arXiv subjects

A. Y. Burdanov

Publications and source records attributed to A. Y. Burdanov.

10 recordsLinked to original sources

arXiv2026

Thermophysical characterization of the potentially hazardous near-Earth object 2024 YR4

The asteroid 2024 YR4 is a potentially hazardous Apollo-type near-Earth object. Its highly eccentric orbit produces close Earth-Moon encounters roughly every 4 years. A collection of light curves, including JWST-NIRCam data, allowed us to constrain the rotation period, spin pole, and convex shape solutions for the object. We analyzed two sets of JWST-MIRI observations obtained in three filters on 26 March 2025. The extracted photometry reveals rotationally driven thermal flux variations. The combination of a spin-shape model from light-curve inversion and the absolutely calibrated 3-band MIR light curves is well reproduced by a convex spin-shape solution with a spin pole at (l,b) = (232, -11), a sidereal period of 19.4633 min, and axis ratios of a/b ~1.28 and b/c ~1.45. The corresponding equivalent-volume diameter is 60.8 +1.8/-3.6 m (pV= 0.11 +0.05/-0.03, assuming HV = 24.14+/-0.25 mag). A high thermal inertia and low surface roughness are required to explain the observed MIRI data. The near-Earth asteroid thermal model has limited reliability for this object, requiring an extreme beaming parameter >3, whereas the fast-rotating model and a full thermophysical model provide consistent and reliable estimates of the size and albedo. The combination of high eccentricity and high thermal inertia implies seasonal skin depths of up to ~3 m and radiative timescales of weeks to months. Although seasonal heating is negligible for the March 2025 observations because of the near-equator-on viewing geometry, the seasonal Yarkovsky drift is expected to be dominant over the diurnal component and might become measurable during future encounters. Although JWST astrometry from February 2026 rules out any possible impact on the Earth or the Moon for at least 100 years, the spin, shape, and radiometric constraints presented here provide an important benchmark for future potentially hazardous objects.

astro-ph.EP↗

arXiv2026

Small-Body Science with the Nautilus Space Observatory: From Cislunar Space Resilience to Mapping the Kuiper-Belt-to-Oort-Cloud Transition

A new generation of space-based observatories can transform small-body science from the local Earth-Moon environment to the Solar System's dynamical frontier, where planetary control gives way to Galactic tides and stellar encounters. Mapping this frontier would reveal how planetesimals were scattered during giant-planet formation, how many primordial bodies survived in distant reservoirs, and whether large objects remain undiscovered in the inner Oort Cloud. At the same time, meter- to decameter-scale natural objects traversing the Earth-Moon system are frequent but poorly characterized. As human and robotic activity expands, their operational relevance depends not simply on abundance but on object size, encounter geometry, exposed infrastructure, warning time, and available response. Lunar impacts and impact-generated ejecta provide one class of events, while fading objects with unresolved Earth or lunar impact probabilities provide another. Here, we explore a two-layer small-body program combining a 4.0 m-diameter Nautilus Quattro Imaging (NQI) unit with an illustrative distributed cislunar layer of ~50 cm-class wide-field optical telescopes. The cislunar layer would characterize the nearby natural-object population, support rapid classification and selective custody of high-interest objects, and monitor lunar impacts and ejecta; the NQI deep-search layer would provide precise astrometry and synthetic tracking for faint-object recovery and distant-Solar-System surveys. Together, the two layers would constrain the small-impactor population, resolve fading planetary-defense targets, and survey the distant Solar System to Vmag ~30, enabling tests of the Kuiper-Belt-to-Oort-Cloud transition while advancing Earth-Moon space resilience.

astro-ph.IM↗

arXiv2026

J0404+1112: A 3-Hour Eclipsing White Dwarf-Brown Dwarf Probing Multiple Atmospheric Regimes

White dwarf-brown dwarf (WD+BD) binaries are rare laboratories for probing both substellar survival through post-main-sequence evolution and the physics of strongly irradiated atmospheres. We present time-resolved eclipse photometry and radial-velocity confirmation of J0404+1112, a compact ($P = 2.93$ hr), totally eclipsing WD+BD system initially reported in a Research Note of the AAS. New high-cadence observations resolve a total eclipse of the WD and, combined with spectroscopy, broadband photometry, and the Gaia parallax, yield a revised system architecture. We find a hot DA WD with $T_{\rm eff} \simeq 28{,}000$ K, $\log g \simeq 8.0$, $M_{\rm WD} \simeq 0.6 \rm{M}_\odot$, and $R_{\rm WD} \simeq 0.015 \rm{R}_\odot$, orbited by a $\sim40 \rm{M}_{\rm Jup}$ BD with radius $\sim0.9 \rm{R}_{\rm Jup}$. These parameters supersede earlier SED-based estimates in which the WD temperature, radius, distance, and extinction were strongly covariant. We break this degeneracy with normalized Balmer-line profile fitting and high-cadence eclipse photometry that constraints the WD's radius geometrically. The total eclipses enable isolation of the BD flux and constrain its nightside emission. With its short orbital period and strong irradiation, J0404+1112 provides a uniquely compact, high-sensitivity JWST benchmark for probing atmospheric heat redistribution and photochemistry in the temperature regime of the hottest ultra-hot Jupiters, spanning dayside and nightside brightness temperatures of $\sim3{,}600$ K and $\sim1{,}800$ K within a single $\sim$3 hr orbit.

astro-ph.SR↗

arXiv2026

Multi-epoch afterglow rebrightenings in GRB 250129A: Evidence for successive shock interactions

Most long gamma-ray bursts (GRBs) exhibit afterglows broadly consistent with external forward-shock emission, typically described by smooth broken power-law decays in the multiband light curve. However, a minority of well-sampled GRBs deviate from this behavior, including GRB 250129A. This object shows multiple late-time rebrightenings at X-ray and optical wavelengths. Rebrightenings are often attributed to energy injection from prolonged central engine activity, refreshed shocks from delayed shell collisions, density jumps in the ambient medium, or angular jet structure and viewing-angle effects. After analysing the prompt emission observed in gamma-rays and the near-infrared, we investigate the origin of X-ray and optical flaring episodes in GRB 250129A. Physical processes in the afterglow light curves were investigated using methods ranging from empirical fitting to Bayesian inference. The well-sampled flares and the connection between the prompt and afterglow emission allow us to test the consistency of the fireball model and alternative scenarios. Conducting the prompt and time-resolved analyses, we obtained an isotropic-equivalent energy of E_iso,gamma = (1.35 +/- 0.12) x 10^53 erg. By modeling the afterglow using an agnostic Bayesian framework (NMMA), we rule out both a single external-shock evolution and a one-time energy-injection scenario. Numerical calculations show that the rebrightening episodes are consistent with refreshed shocks from delayed collisions between relativistic shells. Based on the consistency between our analyses of the prompt and afterglow GRB 250129A data, we find that two statistically significant rebrightening episodes occur within 1.1 days post trigger and can be explained by a sequence of refreshed shocks. Temporally and spectrally rich GRB datasets such as the one presented in this work, provide a powerful means to test current modeling frameworks.

astro-ph.HE↗

arXiv2025

ATREIDES I. Embarking on a trek across the exo-Neptunian landscape with the TOI-421 system

The distribution of close-in exoplanets is shaped by the interplay between atmospheric and dynamical processes. The Neptunian Desert, Ridge, and Savanna illustrate the sensitivity of these worlds to such processes, making them ideal to disentangle their roles. Determining how many Neptunes were brought close-in by early disk-driven migration (DDM; maintaining primordial spin-orbit alignment) or late high-eccentricity migration (HEM; generating large misalignments) is essential to understand how much atmosphere they lost. We propose a unified view of the Neptunian landscape to guide its exploration, speculating that the Ridge is a hot spot for evolutionary processes. Low-density Neptunes would mainly undergo DDM, getting fully eroded at shorter periods than the Ridge, while denser Neptunes would be brought to the Ridge and Desert by HEM. We embark on this exploration via ATREIDES, which relies on spectroscopy and photometry of 60 close-in Neptunes, their reduction with robust pipelines, and their interpretation through internal structure, atmospheric, and evolutionary models. We carried out a systematic RM census with VLT/ESPRESSO to measure the distribution of 3D spin-orbit angles, correlate its shape with system properties and thus relate the fraction of aligned-misaligned systems to DDM, HEM, and atmospheric erosion. Our first target, TOI-421c, lies in the Savanna with a neighboring sub-Neptune TOI-421b. We measured their 3D spin-orbit angles (Psib = 57+11-15 deg; Psic = 44.9+4.4-4.1 deg). Together with the eccentricity and possibly large mutual inclination of their orbits, this hints at a chaotic dynamical origin that could result from DDM followed by HEM. ATREIDES will provide the community with a wealth of constraints for formation and evolution models. We welcome collaborations that will contribute to pushing our understanding of the Neptunian landscape forward.

astro-ph.EP↗

arXiv2023

A large topographic feature on the surface of the trans-Neptunian object (307261) 2002 MS$_4$ measured from stellar occultations

This work aims at constraining the size, shape, and geometric albedo of the dwarf planet candidate 2002 MS4 through the analysis of nine stellar occultation events. Using multichord detection, we also studied the object's topography by analyzing the obtained limb and the residuals between observed chords and the best-fitted ellipse. We predicted and organized the observational campaigns of nine stellar occultations by 2002 MS4 between 2019 and 2022, resulting in two single-chord events, four double-chord detections, and three events with three to up to sixty-one positive chords. Using 13 selected chords from the 8 August 2020 event, we determined the global elliptical limb of 2002 MS4. The best-fitted ellipse, combined with the object's rotational information from the literature, constrains the object's size, shape, and albedo. Additionally, we developed a new method to characterize topography features on the object's limb. The global limb has a semi-major axis of 412 $\pm$ 10 km, a semi-minor axis of 385 $\pm$ 17 km, and the position angle of the minor axis is 121 $^\circ$ $\pm$ 16$^\circ$. From this instantaneous limb, we obtained 2002 MS4's geometric albedo and the projected area-equivalent diameter. Significant deviations from the fitted ellipse in the northernmost limb are detected from multiple sites highlighting three distinct topographic features: one 11 km depth depression followed by a 25$^{+4}_{-5}$ km height elevation next to a crater-like depression with an extension of 322 $\pm$ 39 km and 45.1 $\pm$ 1.5 km deep. Our results present an object that is $\approx$138 km smaller in diameter than derived from thermal data, possibly indicating the presence of a so-far unknown satellite. However, within the error bars, the geometric albedo in the V-band agrees with the results published in the literature, even with the radiometric-derived albedo.

astro-ph.EP↗

arXiv2021

Discovery of a young low-mass brown dwarf transiting a fast-rotating F-type star by the Galactic Plane eXoplanet (GPX) survey

We announce the discovery of GPX-1 b, a transiting brown dwarf with a mass of $19.7\pm 1.6$ $M_{\mathrm{Jup}}$ and a radius of $1.47\pm0.10$ $R_{\mathrm{Jup}}$, the first sub-stellar object discovered by the Galactic Plane eXoplanet (GPX) survey. The brown dwarf transits a moderately bright ($V$ = 12.3 mag) fast-rotating F-type star with a projected rotational velocity $v\sin{ i_*}=40\pm10$ km/s. We use the isochrone placement algorithm to characterize the host star, which has effective temperature $7000\pm200$ K, mass $1.68\pm0.10$ $M_{\mathrm{Sun}}$, radius $1.56\pm0.10$ $R_{\mathrm{Sun}}$ and approximate age $0.27_{-0.15}^{+0.09}$ Gyr. GPX-1 b has an orbital period of $\sim$1.75 d, and a transit depth of $0.90\pm0.03$ %. We describe the GPX transit detection observations, subsequent photometric and speckle-interferometric follow-up observations, and SOPHIE spectroscopic measurements, which allowed us to establish the presence of a sub-stellar object around the host star. GPX-1 was observed at 30-min integrations by TESS in Sector 18, but the data is affected by blending with a 3.4 mag brighter star 42 arcsec away. GPX-1 b is one of about two dozen transiting brown dwarfs known to date, with a mass close to the theoretical brown dwarf/gas giant planet mass transition boundary. Since GPX-1 is a moderately bright and fast-rotating star, it can be followed-up by the means of Doppler tomography.

astro-ph.SR↗

arXiv2019

Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared

The TRAPPIST-1 planetary system is a favorable target for the atmospheric characterization of temperate earth-sized exoplanets by means of transmission spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible obstacle to this technique could come from the photospheric heterogeneity of the host star that could affect planetary signatures in the transit transmission spectra. To constrain further this possibility, we gathered an extensive photometric data set of 25 TRAPPIST-1 transits observed in the near-IR J band (1.2 $μ$m) with the UKIRT and the AAT, and in the NB2090 band (2.1 $μ$m) with the VLT during the period 2015-2018. In our analysis of these data, we used a special strategy aiming to ensure uniformity in our measurements and robustness in our conclusions. We reach a photometric precision of $\sim0.003$ (RMS of the residuals), and we detect no significant temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the period of three years. The few transit depths measured for planets d and f hint towards some level of variability, but more measurements will be required for confirmation. Our depth measurements for planets b and c disagree with the stellar contamination spectra originating from the possible existence of bright spots of temperature 4500 K. We report updated transmission spectra for the six inner planets of the system which are globally flat for planets b and g and some structures are seen for planets c, d, e, and f.

astro-ph.EP↗

arXiv2016

Comparative performance of selected variability detection techniques in photometric time series

Photometric measurements are prone to systematic errors presenting a challenge to low-amplitude variability detection. In search for a general-purpose variability detection technique able to recover a broad range of variability types including currently unknown ones, we test 18 statistical characteristics quantifying scatter and/or correlation between brightness measurements. We compare their performance in identifying variable objects in seven time series data sets obtained with telescopes ranging in size from a telephoto lens to 1m-class and probing variability on time-scales from minutes to decades. The test data sets together include lightcurves of 127539 objects, among them 1251 variable stars of various types and represent a range of observing conditions often found in ground-based variability surveys. The real data are complemented by simulations. We propose a combination of two indices that together recover a broad range of variability types from photometric data characterized by a wide variety of sampling patterns, photometric accuracies, and percentages of outlier measurements. The first index is the interquartile range (IQR) of magnitude measurements, sensitive to variability irrespective of a time-scale and resistant to outliers. It can be complemented by the ratio of the lightcurve variance to the mean square successive difference, 1/h, which is efficient in detecting variability on time-scales longer than the typical time interval between observations. Variable objects have larger 1/h and/or IQR values than non-variable objects of similar brightness. Another approach to variability detection is to combine many variability indices using principal component analysis. We present 124 previously unknown variable stars found in the test data.

astro-ph.IM↗

arXiv2013

New variable stars in the field of open cluster NGC188

A photometric study of variable stars in the field of old open cluster NGC 188 is discussed. Observations were carried out in two bands R and I for 5513 stars up to R = 17 mag in the field of 1.5 x 1.5 grad. around the cluster. The photometric data were processed by the console application "Astrokit", which corrects brightness variations associated with the variability of atmospheric transparency and carries out searching for variable stars. We found 18 new variable stars and determined the parameters of one previously known variable. Among discovered stars one is a low-amplitude pulsating variable, one is a EW eclipsing binary, six are eclipsing variables of EA type, five objects are long period variables, and for five stars variability type remains uncertain.

astro-ph.SR↗