H-alpha features with hot onsets. II. A contrail fibril

The solar chromosphere observed in H-alpha consists mostly of narrow fibrils. The longest typically originate in network or plage and arch far over adjacent internetwork. We use data from multiple telescopes to analyze one well-observed example in a quiet area. It resulted from the earlier passage of an accelerating disturbance in which the gas was heated to high temperature as in the spicule-II phenomenon. After this passage a dark H-Halpha fibril appeared as a contrail. We use Saha-Boltzmann extinction estimation to gauge the onset and subsequent visibilities in various diagnostics and conclude that such H-alpha fibrils can indeed be contrail phenomena, not indicative of the thermodynamic and magnetic environment when they are observed but of more dynamic happenings before. They do not connect across internetwork cells but represent launch tracks of heating events and chart magnetic field during launch, not at present.Comment: Accepted for Astronomy & Astrophysic

Continuous-feed nanocasting process for the synthesis of bismuth nanowire composites

We present a novel, continuous-feed nanocasting procedure for the synthesis of bismuth nanowire structures embedded in the pores of a mesoporous silica template. The immobilization of a bismuth salt inside the silica template from a diluted metal salt solution yields a sufficiently high loading to obtain electrically conducting bulk nanowire composite samples after reduction and sintering the nanocomposite powders. Electrical resistivity measurements of sintered bismuth nanowires embedded in the silica template reveal size-quantization effects

Characterization and formation of on-disk spicules in the Ca II K and Mg II k spectral lines

We characterize, for the first time, type-II spicules in Ca II K 3934\AA\ using the CHROMIS instrument at the Swedish 1-m Solar Telescope. We find that their line formation is dominated by opacity shifts with the K$_{3}$ minimum best representing the velocity of the spicules. The K$_{2}$ features are either suppressed by the Doppler-shifted K$_{3}$ or enhanced via an increased contribution from the lower layers, leading to strongly enhanced but un-shifted K$_{2}$ peaks, with widening towards the line-core as consistent with upper-layer opacity removal via Doppler-shift. We identify spicule spectra in concurrent IRIS Mg II k 2796\AA\ observations with very similar properties. Using our interpretation of spicule chromospheric line-formation, we produce synthetic profiles that match observations.Comment: 10 pages, 8 figures, accepted for publication in Astronomy and Astrophysics Letter

Surges and Si IV bursts in the solar atmosphere. Understanding IRIS and SST observations through RMHD experiments

Surges often appear as a result of the emergence of magnetized plasma from the solar interior. Traditionally, they are observed in chromospheric lines such as H$\alpha$ 6563 \AA and Ca II 8542 \AA. However, whether there is a response to the surge appearance and evolution in the Si IV lines or, in fact, in many other transition region lines has not been studied. In this paper we analyze a simultaneous episode of an H$\alpha$ surge and a Si IV burst that occurred on 2016 September 03 in active region AR12585. To that end, we use coordinated observations from the Interface Region Imaging Spectrograph (IRIS) and the Swedish 1-m Solar Telescope (SST). For the first time, we report emission of Si IV within the surge, finding profiles that are brighter and broader than the average. Furthermore, the brightest Si IV patches within the domain of the surge are located mainly near its footpoints. To understand the relation between the surges and the emission in transition region lines like Si IV, we have carried out 2.5D radiative MHD (RMHD) experiments of magnetic flux emergence episodes using the Bifrost code and including the non-equilibrium ionization of silicon. Through spectral synthesis we explain several features of the observations. We show that the presence of Si IV emission patches within the surge, their location near the surge footpoints and various observed spectral features are a natural consequence of the emergence of magnetized plasma from the interior to the atmosphere and the ensuing reconnection processes.Comment: 13 pages, 8 figures. The Astrophysical Journal (Accepted

Temperature dependent NIR emitting lanthanide-PMO/silica hybrid materials

Two materials - a mesoporous silica (MS) and a periodic mesoporous organosilica (PMO) functionalized with dipyridyl-pyridazine (dppz) units were grafted with near-infrared (NIR) emitting lanthanide (Nd3+, Er3+, Yb3+) complexes in an attempt to obtain hybrid NIR emitting materials. The parent materials: dppz-vSilica and dppz-ePMO were prepared by a hetero Diels-Alder reaction between 3,6-di(2-pyridyl)-1,2,4,5- tetrazine (dptz) and the double bonds of either ethenylene-bridged PMO (ePMO) or vinyl-silica (vSilica) and subsequent oxidation. The dppz-vSilica is reported here for the first time. The prepared lanthanide-PMO/silica hybrid materials were studied in depth for their luminescence properties at room temperature and chosen Nd3+ and Yb3+ samples also at low temperature (as low as 10 K). We show that both the dppz-vSilica and dppz-ePMO materials can be used as "platforms" for obtaining porous materials showing NIR luminescence. To obtain NIR emission these materials can be excited either in the UV or Vis region (into the pi -> pi* transitions of the ligands or directly into the f-f transitions of the Ln(3+) ions). More interestingly, when functionalized with Nd3+ or Yb3+ beta-diketonate complexes these materials showed interesting luminescence properties over a wide temperature range (10-360 K). The Yb3+ materials were investigated for their potential use as ratiometric temperature sensors