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Solar flare energy manifestations were believed to be the result of the same kind of particle acceleration. It is generally accepted that a population of relativistic electrons accelerated during the impulsive phase of solar flares produces microwaves by synchrotron losses in the solar magnetic field and X-rays by collisions in denser regions of the solar atmosphere. We report the discovery of a new intense solar flare spectral radiation component, peaking somewhere in the shorter submillimeter to far-infrared range, identified during the 2003 November 4 large flare. The new solar submillimeter telescope, designed to extend the frequency range to above 100 GHz, detected this new component with increasing fluxes between 212 and 405 GHz. It appears along with, but is separated from, the well-known gyrosynchrotron emission component seen at microwave frequencies. The novel emission component had three major peaks with time, originated in a compact source whose position remained remarkably steady within 15Љ. Intense subsecond pulses are superposed with excess fluxes also increasing with frequency and amplitude increasing with the pulse repetition rate. The origin of the terahertz emission component during the flare impulsive phase is not known. It might be representative of emission due to electrons with energies considerably larger than the energies assumed to explain emission at microwaves. This component can attain considerably larger intensities in the far-infrared, with a spectrum extending to the white-light emission observed for that flare.

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We investigate the origin of the increasing spectra observed at submillimeter wavelengths detected in the flare on 2 November 2003 starting at 17:17 UT. This flare, classified as an X8.3 and 2B event, was simultaneously detected by RHESSI and the Solar Submillimeter Telescope (SST) at 212 and 405 GHz. Comparison of the time profiles at various wavelengths shows that the submillimeter emission resembles that of the high-energy X rays observed by RHESSI whereas the microwaves observed by the Owens Valley Solar Array (OVSA) resemble that of ∼50 keV X rays. Moreover, the centroid position of the submillimeter radiation is seen to originate within the same flaring loops of the ultraviolet and X-ray sources. Nevertheless, the submillimeter spectra are distinct from the usual microwave spectra, appearing to be a distinct spectral component with peak frequency in the THz range. Three possibilities to explain this increasing radio spectra are discussed: (1) gyrosynchrotron radiation from accelerated electrons, (2) bremsstrahlung from thermal electrons, and (3) gyrosynchrotron emission from the positrons produced by pion or radioactive decay after nuclear interactions. The latter possibility is ruled out on the grounds that to explain the submillimeter observations requires 3000 to 2 × 10 5 more positrons than what is inferred from X-ray and γ -ray observations. It is possible to model the emission as thermal; however, such sources would produce too much flux in the ultraviolet and soft X-ray wavelengths. Nevertheless we are able to explain both spectral components at microwave and submillimeter wavelengths by gyrosynchrotron emission from the same population of accelerated electrons that emit hard X rays and γ rays. We find that the same 5 × 10 35 electrons inferred from RHESSI observations are responsible for the compact submillimeter source (0.5 arcsec in radius) in a region of 4500 G low in the atmosphere, and for the traditional microwave spectral component by a more extended source (50 arcsec) in a 480 G magnetic field located higher up in the loops. The extreme values in magnetic field and source size required to account for the submillimeter emission can be relaxed if anisotropy and transport of the electrons are taken into account.

We analyze simultaneous Ha images (from the Big Bear Solar Observatory), soft and hard X-ray images and spectra (from the soft X-ray telescope [SXT], the Bragg Crystal Spectrometer [BCS], and the hard X-ray telescope [HXT] on Y ohkoh), and radio time proÐles (from the Owens Valley Radio Observatory) during the Ðrst 3 minutes of the 1994 June 30 Ñare. The strong blueshifts observed in the Ca XIX soft X-ray line are interpreted as evidence of chromospheric evaporation, with maximum up-Ñow velocities occurring 2 minutes prior to the hard X-ray emission peak. In this study, we search for moving sources in Ha, soft and hard X-ray images that correspond to the blueshifted component. The chromospheric evaporation in this Ñare is divided into two phases : an early phase with up-Ñow velocities of 350È450 km s~1, and a later phase (during the hard X-ray peak) characterized by velocities of 100È200 km s~1. During the Ðrst chromospheric evaporation phase, the footpoints of a loop seen in HXT lowenergy maps are seen to move toward the loop-top source. No source displacement is observed in SXT images at this time. Images of the later phase of chromospheric evaporation show a change in the source morphology. The early HXT loop is no longer visible, and HXT maps during this time display the two footpoints of a new loop visible in SXT images. Now the HXT sources are stationary, and a SXT footpoint source is seen to move toward the loop top. We interpret the observed displacement of footpoint sources in HXT (early phase) and SXT (later phase) maps to be the images of the evaporating front projected onto the solar disk, while the up-Ñow velocities (inferred from the blueshifts) are due to the movement of the same evaporating material along the line of sight. By combining the up-Ñow velocities with the proper motion of the footpoint sources seen in the maps, we constructed a three-dimensional view of the magnetic loop for each chromospheric evaporation phase. The early loop is almost semicircular, with a height of 1.7 ] 109 cm, whereas the later magnetic loop is more elongated (a height of 3.2 ] 109 cm), with its apex closer to the footpoint where most of the evaporation took place. The implications of these magnetic conÐgurations and the distinct evaporation phases are discussed.

Solar maps at 212 and 405 GHz obtained by the Solar Submillimetric Telescope (SST) show regions of enhanced brightness temperature, which coincide with the location of active regions. A statistical study of the radio emission from these active regions was performed for the first time at such high frequencies during 23 days on June and July 2002, when the atmospheric opacity was low. The brightest regions on the maps were chosen for this study, where the brightness excess observed varies from 3 to 20% above quiet Sun levels (i.e., 200 -1000 K) at both wavelengths. Sizes of the regions of enhanced emission calculated at half the maximum value were estimated to be between 2 and 7 . These sizes agree with observed sizes of active regions at other wavelengths such as Hα and ultraviolet. An important result is that the flux density spectra of all sources increase toward submillimeter frequencies, yielding flux density spectral index with an average value of 2.0. The flux density of the active region sources were complemented with that from maps at 17 and 34 GHz from the Nobeyama Radio Heliograph. The resulting spectra at all four frequencies were fit considering the flux density to be due to thermal bremsstrahlung from the active region. In the calculations, the source radius was assumed to be the mean of the measured values at 212 and 405 K. The effective temperatures of the radio emitting source, assumed homogeneous, obtained from this fit were 0.6 -2.9 × 10 4 K, for source diameters of 2 -7 .

Abstract. As a planet eclipses its parent star, a dark starspot may be occulted, causing a detectable variation in the light curve. This work describes how features on the surface of a solar-like star can be studied by using planetary transits. Images of the Sun were used in order to simulate such transits, with the planet being modeled as a dark disk at various positions along its orbit. From modeling of these transits it might be possible to infer the physical properties of the spots, such as size, intensity, position, and temperature. Recent transits observations for HD 209458 were used as tests to the model. The results yield that the limb darkening of HD 209458 is not like that of the Sun, but rather follows a quadratic function. The dark features studied have radii varying between 3 -6 10 4 km, and probably represent a group of spots, namely an active region. As for the temperature, these spots are hotter than sunspots with a temperature range of 4900-5500 K.

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