Chance Alignment Research Articles

Carina High-contrast Imaging Project for massive Stars (CHIPS)

Context.Massive stars like company. However, low-mass companions have remained extremely difficult to detect at angular separations (ρ) smaller than 1″ (approx. 1000–3000 au, considering the typical distance to nearby massive stars) given the large brightness contrast between the companion and the central star. Constraints on the low-mass end of the companions mass-function for massive stars are needed, however, for helping, for example, to distinguish among the various scenarios that describe the formation of massive stars.Aims.With the aim of obtaining a statistically significant constraint on the presence of low-mass companions beyond the typical detection limit of current surveys (Δmag ≲ 5 atρ ≲ 1″), we initiated a survey of O and Wolf-Rayet stars in the Carina region using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) coronagraphic instrument on the Very Large Telescope (VLT). In this, the first paper of the series, we aim to introduce the survey, to present the methodology and to demonstrate the capability of SPHERE for massive stars using the multiple system QZ Car.Methods.We obtained VLT-SPHERE snapshot observations in the IRDIFS_EXT mode, which combines the IFS and IRDIS sub-systems and simultaneously provides us four-dimensional (4D) data cubes in two different fields-of-view: 1.73″ × 1.73″ for IFS (39 spectral channels across theYJHbands) and 12″ × 12″ for IRDIS (two spectral channels across theKband). Angular- and spectral-differential imaging techniques as well as PSF-fitting were applied to detect and measure the relative flux of the companions in each spectral channel. The latter were then flux-calibrated using theoretical SED models of the central object and compared to a grid of ATLAS9 atmosphere model and (pre-)main-sequence evolutionary tracks, providing a first estimate of the physical properties of the detected companions.Results.Detection limits of 9 mag atρ > 200 mas for IFS, and as faint as 13 mag atρ > 1.​″8 for IRDIS (corresponding to sub-solar masses for potential companions), can be reached in snapshot observations of only a few minutes integration times, allowing us to detect 19 sources around the QZ Car system. All but two are reported here for the first time. With near-IR magnitude contrasts in the range of 4 to 7.5 mag, the three brightest sources (Ab, Ad, and E) are most likely to be physically bound. They have masses in the range of 2 to 12M⊙and are potentially co-eval with QZ Car central system. The remaining sources have flux contrast of 1.5 × 105to 9.5 × 106(ΔK ≈ 11 to 13 mag). Their presence can be explained by the local source density and they are, thus, likely to be chance alignments. If they were members of the Carina nebula, they would be sub-solar-mass pre-main sequence stars.Conclusions.Based on this proof of concept, we show that the VLT/SPHERE allows us to reach the sub-solar mass regime of the companion mass function. It paves the way for this type of observation with a large sample of massive stars to provide novel constraints on the multiplicity of massive stars in a region of the parameter space that has remained inaccessible so far.

Strengthening Agricultural Investment through Sustainable Islamic Banking


 
 
 
 This study analyzes how agricultural investments may strengthen the Islamic banking industry that is sustainable in the short and long term. Qualitative data sources are secondary data from BPS, Baznas, ACT Global Waqf and research on BWI in the form of secondary data from March 2007 to December 2018. Data were analyzed using the Error Correction Model (ECM) Methodology. Ziswaf have a signiicnt effect on GDP both of the long term and the short term, with the ECT coeficient was - 1.81E-07 meaning that there are increasing GDP will be adjusted within one (1) year with the residual speed of the balance value of - 181 percent. In the long term, the GDP have inluented simultaneously by all independent variables with affected positively by Exports-Agi, PMDN and Ziswaf signiicantly; and it have inluenced negatively by Export signiicantly at the R-square level of 0.98 meaning that the variables are tested to provide almost all the information needed to predict the GDP. Export-Agi was the most inluence with a value of coeficient variable 44.875570. While in the short term, GDP was signiicantly inluenced by Ziswaf on R-square 0.26 which means that there have 74 per cent of other variables outside the model that affect GDP. 
 
 
 
 
 The selection of competitive plants in the zakat distribution program and the use of idle waqaf land is very important to be considered by institutions / individuals who are interested in PMDN investment in the agricultural sector and ziswaf management institutions. Every land and sea have the blessing and the competitive power of its own and its utilization as well as possible considering the state of the local community as a major source of labor, without neglecting the environmentaspartof sustainabledevelopment goals.Asmart-small- microinanc can be synergized with ziswaf as a step to strengthen the technical and managerial mustahik. Cash waqf can also be used as an instrument for the development of further capital. Economic growth is accompanied by sustainability is the best choice, the chance alignment of a sustainable Islamic inancial investment can be expanded globally in scope and impact. Islamic inancial transactions can be retained should provide investment categories permitted by religion (halal) and did well to supply logistics either through A-PLS or sukuk using the inancing agreements like salam, muzara'ah, and mugharasah; irrigation infrastructure for areas prone to lack of water with Musaqa or Istishna inancing. Careful handling prior to harvest, post - harvest handling of agricultural products and halal food processing industry is part of the growing Islamic Bankings sustainable advantage.
 
 
 
 
 
 
 

The SUPERWIDE Catalog: A Catalog of 99,203 Wide Binaries Found in Gaia and Supplemented by the SUPERBLINK High Proper Motion Catalog

Abstract We present a catalog of 99,203 wide binary systems, initially identified as common proper motion (CPM) pairs from a subset of ∼5.2 million stars with proper motions , selected from Gaia data release 2 (DR2) and the SUPERBLINK high proper motion catalog. CPM pairs are found by searching for pairs of stars with angular separations <1° and proper motion differences . A Bayesian analysis is then applied in two steps. In a first pass, we use proper motion differences and angular separations to distinguish between real binaries and chance alignments. In a second pass, we use parallax data from Gaia DR2 to refine our Bayesian probability estimates. We present a table of 119,390 pairs which went through the full analysis, 99,203 of which have probabilities >95% of being real wide binaries. Of those 99,203 high-probability pairs, we estimate that only about 364 pairs are most likely to be false positives. In addition, we identify 57,506 pairs that have probabilities greater than 10% from the first pass but have high parallax errors and therefore were not vetted in the second pass. We examine the projected physical separation distribution of our highest probability pairs and note that the distribution is a simple exponential tail and shows no evidence of being bimodal. Among pairs with lower probability, wide binaries are detected at larger separations (>104–105 au), consistent with the very wide population suggested in previous studies; however, our analysis suggests that these do not represent a distinct population, but instead represent either the exponential tail of the “normal” wide binary distribution or are simply chance alignments of unrelated field stars. We examine the Hertzsprung–Russell diagram of this set of high-probability wide binaries and find evidence for 980 overluminous components among 2227 K + K wide binaries; assuming these represent unresolved subsystems, we determine that the higher-order multiplicity fraction for K + K wide systems is at least 39.6%.

Short gamma-ray bursts within 200 Mpc

ABSTRACT We present a systematic search for short-duration gamma-ray bursts (GRBs) in the local Universe based on 14 yr of observations with the Neil Gehrels Swift Observatory. We cross-correlate the GRB positions with the GLADE catalogue of nearby galaxies, and find no event at a distance ≲100 Mpc and four plausible candidates in the range 100 Mpc ≲ D ≲ 200 Mpc. Although affected by low statistics, this number is higher than the one expected for chance alignments to random galaxies, and possibly suggests a physical association between these bursts and nearby galaxies. By assuming a local origin, we use these events to constrain the range of properties for X-ray counterparts of neutron star mergers. Optical upper limits place tight constraints on the onset of a blue kilonova, and imply either low masses ($\lesssim 10^{-3}\, \mathrm{M}_{\odot }$) of lanthanide-poor ejecta or unfavorable orientations (θobs ≳ 30 deg). Finally, we derive that the all-sky rate of detectable short GRBs within 200 Mpc is $1.3^{+1.7}_{-0.8}$ yr−1 (68 per cent confidence interval), and discuss the implications for the GRB outflow structure. If these candidates are instead of cosmological origin, we set a upper limit of ≲2.0 yr−1 (90 per cent confidence interval) to the rate of nearby events detectable with operating gamma-ray observatories, such as Swift and Fermi.

A New Microquasar Candidate in M83

Abstract Microquasars are neutron star or black hole X-ray binaries with jets. These jets can create bubbles of hot plasma shock ionized that can masquerade as peculiar supernova remnants (SNRs) in extragalactic surveys. To see if this is the case in the well-studied spiral galaxy M83, where one microquasar candidate (M83-MQ1) has already been identified, we studied the properties of nine SNR candidates, selected because of their elongated or irregular morphology, from the set of previously identified SNRs in that galaxy. Using multiwavelength data from Chandra, the Hubble Space Telescope, Gemini, and the Australia Telescope Compact Array, we found that at least six of our nine sources are best interpreted as SNRs. For one source, we do not have enough observational data to explain its linear morphology. Another source shows a nebular optical spectrum dominated by photoionization by O stars, but its excess [Fe ii] and radio luminosity suggest a possible hidden SNR. Finally, one source (S2) shows an elongated structure of ionized gas, two radio sources along that line, and an accretion-powered X-ray source in between them (the Chandra source L14-139). While S2 could be a chance alignment of multiple SNRs and one X-ray binary, it seems more likely that it is a single physical structure powered by the jet from the accreting compact object. In the latter case, the size and luminosity of S2 suggest a kinetic power of ∼1040 erg s−1, in the same class as the most powerful microquasars in the local universe (e.g., S26 in NGC 7793 and SS 433 in our own Galaxy).

USco1621 B and USco1556 B: Two wide companions at the deuterium-burning mass limit in Upper Scorpius

Aims. Our objective is to identify analogues of gas giant planets, but located as companions at wide separations of very young stars. The main purpose is to characterise the binarity frequency and the properties of these substellar objects, and to elucidate their early evolutionary stages. Methods. To identify these objects, we cross correlated the Visible and Infrared Survey Telescope for Astronomy Hemisphere Survey and the United Kingdom Infrared Telescope Infrared Deep Sky Survey Galactic Clusters Survey catalogues to search for common proper motion companions to 1195 already known members of Upper Scorpius (USco; age ~5–10 Myr, distance ~145 pc). We present the discovery and spectroscopic characterisation of two very wide substellar companions of two early-M stars in Upper Scorpius: USco1621 B and USco1556 B. We obtained optical and near-infrared low-resolution spectroscopy of the candidates to characterise their spectral energy distribution and confirm their youth and membership to the association. We also acquired adaptive optics images of the primaries and secondaries to search for signs of binarity and close companions. Results. By comparison with field dwarfs and other young members of USco, we determined a spectral type of M8.5 in the optical for both companions, along with L0 and L0.5 in the near-infrared for USco1621 B and USco1556 B, respectively. The spectra of the two companions show evident markers of youth, such as weak alkaline Na I and K I lines, along with the triangular shape of the H-band. The comparison with theoretical evolutionary models gives estimated masses of 0.015 ± 0.002 and 0.014 ± 0.002 M⊙, with temperatures of 2270 ± 90 and 2240 ± 100 K, respectively. The physical separations between the components of both systems are 2880 ± 20 and 3500 ± 40 AU for USco1621 and USco1556 systems, respectively. We did not find any additional close companion in the adaptive optics images. The probability that the two secondaries are physically bound to their respective primaries, and not chance alignments of USco members, is 86%, and the probability that none of them are physically related is 1.0%.

Clusters and mirages: cataloguing stellar aggregates in the Milky Way

Context. Many of the open clusters listed in modern catalogues were initially reported by visual astronomers as apparent overdensities of bright stars. As observational techniques and analysis methods continue to improve, some of them have been shown to be chance alignments of stars and not true clusters. Recent publications making use of Gaia DR2 data have provided membership lists for over a thousand clusters, however, many nearby objects listed in the literature have so far evaded detection. Aims. We aim to update the Gaia DR2 cluster census by performing membership determinations for known clusters that had been missed by previous studies and for recently-discovered clusters. We investigate a sub-set of non-detected clusters that, according to their literature parameters, should be easily visible in Gaia. Confirming or disproving the existence of old, inner-disc, high-altitude clusters is especially important as their survival or disruption is linked to the dynamical processes that drive the evolution of the Milky Way. Methods. We employed the Gaia DR2 catalogue and a membership assignment procedure, as well as visual inspections of spatial, proper motion, and parallax distributions. We used membership lists provided by other authors when available. Results. We derived membership lists for 150 objects, including ten that were already known prior to Gaia. We compiled a final list of members for 1481 clusters. Among the objects that we are still unable to identify with the Gaia data, we argue that many (mostly putatively old, relatively nearby, high-altitude objects) are not true clusters. Conclusions. At present, the only confirmed cluster located further than 500 pc away from the Galactic plane within the Solar circle is NGC 6791. It is likely that the objects discussed in this study only represent a fraction of the non-physical groupings erroneously listed in the catalogues as genuine open clusters and that those lists need further cleaning.

Compact groups from semi-analytical models of galaxy formation – I. A comparative study of frequency and nature

ABSTRACT Compact groups (CGs) of galaxies are defined as isolated and dense galaxy systems that appear to be a unique site of multiple galaxy interactions. Semi-analytical models (SAMs) of galaxy formation are a prime tool to understand CGs. We investigate how the frequency and the 3D nature of CGs depends on the SAM and its underlying cosmological parameters. Extracting nine light-cones of galaxies from five different SAMs and selecting CGs as in observed samples, we find that the frequency and nature of CGs depends strongly on the cosmological parameters. Moving from the WMAP1 to the WMAP7 and Planck cosmologies (increasing density of the Universe and decreasing normalization of the power spectrum), the space density of CGs is decreased by a factor 2.5, while the fraction of CGs that are physically dense falls from 50 to 35 per cent. The lower σ8 leads to fewer dense groups, while the higher Ωm causes more chance alignments. However, with increased mass and spatial resolution, the fraction of CGs that are physically dense is pushed back up to 50 per cent. The intrinsic differences in the SAM recipes also lead to differences in the frequency and nature of CGs, particularly those related to how SAMs treat orphan galaxies. We find no dependence of CG properties on the flux limit of the mock catalogues nor on the waveband in which galaxies are selected. One should thus be cautious when interpreting a particular SAM for the frequency and nature of CGs.

Globular cluster candidates in the Galactic bulge: Gaia and VVV view of the latest discoveries

Context. Thanks to the recent wide-area photometric surveys, the number of star cluster candidates have risen exponentially in the last few years. Most detections, however, are based only on the presence of an overdensity of stars in a given region or an overdensity of variable stars, regardless of their distance. As candidates, their detection has not been dynamically confirmed. Therefore, it is currently unknown how many and which of the published candidates are true clusters and which are chance alignments. Aims. We present a method to detect and confirm star clusters based on the spatial distribution, coherence in motion, and appearance on the color-magnitude diagram. We explain and apply this approach to one new star cluster and several candidate star clusters published in the literature. Methods. The presented method is based on data from the second data release of Gaia complemented with data from the VISTA Variables in the Vía Láctea survey for the innermost bulge regions. This method consists of a nearest neighbors algorithm applied simultaneously over spatial coordinates, star color, and proper motions to detect groups of stars that are close in the sky, move coherently, and define narrow sequences in the color-magnitude diagram, such as a young main sequence or a red giant branch. Results. When tested in the bulge area (−10 < ℓ (deg) < +10; −10 < b (deg) < +10) the method successfully recovered several known young and old star clusters. We report in this work the detection of one new, likely old star cluster, while deferring the others to a forthcoming paper. Additionally, the code has been applied to the position of 93 candidate star clusters published in the literature. As a result, only two of these clusters are confirmed as coherently moving groups of stars at their nominal positions.

Multiepoch Ultraviolet HST Observations of Accreting Low-mass Stars

Abstract Variability is a defining characteristic of young low-mass stars that are still accreting material from their primordial protoplanetary disk. Here we present the largest Hubble Space Telescope (HST) variability study of classical T Tauri stars (CTTS) to date. For five of these objects, we obtained a total of 25 spectra with the Space Telescope Imaging Spectrograph. Mass accretion rates and the fraction of the star covered by accretion columns (i.e., filling factors) were inferred using 1D NLTE physical models whose parameters were fit within a Bayesian framework. On week-long timescales, typical changes in the mass accretion rates range up to a factor of about two, while changes of up to a factor of about five are inferred for the filling factors. In addition to this, we observed a possible accretion burst in the transitional disk system GM Aur, and an incident we interpret as a chance alignment of an accretion column and the undisturbed photosphere along our line of sight in the full disk system VW Cha. We also measure correlations between mass accretion rate and line luminosities for use as secondary tracers of accretion. We place our objects in context with recent high-cadence photometric surveys of low-mass star formation regions and highlight the need for more broad-wavelength, contemporaneous data to better understand the physical mechanisms behind accretion variability in CTTS.

Open cluster kinematics with Gaia DR2 (Corrigendum)

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 that has 406 clusters, the median uncertainty of the weighted mean radial velocity is 0.5 km/s. The accuracy, assessed by comparison to ground-based high resolution spectroscopy, is better than 1 km/s. Open clusters nicely follow the velocity distribution of field stars in the close Solar neighbourhood 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. Clusters older than 1 Gyr span distances to the Galactic plane up to 1 kpc with a vertical velocity dispersion of 14 km/s, typical of the thin disc. Five pairs of clusters and one group with five members are possibly physically related. Other binary candidates previously identified turn out to be chance alignment.

On collision course: The nature of the binary star cluster NGC2006/SL 538

Context. The Large Magellanic Cloud (LMC) is known to be the host of a rich variety of star clusters of all ages. A large number of them is seen in close projected proximity. Ages have been derived for few of them showing differences up to few million years, hinting at being binary star clusters. However, final confirmation through spectroscopy measurements and dynamical analysis is needed. Aims. In the present work we focus on one of these LMC cluster pairs (NGC 2006–SL 538) and aim to determine whether the star cluster pair is a bound entity and, therefore, a binary star cluster or a chance alignment. Methods. We used the Magellan Inamori Kyocera Echelle (MIKE) high-resolution spectrograph on the 6.5 m Magellan-II Clay telescope at Las Campanas Observatory to acquire integrated-light spectra of the two clusters, measuring their radial velocities with individual absorption features and cross-correlation of each spectrum with a stellar spectral library. Results. We measured radial velocities by two methods: first by direct line-profile measurement yields νr = 300.3 ± 5 ± 6 km s−1 for NGC 2006 and νr = 310.2 ± 4 ± 6 km s−1 for SL 538. The second one is derived by comparing observed spectra with synthetic bootstrapped spectra yielding νr = 311.0 ± 0.6 km s−1 for NGC 2006 and νr = 309.4 ± 0.5 km s−1 for SL 538. Finally when spectra are directly compared, we find a Δν = 1.08 ± 0.47 km s−1. Full-spectrum spectral energy distribution fits reveal that the stellar population ages of both clusters lie in the range 13–21 Myr with a metallicity of Z = 0.008. We find indications for differences in the chemical abundance patterns as revealed by the helium absorption lines between the two clusters. The dynamical analysis of the system shows that the two clusters are likely to merge within the next ∼150 Myr to form a star cluster with a stellar mass of ∼104 M⊙. Conclusions. The NGC 2006–SL 538 cluster pair shows radial velocities, stellar population and dynamical parameters consistent with a gravitational bound entity and, considering that the velocity dispersion of the stars in LMC is ≲20 km s−1, we reject them as a chance alignment. We conclude that this is a genuine binary cluster pair, and we propose that their differences in ages and stellar population chemistry is most likely due to variances in their chemical enrichment history within their environment. We suggest that they may have formed in a loosely bound star-formation complex which saw initial fragmentation but then had its clusters become a gravitationally bound pair by tidal capture.

KIC 2568888: To Be or Not to Be a Binary

In cases where both components of a binary system show oscillations, asteroseismology has been proposed as a method to identify the system. For KIC 2568888, observed with $Kepler$, we detect oscillation modes for two red giants in a single power density spectrum. Through an asteroseismic study we investigate if the stars have similar properties, which could be an indication that they are physically bound into a binary system. While one star lies on the red giant branch (RGB), the other, more evolved star, is either a RGB or asymptotic-giant-branch star. We found similar ages for the red giants and a mass ratio close to 1. Based on these asteroseismic results we propose KIC 2568888 as a rare candidate binary system ($\sim 0.1\%$ chance). However, when combining the asteroseismic data with ground-based $BVI$ photometry we estimated different distances for the stars, which we cross-checked with $Gaia$ DR2. From $Gaia$ we obtained for one object a distance between and broadly consistent with the distances from $BVI$ photometry. For the other object we have a negative parallax with a not yet reliable $Gaia$ distance solution. The derived distances challenge a binary interpretation and may either point to a triple system, which could explain the visible magnitudes, or, to a rare chance alignment ($\sim 0.05\%$ chance based on stellar magnitudes). This probability would even be smaller, if calculated for close pairs of stars with a mass ratio close to unity in addition to similar magnitudes, which may indeed indicate that a binary scenario is more favourable.

Open cluster kinematics with Gaia DR2

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.

When nature tries to trick us

Bipolar planetary nebulae (PNe) are thought to result from binary star interactions and, indeed, tens of binary central stars of PNe have been found, in particular using photometric time-series that allow for the detection of post-common envelope systems. Using photometry at the NTT in La Silla we have studied the bright object close to the centre of PN M 3-2 and found it to be an eclipsing binary with an orbital period of 1.88 days. However, the components of the binary appear to be two A or F stars, of almost equal mass, and are therefore too cold to be the source of ionisation of the nebula. Using deep images of the central star obtained in good seeing conditions, we confirm a previous result that the central star is more likely much fainter, located 2″ away from the bright star. The eclipsing binary is thus a chance alignment on top of the planetary nebula. We also studied the nebular abundance and confirm it to be a Type I PN.

Discovery of X-Rays from the Old and Faint Pulsar J1154–6250

Abstract We report on the first X-ray observation of the 0.28 s isolated radio pulsar PSR J1154–6250 obtained with the XMM-Newton observatory in 2018 February. A point-like source is firmly detected at a position consistent with that of PSR J1154–6250. The two closest stars are outside the 3σ confidence limits of the source position and thus unlikely to be responsible for the observed X-ray emission. The energy spectrum of the source can be fitted equally well either with an absorbed power law with a steep photon index Γ ≈ 3.3 or with an absorbed blackbody with temperature kT = 0.21 ± 0.04 keV and emitting radius R BB ≈ 80 m (assuming a distance of 1.36 kpc). The X-ray luminosity of 4.4 × 1030 erg s−1 derived with the power-law fit corresponds to an efficiency of , similar to those of other old pulsars. The X-ray properties of PSR J1154–6250 are consistent with an old age and suggest that the spatial coincidence of this pulsar with the OB association Cru OB1 is due to a chance alignment.

A distant sample of halo wide binaries from SDSS

Samples of reliably identified halo wide binaries are scarce. If reasonably free from selection effects and with a small degree of contamination by chance alignments, these wide binaries become a powerful dynamical tool, having provided one of the very few experiments capable of constraining the nature of dark matter in the Milky Way halo. Currently, however, the best available sample of halo wide binaries is confined to the solar neighborhood, and is plagued by small number statistics at the widest separations. We present the results of a program aimed to probe the wide binary population of the Galactic halo at significantly larger distances, and which informs future searches that could improve the statistics by orders of magnitude. Halo stars were taken from the Sloan Digital Sky Survey after analysing the Galactic orbits of stars in the reduced proper motion diagram. We then select candidate binaries by searching for pairs with small differences in proper motion and small projected separation on the sky. Using medium-resolution spectroscopy, a subsample of candidates is validated via radial velocities, finding that about 68\% of candidate pairs up to 20$^{\prime\prime}$ separation can be considered genuine halo wide binaries, to the limits of the available data. Precise parallaxes from \textit{Gaia} confirm that most of our selected pairs have their components at the same distances, independently confirming the robustness of our selection method. These results should prove valuable to guide the optimal assembly of larger catalogs of halo wide binaries from upcoming large databases, e.g., \textit{Gaia} and LSST.

On the identification of wide binaries in the Kepler field

We perform a search for wide binaries in the Kepler field with the prospect of providing new constraints for gyrochronology. First, we construct our base catalog by compiling astrometry for the stars observed by Kepler, and supplement it with parallaxes, radial velocities (RVs), and metallicities. We then mine our base catalog for wide binary candidates by matching the stars' proper motions, as well as parallaxes, RVs, and metallicities, if available. We mitigate the presence of chance alignments among our candidates by performing a comprehensive data-based contamination analysis in the proper motion versus angular separation phase space. Our final sample contains 55 binary candidates. A crossmatch of our pairs with the Second Data Release (DR2) from Gaia validates our candidates and confirms the reliability of our search method, particularly for $\varpi \gtrsim 2$ mas. Due to the implicit Kepler selection function and image scale per pixel, our binary search is incomplete for angular separations of less than 20 arcsec. We crossmatch our candidates with rotation period and asteroseismic ages catalogs, and find that our binary candidates do not follow a simple period-color relation, in agreement with previous studies. Two pairs have an age estimate for one component star and rotation period for its companion, positioning them as potentially new gyrochronology constraints at old ages. This is the first study that uses RVs and metallicities as criteria, rather than as a confirmation, in a binary search.

The first VLBI detection of a spiral DRAGN core

Abstract We present the first observation of 0313−192, the archetypal spiral DRAGN, at very long baseline interferometry (VLBI) resolutions. Spiral DRAGNs are Double-lobed Radio sources Associated with Galactic Nuclei (DRAGNs) that are hosted by spiral galaxies. 0313−192 is an edge-on spiral galaxy that appears to host a 360 kpc double-lobed radio source. The core of this galaxy is clearly detected at L, S, and X bands using the Very Long Baseline Array, signifying an ongoing active nucleus in the galaxy. This rules out the possibility that the spiral DRAGN is merely a chance alignment. The radio core has L1.4 GHz ∼ 3.0 × 1023 W Hz−1. Radio components are detected to the south-west of the core, but there are no detections of a counterjet. Assuming a symmetric, relativistic jet, we estimate an upper limit to the inclination angle of θ ≲ 72 deg. The VLBI-detected radio jet components are extremely well aligned with the larger scale radio source suggesting little to no jet disruption or interaction with the interstellar medium of the host galaxy.

New nearby white dwarfs from Gaia DR1 TGAS and UCAC5/URAT

Aims. Using an accurate Tycho-Gaia Astrometric Solution (TGAS) 25 pc sample that is nearly complete for GK stars and selecting common proper motion (CPM) candidates from the 5th United States Naval Observatory CCD Astrograph Catalog (UCAC5), we search for new white dwarf (WD) companions around nearby stars with relatively small proper motions. Methods. To investigate known CPM systems in TGAS and to select CPM candidates in TGAS+UCAC5, we took into account the expected effect of orbital motion on the proper motion and proper motion catalogue errors. Colour-magnitude diagrams (CMDs) MJ ∕J − Ks and MG ∕G − J were used to verify CPM candidates from UCAC5. Assuming their common distance with a given TGAS star, we searched for candidates that occupied similar regions in the CMDs as the few known nearby WDs (four in TGAS) and WD companions (three in TGAS+UCAC5). The CPM candidates with colours and absolute magnitudes corresponding neither to the main sequence nor to the WD sequence were considered as doubtful or subdwarf candidates. Results. With a minimum proper motion of 60 mas yr−1, we selected three WD companion candidates; two of which are also confirmed by their significant parallaxes measured in URAT data, whereas the third may also be a chance alignment of a distant halo star with a nearby TGAS star that has an angular separation of about 465 arcsec. One additional nearby WD candidate was found from its URAT parallax and GJKs photometry. With HD 166435 B orbiting a well-known G1 star at ≈24.6 pc with a projected physical separation of ≈700 AU, we discovered one of the hottest WDs, classified by us as DA2.0 ± 0.2, in the solar neighbourhood. We also found TYC 3980-1081-1 B, a strong cool WD companion candidate around a recently identified new solar neighbour with a TGAS parallax corresponding to a distance of ≈8.3 pc and our photometric classification as ≈M2 dwarf. This raises the question of whether previous assumptions on the completeness of the WD sample to a distance of 13 pc were correct.