Sidereal Period Research Articles

Photometry and model of near-Earth asteroid 2021 DW1 from one apparition

Aims. Very small asteroids (VSAs, objects with diameters smaller than about 150 m) can be spun up by the YORP effect to rotation periods as short as tens of seconds. This effect has been observed for many of them. It is also hypothesised, that in the same process their spin axes are asymptotically drawn to the position perpendicular to the orbital plane. So far this effect has been observed only for one VSA and needs further verification. For that, spin axes of several other VSAs should be determined by observing their brightness variations at many different positions on the sky. Methods. On 4 March 2021 at 9 UTC a 30-m in diameter near-Earth asteroid 2021 DW1 passed the Earth at a distance of 570 000 km, reaching the maximum brightness of V = 14.6 mag. We observed it photometrically from 2 March, when it was visible at V = 16.5 mag, until 7 March (V = 18.2 mag). During that time 2021 DW1 swept a 170° long arc in the northern sky, spanning solar phase angles in the range from 36° to 86°. This made it an excellent target for physical characterisation, including spin axis and shape derivation. Results. Convex inversion of the asteroid lightcurves gives a sidereal period of rotation Psid = 0.013760 ± 0.000001 h, and two solutions for the spin axis ecliptic coordinates: (A) λ1 = 57° ± 10°, β1 = 29° ± 10° and (B) λ2 = 67° ± 10°, β2 = −40° ± 10°. The magnitude-phase curve can be fitted with a standard H, G function with H = 24.8 ± 0.5 mag and an assumed G = 0.24. The asteroid colour indices are g − i = 0.79 ± 0.01 mag, and i − z = 0.01 ± 0.02 mag which indicates an S taxonomic class, with an average geometric albedo pV = 0.23 ± 0.02. The asteroid effective diameter, derived from H and pV, is Deff = 30 ± 10 m. Conclusions. It was found that the inclination of the spin axis of 2021 DW1 is not perpendicular to the orbital plane (obliquity ϵ = 54° ± 10° or ϵ = 123° ± 10°). More spin axes of VSAs should be determined to check, if 2021 DW1 is an exception or a typical case.

V-band photometry of asteroids from ASAS-SN

We present V-band photometry of the 20 000 brightest asteroids using data from the All-Sky Automated Survey for Supernovae (ASAS-SN) between 2012 and 2018. We were able to apply the convex inversion method to more than 5000 asteroids with more than 60 good measurements in order to derive their sidereal rotation periods, spin axis orientations, and shape models. We derive unique spin state and shape solutions for 760 asteroids, including 163 new determinations. This corresponds to a success rate of about 15%, which is significantly higher than the success rate previously achieved using photometry from surveys. We derive the first sidereal rotation periods for additional 69 asteroids. We find good agreement in spin periods and pole orientations for objects with prior solutions. We obtain a statistical sample of asteroid physical properties that is sufficient for the detection of several previously known trends, such as the underrepresentation of slow rotators in current databases, and the anisotropic distribution of spin orientations driven by the nongravitational forces. We also investigate the dependence of spin orientations on the rotation period. Since 2018, ASAS-SN has been observing the sky with higher cadence and a deeper limiting magnitude, which will lead to many more new solutions in just a few years.

Roaming the Relativistic Realm: Short-term Dynamical Evolution of Atira 2021 PH27

Abstract General relativity effects coupled with those derived from the von Zeipel–Lidov–Kozai mechanism may play a significant role on the evolution of members of the Atira dynamical class, particularly in the case of those with the shortest sidereal orbital periods. Here, we provide a preliminary assessment of the short-term orbital evolution of 2021 PH27, a recently discovered Atira that has the shortest period among known asteroids. Our calculations, based on a publicly available orbit determination and including post-Newtonian terms in the numerical integrations, show that 2021 PH27 is a robust member of the Atira class and it may indeed be used to explore the combined effects of general relativity and the von Zeipel–Lidov–Kozai mechanism once its orbit determination is sufficiently improved.

New constraints on the physical properties and dynamical history of Centaur 174P/Echeclus

ABSTRACT Since 2005 December, recurrent outbursts have been observed for Centaur 174/P Echeclus, confirming it is an active object. Thanks to a large number of photometric data obtained between 2001 April and 2019 December, we were able to compute a shape model of this object. We obtain a sidereal rotation period P = 26.785178 ± 10−6 h and six equally probable pole solutions, each with a large obliquity of the rotational axis (50° or more). We also find the object significantly elongated, with a semi-major axial ratio a/b = 1.32 (and b/c ∼ 1.1 but this second ratio is poorly constrained by the photometric data). Additionally, we present a detailed analysis of the dust emission from the 2016 outburst. Different colour maps are presented that reveal a change in dust colour, which becomes bluer with increasing cometocentric distance. A blue ring-like structure around the nucleus clearly visible in the images obtained on October 4 in the V-R spectral interval points out that the innermost near nucleus region is considerably redder than the surrounding coma. Different jets are also apparent, the main one being oriented southward. A detailed dynamical study is done to investigate past and future orbital elements. These elements appear stable in the period ≈1200 CE to ≈2900 CE. For a period of 12 000 yr the main conclusion is that Echeclus’ perihelion distance was greater than about 4 au, preventing it from following a typical cometary activity like a short-period comet. Close encounters with giant planets nevertheless prevent any study of orbital elements on longer timescale.

Comparison of Deterministic Methods to Estimate Sidereal Rotation Period from Light Curves

The importance of determining the sidereal rotation period of an astronomical object on future investigations pertaining to said object has been well documented in the literature. Researchers, however, have differed in their techniques used to estimate and model objects in the space catalog. In this paper, several period-estimation methods will be explored ranging across Fourier and phase-folding techniques. These methods will be tested using ground-based observations of light curve data for various resident space objects that fall under a rigid body context (i.e., asteroids, satellites, probes, rocket bodies) and celestial objects like stars and extrasolar planets. The effect of varying sample size, the inadequacies in unevenly sampled data processing, autonomy of the method, and complexity of parameters are investigated. For the models of artificial space objects that are not open source, a simulation is used to generate synthetic light curves with which all of the above-mentioned techniques are also employed. To account for heterogeneity in method parameters, each technique is tested with a range of values to optimize the rotational period. Results for uniformly sampled asteroid data as well as nonuniformly sampled stellar objects and generic sinusoidal data show variances in accuracy of the methods, but certain methods stand out.

Lifetimes and rotation within the solar mean magnetic field

ABSTRACT We have used very high-cadence (sub-minute) observations of the solar mean magnetic field (SMMF) from the Birmingham Solar Oscillations Network (BiSON) to investigate the morphology of the SMMF. The observations span a period from 1992 to 2012, and the high-cadence observations allowed the exploration of the power spectrum up to frequencies in the mHz range. The power spectrum contains several broad peaks from a rotationally modulated (RM) component, whose linewidths allowed us to measure, for the first time, the lifetime of the RM source. There is an additional broadband, background component in the power spectrum which we have shown is an artefact of power aliasing due to the low fill of the data. The sidereal rotation period of the RM component was measured as 25.23 ± 0.11 d and suggests that the signal is sensitive to a time-averaged latitude of ∼12°. We have also shown the RM lifetime to be 139.6 ± 18.5 d. This provides evidence to suggest that the RM component of the SMMF is connected to magnetic flux concentrations (MFCs) and active regions (ARs) of magnetic flux, based both on its lifetime and location on the solar disc.

The physical and dynamical characteristics of the asteroid 4940 Polenov

The asteroid (1986 QY4) 4940 Polenov is the first Solar system object whose 3D shape is determined using the observations from the newly built Astronomical Station Vidojevica (ASV). Here we present the results of photometric observations for Polenov, gathered from the ASV, and from the Bulgarian National Astronomical Observatory (BNAO) Rozhen, during 2014, 2019 and 2020 apparitions. Polenov is a 17.8km object located in the outer part of the main belt and belongs to the asteroid family Themis. We have determined the lightcurves, the synodic period of 4.161?0.001 h, as well as the solution for the shape and spin axis. Using the lightcurve inversion method, the combination of our lightcurves and the sparse data from ATLAS{HKO and ATLAS-MLO, we also found the sidereal period, indicating a retrograde rotation of the asteroid, with two possible mirrored pole solutions. The ratio of the largest to smallest reecting surface is about 1.4. In addition, we studied the dynamical properties of the asteroid and obtained a long stability time that exceeds 0.4 Gyrs.

Convex Shape and Rotation Model of Lucy Target (11351) Leucus from Lightcurves and Occultations

Abstract We report new photometric lightcurve observations of the Lucy Mission target (11351) Leucus acquired during the 2017, 2018, and 2019 apparitions. We use these data in combination with stellar occultations captured during five epochs to determine the sidereal rotation period, the spin axis orientation, a convex shape model, the absolute scale of the object, its geometric albedo, and a model of the photometric properties of the target. We find that Leucus is a prograde rotator with a spin axis located within a sky-projected radius of 3° (1σ) from J2000 Ecliptic coordinates (λ = 208°, β = +77°) or J2000 Equatorial Coordinates (R.A. = 248°, decl. = +58°). The sidereal period is refined to P sid = 445.683 ± 0.007 h. The convex shape model is irregular, with maximum dimensions of 60.8, 39.1, and 27.8 km. The convex model accounts for global features of the occultation silhouettes, although minor deviations suggest that local and global concavities are present. We determine a geometric albedo of p V = 0.043 ± 0.002. The derived phase curve supports a D-type classification for Leucus.

Observation of a 27 Days Periodicity in Melanoma Diagnosis

Streams from the dark universe may affect biologic processes on Earth including occurrence of cancer. Here, we have recovered complete daily melanoma incidence rates 1982–2014 in Australia. If there is no other external cause for melanoma, its seasonal rate should be steady with a broad maximum during local summertime due to increased solar UV exposure. The reported melanoma cases show instead: (A) a modulation repeating every [Formula: see text] weeks; (B) a time-dependence which relates also with Moon’s geocentric orbital position, while it does not fit concurrently measured solar activity; and (C) a modulation periodicity strikingly coinciding with the Moon’s sidereal periodicity of 27.3 days, which is fixed to remote stars and not to the Sun. These findings show that the associated cause must be of exo-solar origin, and not only due steady solar UV exposure. A possible interpretation of the finding is the underlying working hypothesis itself, namely the flux of slow speed streaming DM is temporally enhanced due to gravitational (self-)focusing by the solar system. Interestingly, the gravitational focusing effect by the Moon itself towards the Earth covers speeds up to [Formula: see text][Formula: see text]km/s, fitting within the widely assumed velocity distribution of DM constituents at [Formula: see text][Formula: see text]km/s. The derived observations for melanoma diagnosis are a novel model-independent finding with potential public health implications and possible relevance for other diseases. The results of this work also serve as accumulating and independent signatures strengthening previous physics claims being at work at the Sun and Earth’s upper atmosphere, inspiring a novel cross-disciplinary approach for the dark matter (DM) paradigm. In future, the 27.3 days periodicity does not necessarily require long-term physical and medical measurements to search for a direct cause-effect relationship. Potential candidates from the dark sector are the highly ionizing anti-quark nuggets, magnetic monopoles, but also particles like dark photons; other as yet unpredicted DM constituents with sufficient impact on the highly sensitive living matter could be at work.

Analysis of Envisat’s rotation state using epoch method

Envisat has been identified as a candidate target for active debris removal. The research on its rotation state is of great significance. The specular glint times in optical observation data can be used in fitting the rotation state of Envisat by the epoch method. Using well-observed variations in synodic frequencies, and minimizing the goodness-of-fit indicator by a grid-search, complete spin state solutions can be derived. By this method, Envisat’s spin axis longitude α and latitude δ in the orbital coordinate system can be calculated. The latitude δ oscillates widely with time between -55° and -85° with a mean value of δmean=-67.08°. Its distribution has peaks in two areas around -60° and -80°, which is similar to the results through laser ranging measurements from a single pass. In addition, the precession fit of the spin axis longitude α shows that the spin axis may not precess regularly around the negative normal of the orbital plane. Besides, Envisat’s sidereal period from 2013 to 2015 increases exponentially with the expression: Psid(sec)=121.1·exp(4.462×10-4·t), where t is measured in days from the beginning of 2013, RMS of the fit residuals = 1.8586 s.

Physical characterization of double asteroid (617) Patroclus from 2007/2012 mutual events observations

We publish a set of 16 light curves of mutual events inside the synchronous system of the Jupiter Trojan (617) Patroclus. Patroclus is th only binary system of the six target asteroids of the forthcoming NASA Discovery-class mission Lucy. Determining the physical parameters of the system is therefore of primary importance in helping to plan the flyby mission.Light curves were acquired during two follow-up campaigns of 6 months each between January–June 2007 and July–December 2012. Eight small eclipse events of amplitude of 0.2–0.3 mag were recorded in 2007. On the other hand, in 2012, the amplitudes of the phenomena were much deeper, between 0.6 and 0.8 mag, due to a nearly edge-on configuration of the system.We refined the sidereal period to 102.78624 ± 0.00015h = 4.282760 ± 0.000005days. The J2000 ecliptic coordinates of the pole of the system were found to be λ = 235.3 ± 1.2° andβ = − 62.4 ± 0.2°. The volume ratio was determined equal to q = 0.69 ± 0.08. By using a model of inhomogeneous Roche ellipsoids in hydrostatic equilibrium, we derived a bulk density of 0.81 ± 0.16g/cm3 and a surface grain density of 2.69 ± 0.36g/cm3 in agreement with spectroscopic observations of this P-type asteroid.As a validation, our solution was applied to revisit recent results obtained from observations of another type: AO astrometry and stellar occultation. Our model is thus perfectly able to account for these observations after fitting the mutual separation to the value of 695 ± 10km. Consequently, the area-equivalent diameter of the system as a whole is derived DΑ = 168.8 ± 2.6km.

Probing a r−n modification of the Newtonian potential with exoplanets

The growing availability of increasingly accurate data on transiting exoplanets suggests the possibility of using these systems as possible testbeds for modified models of gravity. In particular, we suggest that the post-Keplerian (pK) dynamical effects from the perturbations of the Newtonian potential falling off as the square or the cube of the distance from the mass of the host star break the degeneracy of the anomalistic, draconitic and sidereal periods. The latter are characteristic temporal intervals in the motion of a binary system, and all coincide in the purely Keplerian case. We work out their analytical expressions in presence of the aforementioned perturbations to yield preliminary insights on the potential of the method proposed for constraining the modified models of gravity considered. A comparison with other results existing in the literature is made.

Possible Evidence from the Flaring Activity of Sgr A* for a Star at a Distance of ∼3.3 Schwarzschild Radii from the Black Hole

Abstract The frequent flaring events in the X-ray and the near-IR (NIR) radiation of Sgr A* seem not to be periodic in time. However, statistical regularities, here termed “modulations by a pacemaker,” are found in the recorded arrival times of both types of events. The characteristic time of the X-ray pacemaker is 149 minutes, and that of the NIR pacemaker is 40 minutes. Their reality as derived from observed data can be accepted at larger than 4.6σ and 3.8σ levels of statistical confidence, respectively. These results can be interpreted as evidence for a star that revolves around the black hole (BH) of Sgr A* in a slightly elliptical precessing orbit, at a distance of 3–3.5 Schwarzschild radii of the BH. The period of the X-ray pacemaker, which is not a periodicity of the flare occurrences themselves, is the epicyclic period of the star orbital motion. This is the time interval between two successive passages of the star through the pericenter of its orbit. The NIR pacemaker period is the mean sidereal binary period of the star revolution. The origin of the X-ray flares is in episodes of intense mass loss from the star that occur preferably near the pericenter phase of the binary revolution. The NIR flares originate or are triggered by processes that are internal to the star. The radiation emitted in the direction of Earth is slightly modulated by the changing aspect ratio of the two components of the BH/star binary to the line of sight from Earth at the sidereal binary frequency.

New Evidence for a Physical Link between Asteroids (155140) 2005 UD and (3200) Phaethon*

Abstract In 2018, the near-Earth object (155140) 2005 UD (hereafter UD) experienced a close fly by of the Earth. We present results from an observational campaign involving photometric, spectroscopic, and polarimetric observations carried out across a wide range of phase angles (0.°7–88°). We also analyze archival NEOWISE observations. We report an absolute magnitude of H V = 17.51 ± 0.02 mag and an albedo of p V = 0.10 ± 0.02. UD has been dynamically linked to Phaethon due their similar orbital configurations. Assuming similar surface properties, we derived new estimates for the diameters of Phaethon and UD of D = 5.4 ± 0.5 km and D = 1.3 ± 0.1 km, respectively. Thermophysical modeling of NEOWISE data suggests a surface thermal inertia of and regolith grain size in the range of 0.9–10 mm for UD and grain sizes of 3–30 mm for Phaethon. The light curve of UD displays a symmetric shape with a reduced amplitude of Am(0) = 0.29 mag and increasing at a linear rate of 0.017 mag/° between phase angles of 0° and ∼25°. Little variation in light-curve morphology was observed throughout the apparition. Using light-curve inversion techniques, we obtained a sidereal rotation period P = 5.235 ± 0.005 hr. A search for rotational variation in spectroscopic and polarimetric properties yielded negative results within observational uncertainties of ∼10% μm−1 and ∼16%, respectively. In this work, we present new evidence that Phaethon and UD are similar in composition and surface properties, strengthening the arguments for a genetic relationship between these two objects.

Rotation anomaly of the Sun

AbstractDoes the Sun always rotate correctly? On the basis of the measurements of its mean magnetic field (more than 27 thousand daily values, obtained by seven observatories during 1968–2018) and resonance relations of the solar system, the sidereal spin period of the Sun as a star is determined as 25.165(6) days and that of the solar equator as 25.081(7) days. After 1993, however, a remarkable violation of the solar equatorial rate, through an unknown cause, has happened: the spin coherency of the mean field disintegrated and made way for nearly chaotic variations with quasi‐periods of 24.7–25.4 days. The phenomenon is thought to be tied to anomaly of the Wolf cycles 23 and 24, accompanied presumably by a global change of the Earth's climate (with unclear mechanism of the Sun–Earth influence).

On the orbital evolution of 2020 AV2, the first asteroid ever observed to go around the Sun inside the orbit of Venus

ABSTRACT The innermost section of the Solar system has not been extensively studied because minor bodies moving inside Earth’s orbit tend to spend most of their sidereal orbital periods at very low solar elongation, well away from the areas more frequently observed by programs searching for near-Earth objects. The survey carried out from the Zwicky Transient Facility (ZTF) is the first one that has been able to detect multiple asteroids well detached from the direct gravitational perturbation of the Earth–Moon system. ZTF discoveries include 2019 AQ3 and 2019 LF6, two Atiras with the shortest periods among known asteroids. Here, we perform an assessment of the orbital evolution of 2020 AV2, an Atira found by ZTF with a similarly short period but following a path contained entirely within the orbit of Venus. This property makes it the first known member of the elusive Vatira population. Genuine Vatiras, those long-term dynamically stable, are thought to be subjected to the so-called von Zeipel–Lidov–Kozai oscillation that protects them against close encounters with both Mercury and Venus. However, 2020 AV2 appears to be a former Atira that entered the Vatira orbital domain relatively recently. It displays an anticoupled oscillation of the values of eccentricity and inclination, but the value of the argument of perihelion may circulate. Simulations show that 2020 AV2 might reach a 3:2 resonant orbit with Venus in the future, activating the von Zeipel–Lidov–Kozai mechanism, which in turn opens the possibility to the existence of a long-term stable population of Vatiras trapped in this configuration.

On the variation of solar coronal rotation using SDO/AIA observations

ABSTRACT We report on the variability of the rotation periods of solar coronal layers with respect to temperature (or height). For this purpose, we have used observations from the Atmospheric Imaging Assembly (AIA) telescope on board the Solar Dynamics Observatory (SDO) space mission of National Aeronautics and Space Administration (NASA). The images used are at wavelengths of 94, 131, 171, 193, 211 and 335 Å during the period from 2012–2018. Analysis of solar full-disc images obtained at these wavelengths by AIA is carried out using the flux modulation method. 17 rectangular strips/bins at equal intervals of 10° (extending from 80°S to 80°N) are selected to extract a time series of extreme ultraviolet (EUV) intensity variations to obtain the autocorrelation coefficient. The peak of the Gaussian fit to the first secondary maximum in the autocorrelogram gives the synodic rotation period. Our analysis shows differential rotation with respect to latitude as well as temperature (or height). In the present study, we find that the sidereal rotation periods of different coronal layers decrease with increasing temperature (or height). The average sidereal rotation period at the lowest temperature (∼600 000 K) corresponding to AIA 171-Å, which originates from the upper transition region/quiet corona, is 27.03 days. The sidereal rotation period decreases with temperature (or height) to 25.47 days at a higher temperature (∼10 million K), corresponding to the flaring regions of the solar corona as seen in AIA 131-Å observations.

Attitude analysis of space debris using SLR and light curve data measured with single-photon detector

Attitude is the important parameter for active debris removal and collision avoidance. This paper deduced the spin axis orientation and spin period of the rocket body, CZ-3B R/B (NORAD ID 38253), using the satellite laser ranging and light curve data measured with single-photon detector at Graz station. The epoch method and LC & SLR residuals fitting were combined to determine these values. The derived right ascension angle was around 220°, the declination angle was near 64° and the sidereal period was calculated to be 117.724 s, for 2017-07-03. The results derived from the two distinct methods were mutually validated. Rocket bodies are a major contributor to space debris and this work provides a reference for attitude determination and attitude modelling.

Shape model and spin-state analysis of PHA contact binary (85990) 1999 JV6 from combined radar and optical observations

Context.The potentially hazardous asteroid (85990) 1999 JV6 has been a target of previously published thermal-infrared observations and optical photometry. It has been identified as a promising candidate for possible Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect detection.Aims.The YORP effect is a small thermal-radiation torque considered to be a key factor in spin-state evolution of small Solar System bodies. In order to detect YORP on 1999 JV6 we developed a detailed shape model and analysed the spin-state using both optical and radar observations.Methods.For 1999 JV6, we collected optical photometry between 2007 and 2016. Additionally, we obtained radar echo-power spectra and imaging observations with Arecibo and Goldstone planetary radar facilities in 2015, 2016, and 2017. We combined our data with published optical photometry to develop a robust physical model.Results.We determine that the rotation pole resides at negative latitudes in an area with a 5° radius close to the south ecliptic pole. The refined sidereal rotation period is 6.536787 ± 0.000007 h. The radar images are best reproduced with a bilobed shape model. Both lobes of 1999 JV6 can be represented as oblate ellipsoids with a smaller, more spherical component resting at the end of a larger, more elongated component. While contact binaries appear to be abundant in the near-Earth population, there are only a few published shape models for asteroids in this particular configuration. By combining the radar-derived shape model with optical light curves we determine a constant-period solution that fits all available data well. Using light-curve data alone we determine an upper limit for YORP of 8.5 × 10−8rad day−2.Conclusions.The bifurcated shape of 1999 JV6 might be a result of two ellipsoidal components gently merging with each other, or a deformation of a rubble pile with a weak-tensile-strength core due to spin-up. The physical model of 1999 JV6 presented here will enable future studies of contact binary asteroid formation and evolution.

Intermittency in Solar Wind Turbulence From Fluid to Kinetic Scales

Solar wind is a highly turbulent medium exhibiting fluctuations ranging from the solar sidereal rotation period to proton and electron gyroperiods. Their amplitudes show remarkable scalings with frequency across more than seven decades, suggesting a self‐similar nature for these fluctuations. However, these fluctuations are not globally scale invariant and require a multifractal approach. Multifractality is closely related to intermittency, a phenomenon that has been studied in the solar wind for more than three decades. We now have a rather complete picture of the nature of the most intermittent events and the radial/latitudinal dependence of this phenomenon in the heliosphere. Parallel shocks, slow mode shocks or tangential discontinuities/current sheets identified as the border between adjacent flux tubes are the most intermittent structures within the low‐frequency turbulence. It is more complicated and fascinating to understand the nature of intermittent events at kinetic scales since they are directly related to dissipative phenomena and might be the key to understanding the dissipation mechanisms in the collisionless solar wind plasma. Unfortunately, we still do not have adequate plasma observations at kinetic scales to work on, but several studies, mostly numeric, have addressed this topic suggesting that discontinuities, small‐scale current sheets, and sites which are candidates for reconnection events might be regions where dissipative phenomena are at work with consequent plasma heating and acceleration. This review is intended to provide the reader with a quick overview on the past and most recent understanding of intermittency phenomenon in the solar wind from fluid to kinetic scales.