Gaia DR2 Catalogue Research Articles

Star-Identification System Based on Polygon Recognition

Accurate attitude determination is crucial for satellites and spacecraft. Among attitude determination devices, star sensors are the most accurate. Solving the lost-in-space problem is the most critical function of the star sensor. Our research introduces a novel star-identification system that utilizes a polygon-recognition algorithm to assign a unique complex number to polygons created by stars. This system aims to solve the lost-in-space problem. Our system includes a full solution with a lens, image sensor, processing unit, and algorithm implementation. To test the system’s performance, we analyzed 100 night sky images that resembled what a real star sensor in orbit would experience. We used a k-d tree algorithm to accelerate the search in the star catalog of complex numbers. We implemented various verification methods, including internal polygon verification and a voting mechanism, to ensure the system’s reliability. We obtained the star database used as a reference from the Gaia DR2 catalog, which we filtered, to eliminate irrelevant stars, and which we arranged by apparent magnitude. Despite manually introducing up to three false stars, the system successfully identified at least one star in 97% of the analyzed images.

Изучение структуры и кинематики Галактики по рассеянным звездным скоплениям и ассоциациям в эпоху Gaia

This article is a review, written on the basis of previously published results. It examines the main kinematic and spatial properties of the open star clusters (OCs) of the Galaxy. The results of determining the parameters of galactic rotation are described, which are obtained using the most up-to-date kinematic data on stars. Obtained, in particular, according to the Gaia DR2 and Gaia EDR3 catalogs. The results of the analysis of the residual, freed from the influence of the peculiar motion of the Sun and the rotation of the Galaxy, the velocities of the OCs are reflected. It is described about the manifestation of the galactic spiral density wave in the residual velocities of the OCs. The results of various authors are described, who have found out i) how the variance of the residual velocities of the OCs depends on their age, ii) what are the dispersions of the velocities of OB associations and their structural components, iii) what are the dispersions of the residual velocities of stars inside the OCs themselves.

New members of the Lupus I cloud based on Gaia astrometry

We characterize twelve young stellar objects (YSOs) located in the Lupus I region, spatially overlapping with the Upper Centaurus Lupus (UCL) sub-stellar association. The aim of this study is to understand whether the Lupus I cloud has more members than what has been claimed so far in the literature and gain a deeper insight into the global properties of the region. We selected our targets using the Gaia DR2 catalog based on their consistent kinematic properties with the Lupus I bona fide members. In our sample of twelve YSOs observed by X-shooter, we identified ten Lupus I members. We could not determine the membership status of two of our targets, namely Gaia DR2 6014269268967059840 and 2MASS J15361110-3444473 due to technical issues. We found out that four of our targets are accretors, among them, 2MASS J15551027-3455045, with a mass of ∼0.03 M⊙, is one of the least massive accretors in the Lupus complex identified to date. Several of our targets (including accretors) are formed in situ and off-cloud with respect to the main filaments of Lupus I; hence, our study may hint that there are diffused populations of M dwarfs around Lupus I main filaments. In this context, we would like to emphasize that our kinematic analysis with Gaia catalogs played a key role in identifying the new members of the Lupus I cloud.

Superflares on solar-like stars

Context. Over the past years, thousands of stellar flares have been detected by harvesting data from large photometric surveys. These detections, however, do not account for potential sources of contamination such as background stars or small Solar System objects appearing in the same aperture as the primary target. Aims. We present a new method for identifying the true flare sources in large photometric surveys using data from the Kepler mission as an illustrative example. The new method considers not only the brightness excess in the stellar light curves, but also the location of this excess in the pixel-level data. Methods. Potential flares are identified in two steps. First, we search the light curves for at least two subsequent data points exceeding a 5σ threshold above the running mean. For these two cadences, we subtract the “quiet” stellar flux from the Kepler pixel data to obtain new images where the potential flare is the main light source. In the second step, we use a Bayesian approach to fit the point spread function of the instrument to determine the most likely location of the flux excess on the detector. We match this location with the position of the primary target and other stars from the Gaia DR2 catalog within a radius of 10 arcsec around the primary Kepler target. When the location of the flux excess and the target star coincide, we associate the event with a flare on the target star. Results. We applied our method to 5862 main-sequence stars with near-solar effective temperatures. From the first step we found 2274 events exceeding the 5σ level in at least two consecutive points in the light curves. Applying the second step reduced this number to 342 superflares. Of these, 283 flares occurred on 178 target stars and 47 events are associated with fainter background stars; in 10 cases the flare location could not be distinguished between the target and a background star. We also present cases where flares were reported previously but our technique could not attribute them to the target star. Conclusions. We conclude that identifying outliers in the light curves alone is insufficient to attribute them to stellar flares and that flares can only be uniquely attributed to a certain star when the instrument pixel-level data together with the point spread function are taken into account. As a consequence, previous flare statistics are likely contaminated by instrumental effects and unresolved astrophysical sources.

Новый каталог орбит 152 галактических шаровых скоплений по данным Gaia EDR3

This paper provides a new catalog of orbits and their parameters for a practically complete list of currently known galactic globular clusters (GCs), compiled by Vasiliev (2019) based on the most accurate modern measurements of their velocities and positions. The integration of the orbits of 152 globular clusters for 5 Gyr was performed using the new average proper motions obtained from the Gaia EDR3 catalog (Vasiliev and Baumgardt, 2021) and new average distances (Baumgardt and Vasiliev, 2021) in the axisymmetric three-component potential with spherical bulge, disk component, and spherical dark Navarro-Frank-White halo (Bajkova and Bobylev, 2016). The new orbital parameters are compared with the orbital parameters constructed by us earlier (Bajkova and Bobylev, 2021) in the same gravitational potential using proper motions obtained from the Gaia DR2 catalog (Vasiliev, 2019) and with the distances from the Harris catalog (2010).

Орбиты визуально-двойных и кратных звезд, полученные методом параметров видимого движения в течение последних 40 лет

Summed many years of work at Pulkovo, the orbits of 67 wide pairs of visual double and multiple stars (included in 64 systems) which were obtained by the Apparent Motion Parameters (AMP) method are presented. This short arc orbit determination method uses the most reliable astrometric and astrophysical data corresponding to one instant of time. The rest of the observations accumulated in the world serve to control the quality of the orbit and refine some parameters. All early determined AMP-orbits were compared with new observations, part of them recalculated, new orbits added. For the stars of Pulkovo program of observations with a 26-inch refractor, the data from the Gaia DR2 catalog were analised. The orbits of 16 stars were calculated on these data. The direction of the motion derived from Gaia DR2 at the instant 2015.5 contradicts to the series of all observations for 20 stars. The probable reason is in the presence of inner subsystems. The orientation of the obtained orbits in the Galaxy frame is also given.

MOCK OBSERVATIONS OF SIMULATED STAR CLUSTER ON SOLAR ORBIT

With the advent of the Gaia DR2 catalog, which contains astrometric and photometric parameters for a large number of stars, measured with a high degree of accuracy, data about the cosmos and the Universe, including Star clusters in our Galaxy, are growing. However, when observed, the cluster stars are lost against the background of stars in the dense Galactic field. In addition, observational data alone is not sufficient to study real clusters from birth to destruction. In this regard, a number of numerical simulations of star clusters have been running to explain the processes and to determine the membership of cluster stars. And for this, we need to conduct a mock observation of model clusters. In this paper, we performed analyses on the output data from numerical simulations and developed a method for conducting mock observations of model clusters. We took one model of a star cluster with an age of 350 Myr, with a mass of 6000 , and with a star formation efficiency SFE=0.25, and put it in different galactic longitudes and at different distances from the Sun. In conclusion, using this method, we can put a cluster at any point on the celestial sphere, and this in turn allows you to compare with the real observed clusters and evaluate the possibility of detecting physical parameters in them.

Improvements to Pan-STARRS1 Astrometry. II. Corrections for Differential Chromatic Refraction

In a previous paper, we applied the Gaia DR2 catalog to improve the astrometric accuracy of about 1.7 billion objects in Pan-STARRS1 Data Release 2 (PS1 DR2). We report here on further improvements made by utilizing Gaia EDR3 and correcting for the effects of differential chromatic refraction (DCR) in decl. We extend the correction algorithm in Paper I by iteratively subtracting color- and decl.-dependent PS1/Gaia EDR3 decl. residuals. We determine the astrometric improvement for ∼440 million reference objects that are point-like and cross-match to Gaia EDR3. For this set of objects, Gaia EDR3 provides a ∼3% improvement in PS1 astrometry over Gaia DR2, and DCR corrections provide an additional ∼5% improvement. DCR corrections increase substantially for objects observed away from the zenith. DCR corrections lead to an astrometric improvement of ∼30% for blue objects (0 < g − i < 1) that are 50° away from the zenith. The amplitude of systematic astrometric errors from these effects is substantially reduced to less than 1 mas for objects with PS1 colors in the range 0 < g − i < 4.5, which makes this a useful astrometric reference catalog in fields where there are few Gaia stars. The improved astrometric data will be available through the Mikulski Archive for Space Telescopes PS1 catalog interfaces.

Photometric Metallicity Prediction of Fundamental-mode RR Lyrae Stars in the Gaia Optical and K s Infrared Wave Bands by Deep Learning

RR Lyrae stars are useful chemical tracers thanks to the empirical relationship between their heavy-element abundance and the shape of their light curves. However, the consistent and accurate calibration of this relation across multiple photometric wave bands has been lacking. We have devised a new method for the metallicity estimation of fundamental-mode RR Lyrae stars in the Gaia optical G and near-infrared VISTA K s wave bands by deep learning. First, an existing metallicity prediction method is applied to large photometric data sets, which are then used to train long short-term memory recurrent neural networks for the regression of the [Fe/H] to the light curves in other wave bands. This approach allows an unbiased transfer of our accurate, spectroscopically calibrated I-band formula to additional bands at the expense of minimal additional noise. We achieve a low mean absolute error of 0.1 dex and high R 2 regression performance of 0.84 and 0.93 for the K s and G bands, respectively, measured by cross-validation. The resulting predictive models are deployed on the Gaia DR2 and VVV inner bulge RR Lyrae catalogs. We estimate mean metallicities of −1.35 dex for the inner bulge and −1.7 dex for the halo, which are significantly less than the values obtained by earlier photometric prediction methods. Using our results, we establish a public catalog of photometric metallicities of over 60,000 Galactic RR Lyrae stars and provide an all-sky map of the resulting RR Lyrae metallicity distribution. The software code used for training and deploying our recurrent neural networks is made publicly available in the open-source domain.

Earth through the looking glass: how frequently are we detected by other civilizations through photometric microlensing?

ABSTRACT Microlensing is proving to be one of the best techniques to detect distant, low-mass planets around the most common stars in the Galaxy. In principle, Earth’s microlensing signal could offer the chance for other technological civilizations to find the Earth across Galactic distances. We consider the photometric microlensing signal of Earth to other potential technological civilizations and dub the regions of our Galaxy from which Earth’s photometric microlensing signal is most readily observable as the ‘Earth microlensing zone’ (EMZ). The EMZ can be thought of as the microlensing analogue of the Earth Transit Zone (ETZ) from where observers see Earth transit the Sun. Just as for the ETZ, the EMZ could represent a game-theoretic Schelling point for targeted searches for extra-terrestrial intelligence (SETI). To compute the EMZ, we use the Gaia DR2 catalogue with magnitude G &amp;lt; 20 to generate Earth microlensing probability and detection rate maps to other observers. While our Solar system is a multiplanet system, we show that Earth’s photometric microlensing signature is almost always well approximated by a binary lens assumption. We then show that the Earth is in fact well hidden to observers with technology comparable to our own. Specifically, even if observers are located around every Gaia DR2 star with G &amp;lt; 20, we expect photometric microlensing signatures from the Earth to be observable on average only tens per year by any of them. In addition, the EMZs overlap with the ETZ near the Galactic Centres which could be the main areas for future SETI searches.

Joint Survey Processing. II. Stellar Proper Motions in the COSMOS Field from Hubble Space Telescope ACS and Subaru Telescope HSC Observations

We analyze stellar proper motions in the COSMOS field to assess the presence of bulk motions. At bright magnitudes (G-band 18.5–20.76 AB), we use the proper motions of 1010 stars in the Gaia DR2 catalog. At the faint end, we compute proper motions of 11,519 pointlike objects at i-band magnitudes 19–25 AB using Hubble ACS and Subaru HSC data, which span two epochs about 11 yr apart. In order to measure these proper motions with unprecedented accuracy at faint magnitudes, we developed a foundational set of astrometric tools that will be required for joint survey processing of data from the next generation of optical/infrared surveys. The astrometric grids of Hubble ACS and Subaru HSC mosaics were corrected at the catalog level using proper motion–propagated and parallax-corrected Gaia DR2 sources. These astrometric corrections were verified using compact extragalactic sources. Upon comparison of our measured proper motions with Gaia DR2, we estimate the uncertainties in our measurements to be ∼2–3 mas yr−1 axis−1, down to 25.5 AB mag. We correct proper motions for the mean motion of the Sun, and we find that late-type main-sequence stars predominantly in the thin disk in the COSMOS field have space velocities mainly toward the Galactic center. We detect candidate high-velocity (≥220 km s−1) stars, six of them at ∼0.4–6 kpc, from the Gaia sample, and five of them at ∼20 kpc, from the faint star HSC and ACS sample. The sources from the faint star sample may be candidate halo members of the Sangarius stream.

Investigating the most promising Yarkovsky candidates using Gaia DR2 astrometry

The Yarkovsky drift is a major factor driving the orbital evolution of asteroids. To date, the effect has been detected for a few hundred asteroids, mainly near-Earth objects. Before the start of the European Space Agency Gaia mission, the expectation was to recognize many other asteroids manifesting the Yarkovsky drift through the high precision and accuracy of the Gaia astrometry. In this work, we investigated the most promising Yarkovsky candidates indexed before the start of the mission. We found a reliable detection with signal-to-noise (SNR) ratio ¿ 3 of the Yarkovsky effect (A2) for 12 asteroids. When compared to analytical theory from the literature using known (or assumed) orbital and physical parameters, we find that 7–10 (depending on the cutoff value) out of 12 asteroids with SNR ¿3 are consistent with the estimated analytical drift values. In 17 cases, the resulting A2-parameter signal-to-noise was increased with the usage of the Gaia DR2 catalogue data, but no reliable detection can yet be claimed. We are certain that subsequent releases of the Gaia data will lead to numerous other detections. The Yarkovsky drift detection potential of the Gaia data is highlighted for asteroids such as (66391) Moshup (with a previously detected Yarkovsky drift) for which we noted a sizeable increase of the A2 signal-to-noise ratio from ∼2.5 to ∼13 when using the DR2 data compared to when using only the Minor Planet Center astrometry.

Milky Way Star Clusters and Gaia: A Review of the Ongoing Revolution

The unprecedented quality of the astrometric measurements obtained with the ESA Gaia spacecraft have initiated a revolution in Milky Way astronomy. Studies of star clusters in particular have been transformed by the precise proper motions and parallaxes measured by Gaia over the entire sky as well as Gaia’s deep all-sky photometry. This paper presents an overview of the many topics of cluster science that have been impacted by the Gaia DR1, DR2, and EDR3 catalogues from their release to the end of the year 2021. These topics include the identification of known clusters and the discovery of new objects, the formation of young clusters and associations, and the long-term evolution of clusters and their stellar content. In addition to the abundance of scientific results, Gaia is changing the way astronomers work with high-volume and high-dimensionality datasets and is teaching us precious lessons to deal with its upcoming data releases and with the large-scale astronomical surveys of the future.

Improved Measurements of Molecular Cloud Distances Based on Global Search

Abstract The principle of the background-eliminated extinction-parallax (BEEP) method is examining the extinction difference between on- and off-cloud regions to reveal the extinction jump caused by molecular clouds, thereby revealing the distance in complex dust environments. The BEEP method requires high-quality images of molecular clouds and high-precision stellar parallaxes and extinction data, which can be provided by the Milky Way Imaging Scroll Painting (MWISP) CO survey and the Gaia DR2 catalog, as well as supplementary A V extinction data. In this work, the BEEP method is further improved (BEEP-II) to measure molecular cloud distances in a global search manner. Applying the BEEP-II method to three regions mapped by the MWISP CO survey, we collectively measured 238 distances for 234 molecular clouds. Compared with previous BEEP results, the BEEP-II method measures distances efficiently, particularly for those molecular clouds with large angular size or in complicated environments, making it suitable for distance measurements of molecular clouds in large samples.

FEDReD

Context. The Vela complex is a region of the sky that gathers several stellar and interstellar structures in a few hundred square degrees. Aims.Gaia data now allow us to obtain a 3D view of the Vela interstellar structures through the dust extinction. Methods. We used the FEDReD (Field Extinction-Distance Relation Deconvolver) algorithm on near-infrared 2MASS data, cross-matched with the Gaia DR2 catalogue, to obtain a 3D cube of extinction density. We applied the FellWalker algorithm to this cube to locate clumps and dense structures. Results. We analysed 18 million stars over 450 deg2 to obtain the extinction density of the Vela complex from 0.5 to 8 kpc at ℓ ∈ [250° ,280° ] and b ∈ [ − 10° ,5° ]. This cube reveals the complete morphology of known structures and relations between them. In particular, we show that the Vela Molecular Ridge is more likely composed of three substructures instead of four, as suggested by the 2D densities. These substructures form the shell of a large cavity. This cavity is visually aligned with the Vela supernova remnant but located at a greater distance. We provide a catalogue of location, distance, size, and total dust content of Interstellar Medium (ISM).

Astrometric observations and analysis of Triton during 2013–2019

Triton is the largest irregular satellite of Neptune. A total of 1135 new observed positions of Triton in the period 2013–2019 were collected by the 1.0 m telescopes at Yunnan Astronomical Observatory of CAS during 13 nights. These positions of Triton were obtained based on Gaia DR2 catalogue. We compared our observations to the theoretical positions retrieved from IMCCE ephemeris online service with satellite ephemeris of Emelyanov et al. (2015) model and planetary ephemeris EPM2017. The result shows that the mean residuals are −5 mas and − 2 mas in right ascension and declination, the standard deviation of residuals are 31 mas and 29 mas in right ascension and declination. Such seven-year time span observations with high precision will provide data support for the development of orbit theory of Triton.

STUDY OF AN INTERMEDIATE AGE OPEN CLUSTER IC 1434 USING GROUND-BASED IMAGING AND GAIA DR2 ASTROMETRY

We present a detailed photometric and kinematical analysis of the poorly studied open cluster IC 1434 using CCD VRI, APASS, and Gaia DR2 database for the first time. By determining the membership probability of stars we identify the 238 most probable members with a probability higher than 60%; by using proper motion and parallax data as taken from the Gaia DR2 catalog. The mean proper motion of the cluster is obtained as μx=−3.89±0.19 and μy=−3.34±0.19 mas yr−1 in both the directions of right ascension and declination. The radial distribution of member stars provides the cluster extent as 7.6 arcmin. We estimate the interstellar reddening E(B−V) as 0.34 mag using the transformation equations from the literature. We obtain the values of cluster age and distance as 631±73 Myr and 3.2±0.1 kpc.

Canis Major OB1 stellar group contents revealed by Gaia

ABSTRACT Canis Major OB1 (CMa OB1) is a Galactic stellar association with a very intriguing star-formation scenario. There are more than two dozen known star clusters in its line of sight, but it is not clear which ones are physically associated with CMa OB1. We use a clustering code that employs five-dimensional data from the Gaia DR2 catalogue to identify physical groups and obtain their astrometric parameters and, in addition, we use two different isochrone-fitting methods to estimate the ages of these groups. We find 15 stellar groups with distances between 570 and 1650 pc, including 10 previously known and five new open cluster candidates. Four groups, precisely the youngest ones (&amp;lt; 20 Myr), CMa05, CMa06, CMa07, and CMa08, are confirmed to be part of CMa OB1. We find that CMa08, a new cluster candidate, may be the progenitor cluster of runaway stars. CMa06 coincides with the well-studied CMa R1 star-forming region. While CMa06 is still forming stars, due to the remaining material of the molecular cloud associated with the Sh 2-262 nebula, CMa05, CMa07, and CMa08 seem to be in more evolved stages of evolution, with no recent star-forming activity. The properties of these CMa OB1 physical groups fit well in a monolithic scenario of star formation, with a common formation mechanism, and having suffered multiple episodes of star formation. This suggests that the hierarchical model alone, which explains the populations of other parts of the same association, is not sufficient to explain its whole formation history.

Hot Subdwarf Atmospheric Parameters, Kinematics, and Origins Based on 1587 Hot Subdwarf Stars Observed in Gaia DR2 and LAMOST DR7

Abstract Based on the Gaia DR2 catalog of hot subdwarf star candidates, we identified 1587 hot subdwarf stars with spectra in LAMOST DR7. We present atmospheric parameters for these stars by fitting the LAMOST spectra with Tlusty/Synspec non-LTE synthetic spectra. Combining LAMOST radial velocities and Gaia Early Data Release 3 (EDR3) parallaxes and proper motions, we also present the Galactic space positions, velocity vectors, orbital parameters and the Galactic population memberships of the stars. With our He classification scheme, we identify four groups of He rich hot subdwarf stars in the T eff − log g and T eff − log(nHe/nH) diagrams. We find two extreme He-rich groups (eHe-1 and eHe-2) for stars with log(nHe/nH) ≥ 0 and two intermediate He-rich groups (iHe-1 and iHe-2) for stars with −1 ≤ log(nHe/nH) &lt; 0. We also find that over half of the stars in Group eHe-1 are thick-disk stars, while over half of the stars in Group eHe-2 correspond to thin-disk stars. The disk population fractions of Group iHe-1 are between those of Group eHe-1 and eHe-2. Almost all of the stars in Group iHe-2 belong to the thin disk. These differences indicate that the four groups probably have very different origins. Comparisons between hot subdwarf stars in the halo and in the Galactic globular cluster ω Cen show that only He-deficient stars with −2.2 ≤ log(nHe/nH) &lt; −1 have similar fractions. Hot subdwarfs with log(nHe/nH) ≥ 0 in ω Cen have no counterparts in the thick-disk and halo populations, but they appear in the thin disk.

Three-Dimensional Kinematics of Classical Cepheids

A linear Ogorodnikov-Milne model is applied to study the three-dimensional kinematics of classical Cepheids in the Milky Way. A sample of 832 classical Cepheids from Mr'oz et al. (2019) with distances, line-of-sight velocities, and proper motions from the Gaia DR2 catalogue is used. The Cepheid space velocities have been freed from the differential Galactic rotation found by us previously based on a nonlinear rotation model. Based on a complete Ogorodnikov-Milne model, involving the line-of-sight velocities and proper motions of stars, we have estimated the angular velocity of rotation around the Galactic $y$ axis, $\Omega_y=0.64\pm0.17$~km s$^{-1}$ kpc$^{-1}$. We think that this rotation is associated with the warp of the Galactic thin disk. Our calculations using only the proper motions of Cepheids under the assumption of no deformations due to the disk warp have shown the presence of a residual rotation around the $y$ axis with an angular velocity $\Omega_y=0.54\pm0.15$~km s$^{-1}$ kpc$^{-1}$ and the presence of a positive rotation around the $x$ axis with an angular velocity $\Omega_x=0.33\pm0.10$~km s$^{-1}$ kpc$^{-1}$.