arXiv subjects

Valeri V. Makarov

Publications and source records attributed to Valeri V. Makarov.

At least 37 records · Page 2Linked to original sources

arXiv2023

Secular Orbital Dynamics of the Possibly Habitable Planet K2-18 b with and without the Proposed Inner Companion

The transiting planet K2-18 b is one of the best candidates for a relatively nearby world harboring biological life. The long-term orbital evolution of this planet is investigated using theoretical and purely numerical techniques for two possible configurations: a single planet orbiting the host star, and a two-planet system including the proposed inner planet close to the 4:1 mean motion rationalization. The emphasis is made on the secular changes of eccentricity and orbital inclination, which are important for the climate stability of the planet. It is demonstrated that the secular orbital dynamics of planet K2-18 b with an internal companion are accurately represented by the periodic eccentricity and inclination exchange on the time scales of a few Kyr. A single planet is not expected to experience fast orbital changes, with the much weaker tidal and rotation-driven perturbations mostly reflecting in a slow periastron and nodal precession. The tidal decay of the orbit is too insignificant on the time scale of the stellar age. However, the conditions for the habitability of a single K2-18 b planet are much improved if, like the Earth, it rotates faster than the mean motion and its rotation angle is tilted by a hypothetical moon. Milankovi{ć}'s cycles of the habitable planet's climate are discussed for both configurations.

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arXiv2023

Radio-Optical Reference Catalog, version 1

The fundamental celestial reference frame (CRF) is based on two catalogs of astrometric positions, the third realization of the International Celestial Reference Frame (ICRF3), and the much larger Gaia~CRF, built from the third data release (DR3). The objects in common between these two catalogs are mostly distant AGNs and quasars that are both sufficiently optically bright for Gaia and radio-loud for the VLBI. This limited collection of reference objects is crucially important for the mutual alignment of the two CRFs and maintenance of all the other frames and coordinate systems branching from the ICRF. In this paper, we show that the three components of ICRF3 (S/X, K, and X/Ka band catalogs) have significantly different sky-correlated vector fields of position offsets with respect to Gaia~DR3. When iteratively expanded in the vector spherical harmonics up to degree 4 on a carefully vetted set of common sources, each of these components includes several statistically significant terms. The median sky-correlated offsets from the Gaia positions are found to be 56 $μ$as for the S/X, 100 $μ$as for the K, and 324 $μ$as for the Ka catalogs. The weighted mean vector field is subtracted from the Gaia reference positions, while the deviations from that field are added to each of the ICRF3 components. The corrected positions from each of the four input catalogs are combined into a single weighted mean catalog, which we propose to be the current most accurate realization of an inertial radio-optical CRF.

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arXiv2023

Pathways of Survival of Exomoons and Inner Exoplanets

It is conceivable that a few thousand confirmed exoplanets initially harboured satellites similar to the moons of the Solar system or larger. Could some of them have survived over the aeons of dynamical evolution to the present day? The dynamical conditions are harsh for exomoons in such systems because of the greater influence of the host star and of the tidal torque it exerts on the planet. We investigate the stability niches of exomoons around hundreds innermost exoplanets for which the needed parameters are known today, and determine the conditions of these moons' long-term survival. General lower and upper bounds on the exomoon survival niches are derived for orbital separations, periods, and masses. The fate of an exomoon residing in a stability niche depends on the initial relative rate of the planet's rotation and on the ability of the moon to synchronise the planet by overpowering the tidal action from the star. State of the art models of tidal dissipation and secular orbital evolution are applied to a large sample of known exoplanet systems with their estimated physical parameters. We show that in some plausible scenarios, exomoons can prevent close exoplanets from spiraling into their host stars, thus extending these planets' lifetimes. This is achieved when exomoons synchronise the rotation of their parent planets, overpowering the tidal action from the stars. Massive moons are more likely to survive and to maintain a high rotation rate of their host planets (higher than these planets' mean motion).

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arXiv2022

A catalog of candidate double and lensed quasars from Gaia and WISE data

Making use of strong correlations between closely separated multiple or double sources and photometric and astrometric metadata in Gaia EDR3, we generate a catalog of candidate double and multiply imaged lensed quasars and AGNs, comprising 3140 systems. It includes two partially overlapping parts, a sample of distant (redshifts mostly greater than 1) sources with perturbed data, and systems resolved into separate components by Gaia at separations less than $2\arcsec$. For the first part, which is roughly one third of the published catalog, we synthesized 0.617 million redshifts by multiple machine learning prediction and classification methods, using independent photometric and astrometric data from Gaia EDR3 and WISE with accurate spectroscopic redshifts from SDSS as a training set. Using these synthetic redshifts, we estimate a rate of 4.9\% of interlopers with spectroscopic redshift below 1 in this part of the catalog. Unresolved candidate double and dual AGNs and quasars are selected as sources with marginally high BP/RP excess factor (phot_bp_rp_excess_factor), which is sensitive to source extent, limiting our search to high-redshift quasars. For the second part of the catalog, additional filters on measured parallax and near-neighbor statistics are applied to diminish the propagation of remaining stellar contaminants. The estimated rate of positives (double or multiple sources) is 98\%, and the estimated rate of dual (physically related quasars) is greater than 54\%. A few dozen serendipitously found objects of interest are discussed in more detail, including known and new lensed images, planetary nebulae and young infrared stars of peculiar morphology, and quasars with catastrophic redshift errors in SDSS.

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arXiv2022

Differential proper motion spin of the Hipparcos and Gaia celestial reference frames

The Hipparcos catalog provides the first epoch of the celestial reference frame (CRF) in the optical domain and serves as an indispensable tool to verify and improve the Gaia CRF for the brighter stars ($V<11$ mag) and to identify the elusive astrometric binary stars with dim or invisible companions, including long-period exoplanets. The systems of positions in Hipparcos and Gaia cannot be directly compared, because they refer to two different mean epochs. It is shown that the proper motion systems for carefully filtered common stars are not statistically consistent within the given formal errors. The vector field of proper motion differences is fitted with 126 vector spherical harmonics up to degree 7 revealing a global pattern at high signal-to-noise ratios, including the three terms of rigid rotation. The origin of the differential spin and other large harmonic terms is investigated by producing a similar decomposition of the Gaia$-$HG proper motion field, where HG stands for the long-term proper motions derived from the Hipparcos and Gaia DR3 positions, for the same sample of stars. Hipparcos proper motions emerge as the largest source of sky-correlated distortions of the multi-epoch optical CRF with a median value of $\sim 190$ $μ$as yr$^{-1}$ and a global spin of $\sim 226$ $μ$as yr$^{-1}$, while the Hipparcos positions and Gaia EDR3 proper motions are explicitly consistent by construction at a level of $\sim 10$ $μ$as yr$^{-1}$. The latter, however, include multiple distortions of higher degree, which should be taken into account in astrometric applications using the HG field.

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arXiv2022

The Hipparcos Pleiades parallax error is also a proper motion error

The mean parallax of the Pleiades open cluster from the Hipparcos catalog is larger than the true value by approximately 1 mas. The origin of this error, as well as a possible algorithm of correcting it, was proposed by Makarov (2002). The problem is reassessed using the more accurate Gaia data with a focus on the predicted correction to the Pleiades proper motions. The accurately determined differences Gaia - Hipparcos for 52 common stars are close to these estimates within the formal uncertainties for all three parameters, which strongly suggests that the proposed interpretation was correct. With adjustments for the systematic vector field fitted with 126 vector spherical harmonics to degree 7, these differences amount to $(+0.39,\,-0.74)$ mas yr$^{-1}$. The implications of small-scale proper motion and position errors in Hipparcos for present day astrometry are briefly discussed.

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arXiv2022

Quasars with Proper Motions and the Link to Double and Multiple AGNs

Gaia used a large sample of photometrically selected active galactic nuclei (AGNs) and quasars to remove the residual spin of its global proper motion system in order to achieve a maximally inertial reference frame. A small fraction of these reference objects have statistically significant astrometric proper motions in Gaia EDR3. We compile a source sample of $105,593$ high-fidelity AGNs with accurate spectroscopically determined redshifts above 0.5 from the SDSS and normalized proper motions below 4. The rate of genuinely perturbed proper motions is at least 0.17\%. A smaller high completeness sample of 152 quasars with excess proper motions at a confidence level of 0.9995 is examined in detail. Pan-STARRS images and Gaia-resolved pairs reveal that 29\% of the sample are either double sources or gravitationally lensed quasars. An Anderson--Darling test on parameters of a smaller high-reliability sample and their statistical controls reveals 17 significant factors that favor multiplicity and multi-source structure as the main cause of perturbed astrometry. Using a nearest neighbor distance statistical analysis and counts of close companions in Gaia on a much larger initial sample of AGNs, an excess of closely separated sources in Gaia is detected. At least 0.33\% of all optical quasars are genuinely double or multiply imaged. We provide a list of 44 candidate double or multiple AGNs and four previously known gravitational lenses. Many proper motion quasars may be more closely separated, unresolved doubles exhibiting the variability imposed motion (VIM) effect, and a smaller fraction may be chance alignments with foreground stars causing weak gravitational lensing.

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arXiv2022

USNO Bright Star Catalog, version 1

USNO Bright Star Catalog (UBSC) is a new astrometric catalog of 1423 brightest stars covering the entire sky, which is published online. It is nearly complete to $V=3$ mag except for three stellar systems. A combined astrometric solution of the Hipparcos Intermediate Astrometry Data and two dedicated ground-based campaigns in 2013 -- 2020 is the basis for this catalog. The astrometric parameters for each star include position coordinates, parallax, proper motion components, and their covariances on the Hipparcos mean epoch 1991.25. 64 percent of the catalog are flagged as known or suspected double or binary stars. UBSC lists 68 stars missing in Gaia EDR3 and another 114 stars without Gaia parallaxes or proper motions. The formal precision achieved for proper motions is comparable to that of Gaia.

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arXiv2022

Chaos over Order: Mapping 3D Rotation of Triaxial Asteroids and Minor Planets

Celestial bodies approximated with rigid triaxial ellipsoids in a two-body system can rotate chaotically due to the time-varying gravitational torque from the central mass. At small orbital eccentricity values, rotation is short-term orderly and predictable within the commensurate spin-orbit resonances, while at eccentricity approaching unity, chaos completely takes over. Here, we present the full 3D rotational equations of motion around all three principle axes for triaxial minor planets and two independent methods of numerical solution based on Euler rotations and quaternion algebra. The domains of chaotic rotation are numerically investigated over the entire range of eccentricity with a combination of trial integrations of Euler's equations of motion and the GALI($k$) method. We quantify the dependence of the order--chaos boundaries on shape by changing a prolateness parameter, and find that the main 1:1 spin-orbit resonance disappears for specific moderately prolate shapes already at eccentricities as low as 0.3. The island of short-term stability around the main 1:1 resonance shrinks with increasing eccentricity at a fixed low degree of prolateness and completely vanishes at approximately 0.8. This island is also encroached by chaos on longer time scales indicating longer Lyapunov exponents. Trajectories in the close vicinity of the 3:2 spin-orbit resonance become chaotic at smaller eccentricities, but separated enclaves of orderly rotation emerge at eccentricities as high as 0.8. Initial perturbations of rotational velocity in latitude away from the exact equilibrium result in a spectrum of free libration, nutation, and polar wander, which is not well matched by the linearized analysis omitting the inertial terms.

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arXiv2022

The tidal quality of the hot Jupiter WASP-12b

WASP-12b stands out among the planets of its class of hot Jupiters because of the observed fast orbital decay attributed to tidal dissipation. The measured rate of the orbital period is $\stackrel{\bf\centerdot}{\textstyle{P}}_{\rm orb}\,=\,-\,29\pm3\;\mbox{ms/yr}\;$=$\;(9.2\pm1.0)\times10^{-10}\;\mbox{s/s}$. In the literature heretofore, all attempts to explain this high rate were based on the assumption that the orbital evolution is dominated by the tides in the star. Since the modified tidal quality factor in yellow dwarfs is insufficient to warrant such a decay rate, a hypothesis was put forward that the star may actually be a subgiant. Using the latest data from the Gaia mission, we deduce that WASP-12a at $1.36\,{M_{Sun}}$ is an evolving dwarf at an early stage of post-turn-off evolution that has not yet depleted hydrogen in its core. Its unremarkable position in the color-magnitude diagram and the existence of close planets orbiting red giants of similar mass contradict the hypothesis of an abrupt boost of tidal quality due to structural internal changes. On the other hand, the previous research neglected the tidal dissipation in the planet assuming it to be negligible due to the likely synchronisation of its rotation and a presumed high quality factor. We critically reassess this assumption in the light of recent astrometric results for Jupiter and Saturn. Assuming that the structure of WASP-12b is similar to that of our Jupiter and Saturn, we find that the observed orbital decay is well explained by the tides in the planet. The estimated value of the planet's modified quality factor coincides almost precisely with that of our Jupiter.

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arXiv2022

Testing the Cosmological Principle: Astrometric Limits on Systemic Motion of Quasars at Different Cosmological Epochs

A sample of $60,410$ bona fide optical quasars with astrometric proper motions in Gaia EDR3 and spectroscopic redshifts above 0.5 in an oval 8400 square degree area of the sky is constructed. Using orthogonal Zernike functions of polar coordinates, the proper motion fields are fitted in a weighted least-squares adjustment of the entire sample and of six equal bins of sorted redshifts. The overall fit with 37 Zernike functions reveals a statistically significant pattern, which is likely to be of instrumental origin. The main feature of this pattern is a chain of peaks and dips mostly in the R.A. component with an amplitude of 25~$μ$as yr$^{-1}$. This field is subtracted from each of the six analogous fits for quasars grouped by redshifts covering the range 0.5 through 7.03, with median values 0.72, 1.00, 1.25, 1.52, 1.83, 2.34. The resulting residual patterns are noisier, with formal uncertainties up to 8~$μ$as yr$^{-1}$ in the central part of the area. We detect a single high-confidence Zernike term for R.A. proper motion components of quasars with redshifts around 1.52 representing a general gradient of 30 $μ$as yr$^{-1}$ over $150\degr$ on the sky. We do not find any small- or medium-scale systemic variations of the residual proper motion field as functions of redshift above the $2.5\,σ$ significance level.

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arXiv2021

Astrometric mass ratios of 248 long-period binary stars resolved in Hipparcos and Gaia EDR3

Using the absolute astrometric positions and proper motions for common stars in the Hipparcos and Gaia catalogs separated by 24.75 years in the mean epoch, we compute mass ratios for long-period, resolved binary systems without any astrophysical assumptions or dependencies except the presence of inner binary subsystems that may perturb the observed mean proper motions. The mean epoch positions of binary companions from the Hipparcos Double and Multiple System Annex (DMSA) are used as the first epoch. The mean positions and proper motions of carefully cross-matched counterparts in Gaia EDR3 comprise the second epoch data. Selecting only results with sufficiently high signal-to-noise ratio and discarding numerous optical pairs, we construct a catalog of 248 binary systems, which is published online. Several cases with unusual properties or results are also discussed.

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arXiv2021

Mass ratios of long-period binary stars resolved in precision astrometry catalogs of two epochs

Mass ratios of widely separated, long-period, resolved binary stars can be directly estimated from the available data in major space astrometry catalogs, such as the ESA's Hipparcos and Gaia mission results. The method is based on the universal principle of inertial motion of the system's center of mass in the absence of external forces, and is independent of any assumptions about the physical parameters or stellar models. The application is limited by the precision of input astrometric data, the orbital period and distance to the system, and possible presence of other attractors in the vicinity, such as in triple systems. A generalization of this technique to triples is proposed, as well as approaches to estimation of uncertainties. The known long-period binary HIP 473 AB is discussed as an application example, for which a $m_2/m_1=0.996^{+0.026}_{-0.026}$ is obtained.

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arXiv2021

Looking for astrometric signals below 20 m/s: A Jupiter-mass planet signature in $ε$ Eri

The USNO ground-based astrometric program URAT-Bright in combination with the Hipparcos mission epoch astrometry provides precise proper motions of a thousand bright stars in the southern hemisphere on a time basis of about 25 years. Small but statistically significant differences between these proper motions and Gaia EDR3 data can reveal long-period exoplanets similar to Jupiter in the nearest star systems. The presence of such a planet orbiting the magnetically active dwarf $ε$ Eri is confirmed from both URAT--Hipparcos--EDR3 data and Hipparcos--EDR3 data with a corresponding projected velocity of $(+5,+8)$ and $(+6,+13)$ m s$^{-1}$, respectively. These signals are formally significant at a 0.989 and 1.0 confidence. We conclude that the newest astrometric results confirm the existence of a long-period exoplanet orbiting $ε$ Eri, which was marginally detected from precision radial velocity measurements some 20 years ago.

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arXiv2021

Looking for astrometric signals below 20 m/s: A candidate exo-Jupiter in $δ$ Pav

We use a combination of Hipparcos space mission data with the USNO dedicated ground-based astrometric program URAT-Bright designed to complement and verify Gaia results for the brightest stars in the south to estimate the small perturbations of observed proper motions caused by exoplanets. One of the 1423 bright stars in the program, $δ$ Pav, stands out with a small proper motion difference between our long-term estimate and Gaia EDR3 value, which corresponds to a projected velocity of $(-17,+13)$ m s$^{-1}$. This difference is significant at a 0.994 confidence in the RA component, owing to the proximity of the star and the impressive precision of proper motions. The effect is confirmed by a comparison of long-term EDR3-Hipparcos and short-term Gaia EDR3 proper motions at a smaller velocity, but with formally absolute confidence. We surmise that the close Solar analog $δ$ Pav harbors a long-period exoplanet similar to Jupiter.

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arXiv2021

Spin-orbit resonances of high-eccentricity asteroids: regular, switching, and jumping

Few solar system asteroids and comets are found in high eccentricity orbits ($e > 0.9$) but in the primordial planetesimal disks and in exoplanet systems around dying stars such objects are believed to be common. For 2006 HY51, the main belt asteroid with the highest known eccentricity 0.9684, we investigate the probable rotational states today using our computer-efficient chaotic process simulation method. Starting with random initial conditions, we find that this asteroid is inevitably captured into stable spin-orbit resonances typically within tens to a hundred Myr. The resonances are confirmed by direct integration of the equation of motion in the vicinity of end-points. Most resonances are located at high spin values above 960 times the mean motion (such as 964:1 or 4169:4), corresponding to rotation periods of a few days. We discover three types of resonance in the high-eccentricity regime: 1) regular circulation with weakly librating aphelion velocities and integer-number spin-orbit commensurabilities; 2) switching resonances of higher order with orientation alternating between aligned (0 or $π$) and sidewise ($π/2$) angles at aphelia and perihelia; 3) jumping resonances with aphelion spin alternating between two quantum states in the absence of spin-orbit commensurability. The islands of equilibrium are numerous at high spin rates but small in parameter space area, so that it takes millions of orbits of chaotic wandering to accidentally entrap in one of them. We discuss the implications of this discovery for the origins and destiny of high-eccentricity objects and the prospects of extending this analysis to the full 3D treatment.

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arXiv2021

Functional principal component analysis of radio-optical reference frame tie

The Gaia optical reference frame is intrinsically undefined with respect to global orientation and spin, so it needs to be anchored in the radio-based International Celestial Reference Frame (ICRF) to provide a referenced and quasi-inertial celestial coordinate system. The link between the two fundamental frames is realized through two samples of distant extragalactic sources, mostly AGNs and quasars, but only the smaller sample of radio-loud ICRF sources with optical counterparts is available to determine the mutual orientation. The robustness of this link can be mathematically formulated in the framework of functional principal component analysis using a set of vector spherical harmonics to represent the differences in celestial positions of the common objects. The weakest eigenvectors are computed, which describe the greatest deficiency of the link. The deficient or poorly determined terms are specific vector fields on the sphere which carry the largest errors of absolute astrometry using Gaia in reference to the ICRF. This analysis provides guidelines to the future development of the ICRF maximizing the accuracy of the link over the entire celestial sphere. A measure of robustness of a least-squares solution, which can be applied to any linear model fitting problem, is introduced to help discriminate between reference frame tie models of different degrees.

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arXiv2021

The Science of Fundamental Catalogs

This review paper discusses the science of astrometric catalogs, their current applications and future prospects for making progress in fundamental astronomy, astrophysics and gravitational physics. We discuss the concept of fundamental catalogs, their practical realizations, and future prospects. Particular attention is paid to the astrophysical implementations of the catalogs such as the measurement of the Oort constants, the secular aberration and parallax, and asteroseismology. We also consider the use of the fundamental catalogs in gravitational physics for testing general theory of relativity and detection of ultra-long gravitational waves of cosmological origin.

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