| 其他摘要 | Near-Earth Objects (NEOs) are defined as asteroids and comets with orbits that closely approach Earth and pose a potential impact threat. Among them, NEOs with a Minimum Orbit Intersection Distance (MOID) of 0.05 AU or less and a diameter greater than 140 meters are defined as Potentially Hazardous Asteroids (PHAs). High-precision astrometric studies of NEOs have significant research and application value in understanding the formation and evolution of the solar system and in developing planetary defense strategies. High-precision astrometric results help improve the orbital data of NEOs, thus establishing more accurate orbital models. This is crucial for long-term monitoring of asteroid impact risks and assessing potential threats. This paper is based on the astrometric observations of two NEOs using the 50 cm telescope at Daocheng, Sichuan, and applies shift stacking techniques for fast-moving, faint targets. The specific work is as follows:High-precision astrometric observations and reductions of PHA 1998 HH49.Using 424 effective frames of 1998 HH49 captured in October 2023, the observational
positions (O) of the target were calculated. The theoretical positions (C) of the target
were derived from the ephemerides of the Jet Propulsion Laboratory (JPL), the Institut
de Mécanique Céleste et de Calcul des Éphémérides (IMCCE) in France, and the
Near-Earth Objects Dynamic Site 2 (NEODyS-2). The differences between the observed
positions (O) and the calculated positions (C) from different ephemerides were
then computed. For 1998 HH49, the comparison with the JPL ephemeris showed that
the mean O-C values in right ascension (RA) and declination (Dec) were 0.070″and−0.349″, with standard deviations of 0.136″and 0.130″, respectively. The comparison
with the IMCCE ephemeris indicated that the mean O-C values in RA and Dec
were 0.083″and −0.063″, with standard deviations of 0.144″and 0.123″, respectively.
The comparison with the NEODyS-2 ephemeris showed that the mean O-C values in
RA and Dec were 0.061″and −0.491″, with standard deviations of 0.129″and 0.222″,
respectively. These results indicate good consistency between the observational data
and the ephemeris predictions, although there are slight differences between different
ephemerides. Moreover, compared with the results from other international observatories,
our observations showed superior accuracy, demonstrating that the 50 cm telescope
at Daocheng can perform high-precision measurements of NEOs.Shift stacking and astrometric reductions for the fast-moving, faint target
2011 GA. 2011 GA moves at a relatively high speed of approximately 8″/min, which
causes signiffcant trailing in long-exposure images. In short-exposure images, the target
appears faint with a signal-to-noise ratio of about 3−5. In recent years, other shift stacking studies on solar system objects have dealt with target speeds ranging from 0.1″/min to 1.7″/min.Therefore, this paper attempts to apply the shift stacking technique to the
astrometric observations of this fast-moving and faint near-Earth asteroid. Before performing
the shift stacking, masking techniques were used to separate the moving target
from the background stars, preventing interference from background stars during the
stacking process, thus obtaining higher quality images. After shift stacking and astrometric
reduction of 30 valid frames of PHA 2011 GA, the results compared with the
JPL ephemeris show that the mean values of O-C in RA and Dec directions are 0.035″and −0.050″respectively, with standard deviations of 0.446″and 0.323″(before stacking,
the mean values of O-C in RA and Dec directions were 0.345″and −0.097″, with
standard deviations of 0.477″and 0.370″respectively); compared with the NEODyS-2
ephemeris, the mean values of O-C in RA and Dec directions are 0.024″and −0.078″respectively, with standard deviations of 0.382″and 0.295″(before stacking, the mean
values of O-C in RA and Dec directions were 0.342″and −0.024″, with standard deviations
of 0.477″and 0.371″respectively); compared with the IMCCE ephemeris, the
mean values of O-C in RA and Dec directions are 0.282″and −0.049″respectively,
with standard deviations of 0.390″and 0.287″(before stacking, the mean values of O-C in RA and Dec directions were 0.635″and −0.078″, with standard deviations of0.380″and 0.357″respectively). This indicates that the shift stacking method is also
effective for astrometric measurements of fast-moving and faint targets. The results of this study show overall small differences between the observational
data and ephemeris predictions, demonstrating the capability of the 50 cm telescope
at Daocheng for high-precision astrometry. The implementation of mask-based shift
stacking techniques signiffcantly improved the image quality and observation accuracy
for fast-moving, faint targets. This method can provide technical support for China’s
NEO defense and kinetic impact experiments, among other related efforts. |
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