94 research outputs found
The Dusty and Extremely Red Progenitor of the Type II Supernova 2023ixf in Messier 101
Stars with initial masses in the range of 8-25 solar masses are thought to
end their lives as hydrogen-rich supernova (SNe II). Based on the pre-explosion
images of Hubble Space Telescope (\textit{HST}) and \textit{Spitzer} Space
Telescope, we place tight constraints on the progenitor candidate of type IIP
SN 2023ixf in Messier 101. Fitting of the spectral energy distribution (SED) of
its progenitor with dusty stellar spectral models results in an estimation of
the effective temperature as 3090 K, making it the coolest SN progenitor ever
discovered. The luminosity is estimated as log(L),
consistent with a red supergiant (RSG) star with an initial mass of
12 M. The derived mass loss rate (6-9
M yr) is much lower than that inferred from the flash
spectroscopy of the SN, suggesting that the progenitor experienced a sudden
increase in mass loss when approaching the final explosion. In the mid-infrared
color diagram, the progenitor star is found to show a significant deviation
from the range of regular RSGs, but is close to some extreme RSGs and super
asymptotic giant branch (sAGB) stars. Thus, SN 2023ixf may belong to a rare
subclass of electron-captured supernova for an origin of sAGB progenitor.Comment: 6 figures; under review by Science Bulleti
Intracellular Trafficking Network of Protein Nanocapsules: Endocytosis, Exocytosis and Autophagy
The inner membrane vesicle system is a complex transport system that includes endocytosis, exocytosis and autophagy. However, the details of the intracellular trafficking pathway of nanoparticles in cells have been poorly investigated. Here, we investigate in detail the intracellular trafficking pathway of protein nanocapsules using more than 30 Rab proteins as markers of multiple trafficking vesicles in endocytosis, exocytosis and autophagy. We observed that FITC-labeled protein nanoparticles were internalized by the cells mainly through Arf6-dependent endocytosis and Rab34-mediated micropinocytosis. In addition to this classic pathway: early endosome (EEs)/late endosome (LEs) to lysosome, we identified two novel transport pathways: micropinocytosis (Rab34 positive)-LEs (Rab7 positive)-lysosome pathway and EEs-liposome (Rab18 positive)-lysosome pathway. Moreover, the cells use slow endocytosis recycling pathway (Rab11 and Rab35 positive vesicles) and GLUT4 exocytosis vesicles (Rab8 and Rab10 positive) transport the protein nanocapsules out of the cells. In addition, protein nanoparticles are observed in autophagosomes, which receive protein nanocapsules through multiple endocytosis vesicles. Using autophagy inhibitor to block these transport pathways could prevent the degradation of nanoparticles through lysosomes. Using Rab proteins as vesicle markers to investigation the detail intracellular trafficking of the protein nanocapsules, will provide new targets to interfere the cellular behaver of the nanoparticles, and improve the therapeutic effect of nanomedicine
Circumstellar Material Ejected Violently by A Massive Star Immediately before its Death
Type II supernovae represent the most common stellar explosions in the
Universe, for which the final stage evolution of their hydrogen-rich massive
progenitors towards core-collapse explosion are elusive. The recent explosion
of SN 2023ixf in a very nearby galaxy, Messier 101, provides a rare opportunity
to explore this longstanding issue. With the timely high-cadence flash spectra
taken within 1-5 days after the explosion, we can put stringent constraints on
the properties of the surrounding circumstellar material around this supernova.
Based on the rapid fading of the narrow emission lines and luminosity/profile
of emission at very early times, we estimate that the progenitor
of SN 2023ixf lost material at a mass-loss rate over the last 2-3 years before explosion.
This close-by material, moving at a velocity , accumulates a compact CSM shell at the radius smaller than cm from the progenitor. Given the high mass-loss rate and
relatively large wind velocity presented here, together with the pre-explosion
observations made about two decades ago, the progenitor of SN 2023ixf could be
a short-lived yellow hypergiant that evolved from a red supergiant shortly
before the explosion.Comment: 10 pages, 6 figures in main body, accepted for publication in Science
Bulleti
Quality-of-life outcomes and unmet needs between ileal conduit and orthotopic ileal neobladder after radical cystectomy in a Chinese population: a 2-to-1 matched-pair analysis
Peri-operative outcomes. (DOCX 15 kb
A Promising Future of Ferroptosis in Tumor Therapy
Currently, mechanisms and therapeutic approaches have been thoroughly studied in various prevalent malignant tumors, such as breast and lung cancer. However, there is inevitable tumor progression and drug resistance. Uncovering novel treatment strategies to inhibit tumor development is important. Ferroptosis, a form of cell death associated with iron and lipid peroxidation, has drawn extensive attention. In this paper, we reviewed the underlying mechanisms of ferroptosis (i.e., iron, glutathione, and lipid metabolism) and its role in various tumors (i.e., lung cancer, liver carcinoma, breast cancer, and pancreatic cancer). Moreover, we summarized ferroptosis-related anti-tumor drugs and emphasized the potential of combined treatment of anti-tumor drugs and radiotherapy in an effort to provide novel anti-tumor treatments
Minute-cadence Observations of the LAMOST Fields with the TMTS: III. Statistic Study of the Flare Stars from the First Two Years
Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect
fast-evolving transients in the Universe, which has led to the discovery of
thousands of short-period variables and eclipsing binaries since 2020. In this
paper, we present the observed properties of 125 flare stars identified by the
TMTS within the first two years, with an attempt to constrain their eruption
physics. As expected, most of these flares were recorded in late-type red stars
with > 2.0 mag, however, the flares associated with
bluer stars tend to be on average more energetic and have broader profiles. The
peak flux (F_peak) of the flare is found to depend strongly on the equivalent
duration (ED) of the energy release, i.e., , which is consistent with results derived from the Kepler
and Evryscope samples. This relation is likely related to the magnetic loop
emission, while -- for the more popular non-thermal electron heating model -- a
specific time evolution may be required to generate this relation. We notice
that flares produced by hotter stars have a flatter relation compared to that from cooler stars. This is related to the
statistical discrepancy in light-curve shape of flare events with different
colors. In spectra from LAMOST, we find that flare stars have apparently
stronger H alpha emission than inactive stars, especially at the low
temperature end, suggesting that chromospheric activity plays an important role
in producing flares. On the other hand, the subclass having frequent flares are
found to show H alpha emission of similar strength in their spectra to that
recorded with only a single flare but similar effective temperature, implying
that the chromospheric activity may not be the only trigger for eruptions.Comment: 17 pages, 15 figures, 2 tables, refereed version. For associated data
files, see https://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/523/219
An 18.9-minute Blue Large-Amplitude Pulsator Crossing the 'Hertzsprung Gap' of Hot Subdwarfs
Blue large-amplitude pulsators (BLAPs) represent a new and rare class of hot
pulsating stars with unusually large amplitudes and short periods. Up to now,
only 24 confirmed BLAPs have been identified from more than one billion
monitored stars, including a group with pulsation period longer than
min (classical BLAPs, hereafter) and the other group with pulsation period
below min. The evolutionary path that could give rise to such kinds of
stellar configurations is unclear. Here we report on a comprehensive study of
the peculiar BLAP discovered by the Tsinghua University - Ma Huateng Telescopes
for Survey (TMTS), TMTS J035143.63+584504.2 (TMTS-BLAP-1). This new BLAP has an
18.9 min pulsation period and is similar to the BLAPs with a low surface
gravity and an extended helium-enriched envelope, suggesting that it is a
low-gravity BLAP at the shortest-period end. In particular, the long-term
monitoring data reveal that this pulsating star has an unusually large rate of
period change, P_dot/P=2.2e-6/yr. Such a significant and positive value
challenges its origins from both helium-core pre-white-dwarfs and core
helium-burning subdwarfs, but is consistent with that derived from shell
helium-burning subdwarfs. The particular pulsation period and unusual rate of
period change indicate that TMTS-BLAP-1 is at a short-lived (~10^6 yr) phase of
shell-helium ignition before the stable shell-helium burning; in other words,
TMTS-BLAP-1 is going through a "Hertzsprung gap" of hot subdwarfs.Comment: 26 pages, 12 figures, 4 tables, published on Nature Astronomy, URL:
https://www.nature.com/articles/s41550-022-01783-
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