R. Yamada

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) X M E a r t h 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 30au 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.

Improving the prospects for detecting extrasolar planets in gravitational microlensing events in 2002

Gravitational microlensing events of high magnification have been shown to be promising targets for detecting extrasolar planets. However, only a few events of high magnification have been found using conventional survey techniques. Here we demonstrate that high-magnification events can be readily found in microlensing surveys using a strategy that combines high-frequency sampling of target fields with on-line difference imaging analysis. We present 10 microlensing events with peak magnifications greater than 40 that were detected in real-time towards the Galactic bulge during 2001 by the Microlensing Observations in Astrophysics (MOA) project. We show that Earth-mass planets can be detected in future events such as these through intensive follow-up observations around the event peaks. We report this result with urgency as a similar number of such events are expected in 2002.

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

ABSTRA C T 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 longperiod 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.

A Relation of the PAH3.3μm Feature with Star-forming Activity for Galaxies with aWide Range of Infrared Luminosity

For star-forming galaxies, we investigate a global relation between polycyclic aromatic hydrocarbon (PAH) emission luminosity at 3.3 um, L_PAH3.3, and infrared (8-1000 um) luminosity, L_IR, to understand how the PAH 3.3 um feature relates to the star formation activity. With AKARI, we performed near-infrared (2.5-5 um) spectroscopy of 184 galaxies which have L_IR \sim 10^8 - 10^13 L_sun. We classify the samples into infrared galaxies (IRGs; L_IR 10^12 L_sun). We exclude sources which are likely contaminated by AGN activity, based on the rest-frame equivalent width of the PAH emission feature ( 1; F_nu \propto lambda^Gamma). Of these samples, 13 IRGs, 67 LIRGs and 20 ULIRGs show PAH emission feature at lambda_rest= 3.3 um in their spectra. We find that the L_PAH3.3/L_IR ratio considerably decreases toward the luminous end. Utilizing the mass and temperature of dust grains as well as the BrAlpha emission for the galaxies, we discuss the cause of the relative decrease in the PAH emission with L_IR.

THE 3.3 μm POLYCYCLIC AROMATIC HYDROCARBON EMISSION AS A STAR FORMATION RATE INDICATOR

Polycyclic Aromatic Hydrocarbon (PAH) emission features dominate the mid-infrared spectra of star-forming galaxies and can be useful to calibrate star formation rates and diagnose ionized states of grains. However, the PAH 3.3 micron feature has not been studied as much as other PAH features since it is weaker than others and resides outside of Spitzer capability. In order to detect and calibrate the 3.3 micron PAH emission and investigate its potential as a star formation rate indicator, we carried out an AKARI mission program, AKARI mJy Unbiased Survey of Extragalactic Survey (AMUSES) and compare its sample with various literature samples. We obtained 2 ~5 micron low resolution spectra of 20 flux-limited galaxies with mixed SED classes, which yields the detection of the 3.3 micron PAH emission from three out of 20 galaxies. For the combined sample of AMUSES and literature samples, the 3.3 micron PAH luminosities correlate with the infrared luminosities of star-forming galaxies, albeit with a large scatter (1.5 dex). The correlation appears to break down at the domain of ultra-luminous infrared galaxies (ULIRGs), and the power of the 3.3 micron PAH luminosity as a proxy for the infrared luminosity is hampered at log[L(PAH3.3)/(erg/sec)] > -42.0. Possible origins for this deviation in the correlation are discussed, including contribution from AGN and strongly obscured YSOs, and the destruction of PAH molecules in ULIRGs.Polycyclic aromatic hydrocarbon (PAH) emission features dominate the mid-infrared spectra of star-forming galaxies and can be useful to calibrate star formation rates (SFRs) and diagnose ionized states of grains. However, the PAH 3.3 μm feature has not been studied as much as other PAH features since it is weaker than others and resides outside of Spitzer capability. In order to detect and calibrate the 3.3 μm PAH emission and investigate its potential as an SFR indicator, we carried out an AKARI mission program, AKARI mJy Unbiased Survey of Extragalactic Sources (AMUSES), and compared its sample with various literature samples. We obtained 2-5 μm low-resolution spectra of 20 flux-limited galaxies with mixed spectral energy distribution classes, which yielded the detection of the 3.3 μm PAH emission from 3 out of 20 galaxies. For the combined sample of AMUSES and literature samples, the 3.3 μm PAH luminosities correlate with the infrared luminosities of star-forming galaxies, albeit with a large scatter (1.5 dex). The correlation appears to break down at the domain of ultraluminous infrared galaxies (ULIRGs), and the power of the 3.3 μm PAH luminosity as a proxy for the infrared luminosity is hampered at log[L P_(AH3.3) erg^(–1) s^(–1)] > ~42.0. Possible origins for this deviation in the correlation are discussed, including contributions from active galactic nuclei and strongly obscured young stellar objects, and the destruction of PAH molecules in ULIRGs.

A relationship of polycyclic aromatic hydrocarbon features with galaxy merger in star-forming galaxies at z < 0.2

Using the AKARI, Wide-field Infrared Survey Explorer (WISE), Infrared Astronomical Satellite (IRAS), Sloan Digital Sky Survey (SDSS) and Hubble Space Telescope (HST) data, we investigated the relation of polycyclic aromatic hydrocarbon (PAH) mass (

THE 3.3 MICRON PAH EMISSION OF THE MID-INFRARED EXCESS GALAXIES DISCOVERED BY THE AKARI MID-INFRARED ALL-SKY SURVEY

M_{\rm PAH}

SURVEY OF DUSTY ACTIVE GALACTIC NUCLEI BASED ON THE MID-INFRARED ALL-SKY SURVEY CATALOG

), very small grain mass (

Real-time difference imaging analysis of MOA Galactic bulge observations during 2000

M_{\rm VSG}

Study of variable stars in the MOA data base: long-period red variables in the Large Magellanic Cloud — II. Multiplicity of the period—luminosity relation

), big grain mass (