Rolf Chini

The Southern Galactic Disk Survey (GDS) monitored a mosaic of 268 fields along a 6°‐wide stripe in the southern galactic disk from September 2010 to September 2019. These fields were observed between 21 and 407 times sim ultaneously in () and (), supplemented by between 2 and 147 observations in each of the bands , , , and . Here we present the matched multi‐band catalogue, which integrates photometry and light curve data from all bands, containing photometry for almost 21.7 million Gaia DR3 sources, of which 113,449 are identified as variables. We give an overview of the survey's variable content with respect to its main characteristics and known variability type classifications. The comparison with the cross‐match catalogue of Gaia DR3 sources with variables from the literature compiled by Gavras et al. and the International Variable Star Index (VSX) indicates that approximately of the variable sources remain unclassified in terms of variability type. Light curves for all of these sources are contained in the GDS data catalogues, available via the German Astrophysical Virtual Observatory (GAVO), and can contribute to their classification.

Aims . Despite their key role in astrophysics, the binary properties of RR Lyrae stars (RRLs) are almost completely unknown since only a single RRL is confirmed as belonging to a binary system. Finding companions to RRLs is difficult since most of them will be at wider orbits, given that close orbits will likely cause mass transfer, thus disrupting the conditions for developing stellar pulsations. These wide orbits open the possibility that RRL companions may be more easily found by high-resolution imaging. Methods . We observed 81 RRLs with the speckle interferometers Zorro and ’Alopeke at the Gemini telescopes, reaching the diffraction limit of ∼20 mas of these 8m-class telescopes, and therefore exploring a new parameter space around RRLs. Results . We have detected ten newly identified companions around these 81 RRLs, with projected separations between 20 AU to 220 AU. An analysis of the field contamination shows that all of these detected companions are most likely gravitationally bound binaries. From these observations we can estimate an RRL binary fraction higher than 12%, ruling out a binary fraction higher than 25% at the 99% confidence level. These numbers are significantly more elevated than previous estimations which were close to a binary fraction of only 1%, although derived with methods exploring a different parameter space. For RRLs with thin disk kinematics, we find that the binary fraction is significantly lower, around 6%, with a single thin disk RRLs having a companion out of the 16 observed. The nature of the companions, found to be stars in the lower red giant branch and upper main sequence, is also studied via the measurement of the minimum light colors of the RRL, which is a useful method for the search and analysis of RRLs in binary systems.

Context. Anomalous Cepheids (ACEPs) are radially pulsating stars observed in dwarf galaxies, the Galactic bulge and halo, and globular clusters. Similarly to other radially pulsating stars, they can be used as distance indicators through their period-luminosity relations (PLRs) and the geometrical Baade-Wesselink (BW) method. Aims. We aim to calibrate the zero point of the distance scale of ACEPs using nearby representatives of this class of pulsating stars. Methods. We collected optical/near-infrared photometry and spectra for a sample of nearby ACEPs with two telescopes located at the RolfChini Cerro Murphy Observatory (formerly Observatory Cerro Armazones) and optical telescopes offered by the Las Cumbres Observatory, along with instruments hosted and operated by the European Southern Observatory. Using parallaxes measured by the Gaia space mission and mean magnitudes from our new photometry, we calibrated the zero point of the period-luminosity relations (PLRs) in Johnson B , V , 2MASS J , H , K _S , and Pan-STARRS g , r , i passbands, as well as select Wesenheit indices. The slopes were adopted from the PLRs of the LMC ACEPs from the literature. Using the surface brightness-color relation version of the BW technique, we were also able to determine the projection factors (p-factors) and mean radii of three nearby ACEPs. Results. The precision of the measured zero points is at the level of 0.04–0.05 mag and their systematic uncertainty was estimated to be about 0.1 mag. We used our zero point values and literature photometry related to LMC ACEPs to measure the distance modulus of this galaxy. We obtained a value of 18.454 ± 0.045 (statistical) mag, which is in very good agreement with the most accurate value from eclipsing binaries. The p-factors were 1.38 ± 0.13, 1.59 ± 0.21, and 1.35 ± 0.14 for V716 Oph, XX Vir, and UY Eri, respectively. We suspect that the very high p-factor of XX Vir results from the underestimated parallax of this star in the Gaia catalog, as its radius and absolute brightness are also higher than expected for ACEPs at this period. Finally, the radii measured for V716 Oph and UY Eri are in agreement with the period-radius relation obtained from LMC ACEPs.

Context. Double-peaked emission lines are observed in a small percentage of active galactic nuclei (AGN). These lines allow the determination of fundamental properties of the line-emitting region, known as the broad-line region (BLR). Aims. We investigated the structure and kinematics of the BLR in the nearby Seyfert galaxy NGC 4593 through an analysis of the near-infrared (NIR) line blend of Ca IIλ8498, λ8542, λ8662, and O Iλ8446 observed in a 2019 VLT/MUSE spectrum. Methods. We performed a detailed decomposition of the NIR Ca II triplet and O Iλ8446 blend, extracting clean profiles of Ca IIλ8498, λ8542, λ8662, and O Iλ8446. We then fitted Ca IIλ8662 with a relativistic elliptical line-emitting accretion disk model. Results. The extracted line profiles are double-peaked with a full width at half maximum (FWHM) of ∼3700 km s⁻¹ and exhibit a redward asymmetry with a red-to-blue peak ratio of 4:3. The Ca II triplet lines have an intensity ratio of 1:1:1 and show no evidence of a central narrow or intermediate-width component. The profiles of Ca II and O I are remarkably similar, suggesting a common region of origin. Given the 1:1:1 ratio of the Ca II triplet, this region is likely a high-density emission zone, and the Ca IIλ8662 profile is well described by a mildly eccentric, low-inclination relativistic line-emitting disk with minimal internal turbulence. The profile represents one of the clearest kinematic signatures of a relativistic disk observed in BLR emission lines to date. Conclusions. The double-peaked profiles of the NIR Ca II triplet and O Iλ8446 in NGC 4593 represent the first detection of double-peaked Ca II and O Iλ8446 in a nontransient AGN spectrum. The minimal intrinsic turbulence (the lowest value reported for an AGN emission line to date) and the absence of narrow or intermediate-width components in Ca IIλ8662 make it a powerful diagnostic tool of BLR structure and kinematics. Further investigations of the profiles of Ca II and O I in other AGN are recommended to better constrain BLR properties and the nature of the underlying accretion flow.

The distance to the stars is a fundamental parameter, which is determined via two primary methods—parallax and luminosity. While the parallax is a direct trigonometric method, the luminosity distance is usually influenced by interstellar extinction. As long as the optical properties of dust grains are wavelength-dependent this contamination can be corrected. However, as the grain size increases, the extinction properties become gray, meaning these particles contribute by a constant at wavelengths ≲ 1 μm, making them undetectable by photometry in the optical. In this study, we compare the parallactic and luminosity distances of a pristine sample of 33 well-known early-type stars with nonpeculiar reddening curves and find that the luminosity distance overestimates the parallactic distance in 80% of the cases. This discrepancy can be removed when incorporating a population of large, submicrometer-sized dust grains in a dust model that provides gray extinction, which diminishes the luminosity distance accordingly.

We present the results of a nearly decade-long photometric reverberation mapping (PRM) survey of the Hα emission line in nearby (0.01 ≲ z ≲ 0.05) Seyfert galaxies using small (15–40 cm) telescopes. Broadband filters were used to trace the continuum emission, while narrowband filters tracked the Hα-line signal. We introduce a new PRM formalism to determine the time delay between continuum and line emission using combinations of auto- and cross-correlation functions. We obtain robust delays for 33/80 objects, allowing us to estimate the broad-line region (BLR) size. Additionally, we measure multiepoch delays for six objects whose scatter per source is smaller than the scatter in the BLR size–luminosity relation. Our study enhances the existing Hα size–luminosity relation by adding high-quality results for 31 objects, whose nuclear luminosities were estimated using the flux-variation gradient method, resulting in a scatter of 0.26 dex within our sample. The scatter reduces to 0.17 dex when the six lowest-luminosity sources are discarded, which is comparable to that found for the Hβ line. Single-epoch spectra enable us to estimate black hole masses using the Hα line and derive mass accretion rates from the iron-blend feature adjacent to Hβ. A similar trend, as previously reported for the Hβ line, is implied whereby highly accreting objects tend to lie below the size–luminosity relation of the general population. Our work demonstrates the effectiveness of small telescopes in conducting high-fidelity PRM campaigns of prominent emission lines in bright active galactic nuclei.

We determined the projected rotational velocity (v sin i) of 238 southern O stars selected from the Galactic O-star Survey. The sample contains 130 spectroscopic single stars (C), 36 single-lined binaries (SB1), and 72 SB2 systems (including eight triples). We applied the Fourier method to high-resolution spectra taken at Cerro Murphy, Chile, and supplemented by archival spectra. The overall v sin i statistics peaks at slow rotators (40–100 km/s) with a tail towards medium (100–200 km/s) and fast rotators (200–400 km/s). Binaries, on average, show increased rotation, which differs for close (P_orb < 10 d) and wide binaries (10 d < P_orb < 3700 d), and for primaries and secondaries. The spin-up of close binaries is well explained by the superposition of spin-orbit synchronisation and mass transfer via Roche-lobe overflow. The increased rotation of wide binaries, however, needs another explanation. Therefore, we discuss various spin-up mechanisms. Timescale arguments lead us to favour a scenario where wide O binaries are spun-up by a combination of cloud or disk fragmentation, which lays the basis of triple and multiple stars, and the subsequent merging or swallowing of low-mass by higher-mass stars or proto-stars.

Telescope cycle time estimation is one of the basic issues of observational astronomy. There are not many tools that help to calulate the cycle time for multiple telescopes with multiple instruments. This work presents a new tool for determing the observation time; it was applied at the Cerro Murphy Observatory (OCM) but can be used at any other observatory. The Machine Learning (ML) method was implied, resulting in a fully automatic software module that works without any user intervention. We propose a polynomial multiple regression method and demonstrate all steps to build a reliable ML model like data collecting, data cleaning, model training and error evaluation in relation to the implementation in the observatory software. The method was designed to work for different telescopes with several instruments. Accuracy analysis and the assessment of model errors were based on real data from telescopes, proving the usefulness of the presented method. Error evaluation shows that for 84.2 % of nights, the prediction error in operation time prediction does not exceed 2 %. Converted into a 10-hour observation night, 2 % corresponds to an error of no more than 12 minutes. The described model is already working at the OCM and optimizes the efficiency of the observations.

We present the results of a nearly decade-long photometric reverberation mapping (PRM) survey of the H$α$ emission line in nearby ($0.01\lesssim z \lesssim0.05$) Seyfert-Galaxies using small ($15\,\mathrm{cm}-40\,\mathrm{cm}$) telescopes. Broad-band filters were used to trace the continuum emission, while narrow-band filters tracked the H$α$-line signal. We introduce a new PRM formalism to determine the time delay between continuum and line emission using combinations of auto- and cross-correlation functions. We obtain robust delays for 33/80 objects, allowing us to estimate the broad-line region (BLR) size. Additionally, we measure multi-epoch delays for 6 objects whose scatter per source is smaller than the scatter in the BLR size-luminosity relation. Our study enhances the existing H$α$ size-luminosity relation by adding high-quality results for 31 objects, whose nuclear luminosities were estimated using the flux-variation gradient method, resulting in a scatter of 0.26dex within our sample. The scatter reduces to 0.17dex when the 6 lowest luminosity sources are discarded, which is comparable to that found for the H$β$ line. Single-epoch spectra enable us to estimate black hole masses using the H$α$ line and derive mass accretion rates from the iron-blend feature adjacent to H$β$. A similar trend, as previously reported for the H$β$ line, is implied whereby highly accreting objects tend to lie below the size-luminosity relation of the general population. Our work demonstrates the effectiveness of small telescopes in conducting high-fidelity PRM campaigns of prominent emission lines in bright active galactic nuclei.