How do binaries affect the derived dynamical mass of a star cluster?

The dynamical mass of a star cluster can be derived from the virial theorem, using the measured half-mass radius and line-of-sight velocity dispersion of the cluster. However, this dynamical mass may be a significant overestimation of the cluster mass if the contribution of the binary orbital motion is not taken into account. Here, we describe the mass overestimation as a function of cluster properties and binary population properties, and briefly touch on the issue of selection effects. We find that for clusters with a measured velocity dispersion of σ _los?10 km?s^?1 the presence of binaries does not affect the dynamical mass significantly. For clusters with σ _los?1 km?s^?1 (i.e., low-density clusters), the contribution of binaries to σ _los is significant, and may result in a major dynamical mass overestimation. The presence of binaries may introduce a downward shift of Δlog?(L _V /M _dyn)=0.05–0.4 (in solar units) in the log?(L _V /M _dyn) versus age diagram.     

Monitoring the Microarcsecond Quasar J1819+3845

We present the results of a year-long monitoring campaign on J1819+3845.We interpret the results of this WSRT campaign to infer critical source parameters such as source lifetime and structure on tens of microarcseconds. The long lifetime of the source at such high brightness temperatures requires continuous energy injection or exotic emission processes. We have previously interpreted the extreme scintillation ofJ1819+3845 as due to a relatively nearby (∼ 20 pc) scattering screen. We show this screen has a velocity w.r.t. the LSR of ∼ 25 kms^-1, as measured by the changing scintillation properties throughout the year: the `velocity parallax'. This revised version was published online in July 2006 with corrections to the Cover Date.     

赤潮生物种类特征光谱获取技术

较为系统地研究了赤潮生物水体反射率曲线获取方法。通过对 2类反射率反演方法得出的反射率曲线与实际反射率曲线进行比较 ,得出在不具备大气环境参数的情况下 ,经验线性法的反演结果与实际反射率曲线最接近的结论 ,并进一步对正常海水和赤潮生物水体的光谱特性进行分析 ,提取出赤潮生物水体的特征光谱。这是进行赤潮监测和识别的重要前提     

Oxygen compounds in Titan's stratosphere as observed by Cassini CIRS

We have investigated the abundances of Titan's stratospheric oxygen compounds using 0.5 cm⁻¹ resolution spectra from the Composite Infrared Spectrometer on the Cassini orbiter. The CO abundance was derived for several observations of far-infrared nadir spectra, taken at a range of latitudes (75° S-35° N) and emission angles (0°-60°), using rotational lines that have not been analysed before the arrival of Cassini at Saturn. The derived volume mixing ratios for the different observations are mutually consistent regardless of latitude. The weighted mean CO volume mixing ratio is 47±8 ppm if CO is assumed to be uniform with latitude. H₂O could not be detected and an upper limit of 0.9 ppb was determined. CO₂ abundances derived from mid-infrared nadir spectra show no significant latitudinal variations, with typical values of 16±2 ppb. Mid-infrared limb spectra at 55° S were used to constrain the vertical profile of CO₂ for the first time. A vertical CO₂ profile that is constant above the condensation level at a volume mixing ratio of 15 ppb reproduces the limb spectra very well below 200 km. This is consistent with the long chemical lifetime of CO₂ in Titan's stratosphere. Above 200 km the CO₂ volume mixing ratio is not well constrained and an increase with altitude cannot be ruled out there.     

Spatially resolved spectroscopy of the E+A galaxies in the z= 0.32 cluster AC 114

We present spatially resolved intermediate-resolution spectroscopy of a sample of 12 E+A galaxies in the   z = 0.32  rich galaxy cluster AC 114, obtained with the FLAMES multi-integral field unit system on the Very Large Telescope (VLT) of the European Southern Observatory. Previous integrated spectroscopy of all these galaxies by Couch & Sharples had shown them to have strong Balmer line absorption and an absence of [O  ii ]λ3727 emission – the defining characteristics of the 'E+A' spectral signature, indicative of an abrupt halt to a recent episode of quite vigorous star formation. We have used our spectral data to determine the radial variation in the strength of Hδ absorption in these galaxies and hence map out the distribution of this recently formed stellar population. Such information provides important clues as to what physical event might have been responsible for this quite dramatic change in star formation activity in the recent past of these galaxies. We find a diversity of behaviour amongst these galaxies in terms of the radial variation in Hδ absorption: four galaxies show little Hδ absorption across their entire extent; it would appear they were misidentified as E+A galaxies in the earlier integrated spectroscopic studies. The remainder show strong Hδ absorption, with a gradient that is either negative (Hδ equivalent width decreasing with radius), flat or positive . By comparison with numerical simulations we suggest that the first of these different types of radial behaviour provides evidence for a merger/interaction origin, whereas the latter two types of behaviour are more consistent with the truncation of star formation in normal disc galaxies with the Hδ gradient becoming increasingly positive with time after truncation. It would seem therefore that more than one physical mechanism is responsible for E+A formation in the same environment.     

Accurate jovian radio flux density measurements show ammonia to be subsaturated in the upper troposphere

The availability of new accurate radio flux densities of Jupiter in and around the λ?1.3 cm ammonia absorption band, one from ground-based radio data and five from the WMAP satellite, permits re-examination of the structure of the jovian upper troposphere. These flux densities, with accuracies of 1-3%, indicate that the jovian atmospheric ammonia is globally subsaturated within and above the ammonia cloud tops, 0.4 bar?P?0.6 bar, and subsolar (by a factor of 2) below the cloud base, 0.6 bar?P?2 bar.     

Irregular Satellites of Jupiter: a study of the capture direction

The irregular satellites of Jupiter are believed to be captured asteroids or planetesimals. In the present work is studied the direction of capture of these objects as a function of their orbital inclination. We performed numerical simulations of the restricted three-body problem, Sun-Jupiter-particle, taking into account the growth of Jupiter. The integration was made backward in time. Initially, the particles have orbits as satellites of Jupiter, which has its present mass. Then, the system evolved with Jupiter losing mass and the satellites escaping from the planet. The reverse of the escape direction corresponds to the capture direction. The results show that the Lagrangian points L1 and L2 mainly guide the direction of capture. Prograde satellites are captured through these two gates with very narrow amplitude angles. In the case of retrograde satellites, these two gates are wider. The capture region increases as the orbital inclination increases. In the case of planar retrograde satellites the directions of capture cover the whole 360° around Jupiter. We also verified that prograde satellites are captured earlier in actual time than retrograde ones. This paper was presented at the Asteriods, Comets and Meteors meeting held at Búzios, Rio de Janeiro, Brazil in August 2005 and could not be included in the special issue related to that conference.