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CO and CI maps of the starburst galaxy M82
The first map of an external galaxy in the 3P₁ - 3P0 fine-structure line of atomic carbon (CI) is presented towards the nucleus of the starbuster M82, and compared with the distinction of the CO J = 4 - 3 molecular emission. The CI traces features that are seen in lower transition CO maps, and shows that CI and the CO are well mixed and have similar spatial distributions. There are small differences between the CO J = 4 - 3 line and lower transition CO data towards the NE part of the molecular ring, where the emission is less prominent. The abundance ratio [CI]/[CO] across M82 is very high, with an average value ~ 0.5 across most of the nucleus, a factor at least 5 times that which is typical of dense molecular cloud cores seen in our own Galaxy. This means that on average, CI is overabundant towards M82. This result can be explained using models which provide enhancements to the CI abundance above normal Interstellar Medium values, a result of a greater cosmic ray flux in M82, or where there is substantial mixing of the gas
Comparing Segmentation by Time and by Motion in Visual Search: An fMRI Investigation
Abstract
Brain activity was recorded while participants engaged in a difficult visual search task for a target defined by the spatial configuration of its component elements. The search displays were segmented by time (a preview then a search display), by motion, or were unsegmented. A preparatory network showed activity to the preview display, in the time but not in the motion segmentation condition. A region of the precuneus showed (i) higher activation when displays were segmented by time or by motion, and (ii) correlated activity with larger segmentation benefits behaviorally, regardless of the cue. Additionally, the results revealed that success in temporal segmentation was correlated with reduced activation in early visual areas, including V1. The results depict partially overlapping brain networks for segmentation in search by time and motion, with both cue-independent and cue-specific mechanisms.</jats:p
Closed timelike curves in asymmetrically warped brane universes
In asymmetrically warped spacetimes different warp factors are assigned to
space and to time. We discuss causality properties of these warped brane
universes and argue that scenarios with two extra dimensions may allow for
timelike curves which can be closed via paths in the extra-dimensional bulk. In
particular, necessary and sufficient conditions on the metric for the existence
of closed timelike curves are presented. We find a six-dimensional warped
metric which satisfies the CTC conditions, and where the null, weak and
dominant energy conditions are satisfied on the brane (although only the former
remains satisfied in the bulk). Such scenarios are interesting, since they open
the possibility of experimentally testing the chronology protection conjecture
by manipulating on our brane initial conditions of gravitons or hypothetical
gauge-singlet fermions (sterile neutrinos) which then propagate in the extra
dimensions.Comment: 24 pages, 2 figures; major corrections: CTC metric generalized from
5D to 6D, the new 6D metric satisfies the conclusions attributed
(incorrectly) to the 5D metric in v
CTS 11.7 GHz isolation data for the calendar year 1978
Monthly and annual percent-of-time data on polarization isolation measured for the CTS spacecraft 11.7 GHz downlink are presented. The relationship between isolation and attenuation and the degree to which isolation can be predicted from attenuation data are discussed
Quasi-infra-red fixed points and renormalisation group invariant trajectories for non-holomorphic soft supersymmetry breaking
In the MSSM the quasi-infra-red fixed point for the top-quark Yukawa coupling
gives rise to specific predictions for the soft-breaking parameters. We discuss
the extent to which these predictions are modified by the introduction of
additional ``non-holomorphic'' soft-breaking terms. We also show that in a
specific class of theories there exists an RG-invariant trajectory for the
``non-holomorphic'' terms, which can be understood using a holomorphic spurion
term.Comment: 24 pages, TeX, two figures. Uses Harvmac (big) and epsf. Minor errors
corrected, and the RG trajectory explained in terms of a holomorphic spurion
ter
Water depletion in the disk atmosphere of Herbig AeBe stars
We present high resolution (R = 100,000) L-band spectroscopy of 11 Herbig
AeBe stars with circumstellar disks. The observations were obtained with the
VLT/CRIRES to detect hot water and hydroxyl radical emission lines previously
detected in disks around T Tauri stars. OH emission lines are detected towards
4 disks. The OH P4.5 (1+,1-) doublet is spectrally resolved as well as the
velocity profile of each component of the doublet. Its characteristic
double-peak profile demonstrates that the gas is in Keplerian rotation and
points to an emitting region extending out to ~ 15-30 AU. The OH, emission
correlates with disk geometry as it is mostly detected towards flaring disks.
None of the Herbig stars analyzed here show evidence of hot water vapor at a
sensitivity similar to that of the OH lines. The non-detection of hot water
vapor emission indicates that the atmosphere of disks around Herbig AeBe stars
are depleted of water molecules. Assuming LTE and optically thin emission we
derive a lower limit to the OH/H2O column density ratio > 1 - 25 in contrast to
T Tauri disks for which the column density ratio is 0.3 -- 0.4.Comment: Accepted for publication in Ap
Sub-millimeter images of a dusty Kuiper belt around eta Corvi
We present sub-millimeter and mid-infrared images of the circumstellar disk
around the nearby F2V star eta Corvi. The disk is resolved at 850um with a size
of ~100AU. At 450um the emission is found to be extended at all position
angles, with significant elongation along a position angle of 130+-10deg; at
the highest resolution (9.3") this emission is resolved into two peaks which
are to within the uncertainties offset symmetrically from the star at 100AU
projected separation. Modeling the appearance of emission from a narrow ring in
the sub-mm images shows the observed structure cannot be caused by an edge-on
or face-on axisymmetric ring; the observations are consistent with a ring of
radius 150+-20AU seen at 45+-25deg inclination. More face-on orientations are
possible if the dust distribution includes two clumps similar to Vega; we show
how such a clumpy structure could arise from the migration over 25Myr of a
Neptune mass planet from 80-105AU. The inner 100AU of the system appears
relatively empty of sub-mm emitting dust, indicating that this region may have
been cleared by the formation of planets, but the disk emission spectrum shows
that IRAS detected an additional hot component with a characteristic
temperature of 370+-60K (implying a distance of 1-2AU). At 11.9um we found the
emission to be unresolved with no background sources which could be
contaminating the fluxes measured by IRAS. The age of this star is estimated to
be ~1Gyr. It is very unusual for such an old main sequence star to exhibit
significant mid-IR emission. The proximity of this source makes it a perfect
candidate for further study from optical to mm wavelengths to determine the
distribution of its dust.Comment: 22 pages, 4 figures. Scheduled for publication in ApJ 10 February
2005 issu
Herschel evidence for disk flattening or gas depletion in transitional disks
Transitional disks are protoplanetary disks characterized by reduced near-
and mid-infrared emission with respect to full disks. This characteristic
spectral energy distribution indicates the presence of an optically thin inner
cavity within the dust disk believed to mark the disappearance of the
primordial massive disk. We present new Herschel Space Observatory PACS spectra
of [OI] 63 micron for 21 transitional disks. Our survey complements the larger
Herschel GASPS program "Gas in Protoplanetary Systems" (Dent et al. 2013) by
quadrupling the number of transitional disks observed with PACS at this
wavelength. [OI] 63 micron traces material in the outer regions of the disk,
beyond the inner cavity of most transitional disks. We find that transitional
disks have [OI] 63 micron line luminosities two times fainter than their full
disk counterparts. We self consistently determine various stellar properties
(e.g. bolometric luminosity, FUV excess, etc.) and disk properties (e.g. disk
dust mass, etc.) that could influence the [OI] 63 micron line luminosity and we
find no correlations that can explain the lower [OI] 63 micron line
luminosities in transitional disks. Using a grid of thermo-chemical
protoplanetary disk models, we conclude that either transitional disks are less
flared than full disks or they possess lower gas-to-dust ratios due to a
depletion of gas mass. This result suggests that transitional disks are more
evolved than their full disk counterparts, possibly even at large radii.Comment: Accepted for publication in ApJ; 52 pages, 16 figures, 8 table
The impact of the Herbig Haro object HH2 on local dust and gas
We present results from a study of molecular gas and dust in the vicinity of
the Herbig Haro object HH2. Emission from the sub-mm continuum, 12CO and HCO+
was mapped with angular resolutions ranging from 14 arcsec to 5 arcsec (or
0.01pc at the distance of HH2). The continuum shows an extended dust clump of
mass 3.8Msun and temperature 22K, located downstream of the bright optical HH
knots. However, a compact emission peak lies within ~0.01pc of the
low-excitation H2-prominent shocks, with a luminosity consistent with local
heating by the outflow.
The HCO+ emission shows two velocity components: firstly, ambient-velocity
gas lying in a region roughly corresponding to the dust clump, with abundance
enhanced by a factor of a few close to the H2-prominent knots. Secondly a
component of high-velocity emission (20 km/s linewidth), found mainly in a
collimated jet linking the low-excitation HH objects. In this high-velocity
jet, the line wings show an abundance ratio HCO+/CO proportional to v^2, with
an HCO+ enhancement compared with ambient gas of up to 10^3 at the most extreme
velocities. Such high abundances are consistent with models of shock chemistry
in turbulent mixing layers at the interaction boundaries of jets. Extrapolating
this effect to low velocities suggests that the more modest HCO+ enhancement in
the clump gas could be caused by low velocity shocks. A UV precursor may not,
therefore be necessary to explain the elevated HCO+ abundance in this gas.Comment: 8 pages. 9 figures. To be published in MNRA
Parallel distractor rejection as a binding mechanism in search
The relatively common experimental visual search task of finding a red X amongst red O’s and green X’s (conjunction search) presents the visual system with a binding problem. Illusory conjunctions (ICs) of features across objects must be avoided and only features present in the same object bound together. Correct binding into unique objects by the visual system may be promoted, and ICs minimized, by inhibiting the locations of distractors possessing non-target features (e.g., Treisman and Sato, 1990). Such parallel rejection of interfering distractors leaves the target as the only item competing for selection; thus solving the binding problem. In the present article we explore the theoretical and empirical basis of this process of active distractor inhibition in search. Specific experiments that provide strong evidence for a process of active distractor inhibition in search are highlighted. In the final part of the article we consider how distractor inhibition, as defined here, may be realized at a neurophysiological level (Treisman and Sato, 1990)
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