Virtual Observatory Research Articles (Page 1)

Luminous blue variables (LBVs) represent a brief transitional phase in the evolution of massive stars. Multi-wavelength studies of their circumstellar environments are essential to quantify their feedback at Galactic scales. Dominant emission mechanisms at millimetre wavelengths are, however, still poorly understood. Stellar winds, circumstellar dust, and ionised gas have not been explored together in the case of LBVs. We aim to study the millimetre continuum emission of Galactic LBVs to disclose the presence of these components, to describe their morphology, and to measure their relevance in the mass and energy injection to the interstellar medium. We used the NIKA2 continuum camera at the IRAM 30 m radio telescope to observe and analyse 1.15 and 2 mm continuum from the LBVs HD168607 HD168625 GKF2010 MN87 GKF2010 MN101 and G79.29+0.46 . We used the Virtual Observatory to complement our observations with archival data from optical, infrared, millimetre, and centimetre wavelengths. With this information, we built complete spectral energy distributions (SEDs) for the five sources that cover six decades of the electromagnetic spectrum. All targets except MN87 were detected at both wavelengths, with features including compact sources, extended nebular emission, shells, and unrelated background structures. The spectral indices of compact sources are consistent with thermal emission from stellar winds. We modelled the SEDs and successfully reproduced the emission from stellar photospheres, circumstellar dust, thermal stellar winds, and enshrouding Hii regions. Our models, in agreement with previous literature results, reveal unresolved hot dust very close to the stars and provide the first estimates for the fundamental parameters of MN101. This pilot study highlights the great potential of millimetre continuum studies of LBVs and possibly other evolved massive stars. The millimetre spectral window bridges the far-IR and radio regimes and can disclose the relative contribution of dust and free-free emission in this type of source.

Abstract White dwarfs (WD) with main-sequence (MS) companions are crucial probes of stellar evolution. However, due to the significant difference in their luminosities, the WD is often outshined by the MS star. The aim of this work is to find hidden companions in Gaia’s sample of WD candidates. Our methodology involves applying an unsupervised machine learning algorithm for dimensionality reduction and clustering, known as a self-organizing map (SOM), to Gaia BP/RP (XP) spectra. This strategy allows us to naturally separate WDMS binaries from single WDs from the detection of subtle red flux excesses in the XP spectra that are indicative of low-mass MS companions. We validate our approach using confirmed WDMS binaries from the Sloan Digital Sky Survey and LAMOST surveys, achieving a precision of ∼90%. We demonstrated that the luminosity of the faint companions in the missed systems is ∼50 times lower than that of their WD primaries. Applying our SOM to 90,667 sources, we identify 993 WDMS candidates, 506 of which have not been previously reported in the literature. If confirmed, our sample will increase the known WDMS binaries by 20%. Additionally, we use the Virtual Observatory Spectral Energy Distribution Analyzer tool to refine and parameterize a “golden sample” of 136 WDMS binaries through multiwavelength photometry and a two-body spectral energy distribution fitting. These high-confidence WDMS binaries are composed of low-mass WDs (∼0.42M ⊙), with cool MS companions (∼2800 K). Finally, 13 systems exhibit periodic variability consistent with eclipsing binaries, making them prime targets for further follow-up observations.

Abstract We design an uncertainty-aware cost-sensitive neural network (UA-CSNet) to estimate metallicities from dereddened and corrected Gaia BP/RP (XP) spectra for giant stars. This method accounts for both stochastic errors in the input spectra and the imbalanced density distribution in [Fe/H] values. With a specialized architecture and training strategy, the UA-CSNet improves the precision of the predicted metallicities, especially for very metal-poor (VMP; [Fe/H] ≤ −2.0) stars. With the PASTEL catalog as the training sample, our model can estimate metallicities down to [Fe/H] ∼ −4. We compare our estimates with a number of external catalogs and conduct tests using star clusters, finding overall good agreement. We also confirm that our estimates for VMP stars are unaffected by carbon enhancement. Applying the UA-CSNet, we obtain reliable and precise metallicity estimates for approximately 20 million giant stars, including 360,000 VMP stars and 50,000 extremely metal-poor ([Fe/H] ≤ −3.0) stars. The resulting catalog is publicly available via the Chinese Virtual Observatory at doi: 10.12149/101604. This work highlights the potential of low-resolution spectra for metallicity estimation and provides a valuable data set for studying the formation and chemodynamical evolution of our Galaxy.

Context. The Gaia mission discovered several hundred thousand long-period variables and measured parallaxes for many of them. These stars will allow us to study populations of variable stars in the Milky Way, including asymptotic giant branch (AGB) stars. Aims. This paper describes the identification of Gaia counterparts of a sample of oxygen-rich AGB stars with OH maser emission as a first step towards the compilation of a general Gaia Catalogue of Galactic AGB stars. With this catalogue, tests of evolutionary models for the AGB star population in the solar neighbourhood become feasible. Methods. We cross-matched AGB star candidates showing OH maser emission with the Gaia DR3 release using a cross-match with AllWISE and 2MASS as intermediate steps to avoid ambiguities. With the help of the Virtual Observatory, we retrieved photometric data from the near-ultraviolet to the far-infrared and built spectral energy distributions (SEDs) of the sources. The SEDs were fitted with theoretical models. The fit results, together with information from the literature, allowed us to clean the sample from non-AGB stars. For the AGB stars, bolometric fluxes were obtained. Distances based on Gaia parallaxes were used to derive the stellar luminosities. Results. We identified unique Gaia counterparts for 1487 OH masers. Of these, 1172 had an unambiguous classification as AGB stars. These sources make up the Gaia OH/IR star sample. Parallaxes with relative errors < 20% and astrometric excess noise < 1.5 mas were available for 222 OH/IR stars. Conclusions. The study of the AGB population in the solar neighbourhood is limited by the obscuration by circumstellar dust, as Gaia DR3 only provides parallaxes for a few of our candidates. The location of the OH/IR stars matches that of LPV discovered by Gaia in the (BP–RP; Gabs) diagram, but the OH/IR star sample is biased towards redder colours (BP–RP > 4) mag and larger amplitudes (> 1 mag in the G-band), which are typical for periodic large-amplitude Mira variables.

The paper aims to highlight the formation and progress of the astrometric schools of the National Academy of Sciences of Ukraine — the scientific school of fundamental astronomy, positional astrometry, and global geodynamics of Academician Oleksandr Yakovych Orlov, the Scientific School of fundamental astronomy and selenodesy of the Corresponding member of the Academy of Science professor Avenir Oleksandrovych Yakovkin and the scientific direction of I. G. Kolchinsky, A. B. Onegina, and A. S. Kharin on photographic and positional astrometry. The main directions of research of the scientific school in fundamental astronomy, positional astrometry, and global geodynamics are the next: the creation of catalogs of faint stars, stars of the latitudinal program, radio sources, mathematical methods of researching the change of latitudes, and the movement of the Earth’s poles, fundamental astronomy (study of astronomical constants), application of the movement of the poles and irregularities of the Earth’s rotation (laser ranging of the artificial satellites of the Earth, VLBI-observations, GNSS-observations). Introducing new observational methods and tools contributes to the further development of the school and the preservation of its scientific traditions. The purview of the scientific school of fundamental astronomy and selenodesy concerns the first astrometric mapping of the Moon’s surfacedetails using data from orbital satellites, as well asthe study of stellar dynamics, kinematics and structure of the Galaxy. The researchfindings in photographic and positional astrometry are analyzed. The role of the Ukrainian Virtual Observatory (UkrVO) in the current development of the scientific directionis indicatedbasedon the possibility of digitizing astronomical photographic negativesobtained in the frameworks of vast photographic surveys of the sky, in particular,the FON/FONAK project. Re-reduction of past observational data in up-to-date reference frames allowed the initiatingof the search for asteroids, their earlier positions and precoveries, as well as thereworking of earlier observations of large planets and small bodies of the Solar System.

The volume and diversity of solar physics data have grown exponentially in the last three decades. In view of making solar datasets easily accessible to the scientific community, we have developed the SOLARNET Virtual Observatory (SVO), an IT service that collects metadata from a large range of solar observational datasets in a common catalog to allow smooth data search and access. It follows the virtual observatories (VO) principle, with a provider layer, core metadata database, and user layer. The user layer contains a user-friendly web application, Python and IDL libraries, and a RESTful API. The SVO enables metadata to be searched either across all datasets or within a specific dataset by applying more precise search conditions. Additionally, it allows researchers to query solar events from the HEK database and identify data that overlaps with these events. Data can be previewed and downloaded from the web application. The Python and IDL libraries allow the integration of the SVO data search and functionality with complex data processing pipelines. On the provider side, datasets are ingested through tailored scripts. Recently, a TAP client layer has been added to the SVO, hence, it is possible to populate the SVO automatically with a dataset that is available as a TAP or EPN-TAP service. We describe the service, user, and provider side of the SVO and illustrate its capabilities with four scientific use cases.

Abstract We present the application of the image coaddition algorithm, upsampling and point-spread function (PSF) deconvolution coaddition (UPDC), for stacking multiple exposure images captured by the James Webb Space Telescope (JWST) Near-Infrared Camera. By addressing the PSF effect, UPDC provides visually enhanced and sharper images. Furthermore, the antialiasing and superresolution capabilities of UPDC make it easier to deblend sources overlapped on images, yielding a higher accuracy of aperture photometry. We apply this algorithm to the SMACS J0723 imaging data. Comparative analysis with the Drizzle algorithm demonstrates significant improvements in detecting faint sources, achieving accurate photometry, and effectively deblending (superresolution) closely packed sources. As a result, we have newly detected a pair of close binary stars that were previously unresolvable in the original exposures or the Drizzled image. These improvements significantly benefit various scientific projects conducted by JWST. The resulting data set, named “UPdec-Webb,” can be accessed through the official website of the Chinese Virtual Observatory.

Research on geomagnetic secular variation of China and surrounding areas based on the Geomagnetic Virtual Observatories

This research will be carried out at the basic physics laboratory of the physics education study program at Muhammadiyah University of Makassar. The long-term goal of this research is to produce a prototype model of a basic physics practicum based on the virtual android observatory to facilitate the ICT literacy skills of prospective physics teachers. Based on the results of basic physics practical trials, experiments on determining Earth's gravity, free fall motion, and the Doppler effect based on a virtual android observatory, among others, based on the results of observations from the implementation of basic physics practicals when viewed from the aspect of design ability. Experimental tools and materials for determining gravitational acceleration, free fall motion, and the Doppler effect. Overall, students have very good skills in designing tools, especially in the aspect of using cellphone sensors that are integrated into the virtual android observatory application. The conclusion is that the effectiveness of the results of basic physics practicum trials for determining the earth's gravity, free fall motion, and the virtual android observatory-based Doppler effect is in the very good category, namely 75.41%, and the results of the ICT literacy skills of prospective physics teacher students are in the good category, namely overall. students were able to use the virtual android observatory application as a whole with a proficient percentage level of 56.60%.

We present the database of potential targets for the Large Interferometer For Exoplanets (LIFE), a space-based mid-infrared nulling interferometer mission proposed for the Voyage 2050 science program of the European Space Agency. The database features stars, their planets and disks, main astrophysical parameters, and ancillary observations. It allows users to create target lists based on various criteria to predict, for instance, exoplanet detection yields for the LIFE mission. As such, it enables mission design trade-offs, provides context for the analysis of data obtained by LIFE, and flags critical missing data. Work on the database is in progress, but given its relevance to LIFE and other space missions, including the Habitable Worlds Observatory, we present its main features here. A preliminary version of the LIFE database is publicly available on the German Astrophysical Virtual Observatory.

Aims. This paper is focused on the segregation of FGK dwarf and giant stars through narrow-band photometric data using the Spanish Virtual Observatory (SVO) Filter Profile Service and associated photometric tools. Methods. We selected spectra from the MILES, STELIB, and ELODIE stellar libraries, and used SVO photometric tools to derive the synthetic photometry in 15 J-PAS narrow filters, which were especially selected to cover spectral features sensitive to gravity changes. Using machine-learning techniques as the Gaussian mixture model and the support vector machine, we defined several criteria based on J-PAS colours to discriminate between dwarf and giant stars. Results. We selected five colour-colour diagrams that presented the most promising separation between both samples. Our results show an overall accuracy in the studied sample of ~0.97 for FGK stars, although a dependence on the luminosity type and the stellar effective temperature was found. We also defined a colour-temperature relation for dwarf stars with effective temperatures between 4 000 and 7 000 K, which allows one to estimate the stellar effective temperature from four J-PAS filters (J0450, J0510, J0550, and J0620). Additionally, we extended the study to M-type giant and dwarf stars, achieving a similar accuracy to that for FGK stars.

Context. The upcoming generation of telescopes, instruments, and surveys is poised to usher in an unprecedented “Big Data” era in the field of astronomy. Within this context, even seemingly modest tasks such as spectral line analyses could become increasingly challenging for astronomers. Aims. In this paper, we announce the release of LIME. This package is tailored for multidisciplinary observations with long-slit and integral field spectroscopy (IFS) support. LIME functions encompass the reading of observational files, detecting lines, conditioned line fitting, and the plotting and storage of results. Most importantly, these measurements are structured to support the subsequent chemical and kinematic analyses. Methods. To reduce the coding effort required from users, we introduced a notation system for atomic transitions that is accessible to humans and machine-readable. Along with this system, we present an extensive database of line bands, spanning from the ultraviolet to the infrared wavelength range. Additionally, we propose a model designed to train machine learning algorithms in line detection. LIME features a comprehensive online documentation, which details the command attributes and includes several tutorials. These tutorials range from measuring a single line to analyzing an entire IFS data cube. Results. This library functions and measurements are showcased in an online virtual observatory. The data in this interactive website come from the JWST NIRSpec observations of the CEERs survey. In this regard, LIME offers improvements related to the dissemination and accessibility of astronomical spectra.

Aims. The Archives of Photographic PLates for Astronomical USE (APPLAUSE) project is aimed at digitising astronomical photographic plates from three major German plate collections, making them accessible through integration into the International Virtual Observatory (IVO). Methods. Photographic plates and related materials (logbooks, envelopes, etc.) were scanned with commercial flatbed scanners. Astrometric and photometric calibrations were carried out with the developed PyPlate software, using Gaίa EDR3 data as a reference. The APPLAUSE data publication complies with IVO standards. Results. The latest data release contains images and metadata from 27 plate collections from the partner institutes in Hamburg, Bamberg, and Potsdam, along with digitised archives provided by Tautenburg, Tartu, and Vatican observatories. Altogether, over two billion calibrated measurements extracted from about 70 000 direct photographic plates can readily be used to create long-term light curves. For instance, we constructed the historic light curve of the enigmatic dipping star KIC 8462852. We found no evidence of previously assumed variations on timescales of decades in our light curve. Potential uses of APPLAUSE images for transient sources can be appreciated by following the development of the nova shell of GK Per (1901) over time and the change in brightness of two extragalactic supernovae. The database holds about 10 000 spectral plates. We made use of objective prism plates to follow the temporal changes of Nova DN Gem through 1912 and 1913, highlighting an outburst in early 1913.

The large ecosystem of observations generated by major space telescope missions can be remotely analyzed using interoperable virtual observatory technologies. In this context of astronomical big data analysis, sonification has the potential of adding a complementary dimension to visualization, enhancing the accessibility of the archives, and offering an alternative strategy to be used when overlapping issues are found in purely graphical representations. This article presents a collection of sonification and musification prototypes that explore the case studies of the MILES and STELIB stellar libraries from the Spanish Virtual Observatory and the Kepler and TESS light curve databases from the Space Telescope Science Institute archive. Using automation and deep learning algorithms, it offers a “palette” of resources that could be used in future developments oriented toward an auditory virtual observatory proposal. The work includes a user study with quantitative and qualitative feedback from specialized and nonspecialized users analyzing the use of sine waves and musical instrument mappings for revealing overlapped lines in galaxy transmission spectra, confirming the need for training and prior knowledge for the correct interpretation of accurate sonifications, and providing potential guidelines to inspire future designs of widely accepted auditory representations for outreach purposes.

Multi-messenger astronomy is an emerging field of research aimed at unravelling the physics governing astrophysical transients. GW170817 stands out as the first multi-messenger observation of the coalescence of a binary system of neutron stars, detected by the LIGO and Virgo gravitational-wave interferometers, along with space- and ground-based electromagnetic telescopes. It is a striking example of how multi-messenger observations significantly enhance our understanding of the physics of compact objects, relativistic outflows, and nucleosynthesis. It shows a new way of making cosmology and has the potential to resolve the tension between different measurements of the expansion rate of the Universe. To optimise multi-messenger observational strategies, to evaluate the efficiency of the searches for counterparts, and to identify the host galaxy of the source in a large sky localisation, information about the volumes of galaxies within the gravitational-wave localisation is of paramount importance. This requires the use of galaxy catalogues and appropriate knowledge of their completeness. Here, we describe a new interactive web tool namedGLADEnetthat allows us to identify catalogued galaxies and to assess the incompleteness of the catalogue of galaxies in real time across the gravitational-wave sky localisation. This measure is of particular importance when using catalogues such as the GLADE catalogue (Galaxy List for the Advanced Detector Era), which includes a collection of various catalogues that make completeness differ across different regions of the sky. We discuss the analysis steps to defining a completeness coefficient and provide a comprehensive guide on how to use the web app, detailing its functionalities. The app is geared towards managing the vast collection of over 22 million objects in GLADE. The completeness coefficient and the GLADE galaxy list will be disseminated in real time viaGLADEnet, powered by the Virtual Observatory (VO) standard and tools.

ABSTRACT We present the observational mass–radius (M–R) relation for a sample of 47 magnetized white dwarfs (WDs) with the magnetic field strength (B) ranging from 1 to 773 MG, identified from the SDSS data release 7 (DR7). We derive their effective temperature, surface gravity (log g), luminosity, radius, and mass. While atmospheric parameters are derived using a Virtual Observatory Spectral Energy Distribution Analyzer (VOSA), the mass is derived using their location in the HR diagram in comparison with the evolutionary tracks of different masses. We implement this mass measurement instead of a more traditional method of deriving masses from log g, which is unreliable as is based on SED and generates errors from other physical parameters involved. The main disadvantage of this method is that we need to assume a core composition of WDs. As it is complicated to identify the exact composition of these WDs from low-resolution spectra, we use tracks for the masses 0.2 to 0.4 M⊙ assuming a He-core, 0.5 to 1.0 M⊙ assuming CO core, and above M⊙ assuming O–Ne–Mg core. We compare the observed M–R relation with those predicted by the finite temperature model by considering different B, which are well in agreement considering their relatively low-surface fields, ≲109 G. Currently, there is no direct observational detection of magnetized WDs with B > 109 G. We propose that our model can be further extrapolated to higher B, which may indicate the existence of super-Chandrasekhar mass (M > 1.4 M⊙) WDs at higher B.

Abstract The aim of this article is making use of the Gaia DR3 catalogue and virtual observatory tools, to confirm and characterize 428 binary and multiple stellar systems classified as neglected (only one observation) in the Washington Double Star Catalogue (WDS). The components of the stellar systems have the same parallax and proper motion (within the errors) and are separated by less than 50,000 AU, which minimizes the number of by‐chance counterparts. Effective temperatures calculated using VOSA were used to estimate stellar masses. Binding energies were calculated for 42 binary systems confirming they are physical pairs. Also we found 75 pairs with F/G‐ M spectral types, which are very interesting to improve the determination of the metallicity of the M star from the higher mass component.

We present the results of asteroid images’ identification and creation of positional catalogs based on digitized photographic observations within the framework of the Northern Sky Survey (FON project). Namely, the cooperation between the Ukrainian Virtual Observatory and the Institute of Astrophysics of the Academy of Sciences of Tajikistan makes it possible to expand this work by involving numerous additional archives of digitized observations and processing services to obtain new original data about the small Solar system bodies. The Dushanbe part of the FON project is represented by about 1570 photographic plates obtained in 1985—1992 at the Gissar As- tronomical Observatory of the Institute of Astrophysics of the Academy of Sciences of Tajikistan. To the moment, their digitization and further scanning processing were completed, and a catalog of equatorial coordinates and stellar magnitudes for all registered objects on the plates was created. In parallel with solving the main task of the project to create a catalog of stars and galaxies, we analyzed the results of processing the plates to search for images of asteroids and comets and to create a catalog of their coordinates and magnitudes. More than 2200 positions of asteroids and comets were obtained with visual magnitudes from 7m to 16.5 m. All positions of the asteroids were compared with the ephemeris. A preliminary analysis of the O-C differences and their comparison with similar results obtained from the digitized observations of the Kyiv and Kitab parts of the FON project are conducted. The authors note some differences in the accuracy of the compared catalogs and also analyze the reasons for this and the possibilities of reducing their impact. In addition, the catalog includes several positions of Pluto and comets that were also identified in the negatives.

ABSTRACT We present the first release of the Calar Alto CAFOS direct imaging data, a project led by the Spanish Virtual Observatory with the goal of enhancing the use of the Calar Alto archive by the astrophysics community. Data Release 1 contains 23 903 reduced and astrometrically calibrated images taken from 2008 March to 2019 July with a median of the mean uncertainties in the astrometric calibration of 0.04 arcsec. The catalogue associated to 6132 images in the Sloan griz filters provides accurate astrometry and PSF calibrated photometry for 139 337 point-like detections corresponding to 21 985 different sources extracted from a selection of 2338 good-quality images. The mean internal astrometric and photometric accuracies are 0.05 arcsec and 0.04 mag, respectively. In this work we describe the approach followed to process and calibrate the images, and the construction of the associated catalogue, together with the validation quality tests carried out. Finally, we present three cases to prove the science capabilities of the catalogue: discovery and identification of asteroids, identification of potential transients, and identification of cool and ultracool dwarfs.

Armenian Virtual Observatory: Status and activities