Pietro N. Bernasconi

RESISTIVE EMERGENCE OF UNDULATORY FLUX TUBES

During its 2000 January flight, the Flare Genesis Experiment observed the gradual emergence of a bipolar active region, by recording a series of high-resolution photospheric vector magnetograms and images in the blue wing of the Hα line. Previous analyses of these data revealed the occurrence of many small-scale, transient Hα brightenings identified as Ellerman bombs (EBs). They occur during the flux emergence, and many of them are located near moving magnetic dipoles in which the vector magnetic field is nearly tangential to the photosphere. A linear force-free field extrapolation of one of the magnetograms was performed to study the magnetic topology of small-scale EBs and their possible role in the flux emergence process. We found that 23 out of 47 EBs are cospatial with bald patches (BPs), while 15 are located at the footpoints of very flat separatrix field lines passing through distant BPs. We conclude that EBs can be due to magnetic reconnection, not only at BP locations, but also along their separatrices, occurring in the low chromosphere. The topological analysis reveals, for the first time, that many EBs and BPs are linked by a hierarchy of elongated flux tubes showing aperiodic spatial undulations, whose wavelengths are typically above the threshold of the Parker instability. These findings suggest that arch filament systems and coronal loops do not result from the smooth emergence of large-scale Ω-loops from below the photosphere, but rather from the rise of undulatory flux tubes whose upper parts emerge because of the Parker instability and whose dipped lower parts emerge because of magnetic reconnection. EBs are then the signature of this resistive emergence of undulatory flux tubes.

MICRO-SIGMOIDS AS PROGENITORS OF CORONAL JETS: IS ERUPTIVE ACTIVITY SELF-SIMILARLY MULTI-SCALED?

Observations from the X-ray telescope (XRT) on Hinode are used to study the nature of X-ray-bright points, sources of coronal jets. Several jet events in the coronal holes are found to erupt from small-scale, S-shaped bright regions. This finding suggests that coronal micro-sigmoids may well be progenitors of coronal jets. Moreover, the presence of these structures may explain numerous observed characteristics of jets such as helical structures, apparent transverse motions, and shapes. Analogous to large-scale sigmoids giving rise to coronal mass ejections (CMEs), a promising future task would perhaps be to investigate whether solar eruptive activity, from coronal jets to CMEs, is self-similar in terms of properties and instability mechanisms.

BROADBAND MEASUREMENTS OF FACULAR PHOTOMETRIC CONTRAST USING THE SOLAR BOLOMETRIC IMAGER

We present the first photometric measurements of solar faculae in broadband light. Our measurements were made during the recent flight of the Solar Bolometric Imager (SBI), a 30 cm balloon-borne telescope that imaged the Sun with a spectrally constant response between about 0.31 and 2.6 μm. Our curve of facular contrast versus limb distance agrees well with values obtained by the blackbody correction of monochromatic measurements. This decreases uncertainty in the facular irradiance contribution, which limits searches for other possible mechanisms of solar luminosity variation, besides changes of photospheric magnetism.

Solar constraints on new couplings between electromagnetism and gravity

{The unification of quantum field theory and general relativity is a fundamental goal of modern physics. In many cases, theoretical efforts to achieve this goal introduce auxiliary gravitational fields, ones in addition to the familiar symmetric second-rank tensor potential of general relativity, and lead to nonmetric theories because of direct couplings between these auxiliary fields and matter. Here, we consider an example of a metric-affine gauge theory of gravity in which torsion couples nonminimally to the electromagnetic field. This coupling causes a phase difference to accumulate between different polarization states of light as they propagate through the metric-affine gravitational field. Solar spectropolarimetric observations are reported and used to set strong constraints on the relevant coupling constant k: k 2 ,(2.5 km) 2 .

SOLAR MAGNETIC HELICITY INJECTED INTO THE HELIOSPHERE: MAGNITUDE, BALANCE, AND PERIODICITIES OVER SOLAR CYCLE 23

Relying purely on solar photospheric magnetic field measurements that cover most of solar cycle 23 (1996-2005), we calculate the total relative magnetic helicity injected into the solar atmosphere, and eventually shed into the heliosphere, over the latest cycle. Large active regions dominate the helicity injection process with ~5.7 × 1045 Mx2 of total injected helicity. The net helicity injected is 1% of the above output. Peculiar active-region plasma flows account for ~80% of this helicity; the remaining ~20% is due to solar differential rotation. The typical helicity per active-region CME ranges between (1.8-7) × 1042 Mx2 depending on the CME velocity. Accounting for various minor underestimation factors, we estimate a maximum helicity injection of ~6.6 × 1045 Mx2 for solar cycle 23. Although no significant net helicity exists over both solar hemispheres, we recover the well-known hemispheric helicity preference, which is significantly enhanced by the solar differential rotation. We also find that helicity injection in the solar atmosphere is an inherently disorganized, impulsive, and aperiodic process.

Balloon-borne telescope for high-resolution solar imaging and polarimetry

In January 2000, an 80-cm F/1.5 Ritchey-Chretien solar telescope flew for 17 days suspended from a balloon in the stratosphere above Antarctica. The goal was to acquire long time series of high spatial resolution images and vector- magnetograms of the solar photosphere and chromosphere. Such observations will help to advance our basic scientific understanding of solar activity, in particular flares. Flying well above the turbulent layers of the Earths atmosphere, the telescope should be able to operate close to its diffraction limited resolution of 0.2 arcsec, providing high resolution observations of small scale solar features. To achieve this goal we developed a platform for the optical telescope that is stable to nearly 10 arcsec. We also developed an image motion compensation system that stabilizes the solar image on the CCD focal plane to about 1 arcsec.

The Stratospheric THz Observatory (STO)

The Stratospheric TeraHertz Observatory (STO) is a NASA funded, Long Duration Balloon (LDB) experiment designed to address a key problem in modern astrophysics: understanding the Life Cycle of the Interstellar Medium (ISM). STO will survey a section of the Galactic plane in the dominant interstellar cooling line [C II] (1.9 THz) and the important star formation tracer [N II] (1.46 THz) at ~1 arc minute angular resolution, sufficient to spatially resolve atomic, ionic and molecular clouds at 10 kpc. STO itself has three main components; 1) an 80 cm optical telescope, 2) a THz instrument package, and 3) a gondola [1]. Both the telescope and gondola have flown on previous experiments [2,3]. They have been reoptimized for the current mission. The science flight receiver package will contain four [CII] and four [NII] HEB mixers, coupled to a digital spectrometer. The first engineering test flight of STO was from Ft. Sumner, NM on October 15, 2009. The ~30 day science flight is scheduled for December 2011.

INVERSION OF STOKES VECTOR PROFILES IN TERMS OF A 3-COMPONENT MODEL

Various spectropolarimetric observations show peculiar Stokes profiles that reveal the coexistence of at least two magnetic components in the same resolution ele-ment. An example is given by observations of the full Stokes vector in a complex active region performed with the ZIMPOL I Stokes polarimeter. In order to deduce the physical parameters of the observed regions from such measured profiles, we have extended an existing inversion code, so that it can now fit the data with models composed of up to three different atmospheric components. Two of these components are magnetic and may possess different field strengths, field geometries, temperature stratifications, and velocity fields. The third component describes the field free atmosphere surrounding the magnetic features.

BRRISON IR Camera (BIRC)

BIRC is a multispectral infrared imager designed to operate in 8 bandpasses between 2.5 and 5.0 μm utilizing a cryocooled HgCdTe detector and Ø80 cm telescope. The instrument was flown on a ballooncraft platform and operated in a near-space environment. BIRC was designed to measure the water and CO2 emissions from the comet ISON. The system produces an f/4 image over a field of view of 3 arcminutes, and employs shift/co-add algorithms to observe dim objects. An innovative thermal design holds the system components in separate vacuum and atmospheric zones which are independent of the neighboring instrument deck. This paper summarizes the design, test and integration of the BIRC instrument.

Optical design for the large balloon reflector

We present the details of the optical design, corrector system, mechanical layout, tolerances, pointing requirements, and overall performance of the sub-millimeter wavelength Large Balloon Reflector telescope (LBR).