Differential astrometry over 15°

We observed the pair of radio sources 1150+812 and 1803+784 in November 1993 with a VLBI array, simultaneously recording at 8.4 and 2.3 GHz. We determined the angular separation between the two sources with submilliarcsecond accuracy by using differential techniques. This result demonstrates the feasibility of high precision differential astrometry for radio sources separated in the sky by almost 15°, and opens the avenue to its application to larger samples of radio sources.     

Spin rate distribution of small asteroids

The spin rate distribution of main belt/Mars crossing (MB/MC) asteroids with diameters 3-15 km is uniform in the range from f=1 to 9.5 d⁻¹, and there is an excess of slow rotators with f<1 d⁻¹. The observed distribution appears to be controlled by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. The magnitude of the excess of slow rotators is related to the residence time of slowed down asteroids in the excess and the rate of spin rate change outside the excess. We estimated a median YORP spin rate change of ≈0.022 d⁻¹/Myr for asteroids in our sample (i.e., a median time in which the spin rate changes by 1 d⁻¹ is ≈45 Myr), thus the residence time of slowed down asteroids in the excess is ≈110 Myr. The spin rate distribution of near-Earth asteroids (NEAs) with sizes in the range 0.2-3 km (∼5 times smaller in median diameter than the MB/MC asteroids sample) shows a similar excess of slow rotators, but there is also a concentration of NEAs at fast spin rates with f=9-10 d⁻¹. The concentration at fast spin rates is correlated with a narrower distribution of spin rates of primaries of binary systems among NEAs; the difference may be due to the apparently more evolved population of binaries among MB/MC asteroids.     

Evidence of N2-ice on the surface of the icy dwarf Planet 136472 (2005 FY9)

We present high signal precision optical reflectance spectra of 2005 FY9 taken with the Red Channel Spectrograph and the 6.5-m MMT telescope on 2006 March 4 UT (5000-9500 Å; 6.33 Å pixel⁻¹) and 2007 February 12 UT (6600-8500 Å; 1.93 Å pixel⁻¹). From cross-correlation experiments between the 2006 March 4 spectrum and a pure CH₄-ice Hapke model, we find the CH₄-ice bands in the MMT spectrum are blueshifted by 3 ± 4 Å relative to bands in the pure CH₄-ice Hapke spectrum. The higher resolution MMT spectrum of 2007 February 12 UT enabled us to measure shifts of individual CH₄-ice bands. We find the 7296, 7862, and 7993 Å CH₄-ice bands are blueshifted by 4 ± 2, 4 ± 4, and 6 ± 5 Å. From four measurements we report here and one of our previously published measurements, we find the CH₄-ice bands are shifted by 4 ± 1 Å. This small shift is important because it suggest the presence of another ice component on the surface of 2005 FY9. Laboratory experiments show that CH₄-ice bands in spectra of CH₄ mixed with other ices are blueshifted relative to bands in spectra of pure CH₄-ice. A likely candidate for the other component is N₂-ice because its weak 2.15 μm band and blueshifted CH₄ bands are seen in spectra of Triton and Pluto. Assuming the shift is due to the presence of N₂, spectra taken on two consecutive nights show no difference in CH₄/N₂. In addition, we find no measurable difference in CH₄/N₂ at different depths into the surface of 2005 FY9.     

Spectral observations of blue stellar objects from FBS in the zone δ =+39°

Spectral observations of blue stellar objects from FBS are reported for the purpose of classifying them, discovering interesting new objects, and studying the FBS sample as a whole. 59 FBS objects in the zone with central declination δ =+39° were observed with the 2.6-m telescope at the Byurakan Observatory during 1987–1991. The images have been digitized with a professional scanner and processed by MIDAS in a way similar to CCD spectra. In addition, 4 objects were observed with the BAO-2.6 and OHP-1.93 telescopes using modern techniques during 1997–2000. 3 white dwarfs, 45 hot subdwarfs, 4 HBB stars, and 2 class F stars were discovered. Spectra of 20 of the most interesting objects are shown. __________ Translated from Astrofizika, Vol. 51, No. 1, pp. 51–59 (February 2008).     

射电选和X射线选BL Lacertae天体的射电性质

收集了射电选和X射线选BL Lac天体的射电数据(包括核和延展光度), 并计算了它们的核主导系数R.研究显示: 射电选BL Lac(RBLs)天体的总射电光度是X射线选BL Lac(XBLs)天体的2个量级.详细分析得到这种差别主要是来自于核光度的差别因为延展光度差别只有1个量级.研究RBLs和XBLs的核(延展元)光度与核主导系数之间的关系, 发现延展元光度与核主导系数负相关, 而核(总)光度几乎与核主导系数没有相关.     

Estimating the density of intermediate size KBOs from considerations of volatile retention

By using a hydrodynamic atmospheric escape mechanism (Levi, A., Podolak, M. [2009]. Icarus 202, 681-693) we show how the unusually high mass density of Quaoar could have been predicted (constrained), without any knowledge of a binary companion. We suggest an explanation of the recent spectroscopic observations of Orcus and Charon [Delsanti, A., Merlin, F., Guilbert, A., Bauer, J., Yang, B., Meech, K.J., 2010. Astron. Astrophys. 520, A40; Cook, J.C., Desch, S.J., Roush, T.L., Trujillo, C.A., Geballe, T.R., 2007. Astrophys. J. 663, 1406-1419]. We present a simple relation between the detection of certain volatile ices and the body mass density and diameter. As a test case we implement the relations on the KBO 2003 AZ₈₄ and give constraints on its mass density. We also present a method of relating the latitude-dependence of hydrodynamic gas escape to the internal structure of a rapidly rotating body and apply it to Haumea.     

融合点、对象、关键点等3种基元的点云滤波方法

基元是影响点云滤波精度和效率的关键因素之一。本文提出了一种基于多基元的三角网渐进加密(MPTPD)滤波方法。它包括点云分割、对象关键点提取、基于关键点的对象类别判别3个主要阶段,且3个阶段的基元分别为点、对象、关键点。使用了4景机载激光雷达和摄影测量点云数据对MPTPD、三角网渐进加密(TPD)、基于对象的三角网渐进加密(OTPD)3种滤波方法进行了性能测试。试验表明,MPTPD方法具有整体上最优的性能:在精度方面,MPTPD与OTPD两种方法的精度相当,MPTPD方法的一类误差I、总误差T比TPD的相应误差分别低约22.07%和8.44%;在效率方面,多数情况下TPD、MPTPD、OTPD方法的效率依次降低,且MPTPD的平均耗时是OTPD平均耗时的57.93%。     

How to compare movement? A review of physical movement similarity measures in geographic information science and beyond

In geographic information science, a plethora of different approaches and methods is used to assess the similarity of movement. Some of these approaches term two moving objects similar if they share akin paths. Others require objects to move at similar speed and yet others consider movement similar if it occurs at the same time. We believe that a structured and comprehensive classification of movement comparison measures is missing. We argue that such a classification not only depicts the status quo of qualitative and quantitative movement analysis, but also allows for identifying those aspects of movement for which similarity measures are scarce or entirely missing.

In this review paper we, first, decompose movement into its spatial, temporal, and spatiotemporal movement parameters. A movement parameter is a physical quantity of movement, such as speed, spatial path, or temporal duration. For each of these parameters we then review qualitative and quantitative methods of how to compare movement. Thus, we provide a systematic and comprehensive classification of different movement similarity measures used in geographic information science. This classification is a valuable first step toward a GIS toolbox comprising all relevant movement comparison methods.     

Satellite-tracked drifting buoy observations in the south equatorial current in the Indian Ocean

Three satellite-tracked drifting buoys released in the south equatorial current in the Indian Ocean followed the path of the current moving westward approximately zonally in the vicinity of 10 S latitude. On nearing the east coast of Africa two buoys moved north and the third moved south. Over the open sea regime the buoys moved with a speed of approximately 30 cm/s at an angle of about 35° to the left of the wind. The overall tendencies seen in the buoy drift are similar to those observed elsewhere in the world oceans.