quasars lie behind the Large Magellanic Cloud and nine behind the Small Magellanic Cloud, more th... more quasars lie behind the Large Magellanic Cloud and nine behind the Small Magellanic Cloud, more than tripling the number of quasars previously known in this region. The quasars cover the redshift interval 0.2 < z < 2.8 and apparent mean magnitudes 16.6 ≤ V ≤ 20.1. We discuss the details of quasar candidate selection based on time variability in the MACHO database and present results of spectroscopic follow-up observations. Our follow-up detection efficiency was 20%; the primary contaminants were emissionline Be stars in Magellanic Clouds. For the 47 quasars discovered behind the Magellanic Clouds plus an additional 12 objects previously identified in this region, we present 7.5year MACHO V -and R-band lightcurves with average sampling times of 2-10 days.
The MACHO project is searching for dark matter in the form of massive compact halo objects (Macho... more The MACHO project is searching for dark matter in the form of massive compact halo objects (Machos), by monitoring the brightness of millions of stars in the Magellanic Clouds to search for gravitational microlensing events. Analysis of our first 2.3 years of data for 8.5 million stars in the LMC yields 8 candidate microlensing events, well in excess of the ≈ 1 event expected from lensing by known low-mass stars. The event timescales range from 34 to 145 days, and the estimated optical depth is ∼ 2×10 −7 , about half of that expected from a 'standard' halo. Likelihood analysis indicates the typical lens mass is 0.5 +0.3 −0.2 M ⊙ , suggesting they may be old white dwarfs.
The MACHO Project: Microlensing Toward the Galactic Bulge
The MACHO project has recently completed the analysis of 24 Galactic bulge fields containing 1.3t... more The MACHO project has recently completed the analysis of 24 Galactic bulge fields containing 1.3times 10(7) stars observed for 190 days. Approximately 45 microlensing events have been detected in this data set. These data confirm results of the MACHO and OGLE collaborations based on smaller data samples which indicated a large microlensing optical depth toward the bulge. The variation of the microlensing optical depth and event rate with galactic lattitude and longitude is investigated and compared with ``maximal disk" and Galactic bar models which have been proposed to account for the observed optical depth toward the bulge. These results indicate that the study of microlensing toward the Galactic bulge will have important implications for the structure of the Galaxy and its dark halo.
A Virtual Observatory (VO) provides enhanced distributed access to online astronomical datasets, ... more A Virtual Observatory (VO) provides enhanced distributed access to online astronomical datasets, and frequently incorporates data processing and visualisation facilities. Almost all critical aspects of datagrid research and technology are encountered when developing a Virtual Observatory. Issues include interoperability of datasets and processing software, metadata format standardisation, and resolution of ontological issues. Members of the ANU Supercomputer Facility (ANUSF) are undertaking research and implementation projects in several key VO areas. In this paper we discuss the data sets and astronomy projects with which ANUSF is involved, and outline the VO projects we are undertaking based on these resources.
quasars lie behind the Large Magellanic Cloud and nine behind the Small Magellanic Cloud, more th... more quasars lie behind the Large Magellanic Cloud and nine behind the Small Magellanic Cloud, more than tripling the number of quasars previously known in this region. The quasars cover the redshift interval 0.2 < z < 2.8 and apparent mean magnitudes 16.6 ≤ V ≤ 20.1. We discuss the details of quasar candidate selection based on time variability in the MACHO database and present results of spectroscopic follow-up observations. Our follow-up detection efficiency was 20%; the primary contaminants were emissionline Be stars in Magellanic Clouds. For the 47 quasars discovered behind the Magellanic Clouds plus an additional 12 objects previously identified in this region, we present 7.5year MACHO V -and R-band lightcurves with average sampling times of 2-10 days.
The MACHO project is searching for dark matter in the form of massive compact halo objects (Macho... more The MACHO project is searching for dark matter in the form of massive compact halo objects (Machos), by monitoring the brightness of millions of stars in the Magellanic Clouds to search for gravitational microlensing events. Analysis of our first 2.3 years of data for 8.5 million stars in the LMC yields 8 candidate microlensing events, well in excess of the ≈ 1 event expected from lensing by known low-mass stars. The event timescales range from 34 to 145 days, and the estimated optical depth is ∼ 2×10 −7 , about half of that expected from a 'standard' halo. Likelihood analysis indicates the typical lens mass is 0.5 +0.3 −0.2 M ⊙ , suggesting they may be old white dwarfs.
The MACHO Project: Microlensing Toward the Galactic Bulge
The MACHO project has recently completed the analysis of 24 Galactic bulge fields containing 1.3t... more The MACHO project has recently completed the analysis of 24 Galactic bulge fields containing 1.3times 10(7) stars observed for 190 days. Approximately 45 microlensing events have been detected in this data set. These data confirm results of the MACHO and OGLE collaborations based on smaller data samples which indicated a large microlensing optical depth toward the bulge. The variation of the microlensing optical depth and event rate with galactic lattitude and longitude is investigated and compared with ``maximal disk" and Galactic bar models which have been proposed to account for the observed optical depth toward the bulge. These results indicate that the study of microlensing toward the Galactic bulge will have important implications for the structure of the Galaxy and its dark halo.
A Virtual Observatory (VO) provides enhanced distributed access to online astronomical datasets, ... more A Virtual Observatory (VO) provides enhanced distributed access to online astronomical datasets, and frequently incorporates data processing and visualisation facilities. Almost all critical aspects of datagrid research and technology are encountered when developing a Virtual Observatory. Issues include interoperability of datasets and processing software, metadata format standardisation, and resolution of ontological issues. Members of the ANU Supercomputer Facility (ANUSF) are undertaking research and implementation projects in several key VO areas. In this paper we discuss the data sets and astronomy projects with which ANUSF is involved, and outline the VO projects we are undertaking based on these resources.
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Papers by R. Allsman