Tomislav Jurkić

This study presents Solar Cycle (SC) 25 (2020–2025) results from the homogeneous Kanzelhöhe Solar Observatory (KSO) catalogue project and completes the analysis of SCs 19–25. Only SC18 remains to be processed before the catalogue is finalized. Using KSO white-light observations, we determined sidereal rotation velocities and solar differential rotation (DR) parameters A and B from day-to-day positional changes in sunspot-groups and from robust linear fits to their position–time measurements. Their temporal evolution and relationship with solar activity were analyzed using yearly mean Solar Index and Long-term Solar Observations (SILSO) sunspot numbers. Rotation velocity residuals were also analyzed as a function of time and heliographic latitude in search of possible torsional oscillation (TO) signatures. The obtained DR parameters are consistent with previously published results. For SC25, a strong anticorrelation between the yearly fitted parameters A and B was found, in agreement with earlier studies, although its interpretation is affected by the covariance between the two parameters introduced by the fitting procedure. The residual rotation velocities exhibit temporal behaviour similar to that reported in previous sunspot-group studies. Latitude–time residual maps reveal patterns that may represent TO signatures, however the limited temporal coverage of SC25, the characteristics of sunspot group tracers, and the use of interpolated data require a cautious interpretation.

Coherent and quasi-coherent variability in active galactic nuclei (AGN) can serve as a useful diagnostic of dynamical processes operating in the immediate environments of supermassive black holes. The time-domain capabilities of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) enable systematic searches for such signals across large AGN samples. We identify and classify coherent oscillatory processes in AGN cores using LSST Data Preview 1 (DP1), and compile the results in the QhX Hub, an interactive catalog providing statistical variability features and visualization tools. AGN are selected by cross-matching LSST DP1 sources with external catalogs, and light curves are analyzed with the multiband wavelet-based Quasar harmonic eXplorer ( QhX ), designed to detect coherent signals in irregularly sampled, red-noise-dominated data. The catalog contains 230 objects stratified into variability classes. A single strong coherent candidate is identified: 3D-HST 2351, z = 0.198, LSST DP1 object_id = 611255072642321324, with a period of P = 2.7 6 − 0.06 + 2.65 days, where the large upper bound reflects the limited observational baseline. Its coherent nuclear variability is the primary motivation for follow-up. In subsequent LSST data releases, all catalog sources will be recalculated on progressively longer baselines, enabling more robust population-level characterization of coherent AGN variability.

Aims . We investigate the utility of Rubin ’s Data Preview 1 (DP1) for estimating stellar number density profiles across the Milky Way halo. Methods . We used stellar broad-band near-UV to near-IR ugrizy photometry released in Rubin ’s DP1 to estimate distance and metallicity for blue main sequence stars brighter than r = 24 in three ~1.1 sq. deg. fields at southern Galactic latitudes. Results . Compared to TRILEGAL simulations of the Galaxy’s stellar content, we found a likely deficit of blue main sequence turn-off stars with 22 < r < 24. We interpreted this discrepancy as a signature of a steeper halo number density profile at galactocentric distances 10–50 kpc than the canonical ~1/ r ³ profile assumed in TRILEGAL simulations. Conclusions . This interpretation is consistent with earlier suggestions based on observations of more luminous, but much less numerous, evolved stellar populations, along with a few pencil beam surveys of blue main sequence stars in the northern sky. These results bode well for the future Galactic halo exploration with Rubin ’s Legacy Survey of Space and Time (LSST).

An analysis of the solar differential rotation (DR) during solar cycle No. 24 (SC24) (2009–2019), based on the Kanzelhöhe Observatory for Solar and Environmental Research (KSO) data set, is presented. The white-light images were processed and positions of sunspot groups were extracted using the morphological image processing technique. The sample was constrained to ±58° in central meridian distance (CMD). Two methods were applied to derive the sidereal angular rotation rate (ω) and, in turn, the solar rotation parameters A and B: (a) calculating synodic rotation velocities from daily CMD differences and elapsed time (daily shift method); (b) applying a robust linear least-squares fit to the time series CMD(t) for each sunspot group. To assess the relationship between rotation parameters and solar activity, we analyzed the yearly mean total sunspot number from the Sunspot Index and Long-term Solar Observations (SILSO). This study marks the first complete analysis of SC24 using the KSO sunspot groups’ data. Our goal is to extend the previous analysis of DR from the KSO data to the present, especially because the Solar Optical Observing Network/United States Air Force/National Oceanic and Atmospheric Administration data set (SOON/USAF/NOAA) and Debrecen Photoheliographic Data (DPD) catalogues do not provide data after 2018.

As demonstrated with the Sloan Digital Sky Survey (SDSS), Pan-STARRS, and most recently with Gaia data, broadband near-UV to near-IR stellar photometry can be used to estimate distance, metallicity, and interstellar dust extinction along the line of sight for stars in the Galaxy. Anticipating photometric catalogs with tens of billions of stars from Rubin's Legacy Survey of Space and Time (LSST), we present a Bayesian model and pipeline that build on previous work and can handle LSST-sized datasets. Likelihood computations utilize MIST/Dartmouth isochrones and priors are derived from TRILEGAL-based simulated LSST catalogs from P. Dal Tio et al. The computation speed is about 10 ms per star on a single core for both optimized grid search and Markov Chain Monte Carlo methods; we show in a companion paper by K. Mrakovčić et al. how to utilize neural networks to accelerate this performance by up to an order of magnitude. We validate our pipeline, named PhotoD (in analogy with photo-z, photometric redshifts of galaxies) using both simulated catalogs and SDSS, DECam, and Gaia photometry. We intend to make LSST-based value-added PhotoD catalogs publicly available via the Rubin Science Platform with every LSST data release.

D type symbiotic binaries are an excellent astrophysical laboratory for investigation of the dust properties and dust formation under the influence of theMira stellar wind and nova activity and of...

We present a model of inner dust regions around the cool Mira component of the two symbiotic novae, RR Tel and HM Sge, based on the near-IR photometry, ISO spectra and mid-IR interferometry. The dust properties were determined using the DUSTY code. A compact circumstellar silicate dust shell with inner dust shell temperatures between 900 K and 1300 K and of moderate optical depth can explain all the observations. RR Tel shows the presence of an equatorially enhanced dust density during minimum obscuration. Obscuration events are explained by an increase in optical depth caused by the newly condensed dust. The mass loss rates are significantly higher than in intermediate-period single Miras but in agreement with longer-period O-rich AGB stars.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

The ISO infrared spectra and the SAAO long-term JHKL photometry of RR Tel in the epochs during minimum obscuration are studied in order to construct a circumstellar dust model. the spectral energy distribution in the near- and the mid-IR spectral range (1–15 μm) was obtained for an epoch without the pronounced dust obscuration. the DUSTY code was used to solve the radiative transfer through the dust and to determine the circumstellar dust properties of the inner dust regions around the Mira component. Dust temperature, maximum grain size, dust density distribution, mass-loss rate, terminal wind velocity and optical depth are determined. the spectral energy distribution and the long-term JHKL photometry during an epoch of minimum obscuration show almost unattenuated stellar source and strong dust emission which cannot be explained by a single dust shell model. We propose a two-component model consisting of an optically thin circmustellar dust shell and optically thick dust outside the line of sight in some kind of a flattened geometry, which is responsible for most of the observed dust thermal emission.