Abstracts 
Session: Overview of Gaia & Gaia Alerts
Overview of the Gaia mission (inv)
Anthony Brown (Univ. Leiden, Netherlands)
I will present an overview of the Gaia spacecraft and survey, highlighting the aspects that make Gaia an excellent transient sky survey machine.
Gaia Photometric Science Alerts: where we were, where we are, where we are going (inv)
Simon Hodgkin (Institute of Astronomy, Cambridge, U.K.)
Gaia continues to monitor the whole sky with cadences of seconds (between CCDs), hours (between fields-of-view) and weeks (between visits), with real-time source detection implemented by a fixed, available, and well-understood on-board algorithm. Every Gaia source obtains near-simultaneous spectrophotometry. The Gaia Alerts system has been running routinely and reliably since January 2016, currently publishing more than 12 transients per day (see http://gsaweb.ast.cam.ac.uk/alerts/home), using well-defined selection criteria. We scan the whole sky exploring into the Galactic plane and crowded regions which are typically hard to do from the ground. We describe the challenges we face in searching through half a billion CCD measurements every day to identify and publish Gaia's transient events. We investigate the properties of the alerts published to date and highlight some of our most interesting discoveries, paying special attention to the overlaps between the Alerts, ground-based follow-up programmes, and the third Gaia Data Release. We examine the completeness and purity of our published alerts, and look ahead to the next years of Gaia Photometric Science Alerts.
Machine learning technique for procedures for exocomet hunting in the TESS database
Daria Dobrycheva (Astronomical Obs. of National academy of sciences of Ukraine, Ukraine)
The Transiting Exoplanet Survey Satellites (TESS) currently searches for Earth-size planets around nearby F, G, K - dwarf stars. Analysis of high-quality light curves collected by this space mission allows one to identify and discriminate between different phenomena causing the variations in the stars’ flux such as stars pulsation, spot rotation, exoplanet transits as well as the sporadic dimming of the star flux due to transits of the small bodies - asteroids and comets, which play an important role in the dynamics and physical evolution of the planetary systems. Taking into account the large data sample, the techniques of the artificial intellect are widely used to classify the minima in the star light curves. We present the first work results on the formation of training samples for machine learning methods, which allow us to identify exocomet transits. In order to use machine learning, we composed two samples of light curves to train the machine learning technique: a) the light curve profiles caused by the unidentified yet exoplanet transits from the EXOMAST archive; b) the simulated model brightness profiles due to the exocomet transits. For the latter, we used a comet model based on the orbital and physical characteristics of real comets of the Solar system belonging to the different dynamical groups - Jupiter family comets, Halley-type comets, and dynamical new comets of the Oort cloud. We report the simulated light curves of the planet and exocomet transits for machine learning, which we will apply to detect the exocomet transits in the TESS database. We developed codes for the corresponding light curve analysis
Transient characterization using the Virtual Observatory
Enrique Solano (Centro de Astrobiología (INTA-CSIC), Spain)
Transients can be defined as astrophysical phenomena whose duration is significantly lower than the typical timescale of the stellar and galactic evolution (from seconds to years in contrast to millions
or billions of years). Supernovae, novae, gamma-ray burst,..., are some examples of transient events. In most cases, a fast, multiwavelength characterization is required to properly understand the true nature of the transient. Follow-up observations made by both professional and amateur astronomers using ground- and space-based facilities are key to achieve this goal. In this poster we propose an alternative and complementary approach using the existing information in astronomical archives and benefiting from the advantages that the Virtual Observatory (VO) offers in terms of discovery, access and analysis of astronomical data. Using VO tools and services (STILTS, VOSA, SVO DiscTool) we will describe an automated workflow to validate and characterize potential Cataclysmic Variables identified by the Gaia Science Alerts project.
Session: Distance ladder and Ho tension
Gaia and the Local Distance scale (inv)
Stefano Casertano (Space Telescope Science Institute, USA)
Results from the Gaia mission now play a key role in the accurate determination of the local distance ladder. EDR3 parallaxes now provide the best calibration of the Cepheid Leavitt Law. With addition of DR3 photometry, Gaia will likely also provide one of the strongest calibrations of the Tip of the Red Giant Branch. Recent refinements of the measurement of the Hubble constant in the local Universe appear to confirm and strengthen the well-established tension with the value inferred from Planck and Lambda-CDM cosmology.
Trouble with Hubble (inv)
Nils Schoneberg (Institut de Ciencies del Cosmos, Barcelona, Spain)
While the LCDM cosmological model has seen an uninterrupted chain of successes over the past decades, in the recent years a tension in the value of the Hubble parameter between inferences from early universe probes and measurements in the late universe has emerged. With the significance of this tension slowly rising to around the 5 sigma mark, it is prudent to re-investigate both the experimental and the theoretical side of this tension. In this presentation I give an overview of the recent efforts to independently corroborate the tension using a variety of experimental probes in the early and late universe and the recent theoretical advancements made in finding a model that would resolve the tension.
Session: Regular Variable Stars
Regular Variable Stars (inv)
Marcella Marconi (Osservatorio Astronomico di Capodimonte, Italy)
In this review I will focus on regular variable stars in Gaia and their astrophysical uses. As well known, regular variable stars allow us to investigate the properties of their host stellar population and to measure their distance thanks to the existence of relations connecting the pulsation parameters with evolutionary and structural quantities. Moreover the observed oscillation properties provide a fundamental benchmark for stellar evolution and pulsation models predictions. In this context, the astrometric, photometric and spectroscopic Gaia mission and in particular its latest data release (Gaia DR3) are providing fundamental information and constraints that are improving our knowledge of regular variable stars with important implications in several astrophysical fields.
Follow-up study of TCP J18224935-2408280; a symbiotic star identified during the outburst
Sonith L.S. (Indian Institute of Astrophysics, India)
TCP J18224935-2408280 is a transient discovered by Tadashi Kojima in May 2021. Follow-up spectroscopic observations reported in Astronomerstelegram by J. Merc et al. 2021 and E. Aydi et al. 2021 suggested that it can be a symbiotic star undergoing an outburst. We present our spectroscopic observations from the Himalayan Chandra Telescope (HCT), confirming its symbiotic nature based on the Raman-scattered O VI band. We found that the system was undergoing a classical symbiotic outburst (Z And-type) based on the light curves and spectroscopic observations obtained during the evolution of the outburst. The orbital period of the system is estimated to be ~599 days using GAIA DR3 photometric light curves. Our SED analysis identified that the system contains a cool giant with M1-2 III spectral type. Also, We summarise how significant Gaia light curves and other whole sky survey photometric data are for identifying the new symbiotic sources.
Uncovering the hidden population of symbiotic stars
Manica Perko (University of Ljubljana, Slovenia)
Symbiotic stars are interacting binary systems consisting of a companion star, usually a white dwarf, and a primary star, usually a red giant. In general, there are two phases of symbiotic stars: accreting- only and burning-type. There are several hundred known symbiotic systems, most of which are in the burning phase, but that is due to an observational bias. In the burning-type case, we observe strong nebular continuum and a rich emission line spectrum, so systems in this phase can be easily detected at optical wavelengths throughout the Galaxy and beyond. In order to determine the significance of symbiotic stars, we need to characterize and quantify the entire population in the Galaxy, not just the easily observed systems in the burning phase. Furthermore, we assume that symbiotic stars spend most of their lives in the accreting-only phase. These systems are difficult to detect because the optical spectrum is dominated by the red giant and there are no or only very weak emission lines present. In this presentation we will focus on accreting-only symbiotic stars, which can be distinguished from single giants by observed excess light in the UV and X-rays produced by the accretion disk around the white dwarf. We also observe faint emission lines like Halpha and Hbeta emanating from the area of the accretion disk. Another important feature for detection of accreting-only symbiotic stars is flickering. This rapid change in magnitude is a consequence of chaotic processes, such as density fluctuations in the accretion stream from the donor to the accreting star, which develop on timescales much shorter (around minutes) than those of other sources of variability. We can also distinguish accreting-only systems from other single giants by the IR excess, which may be a consequence of heated dust around the star. In our search for new symbiotic star candidates, specifically the accreting-only variety, we are working with large data sets. Our primary data set is based on spectroscopic observations from the GALAH Survey, where we study spectral features such as Halpha and H emission profiles. We are using color indices to detect UV and IR excess from photometric surveys, such as Gaia and WISE. Another important data used is ASAS light curves to exclude false positives due to pulsating stars. We are also searching for flickering with our own observations with Schmidt telescope in Asiago. Symbiotic stars are important for understanding the evolution and properties of our Galaxy. Due to the accretion of stellar wind from the red giant onto the white dwarf surface, they are considered one of the candidates responsible for the enrichment of the interstellar medium with lithium and other elements due to their nova outbursts. In the case of a white dwarf reaching critical mass, the accretion can lead to an explosion, making them a promising Type Ia supernova progenitor. For these reasons it is important to obtain better knowledge about the phases in which symbiotic stars live and quantify their total number in the Galaxy.
Galactic AGB stars as seen by Gaia-DR3 and the VO
Fran Jiménez-Estebanerko (Spanish Virtual Observatory, Spain)
Although 90% of the stars pass through the Asymptotic Giant Branch (AGB) at the end of their lives, details of this relatively short evolutionary phase are still not well understood. Due to the lack of accurate distances to galactic AGB stars, studies on the AGB evolutionary phase have been mainly done using the Magallanic Cloud AGB population. Now, thanks to the Gaia mission, we are able to explore the galactic AGB population as never before. We present a sample of thousands galactic AGB stars of different chemistries, built by cross-matching available literature compilations of AGB stars and the Gaia DR3 catalogue. Based on the shape of their spectral energy distributions (SEDs), built from a variety of photometric surveys and the help of the Virtual Observatory, we cleaned the AGB sample from interlopers and characterized it. About 30% OH/IR stars and 80% carbon stars have reliable parallax in Gaia DR3, allowing us to estimate their distances and absolute luminosities. In addition, Gaia DR3 provides light curves for many of them, which were used to derived the variability properties of the sample. In this talk I will present the properties of the galactic AGB stars, with special emphasize in the comparison between the O-rich and the C-rich galactic AGB populations.
Session: Transient phenomena
Gaia as a black hole discovery machine (inv)
Lukasz Wyrzykowski (Warsaw University Astronomical Observatory, Poland)
ESA's Gaia space mission monitors the entire sky and provides time-series of brightness, position and spectra of billion of stars. Thanks to the Gaia Science Alerts system, Gaia informs the astronomical community of interesting astrophysical phenomena from the entire sky. Among them, one of the rarest, are gravitational microlensing events - temporal brightenings due to lensing by an invisible object passing in front of a background star. At the same time, Gaia collects positional information, which will yield the most exciting and complete solutions on the nature of the lensing object and an opportunity of finding isolated black holes. I will present the most interesting events found by Gaia so far which were monitored by a ground-based network of telescopes. I will also present the prospects of using Gaia astrometric data for Gaia microlensing events, which will become available with Gaia DR4.
Is there a nearby microlensing stellar remnant hiding in Gaia DR3 astrometry?
MajaJabłońska (University of Warsaw, Poland)
Massive galactic lenses with large Einstein Radii should cause a measurable astrometric microlensing effect, i.e. the light centroid shift due to the motion of the two images. Such a shift in the position of a background star due to microlensing was not included in the Gaia astrometric model, therefore significant deviation should cause Gaia's astrometric parameters to be determined incorrectly. Here we studied one of the photometric microlensing events reported in the Gaia DR3, GaiaDR3-ULENS-001, for which poor goodness of Gaia fit and erroneous parallax could indicate the presence of the astrometric microlensing signal. Based on the photometric microlensing model, we simulated Gaia astrometric time series with the astrometric microlensing effect added. We found that including microlensing with the angular Einstein Radius of 2.23-2.81 mas reproduces well the astrometric quantities reported by Gaia. We estimate the mass of the lens to be 0.57-1.23 M⊙ and its distance to 0.60-1.04 kpc, proposing the lens could be a nearby isolated white dwarf.
The impact of gravitational lensing in the reconstruction of stellar orbits around Sgr A*
Silvia Pietroni (University of Salerno, Italy)
After the amazing discoveries by the GRAVITY collaboration in the last few years on the star S2 orbiting the black hole Sgr A* in the center of the Milky Way, we present a detailed investigation of the impact of gravitational lensing on the reconstruction of stellar orbits around this massive black hole. We evaluate the lensing astrometric effects on the stars S2, S38 and S55 and how these systematically affect the derived orbital parameters. The effect is below current uncertainties, but not negligible. With the addition of more observations on these stars, it will be possible to let the astrometric shift by lensing emerge from the statistical noise and be finally detected. By repeating the analysis on a smaller semimajor axis and various inclinations, we are able to quantify the lensing effects on a broader range of parameters. As expected, for smaller semimajor axes and for nearly edge-on orbits lensing effects increase by about an order of magnitude.
Session: Gaia in the Multi-messenger era
Gaia in the Multi-messenger era (inv)
Zuzanna Kostrzewa-Rutkowska (University of Leiden, Netherlands)
The recent discoveries of gravitational wave events and in one case also its electromagnetic (EM) counterpart allow us to study the Universe in a novel way. The increased sensitivity of the LIGO and Virgo detectors has opened the possibility for regular detections of EM transient events from mergers of stellar remnants. Gravitational wave sources are expected to have sky localisation up to a few hundred square degrees, thus Gaia as an all-sky multi-epoch photometric survey has the potential to be a good tool to search for the EM counterparts. I'll present the current status of searches for EM counterparts of GW events and the possibilities of their detections by Gaia.
Gravitational waves detection in the context of relativistic astrometry
Federica Santucci (Univ. of Turin, Italy)
The formulation of Gaia observable is not designed for the detection of passing gravitational waves, however the high-accuracy astrometry and the relativistic models developed for the Gaia mission could provide impulse to the astrometric research of gravitational waves. As a matter of fact, a general relativistic differential formulation of the astrometric observable allows to devise an astrometric gravitational waves antenna as a three-line-of-sight telescope in space as well as a tool for searching a GW signal in Gaia data. The talk will focus on the potential of the astrometric gravitational wave antenna to determine the amplitude and frequency of gravitational waves and to identify the direction to the gravitational source with unprecedented accuracy, showing the complementarity with the performance of ground-based interferometers and, possibly, its applicability to Gaia data.
Session: Active Galactic Nuclei
AGN, SNe, extended sources, galaxies in the Gaia DR3 variability analysis (inv)
Laurent Eyer (Observatoire de Genève, Switzerland)
The third Gaia data release contains a global variability analysis with associated published catalogues. We implemented a supervised classification of the celestial sources into variable stars and extragalactic sources with corresponding training sets based on a compilation of the literature crossmatched Gaia sources. This presentation provides an overview of what was done for the third Gaia data release
QSOs and the Extragalactic Reference Frame (inv)
Beatrice Bucciarelli (Osservatorio Astronomico di Torino, Italy)
A direct link between the radio and optical realizations of the International Celestial Reference System (ICRS) has been achieved thanks to ESA’s Gaia mission, which at its third data release comprises about 1.6 million QSO-like sources. I will outline the principal steps of this task and present the statistical properties of the defined celestial reference frame; I will also underline some relevant issues related to the astrometric variability of QSOs, such as their internal structure, peculiar motions, and aberration-induced proper motions.
The search for variable AGN with Gaia
Maria Isabel Carnerero (INAF-Osservatorio Astrofisico di Torino, Italy)
The third release of Gaia data, published on June 13, 2022, includes not only astrometric and astrophysical parameters of different types of sources, but also several catalogues of variable sources. Among these, the catalogue of Gaia variable AGN, which is described by Carnerero et al. (2022). To identify the variable AGN, we analyzed the light curves of more than 80 million sources observed by Gaia, selecting 870 thousands of them compliant with requirements on their variability properties (structure function, Butler and Bloom metrics, fractional variability), color indices, astrometric parameters and others. The purpose was to create a variable AGN catalogue as pure as possible. More than 21,000 of these 870 thousand sources (about 2.5% of the total) are identified as variable AGN for the first time. For each source of the catalogue, the Gaia multi-band light curves and the values of the variability parameters have been included in the database.
Binary supermassive black hole candidate in Stripe 82 region
Marta Fatovic (Ruđer Bošković Institute, Croatia)
I will report the results of a search for long-period (100<P<600 days) sources with small-amplitude (A > 0.03 mag) periodic variability in SDSS Stripe 82 region. The SDSS coverage of Stripe 82 enables such a search because there are on average 20 observations per band in ugriz bands for about 1 million sources, collected over about 6 years, with a faint limit of r~22 mag and precisely calibrated 1-2% photometry. Lomb-Scargle periodograms of candidate variable sources from this sample were calculated and carefully scrutinized in order to select only those sources with the highest likelihood of being true periodic variables and avoid the possibility of false periodicity caused by stochastic variability. In addition to periodogram analysis, we cross-matched the candidate periodically variable sources to other surveys across the EM spectrum (photometry and spectroscopy) in order to confirm their variability, its origin and the type of the source. Our analysis yields 11 candidate periodically variable sources and is reinforced by Pan-STARRS and ZTF time series extending the observational baseline to more than 20 years. Furthermore, most of the candidates have optical spectra that allowed determination of the type of the source. The candidate list is dominated by quasars (inferred from the spectroscopy). The highest-ranked candidate has a spectrum consistent with a quasar and a period of 278 days. It is furthermore flagged as a variable source in the Chandra X-ray catalogue. Multiple explanations for the observed periodic behaviour of quasars are found in the literature: radio jet precession, tilted or warped accretion disks, tidal disruption remnants and other accretion-related effects. While these effects can be caused by a single black hole, most models require super-massive binary black holes (SMBBH). If this object indeed proves to be a SMBBH -- one of the loudest sources of gravitational waves, it would become the SMBBH with the shortest known period and therefore likely most compact orbit and remaining time before the merger and emission of GWs. In order to ascertain the nature of this object, and hopefully prepare for longer-term monitoring of it and similar systems, we have received 2.18hrs of Director's Discretionary Time on Gemini telescope’s GMOS-N instrument. This will allow us to study the conspicuous Mg II line visible in extant spectra of lower resolution and signal-to-noise ratio for the presence of asymmetries and additional peaks that could indicate the presence of SMBBH. I would also like to put these finding into the context of future Gaia data releases and time-domain surveys such as Vera C. Rubin Legacy Survey of Space and Time. It has been shown that full 10-year Gaia data could astrometrically resolve orbital motion of final-stage (sub-pc separation) SMBBHs up to z=0.02 and in the magnitude range 10<V<13 (D’Orazio and Loeb, 2019). On the other hand, LSST’s etendue and expected exquisite photometric precision will allow searches in a much larger volume.
Unveiling the Changing Look Quasar candidates by studying the extreme Spectral Index Variability and Light curve variability using SDSS and GAIA DR3
Sarath SS (Univ. Andres Bello, Chile)
Changing Look Quasars (CLQs), where the quasar continuum brightens/dims followed by an appearance/disappearance of broad emission lines, offers an excellent opportunity to probe the quasar central engine powering the luminosity of AGN. If accretion rate changes are responsible for the observed CLQs, quasars undergoing significant spectral index changes are excellent candidates for CLQs. Since its discovery in the year 2015, there are ∼ 100 known CLQs mostly identified using the multi-epoch spectra from Sloan Digital Sky Survey (SDSS) data (Lamassa 2015, Macleoad 2016,). The disappearance of the broad emission lines is often associated with a drop in the continuum flux, suggesting a common physical mechanism. CLQs are usually identified in the following ways: (1) from optical light curves that have a magnitude difference greater than 0.5 (2) from a comparison of emission lines in a multi-epoch spectroscopic dataset like SDSS, and (3) WISE light curves having large magnitude difference. As these methods rely heavily on archival data, most of the time, CLQs are discovered well after the transition. Catching these events during the transition is important to understand the physical conditions prevailing at the time of CLQ transition. In this attempt, we recently carried out a search for identifying quasars showing large spectral index variations using SDSS DR16 data. We targeted quasars with multiple epochs of spectra available from SDSS. We fitted a power law for the AGN continuum and Gaussian models for the emission lines using the PyQSOFit software. Quasars with spectral index differences greater than 0.5 were selected as CLQ candidates. All these candidates are validated to have strong magnitude changes (|∆m| ∼ 0.3) using the available optical light curves from CRTS and GAIA DR3. The well-established” bluer when brighter” trend of the AGN continuum and spectral index indeed points to a connection between the AGN luminosity and the spectral shape. We were able to detect 53 potential candidates having a larger spectral slope difference than the threshold even though GAIA light curves were available only for 42 sources. These potential candidates are proposed for follow-up spectroscopy to understand much about the transient phase of the sources and also to study the physical processes.
Session: Tidal disruption events
A review of tidal disruption events (inv)
Thomas Wevers (European Southern Observatory)
I will introduce tidal disruption events and discuss their observational properties across the electromagnetic spectrum, together with our current understanding of the physics underlying them. I will also highlight some key open questions in the field, such as the origin of the UV/optical emission, and recent work that is helping us answer them. I will end with a brief look towards the future, including the potential of TDEs as multi-messenger sources.
The rise and fall of the iron-strong nuclear transient PS16dtm
Tanja Petrusevska (Univ. of Nova Gorica, Slovenia)
Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centres of galaxies - nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN). Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN. I will present PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy which has been proposed to be a TDE candidate. I will show our multi-year spectroscopic and photometric study of PS16dtm, which can help us to better understand the outbursts originating in NLSy1 galaxies.
The mass fallback rate of the debris in relativistic stellar tidal disruption events
Taj Jankovič (Univ. of Nova Gorica, Slovenia)
Highly energetic stellar tidal disruption events (TDEs) provide a way to study black hole characteristics and their environment. We simulate TDEs in a general relativistic and Newtonian description of a supermassive black hole's gravity. Stars, which are placed on parabolic orbits with different impact parameters, are constructed with the stellar evolution code MESA and therefore have realistic stellar density profiles. We focus our analysis on the mass fallback rate of the debris, which can trace the observed light curve of TDEs. I will present the dependence of the mass fallback rate of the debris on the impact parameter, stellar mass and age as well as the black hole's spin and the choice of the gravity's description.
Session: Gaia in the framework of new facilities
The Rubin LSST transients and variable sky (inv)
Federica Bianco (University of Delaware, USA)
Vera C. Rubin Observatory is approaching completion and about to begin the Legacy Survey of Space and Time, LSST, an unprecedented multi-band optical imaging survey. The combination of flux sensitivity – r~25 limiting magnitude for a single image, r~27 for the 10-year stacks –, area coverage – the whole Southern hemisphere sky and extending to special regions above the celestial equator –, and temporal sampling rate – from hours to decades with repeated images within a night and a few nights apart – will reach areas of the Universe and of the discovery parameter space previously entirely unexplored, making this survey potentially transformative for most if not all fields of astronomy and astrophysics. The survey cadence, image resolution and quality, and state-of-the-art rapid image processing will enable the identification of an expected 10M transients and variable phenomena each night, which will be broadcasted worldwide in real-time with an open data policy. I will review the status of Rubin Observatory and its LSST, the data products and data access rules and modalities, the potential for discovery, and emphasize potential synergies that can truly realize the survey’s potential for discovery
PLATO, TESS and Gaia (inv)
Susana Barros (Instituto de Astrofísica e Ciências do Espaço, Portugal)
I will give an overview of Exoplanet research in the context of the current and next space mission. I will explore the expected exoplanet yield by the GAIA mission and the synergies between GAIA, and TESS, CHEOPS and PLATO. GAIA is expected to discover many planets through astrometry and also a few through transit photometry. GAIA astrometry also allows a better characterisation of the orbits and masses of planetary systems and has had a large impact in the characterisation of the exoplanet host stars. This impacts directly the precision of the derived planetary parameters including those discovered by TESS and in the future PLATO. It also provides valuable information about for candidate validation and it has been used to help select the PLATO field of view.
EUCLID and Gaia (inv)
Jarle Brinchmann (Centro de Astrofisica da Universidade do Porto, Portugal)
I will give a brief overview of what Euclid will provide and how Gaia is indispensable for Euclid and how Euclid will add to the power of Gaia.
The SKA Observatory view of transients: synergies with Gaia (inv)
Philippa Hartley (SKA Observatory), U.K.
The SKA Observatory (SKAO) is building the two largest radio telescope arrays in the world, in an international effort to revolutionise our view of the radio sky. Now under construction in South Africa and Australia, the telescopes will respectively cover the low and mid to high radio frequencies. Large survey programmes will cover a broad range of science objectives, including transient phenomena both galactic and extragalactic. The revolutionary studies of stars, exoplanets and quasars performed by the Gaia mission will be complemented by SKAO studies in the radio, where detection of pulsars, masers and fast radio bursts will likewise probe the nature of our own Galaxy and the nature of spacetime itself. In this talk, I will present an overview of the SKA roadmap before highlighting the synergies that exist with between the SKAO and Gaia relevant to the study of transients.
Long term follow-up coverage of Gaia alert sources
Rene Hudec (Academy of Sciences of Czech Republic, Czechia)
The robotic telescopes at the Ondrejov Observatory provide long-term optical multi-color coverage for selected 25 Gaia alert triggers located in the northern sky hemisphere. I will present and briefly discuss examples of selected results, mostly unpublished, obtained with these devices. In addition to that, I will present and discuss the potential of large historical photographic plate archives located around the globe as sources of both photometric as well as spectroscopic data able to allow really long-term study of photometric and spectroscopic evolution for astrophysical sources in general and for Gaia alert sources in particular. I will include the LDS (Low Dispersion Spectroscopy) performed in various extended sky surveys with optical telescopes using an objective prism and photographic plates offering an interesting opportunity to extend the low-dispersion spectra from the Gaia BP/RP photometers to other epochs and to compare them with historical data, especially for objects with strong emission lines.
