Alfvén waves, transverse incompressible magnetic oscillations, have been proposed as a possible mechanism to heat the Sun's corona to millions of degrees by transporting convective energy from the photosphere into the diffuse corona. We report the detection of Alfvén waves in intensity, line-of-sight velocity, and linear polarization images of the solar corona taken using the FeXIII 1074.7-nanometer coronal emission line with the Coronal Multi-Channel Polarimeter (CoMP) instrument at the National Solar Observatory, New Mexico. Ubiquitous upward propagating waves were seen, with phase speeds of 1 to 4 megameters per second and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. An estimate of the energy carried by the waves that we spatially resolved indicates that they are too weak to heat the solar corona; however, unresolved Alfvén waves may carry sufficient energy.

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We have constructed an instrument to measure the polarization of light emitted by the solar corona in order to constrain the strength and orientation of coronal magnetic fields. We call this instrument the Coronal Multichannel Polarimeter (CoMP). The CoMP is integrated into the Coronal One Shot coronagraph at Sacramento Peak Observatory and employs a combination birefringent filter and polarimeter to form images in two wavelengths simultaneously over a 2.8R field of view. The CoMP measures the complete polarization state at the 1074.7 and 1079.8 Fe XIII coronal emission lines, and the 1083.0 nm He I chromospheric line. In this paper we present design drivers for the instrument, provide a detailed description of the instrument, describe the calibration methodology, and present some sample data along with estimates of the uncertainty of the measured magnetic field.

The J \ 0 ] J@ \ 0 radiative transitions, usually viewed as allowed through two-photon decay, may also be induced by the hyperÐne (HPF) interaction in atoms or ions having a nonzero nuclear spin. We compute new and review existing decay rates for the transitions in ions of the Be nsnp 3PJ o ] ns2 1S J{/0 (n \ 2) and Mg (n \ 3) isoelectronic sequences. The HPF induced decay rates for the J \ 0 ] J@ \ 0 transitions are many orders of magnitude larger than those for the competing two-photon processes, and when present are typically 1 or 2 orders of magnitude smaller than the decay rates of the magnetic quadrupole (J \ 2 ] J@ \ 0) transitions for these ions. Several HPF induced transitions are potentially of astrophysical interest in ions of C, N, Na, Mg, Al, Si, K, Cr, Fe, and Ni. We highlight those cases that may be of particular diagnostic value for determining isotopic abundance ratios and/or electron densities from UV or EUV emission-line data. We present our atomic data in the form of scaling laws so that, given the isotopic nuclear spin and magnetic moment, a simple expression yields estimates for HPF induced decay rates. We examine some UV and EUV solar and nebular data in light of these new results and suggest possible applications for future study. We could not Ðnd evidence for the existence of HPF induced lines in the spectra we examined, but we demonstrate that existing data have come close to providing interesting upper limits. For the planetary nebula SMC N2, we derive an upper limit of 0.1 for 13C/12C from Goddard High-Resolution Spectrograph data obtained by Clegg. It is likely that more stringent limits could be obtained using newer data with higher sensitivities in a variety of objects.

Oscillatory phenomena observed in sunspot umbrae and penumbrae are reviewed and critically discussed. A natural interplay between the thermal atmospheric stratification and the ordered collimation imposed by the intense magnetic field leads naturally to the characteristic properties of the umbral chromospheric and photospheric oscillations and their interpretation as low-beta (beta = 8pip/B2) slow magneto-acoustic-gravity waves guided along the ambient magnetic field.

Using solar soft X-ray irradiance measurements from the SXP instrument on the SNOE satellite, we relate the solar surface flux densities and their variability to those of stars as measured with the PSPC instrument on ROSAT. We translate SNOE-SXP measurements into equivalent ROSAT-PSPC counts using model spectra calculated from the CHIANTI package. Using the SNOE-SXP measurements has significant advantages over earlier studies: the absolute calibration is known to AE25%, SNOE measures the Sun as if it were an unresolved star, it has operated over a significant fraction of the solar cycle, and its three wavelength channels overlap substantially with that of the ROSAT-PSPC instrument. The predicted solar X-ray luminosities and surface flux densities are compared with measurements from the ROSAT database. We find that we can estimate the luminosity of the Sun as seen in the 0.1-2.4 keV ('' RASS '') passband of ROSAT-PSPC to within AE50%, not counting sources of systematic uncertainty mentioned in an appendix: the result lies between 10 27:1 and 10 27:75 ergs s À1 (measured in the existing data set, only partially covering a full solar cycle) and between 10 26:8 and 10 27:9 ergs s À1 (extrapolated to the full activity range of a typical solar cycle). The solar luminosities lie close to the median behavior found for a volume-limited (d < 13 pc) sample of G stars studied in 1997 by Schmitt, revealing the Sun to be a normal or slightly inactive G dwarf. A factor of 1.5 peak-to-peak variation in the RASS passband is predicted due simply to rotational modulations (i.e., those filtered to include periods P < 81 days). The ratio of maximum/minimum RASS luminosities from the magnetic activity cycle (filtered to include periods P > 81 days) are estimated to be 0.7-0.8 in log 10 L RASS , a ratio of 5 or 6. These variations are much smaller than both recent estimates of solar X-ray variability and the range of X-ray luminosities seen within Schmitt's sample. It is suggested that the reported absence of '' solar-like '' cyclic emission in stellar X-rays might partly arise because the Sun is less variable than assumed in some earlier work. Repeated ROSAT observations of Cen A during 1995-1998 show X-ray behavior reminiscent of the Sun during activity minimum conditions.

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The Mount Wilson Ca HK survey revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 to 25 years. This broad range of cycle periods is thought to reflect differences in the rotational properties and the depths of the surface convection zones for stars with various masses and ages. In 2007 we initiated a long-term monitoring campaign of Ca II H and K emission for a sample of 57 southern solar-type stars to measure their magnetic activity cycles and their rotational properties when possible. We report the discovery of a 1.6-year magnetic activity cycle in the exoplanet host star ι Horologii, and we obtain an estimate of the rotation period that is consistent with Hyades membership. This is the shortest activity cycle so far measured for a solar-type star, and may be related to the short-timescale magnetic variations recently identified in the Sun and HD 49933 from helio-and asteroseismic measurements. Future asteroseismic observations of ι Hor can be compared to those obtained near the magnetic minimum in 2006 to search for cycle-induced shifts in the oscillation frequencies. If such short activity cycles are common in F stars, then NASA's Kepler mission should observe their effects in many of its long-term asteroseismic targets.