34 research outputs found
Spin vector and shape of (6070) Rheinland and their implications
Main belt asteroids (6070) Rheinland and (54827) 2001NQ8 belong to a small
population of couples of bodies which reside on very similar heliocentric
orbits. Vokrouhlicky & Nesvorny (2008, AJ 136, 280) promoted a term "asteroid
pairs", pointing out their common origin within the past tens to hundreds of
ky. Previous attempts to reconstruct the initial configuration of Rheinland and
2001NQ8 at the time of their separation have led to the prediction that
Rheinland's rotation should be retrograde. Here we report extensive photometric
observations of this asteroid and use the lightcurve inversion technique to
directly determine its rotation state and shape. We confirm the retrograde
sense of rotation of Rheinland, with obliquity value constrained to be >= 140
deg. The ecliptic longitude of the pole position is not well constrained as
yet. The asymmetric behavior of Rheinland's lightcurve reflects a sharp,
near-planar edge in our convex shape representation of this asteroid. Our
calibrated observations in the red filter also allow us to determine and values of the H-G system. With the
characteristic color index for the S-type asteroids, we
thus obtain for the absolute magnitude of (6070) Rheinland.
This a significantly larger value than previously obtained from analysis of the
astrometric survey observations. We next use the obliquity constraint for
Rheinland to eliminate some degree of uncertainty in the past propagation of
its orbit. This is because the sign of the past secular change of its semimajor
axis due to the Yarkovsky effect is now constrained. Determination of the
rotation state of the secondary component, asteroid (54827) 2001NQ8, is the key
element in further constraining the age of the pair and its formation process.Comment: Published in AJ, 28 pages, 4 figures, 2 table
Photometry of the Didymos System across the DART Impact Apparition
On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite’s orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ∼1 day after impact and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG photometric model. An HG 1 G 2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the system many months after DART impact
Polarimetry and BVRI photometry of the potentially hazardous near-Earth Asteroid (23187) 2000 PN<SUB>9</SUB>
International audienceThe results of V-band polarimetric observations of the potentially hazardous near-Earth Asteroid (23187) 2000 PN 9 at large phase angles are presented as well as its photometric observations in BVRI bands. Observations were made in March-April 2006 during its close approach to the Earth using the 1.82-m Asiago telescope (Italy) and the 0.7-m telescope at the Chuguevskaya Observational Station (Ukraine). We obtained polarimetric measurements at the phase angle of 115°, the largest phase angle ever observed in asteroid polarimetry. Our data show that the maximum value of the polarization phase curve reached 7.7% and occurred in the phase angle range of 90-115°. The measured values of linear polarization degree, BVRI colors and magnitude-phase dependence correspond to the S-type composition of this asteroid. Based on our observations the following characteristics of the Asteroid (23187) 2000 PN 9 were obtained: a rotation period of 2.5325±0.0004 h, a lightcurve amplitude of 0.13 mag, an albedo of 0.24±0.06 and a diameter of 1.6±0.3 km
Wavelength dependence of the opposition effect of asteroid 433 Eros
International audienc