A new auroral phenomenon, the anti-black aurora

Black auroras are small-scale features embedded in the diffuse background aurora, typically occurring post-substorm after magnetic midnight and with an eastward drift imposed. Black auroras show a significant reduction in optical brightness compared to the surrounding diffuse aurora, and can appear as slow-moving arcs or rapidly-moving patches and arc segments. We report, for the first time, an even more elusive small-scale optical structure that has always been observed occurring paired with $$\sim$$ ∼ 10% of black aurora patches. A patch or arc segment of enhanced luminosity, distinctly brighter than the diffuse background, which we name the anti-black aurora, may appear adjacent to the black aurora. The anti-black aurora is of similar shape and size, and always moves in parallel to the drifting black aurora, although it may suddenly switch sides for no apparent reason. The paired phenomenon always drifts with the same average speed in an easterly direction. From the first dual-wavelength (427.8 nm and 844.6 nm) optical observations of the phenomenon recorded on 12 March 2016 outside Tromsø Norway, we show that the anti-black and black auroras have a higher and lower mean energy, respectively, of the precipitating electrons compared to the diffuse background.

A new auroral phenomenon: The anti-black aurora

<p>Black auroras are small-scale features that show a significant reduction in optical brightness, i.e. reduced flux of particle precipitation, compared to the surrounding diffuse aurora. It typically occurs post-substorm after magnetic midnight. This phenomenon also exhibits lower mean energy than the surrounding brighter aurora it is embedded in. The underlying mechanisms that cause black auroras are not yet fully understood, although several theories have been proposed: a coupled ionospheric-magnetospheric generation mechanism, and a magnetospheric generation mechanism. This shift in particle precipitation energy to a lower mean value is confirmed by using synchronised dual-wavelength optical and EISCAT incoherent scatter radar observations that ran in parallel, and agrees with the magnetospheric generation mechanism theory. Now reported for the first time is an even more elusive small-scale optical structure has been observed occurring paired with ~10% of black aurora patches. A patch or arc segment of enhanced luminosity, distinctly brighter than the diffuse background, which we name the anti-black aurora, may appear adjacent to the black aurora. The anti-black aurora always moves in parallel to the black aurora. The paired phenomenon always drifts with the same average speed in an easterly direction. From the first dual-wavelength observations of anti-black and black aurora pairs, we show that the anti-black and black auroras have a higher and lower mean energy, respectively, of the precipitating electrons compared to the diffuse background.</p>

Extreme ultraviolet quasar colours from GALEX observations of the SDSS DR14Q catalogue

ABSTRACT The rest-frame far to extreme ultraviolet (UV) colour–redshift relationship has been constructed from data on over $480\, 000$ quasars carefully cross-matched between SDSS Data Release 14 and the final GALEX photometric catalogue. UV matching and detection probabilities are given for all the quasars, including dependencies on separation, optical brightness, and redshift. Detection limits are also provided for all objects. The UV colour distributions are skewed redward at virtually all redshifts, especially when detection limits are accounted for. The median GALEX far-UV minus near-UV (FUV − NUV) colour–redshift relation is reliably determined up to z ≈ 2.8, corresponding to rest-frame wavelengths as short as 400 Å. Extreme UV (EUV) colours are substantially redder than found previously, when detection limits are properly accounted for. Quasar template spectra were forward modelled through the GALEX bandpasses, accounting for intergalactic opacity, intrinsic reddening, and continuum slope variations. Intergalactic absorption by itself cannot account for the very red EUV colours. The colour–redshift relation is consistent with no intrinsic reddening, at least for SMC-like extinction. The best model fit has a FUV continuum power-law slope αν, FUV = −0.34 ± 0.03 consistent with previous results, but an EUV slope αν, EUV = −2.90 ± 0.04 that is much redder and inconsistent with any previous composite value (all ≳ −2.0). The EUV slope difference can be attributed in part to the tendency of previous studies to preferentially select UV brighter and bluer objects. The weak EUV flux suggests quasar accretion disc models that include outflows such as disc winds.

Photometric and spectroscopic diversity of Type II supernovae

Hydrogen-rich (Type II) supernovae (SNe) exhibit considerable photometric and spectroscopic diversity. Extending previous work that focused exclusively on photometry, we simultaneously model the multi-band light curves and optical spectra of Type II SNe using red supergiant (RSG) progenitors that are characterized by their H-rich envelope masses or the mass and extent of an enshrouding cocoon at the star’s surface. Reducing the H-rich envelope mass yields faster declining light curves, a shorter duration of the photospheric phase, and broader line profiles at early times. However, there is only a modest boost in early-time optical brightness. Increasing the mass of the circumstellar material (CSM) is more effective at boosting the early-time brightness and producing a fast-declining light curve while leaving the duration of the photospheric phase intact. It also makes the optical color bluer, delays the onset of recombination, and can severely reduce the speed of the fastest ejecta material. The early ejecta interaction with CSM is conducive to producing featureless spectra at 10−20 d and a weak or absent Hα absorption during the recombination phase. The slow decliners SNe 1999em, 2012aw, and 2004et can be explained with a 1.2 × 1051 erg explosion in a compact (∼600 R⊙) RSG star from a 15 M⊙ stellar evolution model. A small amount of CSM (<0.2 M⊙) improves the match to the SN photometry before 10 d. With more extended RSG progenitors, models predict lower ejecta kinetic energies, but the SN color stays blue for too long and the spectral line widths are too narrow. The fast decliners SNe 2013ej and 2014G may require 0.5−1.0 M⊙ of CSM, although this depends on the CSM structure. A larger boost to the luminosity (as needed for the fast decliners SNe 1979C or 1998S) requires interaction with a more spatially extended CSM, which might also be detached from the star.

Circumstellar molecular maser emission of AGB and post-AGB stars

Results of long-term studies of circumstellar molecular maser emission of late-type giant and supergiant variable stars are reported. In the 1.35-cm H2O line, the peak flux density correlates with the optical brightness lagging behind it by 0.3–0.4 P (P is the stellar period). “Superperiods” of 10 to 15 P are visible in several stars, demonstrated as high maxima in the visible light curve and associated flares in the H2O maser line. In the 18-cm OH lines, full polarization of the maser emission has been measured. Variable Zeeman patterns suggesting a changing magnetic field of a few milligauss have been detected.

V2492 Cygni: Optical BVRI Variability During the Period 2010–2017

Results from BVRI photometric observations of the young stellar object V2492 Cyg collected during the period from August 2010 to December 2017 are presented. The star is located in the field of the Pelican Nebula and it was discovered in 2010 due to its remarkable increase in the brightness by more than 5 mag in R-band. According to the first hypothesis of the variability, V2492 Cyg is an FUor candidate. During subsequent observations, it was reported that the star shows the characteristics inherent to EXor- and UXor-type variables. The optical data show that during the whole time of observations the star exhibits multiple large amplitude increases and drops in the brightness. In the beginning of 2017, we registered a significant increase in the optical brightness of V2492 Cyg, which seriously exceeds the maximal magnitudes registered after 2010.

EFFECTS OF TOTAL CHLORINE FREE (TCF) BLEACHING ON THE CHARACTERISTICS OF CHEMI MECHANICAL (CMP) PULP AND PAPER FROM MALAYSIAN DURIAN (DURIO ZIBETHINUS MURR.) RIND

The effects of bleaching process on the characteristics of pulp and paper produced from durian rind under chemi‑mechanical pulping (CMP) method were investigated. All process and characteristic tests were conducted according to Malaysian International Organisation for Standardization (MS ISO) and Technical Association of the Pulp and Paper Industry (TAPPI). Three (3) stages of peroxide (P‑P‑P) bleaching sequence through the Total Chlorine Free (TCF) bleaching process were applied to the unbeaten and unbleached durian rind CMP pulp. Bleached CMP durian rind pulp drainage time (32s) decreased (faster) and CSF freeness level (172.50ml) increased as compared to a control pulp. It was obtained that overall optical (brightness (66.36 %)) and mechanical characteristics (tensile index (38.33 Nm/g), tearing index (7.56 mN.m2/g), bursting index (2.42 kPa.m2/g), and number of folds (43)) of durian rind CMP 60 gsm paper sheet improved as the TCF bleaching process was applied to the unbleached CMP durian rind pulp.

Influence of Parameters of Screen Printing on Photoluminescence Properties of Nanophotonic Labels for Smart Packaging

Smart packaging is becoming more popular on world market as a new type of packaging able to react to changes in a packaged product during storage and informs a customer about the safety of consumption of packaged food. This article investigates the main technological issues of the use of nanophotonic printing inks based on ZnO/SiO2 nanoparticles and polyvinylpyrrolidone (PVP) for printing active elements of smart packaging on paper substrates, concerning material properties and parameters of screen printing. It is determined that the use of ink compositions with medium content of ZnO/SiO2 nanoparticles allows obtaining blue-green and blue shades of luminescence color of screen printed images by changing ink layer thickness on papers with different contents of optical brightness agents (OBAs). The minimum content of ZnO/SiO2 nanoparticles in the developed fluorescent inks leads to blue luminescence colors regardless the contents of OBAs of the papers and ink layer thickness. The luminescence intensity is directly proportional to ink layer thickness and partly depends on the content of OBAs in the selected paper. In order to fabricate nanophotonic elements of smart packaging with predetermined photoluminescence properties, the influence of investigated factors on photoluminescence properties of printed nanophotonic labels should be taken into account.