|Mirror diameter (m)||2.36|
|Obscured fraction (area)||13.9%|
|Detectors||6 × 3 H4RG-10|
|Plate scale (arc-sec/pix)||0.11|
|Field of view (deg2)||0.282|
|Baseline duration (years)||5|
|Total survey duration (d)||432|
|Season duration (d)||72|
|Survey area (deg2)||1.96|
|Average slew and settle time (s)||83.1|
|Primary bandpass (μm)||0.93–2.00 (W149)|
|Secondary bandpass (μm)||0.76–0.98 (Z087)|
|Photometric precision||0.01 mag @ W149 ∼ 21.15 mag|
|Exposure time (s)||46.8||286|
|Cadence||15.16 min||12.0 hr|
|Exposures per field||∼ 41000||∼ 860|
|Saturation (mag)||∼ 14.8||∼ 13.9|
|Readout noise★ (counts/pix)||12.12||12.12|
|Thermal + dark† (counts/pix/s)||1.072||0.130|
|Sky background‡ (mag/arcsec2)||21.48||21.55|
|Sky background (counts/pix/s)||3.43||1.04|
|Error floor (mmag)||1.0||1.0|
|Saturation§ (103 counts/pix)||679||679|
∗ Magnitude that produces 1 count per second in the detector.
★ Effective readout noise after multiple non-destructive reads.
† Sum of thermal backgrounds (caused by infrared emission of the telescope and its support structures etc.) and dark current.
‡ Evaluated using a zodiacal light model at a season midpoint.
§ Effective saturation level after full exposure time. For the Roman Space Telescope it is assumed that thanks to multiple reads, useful data can be measured from pixels that saturate after two reads, so for a constant full-well depth, the saturation level increases with exposure time.
GULLS uses a modified version of the Besançon Galactic model (Kerins et al. 2009, Robin et al. 2003), with source star counts normalized to HST star counts from Clarkson et al. (2008) and Calamida et al. (2015), and the microlensing event rates are normalized to corrected event rates (Sumi & Penny 2016) from the MOA-II survey (Sumi et al. 2013). Information on similar Euclid simulations is available in Penny et al. (2013) where the simulator was first discussed and referred to as MaBμLS, Manchester-Besançon microLensing Simulator, and the general information in that paper is applicable to Roman Space Telescope observations as well. GULLS has also been used for an analysis for the predictions for the detection and characterization of a population of free-floating planets with K2 Campaign 9 (Penny et al. 2017).
The microlensing yield depends critically on the underlying Galactic model used within the simulation. This is an extremely active field of research. Recent analyses that make specific reference to the Roman microlensing survey include Terry et al. (2020) and Koshimoto et al. (2021).
OGLE survey). See https://github.com/mtpenny/wfirst-ml-figures for more plots and tables from Penny et al. (2019).
|Stars (W149 < 21)||∼ 38 × 106|
|Stars (W149 < 25)||∼ 240 × 106|
|Microlensing events||∼ 27000|
|Planet Detection (0.1 – 104 M⊕)||∼ 1400|
|Planet Detection (< 3 M⊕)||∼ 200|