4,339 research outputs found
870 micron Imaging of a Transitional Disk in Upper Scorpius: Holdover from the Era of Giant Planet Formation?
We present 880 micron images of the transition disk around the star [PZ99]
J160421.7-213028, a solar-mass star in the nearby Upper Scorpius association.
With a resolution down to 0.34 arcsec, we resolve the inner hole in this disk,
and via model fitting to the visibilities and spectral energy distribution we
determine both the structure of the outer region and the presence of sparse
dust within the cavity. The disk contains about 0.1 Jupiter masses of
mm-emitting grains, with an inner disk edge of about 70 AU. The inner cavity
contains a small amount of dust with a depleted surface density in a region
extending from about 20-70 AU. Taking into account prior observations
indicating little to no stellar accretion, the lack of a binary companion, and
the presence of dust near 0.1 AU, we determine that the most likely mechanism
for the formation of this inner hole is the presence of one or more giant
planets.Comment: 12 pages, 7 figures. To appear in the Astrophysical Journa
A Herschel PACS survey of the dust and gas in Upper Scorpius disks
We present results of far-infrared photometric observations with Herschel
PACS of a sample of Upper Scorpius stars, with a detection rate of previously
known disk-bearing K and M stars at 70, 100, and 160 micron of 71%, 56%, and
50%, respectively. We fit power-law disk models to the spectral energy
distributions of K & M stars with infrared excesses, and have found that while
many disks extend in to the sublimation radius, the dust has settled to lower
scale heights than in disks of the less evolved Taurus-Auriga population, and
have much reduced dust masses. We also conducted Herschel PACS observations for
far-infrared line emission and JCMT observations for millimeter CO lines. Among
B and A stars, 0 of 5 debris disk hosts exhibit gas line emission, and among K
and M stars, only 2 of 14 dusty disk hosts are detected. The OI 63 micron and
CII 157 micron lines are detected toward [PZ99] J160421.7-213028 and [PBB2002]
J161420.3-190648, which were found in millimeter photometry to host two of the
most massive dust disks remaining in the region. Comparison of the OI line
emission and 63 micron continuum to that of Taurus sources suggests the
emission in the former source is dominated by the disk, while in the other
there is a significant contribution from a jet. The low dust masses found by
disk modeling and low number of gas line detections suggest that few stars in
Upper Scorpius retain sufficient quantities of material for giant planet
formation. By the age of Upper Scorpius, giant planet formation is essentially
complete.Comment: 48 pages, 14 figures, accepted A&
Topography and lithology of the Mendocino Ridge
Twenty-two slope-corrected bathymetric profiles of the Mendocino Ridge between 125°W and 129°W are presented, and the method of their development is discussed. The crest of this Ridge lies at an average depth of 2000 m, falling off to 3200 m on the north and to 4400 m on the south. A short, steep scarp, fresh dredge-haul material lacking manganiferous crusts, and earthquake epicenters suggest recent faulting on the north...
Dust masses of disks around 8 Brown Dwarfs and Very Low-Mass Stars in Upper Sco OB1 and Ophiuchus
We present the results of ALMA band 7 observations of dust and CO gas in the
disks around 7 objects with spectral types ranging between M5.5 and M7.5 in
Upper Scorpius OB1, and one M3 star in Ophiuchus. We detect unresolved
continuum emission in all but one source, and the CO J=3-2 line in two
sources. We constrain the dust and gas content of these systems using a grid of
models calculated with the radiative transfer code MCFOST, and find disk dust
masses between 0.1 and 1 M, suggesting that the stellar mass / disk
mass correlation can be extrapolated for brown dwarfs with masses as low as
0.05 M. The one disk in Upper Sco in which we detect CO emission, 2MASS
J15555600, is also the disk with warmest inner disk as traced by its H - [4.5]
photometric color. Using our radiative transfer grid, we extend the correlation
between stellar luminosity and mass-averaged disk dust temperature originally
derived for stellar mass objects to the brown dwarf regime to , applicable to spectral types
of M5 and later. This is slightly shallower than the relation for earlier
spectral type objects and yields warmer low-mass disks. The two prescriptions
cross at 0.27 L, corresponding to masses between 0.1 and 0.2 M
depending on age.Comment: 9 pages,6 figures, accepted to ApJ on 26/01/201
Gravitational Lensing as Signal and Noise in Lyman-alpha Forest Measurements
In Lyman-alpha forest measurements it is generally assumed that quasars are
mere background light sources which are uncorrelated with the forest.
Gravitational lensing of the quasars violates this assumption. This effect
leads to a measurement bias, but more interestingly it provides a valuable
signal. The lensing signal can be extracted by correlating quasar magnitudes
with the flux power spectrum and with the flux decrement. These correlations
will be challenging to measure but their detection provides a direct measure of
how features in the Lyman-alpha forest trace the underlying mass density field.
Observing them will test the fundamental hypothesis that fluctuations in the
forest are predominantly driven by fluctuations in mass, rather than in the
ionizing background, helium reionization or winds. We discuss ways to
disentangle the lensing signal from other sources of such correlations,
including dust, continuum and background residuals. The lensing-induced
measurement bias arises from sample selection: one preferentially collects
spectra of magnified quasars which are behind overdense regions. This
measurement bias is ~0.1-1% for the flux power spectrum, optical depth and the
flux probability distribution. Since the effect is systematic, quantities such
as the amplitude of the flux power spectrum averaged across scales should be
interpreted with care.Comment: 22 pages, 8 figures; v2: references added, discussion expanded,
matches PRD accepted versio
[OI] disk emission in the Taurus star forming region
The structure of protoplanetary disks is thought to be linked to the
temperature and chemistry of their dust and gas. Whether the disk is flat or
flaring depends on the amount of radiation that it absorbs at a given radius,
and on the efficiency with which this is converted into thermal energy. The
understanding of these heating and cooling processes is crucial to provide a
reliable disk structure for the interpretation of dust continuum emission and
gas line fluxes. Especially in the upper layers of the disk, where gas and dust
are thermally decoupled, the infrared line emission is strictly related to the
gas heating/cooling processes. We aim to study the thermal properties of the
disk in the oxygen line emission region, and to investigate the relative
importance of X-ray (1-120 Angstrom) and far-UV radiation (FUV, 912-2070
Angstrom) for the heating balance there. We use [OI] 63 micron line fluxes
observed in a sample of protoplanetary disks of the Taurus/Auriga star forming
region and compare it to the model predictions presented in our previous work.
The data were obtained with the PACS instrument on board the Herschel Space
Observatory as part of the Herschel Open Time Key Program GASPS (GAS in
Protoplanetary diskS), published in Howard et al. (2013). Our theoretical grid
of disk models can reproduce the [OI] absolute fluxes and predict a correlation
between [OI] and the sum Lx+Lfuv. The data show no correlation between the [OI]
line flux and the X-ray luminosity, the FUV luminosity or their sum. The data
show that the FUV or X-ray radiation has no notable impact on the region where
the [OI] line is formed. This is in contrast with what is predicted from our
models. Possible explanations are that the disks in Taurus are less flaring
than the hydrostatic models predict, and/or that other disk structure aspects
that were left unchanged in our models are important. ..abridged..Comment: 9 pages, accepted for publication in A&
The BOSS Emission-Line Lens Survey. III. : Strong Lensing of Ly Emitters by Individual Galaxies
We introduce the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line
Lens Survey (BELLS) for GALaxy-Ly EmitteR sYstems (BELLS GALLERY)
Survey, which is a Hubble Space Telescope program to image a sample of
galaxy-scale strong gravitational lens candidate systems with high-redshift
Ly emitters (LAEs) as the background sources. The goal of the BELLS
GALLERY Survey is to illuminate dark substructures in galaxy-scale halos by
exploiting the small-scale clumpiness of rest-frame far-UV emission in lensed
LAEs, and to thereby constrain the slope and normalization of the
substructure-mass function. In this paper, we describe in detail the
spectroscopic strong-lens selection technique, which is based on methods
adopted in the previous Sloan Lens ACS (SLACS) Survey, BELLS, and SLACS for the
Masses Survey. We present the BELLS GALLERY sample of the 21 highest-quality
galaxy--LAE candidates selected from galaxy spectra
in the BOSS of the Sloan Digital Sky Survey III. These systems consist of
massive galaxies at redshifts of approximately 0.5 strongly lensing LAEs at
redshifts from 2--3. The compact nature of LAEs makes them an ideal probe of
dark substructures, with a substructure-mass sensitivity that is unprecedented
in other optical strong-lens samples. The magnification effect from lensing
will also reveal the structure of LAEs below 100 pc scales, providing a
detailed look at the sites of the most concentrated unobscured star formation
in the universe. The source code used for candidate selection is available for
download as a part of this release.Comment: 14 pages, 5 figures, accepted for publication in the ApJ (ApJ, 824,
86). Minor edits to match the ApJ published versio
Using Experts for Improving Project Cybersecurity Risk Scenarios
This study implemented an expert panel to assess the content validity of hypothetical scenarios to be used in a survey of cybersecurity risk across project meta-phases. Six out of 10 experts solicited completed the expert panel exercise. Results indicate that although experts often disagreed with each other and on the expected mapping of scenario to project meta-phase, the experts generally found risk present in the scenarios and across all three project meta-phases, as hypothesized
Neo-Sumerian account Texts in the Horn Archaeological Museum: Seal Impressions
While Sigrist supplies linguistic analysis, Gavin and his assistants provide composite drawings of the seal impressions. AU Press cataloguehttps://digitalcommons.andrews.edu/books/1080/thumbnail.jp
Assessing the UK policies for broadband adoption
Broadband technology has been introduced to the business community and the public as a rapid way of exploiting the Internet. The benefits of its use (fast reliable connections, and always on) have been widely realised and broadband diffusion is one of the items at the top of the agenda for technology related polices of governments worldwide. In this paper an examination of the impact of the UK government’s polices upon broadband adoption is undertaken. Based on institutional theory a consideration of the manipulation of supply push and demand pull forces in the diffusion of broadband is offered. Using primary and secondary data sources, an analysis of the specific institutional actions related to IT diffusion as pursued by the UK government in the case of broadband is provided. Bringing the time dimension into consideration it is revealed that the UK government has shifted its attention from supply push-only strategies to more interventional ones where the demand pull forces are also mobilised. It is believed that this research will assist in the extraction of the “success factors” in government intervention that support the diffusion of technology with a view to render favourable results if applied to other national settings
- …