Aims.
The orbital motion of the transiting hot Jupiter TrES-5 b was reported to be perturbed by a planetary companion on a nearby orbit. Such compact systems do not frequently occur in nature, and ...investigating their orbital architecture could shed some light on the formation processes of hot Jupiters.
Methods.
We acquired 15 new precise photometric time-series for 12 transits of TrES-5 b between June 2019 and October 2020 using 0.9–2.0 m telescopes. The method of precise transit timing was employed to verify the deviation of the planet from the Keplerian motion.
Results.
Although our results show no detectable short-time variation in the orbital period of TrES-5 b and the existence of the additional nearby planet is not confirmed, the new transits were observed about two minutes earlier than expected. We conclude that the orbital period of the planet could vary on a long timescale. We found that the most likely explanation of the observations is the line-of-sight acceleration of the system’s barycentre caused by the orbital motion induced by a massive, wide-orbiting companion.
Context.
The rotation state of small asteroids is affected by the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, which is a net torque caused by solar radiation directly reflected and thermally ...reemitted from the surface. Due to this effect, the rotation period slowly changes, which can be most easily measured in light curves because the shift in the rotation phase accumulates over time quadratically.
Aims.
By new photometric observations of selected near-Earth asteroids, we want to enlarge the sample of asteroids with a detected YORP effect.
Methods.
We collected archived light curves and carried out new photometric observations for asteroids (10115) 1992 SK, (1620) Geographos, and (1685) Toro. We applied the method of light curve inversion to fit observations with a convex shape model. The YORP effect was modeled as a linear change of the rotation frequency
υ
≡ d
ω
∕d
t
and optimized together with other spin and shape parameters.
Results.
We detected the acceleration
υ
= (8.3 ± 0.6) × 10
−8
rad d
−2
of the rotation for asteroid (10115) 1992 SK. This observed value agrees well with the theoretical value of YORP-induced spin-up computed for our shape and spin model. For (1685) Toro, we obtained
υ
= (3.3 ± 0.3) × 10
−9
rad d
−2
, which confirms an earlier tentative YORP detection. For (1620) Geographos, we confirmed the previously detected YORP acceleration and derived an updated value of
υ
with a smaller uncertainty. We also included the effect of solar precession into our inversion algorithm, and we show that there are hints of this effect in Geographos’ data.
Conclusions.
The detected change of the spin rate of (10115) 1992 SK has increased the total number of asteroids with YORP detection to ten. In all ten cases, the d
ω
∕d
t
value is positive, so the rotation of these asteroids is accelerated. It is unlikely to be just a statistical fluke, but it is probably a real feature that needs to be explained.
ABSTRACT Asteroid (3200) Phaethon is a Near-Earth Apollo asteroid with an unusual orbit that brings it closer to the Sun than any other known asteroid. Its last close approach to the Earth was in ...2017 mid-December and the next one will be on 2026 October. Previous rotationally time-resolved spectroscopy of Phaethon showed that its spectral slope is slightly bluish, in agreement with its B/F taxonomic classification, but at some rotational phases, it changes to slightly reddish. Motivated by this result, we performed time-resolved imaging polarimetry of Phaethon during its recent close approach to the Earth. Phaethon has a spin period of 3.604 h, and we found a variation of the linear polarization with rotation. This seems to be a rare case in which such variation is unambiguously found, also a consequence of its fairly large amplitude. Combining this new information with the brightness and colour variation as well as previously reported results from Arecibo radar observations, we conclude that there is no variation of the mineralogy across the surface of Phaeton. However, the observed change in the linear polarization may be related to differences in the thickness of the surface regolith in different areas or local topographic features.
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.
Context.
EE Cep is one of few eclipsing binary systems with a dark, dusty disc around an invisible object similar to
ε
Aur. The system is characterised by grey and asymmetric eclipses every 5.6 yr ...that have significant variations in their photometric depth, ranging from ∼0
.
m
5 to ∼2
.
m
0.
Aims.
The main aim of the observational campaign of the EE Cep eclipse in 2014 was to test the model of disc precession. We expected that this eclipse would be one of the deepest with a depth of ∼2
.
m
0.
Methods.
We collected multicoloured observations from almost 30 instruments located in Europe and North America. These photometric data cover 243 nights during and around the eclipse. We also analyzed low- and high-resolution spectra from several instruments.
Results.
The eclipse was shallow with a depth of 0
.
m
71 in the
V
band. The multicoloured photometry illustrates small colour changes during the eclipse with a total amplitude of order ∼+0
.
m
15 in the
B
−
I
colour index. We updated the linear ephemeris for this system by including new times of minima, measured from the three most recent eclipses at epochs
E
= 9, 10, and 11. We acquired new spectroscopic observations, covering orbital phases around the eclipse, which were not observed in the past and increased the data sample, filling some gaps and giving better insight into the evolution of the H
α
and Na
I
spectral line profiles during the primary eclipse.
Conclusions.
The eclipse of EE Cep in 2014 was shallower than expected, measuring 0
.
m
71 instead of ∼2
.
m
0. This means that our model of disc precession needs revision.
Opposition effect of Trojan asteroids Shevchenko, V.G.; Belskaya, I.N.; Slyusarev, I.G. ...
Icarus (New York, N.Y. 1962),
2012, 2012-01-00, 20120101, Volume:
217, Issue:
1
Journal Article
Peer reviewed
► We have obtained detailed magnitude–phase relations for three Jupiter Trojans. ► The magnitude–phase relations are linear down to phase angle of 0.1–0.2°. ► We have not revealed any noticeable ...opposition brightening for the V and R bands. ► Such behavior is inherent for dark surfaces where single scattering plays main role.
CCD-photometry of three Jupiter Trojan asteroids were carried out to study their opposition effect. We obtained well-sampled magnitude–phase curves for (588) Achilles, (884) Priamus, and (1143) Odysseus in the maximal attainable phase angle range down to 0.1–0.2°. The magnitude–phase relations have a linear behavior in all observed range of phase angles and do not show any non-linear opposition brightening. We have not found any confident differences between phase slopes measured in B, V and R bands. The values of the measured phase slopes of Trojans are different from available data for Centaurs. They are within the range of phase slopes measured for some low-albedo main belt asteroids, also exhibit a linear behavior down to small phase angles. An absence of non-linear opposition brightening puts constraints on the surface properties of the studied objects, assuming very dark surfaces where single scattering plays dominating role.
We also determined the rotation periods, amplitudes, the values of color indexes B–V and V–R, and the absolute magnitudes of these asteroids.
An analysis of photometric observations of Mars crosser asteroid 1011
Laodamia conducted at Bulgarian National Astronomical Observatory Rozhen over
a twelve year interval (2002, 2003, 2004, 2006, ...2007, 2008, 2011, 2012 and
2013) is made. Based on the obtained lightcurves the spin vector, sense of
rotation, and preliminary shape model of (1011) Laodamia have been determined
using the lightcurve inversion method. The aim of this investigation is to
increase the set of asteroids with known spin and shape parameters and to
contribute in improving the model in combination with other techniques and
sparse data produced by photometric asteroid surveys such as Pan-STARRS or
GAIA.
nema
Aims.
We aim to investigate how polarimetric observations can improve our understanding of the nature and diversity of M/X-type asteroids.
Methods.
Polarimetric observations of the selected M/X-type ...asteroids were carried out at the Tohoku 0.6-m telescope at Haleakala Observatory, Hawaii (simultaneously in
BVR
filters), the 2-m telescope of the Bulgarian National Astronomical Observatory in Rozhen (in R filter), and the 2.15-m telescope of the Complejo Astronómico El Leoncito (CASLEO), Argentina (in V filter). We analysed the polarimetric characteristics of M/X-type asteroids along with the available data obtained by other techniques.
Results.
New polarimetric observations of 22 M/X-type asteroids combined with published observations provide a data set of 41 asteroids for which the depth of a negative polarisation branch and/or inversion angle were determined. We found that the depth of the negative polarisation branch tends to increase with decreasing steepness of the near-infrared spectra. Asteroids with a deeper negative polarisation branch tend to have a higher radar circular polarisation ratio. We show that, based on the relationship of the depth of the negative polarisation branch and inversion angle, two main sub-types can be distinguished among M-type asteroids. We suggest that these groups may be related to different surface compositions similar to (1) irons and stony-irons and (2) enstatite and iron-rich carbonaceous chondrites.
Context . The rotation state of small asteroids is affected in the long term by perturbing torques of gravitational and radiative origin (the YORP effect). The former can be detected by a change in ...the spin-axis orientation in the inertial space; the latter manifests itself by a quadratic increase in the rotation phase. Aims . Direct observational evidence of the YORP effect is the primary goal of our work. This includes both the YORP detection for new objects and an improvement in the accuracy of previously known detections. Methods . We carried out photometric observations of five near-Earth asteroids: (1862) Apollo, (2100) Ra-Shalom, (85989) 1999 JD6, (138852) 2000 WN10, and (161989) Cacus. Then we applied the light-curve inversion method to all available data to determine the spin state and a convex shape model for each of the five studied asteroids. The YORP effect was modeled as a linear change of the rotation frequency υ ≡ d ω /d t . In the case of (2100) Ra-Shalom, the analysis required that the spin-axis precession due to the solar gravitational torque also be included. Results . We obtained two new detections of the YORP effect: (i) υ = (2.9 ± 2.0) × 10 −9 rad d −2 for (2100) Ra-Shalom, and (ii) υ = (5.5 ± 0.7) × 10 −8 rad d −2 for (138852) 2000 WN10. The analysis of Ra-Shalom also reveals a precession of the spin axis with a precession constant α ~ 3000″ yr −1 . This is the first such detection from Earth-bound photometric data. For the other two asteroids, we improved the accuracy of the previously reported YORP detection: (i) υ = (4.94 ± 0.09) × 10 −8 rad d −2 for (1862) Apollo, and (ii) υ = (1.86 ± 0.09) × 10 −8 rad d −2 for (161989) Cacus. With this value, Apollo has the most precisely determined YORP effect so far. Despite the recent report of a detected YORP effect for (85989) 1999 JD6, we show that the model without YORP cannot be rejected statistically. Therefore, the detection of the YORP effect for this asteroid requires future observations. In several of our targets, the currently available observations do not provide enough constraints on the shape model (even at large scales) to compute the theoretical YORP effect with sufficient precision. Nevertheless, the interpretation of the detected signal as the YORP effect is fairly plausible. The spin-axis precession constant of Ra-Shalom determined from observations matches the theoretically expected value. Conclusions . The total number of asteroids with a YORP detection has increased to 12. In all cases, the rotation frequency increases in time. The analysis of a rich photometric data set of irregularly shaped asteroids may require inclusion of spin-axis precession in future studies.
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