Decline In Brightness Research Articles

Improved barrier performance of Al2O3/polymer multi-layers by insertion of Alucone as hydrolysis inhibition layer and interfacial infiltration

Thin-film encapsulation (TFE) with strong barrier properties is essential for dependable flexible display. Hybrid Al2O3 and polymer multi-layered structures are considered the most promising TFE technology. However, hydrolysis of Al2O3 becomes severe with increased temperature and humidity, threatening the reliability of TFE. In this work, Alucone is introduced in the Al2O3/NEA multi-layers, where the Alucone can serve as a hydrolysis inhibition layer, to improve its reliability. In addition, Al2O3 is permeated into the NEA polymer to further improve the barrier performance of Al2O3/NEA multi-layers. The results show that the insertion of Alucone can inhibit effectively the hydrolysis of Al2O3 in the accelerated test environment. The complete interfacial infiltration of Al2O3 into NEA polymer can further improve the barrier performance. The water vapor transmission rates of (Al2O3/Alucone)3/NEA (named AAN composite films) can reach 0.27 × 10−6 g/m2/day. The barrier performance of AAN composite films remains robust even after bending tests and stability examinations. The OLED encapsulated by the AAN composite films, only less than 10 % brightness decline occurs after 7 days, illustrating that AAN composite films can extend the lifetime of OLED. The results demonstrate that the AAN composite films is anticipated to hasten the commercialization of flexible displays.

JWST Reveals a Luminous Infrared Source at the Position of the Failed Supernova Candidate N6946-BH1

N6946-BH1 (BH1) is the first plausible candidate for a failed supernova (SN), a peculiar event in which a massive star disappears without the expected bright SN, accompanied by collapse into a black hole (BH). Following a luminous outburst in 2009, the source experienced a significant decline in optical brightness, while maintaining a persistent IR presence. While it was proposed to be a potential failed SN, such behavior has been observed in SN impostor events in nearby galaxies. Here, we present late-time observations of BH1, taken 14 yr after disappearance, using JWST’s NIRCam and MIRI instruments to probe a never before observed region of the object’s spectral energy distribution (SED). We show for the first time that all previous observations of BH1 (pre- and postdisappearance) are actually a blend of at least three sources. In the near-infrared, BH1 is notably fainter than the progenitor but retains similar brightness to its state in 2017. In the mid-infrared the flux appears to have brightened compared to the inferred fluxes from the best-fitting progenitor model. The total luminosity of the source is between 13% and 25% that of the progenitor. We also show that the IR SED appears consistent with polycyclic aromatic hydrocarbon features that arise when dust is illuminated by near-ultraviolet radiation. At present, the interpretation of BH1 remains uncertain. The observations match expectations for a stellar merger, but theoretical ambiguity in the failed SN hypothesis makes it hard to dismiss.

SNe 2019vxm and 2020tlf: two luminous type II Supernovae with signatures of circumstellar interaction

AbstractWe present optical spectroscopic and photometric observations of type II SNe 2019vxm and 2020tlf. The photometric monitoring of SN 2019vxm continued for 592 days, two spectra were collected. SN 2020tlf was observed for 163 days and we obtained one spectra. The maximum luminosity of both SNe is high: mag for SN 2019vxm and SN 2020tlf, respectively. SN 2019vxm displays typical for most of SNe IIn photometric evolution: long rise to the maximum and slow brightness decline with several changes of the decline rate. The light curve of SN 2020tlf shows it may be considered as an intermediate object between classes II‐P and II‐L. The spectral evolution of SN 2019vxm was typical for SNe IIn, while for SN 2020tlf only weak signs of circumstellar interaction were observed at maximum light.

Initial Results of our Spectro-photometric Monitoring of XZ Tau

We present here initial results of our spectro-photometric monitoring of XZ Tau. During our monitoring period, XZ Tau exhibited several episodes of brightness variations in timescales of months at optical wavelengths in contrast to the mid-infrared wavelengths. The color evolution of XZ Tau during this period suggests that the brightness variations are driven by changes in accretion from the disc. The mid-infrared light curve shows an overall decline in brightness by ∼ 0.5 and 0.7 magnitude respectively in WISE W1 (3.4 μm) and W2 (4.6 μm) bands. The emission profile of the hydrogen recombination lines along with that of Ca II IRT lines points towards magnetospheric accretion of XZ Tau. We have detected P Cygni profile in Hβ indicating of out-flowing winds from regions close to accretion. Forbidden transitions of oxygen are also detected, likely indicating jets originating around the central pre-main sequence star.

Application and stability of fungal pigments using jelly sweets as a food model system

SummaryNatural pigments have seen an increase in usage over the past decades due to their acclaimed safety and active biological properties. This is in line with the shift in consumer market preferences requiring a source replacement for synthetic colourants. Filamentous fungi are amongst the natural sources currently explored for pigment production. In this study, the heat, pH and UV light stability of fungal pigments produced by Penicillium multicolour (dark brown), P. canescens (green) and P. herquie (yellow). Talaromyces verruculosus (red) and Fusarium solani (orange) were evaluated. The antioxidant properties of the pigments as influenced by these conditions were ascertained using the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) assay. The pigments were also applied in a jelly sweet formulation and incubated at ambient temperature for 4 weeks. It was demonstrated that the pigment extracts of P. multicolour and T. verruculosus were significantly affected by higher pH (7.0 and 9.0), where the decline in antioxidant activity was observed. As far as high temperature and UV light exposure are concerned, all the pigment extracts, with exception of P. herquie, maintained an antioxidant activity above 35%. On the other hand, the L*a*b* values showed no overall significant change for heat and UV light exposure with the exception of P. canescens across the four pH levels (3.0, 4.0, 7.0 and 9.0), where an increase in the ‐a (green index) coupled with a decline in brightness (L* index) and b* (blue index) was observed. Finally, there was no significant change in colour over the 4 weeks of incubation. In conclusion, fungal pigments are generally stable at normal storage conditions (ambient temperature and normal light) and can be suitably applied in jelly sweets.

Gaia21bty: An EXor light curve exhibiting a FUor spectrum

ABSTRACT Gaia21bty, a pre-main-sequence star that previously had shown aperiodic dips in its light curve, underwent a considerable ΔG ≈ 2.9 mag brightening that occurred over a few months between 2020 October and 2021 February. The Gaia light curve shows that the star remained near maximum brightness for about 4–6 months, and then started slowly fading over the next 2 yr, with at least three superimposed ∼1 mag sudden rebrightening events. Whereas the amplitude and duration of the maximum is typical for EX Lupi-type stars, optical and near-infrared spectra obtained at the maximum are dominated by features which are typical for FU Ori-type stars (FUors). Modelling of the accretion disc at the maximum indicates that the disc bolometric luminosity is 43 L⊙ and the mass accretion rate is 2.5 × 10−5 M⊙ yr−1, which are typical values for FUors even considering the large uncertainty in the distance ($1.7_{-0.4}^{+0.8}$ kpc). Further monitoring is necessary to understand the cause of the quick brightness decline, the rebrightening, and the other post-outburst light changes, as our multicolour photometric data suggest that they could be caused by a long and discontinuous obscuration event. We speculate that the outburst might have induced large-scale inhomogeneous dust condensations in the line of sight leading to such phenomena, whilst the FUor outburst continues behind the opaque screen.

Fast and not-so-furious: Case study of the fast and faint Type IIb SN 2021bxu

ABSTRACT We present photometric and spectroscopic observations and analysis of SN 2021bxu (ATLAS21dov), a low-luminosity, fast-evolving Type IIb supernova (SN). SN 2021bxu is unique, showing a large initial decline in brightness followed by a short plateau phase. With $M_r = -15.93 \pm 0.16\, \mathrm{mag}$ during the plateau, it is at the lower end of the luminosity distribution of stripped-envelope supernovae (SE-SNe) and shows a distinct ∼10 d plateau not caused by H- or He-recombination. SN 2021bxu shows line velocities which are at least $\sim 1500\, \mathrm{km\, s^{-1}}$ slower than typical SE-SNe. It is photometrically and spectroscopically similar to Type IIb SNe during the photospheric phases of evolution, with similarities to Ca-rich IIb SNe. We find that the bolometric light curve is best described by a composite model of shock interaction between the ejecta and an envelope of extended material, combined with a typical SN IIb powered by the radioactive decay of 56Ni. The best-fitting parameters for SN 2021bxu include a 56Ni mass of $M_{\mathrm{Ni}} = 0.029^{+0.004}_{-0.005}\, \mathrm{{\rm M}_{\odot }}$, an ejecta mass of $M_{\mathrm{ej}} = 0.61^{+0.06}_{-0.05}\, \mathrm{{\rm M}_{\odot }}$, and an ejecta kinetic energy of $K_{\mathrm{ej}} = 8.8^{+1.1}_{-1.0} \times 10^{49}\, \mathrm{erg}$. From the fits to the properties of the extended material of Ca-rich IIb SNe we find a trend of decreasing envelope radius with increasing envelope mass. SN 2021bxu has MNi on the low end compared to SE-SNe and Ca-rich SNe in the literature, demonstrating that SN 2021bxu-like events are rare explosions in extreme areas of parameter space. The progenitor of SN 2021bxu is likely a low-mass He star with an extended envelope.

Highly Stable and Efficient Light-Emitting Diodes Based on Orthorhombic γ-CsPbI3 Nanocrystals

Orthorhombic γ-CsPbI3 possesses the highest structural stability among the optically active (light-emissive) CsPbI3 perovskites. Here, we make use of a seed-assisted heteroepitaxial growth to fabricate seed/core/shell CaIx/γ-CsPbI3/CaI2 nanocrystals. Ultrasmall CaIx nanoparticles serve as seeds to template the Pb-centered octahedral arrangement which enables the formation of the γ-CsPbI3 phase and at the same time inhibit lattice strain by blocking the force transfer that otherwise leads to an octahedral twist and so improve the structural stability of the resulting nanocrystals. An outer shell composed from the same material, CaI2, isolates the formed γ-CsPbI3 nanocrystals from the environment, which also significantly improves their stability under ambient conditions. Optical and electrical studies indicate that the seed/core/shell CaIx/γ-CsPbI3/CaI2 structure possesses a shallower set of trap states as compared to cubic α-CsPbI3 nanocrystals. Light-emitting diodes utilizing these γ-CsPbI3 nanocrystals show a record high external quantum efficiency of 25.3%, high brightness of over 13600 cd/m2, and an operational lifetime of ∼14 h before reaching 50% of their initial luminance. These devices can repeatedly be illuminated over 650 times at ∼500 cd/m2 with no decline of brightness, which indicates their great commercial potential.

5.3: Brightness Decline Mechanism at Low Frequency Display on LTPS LCD

5.3: Brightness Decline Mechanism at Low Frequency Display on LTPS LCD

Collisions in a gas-rich white dwarf planetary debris disc.

ABSTRACTWD 0145+234 is a white dwarf that is accreting metals from a circumstellar disc of planetary material. It has exhibited a substantial and sustained increase in 3–5 n}{}mum flux since 2018. Follow-up Spitzer photometry reveals that emission from the disc had begun to decrease by late 2019. Stochastic brightening events superimposed on the decline in brightness suggest the liberation of dust during collisional evolution of the circumstellar solids. A simple model is used to show that the observations are indeed consistent with ongoing collisions. Rare emission lines from circumstellar gas have been detected at this system, supporting the emerging picture of white dwarf debris discs as sites of collisional gas and dust production.

SOFIA-EXES Observations of Betelgeuse during the Great Dimming of 2019/2020

Abstract In 2019 October Betelgeuse began a decline in V-band brightness that went beyond the minimum expected from its quasi-periodic ∼420 day cycle, becoming the faintest in recorded photometric history. Observations obtained in 2019 December with Very Large Telescope/SPHERE have shown that the southern half of the star has become markedly fainter than in 2019 January, indicating that a major change has occurred in, or near, the photosphere. We present Stratospheric Observatory for Infrared Astronomy (SOFIA) Echelon Cross Echelle Spectrograph (EXES) high spectral-resolution observations of [Fe ii] and [S i] emission lines from Betelgeuse obtained during the unprecedented 2020 February V-band brightness minimum to investigate potential changes in the circumstellar flow. These spectra are compared to observations obtained in 2015 and 2017 when the V magnitude was typical of brighter phases. We find only very small changes in the gas velocities reflected by either of the line profiles, no significant changes in the flux to continuum ratios, and hence no significant changes in the [Fe ii]/[S i] flux ratios. There is evidence that absorption features have appeared in the 2020 continuum. The Alfvén wave-crossing time from the upper photosphere is sufficiently long that one would not expect a change in the large-scale magnetic field to reach the circumstellar [Fe ii] and [S i] line-forming regions, 3 < R (R *) < 20. However, the light-crossing time is of order a few hours and a reduction in luminosity may reduce the dust-gas heating rate and [O i] emission, which has contributions from R > 20R *, where significant circumstellar oxygen-rich dust is observed.

Studies of Seyfert galaxies in Fesenkov Astrophysical Institute

This article provides an overview of the main research results of a large group of Seyfert galaxies, carried out at Fesenkov Astrophysical Institute (FAI) over the past 50 years. Spectral observations have been performed since 1970. At an early stage, a three cascade image-tube (UM-92) was used as a radiation receiver. In the 1990s, the equipment was modernized, and at present, the modern CCD cameras are used as radiation detectors at the output of spectrographs. The results of observations were used to determine the absolute fluxes of the emission lines and to study their profiles. Several additional emission features were detected on the wings of the broad emission lines Hα in the spectra of two galaxies NGC 4151 and Ark 120. These features are emitted by compact ionized objects, rotating in the field of Central Body (CB). Photometric observations of Seyfert galaxies have been carried out at FAI since 2010. Light curves of more than 20 Seyfert galaxies have been obtained. In particular, the light curves of the galaxy NGC 4151, obtained last years, shows that an active stage of its nucleus took place in 2015-2016, when the brightness increased by 0m.5 in the V filter, and by almost 2m in the R filter. Then, in 2018-2019 there was a rather sharp decline of brightness, and B V R magnitudes returned to their minimal values.

Outbursts of the black hole X-ray transient KV UMa (XTE J1118+480) in the optical band

AbstractKV UMa (XTE J1118+480) is an X-ray binary that is known to undergo outbursts in 2000 and 2005. This paper presents the discovery of a large outburst starting in 1927 on the archival photographic plates and an analysis of the long-term optical activity of this system. We used the photographic data from DASCH (Digital Access to a Sky Century @ Harvard). We placed the 1927 outburst in the context of the observed outbursts of KV UMa. We show that it is a double event, with a precursor similar to the one of the outbursts in 2000. We find a big difference between the 1927 and 2000 outbursts as regards the length of the gap between the precursor and the main outburst. It is more than 250 d in 1927, whereas it is about 20 d in 2000, although the brightnesses of all peaks are mutually comparable. We also show that the individual optical outbursts of KV UMa differ from each other by the duration of the stage of a slow decline of brightness (sometimes roughly a plateau). This determines the length of the entire main outburst. Both the peak magnitude and the brightness of the outburst when the slow decline transitions to a steep final decaying branch plausibly reproduce in all three outbursts. In the interpretation, the short duration of the precursor is caused by the fact that only the thermal-viscous instability operated in the accretion disk while also the tidal instability of the disk contributed in the subsequent main outburst.

A Search for Analogs of KIC 8462852 (Boyajian’s Star): A Proof of Concept and the First Candidates

The seemingly normal F dwarf, KIC 8462852 (a.k.a. Boyajian's Star), has been observed to exhibit two types of behavior unique among known variable stars: infrequent episodes of small brightness dips and a long-term decline in brightness between the dips. No satisfactory mechanism has been found for this behavior, at least in part, because there is only one known example. To begin to rectify this, we have searched for other stars exhibiting similar dipping behavior using the Northern Sky Variability Survey and have used data from the All Sky Automated Survey for Supernovae to further investigate the behavior. Twenty-one stars are identified as possible dippers. Fifteen may be similar to Boyajian's star and the other six are likely to be more extreme examples of the same phenomenon. Using data from the Gaia Second Data Release we show that the dipper candidates are located in two restricted regions of the H-R diagram, near the main sequence with masses near 1 solar mass and in the red giant region near the evolutionary track for 2 solar mass stars. Stars in the former group are considered to be likely analogs to Boyajian's star and should be studied in more detail to gain insights into the dipping phenomenon.

Effects of high-molecular-weight glutenin subunit combination in common wheat on the quality of crumb structure.

High-molecular-weight glutenin subunits (HMW-GSs) have important effects on bread-making quality. Allelic variations of HMW-GS in bread wheat varieties contribute in different ways to dough properties and bread volume. However, no systematic analysis has been done on the effects of allelic variation on bread-crumb structure, an important parameter when evaluating bread-making quality. In this study, seven Glu-1 deletion lines and one intact line harboring different encoding loci and derived from a cross between two spring wheat cultivars were used to investigate the contribution of a single Glu-1 locus, or combination of Glu-1 loci, to the crumb structure. Deletion of HMW-GS locus combinations resulted in a decline in slice size, brightness, and fineness of the bread crumb. A desirable crumb structure correlated well with preferred subunit combinations: high levels of GMPs, superior dough properties, and loaf volume. The effects of the HMW-GS combinations were ranked as Dx5 + Dy10 > Bx17 + By18 > Ax1 + Null. The Ax1 + Null allele affected the crumb structure by interacting with the Bx17 + By18 or Dx5 + Dy10. High-molecular-weight glutenin subunits had significant effects on the loaf volume and crumb structure; varying effects from different subunit combinations were observed. © 2018 Society of Chemical Industry.

Superhump and outburst activity of the cataclysmic variable RZ LMi in the U $U$ - and optical passbands

An analysis of the new $U,B,V,R_{C},I_{C}$ -photometry of the cataclysmic variable RZ LMi obtained in 2016–17 showed the largest $(U-B)$ colour excess in quiescence as well as during the decline of brightness, associated with the outbursts activity. The smallest $(U-B)$ colour excess was found during the brightness increase from the quiescence. In contrast to the $(U-B)$ colour index, the $(B-V),(V-R_{C}),(R_{C}-I_{C})$ colour indices exhibits the largest colour excesses near the maximum of the outburst and the smallest during the quiescence. The $(B-V)$ colour index showed also a large excess 1–2 days before a minimum. The detailed study of superhumps during the maximum of activity reveals the largest $(U-B)$ colour excess at the time of the minimum brightness of superhumps. The $(B-R_{C})$ colour index exhibits a similar behaviour, but with a phase shift of $+0.1\mbox{--}{+}0.2$ period of superhumps. The tracks in two-colour and colour-magnitude diagrams during superoutbursts are compared with the data for other cataclysmic variables during their outbursts as well as with published theoretical calculations.

Simultaneous photometric and spectral analysis of new outburst of V1686 Cyg

We present an analysis of the optical observations of Herbig AeBe star V1686 Cyg, which is demonstrating photometric variability up to 3 to 4 magnitudes. We observed this star as a part of our project of young eruptive stars investigation. Observations were performed on 2.6m telescope of Byurakan Observatory. In the course of observations we noticed that this star underwent a new outburst. After data reduction we found that full rise and decline of V1686 Cyg brightness for almost 3 magnitudes lasted about 2 months. We were able to trace the changes of the stellar spectrum during the outburst. They are discussed and compared with other young eruptive variables.

Variation in melanin pigmentation of a sexually selected plumage trait and its adaptive value in the Common SnipeGallinago gallinago

There is increasing evidence that melanin‐based plumage coloration correlates with different components of fitness and that it may act as a social or sexual signal of individual quality. We analysed variation in melanin pigmentation in the outermost tail feathers of the Common SnipeGallinago gallinago. During courtship flights, male Snipe use their outermost tail feathers to generate a drumming sound, which plays a role in territory establishment and mate choice. As the outermost tail feathers are displayed to females during these flights, we predicted that conspicuous variation in their rusty‐brown (pheomelanin‐based) coloration may act as an honest signal of individual quality. To test this prediction, we spectrophotometrically measured brightness (an indicator of total melanin content) and red chroma (an indicator of pheomelanin content) of the outermost tail feathers in 180 juvenile and adult Common Snipe. An age‐related decline in feather brightness was found exclusively in females, suggesting that melanization could have evolved by natural selection to camouflage incubating birds. In both sexes, brightness of the tail feathers was inversely correlated with their structural quality (as measured with mass–length residuals), suggesting that melanization could increase mechanical properties of feathers and, in males, enhance the quality of courtship sonation. Red chroma positively correlated with total plasma protein concentration, supporting our prediction that pheomelanin pigmentation of tail feathers may act as an honest signal of condition. Our study indicated that variation in the melanin‐based coloration of the outermost tail feathers in the Common Snipe could have evolved as a result of several different selection pressures and it emphasizes the complexity of the processes that underlie the evolution of melanin‐based plumage coloration in birds.

Sublimation of icy aggregates in the coma of comet 67P/Churyumov–Gerasimenko detected with the OSIRIS cameras on boardRosetta

Beginning in March 2014, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the morphology, location, and temporal variation of the comet's dust jets. We analyzed the dust monitoring observations shortly after the southern vernal equinox on May 30 and 31, 2015 with the WAC at the heliocentric distance Rh = 1.53 AU, where it is possible to observe that the jet rotates with the nucleus. We found that the decline of brightness as a function of the distance of the jet is much steeper than the background coma, which is a first indication of sublimation. We adapted a model of sublimation of icy aggregates and studied the effect as a function of the physical properties of the aggregates (composition and size). The major finding of this article was that through the sublimation of the aggregates of dirty grains (radius a between 5 microm and 50 microm) we were able to completely reproduce the radial brightness profile of a jet beyond 4 km from the nucleus. To reproduce the data we needed to inject a number of aggregates between 8.5 x $10^{13}$ and 8.5 x $10^{10}$ for a = 5 microm and 50 microm respectively, or an initial mass of $H_2O$ ice around 22kg.

Transient classification and novae ejecta

A third parameter, in addition to luminosity and rate of brightness decline, derived from the spectra of transients is suggested as a means of more accurately classifying objects in outburst. Principal component analysis of the spectra of transients is suggested as the best way to determine the third parameter. A model is suggested for novae ejecta that is based on the ballistic ejection of an ensemble of clouds having a wide range of sizes. Short term brightness fluctuations of novae, the formation of dust, and the production of X-ray emission follow naturally from such a picture of the evolving clouds.