8,670 research outputs found
The ALMA Early Science View of FUor/EXor objects. III. The Slow and Wide Outflow of V883 Ori
We present Atacama Large Millimeter/ sub-millimeter Array (ALMA) observations
of V883 Ori, an FU Ori object. We describe the molecular outflow and envelope
of the system based on the CO and CO emissions, which together
trace a bipolar molecular outflow. The CO emission traces the rotational
motion of the circumstellar disk. From the CO blue-shifted emission, we
estimate a wide opening angle of 150 for the outflow
cavities. Also, we find that the outflow is very slow (characteristic velocity
of only 0.65 km~s), which is unique for an FU Ori object. We calculate
the kinematic properties of the outflow in the standard manner using the
CO and CO emissions. In addition, we present a P Cygni profile
observed in the high-resolution optical spectrum, evidence of a wind driven by
the accretion and being the cause for the particular morphology of the
outflows. We discuss the implications of our findings and the rise of these
slow outflows during and/or after the formation of a rotationally supported
disk.Comment: 12 pages, 7 figures, 2 tables. Accepte
Cryptography using evolutionary computing
We present a method of generating encryptors, in particular, Pseudo Random Number Generators (PRNG), using evolutionary computing. Working with a system called Eureqa, designed by the Cornell Creative Machines Lab, we seed the system with natural noise sources obtained from data that can include atmospheric noise generated by radio emissions due to lightening, for example, radioactive decay, electronic noise and so on. The purpose of this is to `force' the system to output a result (a nonlinear function) that is an approximation to the input noise. This output is then treated as an iterated function which is subjected to a range of tests to check for potential cryptographic strength in terms of a positive Lyapunov exponent, maximum entropy, high cycle length, key diffusion characteristics etc. This approach provides the potential for generating an unlimited number of unique PRNG that can be used on a 1-to-1 basis. Typical applications include the encryption of data before it is uploaded onto the Cloud by a user that is provided with a personalised encryption algorithm rather than just a personal key using a `known algorithm' that may be subject to a `known algorithm attack' and/or is `open' to the very authorities who are promoting its use
On the nature of the deeply embedded protostar OMC-2 FIR 4
We use mid-infrared to submillimeter data from the Spitzer, Herschel, and
APEX telescopes to study the bright sub-mm source OMC-2 FIR 4. We find a point
source at 8, 24, and 70 m, and a compact, but extended source at 160, 350,
and 870 m. The peak of the emission from 8 to 70 m, attributed to the
protostar associated with FIR 4, is displaced relative to the peak of the
extended emission; the latter represents the large molecular core the protostar
is embedded within. We determine that the protostar has a bolometric luminosity
of 37 Lsun, although including more extended emission surrounding the point
source raises this value to 86 Lsun. Radiative transfer models of the
protostellar system fit the observed SED well and yield a total luminosity of
most likely less than 100 Lsun. Our models suggest that the bolometric
luminosity of the protostar could be just 12-14 Lsun, while the luminosity of
the colder (~ 20 K) extended core could be around 100 Lsun, with a mass of
about 27 Msun. Our derived luminosities for the protostar OMC-2 FIR 4 are in
direct contradiction with previous claims of a total luminosity of 1000 Lsun
(Crimier et al 2009). Furthermore, we find evidence from far-infrared molecular
spectra (Kama et al. 2013, Manoj et al. 2013) and 3.6 cm emission (Reipurth et
al 1999) that FIR 4 drives an outflow. The final stellar mass the protostar
will ultimately achieve is uncertain due to its association with the large
reservoir of mass found in the cold core.Comment: Accpeted by ApJ, 17 pages, 11 figure
Symplectic No-core Shell-model Approach to Intermediate-mass Nuclei
We present a microscopic description of nuclei in an intermediate-mass
region, including the proximity to the proton drip line, based on a no-core
shell model with a schematic many-nucleon long-range interaction with no
parameter adjustments. The outcome confirms the essential role played by the
symplectic symmetry to inform the interaction and the winnowing of shell-model
spaces. We show that it is imperative that model spaces be expanded well beyond
the current limits up through fifteen major shells to accommodate particle
excitations that appear critical to highly-deformed spatial structures and the
convergence of associated observables.Comment: 9 pages, 8 figure
MISALIGNED DISKS IN THE BINARY PROTOSTAR IRS 43
Recent high angular resolution (0.2") ALMA observations of the 1.1 mm
continuum and of HCO+ J=3-2 and HCN J=3-2 gas towards the binary protostar IRS
43 reveal multiple Keplerian disks which are significantly misaligned (
60), both in inclination and position angle and also with respect to
the binary orbital plane. Each stellar component has an associated
circumstellar disk while the binary is surrounded by a circumbinary disk.
Together with archival VLA measurements of the stellar positions over 25 years,
and assuming a circular orbit, we use our continuum measurements to determine
the binary separation, a = 74 4 AU, and its inclination, i
30. The misalignment in this system suggests that turbulence has likely
played a major role in the formation of IRS 43.Comment: 7 pages, 4 figure
Evolution of Mass Outflow in Protostars
We have surveyed 84 Class 0, Class I, and flat-spectrum protostars in
mid-infrared [Si II], [Fe II] and [S I] line emission, and 11 of these in
far-infrared [O I] emission. We use the results to derive their mass outflow
rates. Thereby we observe a strong correlation of mass outflow rates with
bolometric luminosity, and with the inferred mass accretion rates of the
central objects, which continues through the Class 0 range the trend observed
in Class II young stellar objects. Along this trend from large to small
mass-flow rates, the different classes of young stellar objects lie in the
sequence Class 0 -- Class I/flat-spectrum -- Class II, indicating that the
trend is an evolutionary sequence in which mass outflow and accretion rates
decrease together with increasing age, while maintaining rough proportionality.
The survey results include two which are key tests of magnetocentrifugal
outflow-acceleration mechanisms: the distribution of the outflow/accretion
branching ratio b, and limits on the distribution of outflow speeds. Neither
rule out any of the three leading outflow-acceleration,
angular-momentum-ejection mechanisms, but they provide some evidence that disk
winds and accretion-powered stellar winds (APSWs) operate in many protostars.
An upper edge observed in the branching-ratio distribution is consistent with
the upper bound of b = 0.6 found in models of APSWs, and a large fraction
(0.31) of the sample have branching ratio sufficiently small that only disk
winds, launched on scales as large as several AU, have been demonstrated to
account for them.Comment: Version submitted to ApJ: 36 pages, 3 tables, 8 figure
Characterizing the Youngest Herschel-detected Protostars I. Envelope Structure Revealed by CARMA Dust Continuum Observations
We present CARMA 2.9 mm dust continuum emission observations of a sample of
14 Herschel-detected Class 0 protostars in the Orion A and B molecular clouds,
drawn from the PACS Bright Red Sources (PBRS) sample (Stutz et al.). These
objects are characterized by very red 24 \micron\ to 70 \micron\ colors and
prominent submillimeter emission, suggesting that they are very young Class 0
protostars embedded in dense envelopes. We detect all of the PBRS in 2.9 mm
continuum emission and emission from 4 protostars and 1 starless core in the
fields toward the PBRS; we also report 1 new PBRS source. The ratio of 2.9 mm
luminosity to bolometric luminosity is higher by a factor of 5 on
average, compared to other well-studied protostars in the Perseus and Ophiuchus
clouds. The 2.9 mm visibility amplitudes for 6 of the 14 PBRS are very flat as
a function of uv-distance, with more than 50\% of the source emission arising
from radii 1500 AU. These flat visibility amplitudes are most consistent
with spherically symmetric envelope density profiles with
~~R. Alternatively, there could be a massive unresolved
structure like a disk or a high-density inner envelope departing from a smooth
power-law. The large amount of mass on scales 1500 AU (implying high
average central densities) leads us to suggest that that the PBRS with flat
visibility amplitude profiles are the youngest PBRS and may be undergoing a
brief phase of high mass infall/accretion and are possibly among the youngest
Class 0 protostars. The PBRS with more rapidly declining visibility amplitudes
still have large envelope masses, but could be slightly more evolved.Comment: Accepted to ApJ, 40 pages, 9 Figures, 4 Table
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