418 research outputs found
Molecular-orbital structure in neutron-rich C isotopes
The molecule-like structure of the C isotopes (A=12, 14, 16) is investigated using a microscopic model. The valence neutrons are classified based on the molecular-orbit (MO) model, and both -orbit and -orbit are introduced around three -clusters. The valence neutrons which occupy the -orbit increase the binding energy and stabilize the linear-chain of 3 against the breathing-like break-up. However, C with the -orbit does not show clear energy minimum against the bending-like path. The combination of the valence neutrons in the - and the -orbit is promising to stabilize the linear-chain state against the breathing- and bending- modes, and it is found that the excited states of C with the configuration for the four valence neutrons is one of the most promising candidates for such structure
Important role of the spin-orbit interaction in forming the 1/2^+ orbital structure in Be isotopes
The structure of the second 0^+ state of ^{10}Be is investigated using a
microscopic model based on the molecular-orbit (MO) model.
The second 0^+ state, which has dominantly the (1/2^+)^2 configuration, is
shown to have a particularly enlarged structure. The kinetic
energy of the two valence neutrons occupying along the axis is
reduced remarkably due to the strong clustering and, simultaneously,
the spin-orbit interaction unexpectedly plays important role to make the energy
of this state much lower. The mixing of states with different spin structure is
shown to be important in negative-parity states. The experimentally observed
small-level spacing between 1^- and 2^- (~ 300 keV) is found to be an evidence
of this spin-mixing effect. ^{12}{Be} is also investigated using
model, in which four valence neutrons are considered to
occupy the (3/2^-)^2(1/2^+)^2 configuration. The energy surface of ^{12}Be is
shown to exhibit similar characteristics, that the remarkable
clustering and the contribution of the spin-orbit interaction make the binding
of the state with (3/2^-)^2(1/2^+)^2 configuration properly stronger in
comparison with the closed p-shell (3/2^-)^2(1/2^-)^2 configuration.Comment: 14 pages, 4 figure
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iPTF15eqv: Multi-wavelength Expos\'e of a Peculiar Calcium-rich Transient
The progenitor systems of the class of "Ca-rich transients" is a key open
issue in time domain astrophysics. These intriguing objects exhibit unusually
strong calcium line emissions months after explosion, fall within an
intermediate luminosity range, are often found at large projected distances
from their host galaxies, and may play a vital role in enriching galaxies and
the intergalactic medium. Here we present multi-wavelength observations of
iPTF15eqv in NGC 3430, which exhibits a unique combination of properties that
bridge those observed in Ca-rich transients and Type Ib/c supernovae. iPTF15eqv
has among the highest [Ca II]/[O I] emission line ratios observed to date, yet
is more luminous and decays more slowly than other Ca-rich transients. Optical
and near-infrared photometry and spectroscopy reveal signatures consistent with
the supernova explosion of a < 10 solar mass star that was stripped of its
H-rich envelope via binary interaction. Distinct chemical abundances and ejecta
kinematics suggest that the core collapse occurred through electron capture
processes. Deep limits on possible radio emission made with the Jansky Very
Large Array imply a clean environment ( 0.1 cm) within a radius of
cm. Chandra X-ray Observatory observations rule out alternative
scenarios involving tidal disruption of a white dwarf by a black hole, for
masses > 100 solar masses). Our results challenge the notion that
spectroscopically classified Ca-rich transients only originate from white dwarf
progenitor systems, complicate the view that they are all associated with large
ejection velocities, and indicate that their chemical abundances may vary
widely between events.Comment: 24 pages, 16 figures. Closely matches version published in The
Astrophysical Journa
Structure of excited states of Be-11 studied with Antisymmetrized Molecular Dynamics
The structures of the ground and excited states of Be-11 were studied with a
microscopic method of antisymmetrized molecular dynamics. The theoretical
results reproduce the abnormal parity of the ground state and predict various
kinds of excited states. We suggest a new negative-parity band with a
well-developed clustering structure which reaches high-spin states. Focusing on
a clustering structure, we investigated structure of the ground and
excited states. We point out that molecular orbits play important roles for the
intruder ground state and the low-lying states. The features of
the breaking of clusters were also studied with the help of data for
Gamow-Teller transitions.Comment: 24 pages, 7 figures, to be submitted to Phys.Rev.
Photometric Evolution of SNe Ib/c 2004ao, 2004gk and 2006gi
Photometric observations of three core collapse supernovae (SNe 2004ao,
2004gk and 2006gi), covering about 200 days of evolution are presented and
analyzed. The photometric behaviour of the three objects is consistent with
their membership of the envelope-stripped type Ib/c class. Pseudo-bolometric
light curves are constructed. The corresponding measured -folding times are
found to be faster compared to the Co decay (i.e. 111.3 d), suggesting
that a proportion of -rays increasing with time have escaped without
thermalization, owing to the low mass nature of the ejecta. SN 2006gi has
almost identical post maximum decline phase luminosities as SN 1999ex, and
found to be similar to both SNe 1999dn and 1999ex in terms of the
quasi-bolometric shape, placing it among the fast decliner Ib objects. SN
2004ao appears to fit within the slow decliner Ib SNe. SNe 2004ao and 2004gk
display almost identical luminosities in the [50-100] days time interval,
similar to SN 1993J. A preliminary simplified ray deposition model is
described and applied to the computed pseudo-bolometric light curves, allowing
one to find a range in the ejecta and Ni masses. The optical and
quasi-bolometric light curves, and the colour evolution of SN 2004gk are
found to show a sudden drop after day 150. Correlating this fact to dust
formation is premature and requires further observational evidence.Comment: Accepted for publication in The Astrophysical Journal; (11
two-columns Pages, 11 figures, 6 Tables; Scheduled for publication in April
2011
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