481 research outputs found
2D Simulations of the Line-Driven Instability in Hot-Star Winds: II. Approximations for the 2D Radiation Force
We present initial attempts to include the multi-dimensional nature of
radiation transport in hydrodynamical simulations of the small-scale structure
that arises from the line-driven instability in hot-star winds. Compared to
previous 1D or 2D models that assume a purely radial radiation force, we seek
additionally to treat the lateral momentum and transport of diffuse
line-radiation, initially here within a 2D context. A key incentive is to study
the damping effect of the associated diffuse line-drag on the dynamical
properties of the flow, focusing particularly on whether this might prevent
lateral break-up of shell structures at scales near the lateral Sobolev angle
of ca. . We first explore nonlinear simulations that cast the
lateral diffuse force in the simple, local form of a parallel viscosity.
Second, to account for the lateral mixing of radiation associated with the
radial driving, we next explore models in which the radial force is azimuthally
smoothed over a chosen scale. Third, to account for both the lateral line-drag
and the lateral mixing in a more self-consistent way, we explore further a
method first proposed by Owocki (1999), which uses a restricted 3-ray approach
that combines a radial ray with two oblique rays set to have an impact
parameter within the stellar core. From numerical simulations,
we find that, compared to equivalent 1-ray simulations, the high-resolution
3-ray models show systematically a much higher lateral coherence.... (Full
abstract in paper)Comment: Accepted by A&A, 12 pages, 7 figures, 3 only shown in version
available at http://www.mpa-garching.mpg.de/~luc/2778.ps.g
Quantitative spectroscopic analysis of and distance to SN1999em
This work presents a detailed quantitative spectroscopic analysis of, and the
determination of the distance to, the type II supernovae (SN) SN1999em with
CMFGEN (Dessart & Hillier 2005a), based on spectrophotometric observations at
eight dates up to 40 days after discovery. We use the same iron-group metal
content for the ejecta, the same power-law density distribution (with exponent
n~10), and a Hubble-velocity law at all times. We adopt a H/He/C/N/O abundance
pattern compatible with CNO-cycle equilibrium values for a RSG/BSG progenitor,
with C/O enhanced and N depleted at later times. Based on our synthetic fits to
spectrophotometric observations of SN1999em, we obtain a distance of 11.5Mpc,
similar to that of Baron et al. (2004) and the Cepheid distance to the galaxy
host of 11.7Mpc (Leonard et al. 2003). Similarly, based on such models, the
Expanding Photosphere Method (EPM) delivers a distance of 11.6Mpc, with
negligible scatter between photometric bandpass sets; there is thus nothing
wrong with the EPM as such. Previous determinations using the tabulated
correction factors of Eastman et al. (1996) all led to 30-50% underestimates:
we find that this is caused by 1) an underestimate of the correction factors
compared to the only other study of the kind by Dessart & Hillier (2005b), 2) a
neglect of the intrinsic >20% scatter of correction factors, and 3) the use of
the EPM at late times when severe line blanketing makes the method inaccurate.
The need of detailed model computations for reliable EPM distance estimates
thus defeats the appeal and simplicity of the method. However, detailed fits to
SN optical spectra, based on tailored models for individual SN observations,
offers a promising approach to obtaining distances with 10-20% accuracy, either
through the EPM or a la Baron et al. (2004).Comment: 20 pages, 13 figures, accepted for publication in A&
Neutrino Signatures and the Neutrino-Driven Wind in Binary Neutron Star Mergers
We present VULCAN/2D multigroup flux-limited-diffusion radiation-hydrodynamics simulations of binary neutron star mergers, using the Shen equation of state, covering ≳ 100 ms, and starting from azimuthal-averaged two-dimensional slices obtained from three-dimensional smooth-particle-hydrodynamics simulations of Rosswog & Price for 1.4M☉ (baryonic) neutron stars with no initial spins, co-rotating spins, or counter-rotating spins. Snapshots are post-processed at 10 ms intervals with a multiangle neutrino-transport solver. We find polar-enhanced neutrino luminosities, dominated by ¯νe and “νμ” neutrinos at the peak, although νe emission may be stronger at late times. We obtain typical peak neutrino energies for νe, ¯νe, and “νμ” of ∼12, ∼16, and ∼22 MeV, respectively. The supermassive neutron star (SMNS) formed from the merger has a cooling timescale of ≾ 1 s. Charge-current neutrino reactions lead to the formation of a thermally driven bipolar wind with (M·) ∼ 10^−3 M☉ s^−1 and baryon-loading in the polar regions, preventing any production of a γ-ray burst prior to black hole formation. The large budget of rotational free energy suggests that magneto-rotational effects could produce a much-greater polar mass loss. We estimate that ≾ 10^−4 M☉ of material with an electron fraction in the range 0.1–0.2 becomes unbound during this SMNS phase as a result of neutrino heating. We present a new formalism to compute the νi ¯νi annihilation rate based on moments of the neutrino-specific intensity computed with our multiangle solver. Cumulative annihilation rates, which decay as ∼t^−1.8, decrease over our 100 ms window from a few ×1050 to ∼ 1049 erg s−1, equivalent to a few ×10^54 to ∼10^53 e−e+ pairs per second
Neutrino signatures and the neutrino-driven wind in Binary Neutron Star Mergers
We present VULCAN/2D multi-group flux-limited-diffusion radiation
hydrodynamics simulations of binary neutron star (BNS) mergers, using the Shen
equation of state, covering ~100 ms, and starting from azimuthal-averaged 2D
slices obtained from 3D SPH simulations of Rosswog & Price for 1.4 Msun
(baryonic) neutron stars with no initial spins, co-rotating spins, and
counter-rotating spins. Snapshots are post-processed at 10 ms intervals with a
multi-angle neutrino-transport solver. We find polar-enhanced neutrino
luminosities, dominated by and ``'' neutrinos at peak,
although emission may be stronger at late times. We obtain typical peak
neutrino energies for , , and ``'' of ~12, ~16,
and ~22 MeV. The super-massive neutron star (SMNS) formed from the merger has a
cooling timescale of ~1 s. Charge-current neutrino reactions lead to the
formation of a thermally-driven bipolar wind with ~10
Msun/s, baryon-loading the polar regions, and preventing any production of a
GRB prior to black-hole formation. The large budget of rotational free energy
suggests magneto-rotational effects could produce a much greater polar mass
loss. We estimate that ~10 Msun of material with electron fraction in
the range 0.1-0.2 become unbound during this SMNS phase as a result of neutrino
heating. We present a new formalism to compute the
annihilation rate based on moments of the neutrino specific intensity computed
with our multi-angle solver. Cumulative annihilation rates, which decay as
, decrease over our 100 ms window from a few 10 to ~10
erg/s, equivalent to a few 10 to ~10 pairs per second.Comment: 23 pages, 20 figures, 2 tables, submitted to ApJ, high resolution
version of the paper available at http://hermes.as.arizona.edu/~luc/ms.pd
PENGARUH BRAND IMAGE DAN HARGA TERHADAP LOYALITAS PELANGGAN PADA DISTRO HYB SUPPLY
ABSTRAK
Manajemen pemasaran merupakan seni dan ilmu untuk memilih pasar sasaran
dan meraih, mempertahankan, serta menumbuhkan pelanggan dengan menciptakan,
menghantarkan dan, mengkomunikasikan niai pelanggan yang unggul.
Penelitian ini bertujuan untuk
mengetahui seberapa besar pengaruh brand
image dan harga terhadap loyalitas pelanggan pada distro Hyb Supply Bandung baik
secara parsial maupun simultan. Metode penelitian yang digunakan adalah deskriptif
dan verifikatif dengan jumlah sample 100 responde
n. Teknik pengumpulan data yang
digunakan adalah observasi, wawancara, dan menyebarkan kuisioner. Metode analisis
data yang digunakan adalah regresi linier berganda, korelasi ganda dan koefisien
determinasi, dan uji hipotesis.
Hasil penelitian menunjukkan
besar pengaruh brand image dan harga terhadap
loyalitas pelanggan pada distro Hyb Supply Bandung dapat dikatakan cukup baik.
Brand image memberikan pengaruh yang lebih kecil pada loyalitas pelanggan
dibandingkan dengan harga terhadap loyalita pelanggan.
Kata Kunci : Brand Image, Harga dan Loyalitas Pelangga
Very late-time spectroscopy of SN 2009ip: Constraints on the ongoing H emission
The peculiar supernova (SN) 2009ip is an ambiguous event that spurred many
questions regarding its true origins. Here, we present very late-time
spectroscopic and photometric observations of SN 2009ip, obtained 9 years (3274
days) after the 2012B outburst. We analyze the H emission still present
in the very late-time spectrum of SN 2009ip. We also obtain photometric
measurements in the , and bands. We obtained observations of SN
2009ip on 2021 September 10 with the IMACS instrument at the 6.5 m Magellan
Baade Telescope, located at the Las Campanas Observatory. SN 2009ip was
detected in the , and bands, with an absolute magnitude in band
of ~mag. We show that the source faded significantly since the last
observations in these bands. We further show that the very late-time spectrum
contains a persistent H emission, although no other emission lines were
detected. We measured a full width at half maximum (FWHM) of $930 \pm 40 \
\textrm{km s}^{-1}\sim 8.0 \times 10^{37} \ \textrm{erg
s}^{-1}\alpha$ emission. The luminosity decreased relatively slowly
in comparison to the last observations and its fading rate is very similar to
other long-living interacting transients, such as SN 2005ip. Finally, we
conclude that although these properties could be consistent with a non-regular
core-collapse SN, they may also be explained through non-terminal explosion
scenarios
The variable stellar wind of Rigel probed at high spatial and spectral resolution
We present a spatially resolved, high-spectral resolution (R=12000) K-band
temporal monitoring of Rigel using AMBER at the VLTI. Rigel was observed in the
Bracket Gamma line and its nearby continuum in 2006-2007, and 2009-2010. These
unprecedented observations were complemented by contemporaneous optical
high-resolution spectroscopy. We analyse the near-IR spectra and visibilities
with the 1D non-LTE radiative-transfer code CMFGEN. The differential and
closure phase signal exhibit asymmetries that are interpreted as perturbations
of the wind. A systematic visibility decrease is observed across the Bracket
Gamma. During the 2006-2007 period the Bracket Gamma and likely the continuum
forming regions were larger than in the 2009-2010 epoch. Using CMFGEN, we infer
a mass-loss rate change of about 20% between the two epochs. We further find
time variations in the differential visibilities and phases. The 2006-2007
period is characterized by noticeable variations of the differential
visibilities in Doppler position and width and by weak variations in
differential and closure phase. The 2009-2010 period is much more quiet with
virtually no detectable variations in the dispersed visibilities but a strong
S-shape signal is observed in differential phase coinciding with a strong
ejection event discernible in the optical spectra. The differential phase
signal that is sometimes detected is reminiscent of the signal computed from
hydrodynamical models of corotating interaction regions. For some epochs the
temporal evolution of the signal suggests the rotation of the circumstellar
structures.Comment: Paper accepted in the A&A journa
A New Mechanism for Gravitational-Wave Emission in Core-Collapse Supernovae
We present a new theory for the gravitational wave signatures of core-collapse supernovae. Previous studies identified axisymmetric rotating core collapse, core bounce, postbounce convection, and anisotropic neutrino emission as the primary processes and phases for the radiation of gravitational waves. Our results, which are based on axisymmetric, Newtonian radiation-hydrodynamics supernova simulations (Burrows et al. 2006), indicate that the dominant emission process of gravitational waves in core-collapse supernovae may be the oscillations of the protoneutron star core. The oscillations are predominantly of g-mode character, are excited hundreds of milliseconds after bounce, and typically last for several hundred milliseconds. Our results suggest that even nonrotating core-collapse supernovae should be visible to current LIGO-class detectors throughout the Galaxy, and depending on progenitor structure, possibly out to Megaparsec distances
Multi-Dimensional Explorations in Supernova Theory
In this paper, we bring together various of our published and unpublished findings from our recent 2D multi-group, flux-limited radiation hydrodynamic simulations of the collapse and explosion of the cores of massive stars. Aided by 2D and 3D graphical renditions, we motivate the acoustic mechanism of core-collapse supernova explosions and explain, as best we currently can, the phases and phenomena that attend this mechanism. Two major foci of our presentation are the outer shock instability and the inner core g-mode oscillations. The former sets the stage for the latter, which damp by the generation of sound. This sound propagates outward to energize the explosion and is relevant only if the core has not exploded earlier by some other means. Hence, it is a more delayed mechanism than the traditional neutrino mechanism that has been studied for the last twenty years since it was championed by Bethe and Wilson. We discuss protoneutron star convection, accretion-induced-collapse, gravitational wave emissions, pulsar kicks, the angular anisotropy of the neutrino emissions, a subset of numerical issues, and a new code we are designing that should supercede our current supernova code VULCAN/2D. Whatever ideas last from this current generation of numerical results, and whatever the eventual mechanism(s), we conclude that the breaking of spherical symmetry will survive as one of the crucial keys to the supernova puzzle
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