Can spicules be detected at disc centre in broad-band Ca II H filter imaging data ?

We estimate the formation height range contributing to broad-band and narrow-band filter imaging data in Ca II H to investigate whether spicules can be detected in such observations at the centre of the solar disc. We apply spectral filters of FWHMs from 0.03 nm to 1 nm to observed Ca line profiles to simulate Ca imaging data. We estimate the relative intensity contributions of off-limb and on-disc structures. We compare the synthetic Ca filter imaging data with intensity maps of Ca spectra at different wavelengths and temperature maps at different optical depths. We determine the intensity response function for the wavelengths covered by the filters of different FWHM. The intensity emitted off the solar limb is about 5% of the intensity at disc centre. For a 0.3 nm-wide Ca II H filter, up to about 1/3 of the off-limb intensity comes from emission in Hepsilon. On the disc, only about 15% of the intensity transmitted through a broad-band filter comes from the line-core region. No traces of elongated fibrillar structures are visible in imaging data at disc centre, opposite to the line-core images of the Ca spectra. The response function for a 0.3 nm-wide filter peaks at about 200 km. Relative contributions from atmospheric layers above 800 km are about 10%. The inversion results suggest that the slightly enhanced emission around the photospheric magnetic network in broad-band Ca imaging data is caused by a thermal canopy at a height of about 600 km. Broad-band Ca II H imaging data do not trace upper chromospheric structures such as spicules in observations at the solar disc because of the too small relative contribution of the line core to the total wavelength-integrated filter intensity.Comment: 10 pages, 11 figures, accepted for publication in A&

Evidence of quiet Sun chromospheric activity related to an emerging small-scale magnetic loop

Aims: We investigate the temporal evolution of magnetic flux emergence in the quiet Sun atmosphere close to disk center. Methods: We combine high-resolution SoHO/MDI magnetograms with TRACE observations taken in the 1216 {\AA} channel in order to analyze the temporal evolution of an emerging small-scale magnetic loop and its traces in the chromosphere. Results: At first place, we find signatures of flux emergence very close to the edge of a supergranular network boundary located at disk center. The new emerging flux appears first in the MDI magnetograms in form of an asymmetric bipolar element, i.e. the patch with negative polarity is roughly two-times weaker than the corresponding patch with opposite polarity. The average values of magnetic flux and magnetic flux densities reach 1.6 x 10^18 Mx, -8.5 x 10^17 Mx, and 55 Mx cm^-2, -30 Mx cm^-2, respectively. The spatial distance between the opposite polarity patches of the emerged feature increases from about 2.5" to 5.0" during the lifetime of the loop which was not longer than 36 min. A more precise lifetime-estimate of the feature was not possible because of a gap in the temporal sequence of the MDI magnetograms. The chromospheric response to the emerged magnetic dipole occurs ~ 9 minutes later with respect to the photospheric magnetograms. It consists of a quasi-periodic sequence of time-localized brightenings visible in the 1216 {\AA} TRACE channel apparent for ~ 14 minutes and being co-spatial with the axis connecting the two patches of opposite magnetic polarity. Conclusions: We identify the observed event as a small-scale magnetic loop emerging at photospheric layers and subsequently rising up to the chromosphere. We discuss the possibility that the fluctuations detected in the chromospheric emission probably reflect magnetic field oscillations which propagate to the chromosphere in form of waves.Comment: 6 pages, 4 figures, 1 table, Astronomy and Astrophysics, in pres

Zur Situation des Arbeitsmarktes für Spezialbibliothekare : Statistische Untersuchungen zur Beschäftigung von Informationsspezialisten in internen Informationseinrichtungen

Die vorliegende Arbeit gibt anhand statistischer Untersuchungen einen Einblick in die derzeitige Arbeitsmarktsituation für Spezialbibliothekare in Deutschland. Es wird untersucht, in welchem Umfang Spezialbibliotheken in deutschen Statistiken erfasst sind. Dabei werden auch Auswertungen hinsichtlich ihrer Bestandsgröße und Personalstellenzahl durchgeführt. Den Schwerpunkt der Arbeit bildet die Analyse von Stellenanzeigen, die Positionen in internen Informationseinrichtungen ausschreiben, im Hinblick auf verschiedene Aspekte. Diese statistischen Untersuchungen geben Aufschluss darüber, wie sich die Arbeitsmarktsituation für Beschäftigte in Spezialbibliotheken derzeit darstellt. Dabei werden einerseits quantitative Aussagen getroffen, die Rückschlüsse auf den Umfang des spezialbibliothekarischen Arbeitsmarktes zulassen. Andererseits erfolgt eine qualitative Analyse, indem die von Arbeitgebern gebotenen Beschäftigungsverhältnisse sowie die an zukünftige Stelleninhaber gestellten spezifischen Anforderungen hinsichtlich ihrer Qualifikation näher betrachtet werden

The polarization signature of photospheric magnetic fields in 3D MHD simulations and observations at disk center

Before using 3D MHD simulations of the solar photosphere in the determination of elemental abundances, one has to ensure that the correct amount of magnetic flux is present in the simulations. The presence of magnetic flux modifies the thermal structure of the solar photosphere, which affects abundance determinations and the solar spectral irradiance. We compare the polarization signals in disk-center observations of the solar photosphere in quiet-Sun regions with those in Stokes spectra computed on the basis of 3D MHD simulations having average magnetic flux densities of about 20, 56, 112 and 224 G. This approach allows us to find the simulation run that best matches the observations. The observations were taken with the Hinode SP, TIP, POLIS and the GFPI, respectively. We determine characteristic quantities of full Stokes profiles in a few photospheric spectral lines in the visible (630 nm) and near-infrared (1083 and 1565 nm). We find that the appearance of abnormal granulation in intensity maps of degraded simulations can be traced back to an initially regular granulation pattern with numerous bright points in the intergranular lanes before the spatial degradation. The linear polarization signals in the simulations are almost exclusively related to canopies of strong magnetic flux concentrations and not to transient events of magnetic flux emergence. We find that the average vertical magnetic flux density in the simulation should be less than 50 G to reproduce the observed polarization signals in the quiet Sun internetwork. A value of about 35 G gives the best match across the SP, TIP, POLIS and GFPI observations.Comment: 12 pages, 11 figures; accepted for publication in Ap

Twist, Writhe & Helicity in the inner penumbra of a sunspot

The aim of this work is the determination of the twist, writhe, and self magnetic helicity of penumbral filaments located in an inner Sunspot penumbra. To this extent, we inverted data taken with the spectropolarimeter (SP) aboard Hinode with the SIR (Stokes Inversion based on Response function) code. For the construction of a 3D geometrical model we applied a genetic algorithm minimizing the divergence of the magnetic field vector and the net magnetohydrodynamic force, consequently a force-free solution would be reached if possible. We estimated two proxies to the magnetic helicity frequently used in literature: the force-free parameter and the current helicity term. We show that both proxies are only qualitative indicators of the local twist as the magnetic field in the area under study significantly departures from a force-free configuration. The local twist shows significant values only at the borders of bright penumbral filaments with opposite signs on each side. These locations are precisely correlated to large electric currents. The average twist (and writhe) of penumbral structures is very small. The spines (dark filaments in the background) show a nearly zero writhe. The writhe per unit length of the intraspines diminishes with increasing length of the tube axes. Thus, the axes of tubes related to intraspines are less wrung when the tubes are more horizontal. As the writhe of the spines is very small, we can conclude that the writhe reaches only significant values when the tube includes the border of a intraspine.Comment: 7 pages, 4 figures; Astrophysical Journal, in pres

Instrument and data analysis challenges for imaging spectropolarimetry

The next generation of solar telescopes will enable us to resolve the fundamental scales of the solar atmosphere, i.e., the pressure scale height and the photon mean free path. High-resolution observations of small-scale structures with sizes down to 50 km require complex post-focus instruments, which employ adaptive optics (AO) and benefit from advanced image restoration techniques. The GREGOR Fabry-Perot Interferometer (GFPI) will serve as an example of such an instrument to illustrate the challenges that are to be expected in instrumentation and data analysis with the next generation of solar telescopes.Comment: 4 pages, 1 figure, accepted for publication in Astronomische Nachrichten/AN, special issue of the 1st EAST-ATST Workshop: "Science with large solar telescopes" in Freiburg, Germany, October 14-16, 200

Spectroscopy at the solar limb: II. Are spicules heated to coronal temperatures ?

Spicules of the so-called type II were suggested to be relevant for coronal heating because of their ubiquity on the solar surface and their eventual extension into the corona. We investigate whether solar spicules are heated to transition-region or coronal temperatures and reach coronal heights (>6 Mm) using multi-wavelength observations of limb spicules in different chromospheric spectral lines (Ca II H, Hepsilon, Halpha, Ca II IR at 854.2 nm, He I at 1083 nm). We determine the line width of individual spicules and throughout the field of view and estimate the maximal height that different types of off-limb features reach. We derive estimates of the kinetic temperature and the non-thermal velocity from the line width of spectral lines from different chemical elements. We find that most regular spicules reach a maximal height of about 6 Mm above the solar limb. The majority of features found at larger heights are irregularly shaped with a significantly larger lateral extension than spicules. Both individual and average line profiles in all spectral lines show a decrease in their line width with height above the limb with very few exceptions. Both the kinetic temperature and the non-thermal velocity decrease with height above the limb. We find no indications that the spicules in our data reach coronal heights or transition-region or coronal temperatures.Comment: Accepted for publication in Solar Physics, 52 pages, 32 figure

A tale of two scholarly blog platforms: comparing and conceptualizing online research communities.

Cornelius Puschmann and Marco Bastos expand on the computational methods employed to understand the contributions and online networks of two prominent scholarly blog platforms, HASTAC and Hypotheses. Their analysis suggests one community is driven more by an emphasis on the new media movement and cross-disciplinary aspiration, compared to the other’s more traditional disciplinary approach with a focus on the new publishing environment. The toolbox for analyzing blog platforms is still evolving and any results need to be treated with care. But it is clear that these computational methods can shed a new light on ongoing developments in science and scholarship