The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33 -0.4 arcsec spatial resolution, two-second temporal resolution, and 1 km s −1 velocity resolution over a field-of-view of up to 175 arcsec × 175 arcsec. . IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative-MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by B. De Pontieu (B) ·Harvard-Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA

The solar atmosphere was traditionally represented with a simple one-dimensional model. Over the past few decades, this paradigm shifted for the chromosphere and corona that constitute the outer atmosphere, which is now considered a dynamic structured envelope. Recent observations by IRIS (Interface Region Imaging Spectrograph) reveal that it is difficult to determine what is up and down even in the cool 6000-K photosphere just above the solar surface: this region hosts pockets of hot plasma transiently heated to almost 100,000 K. The energy to heat and accelerate the plasma requires a considerable fraction of the energy from flares, the largest solar disruptions. These IRIS observations not only confirm that the photosphere is more complex than conventionally thought, but also provide insight into the energy conversion in the process of magnetic reconnection.The energy produced in the core of the Sun by the fusion of hydrogen into helium is transported toward the surface first by radiation, and then by convection. The layer where the photons become free to escape defines the visible surface of the Sun. The atmosphere of the Sun above the surface was traditionally described as one-dimensionally stratified. Moving outward from the photosphere, the innermost layer, the temperature drops before rising again slightly in the middle layer, the chromosphere. When the outgoing energytransported by a heating mechanism that is not yet fully understood -can no longer be buffered by radiative loss and hydrogen ionization, the temperature rises steeply. This transition marks the boundary of the corona, the outermost layer, which is brilliantly visible to the naked eye in a total solar eclipse. Semi-empirical models represent this simplified one-dimensional stratification well (1). However, more advanced observations and models have established that the outer atmosphere (chromosphere and corona) is highly structured and dynamic (2,3,4). Modern models of the solar atmosphere also take

The basic mechanisms responsible for producing winds from cool, late-type stars are still largely unknown. We take inspiration from recent progress in understanding solar wind acceleration to develop a physically motivated model of the time-steady mass loss rates of cool main-sequence stars and evolved giants. This model follows the energy flux of magnetohydrodynamic turbulence from a subsurface convection zone to its eventual dissipation and escape through open magnetic flux tubes. We show how Alfvén waves and turbulence can produce winds in either a hot corona or a cool extended chromosphere, and we specify the conditions that determine whether or not coronal heating occurs. These models do not utilize arbitrary normalization factors, but instead predict the mass loss rate directly from a star's fundamental properties. We take account of stellar magnetic activity by extending standard age-activity-rotation indicators to include the evolution of the filling factor of strong photospheric magnetic fields. We compared the predicted mass loss rates with observed values for 47 stars and found significantly better agreement than was obtained from the popular scaling laws of Reimers, Schröder, and Cuntz. The algorithm used to compute cool-star mass loss rates is provided as a self-contained and efficient computer code. We anticipate that the results from this kind of model can be incorporated straightforwardly into stellar evolution calculations and population synthesis techniques.

Planets have been detected orbiting several solar-type stars using high-precision radial velocity (v r) measurements. While changes in v r can be measured with an accuracy of a few m s ?1 , there has been relatively little study of how other astrophysical processes, such as magnetic activity, may e ect the observed velocities. In this paper, we use published data and simple models to explore the contributions to v r from two activity-related sources, starspots and convective inhomogeneities, as these features rotate across the disk and evolve in time. Radial velocity perturbations due to both of these sources increase with rotation and the level of surface activity. Our models indicate that for solar-age G stars, the amplitude of perturbations due to spots is A S < 5 m s ?1 , increasing to A S 30 to 50 m s ?1 for Hyades-age G stars. If f S is the starspot area coverage, we nd A S / f 0:9 S v sin i. The e ects of convective inhomogeneities (as observed in line bisector variations) appear to depend on both rotation and spectral type. Young (active) F and G dwarfs can have convective v r perturbations with amplitudes A C > 50 m s ?1 , while v r amplitudes are reduced for stars with lower v sin i and cooler T e. We show that v r data from the literature display similar trends with v sin i and T e. A S and A C will be strongest at or near timescales related to magnetic activity variations: rotation, active region growth and decay, and activity cycles. Thus, knowledge of these timescales and typical A S and A C values are important in searching for extra-solar planets, especially those around younger, more active stars or those with small v r re ex amplitudes (i.e., < 20 m s ?1). We discuss implications of our results for current planet detections and planet search strategies.

We further explore nondimensional relationships between the magnetic dynamo cycle period the P cyc