We describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification ...is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg2 were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (≳10), at least one had very high magnification (≳50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid.
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)×MEarth 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.
ABSTRACT
Data for 4.4 million stars from the Microlensing Observations in Astrophysics (MOA) project are compared with the near‐infrared data of the Deep Near Infrared Southern Sky Survey (DENIS). ...More than 4000 stars observed in both projects show a quite periodic light curve. Among them, a number of stars are likely eclipsing variables, and the others seem to be pulsating stars. The KS magnitudes of these red variables are in the range 10–12.5 but a minor clump at KS≈ 12.2 mag is also found. The multiplicity of the period–luminosity relation is confirmed, but most of the regular, large‐amplitude variables are found on the relation established for the Mira stars. We study the properties of the variables on the colour–magnitude diagram constructed with the MOA red band Rm and KS of DENIS. Multiplicity of the period–luminosity relation is briefly discussed in relation to the excitation mechanism of red pulsating variables.
146 long-period red variable stars in the Large Magellanic Cloud (LMC) from the three-year Microlensing Observations in Astrophysics (MOA) project data base were analysed. A careful periodic analysis ...was performed on these stars and a catalogue of their magnitudes, colours, periods and amplitudes is presented. We convert our blue and red magnitudes to K-band values using 19 oxygen-rich stars. A group of red short-period stars separated from the Mira sequence has been found on a (log P,K) diagram. They are located at the short period side of the Mira sequence consistent with the work of Wood & Sebo. There are two interpretations for such stars; a difference in pulsation mode or a difference in chemical composition. We investigated the properties of these stars together with their colour, amplitude and periodicity. We conclude that they have small amplitudes and less regular variability. They are likely to be higher-mode pulsators. A large scatter has also been found on the long-period side of the (log P,K) diagram. This is possibly a systematic spread given that the blue band of our photometric system covers both standard B and V bands and affects carbon-rich stars.
The abundance of oxygen was determined for selected very metal-poor G–K stars (six giants and one turn-off star) based on the high S/N and high-resolution spectra observed with the Keck HIRES in the ...red through near-IR region comprising the permitted O
i lines (7771–5, 8446) along with the O
i forbidden line at 6363 Å. It turned out that both the abundances from the permitted line features, O
i 7771–5 and O
i 8446, agree quite well with each other, while the forbidden line yields somewhat discrepant and divergent abundances with a tendency of being underestimated on the average. The former (7773/8446) solution, which we believe to be more reliable, gives a fairly tight O/Fe vs. Fe/H relation such that increasing steadily from O/Fe∼0.6 (at Fe/H∼−1.5) to O/Fe∼1.0 (at Fe/H∼−3.0) is reasonably consistent with the trend recently reported based on the analysis of the UV OH lines.
Giusa and Roger Cayrel have published more than 170 papers and have been cited in more than 2173 times in the main journals. A total of 104 researchers have collaborated with them. These and other ...statistics are shown.PUBLICATION ABSTRACT
BV photoelectric and spectroscopic observations of the 0.417-day-period eclipsing binary BL Eri were made. Light curves show total eclipses and a considerable photometric disturbance. The light-curve ...analysis reveals that both components are noncontact but nearly fill their respective critical Roche lobes, and the system is almost contact. The spectral type is determined to be around G0 V. The spectrum appears double lined, giving a spectroscopic mass ratio that is in accord with the photometric mass ratio (q = 0.54). The components are undermassive for their radii and luminosities, indicating a post-main-sequence evolutionary state of the system. (Author)
Ultraviolet spectra of HD 77581 obtained with the IUE satellite in December 1982 and January 1983 are analyzed. The effective temperature is found to be 25,000 + or - 1000 K by comparing its ...photospheric absorption lines with those in four well-studied B0-B1 supergiants. The distance of 1.9 + or - 0.2 kpc is derived from its luminosity log L/solar-L = +5.53, which is obtained from the effective temperature and from its radius. Circumstellar matter is detected not only in the C IV and Si IV lines but also in Al III, Fe III, C II, and Mg II lines. Profiles of the C IV and Si IV lines show a similar dependence on the orbital phase as in 1978. Two distinct sharp components are found in the shortward-shifted absorptions of the Al III and Fe III lines. Once component is present only in the second half of the orbital period, and its origin may be a 'trailing wake' behind the neutron star. The other component is seen all over the period, and it can be interpreted as originating in a cool expanding region of gas in the orbital plane.
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