Radio-optical Reference Catalog, Version 1 Makarov, Valeri V.; Johnson, Megan C.; Secrest, Nathan J.
The Astronomical journal,
07/2023, Letnik:
166, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
The fundamental celestial reference frame (CRF) is based on two catalogs of astrometric positions: the third realization of the International Celestial Reference Frame (ICRF3), and the much ...larger Gaia CRF, built from the third data release (DR3). The objects in common between these two catalogs are mostly distant AGNs and quasars that are both sufficiently optically bright for Gaia and radio loud for the VLBI. This limited collection of reference objects is crucially important for the mutual alignment of the two CRFs and the maintenance of all of the other frames and coordinate systems branching from the ICRF. In this paper, we show that the three components of ICRF3 (
S/X, K
, and
X/Ka
band catalogs) have significantly different sky-correlated vector fields of position offsets with respect to Gaia DR3. When iteratively expanded in the vector spherical harmonics up to degree 4 on a carefully vetted set of common sources, each of these components includes several statistically significant terms. The median sky-correlated offsets from the Gaia positions are found to be 56
μ
as for the
S/X
, 100
μ
as for the
K
, and 324
μ
as for the
X/Ka
catalogs. The weighted mean vector field is subtracted from the Gaia reference positions, while the deviations from that field are added to each of the ICRF3 components. The corrected positions from each of the four input catalogs are combined into a single weighted mean catalog, which we propose to be the current most accurate realization of an inertial radio-optical CRF.
ABSTRACT We present high-resolution rotation curves and mass models of 26 dwarf galaxies from "Local Irregulars That Trace Luminosity Extremes, The H i Nearby Galaxy Survey" (LITTLE THINGS). LITTLE ...THINGS is a high-resolution (∼6″ angular; <2.6 km s−1 velocity resolution) Very Large Array H i survey for nearby dwarf galaxies in the local volume within 11 Mpc. The high-resolution H i observations enable us to derive reliable rotation curves of the sample galaxies in a homogeneous and consistent manner. The rotation curves are then combined with Spitzer archival 3.6 m and ancillary optical U, B, and V images to construct mass models of the galaxies. This high quality multi-wavelength data set significantly reduces observational uncertainties and thus allows us to examine the mass distribution in the galaxies in detail. We decompose the rotation curves in terms of the dynamical contributions by baryons and dark matter (DM) halos, and compare the latter with those of dwarf galaxies from THINGS as well as ΛCDM Smoothed Particle Hydrodynamic (SPH) simulations in which the effect of baryonic feedback processes is included. Being generally consistent with THINGS and simulated dwarf galaxies, most of the LITTLE THINGS sample galaxies show a linear increase of the rotation curve in their inner regions, which gives shallower logarithmic inner slopes of their DM density profiles. The mean value of the slopes of the 26 LITTLE THINGS dwarf galaxies is which is in accordance with the previous results found for low surface brightness galaxies ( ) as well as the seven THINGS dwarf galaxies ( ). However, this significantly deviates from the cusp-like DM distribution predicted by DM-only ΛCDM simulations. Instead our results are more in line with the shallower slopes found in the ΛCDM SPH simulations of dwarf galaxies in which the effect of baryonic feedback processes is included. In addition, we discuss the central DM distribution of DDO 210 whose stellar mass is relatively low in our sample to examine the scenario of inefficient supernova feedback in low mass dwarf galaxies predicted from recent ΛCDM SPH simulations of dwarf galaxies where central cusps still remain.
Hearts and lungs from donors with hepatitis C viremia are typically not transplanted. The advent of direct-acting antiviral agents to treat hepatitis C virus (HCV) infection has raised the ...possibility of substantially increasing the donor organ pool by enabling the transplantation of hearts and lungs from HCV-infected donors into recipients who do not have HCV infection.
We conducted a trial involving transplantation of hearts and lungs from donors who had hepatitis C viremia, irrespective of HCV genotype, to adults without HCV infection. Sofosbuvir-velpatasvir, a pangenotypic direct-acting antiviral regimen, was preemptively administered to the organ recipients for 4 weeks, beginning within a few hours after transplantation, to block viral replication. The primary outcome was a composite of a sustained virologic response at 12 weeks after completion of antiviral therapy for HCV infection and graft survival at 6 months after transplantation.
A total of 44 patients were enrolled: 36 received lung transplants and 8 received heart transplants. The median viral load in the HCV-infected donors was 890,000 IU per milliliter (interquartile range, 276,000 to 4.63 million). The HCV genotypes were genotype 1 (in 61% of the donors), genotype 2 (in 17%), genotype 3 (in 17%), and indeterminate (in 5%). A total of 42 of 44 recipients (95%) had a detectable hepatitis C viral load immediately after transplantation, with a median of 1800 IU per milliliter (interquartile range, 800 to 6180). Of the first 35 patients enrolled who had completed 6 months of follow-up, all 35 patients (100%; exact 95% confidence interval, 90 to 100) were alive and had excellent graft function and an undetectable hepatitis C viral load at 6 months after transplantation; the viral load became undetectable by approximately 2 weeks after transplantation, and it subsequently remained undetectable in all patients. No treatment-related serious adverse events were identified. More cases of acute cellular rejection for which treatment was indicated occurred in the HCV-infected lung-transplant recipients than in a cohort of patients who received lung transplants from donors who did not have HCV infection. This difference was not significant after adjustment for possible confounders.
In patients without HCV infection who received a heart or lung transplant from donors with hepatitis C viremia, treatment with an antiviral regimen for 4 weeks, initiated within a few hours after transplantation, prevented the establishment of HCV infection. (Funded by the Mendez National Institute of Transplantation Foundation and others; DONATE HCV ClinicalTrials.gov number, NCT03086044.).
Kinematics of the atomic ISM in M33 on 80 pc scales Koch, Eric W; Rosolowsky, Erik W; Lockman, Felix J ...
Monthly notices of the Royal Astronomical Society,
09/2018, Letnik:
479, Številka:
2
Journal Article
Context.
The link of the
Gaia
frame in terms of non-rotation with respect to the International Celestial Reference System (ICRS), which is realized via very long baseline interferometry (VLBI) at ...radio wavelengths, has to be conducted for the wide range of optical magnitudes in which the spacecraft observes. There is a sufficient number of suitable counterparts between the two measurement systems for optically faint objects. However, the number of common optically bright (
G
≤ 13 mag) objects is sparse as most are faint at radio frequencies, and only a few objects suitable for astrometry have been observed by VLBI in the past. As a result, rotation parameters for the optically bright
Gaia
reference frame are not yet determined with sufficient accuracy.
Aims.
The verification of the
Gaia
bright frame of DR2 and EDR3 is enhanced by the reevaluation of existing VLBI observations and the addition of newly acquired data for a sample of optically bright radio stars.
Methods.
Historical data from the literature were reevaluated, ensuring that the calibrator positions and uncertainties (used for the determination of the absolute star positions in the phase-referencing analysis) were updated and homogeneously referred to the ICRF3, the third realization of the International Celestial Reference Frame. We selected 46 suitable optically bright radio stars from the literature for new radio observations, out of which 32 were detected with the VLBA in continuum mode in the X or C band, along with radio-bright calibrators in the ICRF3. Improved
Gaia
-VLBI rotation parameters were obtained by adding new observations and utilizing more realistic estimates of the absolute position uncertainties for all phase-referenced radio observations.
Results.
The homogenization greatly improved the steadiness of the results when the most discrepant stars were rejected one after another through a dedicated iterative process. For
Gaia
DR2, this homogenization reduced the magnitude of the orientation parameters to less than 0.5 mas but increased that of the spin parameters, with the largest component being the rotation around the Y axis. An adjustment of the position uncertainties improved the reliability of the orientation parameters and the goodness of fit for the iterative solutions. Introducing the new single-epoch positions to the analysis reduced the correlations between the rotation parameters. The final spin for
Gaia
DR2 as determined by VLBI observations of radio stars is (−0.056, −0.113, +0.033) ± (0.046, 0.058, 0.053) mas yr
−1
. A comparison of the new results with external, independently derived spin parameters for
Gaia
DR2 reveals smaller differences than when using the historical data from the literature. Applying the VLBI data to
Gaia
EDR3, which was already corrected for spin during
Gaia
processing, the derived residual spin is (+0.022, +0.065, −0.016) ± (0.024, 0.026, 0.024)mas yr
−1
, showing that the component in Y is significant at the 2.4
σ
level.
Conclusions.
Even though our analysis provides a more accurate frame tie, more VLBI data are needed to refine the results and reduce the scatter between iterative solutions.
The high cost of elder care combined with the shortage of caregivers lead us to consider how service robots can be affordably leveraged to support the independence of elders and the work of their ...caregivers and clinicians. Our objective is to gain design insight into tasks older adults desire to accomplish daily in a low-resource, assisted living setting and how an affordable service robot could suit. A need-finding design approach consisting of focus groups and surveys was completed with three stakeholders groups: Elders, Clinicians, and Caregivers. Stakeholders were asked to identify and then prioritize service tasks by importance and frustration. Thirty-six unique high priority tasks were identified. Instrumental activities of daily living, a desire to have their preferences known, leisure activities, and increased opportunities for socialization were the most important tasks that the elders wanted a low-cost mobile service robot to address. Clinicians and caregivers prioritized highly safety-related reminders and assistance in complying with care plans in assessment of elder task needs. Service robots exist that do some, but not all of these desired tasks. An effective and affordable service robot requires design trade-offs in terms of cost, preference and complexity. A low-cost robot targeting reminders, companion walking, hydration and fetching assistance was suggested as an initial prototype. Prototypes may address high priority desires of all stakeholders, but robots that can intervene and affect long-lasting changes in elder care are still needed.
ABSTRACT
We investigate how the spectral properties of atomic (H i) and molecular (H2) gas, traced by CO(2−1) , are related in M33 on 80 pc scales. We find the H i and CO(2−1) velocity at peak ...intensity to be highly correlated, consistent with previous studies. By stacking spectra aligned to the velocity of H i peak intensity, we find that the CO line width (σHWHM = 4.6 ± 0.9 ${\rm km\, s^{-1}}$ ; σHWHM is the effective Gaussian width) is consistently smaller than the H i line width (σHWHM = 6.6 ± 0.1 ${\rm km\, s^{-1}}$), with a ratio of ∼0.7, in agreement with Druard et al. The ratio of the line widths remains less than unity when the data are smoothed to a coarser spatial resolution. In other nearby galaxies, this line width ratio is close to unity which has been used as evidence for a thick, diffuse molecular disc that is distinct from the thin molecular disc dominated by molecular clouds. The smaller line width ratio found here suggests that M33 has a marginal thick molecular disc. From modelling individual lines of sight, we recover a strong correlation between H i and CO line widths when only the H i located closest to the CO component is considered. The median line width ratio of the line-of-sight line widths is 0.56 ± 0.01. There is substantial scatter in the H i –CO(2−1) line width relation, larger than the uncertainties, that results from regional variations on <500 pc scales, and there is no significant trend in the line widths, or their ratios, with galactocentric radius. These regional line width variations may be a useful probe of changes in the local cloud environment or the evolutionary state of molecular clouds.
Abstract
The third iteration of the International Celestial Reference Frame (ICRF3) is made up of 4536 quasars observed at
S/X
bands using very-long-baseline interferometry. These sources are ...high-redshift quasars, typically between 1 <
z
< 2, that are believed to host active galactic nuclei at their centers. The position of compact radio sources can be determined better than sources with large amounts of extended radio structure. Here we report information on a series of 20 observations from 2017 January through December 2017 that were designed for precise astrometry and to monitor the structure of sources included in the ICRF3. We targeted 3627 sources over the one year campaign and found the median flux density of 2697 detected sources at
S
band is 0.13 Jy, and the median flux density of 3209 sources detected at
X
band is 0.09 Jy. We find that 70% of detected sources in our campaign are considered compact at
X
band and ideal for use in the ICRF and 89% of the 2615 sources detected at both frequencies have a flat spectral index,
α
> 0.5
Abstract
Using the Very Long Baseline Array, we observed the active galactic nucleus (AGN) in NGC 3079 over a span of six months to test for variability in the two main parsec-scale radio components,
...A
and
B
, which lie on either side of the AGN. We found evidence for positional differences in the positions of
A
and
B
over the six months consistent with the apparent motion of these components extrapolated from older archival data, finding that their projected rate of separation, (0.040 ± 0.003)
c
, has remained constant since ∼2004 when a slowdown concurrent with a dramatic brightening of source
A
occurred. This behavior is consistent with an interaction of source
A
with the interstellar medium (ISM), as has previously been suggested in the literature. We calculated the amount of mechanical feedback on the ISM for both the scenario in which
A
is an expulsion of material from the central engine and the scenario in which
A
is a shock front produced by a relativistic jet, the latter of which is favored by several lines of evidence we discuss. We find that the cumulative mechanical feedback on the ISM is between 2 × 10
44
and 1 × 10
48
erg for the expulsion scenario or between 3 × 10
50
and 1 × 10
52
erg for the jet scenario. Integrated over the volume-complete Fundamental Reference AGN Monitoring Experiment (FRAMEx) sample, our results imply that jet-mode mechanical feedback plays a negligible role in the energetics of AGNs in the local Universe.
Although palliative care is critical to managing symptoms, pain, and transitions to end-of-life care among those facing serious or chronic illness, it is often underused, which may be due to stigma ...associated with palliative care representing giving up fighting one's illness. The goal of the present studies was to test the theoretical framework of stigma within the context of palliative care to inform future work on intervention development that addresses potential barriers to palliative care utilization.
In study 1, participants (n = 152) had an oncologist describe two treatment options to a terminally ill cancer patient: (1) palliative care and (2) chemotherapy. Participants were then randomly assigned to read that the patient chose palliative care or chemotherapy. In study 2, these stereotypes about those receiving palliative care were examined as a potential mediator between perceived palliative care stigma and prospective palliative care use. Participants (n = 199) completed self-report measures of palliative care stigma, negative stereotypes about palliative care users, and prospective use of palliative care. Mediation analysis tested the mediational effects of stereotypes on the relationship between palliative care stigma and prospective usage of palliative care.
In study 1, those in the palliative care condition endorsed significantly higher levels of negative stereotypes about the patient, viewed the decision more negatively, and saw the patient as less afraid of death. In study 2, palliative care stigma was associated with less prospective usage of palliative care for self and for one's family member. This relationship was mediated by negative stereotypes about individuals receiving palliative care.
Results suggest that palliative care stigma exists (study 1) and that this stigma may be a barrier to the utilization of palliative care (study 2). Future research should examine stigma reduction as a potential intervention target to improve palliative care utilization.
PDF
