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We present a cryogenic configurable slit unit (CSU) for a multi-object infrared spectrograph with an effective field of view of 9 ′. 1 × 9 ′. 1 that was completely conceived and designed in the laboratory at TIFR. Several components of the CSU including the controller for the commercially procured piezo-walkers, controlled loop position sensing mechanism using digital slide calipers and a cryogenic test facility for the assembled prototype were also developed in-house. The principle of the CSU involves division of the field of view of the spectrometer into contiguous and parallel spatial bands, each one associated with two opposite sliding metal bars that can be positioned to create a slit needed to make spectroscopic observations of one astronomical object. A three-slit prototype of the newly designed CSU was built and tested extensively at ambient and cryogenic temperatures. The performance of the CSU was found to be as per specifications. [ABSTRACT FROM AUTHOR]

Geometric optical distortion is a significant contributor to the astrometric error budget in large telescopes using adaptive optics. To increase astrometric precision, optical distortion calibration is necessary. We investigate using smartphone Organic Light-Emitting Diode (OLED) screens as astrometric calibrators. Smartphones are low-cost, have stable illumination, and can be quickly reconfigured to probe different spatial frequencies of an optical system's geometric distortion. In this work, we characterize the astrometric accuracy of a Samsung S20 smartphone, with a view towards providing large format, flexible astrometric calibrators for the next generation of astronomical instruments. We find the placement error of the pixels to be 189 nm ± 15 nm Root Mean Square (RMS). At this level of error, milliarcsecond astrometric accuracy can be obtained on modern astronomical instruments. [ABSTRACT FROM AUTHOR]

In addition to the complete set of fundamental parameters of its individual components, we present the solution for the discrepancy between the two main astrometric space telescopes Gaia and Hipparcos, in their measurements of the trigonometric parallax for the stellar binary system Hip 84976. In our analysis of the system, we followed Al-Wardat's method for analyzing binary and multiple stellar systems along with Tokovinin's dynamical method. Using these two methods, we estimated the system's atmospheric, dynamical, and geometrical parameters including the individual masses. The estimated masses and the modified orbital elements were used to give a new dynamical parallax for the system as ( π Dyn = 11.48 ± 0.45 mas), which lies between the measurements given by the old (9.01 ± 1.22 mas) and the new (11.80 ± 1.23 mas) Hipparcos catalogs. It also shows that Hipparcos 2's (2007) parallax measurement is more accurate than that given by Gaia DR3 (12.5899 ± 0.3496 mas) for this system, while that given by Gaia DR2 (24.1841 ± 1.8560 mas) is far from accurate. The results were used to put the two components of the system on the right positions on the H-R diagram, evolutionary tracks, and isochrones, and proposed that the system was formed by fragmentation 1.99 Gyr ago. [ABSTRACT FROM AUTHOR]

Highlights • There is a physical link between SRP albedo-area and observed albedo-area. • The same BRDFs must be used to model both SRP force and light curves. • Data fusion is key in estimating mass and albedo-area of an RSO. Abstract There are many Resident Space Objects (RSOs) in the Geostationary Earth Orbit (GEO) regime, both operational and debris. The primary non-gravitational force acting on these RSOs is Solar Radiation Pressure (SRP), which is sensitive to the RSO's area-to-mass ratio. Sparse observation data and mismodeling of non-gravitational forces has constrained the state of practice in tracking and characterizing RSOs. Accurate identification, characterization, tracking, and motion prediction of RSOs is a high priority research issue as it shall aid in assessing collision probabilities in the GEO regime, and orbital safety writ large. Previous work in characterizing RSOs has taken a preliminary step in exploiting fused astrometric and photometric data to estimate the RSO mass, shape, attitude, and size. This works, in theory, since angles data are sensitive to SRP albedo-area-to-mass ratio, and photometric data are sensitive to shape, attitude, and observed albedo-area. By fusing these two data types, mass and albedo-area both become observable parameters and can be estimated as independent quantities. However, previous work in mass and albedo-area estimation has not quantified and assessed the fundamental physical link between SRP albedo-area and observed albedo-area. The observed albedo-area is always a function of the SRP albedo-area along the line of sight of the observer. This is the physical relationship that this current research exploits. It is shown through simulation that due to this physical link, and through the fusion of astrometric and photometric data, it is possible to observe the mass of a space object when the area is not known. Results for data from 100 trajectories generated from randomly sampled initial conditions are shown. It is seen that even when the area of the object is not known, the uncertainty in mass can be lowered from an initial value of 800 kg to the range 500–700 kg for 72% of the samples, 200–500 kg for 13% of the samples, and 0–200 kg for 15% of the samples. It is further shown that although the uncertainties are large, the actual errors in mass are much lower, with the error RMS being less than 100 kg for 30% of the samples, between 100 and 200 kg for another 30%, and between 200 and 300 kg for 24% of the samples. [ABSTRACT FROM AUTHOR]

We provide new astrometric observations of Enceladus from images taken using the Cassini Imaging Science Subsystem (ISS) Narrow-Angle Camera. Astrometric reduction was performed using a new fully automatic camera repointing technique built within the Caviar software package. The new automatic procedure is based on the k-d tree technique and has been developed as an alternative to the manual technique currently available in Caviar. We describe the new procedure and demonstrate its effectiveness compared with manual processing. Repointing corrections were computed using reference stars from the UCAC4 and Gaia DR1 star catalogues. We compare the observed-minus-computed (O−C) residuals of Enceladus based on UCAC4 with those based on Gaia DR1, relative to the JPL SAT375 ephemeris and the IMCCE NOE ephemeris, respectively. We reduced all available Cassini ISS images of Enceladus during the period 2013–2017, producing a total of 1109 Cassini -centred astrometric observations. These are provided in right ascension (α) and declination (δ) in the International Celestial Reference Frame (ICRF). Estimated mean O−C residuals relative to JPL's SAT375 ephemeris were 0.7 km in α  × cos(δ) and 1.8 km in δ, with standard deviations of 2.4 and 3.2 km, respectively. No improvement in the precision of the observations was obtained when using the GAIA DR1 star catalogue compared with UCAC4. [ABSTRACT FROM AUTHOR]

Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources. The resulting Hertzsprung–Russel diagram reveals fine structures throughout the mass range. Aims. This paper aims to investigate the content of Gaia DR2 at the low-mass end and to characterize ultra-cool and brown dwarfs. Methods. We first retrieved the sample of spectroscopically confirmed ultra-cool and brown dwarfs in Gaia DR2. We used their locus in the precise Hertzsprung–Russel diagram to select new candidates and to investigate their properties. Results. The number of spectroscopically confirmed objects recovered in Gaia DR2 corresponds to 61% and 74% of the expected number of objects with an estimated Gaia magnitude Gest ≤ 21.5 and 20.3, respectively. This fills much of the gap to Gaia DR1. Furthermore, Gaia DR2 contains Ȉ13 000 ≥ M7 and 631 new L candidates. A tentative classification suggests that a few hundred of them are young or subdwarf candidates. Their distance distribution shows that the solar neighborhood census is still incomplete. Conclusions. Gaia DR2 offers a great wealth of information on low-mass objects. It provides a homogeneous and precise catalog of candidates that is worthwhile to be further characterized with spectroscopic observations. [ABSTRACT FROM AUTHOR]

Aims. MASCARA and bRing are photometric surveys designed to detect variability caused by exoplanets in stars with mV < 8.4. Such variability signals are typically small and require an accurate calibration algorithm, tailored to the survey, in order to be detected. This paper presents the methods developed to calibrate the raw photometry of the MASCARA and bRing stations and characterizes the performance of the methods and instruments. Methods. For the primary calibration, a modified version of the coarse decorrelation algorithm is used, which corrects for the extinction due to the earth's atmosphere, the camera transmission, and intrapixel variations. Residual trends are removed from the light curves of individual stars using empirical secondary calibration methods. In order to optimize these methods, as well as characterize the performance of the instruments, transit signals were injected in the data. Results. After optimal calibration an RMS scatter of 10 mmag at mV ~ 7.5 is achieved in the light curves. By injecting transit signals with periods between one and five days in the MASCARA data obtained by the La Palma station over the course of one year, we demonstrate that MASCARA La Palma is able to recover 84.0, 60.5 and 20.7% of signals with depths of 2, 1 and 0.5%, respectively, with a strong dependency on the observed declination, recovering 65.4% of all transit signals at δ > 0° versus 35.8% at δ < 0°. Using the full three years of data obtained by MASCARA La Palma to date, similar recovery rates are extended to periods up to ten days. We derive a preliminary occurrence rate for hot Jupiters around A-stars of >0.4%, knowing that many hot Jupiters are still overlooked. In the era of TESS, MASCARA and bRing will provide an interesting synergy for finding long-period (>13.5 days) transiting gas-giant planets around the brightest stars. [ABSTRACT FROM AUTHOR]

Context. Line shapes of the magnesium resonance lines in white dwarf spectra are determined by the properties of magnesium atoms and the structure of the white dwarf atmosphere. Through their blanketing effect, these lines have a dominant influence on the model structure and thus on the determination from the spectra of other physical parameters that describe the stellar atmosphere and elemental abundances. Aims. In continuation of previous work on Mg+He lines in the UV, we present theoretical profiles of the resonance line of neutral Mg perturbed by He at the extreme density conditions found in the cool largely transparent atmosphere of DZ white dwarfs. Methods. We accurately determined the broadening of Mg by He in a unified theory of collisional line profiles using ab initio calculations of MgHe potential energies and transition matrix elements among the singlet electronic states that are involved for the observable spectral lines. Results. We computed the shapes and line parameters of the Mg lines and studied their dependence on helium densities and temperatures. We present results over the full range of temperatures from 4000 to 12 000 K needed for input to stellar spectra models. Atmosphere models were constructed for a range of effective temperatures and surface gravities typical for cool DZ white dwarfs. We present synthetic spectra tracing the behavior of the Mg resonance line profiles under the low temperatures and high gas pressures prevalent in these atmospheres. Conclusions. The determination of accurate opacity data of magnesium resonance lines together with an improved atmosphere model code lead to a good fit of cool DZ white dwarf stars. The broadening of spectral lines by helium needs to be understood to accurately determine the H/He and Mg/He abundance ratio in DZ white dwarf atmospheres. We emphasize that no free potential parameters or ad hoc adjustments were used to calculate the line profiles. [ABSTRACT FROM AUTHOR]

Context. Galaxy clusters form at the intersections of the filamentary large scale structure in merging events and by the accretion of matter along these filaments. Imprints of these formation processes should be visible in the intracluster medium and can arise in shock fronts, which are detectable via discontinuities in, for example, the gas temperature and density profiles. However, relatively few observational examples of prominent shocks have been detected in X-rays so far. Aims. In this study, we investigate the X-ray properties of the intracluster gas and the radio morphology of the extraordinary cluster A2163. This cluster shows an irregular morphology in various wavelengths and has one of the most luminous and extended radio halos known. Additionally, it is one of the hottest clusters known. We aim to measure the temperature and density profiles in two azimuthal directions to search for the presence of shock fronts. Methods. We performed a spectral analysis of data from two Suzaku observations, one in the north-east (NE) and one in the southwest (SW) direction of A2163, and used archival XMM-Newton data to remove point sources in the field of view. We deprojected the temperature and density profiles and accounted for the Suzaku point spread function. From the detected discontinuities in the density and temperature profiles, we estimated the Mach numbers and velocities of the shock fronts. To compare our findings in the X-ray regime with the radio emission, we obtained radio images of the cluster from an archival Very Large Array (VLA) observation at 20 cm. Results. We identify three shock fronts in A2163 in our spectral X-ray study. A clear shock front lies in the NE direction at a distance of 1.4 Mpc from the center, with a Mach number of M = 1.7+0.3−0.2 M = 1.7 − 0.2 + 0.3 $ M=1.7_{-0.2}^{+0.3} $ , estimated from the temperature discontinuity. This shock coincides with the position of a known radio relic. We identify two additional shocks in the SW direction, one with M = 1.5+0.5−0.3 M = 1.5 − 0.3 + 0.5 $ M=1.5_{-0.3}^{+0.5} $ at a distance of 0.7 Mpc, which is likely related to a cool core remnant, and a strong shock with M = 3.2+0.6−0.7 M = 3.2 − 0.7 + 0.6 $ M=3.2_{-0.7}^{+0.6} $ at a distance of 1.3 Mpc, which also closely matches the radio contours. The complex structure of A2163 as well as the different Mach numbers and shock velocities suggest a merging scenario with two unequal merging constituents, where two shock fronts emerged at an early stage of the merger and traveled outwards while an additional shock front developed in front of the merging cluster cores. [ABSTRACT FROM AUTHOR]

Context. Open clusters are very good tracers of the evolution of the Galactic disc. Thanks to Gaia, their kinematics can be investigated with an unprecedented precision and accuracy. Aims. The distribution of open clusters in the 6D phase space is revisited with Gaia DR2. Methods. The weighted mean radial velocity of open clusters was determined, using the most probable members available from a previous astrometric investigation that also provided mean parallaxes and proper motions. Those parameters, all derived from Gaia DR2 only, were combined to provide the 6D phase-space information of 861 clusters. The velocity distribution of nearby clusters was investigated, as well as the spatial and velocity distributions of the whole sample as a function of age. A high-quality subsample was used to investigate some possible pairs and groups of clusters sharing the same Galactic position and velocity. Results. For the high-quality sample of 406 clusters, the median uncertainty of the weighted mean radial velocity is 0.5 km s−1. The accuracy, assessed by comparison to ground-based high-resolution spectroscopy, is better than 1 km s−1. Open clusters nicely follow the velocity distribution of field stars in the close solar neighbourhood as previously revealed by Gaia DR2. As expected, the vertical distribution of young clusters is very flat, but the novelty is the high precision to which this can be seen. The dispersion of vertical velocities of young clusters is at the level of 5 km s−1. Clusters older than 1 Gyr span distances to the Galactic plane of up to 1 kpc with a vertical velocity dispersion of 14 km s−1, typical of the thin disc. Five pairs of clusters and one group with five members might be physically related. Other binary candidates that have been identified previously are found to be chance alignments. [ABSTRACT FROM AUTHOR]

We present the results of a detailed X-ray timing and spectral analysis of the BL Lacertae source OJ 287 with X-ray telescope (XRT) onboard Neil Gehrels Swift Observatory, focused on the period of its significantly enhanced X-ray flaring activity during 2016 October–2017 April. In this epoch, the 0.3–10 keV count rate from the XRT observations showed an increase by a factor of ∼10 compared to the quiescent level observed in 2016 April–May, and the mean X-ray flux was a factor of 4.5 higher than in previous years. The source underwent high X-ray flaring activity on weekly time-scales and showed 32 instances of 0.3–10 keV intraday variability (detected within the exposures shorter than 1 ks in the majority of cases) with fractional variability amplitudes of 7–60 per cent. Most of the 0.3–10 keV spectra spectra fitted well with a simple power law, yielding a wide range of the 0.3–10 keV photon index Γ = 1.90–2.90. We found 29 spectra showing an upward curvature due to the significant contribution made by the X-ray photons of inverse Compton origin. The spectral variability of OJ 287 was characterized by the dominance of a 'softer-when-brighter' spectral trend, explained by the emergence of a new soft component during X-ray flares. Similar to X-rays, the source underwent a strong outburst by factors of 4.6–6.5 in the optical–ultraviolet energy range which showed a positive correlation with the X-ray emission, indicating its origin to be related to the same electron population, predominantly via the synchrotron mechanism. [ABSTRACT FROM AUTHOR]

The Galactic supernova remnant $$\rm{HESS\,J1534}-{\rm 571}$$ (also known as G323.7 − 1.0) has a shell-like morphology in TeV gamma-ray emission and is a key object in the study of cosmic ray origin. Little is known about its distance and local environment. We examine Mopra 12CO/13CO(1–0) data, Australian Telescope Compact Array $$\rm{H\,{\small I}}$$, and Parkes $$\rm{H\,{\small I}}$$ data towards $$\rm{HESS\,J1534}-{\rm 571}$$. We trace molecular clouds in at least five velocity ranges, including clumpy interstellar medium structures near a dip in $$\rm{H\,{\small I}}$$ emission at a kinematic velocity consistent with the Scutum–Crux arm at ∼3.5 kpc. This feature may be a cavity blown-out by the progenitor star, a scenario that suggests $$\rm{HESS\,J1534}-{\rm 571}$$ resulted from a core-collapse event. By employing parametrizations fitted to a sample of supernova remnants of known distance, we find that the radio continuum brightness of $$\rm{HESS\,J1534}-{\rm 571}$$ is consistent with the ∼3.5 kpc kinematic distance of the Scutum–Crux arm $$\rm{H\,{\small I}}$$ dip. Modelling of the supernova evolution suggests a ∼8–24 kyr age for $$\rm{HESS\,J1534}-{\rm 571}$$ at this distance. [ABSTRACT FROM AUTHOR]

The Deep Extragalactic VIsible Legacy Survey (DEVILS) is a large spectroscopic campaign at the Anglo-Australian Telescope (AAT) aimed at bridging the near and distant Universe by producing the highest completeness survey of galaxies and groups at intermediate redshifts (0.3 < $$z$$ < 1.0). Our sample consists of ∼60 000 galaxies to Y < 21.2 mag, over ∼6 deg2 in three well-studied deep extragalactic fields (Cosmic Origins Survey field, COSMOS; Extended Chandra Deep Field South, ECDFS; and the X-ray Multi-Mirror Mission Large-Scale Structure region, XMM-LSS – all Large Synoptic Survey Telescope deep-drill fields). This paper presents the broad experimental design of DEVILS. Our target sample has been selected from deep Visible and Infrared Survey Telescope for Astronomy (VISTA) Y -band imaging (VISTA Deep Extragalactic Observations, VIDEO and UltraVISTA), with photometry measured by ProFound. Photometric star/galaxy separation is done on the basis of near-infrared colours and has been validated by visual inspection. To maximize our observing efficiency for faint targets, we employ a redshift feedback strategy, which continually updates our target lists, feeding back the results from the previous night's observations. We also present an overview of the initial spectroscopic observations undertaken in late 2017 and early 2018. [ABSTRACT FROM AUTHOR]

Results of visual measurements of the proper motions of 61 Cygni and Groombridge 1830, using an undriven 10-inch (250mm) Dobsonian telescope and an astrometric eyepiece, are presented. It is shown that reasonably accurate measurements of the propermotions of these stars can be made visually, using simple equipment, over a period of time that is less than two years. [ABSTRACT FROM AUTHOR]

The description of an optical complex at the Assy-Turgen Observatory (Kazakhstan) is given. This complex is suited for astrometric and photometric observations of active and passive objects (small-size space debris included) in geostationary orbits. It may be used to reveal, identify, and track potentially hazardous objects (asteroids and comets). The results of test observations are presented. [ABSTRACT FROM AUTHOR]

The astrometric detection of an unseen companion is based on an analysis of the apparent motion of its host star around the system's barycentre. Systems with an orbital period close to 1 yr may escape detection if the orbital motion of their host stars is observationally indistinguishable from the effects of parallax. Additionally, an astrometric solution may produce a biased parallax estimation for such systems. We examine the effects of the orbital motion of the Earth on astrometric detectability in terms of a correlation between the Earth's orbital position and the position of the star relative to its system barycentre. The Χ²statistic for parallax estimation is calculated analytically, leading to expressions that relate the decrease in detectability and accompanying parallax bias to the position correlation function. The impact of the Earth's motion critically depends on the exoplanet's orbital period, diminishing rapidly as the period deviates from 1 yr. Selection effects against 1-yr-period systems is, therefore, expected. Statistical estimation shows that the corresponding loss of sensitivity results in a typical 10 per cent increase in the detection threshold. Consideration of eccentric orbits shows that the Earth's motion has no effect on detectability for e ≥ 0.5. The dependence of the detectability on other parameters, such as orbital phases and inclination of the orbital plane to the ecliptic, are smooth and monotonic because they are described by simple trigonometric functions. [ABSTRACT FROM AUTHOR]

We present here a simple, systematic method for determining the correct global rotation count of a radio pulsar; an essential step for the derivation of an accurate phase-coherent ephemeris. We then build on this method by developing a new algorithm for determining the global rotational count for pulsars with sparse timing data sets. This makes it possible to obtain phase-coherent ephemerides for pulsars for which this has been impossible until now. As an example, we do this for PSR J0024-7205aa, an extremely faint Millisecond pulsar (MSP) recently discovered in the globular cluster 47 Tucanae. This algorithm has the potential to significantly reduce the number of observations and the amount of telescope time needed to follow up on new pulsar discoveries. [ABSTRACT FROM AUTHOR]

The Galactic Centre is a crowded stellar field and frequent unrecognized events of source confusion, which involve undetected faint stars, are expected to introduce astrometric noise on a sub-mas level. This confusion noise is the main non-instrumental effect limiting the astrometric accuracy and precision of current near-infrared imaging observations and the longterm monitoring of individual stellar orbits in the vicinity of the central supermassive black hole. We self-consistently simulate the motions of the known and the yet unidentified stars to characterize this noise component and show that a likely consequence of source confusion is a bias in estimates of the stellar orbital elements, as well as the inferred mass and distance of the black hole, in particular if stars are being observed at small projected separations from it, such as the star S2 during pericentre passage. Furthermore, we investigate modelling the effect of source confusion as an additional noise component that is time-correlated, demonstrating a need for improved noise models to obtain trustworthy estimates of the parameters of interest (and their uncertainties) in future astrometric studies. [ABSTRACT FROM AUTHOR]

We present a deep survey of the Super-Cluster Assisted Shear Survey (SuperCLASS) supercluster – a region of sky known to contain five Abell clusters at redshift z ∼ 0.2 – performed using the Arcminute Microkelvin Imager (AMI) Large Array (LA) at 15.5 GHz. Our survey covers an area of approximately 0.9 deg2.We achieve a nominal sensitivity of 32.0 μJy beam−1 towards the field centre, finding 80 sources above a 5σ threshold. We derive the radio colour– colour distribution for sources common to three surveys that cover the field and identify three sources with strongly curved spectra – a high-frequency-peaked source and two GHz-peakedspectrum sources. The differential source count (i) agrees well with previous deep radio source counts, (ii) exhibits no evidence of an emerging population of star-forming galaxies, down to a limit of 0.24 mJy, and (iii) disagrees with some models of the 15 GHz source population. However, our source count is in agreement with recent work that provides an analytical correction to the source count from the Square Kilometre Array Design Study (SKADS) Simulated Sky, supporting the suggestion that this discrepancy is caused by an abundance of flat-spectrum galaxy cores as yet not included in source population models. [ABSTRACT FROM AUTHOR]

We show numerical simulations with monochromatic light in the visible for the LBTI Fizeau imager, including opto-dynamical aberrations due here to adaptive optics (AO) errors and to differential piston fluctuations, while other errors have been neglected. The achievable Strehl by the LBTI using two AO is close to the Strehl provided by a single standalone AO system, as long as other differential wavefront errors are mitigated. The LBTI Fizeau imager is primarily limited by the AO performance and by the differential piston/tip-tilt errors. Snapshots retain high-angular resolution and high-contrast imaging information by freezing the fringes against piston errors. Several merit functions have been critically evaluated in order to characterize point spread functions and the modulation transfer functions for highcontrast imaging applications. The LBTI Fizeau mode can provide an image quality suitable for standard science cases (i.e. a Strehl above 70 per cent) by performing both at a time: an AO correction better than ≈λ/18 RMS for both short and long exposures, and a piston correction better than ≈λ/8 RMS for long exposures or simply below the coherence length for short exposures. Such results, which can be applied to any observing wavelength, suggest that AO and piston control at the LBTI would already improve the contrast at near- and mid-infrared wavelengths. Therefore, the LBTI Fizeau imager can be used for high-contrast imaging, providing a high-Strehl regime (by both AO systems), a cophasing mode (by a fringe tracker) and a burst mode (by a fast camera) to record fringed speckles in short exposures. [ABSTRACT FROM AUTHOR]

If the dark matter haloes of galaxies contain large numbers of subhaloes as predicted by the ⋀ cold dark matter model, these subhaloes are expected to appear in strong galaxy-galaxy lens systems as small-scale perturbations in individual images. We simulate observations of multiply lensed sub-mm galaxies at z ~ 2 as a probe of the dark matter halo of a lens galaxy at z ~ 0.5.We present detection limits for dark substructures based on a visibility plane analysis of simulated Atacama Large Millimeter/submillimeter Array (ALMA) data in bands 7, 8 and 9. We explore two effects: local surface brightness anomalies on angular scales similar to the Einstein radius and the astrometric shift of macroimages. This improves the sensitivity of our lens modelling to the mass of the lens perturber. We investigate the sensitivity of the detection of low-mass subhaloes to the projected position of the subhalo on the image plane as well as the source structure and inner density profile of the lens. We demonstrate that, using the most extended ALMA configuration, pseudo-Jaffe subhaloes can be detected with 99 per cent confidence down to M = 107M☉. We show how the detection threshold for the three ALMA bands depends on the projected position of the subhalo with respect to the lensed images and conclude that, despite the highest nominal angular resolution, band 9 provides the poorest sensitivity due to observational noise. All simulations use the ALMA Full ops most extended ALMA configuration setup in CASA. [ABSTRACT FROM AUTHOR]

The SCUBA-2 Ambitious Sky Survey (SASSy) is composed of shallow 850-μm imaging using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) on the James Clerk Maxwell Telescope. Here we describe the extraction of a catalogue of beam-sized sources from a roughly 120 deg2 region of the Galactic plane mapped uniformly (to an rms level of about 40 mJy), covering longitude 120° < l < 140° and latitude b < 2. ° 9. We used a matched-filtering approach to increase the signal-to-noise ratio (S/N) in these noisy maps and tested the efficiency of our extraction procedure through estimates of the false discovery rate, as well as by adding artificial sources to the real images. The primary catalogue contains a total of 189 sources at 850 μm, down to an S/N threshold of approximately 4.6. Additionally, we list 136 sources detected down to S/N = 4.3, but recognize that as we go lower in S/N, the reliability of the catalogue rapidly diminishes. We perform follow-up observations of some of our lower significance sources through small targeted SCUBA-2 images and list 265 sources detected in these maps down to S/N = 5. This illustrates the real power of SASSy: inspecting the shallow maps for regions of 850-μm emission and then using deeper targeted images to efficiently find fainter sources. We also perform a comparison of the SASSy sources with the Planck Catalogue of Compact Sources and the IRAS Point Source Catalogue, to determine which sources discovered in this field might be new, and hence potentially cold regions at an early stage of star formation. [ABSTRACT FROM AUTHOR]

Aims: Our long-term aim is to derive model-independent stellar masses and distances for long period massive binaries by combining apparent astrometric orbit with double-lined radial velocity amplitudes (SB2). Methods. We followed-up ten O+O binaries with AMBER, PIONIER and GRAVITY at the VLTI. Here, we report on 130 astrometric observations over the last seven years. We combined this dataset with distance estimates to compute the total mass of the systems. We also computed preliminary individual component masses for the five systems with available SB2 radial velocities. Results: Nine of the ten binaries have their three-dimensional orbit well constrained. Four of them are known to be colliding wind, non-thermal radio emitters, and thus constitute valuable targets for future high angular resolution radio imaging. Two binaries break the correlation between period and eccentricity tentatively observed in previous studies. This suggests either that massive star formation produces a wide range of systems, or that several binary formation mechanisms are at play. Finally, we found that the use of existing SB2 radial velocity amplitudes can lead to unrealistic masses and distances. Conclusions: If not understood, the biases in radial velocity amplitudes will represent an intrinsic limitation for estimating dynamical masses from SB2+interferometry or SB2+Gaia. Nevertheless, our results can be combined with future Gaia astrometry to measure the dynamical masses and distances of the individual components with an accuracy of 5 to 15%, completely independently of the radial velocities. [ABSTRACT FROM AUTHOR]

Context: The study of the Milky Way relies on our ability to interpret the light from stars correctly. With the advent of the astrometric ESA mission Gaia we will enter a new era where the study of the Milky Way can be undertaken on much larger scales than currently possible. In particular we will be able to obtain full 3D space motions of red giant stars at large distances. This calls for a reinvestigation of how reliably we can determine, for example, iron abundances in such stars and how well they reproduce those of dwarf stars. Aims: Here we explore robust ways of determining the iron content of metal-rich giant stars. We aim to understand what biases and shortcomings the widely applied methods suffer from. Methods: In this study we were mainly concerned with standard methods of analysing stellar spectra. These include the analysis of individual lines to determine stellar parameters, and analysis of the broad wings of certain lines (e.g. Hα and calcium lines) to determine effective temperature and surface gravity for the stars. Results: For NGC 6528 we find that [Fe/H] = + 0.04 dex with a scatter of σ = 0.07 dex, which gives an error in the derived mean abundance of 0.02 dex. Conclusions: Our work has two important conclusions for analysis of metal-rich red giant branch stars. Firstly, for spectra with S/N of below about 35 per reduced pixel, [Fe/H] becomes too high. Secondly, determination of Teff using the wings of the Hα line results in [Fe/H] values about 0.1 dex higher than if excitational equilibrium is used. The last conclusion is perhaps unsurprising, as we expect the NLTE effect to become more prominent in cooler stars and we can not use the wings of the Hα line to determine Teff for the cool stars in our sample. We therefore recommend that in studies of metal-rich red giant stars care should be taken to obtain sufficient calibration data to enable use of the cooler stars. [ABSTRACT FROM AUTHOR]

Detection of the epoch of reionization HI signal requires a precise understanding of the intervening galaxies and AGN, both for instrumental calibration and foreground removal. We present a catalogue of 7394 extragalactic sources at 182 MHz detected in the RA = 0 field of the Murchison Widefield Array Epoch of Reionization observation programme. Motivated by unprecedented requirements for precision and reliability we develop new methods for source finding and selection.We apply machine learning methods to self-consistently classify the relative reliability of 9490 source candidates. A subset of 7466 are selected based on reliability class and signal-to-noise ratio criteria. These are statistically cross-matched to four other radio surveys using both position and flux density information. We find 7369 sources to have confident matches, including 90 partially resolved sources that split into a total of 192 sub-components. An additional 25 unmatched sources are included as new radio detections. The catalogue sources have a median spectral index of -0.85. Spectral flattening is seen towards lower frequencies with a median of -0.71 predicted at 182 MHz. The astrometric error is 7 arcsec compared to a 2.3 arcmin beam FWHM. The resulting catalogue covers ~1400 deg2 and is complete to approximately 80 mJy within half beam power. This provides the most reliable discrete source sky model available to date in the MWA EoR0 field for precision foreground subtraction. [ABSTRACT FROM AUTHOR]