellar disk. Our visible and ultraviolet observations of 2 Andromedae indicated that this A3 star has β Pictoris–like gas infall. We present the far-ultraviolet spectrum (905–1195 A) of 2 And we obtained with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer (FUSE). Unlike β Pic, 2 And's FUSE spectrum does not show strong chromospheric emission lines from C III and O VI. However, 2 And's FUSE spectrum contains many nonphotospheric lines that allow us to probe the circumstellar gas. For example, between 1120 and 1140 A, we detected several Fe III absorption lines arising from hyperfine levels of ground state, which cannot be formed in the interstellar medium. These lines are good diagnostics of the circumstellar gas. We also detected circumstellar Fe II, Cr III, Mn III, and O I (1D) lines. The simultaneous presence of these species suggests that the circumstellar environment of 2 And could include regions with different temperatures and densities.

Isolated Swift gamma-ray burst (GRB) pulses, like their higher-energy BATSE counterparts, emit the bulk of their pulsed emission as a hard-to-soft component that can be fitted by the Norris et al. (2005) empirical pulse model. This signal is overlaid by a fainter, three-peaked signal that can be modeled by an empirical wave-like function (Hakkila and Preece, 2014): the two fits combine to reproduce GRB pulses with distinctive three-peaked shapes. The precursor peak appears on or before the pulse rise and is often the hardest component, the central peak is the brightest, and the decay peak converts exponentially decaying emission into a long, soft, power-law tail. Accounting for systematic instrumental differences, the general characteristics of the fitted pulses are remarkably similar. Isolated GRB pulses are dominated by hard-to-soft evolution; this is more pronounced for asymmetric pulses than for symmetric ones. Isolated GRB pulses can also exhibit intensity tracking behaviors that, when observed, are tied to the timing of the three peaks: pulses with the largest maximum hardnesses are hardest during the precursor, those with smaller maximum hardnesses are hardest during the central peak, and all pulses can re-harden during the central peak and/or during the decay peak. Since these behaviors are essentially seen in all isolated pulses, the distinction between "hard-to-soft" and "intensity-tracking" pulses really no longer applies. Additionally, the triple-peaked nature of isolated GRB pulses seems to indicate that energy is injected on three separate occasions during the pulse duration: theoretical pulse models need to account for this., Comment: accepted for publication in The Astrophysical Journal

We review the results of the 1988 multi-wavelength campaign on the late-type eclipsing binary YY Geminorum. Observations include: broad-band optical and near infra-red photometry, simultaneous optical and ultraviolet (IUE) spectroscopy, X-ray (Ginga) and radio (VLA) data. From models fitted to the optical light curves, fundamental physical parameters have been determined together with evidence for transient maculations (spots) located near quadrature longitudes and intermediate latitudes. Eclipses were observed at optical, ultraviolet and radio wavelengths. Significant drops in 6cm radio emission near the phases of both primary and secondary eclipse indicate relatively compact radio emitting volumes that may lie between the binary components. IUE observations during secondary eclipse are indicative of a uniform chromosphere saturated with MgII plage-type emission and an extended volume of Ly$\alpha$ emission. Profile fitting of high-dispersion H alpha spectra confirms the chromospheric saturation and indicates significant H$\alpha$ opacity to heights of a few percent of the photospheric radius. There is evidence for an enhanced H alpha emission region visible near phase 0.25-0.35 which may be associated with a large spot on the primary and with two small optical flares which were also observed at other wavelengths: one in microwave radiation and the other in X-rays. For both flares, L_X/L_opt is consistent with energy release in closed magnetic structures., Comment: 17 pages, 10 figures

w Ori (HD 37490, HR 1934) is a Be star known to have presented variations. In order to investigate the nature and origin of its short-term and mid-term variability, a study is performed of several spectral lines (Ha, Hδ, HeI 4471, 4713, 4921, 5876, 6678, CII 4267, 6578, 6583, MgII 4481, SiIII 4553 and Sill 6347), based on 249 high signal-to-noise high-resolution spectra taken with 8 telescopes over 22 consecutive nights during the MuSiCoS (Multi Site Continuous Spectroscopy) campaign in November-December 1998. The stellar parameters are revisited and the projected rotational velocity (v sin i = 179 kms - 1 ) is redetermined using several methods. With the MuSiCoS 98 dataset, a time series analysis of line-profile variations (LPVs) is performed using the Restricted Local Cleanest (RLC) algorithm and a least squares method. The behaviour of the velocity of the centroid of the lines, the equivalent widths and the apparent vsini for several lines, as well as Violet and Red components of photospheric lines affected by emission (red He I lines, Sill 6347, CII 6578, 6583) are analyzed. The non-radial pulsation (NRP) model is examined using phase diagrams and the Fourier-Doppler Imaging (FDI) method. The LPVs are consistent with a NRP mode with l = 2 or 3, ‖m‖ = 2 with frequency 1.03 cd - 1 . It is shown that an emission line outburst occurred in the middle of the campaign. Two scenarios are proposed to explain the behaviour of a dense cloud, temporarily orbiting around the star with a frequency 0.46 cd - 1 , in relation to the outburst.

We present results from a study of starspots on active stars using a pair of vibrational-rotational absorption lines of the OH molecule near 1.563 μm. We detect excess OH absorption due to dark, cool starspots on several active stars of the RS CVn and BY Dra classes. Our results for the single-lined spectroscopic binaries II Pegasi, V1762 Cygni, and λ Andromedae augment those from a previous study that used a less sensitive detector. In this study, we were able for the first time to use molecular absorption features to measure starspot properties on double-lined spectroscopic binaries. Measuring the equivalent widths of these OH lines in inactive giant and dwarf stars of spectral types G, K, and M, we find that the total equivalent width of the line pair increases approximately linearly as effective temperature decreases from 5000 to 3000 K. We measure starspot filling factors by fitting the spectra of active stars with linear combinations of comparison star spectra representing the spot and nonspot regions of the star.

We conducted a multiwavelength campaign observing V824 Ara (HD 155555, G5 IV + K0 IV–V) continuously throughout one complete orbital cycle (~1.7 days) in early May of 1996. At the core of this campaign were observations using the GHRS on the Hubble Space Telescope (HST). In all, about 48,000 spectra, many in rapid readout mode, were obtained with the GHRS covering the C IV, Mg II, and Fe XXI wavelength regions at 11–15 separate phases. Simultaneous observations were made with the Extreme Ultraviolet Explorer (EUVE). Radio observations (3.5 and 6 cm) were conducted at the Australian Telescope, while ground-based visual spectroscopic and photometric observations were made at European Southern Observatory, Cerro Tololo Inter-American Observatory, the Anglo-Australian Telescope, and South African Astronomical Observatory. Additional ground-based observations were obtained before, during, and after the campaign. Our primary intent was to obtain a three-dimensional model of the atmosphere extending from the photosphere to the corona. Variability was clearly detected, including several flares observed in the HST, EUVE, and radio data. We present results from modeling the ultraviolet transition region lines using an anisotropic macroturbulence model. Previous studies of transition region lines in late-type active stars have used multiple Gaussians to fit the observed line profiles, adding broad components to account for the extended wings observed in several active systems, including V711 Tau (HR 1099). This broad component has been interpreted as arising from the continuous presence of microflaring. We demonstrate that anisotropic macroturbulence models can also explain the observed Mg II profiles.

We present the results of an extensive observing campaign on the O7.5 III star Persei. The UV obser- vations were obtained with the International Ultraviolet Explorer. Per was monitored continuously in October 1994 during 10 days at ultraviolet and visual wavelengths. The ground-based optical observations include mag- netic eld measurements, H and He i 6678 spectra, and were partially covered by photometry and polarimetry. We describe a method to automatically remove the variable contamination of telluric lines in the groundbased spectra. The aim of this campaign was to search for the origin of the cyclical wind variability in this star. We determined a very accurate period of 2.086(2) d in the resonance lines of Si iv and in the subordinate Niv and H line proles. The epochs of maximum absorption in the UV resonance lines due to discrete absorption com- ponents (DACs) coincide in phase with the maxima in blue-shifted H absorption. This implies that the periodic variability originates close to the stellar surface. The phase velocity relation shows a maximum at 1400 km s 1 . The general trend of these observations can be well explained by the corotating interaction region (CIR) model. In this model the wind is perturbed by one or more xed patches on the stellar surface, which are most probably due to small magnetic eld structures. Our magnetic eld measurements gave, however, only a null-detection with a1 errorbar of 70 G in the longitudinal component. Some observations are more dicult to t into this picture. The 2-day period is not detected in the photospheric/transition region line He i 6678. The dynamic spectrum of this line shows a pattern indicating the presence of non-radial pulsation, consistent with the previously reported period of 3.5 h. The edge variability around 2300 km s 1 in the saturated wind lines of C iv and N v is nearly identical to the edge variability in the unsaturated Si iv line, supporting the view that this type of variability is also due to the moving DACs. A detailed analysis using Fourier reconstructions reveals that each DAC actually consists of 2 dierent components: a \fast" and a \slow" one which merge at higher velocities.

In October 1994 the RS CVn eclipsing binary AR Lacertae was monitored by IUE during two orbital cycles. We have used 59 low resolution spectra, acquired in the range 1150-1950 A, to derive light curves for emission lines formed at different temperatures between about 10 000 and 200 000 K and to study the flare signatures versus temperature of line formation. We have analyzed a sequence of 59 high resolution Mgii k line profiles using multi-Gaussian fits (the spectral imaging technique) to derive information of the spatial structure of the chromospheres of both stars in the AR Lac system. We discuss the quiet chromospheric emission from both stars, and we show that enhanced Mgii emission is present in extended structures corotating with the K0 IV star and close to the system center-of-mass. We also report on evidence for absorbing structures toward both the stars. This study of AR Lac used the new orbital elements of Marino et al. ([CITE]) and spectra reduced and calibrated with NEWSIPS. A comparison between fluxes derived from the analyzed NEWSIPS spectra and from IUESIPS spectra is provided.

We present results from a study of starspot areas (fS) and temperatures (TS), primarily on active, single-lined spectroscopic binaries, determined using molecular absorption bands. Expanding upon our previous studies, we have analyzed multiorder echelle spectra of eight systems to simultaneously measure several different molecular bands and chromospheric emission lines. We determined starspot parameters by fitting the molecular bands of interest, using spectra of inactive G and K stars as proxies for the nonspotted photosphere of the active stars, and using spectra of M stars as proxies for the spots. At least two bands with different Teff sensitivities are required. We found that fitting bands other than the TiO 7055 and 8860 A features does not greatly extend the temperature range or sensitivity of our technique. The 8860 A band is particularly important because of its sharply different temperature sensitivity. We did not find any substantial departures from fS or TS that we have measured previously based on single-order spectra. We refined our derived spot parameters using contemporaneous photometry where available. We found that using M giants as spot proxies for subgiant active stars often underestimates fS needed to fit the photometry; this is presumably due to the increase in strength of the TiO bands with decreasing gravity. We also investigated correlations between fS and chromospheric emission, and we developed a simple method to measure nonspot temperature (TQ) solely from our echelle spectra.

We describe multi-wavelength, simultaneous observations of the RS CVn star, II Pegasi, most of which were obtained during the first three weeks of September 1992. These observations were made using optical and infra-red broad-band photometry, ultraviolet and optical spectroscopy and microwave monitoring. We have detected photospheric spots and chromospheric flares, as well as deriving a description of mean conditions in the quiet chromosphere. One of the flares, observed in optical photometry and ultraviolet spectroscopy is one of the most energetic ever observed on this star. We demonstrate that in its "quiescent” state II Peg is continually variable in most of its chromospheric emissions, as well as in its coronal output.

Ultraviolet observations of 2 Andromedae with the Goddard High Resolution Spectrograph on board the Hubble Space Telescope (HST) clearly reveal the existence of circumstellar gas, in addition to previously known anomalous interstellar features, in the line of sight toward this nearby star. We also detect varying, redshifted Ca II absorptions, which we interpret as gaseous infalls. These variable Ca II absorption features and the presence of circumstellar absorptions from Al III λλ1854.716 and 1862.790 and from excited fine-structure levels of Fe II near 2600 A seen in 2 And are similar to those observed in spectra of β Pic.

Throughout its eighteen years of operation, the International Ultraviolet Explorer has afforded us the opportunity to make many new discoveries regarding the nature of the outer atmospheres of magnetically active, late-type stars. High-resolution spectra obtained continuously throughout the rotational cycle of rapidly-rotating stars have been used to map the spatial structure of the magnetic active regions in stellar chromospheres. The RS CVn-type binary system AR Lacertae has been observed intensively at 3 epochs, with additional observations with less complete phase coverage was obtained at 4 other epochs. Taken together, we are able to probe the evolution of atmospheric structure of AR Lac over a 13-year timeline. I briefly review techniques of chromospheric emission line mapping, and I summarize the IUE results for AR Lac, V711 Tau, EI Eri, V1794 Cyg, and TY Pyx. I conclude with a description of chromospheric imaging programs (present and future) that make use of the Hubble Space Telescope.

MUSICOS (for MUlti-SIte COntinuous Spectroscopy) is an international project to facilitate and organize world-wide multi-site campaigns in high resolution spectroscopy, in view of obtaining a complete time coverage of various types of variable stellar phenomena.

Since the IRAS discovery of Vega’s large thermal infrared excess over the expected photospheric flux, dust disks have been found around a large fraction of main‐sequence A‐type stars. While dust in debris disks has been studied extensively with Spitzer, relatively little is known about their gas content. We have carried out detailed studies of the circumstellar environments of all nearby A‐type stars. We have studied both thermal emission from their circumstellar dust and absorption from circumstellar gas. With high‐resolution and high signal‐to‐noise visible spectra, we identified about a dozen main‐sequence A‐type stars with circumstellar gas through a volume‐limited survey. Although these spectra confirm the existence of the circumstellar gas and serve as a probe of the gas dynamics, they do not allow us to determine the gas density and temperature. Fortunately, there are many absorption lines in the UV and FUV range that are sensitive to the gas density and temperature. Through our FUSE, IUE, HST, and...

The chromospheric and transition region emission lines of the most active stars have routinely been shown to consist of very broad wings superimposed on the narrower, rotationally‐broadened emission core. If these wings are attributed to a single emission mechanism in the stellar atmosphere, the implied thermal broadening often strains credibility. If they are due to active regions or loops rotating into and out of view, they should be present only for a small range of rotational phase. They have also been attributed to continuous flaring and to circumstellar material (loops, disks, etc.). We have been analyzing spectra of very active stars in the FUSE continuous viewing zone, allowing them to be observed continuously over one or more complete rotations. This helps to distinguish between spatial (repeatable, phase‐dependent) and temporal variations and provides further insight into the mechanism(s) responsible for the broad wing emission.

If magnetic activity in outer stellar atmospheres is due to an interplay between rotation and subsurface convection, as is generally presumed, then one would not expect to observe indicators of activity in stars with T_eff > 8300 K. Any X-ray or ultraviolet line emission from hotter stars must be due either to a different mechanism or to an unresolved, active, binary companion. Due to their poor spatial resolution, X-ray instruments have been especially susceptible to source confusion. At wavelengths longward of 1216 Angstroms, the near ultraviolet spectra of stars hotter than this putative dividing line are dominated by photospheric continuum. We have used FUSE to obtain spectra of the subcoronal O VI emission lines, which lie at a wavelength where the photospheric continuum of the mid- and early-A stars is relatively weak. We observed 14 stars spanning a range in T_eff from 7720 to 10,000 K. Eleven of the 14 stars showed O VI emission lines, including 6 of the 8 targets with T_eff > 8300 K. At face value, this suggests that activity does not fall off with increasing temperature. However, the emission lines are narrower than expected from the projected rotational velocities of these rapidly-rotating stars, suggesting that the emission could come from unresolved late-type companions. Furthermore, the strength of the O VI emission is consistent with that expected from an unseen active K or M dwarf binary companinon, and the high x-ray to far uv luminosity ratios observed indicate that this must be the case. Our results are therefore consistent with earlier studies that have shown a rapid drop-off in activity at the radiative/convective boundary expected at T_eff about 8300 K, in agreement with conventional stellar structure models.

Current models of stellar chromospheres match either the global flux in the far ultraviolet emission lines or the details of a global line profile in order to obtain the atmospheric temperature structure. With this, it has been possible to model the global energy balance and derive a solution to the globally averaged physical properties of stellar chromospheres. However, such one component models do not actually characterize the physical structures which comprise the chromosphere, only the apparent mean structure.

We present results from the 1996 MUSICOS (MUlti-SIte COntinuous Spectroscopy) campaign on the T Tauri star SU Aurigae. We find a 2.7-d periodicity in the He I (587.6 nm) line and somewhat longer, less well-pronounced periodicities in the Balmer lines and in Na D. Our observations support the suggestion that the wind and infall signatures are out of phase on SU Aur. We present Doppler images of SU Aur that have been obtained from least-squares deconvolved profiles. Images taken about one rotation apart show only limited overlap, in particular at low latitudes. This is in part due to limitations in signal-to-noise, and in part due to line profile deformations that arise from short-lived and/or non-surface features. The agreement at high latitudes is better and suggests that at least some longer-lived features are present. The analysis of Stokes V profiles yields a marginal magnetic field detection during one of the phases., Comment: 22 pages, 20 figures, accepted for publication in MNRAS

The College of Charleston (CofC) is one of three institutions that belong to a consortium led by the Division of Science and Mathematics at the University of the Virgin Islands (UVI) to maintain and operate a research grade telescope at Etelman Observatory on the island of St. Thomas (18deg, 21′ N, 65deg W at an elevation ∼ 1325 ft with ⩽ 1″ seeing). The location provides 80% sky coverage of the southern celestial hemisphere and, on average, ∼ 6 hours of clear sky per night, except during the peak of hurricane season. This makes the observatory an ideal facility for observing Gamma‐Ray Bursts (GRBs). The observatory will serve a variety of needs to the consortium members that include research, teaching, and public outreach. The primary research function of this facility will be to perform rapid, automated followup observations of Gamma‐Ray Bursts (GRBs) observed with NASA’s Swift spacecraft, to be launched in June 2004, via the GCN. The newly renovated observatory houses a new robotic 0.5 m Cassegrain tel...

The Kepler satellite provides a unique window into stellar temporal variability by observing a wide variety of stars with multi-year, near-continuous, high precision, optical photometric time series. While most Kepler targets are faint stars with poorly known physical properties, many unexpected discoveries should result from a long photometric survey of such a large area of sky. During our Kepler Guest Observer programs that monitored late-type stars for starspot and flaring variability, we discovered a previously unknown dwarf nova that lies within a few arcseconds of the mid-G dwarf star KIC 5438845. This dwarf nova underwent nine outbursts over a 4 year time span. The two largest outbursts lasted ~17–18 days and show strong modulations with a 110.8 minute period and a declining amplitude during the outburst decay phase. These properties are characteristic of an SU UMa-type cataclysmic variable. By analogy with other dwarf nova light curves, we associate the 110.8 minute (1.847 hr) period with the superhump period, close to but slightly longer than the orbital period of the binary. No precursor outbursts are seen before the super-outbursts and the overall super-outburst morphology corresponds to Osaki & Meyer "Case B" outbursts, which are initiated when the outer edge of the disk reaches the tidal truncation radius. "Case B" outbursts are rare within the Kepler light curves of dwarf novae. The dwarf nova is undergoing relatively slow mass transfer, as evidenced by the long intervals between outbursts, but the mass transfer rate appears to be steady, because the smaller "normal" outbursts show a strong correlation between the integrated outburst energy and the elapsed time since the previous outburst. At super-outburst maximum the system was at V ~ 18, but in quiescence it is fainter than V ~ 22, which will make any detailed quiescent follow-up of this system difficult.

Photometric and spectroscopic variability of late-type stars frequently has been interpreted as evidence of magnetic activity. The standard picture of stellar activity – inherited from solar observations – includes cool, dark “spots” in the photosphere and hot, dense regions in the chromosphere and coronae. The immediate cause of each of these phenomena is a closed topology of the local magnetic field. Because stars appear as mere points of light, these localized phenomena have not been directly resolvable on stars other than the Sun. Most observed effects are produced by an asymmetric distribution of starspots. If the distribution is symmetric, it would escape detection by most current techniques of light-curve and line-profile modeling. Even more troubling, the stellar properties measured with these techniques describe only a difference between contrasting hemispheres, not an absolute measure.

We present the first results of the MUSICOS campaign on the 07.5III star ξ Persei, held in November 1996, which was aimed to study its wind variability, rotation, pulsation and magnetic field in order to study their mutual effects. During 10 days at 8 observatories around the globe we obtained more than 300 high-resolution optical spectra between 4100 and 8000 A, as well as magnetic field measurements from Hawaii and La Palma. So far we analysed the spectral lines of Hα, He i λ5875 and O iii λ5592. CLEANed Fourier transforms of the three studied lines yield a complicated multiperiod behaviour and indicate that the most likely rotation period is about 4 days. Combining these data with data from earlier campaigns, we find strong evidence in the photospheric lines for prograde non-radial pulsations with a period of 3.5 h. Since the pulsation period is much shorter than the dominant cyclic period in the stellar wind features (as found in the UV lines, recorded in an earlier campaign including the IUE satellite), we can conclude that pulsation is very unlikely the driving agent for the cyclic wind variations, at least for ξ Per. The analysis of the magnetic field measurements is still in progress. Whether magnetic fields are responsible for the observed wind modulation can therefore not be answered at the present stage, but remains still the most likely option.

We present preliminary results of the spectroscopic monitoring of AB Aur obtained during the MUSICOS 96 campaign. The analysis is mainly focussed on the He I D3 line, on the Hα line, and on a set of photospheric lines. The star was monitored irregularly for more than 200 hours.

The eclipsing RS CVn-type system AR Lacertae (K0 IV-G2 IV) has been observed with IUE satellite approximately every two years from 1981 to 1994. The principal purpose of these observations was to obtain systematic series of high-resolution (Δ ⋍ 0.24 A) Mg II h & k line spectra suitable for Spectral Imaging analysis and long-term activity study (Walter et al. 1987, Neff et al. 1989).

We report on our search for possible planetary system candidates in a volumelimited sample of 62 nearby A stars. Since the evolutionary lifetimes of A stars (≤ 109 yrs) roughly correspond to the era of planet formation and subsequent “heavy bombardment” in our solar system, our study could provide valuable insight into the origin of our own Solar System. From our ground-based visual and IUE high-resolution spectroscopy of all the northern nearby A stars, we have identified at least 12 stars with circumstellar gas. Combining these results with our previous IRAS survey we are probing the link between stars with circumstellar gas and those showing circumstellar dust disks. Our aim is not just to identify stars with gas, or stars with both gas and dust, but to identify systems with dynamic spectral activity similar to s Pic, a well known proto-planetary system candidate. By measuring the gas dynamics in the disks of these s Pic-like stars, we can begin to study the physics of accretion disks of young evolving systems.

I present preliminary results from the analysis of a series of ultraviolet spectra AR Lac obtained in 1987. These spectra are being used to image the spatial structure of the chromosphere and to study the dynamics of flaring regions. Comparing these results with previous results, I will discuss the evolution of the chromospheric structure from 1983 to 1987.

I discuss the general problem of mapping the spatial structure in the atmospheres of active, late-type stars. There are several major differences between the problems of imaging photospheres and of imaging chromospheres. Because of these differences, chromospheric spectral imaging must be based on a direct decomposition of the observed emission line profiles.

Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by AURA, Inc. under cooperative agreement with the National Science Foundation. Guest Investigator with the International Ultraviolet Explorer satellite, which is sponsored and operated \jy Uic Na.(,k>jiitl Aeronautics and Space Administration, by the the Science Research Council of the United Kingdom, and by the European Space Agency. Visiting Astronomer, National Solar Observatory, National Optical Astronomy Observatories, which is operated by AURA, Inc. under cooperative agreement, with the National Science Foundation. (NASA-CR-199871) A MULTIWAVELENGTH N96-19048 CAMPAIGN OF ACTIVE STARS WITH INTERMEDIATE ROTATION RATES Final Report (Space Telescope Science Unclas Inst.) 54 p

Goddard High Resolution Spectrograph (GHRS) observations of the RS CVn-type binary V711 Tau (Kl IV+G5 IV) were obtained at several phases over two consecutive stellar orbital cycles in order to study ultraviolet emission-line profile and flux variability. Spectra cover the Mg II h and k lines, C IV doublet, and Si IV region, as well as the density-sensitive lines of C III] (1909 A) and Si III] (1892 A). IUE spectra, Extreme Ultra Violet (EUV) data, and Ultraviolet, Blue, Visual (UBV) photometry were obtained contemporaneously with the GHRS data. Variable extended wings were detected in the Mg II lines. We discuss the Mg II line profile variability using various Gaussian emission profile models. No rotational modulation of the line profiles was observed, but there were several large flares. These flares produced enhanced emission in the extended line wings, radial velocity shifts, and asymmetries in some line profiles. Nearly continuous flaring for more than 24 hr, as indicated in the IUE data, represents the most energetic and long-lived chromospheric and transition region flare ever observed with a total energy much greater than 5 x 10(exp 35) ergs. The C III] to Si III] line ratio is used to estimate the plasma density during the flares.

I discuss the general problem of determining the spatial structure in the outer atmospheres of active, late-type stars. There are several major differences between the problems of imaging photospheres and of imaging chromospheres. Because of these differences, chromospheric spectral imaging must be based on a direct deconvolution of the observed emission line profiles. I present results based on IUE spectra of AR Lac (=HD 210334).

Approximately 10 very bright flares in RS CVn systems have been observed with the IUE. In several cases, high-resolution spectra of the Mg II k line profiles were obtained before, during, and after the flare. Such data permit us to measure the position and size of the flaring region, the amount of line broadening, and any systematic flow velocity. In two cases, several spectra were obtained during the flare decay, permitting us to study the change in these quantities during the flare decay.

An unconstrained four gaussian fit to the Mg II profile near the flare peak indicates that the flare occurred near the central meridian of the K1 IV star, perhaps above a spot. A more likely fit to the same data places the flare at +90 ±30 km s–1 relative to the K1 IV star, indicating significant downflowing plasma.

We have isolated Mg II k emission line profiles arising solely from the flaring region during flares on AR Lac and V 711 Tau. From several high-resolution spectra obtained during the lifetime of the flare, we have determined the size and position of the flaring regions and studied the decay of the emission line width, radial velocity, and integrated line flux.

We have observed two W UMa-type contact binaries, XY Leo and VW Cep, simultaneously with EXOSAT, the VLA, and, in the case of XY Leo, optically. The temporal coverage of each star was sufficient to monitor them throughout two orbital revolutions (P~0.25 days), however, no orbital modulation of either the X-ray or 6 cm data was seen for either star. A large flare from VW Cep was detected, the first such simultaneous flare ever seen on a star other than the Sun. Its behavior before, during, and after the flare is remarkably similar to that found in solar flares. For both stars, it is demonstrated that the 6 cm emission cannot be the result of Bremsstrahlung radiation of the X-ray emitting plasma.

Using a sample of ISEE 1 and 2 magnetopause crossings previously identified as times of quasi-steady reconnection, flows of medium energy ions in the magnetosheath are identified. The paper then investigates the particle pitch angle distribution immediately before and after each of these events for the signature of quasi-trapped distributions of energetic ions. Several of the ion flows identified were observed simultaneously with previously identified flux transfer events (FTEs). While FTEs identified from the magnetometer tracings typically show evidence of ion flows, the converse is not necessarily true. However, all properties of the magnetosheath ion flows are the same regardless of whether an FTE can be identified from the magnetometer data. Evidence is found for small-scale reconnection processes (FTEs, ion flows) embedded within a larger region of interconnected field, which is traced out by the quasi-trapped particles. Quasi-trapped distributions of medium-energy ions are seen to sandwich reconnection-associated ion flows in the magnetosheath. The results of this survey have been used to suggest a morphology for reconnection events that incorporates both large- and small-scale features.