Synodic Rotation Period Research Articles

Physical properties of the slow-rotating near-Earth asteroid (2059) Baboquivari from one apparition

In this study, we carried out photometric, spectroscopic, and for the first time, polarimetric observations of the Amor-type near-Earth asteroid (2059) Baboquivari. Our findings represent the first reliable determination of Baboquivari's physical properties. We used data from a 1m-class telescope (T100) along with ALCDEF data for photometric analyses and a 1.5-m-class telescope (RTT150) for polarimetric, spectroscopic, and additional photometric observations. We obtained the synodic rotation period of Baboquivari as 129.93 ​± ​2.31 ​h and the standard phase function parameters H and G as 16.05 ​± ​0.05, 0.22 ​± ​0.02, respectively. Our colour index (V-R) measurement of 0.45 ​± ​0.02 is consistent with spectroscopic observations, indicating an S (or sub-S) spectral type. Using the polarimetric and spectroscopic data, we found that the geometric albedo is 0.15 ​± ​0.03, and the spectral type is Sq. Based on the estimated albedo and absolute magnitude, Baboquivari has an effective diameter of 2.12 ​± ​0.21 ​km. Due to the scattered data in the light curve, its slow rotation and location among the NEAs suggest that Baboquivari may be a non-principal axis (NPA) rotator.

Spin vectors in the Koronis family: V. Resolving the ambiguous rotation period of (3032) Evans

A sidereal rotation counting approach is demonstrated by resolving an ambiguity in the synodic rotation period of Koronis family member (3032) Evans, whose rotation lightcurves’ features did not easily distinguish between doubly- and quadruply-periodic. It confirms that Evans’s spin rate does not exceed the rubble-pile spin barrier and thus presents no inconsistency with being a ∼14-km reaccumulated object. The full spin vector solution for Evans is comparable to those for the known prograde low-obliquity comparably-fast rotators in the Koronis family, consistent with having been spun up by YORP thermal radiation torques.

Towards an AI-based understanding of the solar wind: A critical data analysis of ACE data

All artificial intelligence models today require preprocessed and cleaned data to work properly. This crucial step depends on the quality of the data analysis being done. The Space Weather community increased its use of AI in the past few years, but a thorough data analysis addressing all the potential issues is not always performed beforehand. Here is an analysis of a largely used dataset: Level-2 Advanced Composition Explorer’s SWEPAM and MAG measurements from 1998 to 2021 by the ACE Science Center. This work contains guidelines and highlights issues in the ACE data that are likely to be found in other space weather datasets: missing values, inconsistency in distributions, hidden information in statistics, etc. Amongst all specificities of this data, the following can seriously impact the use of algorithms: Histograms are not uniform distributions at all, but sometime Gaussian or Laplacian. Algorithms will be inconsistent in the learning samples as some rare cases will be underrepresented. Gaussian distributions could be overly brought by Gaussian noise from measurements and the signal-to-noise ratio is difficult to estimate. Models will not be reproducible from year to year due to high changes in histograms over time. This high dependence on the solar cycle suggests that one should have at least 11 consecutive years of data to train the algorithm. Rounding of ion temperatures values to different orders of magnitude throughout the data, (probably due to a fixed number of bits on which measurements are coded) will bias the model by wrongly over-representing or under-representing some values. There is an extensive number of missing values (e.g., 41.59% for ion density) that cannot be implemented without pre-processing. Each possible pre-processing is different and subjective depending on one’s underlying objectives A linear model will not be able to accurately model the data. Our linear analysis (e.g., PCA), struggles to explain the data and their relationships. However, non-linear relationships between data seem to exist. Data seem cyclic: we witness the apparition of the solar cycle and the synodic rotation period of the Sun when looking at autocorrelations.Some suggestions are given to address the issues described to enable usage of the dataset despite these challenges.

Polarimetric properties of the near-Sun asteroid (155140) 2005 UD in comparison with other asteroids and meteoritic samples

ABSTRACTThe investigation of asteroids near the Sun is important for understanding the final evolutionary stage of primitive Solar system objects. A near-Sun asteroid (NSA), (155140) 2005 UD, has orbital elements similar to those of (3200) Phaethon (the target asteroid for the JAXA’s DESTINY+ mission). We conducted photometric and polarimetric observations of 2005 UD and found that this asteroid exhibits a polarization phase curve similar to that of Phaethon over a wide range of observed solar phase angles (α = 20–105°) but different from those of (101955) Bennu and (162173) Ryugu (asteroids composed of hydrated carbonaceous materials). At a low phase angle (α ≲ 30°), the polarimetric properties of these NSAs (2005 UD and Phaethon) are consistent with anhydrous carbonaceous chondrites, while the properties of Bennu are consistent with hydrous carbonaceous chondrites. We derived the geometric albedo, pV ∼ 0.1 (in the range of 0.088–0.109); mean V-band absolute magnitude, HV = 17.54 ± 0.02; synodic rotational period, $T_\mathrm{rot} = 5.2388 \pm 0.0022 \, \mathrm{h}$ (the two-peaked solution is assumed); and effective mean diameter, $D_\mathrm{eff} = 1.32 \pm 0.06 \, \mathrm{km}$. At large phase angles (α ≳ 80°), the polarization phase curve are likely explained by the dominance of large grains and the paucity of small micron-sized grains. We conclude that the polarimetric similarity of these NSAs can be attributed to the intense solar heating of carbonaceous materials around their perihelia, where large anhydrous particles with small porosity could be produced by sintering.

Fourth Harmonic Behaviour of the 27-Day Periodicity in Galactic Cosmic Rays During Different Solar Magnetic Polarity Intervals

Galactic cosmic rays as observed by the Hermanus and Jungfraujoch Neutron Monitors between 1960 and 2018 have been analysed using various spectral analysis techniques. Daily mean neutron monitor measurements are used to identify how several harmonics of the roughly 27-day synodic rotation period change during each of these years. Spectral analysis using Lomb-Scargle and Morlet wavelet techniques of Hermanus and Jungfraujoch data revealed in particular that the fourth harmonic (∼7-day) of the solar rotation period is exceptionally strong during the minima of solar cycles when A 0 (solar dipole pointing north). The power spectrum results obtained in this investigation showed that galactic cosmic rays at both Hermanus and Jungfraujoch exhibit peculiar short-term periodicity behaviour as a result of solar polarity dependent magnetic drifts during negative minima.

Variability in the Energetic Electron Bombardment of Ganymede

AbstractThis study examines the bombardment of energetic magnetospheric electrons onto Ganymede as a function of Jovian magnetic latitude. We use the output from a three‐dimensional, hybrid model to constrain features of the electromagnetic environment during the G1, G8, and G28 Galileo encounters when Ganymede was located far above, within, or far below Jupiter's magnetospheric current sheet, respectively. To quantify electron fluxes, we use a test‐particle model and trace relativistic electrons at discrete energies between 4.5 keV ≤E ≤ 100 MeV while exposed to these fields. For each location with respect to Jupiter's current sheet, electrons of all energies bombard Ganymede's poles with average number and energy fluxes of 1 · 108 cm−2 s−1 and 3 · 109 keV cm−2 s−1, respectively. However, bombardment is locally inhomogeneous: poleward of the open‐closed field line boundary, fluxes are enhanced in the trailing hemisphere but reduced in the leading hemisphere. When embedded within the Jovian current sheet, closed field lines of Ganymede's minimagnetosphere shield electrons below 40 MeV from accessing the equator. Above these energies, equatorial fluxes are longitudinally inhomogeneous between the sub‐Jovian and anti‐Jovian hemispheres, but the averaged number flux (4 · 103 cm−2 s−1) is comparable to the flux deposited here by each of the dominant energetic ion species near Ganymede. When located outside of the Jovian current sheet, electrons below 100 keV enter Ganymede's minimagnetosphere via the downstream reconnection region and bombard the leading apex, while electrons of all energies are shielded from the trailing apex. Averaged over a full synodic rotation period of Jupiter, the energetic electron flux pattern agrees well with brightness features observed across Ganymede's polar and equatorial surface.

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.

Time-variable Electromagnetic Star–Planet Interaction: The TRAPPIST-1 System as an Exemplary Case

Exoplanets sufficiently close to their host star can in principle couple electrodynamically to the star. This process is known as electrodynamic star-planet interaction (SPI). The expected emission associated with this coupling is however difficult to observe due to the bright intrinsic stellar emission. Identification of time-variability in the stellar lightcurve is one of the most promising approaches to identify SPI. In this work we therefore systematically investigate various mechanisms and their associated periods, which generate time-variability to aid the search for SPI. We find that the synodic and half the synodic rotation periods of the stars as measured in the rest frames of the orbiting exoplanets are basic periods occurring in SPI. We apply our findings to the example of TRAPPIST-1 with its seven close-in planets for which we investigate the possibility of SPI and the associated time-variabilities. We show that especially TRAPPIST-1b and c, are very likely subject to sub-Alfv\'{e}nic interaction, a necessary condition for SPI. Both planets are therefore expected to generate Alfv\'{e}n wings, which can couple to the star. The associated Poynting fluxes are on the order of $10^{11}$ to $10^{15}$ W and thus can hardly be the direct source of currently observable time-variability from TRAPPIST-1. However these Poynting fluxes might trigger flares on the star. We find correlations between the observed flares and the expected planetary induced signals, which could be due to SPI but our findings are not conclusive and warrant further observations and modelling.

Studies of irregular satellites: I. Lightcurves and rotation periods of 25 Saturnian moons from Cassini observations

Disk-integrated time-resolved photometric observations have been performed for 25 irregular moons of Saturn with the ISS camera of the Cassini spacecraft in a wide range of solar phase angles. From the derived lightcurves, synodic rotation periods were determined, ranging from ~5.5 h to ~76 h; the fastest observed spin rate is much slower than the disruption rotation barrier of asteroids at ~2 h. The lightcurves show very different structures which indicates that Saturn's irregular moons have a large variety of shapes. All lightcurves except for Phoebe and Paaliaq show 2-maxima/2-minima or 3-maxima/3-minima patterns. The lightcurve amplitudes range between 0.1 mag and > 2 mag, the latter is measured in observations of objects Ymir, Kiviuq, and Siarnaq at phase angles α > 60°. While most lightcurve amplitudes from observations obtained at α < 30° are <0.5 mag, most at α > 50° are >0.5 mag. This campaign marks the first utilization of an interplanetary spacecraft for a systematic photometric survey of irregular moons.

Solar Irradiance Variability, Influenced by r Modes

Abstract A spectrum of the four-decade solar irradiance record has a prominent cluster of power for periodicities near 1 yr. Correlating irradiance with a bandpass filter showed that periodicity values were not constant, but varied sinusoidally with each cycle lasting 14 ± 1 yr. The large modulation amplitude makes solar frequencies ≥1 yr−1 hard to detect at the solar surface. After removing the modulation, a Lomb–Scargle spectrum exposed two true periodicities: 1.006 and 0.920 yr. They are interpreted as the synodic rotation periods of r modes of lowest angular degree (ℓ = 1). The first propagates in the stable interior and the second in the convective envelope perturbed by its several flow fields. The rotational beat period of the two modes is about 10.9 yr. This is close to the average length of a solar cycle and possibly controls this average. The 1.006 yr periodicity dominates most of the filtered irradiance record but an abrupt change to about 0.8 yr occurs in mid-2010. Also found was evidence for higher-degree r modes (ℓ = 2 to 8) and a curious sawtooth modulation with a recurrence period of 2.6 yr.

27-day variation in solar-terrestrial parameters: Global characteristics and an origin based approach of the signals

The Earth and the near interplanetary medium are affected by the Sun in different ways. Those processes generated in the Sun that induce perturbations into the Magnetosphere-Ionosphere system are called geoeffective processes and show a wide range of temporal variations, like the 11-year solar cycle (long term variations), the variation of ∼27 days (recurrent variations), solar storms enduring for some days, particle acceleration events lasting for some hours, etc.In this article, the periodicity of ∼27 days associated with the solar synodic rotation period is investigated. The work is mainly focused on studying the resulting 27-day periodic signal in the magnetic activity, by the analysis of the horizontal component of the magnetic field registered on a set of 103 magnetic observatories distributed around the world. For this a new method to isolate the periodicity of interest has been developed consisting of two main steps: the first one consists of removing the linear trend corresponding to every calendar year from the data series, and the second one of removing from the resulting series a smoothed version of it obtained by applying a 30-day moving average. The result at the end of this process is a data series in which all the signal with periods larger than 30 days are canceled.The most important characteristics observed in the resulting signals are two main amplitude modulations: the first and most prominent related to the 11-year solar cycle and the second one with a semiannual pattern. In addition, the amplitude of the signal shows a dependence on the geomagnetic latitude of the observatory with a significant discontinuity at approx. ±60°.The processing scheme was also applied to other parameters that are widely used to characterize the energy transfer from the Sun to the Earth: F10.7 and Mg II indices and the ionospheric vertical total electron content (vTEC) were considered for radiative interactions; and the solar wind velocity for the non-radiative interactions between the solar wind and the magnetosphere. The 27-day signal obtained in the magnetic activity was compared with the signals found in the other parameters resulting in a series of cross-correlations curves with maximum correlation between 3 and 5 days of delays for the radiative and between 0 and 1 days of delay for the non-radiative parameters. This result supports the idea that the physical process responsible for the 27-day signal in the magnetic activity is related to the solar wind and not to the solar electromagnetic radiation.

Photometric survey, modelling, and scaling of long-period and low-amplitude asteroids

Context. The available set of spin and shape modelled asteroids is strongly biased against slowly rotating targets and those with low lightcurve amplitudes. This is due to the observing selection effects. As a consequence, the current picture of asteroid spin axis distribution, rotation rates, radiometric properties, or aspects related to the object’s internal structure might be affected too. Aims. To counteract these selection effects, we are running a photometric campaign of a large sample of main belt asteroids omitted in most previous studies. Using least chi-squared fitting we determined synodic rotation periods and verified previous determinations. When a dataset for a given target was sufficiently large and varied, we performed spin and shape modelling with two different methods to compare their performance. Methods. We used the convex inversion method and the non-convex SAGE algorithm, applied on the same datasets of dense lightcurves. Both methods search for the lowest deviations between observed and modelled lightcurves, though using different approaches. Unlike convex inversion, the SAGE method allows for the existence of valleys and indentations on the shapes based only on lightcurves. Results. We obtain detailed spin and shape models for the first five targets of our sample: (159) Aemilia, (227) Philosophia, (329) Svea, (478) Tergeste, and (487) Venetia. When compared to stellar occultation chords, our models obtained an absolute size scale and major topographic features of the shape models were also confirmed. When applied to thermophysical modelling (TPM), they provided a very good fit to the infrared data and allowed their size, albedo, and thermal inertia to be determined. Conclusions. Convex and non-convex shape models provide comparable fits to lightcurves. However, some non-convex models fit notably better to stellar occultation chords and to infrared data in sophisticated thermophysical modelling (TPM). In some cases TPM showed strong preference for one of the spin and shape solutions. Also, we confirmed that slowly rotating asteroids tend to have higher-than-average values of thermal inertia, which might be caused by properties of the surface layers underlying the skin depth.

The Rotation and Other Properties of Comet 49P/Arend–Rigaux, 1984–2012

Abstract We analyzed images of comet 49P/Arend–Rigaux on 33 nights between 2012 January and May and obtained R-band lightcurves of the nucleus. Through usual phasing of the data, we found a double-peaked lightcurve having a synodic rotation period of 13.450 ± 0.005 hr. Similarly, phase dispersion minimization and the Lomb–Scargle method both revealed rotation periods of 13.452 hr. Throughout the 2011/2012 apparition, the rotation period was found to increase by a small amount, consistent with a retrograde rotation of the nucleus. We also reanalyzed the publicly available data from the 1984/1985 apparition by applying the same techniques, finding a rotation period of 13.45 ± 0.01 hr. Based on these findings, we show that the change in rotation period is less than 14 s per apparition. Furthermore, the amplitudes of the lightcurves from the two apparitions are comparable, to within reasonable errors, even though the viewing geometries differ, implying that we are seeing the comet at a similar sub-Earth latitude. We detected the presence of a short-term jet-like feature in 2012 March, which appears to have been created by a short-duration burst of activity on March 15. Production rates obtained in 2004/2005, along with reanalysis of the previous results from 1984/1985, imply a strong seasonal effect and a very steep fall-off after perihelion. This, in turn, implies that a single source region, rather than leakage from the entire nucleus, dominates activity.

Variations in the Solar Coronal Rotation with Altitude – Revisited

Here we report in depth reanalysis of a paper by Vats et al. (2001) [Astrophys. J. 548, L87] based on the measurements of differential rotation with altitude as a function of observing frequencies (as lower and higher frequencies indicate higher and lower heights, respectively) in the solar corona. The radial differential rotation of the solar corona is estimated from daily measurements of the disc-integrated solar radio flux at 11 frequencies: (275, 405, 670, 810, 925, 1080, 1215, 1350, 1620, 1755 MHz and 2800 MHz). We use the same data as were used in Vats et al. (2001), but instead of the 12th maxima of autocorrelograms used there, we use the 1st secondary maxima to derive the synodic rotation period. We estimate synodic rotation by Gaussian fit of the 1st secondary maxima. Vats et al. (2001) reported that the sidereal rotation period increases with increasing frequency. The variation found by them was from 23.6 to 24.15 days in this frequency range with a difference of only 0.55 days. The present study finds that sidereal rotation period increases with decreasing frequency. The variation range is from 24.4 to 22.5 days and difference is about three times larger (1.9 days). However, at 925 MHz both studies give similar rotation period. In Vats et al. (2001) the Pearson factor with trend line was 0.86 whereas present analysis obtained a ~ 0.97 Pearson factor with the trend line. Our study shows that the solar corona rotates slower at higher altitudes, which is in contradiction to the findings reported in Vats et al. (2001). Key words: Solar radio flux- flux modulation method- Gaussian fit- sidereal rotation period.

An investigation of the low-ΔV near-Earth asteroids (341843) 2008 EV5 and (52381) 1993 HA

Context. The Asteroid Redirect Mission (ARM) under development by NASA is being planned to collect a multi-meter boulder from a near-Earth asteroid (NEA), and to bring it to the cis-lunar space in the mid-2020’s for future study and exploitation by a crewed mission. The MarcoPolo-M5 project is being proposed in 2016 for the M5 mission opportunity by ESA, to bring back to Earth a sample from a very primitive D-type NEA. As D-types are very rare within the NEA population, considerable effort is still in progress to characterize easily accessible targets with unknown surface composition, in order to discover further asteroids that belong to this taxonomic group. Aims. We aim to further characterize the physical properties of two optimal targets for sample return space missions, the low-ΔV NEAs (341843) 2008 EV5 and (52381) 1993 HA. The asteroid 2008 EV5 is the baseline target of ARM, but only one spectrum of this object exists in the literature. The asteroid 1993 HA is a very favourable target for a space mission based on its dynamical properties: here we intend to assess if it is a suitable target for MarcoPolo-M5. Methods. We obtained visible spectroscopy of 2008 EV5 with the FORS2 instrument at ESO-VLT (Paranal, Chile), at different rotational phases. We also obtained visible and near-infrared spectroscopy of 1993 HA, using the EFOSC2 and SOfI instruments at ESO-NTT (La Silla, Chile). Visible photometry of 1993 HA was carried out within the IMPACTON project at the Observatório Astronômico do Sertão de Itaparica (Itacuruba, Brazil). Results. Our new observations are in agreement with the C-type classification of 2008 EV5, which is a requirement for the ARM mission. We obtained five visible spectra which do not show any variability within the limits of noise, suggesting a homogeneous surface. We obtained the first ever spectroscopic dataset (~0.4–1.6 μm) for 1993 HA, finding a featureless, red-sloped behaviour typical of D-types (a T or X classification is also possible, with decreasing confidence). We also found that the synodic rotation period of 1993 HA is 4.107 ± 0.002 h, a value that is optimal for the execution of a sample return mission. The derived lightcurve also suggests an elongated shape (axis ratio a/b ≥ 1.71). At this stage 1993 HA does indeed seem to be the most favourable target for MarcoPolo-M5, though future observations are necessary to study it further.

Photometric Observation and Modeling Study of the Asteroid (26) Proserpina

We present the new CCD observations on the asteroid (26) Proserpina performed between 2011 December and 2012 February. Based upon the new observations, a synodic rotation period of (13.107 ± 0.002) h is obtained. Using all the light curves available sofar, the rotation vector, rotation period, and the shape model of the asteroid are determined with the convex-hull inversion method. Further more, a bootstrap method is applied to estimating the uncertainties of the rotation parameters. We derive a pair of possible rotation poles for (26) Proserpina, and believe that it has a retrograde rotation. The rotation poles are determined to be λ1 = 90.8° ± 1.4°, β1 = −53.1° ± 3.2°, and λ2 = 259.3° ± 2.2°, β2 = −62.0° ± 2.0°. The sidereal rotation periods corresponding to the two poles are almost the same as (13.109777 ± 3.8 × 10-6) h. And corresponding to this pair of rotation poles, the convex-hull shapes of the asteroid are the mirror images of each other.

The synodic rotational period of asteroid 4332 Milton

The results of our new photometric observations of the main-belt asteroid 4332 Milton are presented. These observations were obtained on two successive nights in August 2012 at Çanakkale University Observatory. The bimodal light curve amplitude and period were determined to be 0.16 ± 0.01 mag and 3.295 ± 0.005 h, respectively.

Short-term variability of comet C/2012 S1 (ISON) at 4.8 AU from the Sun

We observed comet C/2012 S1 (ISON) during six nights in February 2013 when it was at 4.8 AU from the sun. At this distance and time the comet was not very active and it was theoretically possible to detect photometric variations likely due to the rotation of the cometary nucleus. The goal of this work is to obtain differential photometry of the comet inner coma using different aperture radii in order to derive a possible rotational period. Large field of view images were obtained with a 4k x 4k CCD at the f/3 0.77m telescope of La Hita Observatory in Spain. Aperture photometry was performed in order to get relative magnitude variation versus time. Using calibrated star fields we also obtained ISON's R-magnitudes versus time. We applied a Lomb-Scargle periodogram analysis to get possible periodicities for the observed brightness variations, directly related with the rotation of the cometary nucleus. The comet light curve obtained is very shallow, with a peak-to-peak amplitude of 0.03 $\pm$ 0.02 mag. A tentative synodic rotational period (single-peaked) of 14.4 $\pm$ 1.2 hours for ISON's nucleus is obtained from our analysis, but there are other possibilities. We studied the possible effect of the seeing variations in the obtained periodicities during the same night, and from night to night. These seeing variations had no effect on the derived periodicity. We discuss and interpret all possible solutions for the rotational period of ISON's nucleus.

The Centaur 10199 Chariklo: investigation into rotational period, absolute magnitude, and cometary activity

Context. Rings have recently been discovered around the Centaur 10199 Chariklo.Aims. In this paper we present new photometric data, obtained at the 4.2 m SOAR Telescope, aiming to investigate Chariklo’s absolute magnitude and rotational period, which is still unknown, and to look for potential cometary activity.Methods. The field background of the images was very crowded so several approaches were used for the extraction of Chariklo fluxes. The background sources were subtracted using difference image analysis and then aperture photometry was applied. A Fourier polynomial fit was used to determine the period.Results. We find a synodic rotation period of 7.004±0.036 h. The visual absolute magnitude derived from the SOAR data is H v = 7.03 ± 0.10. We model the rings’ contribution to the flux, and find that the derived H v is consistent with the predicted ring system aspect angle. We also revised the Chariklo system albedo (4.2%) and effective radius (119 ± 5 km) from a re-analysis of Herschel and WISE thermal data obtained during 2010 with the correct H v value. No coma is detected from the SOAR data, nor in previous VLT images acquired in 2007−2008, where the rings’ aspect angle was close to zero. The upper limit to the dust production rate is 2.5 kg/s.

ROTATIONAL PROPERTIES OF THE MARIA ASTEROID FAMILY

Maria family is regarded as an old-type (~3 +/- 1 Gyr) asteroid family which has experienced substantial collisional and dynamical evolution in the Main-belt. It is located nearby the 3:1 Jupter mean motion resonance area that supplies Near-Earth asteroids (NEAs) to the inner Solar System. We carried out observations of Maria family asteroids during 134 nights from 2008 July to 2013 May, and derived synodic rotational periods for 51 objects, including newly obtained periods of 34 asteroids. We found that there is a significant excess of fast and slow rotators in observed rotation rate distribution. The two-sample Kolmogorov-Smirnov test confirms that the spin rate distribution is not consistent with a Maxwellian at a 92% confidence level. From correlations among rotational periods, amplitudes of lightcurves, and sizes, we conclude that the rotational properties of Maria family asteroids have been changed considerably by non-gravitational forces such as the YORP effect. Using a lightcurve inversion method (Kaasalainen & Torppa 2001; Kaasalainen et al. 2001), we successfully determined the pole orientations for 13 Maria members, and found an excess of prograde versus retrograde spins with a ratio (N_p/N_r) of 3. This implies that the retrograde rotators could have been ejected by the 3:1 resonance into the inner Solar System since the formation of Maria family. We estimate that approximately 37 to 75 Maria family asteroids larger than 1 km have entered the near-Earth space every 100 Myr.