V. D. Ivanov
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View article: Transients as Determinants of Habitability
Transients as Determinants of Habitability Open
Stellar magnetic activity, manifested through spots (faculae and flares), fundamentally shapes the exoplanets' environments. For low-mass stars in particular, where most habitable-zone planets reside, the variable magnetic phenomena can do…
View article: PLATOSpec: a precise spectrograph in support of space missions
PLATOSpec: a precise spectrograph in support of space missions Open
The upcoming space missions that will characterize exoplanets, such as PLATO and Ariel, will collect huge amounts of data that will need to be complemented with ground-based observations. The aim of the PLATOSpec project is to perform scie…
View article: High energy gamma-ray sources in the VVV survey – III. Spectroscopic confirmation of an AGN at low Galactic latitudes
High energy gamma-ray sources in the VVV survey – III. Spectroscopic confirmation of an AGN at low Galactic latitudes Open
We aim to spectroscopically confirm the nature of VVV-J181258.71-314346.7, a candidate counterpart to the unassociated gamma-ray source 4FGLJ1812.8−3144. This object was selected based on its near-infrared photometric properties and modera…
View article: Spatially resolved near-infrared spectroscopic indices for the massive elliptical galaxy IC 4296
Spatially resolved near-infrared spectroscopic indices for the massive elliptical galaxy IC 4296 Open
Context. In the near-infrared (NIR) region, a large number of absorption features may be used to constrain the properties of unresolved stellar populations of galaxies. Aims. We present the results of a pilot project assessing the feasibil…
View article: The VMC Survey
The VMC Survey Open
Context. Anomalous Cepheids (ACs) are pulsating variable stars, and are less studied compared to the well-known Classical Cepheids (CCs) and RR Lyrae stars. The ACs are metal poor ([Fe/H] < 1.5) and follow distinct period-luminosity (PL) a…
View article: The VMC survey
The VMC survey Open
Context. The near-infrared YJK s Visual and Infrared Survey Telescope for Astronomy (VISTA) survey of the Magellanic Clouds (VMC) is complete, along with data from additional programmes contributing to the enhancement of its quality over t…
View article: Optical constraints on the coldest metal-poor population
Optical constraints on the coldest metal-poor population Open
Context. The coldest metal-poor population made up of T and Y dwarfs can serve as an archaeological tracer of our Galaxy because these very old objects have retained their pristine material. The optical properties of these objects are impo…
View article: The VMC Survey – LI. Classifying extragalactic sources using a probabilistic random forest supervised machine learning algorithm
The VMC Survey – LI. Classifying extragalactic sources using a probabilistic random forest supervised machine learning algorithm Open
We used a supervised machine learning algorithm (probabilistic random forest) to classify ∼130 million sources in the VISTA Survey of the Magellanic Clouds (VMC). We used multi-wavelength photometry from optical to far-infrared as features…
View article: The VMC Survey : LI. Classifying extragalactic sources using a probabilistic random forest supervised machine learning algorithm
The VMC Survey : LI. Classifying extragalactic sources using a probabilistic random forest supervised machine learning algorithm Open
We used a supervised machine learning algorithm (probabilistic random forest) to classify ~130 million sources in the VISTA Survey of the Magellanic Clouds (VMC). We used multi-wavelength photometry from optical to far-infrared as features…
View article: VIRAC2: NIR astrometry and time series photometry for 500M+ stars from the VVV and VVVX surveys
VIRAC2: NIR astrometry and time series photometry for 500M+ stars from the VVV and VVVX surveys Open
We present VIRAC2, a catalogue of positions, proper motions, parallaxes and Z, Y, J, H, and $K_s$ near-infrared photometric time series of 545 346 537 unique stars. The catalogue is based on a point spread function fitting reduction of nea…
View article: Optical constraints on the coldest metal-poor population
Optical constraints on the coldest metal-poor population Open
The coldest metal-poor population made of T and Y dwarfs are archaeological tracers of our Galaxy because they are very old and have kept the pristine material. The optical properties of these objects are important to characterise their at…
View article: Obscured star clusters in the inner Milky Way
Obscured star clusters in the inner Milky Way Open
Context. Milky Way star clusters provide important clues about the history of star formation in our Galaxy. However, the dust in the disk and in the innermost regions hides them from the observers. Aims. Our goal is twofold. First, to dete…
View article: Obscured star clusters in the Inner Milky Way. How many massive young clusters are still awaiting detection?
Obscured star clusters in the Inner Milky Way. How many massive young clusters are still awaiting detection? Open
Aims. Our goal is twofold. First, to detect new clusters we apply the newest methods for the detection of clustering with the best available wide-field sky surveys in the mid-infrared because they are the least affected by extinction. Seco…
View article: An automated method to detect and characterise semi-resolved star clusters
An automated method to detect and characterise semi-resolved star clusters Open
We present a novel method for automatically detecting and characterising semi-resolved star clusters: clusters where the observational point-spread function (PSF) is smaller than the cluster's radius, but larger than the separations betwee…
View article: The VISTA Variables in the Vía Láctea extended (VVVX) ESO public survey: Completion of the observations and legacy
The VISTA Variables in the Vía Láctea extended (VVVX) ESO public survey: Completion of the observations and legacy Open
Context. The ESO public survey VISTA Variables in the Vía Láctea (VVV) surveyed the inner Galactic bulge and the adjacent southern Galactic disk from 2009–2015. Upon its conclusion, the complementary VVV extended (VVVX) survey has expanded…
View article: The VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey: Completion of the observations and legacy
The VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey: Completion of the observations and legacy Open
The ESO public survey VISTA Variables in the Vía Láctea (VVV) surveyed the inner Galactic bulge and the adjacent southern Galactic disk from $2009-2015$. Upon its conclusion, the complementary VVV eXtended (VVVX) survey has expanded both t…
View article: Search and Study of the Brightest Stars in the Galaxy IC 342
Search and Study of the Brightest Stars in the Galaxy IC 342 Open
We have selected candidate massive stars in the galaxy IC 342 based on archival images from the Hubble Space Telescope and images from the 2 m telescope at the Natioal Astronomical Observatory Rozhen, Bulgaria. Spectral observations of 24 …
View article: Results of a long-term optical variability study of 11 quasars and VRI photometry of comparison stars
Results of a long-term optical variability study of 11 quasars and VRI photometry of comparison stars Open
We present the results of a 15-yr long-term optical monitoring of 11 quasars conducted with the 2-m Ritchey–Chretien–Coude and the 50/70 cm Schmidt telescopes at the Rozhen National Astronomical Observatory, Bulgaria. Our observations are …
View article: HD 110067 c has an aligned orbit
HD 110067 c has an aligned orbit Open
Planetary systems in mean motion resonances hold a special place among the planetary population. They allow us to study planet formation in great detail as dissipative processes are thought to have played an important role in their existen…
View article: Accretion Funnel Reconfiguration during an Outburst in a Young Stellar Object: EX Lupi
Accretion Funnel Reconfiguration during an Outburst in a Young Stellar Object: EX Lupi Open
EX Lupi, a low-mass young stellar object, went into an accretion-driven outburst in 2022 March. The outburst caused a sudden phase change of ∼112° ± 5° in periodically oscillating multiband lightcurves. Our high-resolution spectra obtained…
View article: HD 110067 c has an aligned orbit
HD 110067 c has an aligned orbit Open
Planetary systems in mean motion resonances hold a special place among the planetary population. They allow us to study planet formation in great detail as dissipative processes are thought to have played an important role in their existen…
View article: New quasars behind the Magellanic Clouds
New quasars behind the Magellanic Clouds Open
Context. Quasi-stellar objects (QSOs) are a basis for an absolute reference system for astrometric studies. A system like this at the far side of nearby galaxies is required to facilitate measuring of the proper motions of these galaxies. …
View article: New quasars behind the Magellanic Clouds. II. Spectroscopic confirmation of 136 near-infrared selected candidates
New quasars behind the Magellanic Clouds. II. Spectroscopic confirmation of 136 near-infrared selected candidates Open
Quasi-stellar objects (QSOs) are a basis for an absolute reference system for astrometric studies. There is a need for creating such system behind nearby galaxies, to facilitate the measuring of the proper motions of these galaxies. Howeve…
View article: Accretion Funnel Reconfiguration during an Outburst in a Young Stellar Object: EX Lupi
Accretion Funnel Reconfiguration during an Outburst in a Young Stellar Object: EX Lupi Open
EX Lupi, a low-mass young stellar object, went into an accretion-driven outburst in March of 2022. The outburst caused a sudden phase change of ~ 112$^{\circ}$ $\pm$ 5$^{\circ}$ in periodically oscillating multiband lightcurves. Our high r…
View article: Stellar obliquity measurements of six gas giants
Stellar obliquity measurements of six gas giants Open
One can infer the orbital alignment of exoplanets with respect to the spin of their host stars using the Rossiter-McLaughlin effect, thereby giving us the chance to test planet formation and migration theories and improve our understanding…
View article: Near-infrared spectroscopic indices for unresolved stellar populations. III. Composite indices definition as age and metallicity tracers and model comparison
Near-infrared spectroscopic indices for unresolved stellar populations. III. Composite indices definition as age and metallicity tracers and model comparison Open
Recent advances in the stellar population studies of unresolved galaxies in the NIR domain demonstrated that it contains several line-strength indices to be potentially used as diagnostics for stellar population properties. Reduction of th…
View article: Stellar obliquity measurements of six gas giants
Stellar obliquity measurements of six gas giants Open
One can infer the orbital alignment of exoplanets with respect to the spin of their host stars using the Rossiter-McLaughlin effect, thereby giving us the chance to test planet formation and migration theories and improve our understanding…
View article: The Wide-field Spectroscopic Telescope (WST) Science White Paper
The Wide-field Spectroscopic Telescope (WST) Science White Paper Open
The Wide-field Spectroscopic Telescope (WST) is proposed as a new facility dedicated to the efficient delivery of spectroscopic surveys. This white paper summarises the initial concept as well as the corresponding science cases. WST will f…
View article: The VMC survey
The VMC survey Open
Context. Type II Cepheids (T2Cs) are the less frequently used counterparts of classical or type I Cepheids (CCs) which provide the primary calibration of the distance ladder for measuring the Hubble constant in the local Universe. In the e…
View article: The most variable VVV sources: eruptive protostars, dipping giants in the nuclear disc and others
The most variable VVV sources: eruptive protostars, dipping giants in the nuclear disc and others Open
We have performed a comprehensive search of a VISTA Variables in the Via Lactea (VVV) data base of 9.5 yr light curves for variable sources with ΔKs ≥ 4 mag, aiming to provide a large sample of high amplitude eruptive young stellar objects…