Study of variable stars in the MOA data base: long-period red variables in the Large Magellanic Cloud

One hundred and forty six long-period red variable stars in the Large Magellanic Cloud (LMC) from the three year MOA project database 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 and Sebo (1996). 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 been also 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.Comment: 19 pages, 19 figures, accepted for publication in MNRA

The d Scuti star FG Vir. V. The 2002 photometric multisite campaign

Astronomy and Astrophysics, v. 419, n. 2, p. 695-701, 2004. http://dx.doi.org/10.1051/0004-6361:20035830International audienc

Potential Direct Single-Star Mass Measurement

28 pages including 7 figures. Submitted to ApJWe analyze the lightcurve of the microlensing event OGLE-2003-BLG-175/MOA-2003-BLG-45 and show that it has two properties that, when combined with future high resolution astrometry, could lead to a direct, accurate measurement of the lens mass. First, the lightcurve shows clear signs of distortion due to the Earth\'s accelerated motion, which yields a measurement of the projected Einstein radius \\tilde r_E. Second, from precise astrometric measurements, we show that the blended light in the event is coincident with the microlensed source to within about 15 mas. This argues strongly that this blended light is the lens and hence opens the possibility of directly measuring the lens-source relative proper motion \\vec\\mu_\\rel and so the mass M=(c^2/4G)\\mu_\\rel t_E \\tilde r_E, where t_E is the measured Einstein timescale. While the lightcurve-based measurement of \\tilde r_E is, by itself, severely degenerate, we show that this degeneracy can be completely resolved by measuring the direction of proper motion \\vec\\mu_\\rel