The long-term benefit of computer-assisted surgical navigation in unicompartmental knee arthroplasty

We reviewed the outcomes of 30 consecutive primary unicompartmental knee arthroplasties (UKA) performed by a single surgeon for medial compartmental osteoarthritis. Fifteen Allegretto knees were implanted without computer navigation and 15 EIUS knees were implanted with navigation. We compared the survivorship, radiological and clinical outcomes of the two groups at an average of 8.9 years and 6.9 years respectively. The patients were assessed clinically using the Oxford Knee Score (OKS) and radiologically using long-leg weightbearing films and non-weightbearing computed tomography alignment measurements. The overall survivorship was 86.7% at 9 years. A higher proportion of navigated knees were well aligned with a more reproducible position and malaligned knees tended to have a less favourable OKS. However, we found no statistically significant difference in survivorship, clinical outcome and radiological alignment between the two groups

The accretion history of high-mass stars: An ArTéMiS pilot study of Infrared Dark Clouds

The mass growth of protostars is a central element to the determination of fundamental stellar population properties such as the initial mass function. Constraining the accretion history of individual protostars is therefore an important aspect of star formation research. The goal of the study presented here is to determine whether high-mass (proto)stars gain their mass from a compact (<0.1 pc) fixed-mass reservoir of gas, often referred to as dense cores, in which they are embedded, or whether the mass growth of high-mass stars is governed by the dynamical evolution of the parsec-scale clump that typically surrounds them. To achieve this goal, we performed a 350μm continuum mapping of 11 infrared dark clouds, along side some of their neighbouring clumps, with the ArTéMiS camera on APEX. By identifying about 200 compact ArTéMiS sources, and matching them with Herschel Hi-GAL 70μm sources, we have been able to produce mass vs. temperature diagrams. We compare the nature (i.e. starless or protostellar) and location of the ArTéMiS sources in these diagrams with modelled evolutionary tracks of both core-fed and clump-fed accretion scenarios. We argue that the latter provide a better agreement with the observed distribution of high-mass star-forming cores. However, a robust and definitive conclusion on the question of the accretion history of high-mass stars requires larger number statistics

The census of dense cores in the Serpens region from the Herschel Gould Belt Survey

Abstract The Herschel Gould Belt survey mapped the nearby (d < 500 pc) star-forming regions to understand better how the prestellar phase influences the star formation process. Here we report a complete census of dense cores in a ∼15 deg2 area of the Serpens star-forming region located between d ∼ 420 pc and 484 pc. The PACS and SPIRE cameras imaged this cloud from 70 μm to 500 μm. With the multi-wavelength source extraction algorithm getsources , we extract 833 sources, of which 709 are starless cores and 124 are candidate proto-stellar cores. We obtain temperatures and masses for all the sample, classifying the starless cores in 604 prestellar cores and 105 unbound cores. Our census of sources is $80\%$ complete for M > 0.8 M⊙ overall. We produce the core mass function (CMF) and compare it with the initial mass function (IMF). The prestellar CMF is consistent with log-normal trend up to ∼2 M⊙, after which it follows a power-law with slope of −2.05 ± 0.34. The tail of its CMF is steeper but still compatible with the IMF for the region we studied in this work. We also extract the filaments network of the Serpens region, finding that $81\%$ of prestellar cores lie on filamentary structures. The spatial association between cores and filamentary structure supports the paradigm, suggested by other Herschel observations, that prestellar cores mostly form on filaments. Serpens is confirmed to be a young, low-mass and active star-forming region

The NIKA2 large-field-of-view millimetre continuum camera for the 30 m IRAM telescope

Context. Millimetre-wave continuum astronomy is today an indispensable tool for both general astrophysics studies (e.g. star formation, nearby galaxies) and cosmology (e.g. cosmic microwave background and high-redshift galaxies). General purpose, large-field-of-view instruments are needed to map the sky at intermediate angular scales not accessible by the high-resolution interferometers (e.g. ALMA in Chile, NOEMA in the French Alps) and by the coarse angular resolution space-borne or ground-based surveys (e.g. Planck, ACT, SPT). These instruments have to be installed at the focal plane of the largest single-dish telescopes, which are placed at high altitude on selected dry observing sites. In this context, we have constructed and deployed a three-thousand-pixel dual-band (150 GHz and 260 GHz, respectively 2 mm and 1.15 mm wavelengths) camera to image an instantaneous circular field-of-view of 6.5 arcmin in diameter, and configurable to map the linear polarisation at 260 GHz. Aims. First, we are providing a detailed description of this instrument, named NIKA2 (New IRAM KID Arrays 2), in particular focussing on the cryogenics, optics, focal plane arrays based on Kinetic Inductance Detectors, and the readout electronics. The focal planes and part of the optics are cooled down to the nominal 150 mK operating temperature by means of an adhoc dilution refrigerator. Secondly, we are presenting the performance measured on the sky during the commissioning runs that took place between October 2015 and April 2017 at the 30-m IRAM telescope at Pico Veleta, near Granada (Spain). Methods. We have targeted a number of astronomical sources. Starting from beam-maps on primary and secondary calibrators we have then gone to extended sources and faint objects. Both internal (electronic) and on-the-sky calibrations are applied. The general methods are described in the present paper. Results. NIKA2 has been successfully deployed and commissioned, performing in-line with expectations. In particular, NIKA2 exhibits full width at half maximum angular resolutions of around 11 and 17.5 arcsec at respectively 260 and 150 GHz. The noise equivalent flux densities are, at these two respective frequencies, 33±2 and 8±1 mJy s1/2. A first successful science verification run was achieved in April 2017. The instrument is currently offered to the astronomy community and will remain available for at least the following ten years

The spine of the swan: A Herschel study of the DR21 ridge and filaments in Cygnus X

In order to characterise the cloud structures responsible for the formation of high-mass stars, we present Herschel observations of the DR21 environment. Maps of the column density and dust temperature unveil the structure of the DR21 ridge and several connected filaments. The ridge has column densities larger than 1e23/cm^2 over a region of 2.3 pc^2. It shows substructured column density profiles and branching into two major filaments in the north. The masses in the studied filaments range between 130 and 1400 Msun whereas the mass in the ridge is 15000 Msun. The accretion of these filaments onto the DR21 ridge, suggested by a previous molecular line study, could provide a continuous mass inflow to the ridge. In contrast to the striations seen in e.g., the Taurus region, these filaments are gravitationally unstable and form cores and protostars. These cores formed in the filaments potentially fall into the ridge. Both inflow and collisions of cores could be important to drive the observed high-mass star formation. The evolutionary gradient of star formation running from DR21 in the south to the northern branching is traced by decreasing dust temperature. This evolution and the ridge structure can be explained by two main filamentary components of the ridge that merged first in the south.Comment: 8 pages, 5 figures, accepted for publication as a Letter in Astronomy and Astrophysic

How the power spectrum of dust continuum images may hide the presence of a characteristic filament width

Context. Herschel observations of interstellar clouds support a paradigm for star formation in which molecular filaments play a central role. One of the foundations of this paradigm is the finding, based on detailed studies of the transverse column density profiles observed with Herschel, that nearby molecular filaments share a common inner width of ∼0.1 pc. The existence of a characteristic filament width has been recently questioned, however, on the grounds that it seems inconsistent with the scale-free nature of the power spectrum of interstellar cloud images. Aims. In an effort to clarify the origin of this apparent discrepancy, we examined the power spectra of the Herschel/SPIRE 250 μm images of the Polaris, Aquila, and Taurus–L1495 clouds in detail and performed a number of simple numerical experiments by injecting synthetic filaments in both the Herschel images and synthetic background images. Methods. We constructed several populations of synthetic filaments of 0.1 pc width with realistic area filling factors (Afil) and distributions of column density contrasts (δc). After adding synthetic filaments to the original Herschel images, we recomputed the image power spectra and compared the results with the original, essentially scale-free power spectra. We used the χ2variance of the residuals between the best power-law fit and the output power spectrum in each simulation as a diagnostic of the presence (or absence) of a significant departure from a scale-free power spectrum. Results. We find that χ2variance depends primarily on the combined parameter δ22 Afil. According to our numerical experiments, a significant departure from a scale-free behavior and thus the presence of a characteristic filament width become detectable in the power spectrum when δ22 Afil ⪆ 0.1 for synthetic filaments with Gaussian profiles and δ22 Afil ⪆ 0.4 for synthetic filaments with Plummer-like density profiles. Analysis of the real Herschel 250 μm data suggests that δ22 Afil is ∼0.01 in the case of the Polaris cloud and ∼0.016 in the Aquila cloud, significantly below the fiducial detection limit of δ22 Afil ∼ 0.1 in both cases. In both clouds, the observed filament contrasts and area filling factors are such that the filamentary structure contributes only ∼1/5 of the power in the image power spectrum at angular frequencies where an effect of the characteristic filament width is expected. Conclusions. We conclude that the essentially scale-free power spectra of Herschel images remain consistent with the existence of a characteristic filament width ∼0.1 pc and do not invalidate the conclusions drawn from studies of the filament profiles