Las Cumbres Observatory is pleased to announce that the complete data from a three-year LCO Key Project to monitor the Galactic Bulge of the Milky Way has been released. This project was a collaboration between an international team of researchers, led by Dr. Yiannis Tsapras at the University of Heidelberg, Germany. The data release was announced in a paper led by LCO Senior Scientist Dr. Rachel Street, published last year in the Astronomical Society of the Pacific. Her work was made possible thanks to a NASA grant.
The Robotic Observations of Microlensing Events/Reactive Event Assessment Survey (ROME/REA) continuously monitored 20 selected fields in the Galactic Bulge over a three-year period, between 2017 March and 2020 March. The central bulge of our galaxy, the Milky Way, is a dense region of older stars and is about 10,000 light years across.
This region has been the subject of consistent photometric monitoring for ∼30 yr, due to the high rate of microlensing events that occur within this region. Microlensing occurs when a foreground massive body, called the lens, crosses the observer’s line of sight to a background luminous source. The gravity of the lens deflects the source star’s light, causing the observer to see a gradual brightening and fading of the source as the objects move through alignment. These events are inherently rare, so surveys seeking to discover them have traditionally concentrated on crowded regions, such as the Galactic Bulge, in order to monitor as many stars as possible. Although these transient events are challenging to discover, microlensing events are scientifically valuable as they provide the means to measure the masses of objects that would otherwise be too faint to observe, including free-floating planets and even isolated compact objects such as black holes and neutron stars.
The ROME/REA Project consisted of two elements: a regular survey of selected fields in the Galactic Bulge plus additional observations made in response to alerts of microlensing events within those fields. In this manner, the project took advantage of the unique features of the LCO telescope network, by using its geographically distributed sites to maintain around-the-clock monitoring of the fields, while using the multiple telescopes at each site to simultaneously coordinate targeted observations of high priority events. The wealth of stars within the field means that the resulting data is not only highly valuable for microlensing but also for a wide range of other galactic time domain science.
The three years of observations and data reduction by a team of scientists have resulted in a catalog of light curves that are available through the NASA Exoplanet Archive. The full timeseries photometry for all ∼8 million stars is provided in the data release and the data include >1000 microlensing events. The ROME/REA data have also been crossmatched against catalogs to identify >56,000 objects exhibiting a wide range of stellar variability. Releasing the full photometric catalog from this survey, annotated with stellar variability in this way, will enable the data to be used to train machine learning algorithms to more accurately identify variable stars in crowded fields during future surveys.
Dr. Rachel Street is pleased with the release of this unique data set, “LCO is one of only a very few observatories that could undertake the ROME/REA Survey, and we have really only started to scratch the surface of the science that can be done with these long timeseries data. I am grateful to the NASA Exoplanet Archive for working to make these data publicly accessible so that other research teams can benefit!”
Senior Scientist Dr. Rachel Street of Las Cumbres Observatory is the lead author of the ROME/REA Data Release.
Dr. Street gratefully acknowledges support from NASA grant 80NSSC19K0291.
The ROME/REA Project was a collaboration between researchers at University of Heidelberg, Germany, University of St. Andrews, UK, University of Salerno, Italy, New York University Abu Dhabi, Institute de Paris, France, Pontificia Universidad Catolica de Chile, Tsinghua University, China and NOIRLab, the NSF’s National Optical-InfraRed Astronomy ResearchLaboratory.
