The MOA catalogue of eclipsing binary stars in the Small Magellanic Cloud

We present a catalogue of 167 eclipsing binary stars in the Small Magellanic Cloud (SMC) derived from the data base of time-series photometry for 400 000 SMC stars acquired by the Microlensing Observations in Astrophysics (MOA) project during 1997. We print coordinates, ephemerides, magnitudes and light curves for the 35 new detections; similar data and finding charts are available electronically for the whole catalogue. The majority of periods lie within the range 0.4 to 20 d; six systems are possibly eccentric while 14 are probably or certainly so. The majority of the newly identified systems lie in the outer regions of the SMC.     

Study by MOA of extrasolar planets in gravitational microlensing events of high magnification

A search for extrasolar planets was carried out in three gravitational microlensing events of high magnification, MACHO  98–BLG–35  , MACHO  99–LMC–2  and OGLE  00–BUL–12  . Photometry was derived from observational images by the MOA and OGLE groups using an image subtraction technique. For MACHO  98–BLG–35  , additional photometry derived from the MPS and PLANET groups was included. Planetary modelling of the three events was carried out in a supercluster computing environment. The estimated probability for explaining the data on MACHO  98–BLG–35  without a planet is <1 per cent. The best planetary model has a planet of mass ∼(0.4–1.5)× M _Earth at a projected radius of either ∼1.5 or ∼2.3 au. We show how multiplanet models can be applied to the data. We calculate exclusion regions for the three events and find that Jupiter-mass planets can be excluded with projected radii from as wide as about 30 au to as close as around 0.5 au for MACHO  98–BLG–35  and OGLE  00–BUL–12  . For MACHO  99–LMC–2  , the exclusion region extends out to around 10 au and constitutes the first limit placed on a planetary companion to an extragalactic star. We derive a particularly high peak magnification of ∼160 for OGLE  00–BUL–12  . We discuss the detectability of planets with masses as low as Mercury in this and similar events.     

Large-scale structure of galaxies in the Ophiuchus region

The large-scale structure around the Ophiuchus cluster of galaxies in the vicinity of the Galactic Centre ( l =05, b =95, cz =8500 km s⁻¹) is investigated on the basis of a galaxy survey and spectroscopic observations made for a 12°×17° area. The galaxy survey was performed using six ESO/SERC Sky Survey Atlas films, and 4021 galaxies were detected in total. Recession velocities were newly obtained for 179 galaxies to make the total number of galaxies in the survey area with known velocities 219.
In the distribution of bright galaxies, we identified seven new clumps of galaxies. Comparing the surface number density of bright galaxies with the Galactic extinction, which is estimated from the 100‐μm flux density in the IRAS Sky Survey Atlas, we demonstrate that the seven clumps are not spurious as a result of the inhomogeneity of the Galactic extinction. Among the seven clumps, two are found to be clusters and four to be groups on the basis of the histogram of recession velocities and the number of member galaxies. The Ophiuchus cluster, two newly identified clusters, and four groups are all concentrated at 9000 km s⁻¹. Field galaxies are also distributed centred at 8500 km s⁻¹. Hence field galaxies occupy a common three-dimensional region with galaxies in the clusters and groups, and altogether they form a large-scale structure of supercluster size. As opposed to the overdensity in the supercluster region, the mean number density of galaxies in the velocity range 0–5000 km s⁻¹ is only 25 per cent of the mean number density of the Universe, comparable with the density of the well-known Böotes void. Hence this nearby three-dimensional region in Ophiuchus is a void of galaxies also.     

Scientific role of ACA for low-mass star-formation study

We discuss the scientific role of the Atacama Compact Array (ACA), the Japanese contribution to the ALMA project, for low-mass star-formation study. Our recent observations of several low-mass protostellar envelopes in the submillimeter CS (J=7–6) and HCN (J=4–3) lines with the SMA and ASTE have revealed that these submillimeter emissions are more extended than ∼2000 AU and show different velocity structures from those traced by millimeter lines. These results suggest the importance of taking short-spacing informations the ACA can offer. Our comprehensive imaging simulations of these protostellar envelopes, as well as prestellar cores and debris disks, unprecedentedly demonstrate the scientific importance of ACA.     

A photometric and polarimetric study of the moon's surface

The results of the photometric and polarimetric observation of the Moon's surface with high resolution from October 1969 to March 1971 are discussed. It is found that, for a wide part of the Moon's illuminated surface, the brightnessm, expressed by visual magnitude per square second of arc, can be expressed as $$m = 5.0 - 2.5\log H + 2.5\log \{ {{P_v } \mathord{\left/ {\vphantom {{P_v } P}} \right. \kern-\nulldelimiterspace} P}(\alpha )\} ,$$ whereH is the variable part of Hapke's formula,P _v is the observed polarization degree, andP(α) is a function of the phase angleα. The color shows a tendency to reddening at the enhancement of the lunar brightness, and this is expressed by the relation $$B - V = - 0.2\Delta m + 1.7,$$ where Δm =m + 2.5 logH which is a sort of residual from the brightness calculated by Hapke's formula. Remarkable enhancements of the lunar brightness correspond to solar flares which appeared just before the observations. Because of this the above formula for the observed brightness can be interpreted by assuming the luminescence on the lunar surface stimulated by the solar activity.     

Rocket observations of atomic oxygen density and airglow emission rate in the WAVE2000 campaign

Atomic oxygen density and airglow volume emission rate profiles measured in the rocket experiment S-310-29 carried out as a part of the Waves in Airglow Structures Experiment over Kagoshima in 2000 (WAVE2000) campaign are presented, and the excitation processes of the atomic oxygen 557.7 nm line and the molecular oxygen atmospheric band airglow emissions are discussed. The volume emission rate profiles calculated from the measured atomic oxygen densities using the methods and parameters proposed by the ETON campaign (EATON model) are found to well represent the shapes of measured twin-peak emission rate profiles seen during this campaign suggesting that the EATON model is valid for a perturbed atmosphere. There is some discrepancy in the modeled absolute values for the emissions. Applying the model to the current O density measurements results in predicted emission rates that are a factor of 3.2 and 1.5 too high for the 557.7 nm line and Atmospheric band, respectively. This suggests either that the atomic oxygen densities of the present campaign are too large by a factor of 1.2 (=1.5^1/2) to 1.5 (=3.2^1/3), or that those of the ETON campaign were too small by the same factor or that the combined errors in both campaigns can account for the discrepancy (the modeled volume emission rates of the 557.7 nm line and atmospheric band are roughly in proportion to [O]³ and [O]², respectively). Our present data findings do not favor the 2-step more than the 1-step excitation process for the atmospheric band because a calculation of the quantum efficiency based on the observed O density does not show a steep gradient around 100 km.     

On the fissions of a solid body under influence of tidal force; with application to the problem of twin craters on the moon

The internal strain due to the tidal force in the proximity of a tide-generating body (in the present case, the Moon) is calculated according to the Lord Kelvin theory of Earth tides. The conditions for which uniform elastic sphere possessing a definite tensile strength is crushed near the surface of the Moon is investigated. The state of internal stress is almost independent of the value of elastic constants. Many lunar features, such as twin craters, craterous walled plains of irregular forms, compound craters, may be explained by fission of the meteoritic material before impact.     

Hierarchical traveltime tomography

A new traveltime tomographic method was developed with hierarchical shape functions of the finite element method as slowness or velocity interpolation functions. The degree of the approximation of velocity modelling is adjusted by selecting a set of hierarchical shape functions in each element. The ray density parameter of each element controls the selection to make the approximation fine or coarse in the high- or low-ray-density area. The proposed method is applied to both synthetic traveltime data and actual data. The AIC is used to determine the number of model parameters. The result of the synthetic data shows that low-resolution model parameters can be eliminated by the ray density parameter. The result of the actual data shows that the velocity pattern is approximately the same in the fine approximation area and that the velocity fluctuation is suppressed in the coarse approximation area, compared with that obtained from a full set of hierarchical shape functions. The number of model parameters is drastically reduced. The resolution can be estimated by the checkerboard restoration test. The result of the real data set was compared with that of the linear velocity grid model.