1,168 research outputs found
The first ALMA view of IRAS 16293-2422: Direct detection of infall onto source B and high-resolution kinematics of source A
Aims: We focus on the kinematical properties of a proto-binary to study the
infall and rotation of gas towards its two protostellar components. Methods: We
present ALMA Science Verification observations with high-spectral resolution of
IRAS 16293-2422 at 220.2 GHz. The wealth of molecular lines in this source and
the very high spectral resolution offered by ALMA allow us to study the gas
kinematics with unprecedented detail. Results: We present the first detection
of an inverse P-Cygni profile towards source B in the three brightest lines.
The line profiles are fitted with a simple two-layer model to derive an infall
rate of 4.5x10^-5 Msun/yr. This infall detection would rule-out the previously
suggested possibility that source B is a T Tauri star. A position velocity
diagram for source A shows evidence for rotation with an axis close to the
line-of-sight.Comment: Accepted by A&A Letters. 4 pages, 3 figures, 3 appendices (one for
Tables, one for additional figures). This second version includes small
language modifications and changes to keep the letter within the 4 page limi
Axisymmetric general relativistic hydrodynamics: Long-term evolution of neutron stars and stellar collapse to neutron stars and black holes
We report a new implementation for axisymmetric simulation in full general
relativity. In this implementation, the Einstein equations are solved using the
Nakamura-Shibata formulation with the so-called cartoon method to impose an
axisymmetric boundary condition, and the general relativistic hydrodynamic
equations are solved using a high-resolution shock-capturing scheme based on an
approximate Riemann solver. As tests, we performed the following simulations:
(i) long-term evolution of non-rotating and rapidly rotating neutron stars,
(ii) long-term evolution of neutron stars of a high-amplitude damping
oscillation accompanied with shock formation, (iii) collapse of unstable
neutron stars to black holes, and (iv) stellar collapses to neutron stars. The
tests (i)--(iii) were carried out with the -law equation of state, and
the test (iv) with a more realistic parametric equation of state for
high-density matter. We found that this new implementation works very well: It
is possible to perform the simulations for stable neutron stars for more than
10 dynamical time scales, to capture strong shocks formed at stellar core
collapses, and to accurately compute the mass of black holes formed after the
collapse and subsequent accretion. In conclusion, this implementation is robust
enough to apply to astrophysical problems such as stellar core collapse of
massive stars to a neutron star and black hole, phase transition of a neutron
star to a high-density star, and accretion-induced collapse of a neutron star
to a black hole. The result for the first simulation of stellar core collapse
to a neutron star started from a realistic initial condition is also presented.Comment: 28 pages, to appear in PRD 67, 0440XX (2003
Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines
We have mapped 20 molecular lines in the Central Molecular Zone (CMZ) around
the Galactic Centre, emitting from 85.3 to 93.3 GHz. This work used the 22-m
Mopra radio telescope in Australia, equipped with the 8-GHz bandwidth UNSW-MOPS
digital filter bank, obtaining \sim 2 km/s spectral and \sim 40 arcsec spatial
resolution. The lines measured include emission from the c-C3H2, CH3CCH, HOCO+,
SO, H13CN, H13CO+, SO, H13NC, C2H, HNCO, HCN, HCO+, HNC, HC3N, 13CS and N2H+
molecules. The area covered is Galactic longitude -0.7 to 1.8 deg. and latitude
-0.3 to 0.2 deg., including the bright dust cores around Sgr A, Sgr B2, Sgr C
and G1.6-0.025. We present images from this study and conduct a principal
component analysis on the integrated emission from the brightest 8 lines. This
is dominated by the first component, showing that the large-scale distribution
of all molecules are very similar. We examine the line ratios and optical
depths in selected apertures around the bright dust cores, as well as for the
complete mapped region of the CMZ. We highlight the behaviour of the bright
HCN, HNC and HCO+ line emission, together with that from the 13C isotopologues
of these species, and compare the behaviour with that found in extra-galactic
sources where the emission is unresolved spatially. We also find that the
isotopologue line ratios (e.g. HCO+/H13CO+) rise significantly with increasing
red-shifted velocity in some locations. Line luminosities are also calculated
and compared to that of CO, as well as to line luminosities determined for
external galaxies.Comment: 27 pages, 15 figures, 12 tables, accepted by MNRA
First detection of ND in the solar-mass protostar IRAS16293-2422
In the past decade, much progress has been made in characterising the
processes leading to the enhanced deuterium fractionation observed in the ISM
and in particular in the cold, dense parts of star forming regions such as
protostellar envelopes. Very high molecular D/H ratios have been found for
saturated molecules and ions. However, little is known about the deuterium
fractionation in radicals, even though simple radicals often represent an
intermediate stage in the formation of more complex, saturated molecules. The
imidogen radical NH is such an intermediate species for the ammonia synthesis
in the gas phase. Herschel/HIFI represents a unique opportunity to study the
deuteration and formation mechanisms of such species, which are not observable
from the ground. We searched here for the deuterated radical ND in order to
determine the deuterium fractionation of imidogen and constrain the deuteration
mechanism of this species. We observed the solar-mass Class 0 protostar
IRAS16293-2422 with the heterodyne instrument HIFI as part of the Herschel key
programme CHESS (Chemical HErschel Surveys of Star forming regions). The
deuterated form of the imidogen radical ND was detected and securely identified
with 2 hyperfine component groups of its fundamental transition in absorption
against the continuum background emitted from the nascent protostar. The 3
groups of hyperfine components of its hydrogenated counterpart NH were also
detected in absorption. We derive a very high deuterium fractionation with an
[ND]/[NH] ratio of between 30 and 100%. The deuterium fractionation of imidogen
is of the same order of magnitude as that in other molecules, which suggests
that an efficient deuterium fractionation mechanism is at play. We discuss two
possible formation pathways for ND, by means of either the reaction of N+ with
HD, or deuteron/proton exchange with NH.Comment: Accepted; To appear in A&A Herschel/HIFI Special Issu
Dusty Planetary Systems
Extensive photometric stellar surveys show that many main sequence stars show
emission at infrared and longer wavelengths that is in excess of the stellar
photosphere; this emission is thought to arise from circumstellar dust. The
presence of dust disks is confirmed by spatially resolved imaging at infrared
to millimeter wavelengths (tracing the dust thermal emission), and at optical
to near infrared wavelengths (tracing the dust scattered light). Because the
expected lifetime of these dust particles is much shorter than the age of the
stars (>10 Myr), it is inferred that this solid material not primordial, i.e.
the remaining from the placental cloud of gas and dust where the star was born,
but instead is replenished by dust-producing planetesimals. These planetesimals
are analogous to the asteroids, comets and Kuiper Belt objects (KBOs) in our
Solar system that produce the interplanetary dust that gives rise to the
zodiacal light (tracing the inner component of the Solar system debris disk).
The presence of these "debris disks" around stars with a wide range of masses,
luminosities, and metallicities, with and without binary companions, is
evidence that planetesimal formation is a robust process that can take place
under a wide range of conditions. This chapter is divided in two parts. Part I
discusses how the study of the Solar system debris disk and the study of debris
disks around other stars can help us learn about the formation, evolution and
diversity of planetary systems by shedding light on the frequency and timing of
planetesimal formation, the location and physical properties of the
planetesimals, the presence of long-period planets, and the dynamical and
collisional evolution of the system. Part II reviews the physical processes
that affect dust particles in the gas-free environment of a debris disk and
their effect on the dust particle size and spatial distribution.Comment: 68 pages, 25 figures. To be published in "Solar and Planetary
Systems" (P. Kalas and L. French, Eds.), Volume 3 of the series "Planets,
Stars and Stellar Systems" (T.D. Oswalt, Editor-in-chief), Springer 201
Gravitational Waves from Gravitational Collapse
Gravitational wave emission from the gravitational collapse of massive stars
has been studied for more than three decades. Current state of the art
numerical investigations of collapse include those that use progenitors with
realistic angular momentum profiles, properly treat microphysics issues,
account for general relativity, and examine non--axisymmetric effects in three
dimensions. Such simulations predict that gravitational waves from various
phenomena associated with gravitational collapse could be detectable with
advanced ground--based and future space--based interferometric observatories.Comment: 68 pages including 13 figures; revised version accepted for
publication in Living Reviews in Relativity (http://www.livingreviews.org
A Study of Time-Dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the Upsilon(4S)
We present a measurement of time-dependent CP-violating asymmetries in
neutral B meson decays collected with the BABAR detector at the PEP-II
asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data
sample consists of 29.7 recorded at the
resonance and 3.9 off-resonance. One of the neutral B mesons,
which are produced in pairs at the , is fully reconstructed in
the CP decay modes , , , () and , or in flavor-eigenstate
modes involving and (). The flavor of the other neutral B meson is tagged at the time of
its decay, mainly with the charge of identified leptons and kaons. The proper
time elapsed between the decays is determined by measuring the distance between
the decay vertices. A maximum-likelihood fit to this flavor eigenstate sample
finds . The value of the asymmetry amplitude is determined from
a simultaneous maximum-likelihood fit to the time-difference distribution of
the flavor-eigenstate sample and about 642 tagged decays in the
CP-eigenstate modes. We find , demonstrating that CP violation exists in the neutral B meson
system. (abridged)Comment: 58 pages, 35 figures, submitted to Physical Review
Measurement of the Branching Fraction for B- --> D0 K*-
We present a measurement of the branching fraction for the decay B- --> D0
K*- using a sample of approximately 86 million BBbar pairs collected by the
BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is
detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the
K*- through its decay to K0S pi-. We measure the branching fraction to be
B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid
Communications
On the co-evolution of supermassive black holes and their host galaxies since z = 3
[Abridged] To investigate the evolution in the relation between galaxy
stellar and central black hole mass we construct a volume limited complete
sample of 85 AGN with host galaxy stellar masses M_{*} > 10^{10.5} M_{sol}, and
specific X-ray luminosities L_{X} > 2.35 x 10^{43} erg s^{-1} at 0.4 < z < 3.
We calculate the Eddington limiting masses of the supermassive black holes
residing at the centre of these galaxies, and observe an increase in the
average Eddington limiting black hole mass with redshift. By assuming that
there is no evolution in the Eddington ratio (\mu) and then that there is
maximum possible evolution to the Eddington limit, we quantify the maximum
possible evolution in the M_{*} / M_{BH} ratio as lying in the range 700 <
M_{*}/M_{BH} < 10000, compared with the local value of M_{*}/M_{BH} ~ 1000. We
furthermore find that the fraction of galaxies which are AGN (with L_{X} > 2.35
x 10^{43} erg s^{-1}) rises with redshift from 1.2 +/- 0.2 % at z = 0.7 to 7.4
+/- 2.0 % at z = 2.5. We use our results to calculate the maximum timescales
for which our sample of AGN can continue to accrete at their observed rates
before surpassing the local galaxy-black hole mass relation. We use these
timescales to calculate the total fraction of massive galaxies which will be
active (with L_{X} > 2.35 x 10^{43} erg s^{-1}) since z = 3, finding that at
least ~ 40% of all massive galaxies will be Seyfert luminosity AGN or brighter
during this epoch. Further, we calculate the energy density due to AGN activity
in the Universe as 1.0 (+/- 0.3) x 10^{57} erg Mpc^{-3} Gyr^{-1}, potentially
providing a significant source of energy for AGN feedback on star formation. We
also use this method to compute the evolution in the X-ray luminosity density
of AGN with redshift, finding that massive galaxy Seyfert luminosity AGN are
the dominant source of X-ray emission in the Universe at z < 3.Comment: 25 pages, 10 figures, accepted for publication in MNRA
Evidence for the Rare Decay B -> K*ll and Measurement of the B -> Kll Branching Fraction
We present evidence for the flavor-changing neutral current decay and a measurement of the branching fraction for the related
process , where is either an or
pair. These decays are highly suppressed in the Standard Model,
and they are sensitive to contributions from new particles in the intermediate
state. The data sample comprises
decays collected with the Babar detector at the PEP-II storage ring.
Averaging over isospin and lepton flavor, we obtain the branching
fractions and , where the
uncertainties are statistical and systematic, respectively. The significance of
the signal is over , while for it is .Comment: 7 pages, 2 postscript figues, submitted to Phys. Rev. Let
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