Lightcurve and spectral modelling of the Type IIb SN 2020acat. Evidence for a strong Ni bubble effect on the diffusion time

We use the light curve and spectral synthesis code JEKYLL to calculate a set of macroscopically mixed Type IIb supernova (SN) models, which are compared to both previously published and new late-phase observations of SN 2020acat. The models differ in the initial mass, the radial mixing and expansion of the radioactive material, and the properties of the hydrogen envelope. The best match to the photospheric and nebular spectra and lightcurves of SN 2020acat is found for a model with an initial mass of 17 solar masses, strong radial mixing and expansion of the radioactive material, and a 0.1 solar mass hydrogen envelope with a low hydrogen mass-fraction of 0.27. The most interesting result is that strong expansion of the clumps containing radioactive material seems to be required to fit the observations of SN 2020acat both in the diffusion phase and the nebular phase. These "Ni bubbles" are expected to expand due to heating from radioactive decays, but the degree of expansion is poorly constrained. Without strong expansion there is a tension between the diffusion phase and the subsequent evolution, and models that fit the nebular phase produce a diffusion peak that is too broad. The diffusion phase lightcurve is sensitive to the expansion of the "Ni bubbles", as the resulting Swiss-cheese-like geometry decreases the effective opacity and therefore the diffusion time. This effect has not been taken into account in previous lightcurve modelling of stripped-envelope SNe, which may lead to a systematic underestimate of their ejecta masses. It should be emphasized, though, that JEKYLL is limited to a geometry that is spherically symmetric on average, and large-scale asymmetries may also play a role. The relatively high initial mass found for the progenitor of SN 2020acat places it at the upper end of the mass distribution of Type IIb SN progenitors, and a single star origin can not be excluded.Comment: Accepted for publication by Astronomy and Astrophysic

Probing pre-supernova mass loss in double-peaked Type Ibc supernovae from the Zwicky Transient Facility

Eruptive mass loss of massive stars prior to supernova (SN) explosion is key to understanding their evolution and end fate. An observational signature of pre-SN mass loss is the detection of an early, short-lived peak prior to the radioactive-powered peak in the lightcurve of the SN. This is usually attributed to the SN shock passing through an extended envelope or circumstellar medium (CSM). Such an early peak is common for double-peaked Type IIb SNe with an extended Hydrogen envelope but is uncommon for normal Type Ibc SNe with very compact progenitors. In this paper, we systematically study a sample of 14 double-peaked Type Ibc SNe out of 475 Type Ibc SNe detected by the Zwicky Transient Facility. The rate of these events is ~ 3-9 % of Type Ibc SNe. A strong correlation is seen between the peak brightness of the first and the second peak. We perform a holistic analysis of this sample's photometric and spectroscopic properties. We find that six SNe have ejecta mass less than 1.5 Msun. Based on the nebular spectra and lightcurve properties, we estimate that the progenitor masses for these are less than ~ 12 Msun. The rest have an ejecta mass > 2.4 Msun and a higher progenitor mass. This sample suggests that the SNe with low progenitor masses undergo late-time binary mass transfer. Meanwhile, the SNe with higher progenitor masses are consistent with wave-driven mass loss or pulsation-pair instability-driven mass loss simulations.Comment: Submitted to ApJ. Comments are welcome. arXiv admin note: text overlap with arXiv:2210.0572

A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients

We present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 d < t1/2 < 12 d, of which 28 have blue (g-r<-0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had high-S/N predominantly featureless spectra and luminous radio emission: AT2018lug and AT2020xnd. Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad H$\alpha$ in emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (six) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 22 of the transients. All X-ray and radio observations resulted in non-detections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs, and use ZTF's SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate.Comment: Replaced following peer-review process. 46 pages, 20 figures. Accepted for publication in Ap

Product Inhibition of Biological Hydrogen Production in Batch Reactors

In this paper, the inhibitory effects of added hydrogen in reactor headspace on fermentative hydrogen production from acidogenesis of glucose by a bacterium, Clostridium acetobutylicum, was investigated experimentally in a batch reactor. It was observed that hydrogen itself became an acute inhibitor of hydrogen production if it accumulated excessively in the reactor headspace. A mathematical model to simulate and predict biological hydrogen production process was developed. The Monod model, which is a simple growth model, was modified to take inhibition kinetics on microbial growth into account. The modified model was then used to investigate the effect of hydrogen concentration on microbial growth and production rate of hydrogen. The inhibition was moderate as hydrogen concentration increased from 10% to 30% (v/v). However, a strong inhibition in microbial growth and hydrogen production rate was observed as the addition of H2 increased from 30% to 40% (v/v). Practically, an extended lag in microbial growth and considerably low hydrogen production rate were detected when 50% (v/v) of the reactor headspace was filled with hydrogen. The maximum specific growth rate (µmax), substrate saturation constant (ks), a critical hydrogen concentration at which microbial growth ceased (H2*) and degree of inhibition were found to be 0.976 h−1, 0.63 ± 0.01 gL, 24.74 mM, and 0.4786, respectivel

Unconventional Dexter–Silverton Type Manganese Heteropolytungstate [Mn₇(MnW₁₂O₄₂(OH)₄·8H₂O)] Hollow Microsphere: Synthesis, Crystal Structure, Growth Mechanism, and Optical Property Study

An uncommon yet highly symmetric crystal form of a Mn-based heteropolytungstate (Mn-HPT), Mn₇(MnW₁₂O₄₂(OH)₄)·8H₂O, has been synthesized by a unique solvothermal method at 180 °C for 6 h. The nature of the solvent (water/ethanol = 50/50 by volume) and the presence of citric acid were the key reasons for the formation of the Mn-HPT phase and its hollow spherical morphology under the said experimental conditions. Combined powder X-ray diffraction analysis and field emission scanning electron miroscopy (FESEM) analysis reveals that the structure (cubic, space group <i>Im</i>3) consisted of [MnW₁₂O₄₂]^10– polyanion with Mn in a central 12-coordinated cavity, which cross-linked three dimensionally with other MnO₆ octahedra, to form the characteristic rhombododecahedron shaped particles of size ∼150 nm. Each polyanion was made of six pair of face shared WO₆ dimers (W₂O₉) with mean W···W separation of 2.98 Å. The WO₆ octahedrons were tilted to an O–W–O angle of 99.1° with four different types of W–O bonds. The structure was further characterized by thermogravimetric (TG), infrared (IR), Raman, and X-ray photoelectron spectroscopy (XPS) study. UV–vis diffuse reflectance spectroscopy (DRS) analysis suggests that the material essentially was an indirect band gap semiconductor with <i>E</i>_g = 2.33 and 2.93 eV corresponding to the transitions from two different sets of nonbonding HOMO (O 2p) to the π* LUMO (W 5d). Room temperature photoluminescence (PL) analysis further delineates the HOMO–LUMO transition in the blue (412 nm) to green (525 nm) region with characteristic mean decay lifetime ∼8 ns

Solvent Dependent Phase Transition between Two Polymorphic Phases of Manganese–Tungstate: From Rigid to Hollow Microsphere

Crystallization of manganese (Mn²⁺) and tungstate (WO₄^2–) ions in the presence of citric acid under different water/ethanol mixtures has been systematically investigated under solvothermal conditions. A unique phase transition between two polymorphic phases, formulated as MnWO₄, manganese tungstate, and Mn₈W₁₂O₄₂(OH)₄·8H₂O, manganese heteropolytungstate (Mn-HPT), was observed along with a striking morphological alteration from rigid to hollow microsphere. The effective coordination of citrate ion to tungstate (tungstate–citrate 1:1 complex) in aqueous solution before the hydrothermal treatment drives the system to nucleate the less symmetric, monoclinic (space group: <i>P</i>2/<i>c</i>) MnWO₄ phase, which is the thermodynamically preferred polymorph. However, formation of the tungstate–citrate complex can be tuned by changing the dielectric constant of the solvent or by decreasing the citric acid to tungstate molar ratio. Results show that both conditions assist in the formation of the kinetically stable, more symmetric, cubic Mn-HPT (space group: <i>Im</i>3̅) phase at the same reaction temperature and time. The formation of the Mn-HPT phase is mediated by a kinetically advantageous crystallization process from an amorphous precursor, while later on it gradually converted into more stable MnWO₄ phase according to “Ostwald rule of successive phase transformation”. Optimum reaction conditions for the synthesis and plausible growth mechanisms of both microspheres were proposed on the basis of solvent, reaction time, temperature, and the presence of citric acid. Magnetic properties of both samples were investigated in order to illuminate the nature of magnetic interaction within the crystal lattice

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Not AvailableThe systematic research on the effect of medium-term conservation agriculture (CA) on soil quality, especially under the rice (Oryza sativa L.)-based cropping systems is limited. Hence, the specific objective of the study was to develop soil quality indices with key soil physical, chemical and biological indicators under the conservation and conventional tillage practices in a rice–mustard [Brassica juncea (L.) Czern.] cropping system. Eight treatment combinations including tillage and crop establishment, crop residue and cropping system intensification with inclusion of short duration summer mungbean [Vigna radiata (L.) Wilczek] were adopted in rice - mustard cropping system in hot semi-arid, sub-tropical north-western Indo-Gangetic Plains agro-ecoregion of India. Soil samples collected from topsoil (0 5 cm) and 5 15 cm soil layer were analyzed for 15 physical, chemical and biological properties to develop unified soil quality index (SQI) through principal component analysis (PCA). The highest SQI was obtained in the zero till direct seeded rice (ZTDSR) – zero till mustard (ZTM) –ZT summer mungbean (ZTSMB) ( + R) (mungbean residue in ZTDSR - rice residue in ZTM- mustard residue in ZTSMB) treatment followed by the ZTDSR + BM (brown manuring) – ZTM ( + R) (mustard residue in ZTDSR with BM – rice residue in ZTM). The lowest SQI was obtained in transplanted puddled rice (TPR) - conventional till mustard (CTM) for both soil layers. The identified key indicators for SQI in this Inceptisol were saturated hydraulic conductivity (Ks), pH, total N, available P, and available K. Besides, the plots under ZTDSR – ZTM – ZTSMB ( + R) resulted in 14 % higher total organic C in topsoil and 28 % higher aggregate stability than the TPR - CTM plots. This ZTDSR – ZTM -ZTSMB ( + R) treatment had 65 % higher surface soil microbial biomass C than the TPR – CTM treatment. The ZTDSR – ZTM -ZTSMB ( + R) treatment also led to higher Ks, which was in the order of triple ZT >double ZT > ZT > conventional tillage. Thus, the medium-term CA with triple or double zero tillage with crop residue retention could lead to maintain agricultural sustainability under rice-mustard system. Hence, it may be recommended to the farmers for adoption.Not Availabl