Precise Astrometric Measurements Research Articles

A Novel Preparation Approach for Supervised ML Membership Determination of Open Clusters

Machine Learning methods have emerged as powerful tools for analyzing stellar clusters, which pose significant challenges. techniques such as DBSCAN and GMM have advanced remarkably in this domain. However, these clustering techniques exhibit imperfections and limitations, highlighting the need for careful data tuning and consideration of data characteristics to ensure meaningful result. The utilization of supervised Machine Learning techniques for membership determination of the stellar clusters, especially open clusters, can lead to more accurate results. However, the absence of dataset for training on an open cluster presents a significant hurdle. To address the problem, we’ve introduced a novel approach to generate a labeled dataset for training the super- vised Machine Learning models. Our approach leverages data from Gaia DR3 Catalog, which provides precise astrometric and photometric measurements for millions stars in Milky Way, to construct a comprehensive dataset. Our findings have significant implications for future astronomical research. By using Supervised machine learning techniques, we can achieve more accurate and efficient membership determination for stellar clusters, which can lead to a better understanding of the formation and evolution of galaxies. Our method not only enhances the accuracy of membership determination but also provides insights into the underlying data characteristics that influence cluster analysis.

A New Tidal Stream Discovered in Gaia DR3

Thanks to the precise astrometric measurements of proper motions by the Gaia mission, a new tidal stellar stream has been discovered in the northern hemisphere. The distribution of star count shows that the stream is approximately 80° long and 1.°70 wide. Observations of 21 member stars, including 14 RR Lyrae stars, indicate that the stream has an eccentric and retrograde orbit with e = 0.58. The low metallicity, high total energy, and large angular momentum suggest that it is associated with the merging event Sequoia. This discovery suggests the possibility of finding more substructures with high eccentricity orbits, even in the inner halo.

OGLE-2014-BLG-0221Lb: A Jupiter Mass Ratio Companion Orbiting Either a Late-type Star or a Stellar Remnant

We present the analysis of the microlensing event OGLE-2014-BLG-0221, a planetary candidate event discovered in 2014. The photometric light curve is best described by a binary-lens single-source model. Our light-curve modeling finds two degenerate models, with event timescales of t E ∼ 70 days and ∼110 days. These timescales are relatively long, indicating that the discovered system would possess a substantial mass. The two models are similar in their planetary parameters with a Jupiter mass ratio of q ∼ 10−3 and a separation of s ∼ 1.1. Bayesian inference is used to estimate the physical parameters of the lens, revealing that the shorter timescale model predicts 65% and 25% probabilities of a late-type star and white dwarf host, respectively, while the longer timescale model favors a black hole host with a probability ranging from 60% to 95%, under the assumption that stars and stellar remnants have equal probabilities of hosting companions with planetary mass ratios. If the lens is a remnant, this would be the second planet found by microlensing around a stellar remnant. The current separation between the source and lens stars is 41–139 mas depending on the models. This indicates the event is now ready for high-angular-resolution follow-up observations to rule out either of the models. If precise astrometric measurements are conducted in multiple bands, the centroid shift due to the color difference between the source and lens would be detected in the luminous lens scenario.

Fuzzy dark matter dynamics in tidally perturbed dwarf spheroidal galaxy satellites

Fuzzy dark matter (FDM) has dynamical properties that differ significantly from cold dark matter (CDM).These dynamical differences are strongly manifested on the spatial scale of dwarf spheroidal galaxies (dSphs), which roughly corresponds to the de Broglie wavelength of a canonical mass FDM particle.We study simulations of a dSph satellite which is tidally perturbed by its host galaxy, in order to identify dynamical signatures that are unique to FDM, and to quantify the imprints of such perturbations on an observable stellar tracer population.We find that a perturbed FDM soliton develops a long-standing breathing mode, whereas for CDM such a breathing mode quickly phase-mixes and disappears. We also demonstrate that such signatures become imprinted on the dynamics of a stellar tracer population, making them observable with sufficiently precise astrometric measurements.

VLA proper motion constraints on the origin, age, and potential magnetar future of PSR J1734−3333

Context.The characteristic age of PSR J1734−3333 estimated from its current spin down rate implies that it is a young pulsar (τc = 8.1 kyr). However, the time derivative of its spin-down rate differs markedly from that assumed for normal radio pulsars, meaning its actual age is uncertain. G354.8−0.8 is a supernova remnant (SNR) whose centre is located 21′ away from the pulsar, and which has a morphology that suggests an association with the pulsar.Aims.We aim to assess the likelihood of the association between PSR J1734−3333 and G354.8−0.8 or other nearby SNRs quantitatively, with the objective of shedding light on the real age of this pulsar.Methods.Observations with the Karl G. Jansky Very Large Array were carried out in 2015 and 2019 that allow precise astrometric measurements and consequently a proper motion estimate for the pulsar.Results.The proper motion was found to beμα = 10 ± 10 mas yr−1andμδ = −29 ± 11 mas yr−1(error bars are 1-σ). Though marginal, this detection rules out the association with G354.8−0.8 because it means the pulsar is not moving away from the centre of the SNR. No SNR consistent with the measured proper motion and an ageτccould be found. We also present the first measurement of the spectral index for this pulsar,α = −1.1 ± 0.3, measured between 1.5 and 3.0 GHz.Conclusions.The SNR produced by the birth supernova of PSR J1734−3333 could have already faded to undetectable brightness, estimates of which suggest timescales of 10 − 100 kyr. This and other considerations lead us to conclude that the pulsar is possibly older than 45 − 100 kyr. PSR J1734−3333 is a pulsar with rotational properties that place it between standard radio pulsars and magnetars, and we interpret our result in the context of a possible future life as a magnetar for this pulsar.

22Ne Phase Separation as a Solution to the Ultramassive White Dwarf Cooling Anomaly

Abstract The precise astrometric measurements of the Gaia Data Release 2 have opened the door to detailed tests of the predictions of white dwarf cooling models. Significant discrepancies between theory and observations have been identified, the most striking affecting ultramassive white dwarfs. Cheng et al. found that a small fraction of white dwarfs on the so-called Q branch must experience an extra cooling delay of ∼8 Gyr not predicted by current models. 22Ne phase separation in a crystallizing C/O white dwarf can lead to a distillation process that efficiently transports 22Ne toward its center, thereby releasing a considerable amount of gravitational energy. Using state-of-the-art Monte Carlo simulations, we show that this mechanism can largely resolve the ultramassive cooling anomaly if the delayed population consists of white dwarfs with moderately above-average 22Ne abundances. We also argue that 22Ne phase separation can account for the smaller cooling delay currently missing for models of white dwarfs with more standard compositions.

Astrometric errors introduced by interpixel capacitive coupling in hybridized arrays

Interpixel capacitance (IPC) between adjacent pixels in hybridized arrays gives rise to an electrostatic cross talk. This cross talk causes MTF degradation and blurring of images or spectra collected using these devices. As pixel size is driven down from the 18-μm pixel pitch of the H2RG read out circuits to the 10- or 15-μm H4RGs IPC is driven up resulting in greater cross talk, all else being equal. Mounting evidence indicates that IPC varies as a function of depletion state of the photo-active diodes. For single pixel events, increasing the event intensity corresponds to a decreasing fractional coupling. If left uncorrected, IPC can give rise to systematic errors in precision astrometric and photometric measurements, in particular when dealing with confused point sources or spatially extended structures for shape measurements as demonstrated through comparison of registered sources from ESO HAWK-I and HST ACS WFC datasets. Furthermore, these errors will be the most significant when operating near the sensitivity limit of these devices. Deconvolution-based correction methods are invalidated by this same signal dependence. Instead, a numerical method of successive approximation can be used to correct coupling due to a well-characterized IPC. Examination of single pixel reset data above flat fields could be used to characterize IPC’s functional relationship for neighboring pixels. This higher quality characterization can result in more accurate correction.

Weighing the Darkness: Astrometric Mass Measurement of Hidden Stellar Companions Using Gaia

Abstract In astrometric binaries, the presence of a dark, unseen star can be inferred from the gravitational pull it induces on its luminous binary companion. While the orbit of such binaries can be characterized with precise astrometric measurements, constraints made from astrometry alone are not enough to measure the component masses. In this work, we determine the precision with which Gaia can astrometrically measure the orbits and—with additional observations—the component masses, for luminous stars hosting hidden companions. Using realistic mock Gaia observations, we find that Gaia can precisely measure the orbits of binaries hosting hidden brown dwarfs out to tens of parsecs and hidden white dwarf and neutron star companions at distances as far as several hundred parsecs. Heavier black hole companions may be measured out to 1 kpc or farther. We further determine how orbital period affects this precision, finding that Gaia can characterize orbits with periods as short as 10 days and as long as a few 103 days, with the best measured orbits having periods just short of Gaia’s mission lifetime. Extending Gaia’s nominal five-year mission lifetime by an additional five years not only allows for the measurement of longer period orbits, but those longer period binaries can be seen at even greater distances.

Post-linear metric of a compact source of matter

The Multipolar Post-Minkowskian (MPM) formalism represents an approach for determining the metric density in the exterior of a compact source of matter. In the MPM formalism the metric density is given in harmonic coordinates and in terms of symmetric tracefree (STF) multipoles. In this investigation, the post-linear metric density of this formalism is used in order to determine the post-linear metric tensor in the exterior of a compact source of matter. The metric tensor is given in harmonic coordinates and in terms of STF multipoles. The post-linear metric coefficients are associated with an integration procedure. The integration of these post-linear metric coefficients is performed explicitly for the case of a stationary source, where the first multipoles (monopole and quadrupole) of the source are taken into account. These studies are a requirement for further investigations in the theory of light propagation aiming at highly precise astrometric measurements in the solar system, where the post-linear coefficients of the metric tensor of solar system bodies become relevant.

Astrometric and photometric study of NGC 6067, NGC 2506, and IC 4651 open clusters based on wide-field ground and Gaia DR2 data

ABSTRACT We present an analysis of three southern open star clusters NGC 6067, NGC 2506, and IC 4651 using wide-field photometric and Gaia DR2 astrometric data. They are poorly studied clusters. We took advantage of the synergy between Gaia DR2 high precision astrometric measurements and ground-based wide-field photometry to isolate cluster members and further study these clusters. We identify the cluster members using proper motions, parallax and colour–magnitude diagrams. Mean proper motion of the clusters in μαcosδ and μδ is estimated as −1.90 ± 0.01 and −2.57 ± 0.01 mas yr−1 for NGC 6067, −2.57 ± 0.01, and 3.92 ± 0.01 mas yr−1 for NGC 2506 and −2.41 ± 0.01 and −5.05 ± 0.02 mas yr−1 for IC 4651. Distances are estimated as 3.01 ± 0.87, 3.88 ± 0.42, and 1.00 ± 0.08 kpc for the clusters NGC 6067, NGC 2506, and IC 4651, respectively, using parallaxes taken from Gaia DR2 catalogue. Galactic orbits are determined for these clusters using Galactic potential models. We find that these clusters have circular orbits. Cluster radii are determined as 10 arcmin for NGC 6067, 12 arcmin for NGC 2506, and 11 arcmin for IC 4651. Ages of the clusters estimated by isochrones fitting are 66 ± 8 Myr, 2.09 ± 0.14 Gyr, and 1.59 ± 0.14 Gyr for NGC 6067, NGC 2506, and IC 4651, respectively. Mass function slope for the entire region of cluster NGC 2506 is found to be comparable with the Salpeter value in the mass range of 0.77–1.54 M⊙. The mass function analysis shows that the slope becomes flat when one goes from halo to core region in all the three clusters. A comparison of dynamical age with cluster’s age indicates that NGC 2506 and IC 4651 are dynamically relaxed clusters.

Measuring the Yarkovsky effect with Las Cumbres Observatory

The Las Cumbres Observatory (LCOGT) provides an ideal platform for follow-up and characterization of Solar System objects (e.g. asteroids, Kuiper belt objects (KBOs), comets, and near-Earth objects (NEOs)) as well as for the discovery of new objects. The LCOGT network allows for regular monitoring of a sample of targets, such as that of NEOs for which we can attempt to measure the Yarkovsky effect. We have used LCOGT’s global network of nine 1.0-m telescopes to measure the Yarkovsky effect on 36 asteroids through precise astrometric measurements using the Gaia-DR1 catalog; 18 (50%) of the 36 asteroids yielded > 3σ Yarkovsky detections. The target asteroids were selected through simulated observations each month to determine the objects for which new astrometry would yield the highest likelihood of a Yarkovsky detection. The Gaia-DR1 release has greatly improved the quality of the astrometry obtained, making the detection of the Yarkovsky effect more likely and secure by greatly reducing systematic catalog zonal errors. LCOGT is ideally suited to perform these observations due to its ability to monitor many targets over several days by employing dynamic scheduling, weather avoidance, and use of multiple sites around the globe.

Prediction of astrometric microlensing events from Gaia DR2 proper motions

Context. Astrometric gravitational microlensing is an excellent tool to determine the mass of stellar objects. Using precise astrometric measurements of the lensed position of a background source in combination with accurate predictions of the positions of the lens and the unlensed source it is possible to determine the mass of the lens with an accuracy of a few percent. Aims. Making use of the recently published Gaia Data Release 2 (DR2) catalogue, we want to predict astrometric microlensing events caused by foreground stars with high proper motion passing a background source in the coming decades. Results. We selected roughly 148 000 high-proper-motion stars from Gaia DR2 with μtot > 150 mas yr−1 as potential lenses. We then searched for background sources close to their paths. Using the astrometric parameters of Gaia DR2, we calculated the future positions of source and lens. With a nested-intervals algorithm we determined the date and separation of the closest approach. Using Gaia DR2 photometry we determined an approximate mass of the lens, which we used to calculate the expected microlensing effects. Conclusions. We predict 3914 microlensing events caused by 2875 different lenses between 2010 and 2065, with expected shifts larger than 0.1 mas between the lensed and unlensed positions of the source. Of those, 513 events are expected to happen between 2014.5 and 2026.5 and might be measured by Gaia. For 127 events we also expect a magnification between 1 mmag and 3 mag.

MultiView High Precision VLBI Astrometry at Low Frequencies

AbstractObservations at low frequencies (<8GHz) are dominated by distinct direction dependent ionospheric propagation errors, which place a very tight limit on the angular separation of a suitable phase referencing calibrator and astrometry. To increase the capability for high precision astrometric measurements an effective calibration strategy of the systematic ionospheric propagation effects that is widely applicable is required. The MultiView technique holds the key to the compensation of atmospheric spatial-structure errors, by using observations of multiple calibrators and two dimensional interpolation. In this paper we present the first demonstration of the power of MultiView using three calibrators, several degrees from the target, along with a comparative study of the astrometric accuracy between MultiView and phase-referencing techniques. MultiView calibration provides an order of magnitude improvement in astrometry with respect to conventional phase referencing, achieving ~100micro-arcseconds astrometry errors in a single epoch of observations, effectively reaching the thermal noise limit.

Microlensing Constraints on the Mass of Single Stars from HST Astrometric Measurements*

Abstract We report on the first results from a large-scale observing campaign aiming to use astrometric microlensing to detect and place limits on the mass of single objects, including stellar remnants. We used the Hubble Space Telescope to monitor stars near the Galactic Center for three years, and we measured the brightness and positions of ∼2 million stars at each observing epoch. In addition to this, we monitored the same pointings using the VIMOS imager on the Very Large Telescope. The stars we monitored include several bright microlensing events observed from the ground by the OGLE collaboration. In this paper, we present the analysis of our photometric and astrometric measurements for six of these events, and derive mass constraints for the lens in each of them. Although these constraints are limited by the photometric precision of ground-based data, and our ability to determine the lens distance, we were able to constrain the size of the Einstein ring radius thanks to our precise astrometric measurements—the first routine measurements of this type from a large-scale observing program. This demonstrates the power of astrometric microlensing as a tool to constrain the masses of stars, stellar remnants, and, in the future, extrasolar planets, using precise ground- and space-based observations.

Image Restoration Based on Statistic PSF Modeling for Improving the Astrometry of Space Debris

Space debris is a special kind of fast-moving, near-Earth objects, and it is also considered to be an interesting topic in time-domain astronomy. Optical survey is the main technique for observing space debris, which contributes much to the studies of space environment. However, due to the motion of registered objects, image degradation is critical in optical space debris observations, as it affects the efficiency of data reduction and lowers the precision of astrometry. Therefore, the image restoration in the form of deconvolution can be applied to improve the data quality and reduction accuracy. To promote the image processing and optimize the reduction, the image degradation across the field of view is modeled statistically with principal component analysis and the efficient mean point-spread function (PSF) is derived from raw images, which is further used in the image restoration. To test the efficiency and reliability, trial observations were made for both low-Earth orbital and high-Earth orbital objects. The positions of all targets were measured using our novel approach and compared with the reference positions. The performance of image restoration employing our estimated PSF was compared with several competitive approaches. The proposed image restoration outperformed the others so that the influence of image degradation was distinctly reduced, which resulted in a higher signal-to-noise ratio and more precise astrometric measurements.

MultiView High Precision VLBI Astrometry at Low Frequencies

Abstract The arrival of the Square Kilometer Array (SKA) will revitalize all aspects of Very Long Baseline Interferometry (VLBI) astronomy at lower frequencies. In the last decade, there have been huge strides toward routinely achieving high precision VLBI astrometry at frequencies dominated by tropospheric contributions, most notably at 22 GHz, using advanced phase-referencing techniques. Nevertheless, to increase the capability for high precision astrometric measurements at low radio frequencies (<8 GHz), an effective calibration strategy of the systematic ionospheric propagation effects that is widely applicable is required. Observations at low frequencies are dominated by distinct direction-dependent ionospheric propagation errors, which place a very tight limit on the angular separation of a suitable phase-referencing calibrator. The MultiView technique holds the key to compensating for atmospheric spatial-structure errors, by using observations of multiple calibrators and two-dimensional interpolation in the visibility domain. In this paper we present the first demonstration of the power of MultiView using three calibrators, several degrees from the target, along with a comparative study of the astrometric accuracy between MultiView and phase-referencing techniques. MultiView calibration provides an order of magnitude improvement in astrometry with respect to conventional phase referencing, achieving ∼100 μas astrometry errors in a single epoch of observations, effectively reaching the thermal noise limit. MultiView will achieve its full potential with the enhanced sensitivity and multibeam capabilities of SKA and the pathfinders, which will enable simultaneous observations of the target and calibrators. Our demonstration indicates that the 10 μas goal of astrometry at ∼1.6 GHz using VLBI with SKA is feasible using the MultiView technique.

Spectrophotometric variability of quasars caused by lensing of diffuse massive substructure: consequences on flux anomaly and precise astrometric measurements

We investigate the spectro-photometric variability of quasars due to lensing of small mass substructure (from several tens to several hundreds solar masses). The aim of this paper is to explore the milli/microlensing influence on the flux anomaly observed between images of a lensed quasar in different spectral bands and possible influence of small mass structure lensing of non-macrolensed quasars.We find that spectro-photometric variability may be also caused by lensing of small mass diffuse structure and can produce the flux anomaly which is sometimes seen in different images of a lensed quasar. Additionally, we found that the lensing by small mass diffuse structure may produce significant changes in photo-center position of a quasar, and sometimes can split or deviate images of one source that can be detected as separate from the scale from 0.1 to several milliarcseconds. This can be measured ith Gaialike space astrometric missions. We point out a special case where a low redshifted deflector zd = 0.01 is lensing a high redshifted source, for which the variability in the flux and photocenter (several milliarcseconds) may be detected on a relatively short time scale.

A very long baseline interferometry detection of the class I protostar IRS 5 in Corona Australis

Aims: Very Long Baseline Interferometry yields physical constraints on the compact radio emission of young stellar objects. At the same time, such measurements can be used for precise astrometric measurements of parallaxes and proper motions. Here, we aimed to make the first detections of very compact radio emission from class I protostars in the Corona Australis star-forming region. Methods: We have used the Long Baseline Array (LBA) to observe the protostars IRS 5 and IRS 7 in the Corona Australis star-forming region in three separate epochs Results: We report the first firm radio detection of a class I protostar using very long baseline interferometry. We have detected the previously known non-thermal source IRS 5b, part of a binary system. IRS 5a and IRS 5N were undetected, as were all sources in the IRS 7 region. Conclusions: These results underline the unusual nature of IRS 5b as a genuine protostar with confirmed non-thermal radio emission. Also, these observations highlight the potential of the LBA as a tool to provide precision astrometric measurements of individual young stellar objects in southern star-forming regions that are not accessible to the Very Long Baseline Array in the northern hemisphere.

GJ 1214 reviewed

GJ 1214 is orbited by a transiting super-Earth-mass planet. It is a primary target for ongoing efforts to understand the emerging population of super-Earth-mass planets around M dwarfs. We present new precision astrometric measurements, a re-analysis of HARPS radial velocity measurements, and medium-resolution infrared spectroscopy of GJ 1214. We combine these measurements with recent transit follow-up observations and new catalog photometry to provide a comprehensive update of the star-planet properties. The distance is obtained with 0.6% relative uncertainty using CAPScam astrometry. The new value increases the nominal distance to the star by ~10% and is significantly more precise than previous measurements. Updated Doppler measurements combined with published transit observations significantly refine the constraints on the orbital solution. The analysis of the infrared spectrum and photometry confirm that the star is enriched in metals compared to the Sun. Using all this information, combined with empirical mass-luminosity relations for low mass stars, we derive updated values for the bulk properties of the star-planet system. We also use infrared absolute fluxes to estimate the stellar radius and to re-derive the star-planet properties. Both approaches provide very consistent values for the system. Our analysis shows indicates that the favoured mean density of GJ 1214b is 1.6 +/-0.6 g cm^{-3}. We illustrate how fundamental properties of M dwarfs are of paramount importance in the proper characterization of the low mass planetary candidates orbiting them. Given that the distance is now known to better than 1%, interferometric measurements of the stellar radius, additional high precision Doppler observations, and/or or detection of the secondary transit (occultation), are necessary to further improve the constraints on the GJ 1214 star-planet properties.

Asymptotic solutions for the case of nearly symmetric gravitational lens systems

Gravitational lensing provides a powerful tool to determine the Hubble parameter H0 from the measurement of the time delay Δt between two lensed images of a background variable source. Nevertheless, knowledge of the deflector mass distribution constitutes a hurdle. We propose in the present work interesting solutions for the case of nearly symmetric gravitational lens systems. For the case of a small misalignment between the source, the deflector and the observer, we first consider power-law (ɛ) axially symmetric models for which we derive an analytical relation between the amplification ratio and source position which is independent of the power-law slope ɛ. According to this relation, we deduce an expression for H0 also irrespective of the value ɛ. Secondly, we consider the power-law axially symmetric lens models with an external large-scale gravitational field, the shear γ, resulting in the so-called ɛ−γ models, for which we deduce simple first-order equations linking the model parameters and the lensed image positions, the latter being observable quantities. We also deduce simple relations between H0 and observables quantities only. From these equations, we may estimate the value of the Hubble parameter in a robust way. Nevertheless, comparison between the ɛ−γ and singular isothermal ellipsoid (SIE) models leads to the conclusion that these models remain most often distinct. Therefore, even for the case of a small misalignment, use of the first-order equations and precise astrometric measurements of the positions of the lensed images with respect to the centre of the deflector enables one to discriminate between these two families of models. Finally, we confront the models with numerical simulations to evaluate the intrinsic error of the first-order expressions used when deriving the model parameters under the assumption of a quasi-alignment between the source, the deflector and the observer. From these same simulations, we estimate for the case of the ɛ−γ family of models that the standard deviation affecting H0 is which merely reflects the adopted astrometric uncertainties on the relative image positions, typically arcsec. In conclusions, we stress the importance of getting very accurate measurements of the relative positions of the multiple lensed images and of the time delays for the case of nearly symmetric gravitational lens systems, in order to derive robust and precise values of the Hubble parameter.