674 research outputs found
R-matrix calculation of electron collisions with electronically excited O2 molecules
Low-energy electron collisions with O molecules are studied using the
fixed-bond R-matrix method. In addition to the O ground
state, integrated cross sections are calculated for elecron collisions with the
and excited states of O molecules. 13
target electronic states of O are included in the model within a valence
configuration interaction representations of the target states. Elastic cross
sections for the and excited states are
similar to the cross sections for the ground state. As in
case of excitation from the state, the O
resonance makes the dominant contribution to excitation cross sections from the
and states. The magnitude of excitation
cross sections from the state to the
state is about 10 time larger than the corresponding cross sections from the
to the state. For this
transition, our cross section at
4.5 eV agrees well with the available experimental value. These results should
be important for models of plasma discharge chemistry which often requires
cross sections between the excited electronic states of O.Comment: 26 pages, 10 figure
Constraints on core-collapse supernova progenitors from explosion site integral field spectroscopy
Observationally, supernovae (SNe) are divided into subclasses pertaining to
their distinct characteristics. This diversity reflects the diversity in the
progenitor stars. It is not entirely clear how different evolutionary paths
leading massive stars to become a SN are governed by fundamental parameters
such as progenitor initial mass and metallicity. This paper places constraints
on progenitor initial mass and metallicity in distinct core-collapse SN
subclasses, through a study of the parent stellar populations at the explosion
sites. Integral field spectroscopy (IFS) of 83 nearby SN explosion sites with a
median distance of 18 Mpc has been collected and analysed, enabling detection
and spectral extraction of the parent stellar population of SN progenitors.
From the parent stellar population spectrum, the initial mass and metallicity
of the coeval progenitor are derived by means of comparison to simple stellar
population models and strong-line methods. Additionally, near-infrared IFS was
employed to characterise the star formation history at the explosion sites. No
significant metallicity differences are observed among distinct SN types. The
typical progenitor mass is found to be highest for SN Ic, followed by type Ib,
then types IIb and II. SN IIn is the least associated with young stellar
populations and thus massive progenitors. However, statistically significant
differences in progenitor initial mass are observed only when comparing SNe IIn
with other subclasses. Stripped-envelope SN progenitors with initial mass
estimate lower than 25~ are found; these are thought to be the result
of binary progenitors. Confirming previous studies, these results support the
notion that core-collapse SN progenitors cannot arise from single-star channel
only, and both single and binary channels are at play in the production of
core-collapse SNe. [ABRIDGED]Comment: 18 pages, 10 figures, accepted to A&
Mechanisms of Single-Walled Carbon Nanotube Nucleation, Growth and Chirality-Control: Insights from QM/MD Simulations
Supernovae in the Subaru Deep Field: An Initial Sample, and Type Ia Rate, out to Redshift 1.6
Large samples of high-redshift supernovae (SNe) are potentially powerful
probes of cosmic star formation, metal enrichment, and SN physics. We present
initial results from a new deep SN survey, based on re-imaging in the R, i', z'
bands, of the 0.25 deg2 Subaru Deep Field (SDF), with the 8.2-m Subaru
telescope and Suprime-Cam. In a single new epoch consisting of two nights of
observations, we have discovered 33 candidate SNe, down to a z'-band magnitude
of 26.3 (AB). We have measured the photometric redshifts of the SN host
galaxies, obtained Keck spectroscopic redshifts for 17 of the host galaxies,
and classified the SNe using the Bayesian photometric algorithm of Poznanski et
al. (2007) that relies on template matching. After correcting for biases in the
classification, 55% of our sample consists of Type Ia supernovae and 45% of
core-collapse SNe. The redshift distribution of the SNe Ia reaches z ~ 1.6,
with a median of z ~ 1.2. The core-collapse SNe reach z ~ 1.0, with a median of
z ~ 0.5. Our SN sample is comparable to the Hubble Space Telescope/GOODS sample
both in size and redshift range. The redshift distributions of the SNe in the
SDF and in GOODS are consistent, but there is a trend (which requires
confirmation using a larger sample) for more high-z SNe Ia in the SDF. This
trend is also apparent when comparing the SN Ia rates we derive to those based
on GOODS data. Our results suggest a fairly constant rate at high redshift that
could be tracking the star-formation rate. Additional epochs on this field,
already being obtained, will enlarge our SN sample to the hundreds, and
determine whether or not there is a decline in the SN Ia rate at z >~ 1.Comment: 20 pages, 8 figures, MNRAS accepte
SN 2016jhj at redshift 0.34: extending the Type II supernova Hubble diagram using the standard candle method
Although Type Ia supernova cosmology has now reached a mature state, it is important to develop as many independent methods as possible to understand the true nature of dark energy. Recent studies have shown that Type II supernovae (SNe II) offer such a path and could be used as alternative distance indicators. However, the majority of these studies were unable to extend the Hubble diagram above redshift z = 0.3 because of observational limitations. Here, we show that we are now ready to move beyond low redshifts and attempt high-redshift (z ≳ 0.3) SN II cosmology as a result of new-generation deep surveys such as the Subaru/Hyper Suprime-Cam survey. Applying the ´standard candle method´ to SN 2016jhj (z = 0.3398 ± 0.0002; discovered by HSC) together with a low-redshift sample, we are able to construct the highest-redshift SN II Hubble diagram to date with an observed dispersion of 0.27 mag (i.e. 12-13 per cent in distance). This work demonstrates the bright future of SN II cosmology in the coming era of large, wide-field surveys like that of the Large Synoptic Survey Telescope.Fil: de Jaeger, T.. University of California at Berkeley; Estados UnidosFil: Galbany, L.. University of Pittsburgh at Johnstown; Estados UnidosFil: Filippenko, A. V.. University of California at Berkeley; Estados UnidosFil: González Gaitán, S.. Universidad de Chile; ChileFil: Yasuda, N.. University of Tokio; JapónFil: Maeda, K.. University of Tokio; JapónFil: Tanaka, M.. University of Tokio; JapónFil: Morokuma, T.. University of Tokio; JapónFil: Moriya, T. J.. National Astronomical Observatory of Japan; JapónFil: Tominaga, N.. University of Tokyo; JapónFil: Nomoto, Ken’ichi. University of Tokyo; JapónFil: Komiyama, Y.. National Astronomical Observatory of Japan; JapónFil: Anderson, J. P.. European Southern Observatory; ChileFil: Brink, T. G.. University of California at Berkeley; Estados UnidosFil: Carlberg, R. G.. University of Toronto; CanadáFil: Folatelli, Gaston. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y GeofÃsicas; Argentina. University of Tokyo; JapónFil: Hamuy, M.. Universidad de Chile; ChileFil: Pignata, G.. Universidad Andrés Bello; ChileFil: Zheng, W.. University of California at Berkeley; Estados Unido
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