291 research outputs found
ALMA 1.3 Millimeter Map of the HD 95086 System
Planets and minor bodies such as asteroids, Kuiper-belt objects and comets
are integral components of a planetary system. Interactions among them leave
clues about the formation process of a planetary system. The signature of such
interactions is most prominent through observations of its debris disk at
millimeter wavelengths where emission is dominated by the population of large
grains that stay close to their parent bodies. Here we present ALMA 1.3 mm
observations of HD 95086, a young early-type star that hosts a directly imaged
giant planet b and a massive debris disk with both asteroid- and Kuiper-belt
analogs. The location of the Kuiper-belt analog is resolved for the first time.
The system can be depicted as a broad (0.84), inclined
(30\arcdeg3\arcdeg) ring with millimeter emission peaked at 2006 au
from the star. The 1.3 mm disk emission is consistent with a broad disk with
sharp boundaries from 1066 to 32020 au with a surface density
distribution described by a power law with an index of --0.50.2. Our deep
ALMA map also reveals a bright source located near the edge of the ring, whose
brightness at 1.3 mm and potential spectral energy distribution are consistent
with it being a luminous star-forming galaxy at high redshift. We set
constraints on the orbital properties of planet b assuming co-planarity with
the observed disk.Comment: accepted for publication in A
Long-term and recent changes in sea level in the Falkland Islands
Mean sea level measurements made at Port Louis in the Falkland Islands in 1981-2, 1984 and 2009, together with values from the nearby permanent tide gauge at Port Stanley, have been compared to measurements made at Port Louis in 1842 by James Clark Ross. The long-term rate of change of sea level is estimated to have been +0.75 ± 0.35 mm/year between 1842 and the early 1980s, after correction for air pressure effects and for vertical land movement due to Glacial Isostatic Adjustment (GIA). The 2009 Port Louis data set is of particular importance due to the availability of simultaneous information from Port Stanley. The data set has been employed in two ways, by providing a short recent estimate of mean sea level itself, and by enabling the effective combination of measurements at the two sites. The rate of sea level rise observed since 1992, when the modern Stanley gauge was installed, has been larger at 2.51 ± 0.58 mm/year, after correction for air pressure and GIA. This rate compares to a value of 2.79 ± 0.42 mm/year obtained from satellite altimetry in the region over the same period. Such a relatively recent acceleration in the rate of sea level rise is consistent with findings from other locations in the southern hemisphere and globall
RZ Piscium Hosts a Compact and Highly Perturbed Debris Disk
RZ Piscium (RZ Psc) is well-known in the variable star field because of its
numerous, irregular optical dips in the past five decades, but the nature of
the system is heavily debated in the literature. We present multiyear infrared
monitoring data from Spitzer and WISE to track the activities of the inner
debris production, revealing stochastic infrared variability as short as weekly
timescales that is consistent with destroying a 90-km-size asteroid every year.
ALMA 1.3 mm data combined with spectral energy distribution modeling show that
the disk is compact (0.1--13 au radially) and lacks cold gas. The disk is
found to be highly inclined and has a significant vertical scale height. These
observations confirm that RZ Psc hosts a close to edge-on, highly perturbed
debris disk possibly due to migration of recently formed giant planets which
might be triggered by the low-mass companion RZ Psc B if the planets formed
well beyond the snowlines.Comment: 16 pages, 5 figures, accepted for publication in Ap
Dust and gas in the magellanic clouds from the heritage herschel key project. II. Gas-to-dust ratio variations across interstellar medium phases
The spatial variations of the gas-to-dust ratio (GDR) provide constraints on the chemical evolution and lifecycle of dust in galaxies. We examine the relation between dust and gas at 10-50 pc resolution in the Large and Small Magellanic Clouds (LMC and SMC) based on Herschel far-infrared (FIR), HI 21 cm, CO, and Hiα observations. In the diffuse atomic interstellar medium (ISM), we derive the GDR as the slope of the dust-gas relation and find GDRs of 380-130+250 ± 3 in the LMC, and 1200-420+1600 ± 120 in the SMC, not including helium. The atomic-to-molecular transition is located at dust surface densities of 0.05 M⊙ pc-2 in the LMC and 0.03 M⊙ pc-2 in the SMC, corresponding to AV ∼ 0.4 and 0.2, respectively. We investigate the range of CO-to-H2 conversion factor to best account for all the molecular gas in the beam of the observations, and find upper limits on XCO to be 6 × 1020 cm-2 K-1 km-1 s in the LMC (Z = 0.5 Z⊙) at 15 pc resolution, and 4 × 1021 cm-2 K-1 km-1 s in the SMC (Z = 0.2 Z⊙) at 45 pc resolution. In the LMC, the slope of the dust-gas relation in the dense ISM is lower than in the diffuse ISM by a factor ∼2, even after accounting for the effects of CO-dark H2 in the translucent envelopes of molecular clouds. Coagulation of dust grains and the subsequent dust emissivity increase in molecular clouds, and/or accretion of gas-phase metals onto dust grains, and the subsequent dust abundance (dust-to-gas ratio) increase in molecular clouds could explain the observations. In the SMC, variations in the dust-gas slope caused by coagulation or accretion are degenerate with the effects of CO-dark H2. Within the expected 5-20 times Galactic XCO range, the dust-gas slope can be either constant or decrease by a factor of several across ISM phases. Further modeling and observations are required to break the degeneracy between dust grain coagulation, accretion, and CO-dark H2. Our analysis demonstrates that obtaining robust ISM masses remains a non-trivial endeavor even in the local Universe using state-of-the-art maps of thermal dust emissio
TADPOL: A 1.3 mm Survey of Dust Polarization in Star-forming Cores and Regions
We present {\lambda}1.3 mm CARMA observations of dust polarization toward 30
star-forming cores and 8 star-forming regions from the TADPOL survey. We show
maps of all sources, and compare the ~2.5" resolution TADPOL maps with ~20"
resolution polarization maps from single-dish submillimeter telescopes. Here we
do not attempt to interpret the detailed B-field morphology of each object.
Rather, we use average B-field orientations to derive conclusions in a
statistical sense from the ensemble of sources, bearing in mind that these
average orientations can be quite uncertain. We discuss three main findings:
(1) A subset of the sources have consistent magnetic field (B-field)
orientations between large (~20") and small (~2.5") scales. Those same sources
also tend to have higher fractional polarizations than the sources with
inconsistent large-to-small-scale fields. We interpret this to mean that in at
least some cases B-fields play a role in regulating the infall of material all
the way down to the ~1000 AU scales of protostellar envelopes. (2) Outflows
appear to be randomly aligned with B-fields; although, in sources with low
polarization fractions there is a hint that outflows are preferentially
perpendicular to small-scale B-fields, which suggests that in these sources the
fields have been wrapped up by envelope rotation. (3) Finally, even at ~2.5"
resolution we see the so-called "polarization hole" effect, where the
fractional polarization drops significantly near the total intensity peak. All
data are publicly available in the electronic edition of this article.Comment: 53 pages, 37 figures -- main body (13 pp., 3 figures), source maps
(32 pp., 34 figures), source descriptions (8 pp.). Accepted by the
Astrophysical Journal Supplemen
CO and dust properties in the TW Hya disk from high-resolution ALMA observations
We analyze high angular resolution ALMA observations of the TW Hya disk to
place constraints on the CO and dust properties. We present new, sensitive
observations of the CO line at a spatial resolution of 8 AU
(0\farcs14). The CO emission exhibits a bright inner core, a shoulder at
AU, and a prominent break in slope at AU. Radiative
transfer modeling is used to demonstrate that the emission morphology can be
reasonably reproduced with a CO column density profile featuring a steep
decrease at AU and a secondary bump peaking at AU.
Similar features have been identified in observations of rarer CO
isotopologues, which trace heights closer to the midplane. Substructure in the
underlying gas distribution or radially varying CO depletion that affects much
of the disk's vertical extent may explain the shared emission features of the
main CO isotopologues. We also combine archival 1.3 mm and 870 m continuum
observations to produce a spectral index map at a spatial resolution of 2 AU.
The spectral index rises sharply at the continuum emission gaps at radii of 25,
41, and 47 AU. This behavior suggests that the grains within the gaps are no
larger than a few millimeters. Outside the continuum gaps, the low spectral
index values of indicate either that grains up to centimeter
size are present, or that the bright continuum rings are marginally optically
thick at millimeter wavelengths.Comment: 27 pages, 11 figures, accepted by ApJ; FITS image files available at
https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/PXDKB
Dust Populations in the Iconic Vega Planetary System Resolved by ALMA
The Vega planetary system hosts the archetype of extrasolar Kuiper belts, and
is rich in dust from the sub-au region out to 100's of au, suggesting intense
dynamical activity. We present ALMA mm observations that detect and resolve the
outer dust belt from the star for the first time. The interferometric
visibilities show that the belt can be fit by a Gaussian model or by power-law
models with a steep inner edge (at 60-80 au). The belt is very broad, extending
out to at least 150-200 au. We strongly detect the star and set a stringent
upper limit to warm dust emission previously detected in the infrared. We
discuss three scenarios that could explain the architecture of Vega's planetary
system, including the new {ALMA} constraints: no outer planets, a chain of
low-mass planets, and a single giant planet. The planet-less scenario is only
feasible if the outer belt was born with the observed sharp inner edge. If
instead the inner edge is currently being truncated by a planet, then the
planet must be 6 M and at au to have cleared
its chaotic zone within the system age. In the planet chain scenario, outward
planet migration and inward scattering of planetesimals could produce the hot
and warm dust observed in the inner regions of the system. In the single giant
planet scenario, an asteroid belt could be responsible for the warm dust, and
mean motion resonances with the planet could put asteroids on star-grazing
orbits, producing the hot dust.Comment: 18 pages, 3 figures, Accepted for publication in Ap
Coming Back to Life: The Permeability of Past and Present, Mortality and Immortality, Death and Life in the Ancient Mediterranean
The lines between death and life were neither fixed nor finite to the peoples of the ancient Mediterranean. For most, death was a passageway into a new and uncertain existence. The dead were not so much extinguished as understood to be elsewhere, and many perceived the deceased to continue to exercise agency among the living. Even for those more skeptical of an afterlife, notions of coming back to life provided frameworks in which to conceptualize the on-going social, political, and cultural influence of the past. This collection of essays examines how notions of coming back to life shape practices and ideals throughout the ancient Mediterranean. All contributors focus on the common theme of coming back to life as a discursive and descriptive space in which antique peoples construct, maintain, and negotiate the porous boundaries between past and present, mortality and immortality, death and life
Internal waves and turbulence in the Antarctic Circumpolar Current
Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 259–282, doi:10.1175/JPO-D-11-0194.1.This study reports on observations of turbulent dissipation and internal wave-scale flow properties in a standing meander of the Antarctic Circumpolar Current (ACC) north of the Kerguelen Plateau. The authors characterize the intensity and spatial distribution of the observed turbulent dissipation and the derived turbulent mixing, and consider underpinning mechanisms in the context of the internal wave field and the processes governing the waves’ generation and evolution.
The turbulent dissipation rate and the derived diapycnal diffusivity are highly variable with systematic depth dependence. The dissipation rate is generally enhanced in the upper 1000–1500 m of the water column, and both the dissipation rate and diapycnal diffusivity are enhanced in some places near the seafloor, commonly in regions of rough topography and in the vicinity of strong bottom flows associated with the ACC jets. Turbulent dissipation is high in regions where internal wave energy is high, consistent with the idea that interior dissipation is related to a breaking internal wave field. Elevated turbulence occurs in association with downward-propagating near-inertial waves within 1–2 km of the surface, as well as with upward-propagating, relatively high-frequency waves within 1–2 km of the seafloor. While an interpretation of these near-bottom waves as lee waves generated by ACC jets flowing over small-scale topographic roughness is supported by the qualitative match between the spatial patterns in predicted lee wave radiation and observed near-bottom dissipation, the observed dissipation is found to be only a small percentage of the energy flux predicted by theory. The mismatch suggests an alternative fate to local dissipation for a significant fraction of the radiated energy.SW acknowledges the support of the Grantham Institute for Climate Change, Imperial College London. ACNG acknowledges the support of a NERC Advanced Research
Fellowship (Grant NE/C517633/1). KLP acknowledges support from Woods Hole Oceanographic Institution
bridge support funds.2013-08-0
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