3,119 research outputs found
Type Ia Supernova Scenarios and the Hubble Sequence
The dependence of the Type Ia supernova (SN Ia) rate on galaxy type is
examined for three currently proposed scenarios: merging of a
Chandrasekhar--mass CO white dwarf (WD) with a CO WD companion, explosion of a
sub--Chandrasekhar mass CO WD induced by accretion of material from a He star
companion, and explosion of a sub--Chandrasekhar CO WD in a symbiotic system.
The variation of the SNe Ia rate and explosion characteristics with time is
derived, and its correlation with parent population age and galaxy redshift is
discussed. Among current scenarios, CO + He star systems should be absent from
E galaxies. Explosion of CO WDs in symbiotic systems could account for the SNe
Ia rate in these galaxies. The same might be true for the CO + CO WD scenario,
depending on the value of the common envelope parameter. A testable prediction
of the sub--Chandrasekhar WD model is that the average brightness and kinetic
energy of the SN Ia events should increase with redshift for a given Hubble
type. Also for this scenario, going along the Hubble sequence from E to Sc
galaxies SNe Ia events should be brighter on average and should show larger
mean velocities of the ejecta. The observational correlations strongly suggest
that the characteristics of the SNe Ia explosion are linked to parent
population age. The scenario in which WDs with masses below the Chandrasekhar
mass explode appears the most promising one to explain the observed variation
of the SN Ia rate with galaxy type together with the luminosity--expansion
velocity trend.Comment: 16 pages uuencoded compressed Postscript, 2 figures included. ApJ
Letters, in pres
Confrontación de diversos métodos de ruptura sobre N-11, bacteria capaz de desarrollarse en medios deficientes en fósforo
Mediante el empleo de distintos métodos de ruptura de células bacterianas: ondas ultrasónicas, congelaciones y descongelaciones sucesivas y lisis enzimática, estudiamos su acción y rendimiento sobre la bacteria denominada N-11, caracterizada por su capacidad para desarrollarse en medios deficientes en fósforo. El empleo de ondas ultrasónicas ha resultado ser la técnica más eficaz de todas las ensayadas. La liberación de proteinas citoplasmáticas se muestra mínima ,en medios deficientes en fósforo (medio P).The desintegration of a special strain N-U -which shows a peculiar
ability to grow on phosphorus defident media- with the use of different
methods for d-esintegration ultrasonic waves. ice and thaw, and lysis enzymatic, wac studied.
Ultrasonic waves was more efficient technique that other methods
used. It also was shown than in P medium (a phosphorus deficient media)
the protein release was minimum
Synovial two-phase sarcoma in third portion duodenal: clinical case and review of the literature
Structural basis for the inactivation of cytosolic DNA sensing by the vaccinia virus.
Detection of cytosolic DNA is a central element of the innate immunity system against viral infection. The Ku heterodimer, a component of the NHEJ pathway of DNA repair in the nucleus, functions as DNA sensor that detects dsDNA of viruses that replicate in the cytoplasm. Vaccinia virus expresses two proteins, C4 and C16, that inactivate DNA sensing and enhance virulence. The structural basis for this is unknown. Here we determine the structure of the C16 - Ku complex using cryoEM. Ku binds dsDNA by a preformed ring but C16 sterically blocks this access route, abrogating binding to a dsDNA end and its insertion into DNA-PK, thereby averting signalling into the downstream innate immunity system. C4 replicates these activities using a domain with 54% identity to C16. Our results reveal how vaccinia virus subverts the capacity of Ku to recognize viral DNA
The End of Amnesia: A New Method for Measuring the Metallicity of Type Ia Supernova Progenitors Using Manganese Lines in Supernova Remnants
We propose a new method to measure the metallicity of Type Ia supernova
progenitors using Mn and Cr lines in the X-ray spectra of young supernova
remnants. We show that the Mn to Cr mass ratio in Type Ia supernova ejecta is
tightly correlated with the initial metallicity of the progenitor, as
determined by the neutron excess of the white dwarf material before
thermonuclear runaway. We use this correlation, together with the flux of the
Cr and Mn Kalpha X-ray lines in the Tycho supernova remnant recently detected
by Suzaku (Tamagawa et al. 2008) to derive a metallicity of log(Z) = -1.32
(+0.67,-0.33) for the progenitor of this supernova, which corresponds to
log(Z/Zsun)= 0.60 (+0.31,-0.60) according to the latest determination of the
solar metallicity by Asplund et al. (2005). The uncertainty in the measurement
is large, but metallicities much smaller than the solar value can be
confidently discarded. We discuss the implications of this result for future
research on Type Ia supernova progenitors.Comment: 5 pages, 4 figures, accepted by ApJ
Consistent estimates of (56)Ni yields for type Ia supernovae
We present (56)Ni mass estimates for seventeen well-observed type Ia
supernovae determined by two independent methods. Estimates of the (56)Ni mass
for each type Ia supernova are determined from (1) modeling of the late-time
nebular spectrum and (2) through the combination of the peak bolometric
luminosity with Arnett's rule. The attractiveness of this approach is that the
comparison of estimated (56)Ni masses circumvents errors associated with the
uncertainty in the adopted values of reddening and distance. We demonstrate
that these two methods provide consistent estimates of the amount of (56)Ni
synthesized. We also find a strong correlation between the derived (56)Ni mass
and the absolute B-band magnitude (M(B)). Spectral synthesis can be used as a
diagnostic to study the explosion mechanism. By obtaining more nebular spectra
the Nif--M(B) correlation can be calibrated and can be used to investigate any
potential systematic effects this relationship may have on the determination of
cosmological parameters, and provide a new way to estimate extra-galactic
distances of nearby type Ia supernovae.Comment: Accepted for publication in A&A, constructive comments welcome
Biological behavior of familial papillary thyroid microcarcinoma: Spanish multicenter study
Purpose Familial papillary thyroid microcarcinoma (FPTMC) can present a more aggressive behavior than the sporadic microcarcinoma. However, few studies have analyzed this situation. The objective is to analyze the recurrence rate of FPTMC and the prognostic factors which determine that recurrence in Spain. Methods Spanish multicenter longitudinal analytical observational study was conducted. Patients with FPTMC received treatment with curative intent and presented cure criteria 6 months after treatment. Recurrence rate and disease-free survival (DFS) were analyzed. Two groups were analyzed: group A (no tumor recurrence) vs. group B (tumor recurrence). Results Ninety-four patients were analyzed. During a mean follow-up of 73.3 +/- 59.3 months, 13 recurrences of FPTMC (13.83%) were detected and mean DFS was 207.9 +/- 11.5 months. There were multifocality in 56%, bilateral thyroid involvement in 30%, and vascular invasion in 7.5%; that is to say, they are tumors with histological factors of poor prognosis in a high percentage of cases. The main risk factors for recurrence obtained in the multivariate analysis were the tumor size (OR: 2.574, 95% CI 1.210-5.473; p = 0.014) and the assessment of the risk of recurrence of the American Thyroid Association (ATA), both intermediate risk versus low risk (OR: 125, 95% CI 10.638-1000; p < 0.001) and high risk versus low risk (OR: 45.454, 95% CI 5.405-333.333; p < 0.001). Conclusion FPTMC has a recurrence rate higher than sporadic cases. Poor prognosis is mainly associated with the tumor size and the risk of recurrence of the ATA
Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger
On 2017 August 17, Swope Supernova Survey 2017a (SSS17a) was discovered as
the optical counterpart of the binary neutron star gravitational wave event
GW170817. We report time-series spectroscopy of SSS17a from 11.75 hours until
8.5 days after merger. Over the first hour of observations the ejecta rapidly
expanded and cooled. Applying blackbody fits to the spectra, we measure the
photosphere cooling from K to K,
and determine a photospheric velocity of roughly 30% of the speed of light. The
spectra of SSS17a begin displaying broad features after 1.46 days, and evolve
qualitatively over each subsequent day, with distinct blue (early-time) and red
(late-time) components. The late-time component is consistent with theoretical
models of r-process-enriched neutron star ejecta, whereas the blue component
requires high velocity, lanthanide-free material.Comment: 33 pages, 5 figures, 2 tables, Accepted to Scienc
Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
On 2017 August 17, gravitational waves were detected from a binary neutron
star merger, GW170817, along with a coincident short gamma-ray burst,
GRB170817A. An optical transient source, Swope Supernova Survey 17a (SSS17a),
was subsequently identified as the counterpart of this event. We present
ultraviolet, optical and infrared light curves of SSS17a extending from 10.9
hours to 18 days post-merger. We constrain the radioactively-powered transient
resulting from the ejection of neutron-rich material. The fast rise of the
light curves, subsequent decay, and rapid color evolution are consistent with
multiple ejecta components of differing lanthanide abundance. The late-time
light curve indicates that SSS17a produced at least ~0.05 solar masses of heavy
elements, demonstrating that neutron star mergers play a role in r-process
nucleosynthesis in the Universe.Comment: Accepted to Scienc
Double-Peaked Balmer Emission Indicating Prompt Accretion Disk Formation in an X-Ray Faint Tidal Disruption Event
We present the multi-wavelength analysis of the tidal disruption event (TDE)
AT~2018hyz (ASASSN-18zj). From follow-up optical spectroscopy, we detect the
first unambiguous case of resolved double-peaked Balmer emission in a TDE. The
distinct line profile can be well-modelled by a low eccentricity
() accretion disk extending out to 100 and a
Gaussian component originating from non-disk clouds, though a bipolar outflow
origin cannot be completely ruled out. Our analysis indicates that in
AT~2018hyz, disk formation took place promptly after the most-bound debris
returned to pericenter, which we estimate to be roughly tens of days before the
first detection. Redistribution of angular momentum and mass transport,
possibly through shocks, must occur on the observed timescale of about a month
to create the large \Ha-emitting disk that comprises 5\% of the
initial stellar mass. With these new insights from AT~2018hyz, we infer that
circularization is efficient in at least some, if not all optically-bright,
X-ray faint TDEs. In these efficiently circularized TDEs, the detection of
double-peaked emission depends on the disk inclination angle and the relative
strength of the disk contribution to the non-disk component, possibly
explaining the diversity seen in the current sample.Comment: 24 pages, 8 figures, 6 tables. Accepted for publication in Ap
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