By employing the previous Voronoi approach and replacing its nearest neighbor approx- imation with Drizzle in iterative signal extraction, we develop a fast iterative Drizzle algorithm, namedfiDrizzle, to reconstruct the underlying band-limited image from undersampled dithered frames. Compared with the existing iDrizzle, the new algorithm improves rate of convergence and accelerates the computational speed. Moreover, under the same conditions （e.g. the same number of dithers and iterations）, fiDrizzle can make a better quality reconstruction than iDrizzle, due to the newly discov- ered High Sampling caused Decelerating Convergence （HSDC） effect in the iterative signal extraction process.fiDrizzle demonstrates its powerful ability to perform image deconvolution from undersampled dithers.
The formation of the present configuration of three hot super-Earths in the planet system HD 40307 is a challenge to dynamical astronomers.With the two successive period ratios both near and slightly larger than 2,the system may have evolved from pairwise2:1 mean motion resonances(MMRs).In this paper,we investigate the evolutions of the period ratios of the three planets after the primordial gas disk was depleted.Three routines are found to probably result in the current configuration under tidal dissipation with the center star,they are:(i)through apsidal alignment only;(ii)out of pairwise 2:1 MMRs,then through apsidal alignment;(iii)out of the 4:2:1 Laplace Resonance(LR),then through apsidal alignment.All the three scenarios require the initial eccentricities of planets～0.15,which implies a planetary scattering history during and after the gas disk was depleted.All the three routines will go through the apsidal alignment phase,and enter a state with near-zero eccentricities finally.We also find some special characteristics for each routine.If the system went through pairwise 2:1 MMRs at the beginning,the MMR of the outer two planets would be broken first to reach the current state.As for routine(iii),the planets would be out of the LR at the place where some high-order resonances are located.At the high-order resonances 17:8 or 32:15 of the planets c and d,the system will possibly enter the current state as the final equilibrium.
Time-series photometric observations were made for the high amplitudeδScuti star CW Ser between 2011 and 2012 at the Xinglong Station of National Astronomical Observatories,Chinese Academy of Sciences.After performing the frequency analysis of the light curves,we confirmed the fundamental frequency of f=5.28677 c d 1,together with seven harmonics of the fundamental frequency,which are newly detected.No additional frequencies were detected.The O C diagram,produced with the 21 newly determined times of maximum light combined with those provided in the literature,helps to obtain a new ephemeris formula of the times of maximum light with the pulsation period of 0.189150355±0.000000003 d.
We determine the proportions of two mixed crater populations distinguishable by size distributions on the Moon. A ＂multiple power-law＂ model is built to formulate crater size distribution N（D） ∝ D-αwhose slope α varies with crater diameter D. This model is then used to fit size distributions of lunar highland craters and Class 1 craters. The former is characterized by α = 1.17 ± 0.04, 1.88 ± 0.07,3.17 ± 0.10 and 1.40 ± 0.15 for D ranges ~ 10- 49, 49- 120, 120- 251 and ~ 251- 2500 km, while the latter has a single slope α = 1.96 ± 0.14 for about 10- 100 km. They are considered as Population 1 and2 crater size distributions, whose sum is then fitted to the global size distribution of lunar craters with D between 10 and 100 km. Estimated crater densities of Population 1 and 2 are 44 × 10-5and 5 × 10-5km-2respectively, leading to the proportion of the latter being 10%. This result underlines the need for more thoroughly investigating Population 1 craters and their related impactors, the primordial main-belt asteroids, which dominated the late heavy bombardment.
