arXiv subjects

V. D. Ivanov

Publications and source records attributed to V. D. Ivanov.

At least 19 recordsLinked to original sources

arXiv2026

Unresolved triple systems in the aged open cluster Trumpler 19: Discovery, confirmation, and implications

It is difficult to identify unresolved triple and higher-order systems beyond the solar vicinity. Star clusters yield controlled environments with known physical parameters, providing a way to explore homogeneous stellar samples. Combining modern optical and near-IR surveys, our main goal is to explore the region of the color-magnitude diagrams located above the sequence of equal-mass binaries, which is inhabited by unresolved triple and quadruple systems. Specifically, here we aim to discover and characterize the presence of multiple systems in the aged open star cluster Trumpler 19. We selected cluster members using Gaia astrometry and photometry from the VVVX and DECAPS2 surveys. We made optical and near-IR color-magnitude diagrams to select stars located >0.75 mag above the cluster main sequence, including suitable unresolved triple and quadruple systems. We confirm previous results that there is a sizable sequence of unresolved binaries in Trumpler 19. We also report the discovery of a sequence of unresolved multiple systems in this cluster, and confirm some of these multiple systems via radial velocities measured by the ESO KMOS VVVX-GalCen spectroscopic survey. The fraction of multiple stars in this cluster is comparable to that of the solar neighborhood, with the caveat that the local sample probes deeper down the main sequence. The fraction of unresolved triples and quadruples is also three times higher than that of the open cluster M 67, which is of a similar age and chemical composition. The discovery of unresolved triple systems in Trumpler 19 leads to our main conclusion that these systems were able to survive within the cluster for nearly 4 Gyr. In addition, this cluster contains more multiple systems than M 67, which has a similar total present mass. Further investigations are needed to unveil if this is a primordial feature or the result of dynamical evolution.

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arXiv2026

Infrared-excess sources in VVV: candidate debris discs, SED characterization, and variability analysis

Debris disks around main-sequence stars provide important insights into planetary formation and evolution; however, identifying these systems in the Galactic plane, where high interstellar extinction and source crowding are significant, remains challenging. Deep, wide-area surveys such as the VISTA Variables in the Via Lactea (VVV) ESO Public Survey provide multi-epoch infrared observations, enabling systematic searches in these environments. We present a method to construct a refined sample of main-sequence candidates by cross-matching data from Gaia DR3, GLIMPSE, DECaPS, and VIRAC2, to identify infrared excesses through spectral energy distribution (SED) analysis, and to analyse time-series data to detect variability potentially associated with circumstellar material or other astrophysical phenomena. Although infrared excess is commonly associated with debris disks, contributions from unresolved binaries or line-of-sight contamination cannot be excluded. Applying this methodology to the VVV tile d077 using the VIRAC2 catalogue, we analyse an initial sample of 879,556 sources and identify 446 sources flagged by the VO SED Analyser (VOSA) excess-detection algorithm as having infrared excess, of which 171 show candidate periodic variability in the VIRAC2 Ks-band light curves. We further perform SED fitting using theoretical models to derive physical parameters and approximate spectral types for these sources. This work provides a catalogue of infrared-excess candidates in a Galactic field affected by high extinction, along with a reproducible method suitable for future large-scale applications.

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arXiv2026

Deep VISTA observations of the Magellanic Clouds (VMCDeep)

The central regions of galaxies challenge observers with a high density of stars, gas and dust. The LMC hosts a dense stellar bar whereas the SMC hosts a dense core, which have eluded even the most sensitive large-scale wide-field surveys of individual stars from the ground and from space. This work describes deep imaging observations obtained with VISTA of the inner regions of the Clouds. They were obtained to resolve stars fainter than the red clump, that due to crowding were missed in previous observations, and to quantify features associated with the star formation, kinematics and structure of the galaxies. These studies will allow us to establish how the dynamical interactions between the LMC and the SMC, and the interaction between the Clouds and the Milky Way have influenced the most gravitationally bound regions. Multiple near-infrared images were obtained in the J and Ks filters during excellent weather conditions. The data were reduced using the VDFS which provides single-filter and band-merged calibrated images and catalogues, with associated confidence maps, for individual observations and combined observations for deep tiles. Approximately one million sources, with only minor quality issues and about 40 epochs per filter, are detected in the central 1.77 sq. deg. They provide a more contiguous spatial area coverage than sources in the VMC survey, which covers the same regions by overlapping two VISTA tiles per galaxy. The catalogues, which are made available with this work, contain attributes to select unique good quality detections for which we provide examples of ongoing scientific applications. These data represent valuable complementary information to deep imaging observations at other wavelengths and provide additional epochs for proper motion and photometric variability studies extending the time baseline to 11 yr, as well as targets for spectroscopic observations.

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arXiv2026

The VMC survey -- LV. The coherent expansion of the SMC

The Small Magellanic Cloud (SMC) exhibits significant kinematic disequilibrium due to interactions with the Large Magellanic Cloud (LMC). Here, we investigate the two-dimensional stellar kinematics of the SMC to understand the dynamical effects of these interactions by exploiting the increased time baseline of 6-11 years from the VISTA Survey of the Magellanic Clouds (VMC) data release 7. We derive proper motions with a threefold improvement in precision compared to previous studies based on VMC data. We used a geometric framework accounting for perspective effects from line of sight motion to model the systemic motion across the SMC and construct a residual proper motion map. We further introduce an anisotropic linear velocity gradient model to quantify the stretching of the galaxy. For the first time across all stellar populations, the residual proper motion map reveals expansion along the south-east and north-west directions, consistent with LMC-induced tidal forces, detectable even in the central regions. The gradient-corrected residuals show predominantly radial motions towards the SMC centre with no evidence of rotation. Velocity maps for different stellar populations, without assuming a rotating-disk model, reveal a coherent northward motion away from the centre exclusively in older red giant branch stars, interpreted as a kinematic signature of a past (>2 Gyr ago) interaction. This study highlights the inadequacy of simple rotating-disk models in capturing the internal kinematics of the galaxy.

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arXiv2026

IRAM 04191+1522: a compact proto-brown dwarf binary candidate

Very low-luminosity objects in nearby star-forming regions have been identified as promising proto-brown dwarf candidates. The study of their multiplicity can shed light on the dominant formation mechanism of these substellar objects. We aim at studying the multiplicity of the very low luminosity object IRAM 04191+1522. To do so, we have obtained 0.89mm ALMA observations with a very extended configuration, achieving an angular resolution of ~0.04 arcsec (6 au at 140 pc). We have complemented our data with new VLA observations, and ALMA archival data at 1.3mm. As a result, we resolve IRAM04191+1522 into a close binary candidate for the first time. The binary is detected in the ALMA continuum data with a projected separation of ~80 mas, or 11 au at a distance of 140 pc. The two sources are oriented in the East-West direction, with the eastern component being brighter and more extended than the western one, which is marginally resolved. The analysis of C18O(2-1) archival data reveals gaseous material in rotation around the binary, presumably from a circumbinary disk with ~27 au of radius centered on the faintest ALMA component. A fit of the position-velocity diagram allows us to estimate a total dynamical mass for the system of 50+-40 MJup. Therefore, we classify IRAM04191 as a tight proto-brown dwarf binary candidate. The VLA data reveals the detection of a single object closer to the western ALMA source, and with a spectral index consistent with a radio jet.

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arXiv2026

Quasars behind the disk of M31 galaxy

We aim to increase the limited number of quasars behind M31, necessary for probing the chemical content of the gas and for proper motion reference, with reliable and homogeneous redshift measurements from emission lines. We carried out spectroscopic follow up of 32 quasar candidates. We confirm 23 quasars: two are new discoveries (J004029.727+403705.68 and J004215.489+412031.52) and the rest were reported elsewhere, but with somewhat deficient analysis; 16 spectra are published for the first time. We report new homogeneous redshifts for 34 quasars (from 40 spectra, adding 17 from archives) and summarize all available information about bona-fide quasars with reliable redshift, bringing their number to 124 within the mu_B=26 mag/arcsec^2 isophote. We carried out a comparison of redshifts from different sources and excluded some objects with redshifts derived from low-resolution spectra. We derive the reddening for them from the color excess with respect to dereddened counterparts with similar redshifts in the field. Comparisons of our reddenings with M31 reddening maps found no significant correlations. Most QSOs behind M31 show low reddening and do not probe high-extinctions underlining the need to identify fainter quasars behind nearby galaxies, especially behind higher extinction regions -- probably due to a bias towards following up brighter and less extinct candidates. Finally, the redshifts derived from low-resolution spectra must be treated with caution, because they can contain significant errors.

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arXiv2025

PLATOSpec: a precise spectrograph in support of space missions

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 science with an echelle spectrograph capable of measuring precise radial velocities. The main focus of the spectrograph will be to perform the initial screening and validation of exoplanetary candidates, in addition to study stellar variability. It will be possible to determine the physical properties of large exoplanets. The PLATOSpec blue-sensitive spectrograph, with a spectral range of 380 to 700\,nm and a resolving power of R=70,000, is installed on the 1.5-m telescope at the ESO La Silla Observatory in Chile. Initial results show that the radial-velocity limit given by the wavelength calibration is about 2-3 m/s. Tests on bright F-K main-sequence standard stars reveal a scatter of about 5 m/s over a few hours. The scatter over a few months is slightly higher. We demonstrate the capabilities of PLATOSpec on the mass determination of WASP-79 b and the spin-orbit alignment of WASP-62\,b via the Rossiter-McLaughlin effect. We show its possible usage on variable star research as demonstrated on the false-positive exoplanetary candidate TIC 238060327, which is proven a binary star. Investigation of line-profile variations of the roAp star alpha Cir shows that PLATOSpec can also be used for the surface mapping. Finally, we present new results on the active star UY Pic in the PLATO southern field. Our results show that PLATOSpec is a versatile spectrograph with great precision.

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arXiv2025

The VMC survey -- LIV. The internal kinematics of the LMC with new VISTA observations

Context: Studying the internal kinematics of galaxies provides insights into their past evolution, current dynamics, and future trajectory. The Large Magellanic Cloud (LMC), as the largest and one of the nearest satellite galaxies of the Milky Way, presents unique opportunities to investigate these phenomena in great detail. In this study, we investigate the internal kinematics of the LMC by deriving precise stellar proper motions using data from the VISTA survey of the Magellanic Clouds system (VMC). The main objective is to refine the LMC's dynamical parameters using improved proper motion measurements, including one additional epoch of VISTA observations, which extended the time baseline from ~ 2 to 10 years. The precision of the proper motion was enhanced, reducing uncertainties from 6 mas/yr to 1.5 mas/yr. We derived geometrical and kinematic parameters, generating velocity maps and rotation curves, for both young and old stellar populations. Finally, we compared a suite of dynamical models, which simulate the interaction of the LMC with the Milky Way and Small Magellanic Cloud (SMC), against the observations. The tangential rotation curve reveals an asymmetric drift between young and old stars, while the radial velocity curve for the young population shows an increasing trend within the inner bar region, suggesting non-circular orbits. We confirm the clockwise rotation around the dynamical centre of the LMC, consistent with previous predictions. A significant residual motion was detected toward the north-east of the LMC, directed away from the centre. This feature observed in the inner disk region is kinematically connected with a substructure identified in the periphery known as Eastern Substructure 1. This motion suggests a possible tidal influence from the Milky Way, combined with the effects of the recent close pericentre passage of the SMC ~150 Myr ago.

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arXiv2025

viper: High-precision radial velocities from the optical to the infrared (Reaching 3 m/s in the K band of CRIRES+ with telluric modelling)

In recent years, a number of new instruments and data reduction pipelines have been developed to obtain high-precision radial velocities (RVs). In particular in the optical, considerable progress has been made and RV precision below 50 cm/s has been reached. Yet, the RV precision in the near-infrared (NIR) is trailing behind. This is due to a number of factors, such as imprinted atmospheric absorption lines, lower stellar information content, different types of detectors, and usable calibration lamps. However, observations in the NIR are important for the search and study of exoplanets around cool low-mass stars that are faint at optical wavelengths. Not only are M dwarfs brightest in the NIR, the signal of stellar activity is also reduced at longer wavelengths. In this paper we introduce the RV pipeline viper (Velocity and IP EstimatoR). The philosophy of viper is to offer a publicly available and user-friendly code that is able to process data from various spectrographs. Originally designed to handle data from optical instruments, the code now has been extended to enable the processing of NIR data. viper uses a least-square fitting to model the stellar RV as well as the temporal and spatial variable IP. We have improved upon this method by adding a term for the telluric spectrum that enables the forward modelling of molecules present in the Earth's atmosphere. In this paper we use CRIRES+ observations in the K band to demonstrate viper's ability to handle data in the NIR. We show that it is possible to achieve an RV accuracy of 3 m/s over a period of 2.5 years with the use of a gas cell. Additionally, we present a study of the stability of atmospheric lines in the NIR. With viper it is possible to handle data taken with or without a gas cell, and we show that a long-term RV precision of around 10 m/s can be achieved when using only telluric lines for the wavelength calibration.

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arXiv2025

The VMC survey -- LIII. Data release #7. Complete survey data and data from additional programmes

The near-infrared YJKs Visual and Infrared Survey Telescope for Astronomy (VISTA) survey of the Magellanic Clouds (VMC) is complete and there are also data from additional programmes enhancing its quality over the original footprint. This work presents the final data release of the VMC survey, which includes additional observations and provides an overview of the scientific results. The overall data quality has been revised and reprocessed standard data products, that already appeared in previous data releases, are made available together with new data products. These include individual stellar proper motions, reddening towards red clump stars and source classifications. Several data products, such as the parameters of some variable stars and of background galaxies, from the VMC publications are associated to a data release for the first time. The data are processed using the VISTA Data Flow System and additional products, e.g. catalogues with point-spread function photometry or tables with stellar proper motions, are obtained with software developed by the survey team. This release supersedes all previous data releases of the VMC survey for the combined (deepstacked) data products, whilst providing additional (complementary) images and catalogues of single observations per filter. Overall, it includes about 64 million detections, split nearly evenly between sources with stellar or galaxy profiles. The VMC survey provides a homogeneous data set resulting from deep and multi-epoch YJKs-band imaging observations of the Large and Small Clouds, the Bridge and two fields in the Stream. The VMC data represent a valuable counterpart for sources detected at other wavelengths for both stars and background galaxies.

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arXiv2025

Identification of quasars variable over long time scales from infrared surveys. Ensemble variability and structure function properties

Quasars are variable and their variability can both constrain their physical properties and help to identify them. We look for ways to efficiently identify quasars exhibiting consistent variability over multi-year time-scales, based on a small number of epochs. Using infrared (IR) is desirable to avoid bias against reddened objects. We compare the apparent brightness of known quasars that have been observed with two IR surveys, covering up to a twenty-year baseline: the Two Micron All Sky Survey (2MASS; 1997-2001) and the VISTA Hemisphere Survey (VHS; 2009-2017). We look at the previous studies of the selected variable quasars to see if their variable behaviour is known and when available we use multi-epoch monitoring with the Zwicky Transient Facility (ZTF) to obtain a measure of optical variability of individual objects. We build a sample of ~2500 quasars that show statistically significant variability between the 2MASS and VHS. About 1500 of these come from the new Quaia sample based on Gaia spectra and about 1/3 of these have hardly been studied. The Quaia sample constitutes the main product of this work. Based on ensemble variability and structure function analysis we demonstrate that the selected objects in our sample are representative of the typical quasar population and show behaviour, consistent with other quasar samples. Our analysis strengthens previous results, for example that variability decreases with the rest-frame wavelength and that it exhibits peaks for certain absolute magnitudes of the quasars. Similarly, the structure function shows an increase in variability for rest-frame time lags below ~1500 d and a decrease for longer lags, just like in previous studies. Our selection, even though it is based on two epochs only, seems to be surprisingly robust, showing up to ~11% contamination by quasars that show stable non-variable behaviour in ZTF.

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arXiv2024

The young exoplanetary system TOI-4562: Confirming the presence of a third body in the system

Young planetary systems represent an opportunity to investigate the early stages of (exo)planetary formation because the gravitational interactions have not yet significantly changed the initial configuration of the system. TOI-4562 b is a highly eccentric temperate Jupiter analogue orbiting a young F7V-type star of $<700$ Myr in age with an orbital period of $P_{orb} \sim 225$ days and an eccentricity of $e=0.76$, and is one of the largest known exoplanets to have formed in situ. We observed a new transit of TOI-4562 b using the 0.6-m Zeiss telescope at the Pico dos Dias Observatory (OPD/LNA) in Minas Gerais, Brazil, and combine our data with Transiting Exoplanet Survey Satellite (TESS) and archive data, with the aim being to improve the ephemerides of this interesting system. The $O-C$ diagram for the new ephemeris is consistent with the presence of a giant planet in an outer orbit around TOI-4562. TOI-4562 c is a planet with a mass of $M=5.77 M_{Jup}$, an orbital period of $P_{orb}= 3990$ days, and a semi-major axis of $a = 5.219$ AU. We report the discovery of TOI-4562 c, the exoplanet with the longest orbital period discovered to date via the transit timing variation (TTV) method. The TOI-4562 system is in the process of violent evolution with intense dynamical changes - judging by its young age and high eccentricity - and is therefore a prime target for studies of formation and evolution of planetary systems.

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arXiv2024

The VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey: Completion of the observations and legacy

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 the temporal as well as spatial coverage of the original VVV area, widening it from $562$ to $1700$ sq. deg., as well as providing additional epochs in $JHK_{\rm s}$ filters from $2016-2023$. With the completion of VVVX observations during the first semester of 2023, we present here the observing strategy, a description of data quality and access, and the legacy of VVVX. VVVX took $\sim 2000$ hours, covering about 4% of the sky in the bulge and southern disk. VVVX covered most of the gaps left between the VVV and the VISTA Hemisphere Survey (VHS) areas and extended the VVV time baseline in the obscured regions affected by high extinction and hence hidden from optical observations. VVVX provides a deep $JHK_{\rm s}$ catalogue of $\gtrsim 1.5\times10^9$ point sources, as well as a $K_{\rm s}$ band catalogue of $\sim 10^7$ variable sources. Within the existing VVV area, we produced a $5D$ map of the surveyed region by combining positions, distances, and proper motions of well-understood distance indicators such as red clump stars, RR Lyrae, and Cepheid variables. In March 2023 we successfully finished the VVVX survey observations that started in 2016, an accomplishment for ESO Paranal Observatory upon 4200 hours of observations for VVV+VVVX. The VVV+VVVX catalogues complement those from the Gaia mission at low Galactic latitudes and provide spectroscopic targets for the forthcoming ESO high-multiplex spectrographs MOONS and 4MOST.

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arXiv2024

Search and Study of the Brightest Stars in the Galaxy IC 342

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 out of 27 selected stars are carried out with the 6 m BTA telescope at the SAO RAS and with the 3.5 m Apache Point Observatory telescope (USA) as part of the program for searching bright massive stars in galaxies outside the Local Group. Our analysis reveals that 12 objects have spectra lacking prominent features, except for the emission lines of the surrounding nebulae and are identified as single supergiants of classes O9 to F5 or spatially unresolved young compact clusters. One source with an absorption spectrum probably belongs to our Galaxy. The spectra of seven other objects show features typical of Wolf-Rayet stars or compact clusters containing Wolf-Rayet stars. Another source is a compact supernova remnant. Two other objects are tentatively classified as cold LBV candidates, and one object is classified as a B[e]-supergiant candidate.

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arXiv2024

HD 110067 c has an aligned orbit

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 existence. Additionally, planetary masses in bright resonant systems may be independently measured both by radial velocities (RVs) and transit timing variations (TTVs). In principle, they also allow us to quickly determine the inclination of all planets in the system, as for the system to be stable, they are likely all in coplanar orbits. To describe the full dynamical state of the system, we also need the stellar obliquity that provides the orbital alignment of a planet with respect to the spin of their host star and can be measured thanks to the Rossiter-McLaughlin effect. It was recently discovered that HD 110067 harbours a system of six sub-Neptunes in resonant chain orbits. We here analyze an ESPRESSO high-resolution spectroscopic time series of HD 110067 during the transit of planet c. We find the orbit of HD 110067 c to be well aligned with sky projected obliquity $λ=6^{+24}_{-26}$ deg. This result is indicative that the current architecture of the system has been reached through convergent migration without any major disruptive events. Finally, we report transit-timing variation in this system as we find a significant offset of 19 $\pm$ 4 minutes in the center of the transit compared to the published ephemeris.

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arXiv2024

Stellar obliquity measurements of six gas giants

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 of the currently observed population. We analyze archival HARPS and HARPS-N spectroscopic transit time series of six gas giant exoplanets on short orbits, namely WASP-77 Ab, WASP-101b, WASP-103b, WASP-105b, WASP-120b and WASP-131b. We find a moderately misaligned orbit for WASP-101b ($λ=34\degree\ \pm$ 3) and a highly misaligned orbit for WASP-131b ($λ=161\degree\ \pm$ 5), while the four remaining ones appear aligned: WASP-77 Ab ($λ=-8\degree\ ^{+19}_{-18}$), WASP-103b ($λ=2\degree\ ^{+35}_{-36}$), WASP-105b ($λ=-14\degree\ ^{+28}_{-24}$), and WASP-120b ($λ=-2\degree\ \pm$ 4). For WASP-77 Ab, we were able to infer its true orbital obliquity ($Ψ=48\degree\ ^{+22}_{-21}$). We additionally perform transmission spectroscopy of the targets in search of strong atomic absorbers in the exoatmospheres, but are unable to detect any features, most likely due to the presence of high-altitude clouds or Rayleigh scattering muting the strength of the features. Finally, we comment on future perspectives for studying these targets with the upcoming space missions to investigate the evolution and migration histories of these planets.

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arXiv2024

The most variable VVV sources: eruptive protostars, dipping giants in the Nuclear Disc and others

We have performed a comprehensive search of a VISTA Variables in the Via Lactea (VVV) database of 9.5 yr light curves for variable sources with $ΔK_s \ge 4$ mag, aiming to provide a large sample of high amplitude eruptive young stellar objects (YSOs) and detect unusual or new types of infrared variable source. We find 222 variable or transient sources in the Galactic bulge and disc, most of which are new discoveries. The sample mainly comprises novae, YSOs, microlensing events, Long Period Variable stars (LPVs) and a few rare or unclassified sources. Additionally, we report the discovery of a significant population of aperiodic late-type giant stars suffering deep extinction events, strongly clustered in the Nuclear Disc of the Milky Way. We suggest that these are metal-rich stars in which radiatively driven mass loss has been enhanced by super-solar metallicity. Among the YSOs, 32/40 appear to be undergoing episodic accretion. Long-lasting YSO eruptions have a typical rise time of $\sim$2 yr, somewhat slower than the 6-12 month timescale seen in the few historical events observed on the rise. The outburst durations are usually at least 5 yr, somewhat longer than many lower amplitude VVV events detected previously. The light curves are diverse in nature, suggesting that multiple types of disc instability may occur. Eight long-duration extinction events are seen wherein the YSO dims for a year or more, attributable to inner disc structure. One binary YSO in NGC 6530 displays periodic extinction events (P=59 days) similar to KH 15D.

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arXiv2023

BV photometric observations of the flickering of the dwarf nova RX And

We report photometry of the intranight variability of the dwarf nova RX And in two bands (B and V). The observations are carried out during three nights in November-December 2022 at the 50/70~cm Schmidt telescope of the Rozhen National Astronomical Observatory. The observations indicate that the amplitude of the flickering is about 0.5 mag in B band when the star is in faint state (m_V=13.5), but it is considerably lower (less than 0.1 mag) when the star is bright (m_V=10.9). The mass accretion rate in high state is estimated to be $1.2 \times 10^{-9}$ M$_\odot$ yr$^{-1}$. Combining our data and GAIA distances we find for the mass donor in RX~And spectral type K6V-K7V. The data are available upon request from the authors.

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