The growing density of Earth-orbiting objects demands improved Space Situational Awareness (SSA) to mitigate collision risks and sustain space operations. This study demonstrates a dual-purpose star tracker (ST) for SSA using data from the Resident Space Object Near-space Astrometric Reconnaissance (RSONAR) stratospheric balloon campaign under the 2022 Canadian Space Agency-Centre National d'Études Spatiales (CSA-CNES) STRATOS program. The low-cost optical payload-a wide-field monochromatic imager flown at 36 km altitude-acquired imagery subsequently used for post-processed attitude determination and Resident Space Object (RSO) detection. During stabilized pointing, over 27,000 images yielded sub-pixel astrometry and stable image quality (mean full-width-Half-maximum ≈ 388 arcsec). Photometric calibration to the Tycho-2 catalog achieved 0.37 mag root mean square (RMS) scatter, confirming radiometric uniformity. Apparent angular velocities of 7×102 to 8×103 arcsec s-1 corresponded to sunlit low-Earth-orbit (LEO) objects observed at 25°-35° phase angles. Covariance-weighted Mahalanobis correlation with two-line elements (TLEs) achieved sub-arcminute positional agreement. The Proximity Filtering and Tracking (PFT) algorithm identified 22,036 total RSO and 387 total streaks via image stacking. Results confirm that commercial off-the-shelf STs can serve as dual-use SSA payloads, and that stratospheric ballooning offers a viable alternative for optical SSA research.

Abstract We present the essential stellar parameters of the close visual triple system HD 2893 using Al-Wardat's method for analyzing binary and multiple star systems in conjunction with Kurucz's model atmospheres. This method accurately computes the spectrophotometric stellar masses through a combined synthetic spectral energy distribution approach that compares the results with observed data. The vigorous approach uses spectroscopic, photometric, and dynamical analysis to yield precise results. The method implements Gaia DR3 measurements and other measurements like those of Hipparcos and 2MASS All-Sky Catalog as a guide for the best fit between the synthetic spectra and observed photometry. The analysis gives precise spectrophotometric stellar masses for the system being M Sph A = 1.20 ± 0.07 M ⊙ , M Sph B = 1.09 ± 0.06 M ⊙ , and M Sph C = 0.46 ± 0.01 M ⊙ . It shows that the three components are main sequence stars with an estimated age of around 1.0 Gyr. When integrated with the dynamical analysis, a new dynamical parallax for the system is obtained, π dyn = 13.8528 ± 0.20 mas. Additionally, the discussion covers the formation and evolution of the triple system.

An incorrect designation of the white dwarf GD 140 is present in the first sentence of Sect.5.4.It should read: "We confirm the significant PMa signal detected by Kervella et al. (2019) in two of the 17 white dwarfs of the HIPPARCOS catalog (Table A.5; Fig. 25): GD 140 and LAWD 37." We thank the reader who pointed out this typo.

Hidden within the Gaia satellite’s multiple data releases lies a valuable cache of dark companions. To facilitate the efficient and reliable detection of these companions via combined analyses involving the Gaia, Hipparcos, and Tycho-2 catalogs, we introduce an astrometric modeling framework. This method incorporates analytical least-square minimization and nonlinear parameter optimization techniques to a set of common calibration sources across the different space-based astrometric catalogs. This enables us to discern the error inflation, astrometric jitter, differential parallax zero-points, and frame rotation of various catalogs relative to Gaia Data Release 3 (DR3). Our findings yield the most precise Gaia DR2 calibration parameters to date, revealing notable dependencies on magnitude and color. Intriguingly, we identify submilliarcsecond frame rotation between Gaia DR1 and DR3, along with an estimated astrometric jitter of 2.16 mas for the revised Hipparcos catalog. In a thorough comparative analysis with previous studies, we offer recommendations on calibrating and utilizing different catalogs for companion detection. Furthermore, we provide a user-friendly pipeline (https://github.com/ruiyicheng/Download_HIP_Gaia_GOST) for catalog download and bias correction, enhancing accessibility and usability within the scientific community.

From the Gaia DR3 data twenty three bright hypervelocity stars that have Tycho catalogue numbers are presented. All these stars are of high galactic latitude and some may be galactic halo stars. All of them have accurate Gaia DR3 parallaxes and radial velocities. There is hardly any relevant literature on some of these stars. The Gaia DR3 astrophysical parameters of some of these stars indicate that they are of late spectral types and some are metal-poor. The astrophysical parameters are available for some of these stars in the literature but they differ from the Gaia DR3 results. Detailed chemical composition determination of these stars from an analysis of high resolution spectra is very much needed to further understand the evolutionary status and how these stars acquired such high radial velocities.

A lost-in-space star identification algorithm based on regularized pattern recognition

Context. Open clusters are groups of coeval stars sharing properties such as distance and metallicity, and they are key to understanding stellar evolution. Aims. Our main goal is to study the evolution of open clusters with a special focus on the universality of the luminosity function. Methods. We applied an upgraded version of the convergent point technique on about 50 open clusters. The selection of cluster members was based purely on the exquisite astrometry of the Gaia DR3 and HIPPARCOS catalogues in the five-dimensional or full six-dimensional space. Results. We present updated lists of bona fide members of ∼50 open clusters within 500 pc and younger than 1 Gyr, exploiting the full depth of the third Gaia data release complemented by HIPPARCOS at the bright end, excluding regions in the Galactic plane. Our catalogues also are complemented by optical and infrared photometry from the major large-scale public surveys. All the data will be made available on a dedicated webpage with interactive plots and a direct link to Aladin and Vizier hosted at the Centre de Données de Strasbourg. We derived luminosity functions for all bound clusters and compared them in three age groups of ∼50 Myr, ∼150 Myr, and ∼600 Myr, discussing similarities and differences to constrain their dynamical evolution. Conclusions. Luminosity functions of clusters at 50 Myr are more likely similar to each other and show a greater degree of similarity than older clusters. We explain this observation with the universal luminosity function within the volume of our sample (500 pc). Luminosity functions of clusters with ages similar to the Pleiades or Hyades are more diverse, perhaps due to internal dynamical evolution, but more work is needed to provide additional evidence.

Context.GaiaData Release 3 (DR3) contains the first release of magnitudes estimated from the integration of Radial Velocity Spectrometer (RVS) spectra for a sample of about 32.2 million stars brighter thanGRVS ∼ 14 mag (orG ∼ 15 mag).Aims.In this paper, we describe the data used and the approach adopted to derive and validate theGRVSmagnitudes published in DR3. We also provide estimates of theGRVSpassband and associatedGRVSzero-point.Methods.We derivedGRVSphotometry from the integration of RVS spectra over the wavelength range from 846 to 870 nm. We processed these spectra following a procedure similar to that used for DR2, but incorporating several improvements that allow a better estimation ofGRVS. These improvements pertain to the stray-light background estimation, the line spread function calibration, and the detection of spectra contaminated by nearby relatively bright sources. We calibrated theGRVSzero-point every 30 h based on the reference magnitudes of constant stars from the HIPPARCOScatalogue, and used them to transform the integrated flux of the cleaned and calibrated spectra into epoch magnitudes. TheGRVSmagnitude of a star published in DR3 is the median of the epoch magnitudes for that star. We estimated theGRVSpassband by comparing the RVS spectra of 108 bright stars with their flux-calibrated spectra from external spectrophotometric libraries.Results.TheGRVSmagnitude provides information that is complementary to that obtained from theG,GBP, andGRPmagnitudes, which is useful for constraining stellar metallicity and interstellar extinction. The median precision ofGRVSmeasurements ranges from about 0.006 mag for the brighter stars (i.e. with 3.5≲GRVS≲6.5 mag) to 0.125 mag at the faint end. The derivedGRVSpassband shows that the effective transmittance of the RVS is approximately 1.23 times better than the pre-launch estimate.

ABSTRACT Disintegrating multiple systems have been previously discovered from kinematic studies of the Hipparcos catalogue. They are presumably the result of dynamical encounters taking place in the Galactic disc between single/multiple systems. In this paper, we aim to expand the search for such systems, to study their properties, as well as to characterize possible low-mass ejecta (i.e. brown dwarfs and planets). We have assembled a list of 15 candidate systems using astrometry from the Tycho-Gaia astrometric solution (later upgraded with Gaia DR3), and here we present the discovery and follow-up of five of them. We have obtained DECam imaging for all five systems and by combining near-infrared photometry and proper motion, we searched for ultracool ejected components. We find that the system consisting of TYC 7731-1951-1, TYC 7731-2128 AB, and TYC 7731-1995-1ABC?, contains one very promising ultracool dwarf candidate. Using additional data from the literature, we have found that three out of five disintegrating system candidates are likely to be true disintegrating systems.

Aims. Using the direct-imaging technique, we searched for low-mass companions around the star AF Lep, which presents a significant proper-motion anomaly (PMa) signal obtained from the comparison of HIPPARCOS and Gaia eDR3 catalogs. Methods. We observed AF Lep in two epochs with VLT/SPHERE using its subsystems IFS and IRDIS in the near-infrared, covering wavelengths ranging from the Y to the K spectral bands (between 0.95 and 2.3 μm). We then reduced the data using the high-contrast imaging techniques angular differential imaging (ADI) and spectral differential imaging in order to be able to retrieve the signal from low-mass companions of the star. Results. A faint companion was retrieved at a separation of ~0.335″ from the star and with a position angle of ~70.5° in the first epoch and with a similar position in the second epoch. This corresponds to a projected separation of ~9 au. The extracted photometry allowed us to estimate a mass for the companion of between 2 and 5 MJup. This mass is in good agreement with astrometric measurements of the dynamic mass of the companion, which give 5.2–5.5 MJup. This is the first companion with a mass well below the deuterium burning limit that was discovered by coupling direct imaging with PMa measurements. Orbital fitting done using the orvara tool allowed us to further confirm the companion mass and to define its main orbital parameters.

Abstract We present differential Strömgren uvby observations from the Four College Automated Photometric Telescope (FCAPT) in Washington Camp, AZ of eight magnetic Chemically Peculiar (mCP) stars: HD 32966, HD 35298, HD 68292, HD 93226, HD 171247, HD 217833, HD 220147, and HD 223358. We use multiple period‐finding algorithms and incorporate data from the ESA Hipparcos catalogue to study the amplitudes, periods, and asymmetries in the light curves. No previous FCAPT data have been published for HD 68292. For the seven other stars, these studies substantially extend the analyses of published FCAPT datasets.

The mean parallax of the Pleiades open cluster from the Hipparcos catalog is larger than the true value by approximately 1 mas. The origin of this error, as well as a possible algorithm of correcting it, was proposed by Makarov (2002). The problem is reassessed using the more accurate Gaia data with a focus on the predicted correction to the Pleiades proper motions. The accurately determined differences Gaia − Hipparcos for 52 common stars are close to these estimates within the formal uncertainties for all three parameters, which strongly suggests that the proposed interpretation was correct. With adjustments for the systematic vector field fitted with 126 vector spherical harmonics to degree 7, these differences amount to (+0.39, −0.74) mas yr−1 . The implications of small-scale proper motion and position errors in Hipparcos for present day astrometry are briefly discussed.

The Hipparcos catalog provides the first epoch of the celestial reference frame (CRF) in the optical domain and serves as an indispensable tool to verify and improve the Gaia CRF for the brighter stars (V < 11 mag) and to identify the elusive astrometric binary stars with dim or invisible companions, including long-period exoplanets. The systems of positions in Hipparcos and Gaia cannot be directly compared, because they refer to two different mean epochs. It is shown that the proper motion systems for carefully filtered common stars are not statistically consistent within the given formal errors. The vector field of proper motion differences is fitted with 126 vector spherical harmonics up to degree 7 revealing a global pattern at high signal-to-noise ratios, including the three terms of rigid rotation. The origin of the differential spin and other large harmonic terms is investigated by producing a similar decomposition of the Gaia−HG proper motion field, where HG stands for the long-term proper motions derived from the Hipparcos and Gaia DR3 positions, for the same sample of stars. Hipparcos proper motions emerge as the largest source of sky-correlated distortions of the multiepoch optical CRF with a median value of ∼190 μas yr−1 and a global spin of ∼226 μas yr−1, while the Hipparcos positions and Gaia EDR3 proper motions are explicitly consistent by construction at a level of ∼10 μas yr−1. The latter, however, include multiple distortions of higher degree, which should be taken into account in astrometric applications using the HG field.

Trigonometric parallax discrepancies in space telescopes measurements I: The case of the stellar binary system Hip 84976

We present the direct-imaging discovery of a substellar companion in orbit around a Sun-like star member of the Hyades open cluster. So far, no other substellar companions have been unambiguously confirmed via direct imaging around main-sequence stars in Hyades. The star HIP 21152 is an accelerating star as identified by the astrometry from the Gaia and Hipparcos satellites. We detected the companion, HIP 21152 B, in multiple epochs using the high-contrast imaging from SCExAO/CHARIS and Keck/NIRC2. We also obtained the stellar radial-velocity data from the Okayama 188 cm telescope. The CHARIS spectroscopy reveals that HIP 21152 B’s spectrum is consistent with the L/T transition, best fit by an early T dwarf. Our orbit modeling determines the semimajor axis and the dynamical mass of HIP 21152 B to be 17.5 au and 27.8 M Jup, respectively. The mass ratio of HIP 21152 B relative to its host is ≈2%, near the planet/brown dwarf boundary suggested by recent surveys. Mass estimates inferred from luminosity-evolution models are slightly higher (33–42 M Jup). With a dynamical mass and a well-constrained age due to the system’s Hyades membership, HIP 21152 B will become a critical benchmark in understanding the formation, evolution, and atmosphere of a substellar object as a function of mass and age. Our discovery is yet another key proof of concept for using precision astrometry to select direct-imaging targets.

The GAia Map of the Brightness Of the Natural Sky (GAMBONS) is a model to map the natural night brightness of the sky in cloudless and moonless nights. It computes the star radiance from the photometric data in Gaia and Hipparcos catalogues, adding the contributions of the diffuse galactic and extragalactic light, zodiacal light and airglow, and taking into account the effects of atmospheric attenuation and scattering. The model allows computing the natural sky brightness in any given photometric band for a ground-based observer, if appropriate transformations from the Gaia bands are available. In this work we present the most recent improvements of the model, including the use of Gaia EDR3 data, the inclusion of a wide set of photometric bands and the derivation of additional sky brightness indicators, as the horizontal irradiance and the average hemispheric radiance.

Context. The multiplicity fraction of stars, down to the substellar regime, is a parameter of fundamental importance for stellar formation, evolution, and planetology. The census of multiple stars in the solar neighborhood is however incomplete. Aims. Our study is aimed at detecting companions of HIPPARCOS catalog stars from the proper motion anomaly (PMa) they induce on their host star, namely, the difference between their long-term HIPPARCOS-Gaia and short-term Gaia proper motion vectors. We also aim to detect resolved, gravitationally bound companions of the HIPPARCOS catalog stars (117 955 stars) and of the Gaia EDR3 stars closer than 100 pc (542 232 stars). Methods. Using the HIPPARCOS and EDR3 data, we revised the PMa catalog for the HIPPARCOS stars. In order to identify gravitationally bound visual companions of our sample, we searched the Gaia EDR3 catalog for common proper-motion (CPM) candidates. Results. The detection of tangential velocity anomalies with a median accuracy of σ(ΔvT) = 26 cm s−1 per parsec of distance is demonstrated with the EDR3. This improvement by a factor 2.5 in accuracy, as compared to Gaia DR2, results in PMa detection limits on companions that are well into the planetary mass regime for many targets. We identify 37 515 HIPPARCOS stars presenting a PMa at significant level (S/N &gt; 3), namely, a fraction of 32% (compared to 30% for the DR2) and 12 914 (11%) hosting CPM bound candidate companions. After including the Gaia EDR3 renormalised unit weight error (RUWE &gt; 1.4) as an additional indicator, 50 720 stars of the HIPPARCOS catalog (43%) exhibit at least one signal of binarity. Among the Gaia EDR3 stars located within 100 pc, we find CPM bound candidate companions for 39 490 stars (7.3% of the sample). Conclusions. The search for companions using a combination of the PMa, CPM, and RUWE indicators significantly improves the exhaustivity of the multiplicity survey. The detection of CPM companions of very bright stars (heavily saturated on the Gaia detectors) that are classical benchmark objects for stellar physics provides a useful proxy for estimating their distance with a higher accuracy than with HIPPARCOS.

In the Tycho-2 catalogue system the processing of 1529 photographic plates of the FON Dushanbe project from the collection of the Institute of Astrophysics of the National Academy of Sciences of Tajikistan was completed. The photographic plates with the size of 8º×8º (30x30 cm) were exposed in the zones from -8º to + 84º in the period of 1985-1992 years. In years 2017 – 2020 the plates were digitized using a Microtek ScanMaker 1000XL Plus scanner with the resolution of 1200 dpi, so the size of the digitized images is near 13000x13000 px. Based on the results of the processing of digitized images a catalogue of equatorial coordinates α, δ and B-magnitudes of stars for the northern hemisphere of the sky was created. The catalog contains about 30 million stars and galaxies for the epoch 1988.74. The average internal accuracy of the catalogue for all objects is σαδ = ±0.32" and σB = ± 0.11 m (for stars in the range of B = 8 m -14 m the errors are σαδ = ±0.19" and σB =±0.07 m ) for equatorial coordinates and B-magnitudes respectively. The convergence between calculated and reference positions from the Tycho-2 catalogue is σαδ = ±0.07" and the convergence with photoelectric B-magnitudes is σB = ±0.16 m . Five astronomical institutions took part in the processing of the photographic plates and in the creating of the FON-Dushanbe catalogue: Institute of Astrophysics of NAS of Tajikistan; Walter Hohmann Observatory, Essen, Germany; Ulugh Beg Astronomical Institute UAS, Uzbekistan; Research Institute “Mykolaiv Astronomical Observatory”, Ukraine and Main Astronomical Observatory NASU, Ukraine.

For more than 50 years, the continuous photographic observations of asteroids have been carried outwith telescopes of the Astronomical Observatory of the Taras Shevchenko National University of Kyiv and the Main Astronomical Observatory of the National Academy of Sciences of Ukraine. About 3,000 photographic plates were obtained, some of which were exposed in 1908. We collected the data on more than 5,500 positions and magnitudes of asteroids on these astroplates taking into account all results of the processing of observations available in various publications and in the Minor Planet Center database. All positional data were compared with JPL ephemeris and analyzed. From different series of asteroid observations the values of positional accuracy were obtained, depending on the methods of measuring and processing the plates and reference catalogs of stars. In order to systematically improve the obtained asteroid positions, we evaluated the possibilities of reprocessing some of the earliest asteroid observations applying the modern star high accuracy catalogs. Using the Tycho-2, Gaia DR2, and Gaia EDR3 as the reference catalogs, the 590 astroplates exposed on the MAO NASU Double Long-Focus Astrograph (DLA) in 1952-1986 were reprocessed based on old plate measurements. All newly determined and previous original asteroid positions were compared with the JPL ephemeris. The comparison results show an improvement in the systematic and random components of the accuracy of coordinates for new positions of asteroids. When comparing the new positions of the asteroids determined in the Tycho-2 and Gaia catalog systems, no significant changes in accuracy were found.

Abstract Using the absolute astrometric positions and proper motions for common stars in the Hipparcos and Gaia catalogs separated by 24.75 yr in the mean epoch, we compute mass ratios for long-period, resolved binary systems without any astrophysical assumptions or dependencies, except the presence of inner binary subsystems that may perturb the observed mean proper motions. The mean epoch positions of binary companions from the Hipparcos Double and Multiple System Annex are used as the first epoch. The mean positions and proper motions of carefully cross-matched counterparts in Gaia EDR3 comprise the second epoch data. Selecting only results with sufficiently high signal-to-noise ratio and discarding numerous optical pairs, we construct a catalog of 248 binary systems, which is published online. Several cases with unusual properties or results are also discussed.