Evidence for two distinct populations of type Ia supernovae Wang, Xiaofeng; Wang, Lifan; Filippenko, Alexei V ...
Science (American Association for the Advancement of Science),
2013-Apr-12, 2013-04-12, 20130412, Letnik:
340, Številka:
6129
Journal Article
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Type Ia supernovae (SNe Ia) have been used as excellent standardizable candles for measuring cosmic expansion, but their progenitors are still elusive. Here, we report that the spectral diversity of ...SNe Ia is tied to their birthplace environments. We found that those with high-velocity ejecta are substantially more concentrated in the inner and brighter regions of their host galaxies than are normal-velocity SNe Ia. Furthermore, the former tend to inhabit larger and more luminous hosts. These results suggest that high-velocity SNe Ia likely originate from relatively younger and more metal-rich progenitors than do normal-velocity SNe Ia and are restricted to galaxies with substantial chemical evolution.
SNe Ia play key roles in revealing the accelerating expansion of the universe, but our knowledge of their progenitors is still very limited. Here we report the discovery of a rigid dichotomy in ...circumstellar (CS) environments around two subclasses of SNe Ia as defined by their distinct photospheric velocities. For the SNe Ia with high photospheric velocities (HVs), we found a significant excess flux in blue light 60-100 days past maximum, while this phenomenon is absent for SNe with normal photospheric velocity. This blue excess can be attributed to light echoes by circumstellar dust located at a distance of about (1-2) × 1017 cm from the HV subclass. Moreover, we also found that the HV SNe Ia show systematically evolving Na i absorption line by performing a systematic search of variable Na i absorption lines in spectra of all SNe Ia, whereas this evolution is rarely seen in normal ones. The evolving Na i absorption can be modeled in terms of photoionization model, with the location of the gas clouds at a distance of about 2 × 1017 cm, in striking agreement with the location of CS dust inferred from B-band light-curve excess. These observations show clearly that the progenitors of HV subclass are likely from single-degenerate progenitor system (i.e., symbiotic binary), while the NV subclass may arise from double-degenerate system.
Large-scale rotating mechanical equipment in the mining arena plays a pivotal role in mining production, where vibration issues directly influence production efficiency and safety. This Review aims ...to provide a comprehensive review of the latest advancements and methodologies related to the generation mechanisms, identification, and applications of vibrational characteristics in large-scale mining rotating mechanical equipment. Semi-autogenous mills, ball mills, and coal mills are selected as archetype equipment, and the Lagrangian motion equation is employed to unveil the generation mechanisms of vibrations and the embedded physical information in the signals of these machines. Initially, the research delves deeply into the acquisition, extraction, and identification of vibrational signal features, emphasizing that while mechanical vibration signals can reveal the internal operational state and fault information of machinery, there remains a need to enhance their capability to depict complex vibrational signals. Subsequently, this Review discusses in depth the studies focused on predicting the vibrational state of equipment by establishing accurate and reliable soft measurement models, pointing out that current models still have room for improvement in prediction accuracy and generalization capabilities. Conclusively, based on the elucidation of mechanical vibration mechanisms and the collation and outlook of the existing research study, the importance of on-site monitoring, deep learning, Internet of Things technology, and full lifecycle management is accentuated. To better support practical engineering applications, further exploration into the physical properties of vibrational signals and the mechanisms of mechanical vibrations is essential.
We present extensive optical observations of a Type IIn supernova (SN IIn) 2010j1 for the first 1.5 years after its discovery. The UBVRI light curves demonstrated an interesting two-stage evolution ...during the nebular phase, which almost flatten out after about 90 days from the optical maximum. These lines can be well decomposed into a narrow component and an intermediate-width component. The intermediate-width component showed a steady increase in both strength and blueshift with time until t ~ 400 days after maximum, but it became less blueshifted at t ~ 500 days, when the line profile appeared relatively symmetric again. Considering a slow-moving stellar wind (e.g., ~28 km s-l) inferred for the preexisting, dense CSM shell and the extremely high mass-loss rate (1-2 M sub(odot) yr super(-1)), we suggest that the progenitor of SN 2010jl might have experienced a red supergiant stage and may explode finally as a post-red supergiant star with an initial mass above 30-40 M sub(odot).
Abstract
Naturally derived biopolymers have attracted great interest to construct photonic materials with multi-scale ordering, adaptive birefringence, chiral organization, actuation and robustness. ...Nevertheless, traditional processing commonly results in non-uniform organization across large-scale areas. Here, we report magnetically steerable uniform biophotonic organization of cellulose nanocrystals decorated with superparamagnetic nanoparticles with strong magnetic susceptibility, enabling transformation from helicoidal cholesteric (chiral nematic) to uniaxial nematic phase with near-perfect orientation order parameter of 0.98 across large areas. We demonstrate that magnetically triggered high shearing rate of circular flow exceeds those for conventional evaporation-based assembly by two orders of magnitude. This high rate shearing facilitates unconventional unidirectional orientation of nanocrystals along gradient magnetic field and untwisting helical organization. These translucent magnetic films are flexible, robust, and possess anisotropic birefringence and light scattering combined with relatively high optical transparency reaching 75%. Enhanced mechanical robustness and uniform organization facilitate fast, multimodal, and repeatable actuation in response to magnetic field, humidity variation, and light illumination.
ABSTRACT We present well-sampled optical observations of the bright Type Ia supernova (SN Ia) SN 2011fe in M101. Our data, starting from ∼16 days before maximum light and extending to ∼463 days after ...maximum, provide an unprecedented time series of spectra and photometry for a normal SN Ia. Fitting the early-time rising light curve, we find that the luminosity evolution of SN 2011fe follows a tn law, with the index n being close to 2.0 in the VRI bands but slightly larger in the U and B bands. Combining the published ultraviolet (UV) and near-infrared (NIR) photometry, we derive the contribution of UV/NIR emission relative to the optical. SN 2011fe is found to have stronger UV emission and reaches its UV peak a few days earlier than other SNe Ia with similar Δm15(B), suggestive of less trapping of high-energy photons in the ejecta. Moreover, the U-band light curve shows a notably faster decline at late phases (t 100-300 days), which also suggests that the ejecta may be relatively transparent to UV photons. These results favor the notion that SN 2011fe might have a progenitor system with relatively lower metallicity. On the other hand, the early-phase spectra exhibit prominent high-velocity features (HVFs) of O i λ7773 and the Ca ii NIR triplet, but only barely detectable in Si ii 6355. This difference can be caused by either an ionization/temperature effect or an abundance enhancement scenario for the formation of HVFs; it suggests that the photospheric temperature of SN 2011fe is intrinsically low, perhaps owing to incomplete burning during the explosion of the white dwarf.
ABSTRACT The high-velocity features (HVFs) in optical spectra of type Ia supernovae (SNe Ia) are examined with a large sample including very early-time spectra (e.g., t < −7 days). Multiple Gaussian ...fits are applied to examine the HVFs and their evolutions, using constraints on expansion velocities for the same species (i.e., Si ii 5972 and Si ii 6355). We find that strong HVFs tend to appear in SNe Ia with smaller decline rates (e.g., Δm15(B) ), clarifying that the finding by Childress et al. for the Ca-HVFs in near-maximum-light spectra applies both to the Si-HVFs and Ca-HVFs in the earlier phase. The Si-HVFs seem to be more common in rapidly expanding SNe Ia, which is different from the earlier result that Ca-HVFs are associated with SNe Ia that have slower Si ii 6355 velocities at maximum light (i.e., VSimax). Moreover, SNe Ia with both stronger HVFs at early phases and larger VSimax are found to have noticeably redder colors and to occur preferentially in the inner regions of their host galaxies, while those with stronger HVFs but smaller VSimax show opposite tendencies, suggesting that these two subclasses have different explosion environments and their HVFs may have different origins. We further examine the relationships between the absorption features of Si ii 6355 and Ca ii IR lines, and find that their photospheric components are well correlated in velocity and strength but that the corresponding HVFs show larger scatter. These results cannot be explained with ionization and/or thermal processes alone, and different mechanisms are required for the creation of HVF-forming regions in SNe Ia.
ABSTRACT The absorption feature O i λ7773 is an important spectral indicator for type Ia supernovae (SNe Ia) that can be used to trace the unburned material in outer layers of the exploding white ...dwarf (WD). In this work, we use a large sample of SNe Ia to examine this absorption at early phases (i.e., −13 day t −7 day) and make comparisons with the absorption features of Si ii λ6355 and the Ca ii near-infrared triplet. We show that for a subgroup of spectroscopically normal SNe with normal photospheric velocities (i.e., vsi 12,500 km s−1 at optical maximum), the line strength of the high velocity feature (HVF) of O i is inversely correlated with that of Si ii (or Ca ii), and this feature also shows a negative correlation with the luminosity of SNe Ia. This finding, together with other features we find for the O i HVF, reveal that for this subgroup of SNe Ia, explosive oxygen burning occurs in the outermost layer of the SN. Differences in the oxygen burning could lead to the observed diversity, which is in remarkable agreement with the popular delayed-detonation model of Chandrasekhar mass WDs.
Abstract
Although type Ia supernovae (SNe Ia) are very important in many astrophysical fields, such as cosmology, their explosion mechanisms and progenitor systems still remain unclear. In physics, ...the relative equivalent width (REW) of the Si
ii
635.5 nm absorption feature reflects the velocity interval of the silicon in the SN ejecta, which may then provide constraints on the explosion mechanisms of SNe Ia. In this paper, we divide the SNe Ia into broad-line (BL) and normal-line (NL) subsamples, based on the REW of the Si
ii
635.5 nm absorption lines around their maximum lights, and we find that the BL SNe Ia have a dimmer mean brightness than the NL ones, which is possibly a result of their different metallicities. However, based on a pixel statistics study of the environments of the two subsamples, we do not find any significant potential differences in the environments of the BL and NL SNe Ia, which implies that the explosion mechanisms of SNe Ia could be independent of their progenitor populations.
Syndecan-binding protein (SDCBP) was reported to stimulate the advancement of esophageal squamous cell carcinoma (ESCC) and could potentially be a target for ESCC treatment. There is a growing corpus ...of research on the anti-tumor effects of iron chelators; however, very few studies have addressed the involvement of dexrazoxane in cancer. In this study, structure-based virtual screening was employed to select drugs targeting SDCBP from the Food and Drug Administration (FDA)-approved drug databases. The sepharose 4B beads pull-down assay revealed that dexrazoxane targeted SDCBP by interacting with its PDZ1 domain. Additionally, dexrazoxane inhibited ESCC cell proliferation and anchorage-independent colony formation via SDCBP. ESCC cell apoptosis and G2 phase arrest were induced as measured by the flow cytometry assay. Subsequent research revealed that dexrazoxane attenuated the binding ability between SDCBP and EGFR in an immunoprecipitation assay. Furthermore, dexrazoxane impaired EGFR membrane localization and inactivated the EGFR/PI3K/Akt pathway. In vivo, xenograft mouse experiments indicated that dexrazoxane suppressed ESCC tumor growth. These data indicate that dexrazoxane might be established as a potential anti-cancer agent in ESCC by targeting SDCBP.
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