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Register a new userPredictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey II: Free-Floating Planet Detection Rates
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The Nancy Grace Roman Space Telescope (Roman) will perform a Galactic Exoplanet Survey (RGES) to discover bound exoplanets with semi-major axes greater than 1 au using gravitational microlensing. Roman will even be sensitive to planetary mass objects that are not gravitationally bound to any host star. Such free-floating planetary mass objects (FFPs) will be detected as isolated microlensing events with timescales shorter than a few days. A measurement of the abundance and mass function of FFPs is a powerful diagnostic of the formation and evolution of planetary systems, as well as the physics of the formation of isolated objects via direct collapse. We show that Roman will be sensitive to FFP lenses that have masses from that of Mars ($0.1 M_oplus$) to gas giants ($Mgtrsim100M_oplus$) as isolated lensing events with timescales from a few hours to several tens of days, respectively. We investigate the impact of the detection criteria on the survey, especially in the presence of finite-source effects for low-mass lenses. The number of detections will depend on the abundance of such FFPs as a function of mass, which is at present poorly constrained. Assuming that FFPs follow the fiducial mass function of cold, bound planets adapted from Cassan et al. (2012), we estimate that Roman will detect $sim250$ FFPs with masses down to that of Mars (including $sim 60$ with masses $le M_oplus$). We also predict that Roman will improve the upper limits on FFP populations by at least an order of magnitude compared to currently-existing constraints.
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We investigate the possibility that a statistical detection of the galaxy parallax shift due to the Earths motion with respect to the CMB frame (cosmic secular parallax) could be made by the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) or by the Nancy Grace Roman Space Telescope (NGRST), and used to measure the Hubble constant. We make mock galaxy surveys which extend to redshift z=0.06 from a large N-body simulation, and include astrometric errors from the LSST and NGRST science requirements, redshift errors and peculiar velocities. We include spectroscopic redshifts for the brightest galaxies (r < 18) in the fiducial case. We use these catalogues to make measurements of parallax versus redshift,for various assumed survey parameters and analysis techniques. We find that in order to make a competitive measurement it will be necessary to model and correct for the peculiar velocity component of galaxy proper motions. It will also be necessary to push astrometry of extended sources into a new regime, and combine information from the different elements of resolved galaxies. In an appendix we describe some simple tests of galaxy image registration which yield relatively promising results. For our fiducial survey parameters, we predict an rms error on the direct geometrical measurement of H0 of 2.8% for LSST and 0.8% for NGRST.
The textit{Nancy Grace Roman Space Telescope} (textit{ Roman}) will provide an enormous number of microlensing light curves with much better photometric precisions than ongoing ground-based observations. Such light curves will enable us to observe high-order microlensing effects which have been previously difficult to detect. In this paper, we investigate textit{Roman}s potential to detect and characterize short-period planets and brown dwarfs (BDs) in source systems using the orbital motion of source stars, the so-called xallarap effect. We analytically estimate the measurement uncertainties of xallarap parameters using the Fisher matrix analysis. We show that the textit{Roman} Galactic Exoplanet Survey (RGES) can detect warm Jupiters with masses down to 0.5 $M_{rm Jup}$ and orbital period of 30 days via the xallarap effect. Assuming a planetary frequency function from citet{Cumming+2008}, we find textit{Roman} will detect $sim10$ hot and warm Jupiters and $sim30$ close-in BDs around microlensed source stars during the microlensing survey. These detections are likely to be accompanied by the measurements of the companions masses and orbital elements, which will aid in the study of the physical properties for close-in planet and BD populations in the Galactic bulge.
The Coronagraph Instrument (CGI) on the Nancy Grace Roman Space Telescope will demonstrate the high-contrast technology necessary for visible-light exoplanet imaging and spectroscopy from space via direct imaging of Jupiter-size planets and debris disks. This in-space experience is a critical step toward future, larger missions targeted at direct imaging of Earth-like planets in the habitable zones of nearby stars. This paper presents an overview of the current instrument design and requirements, highlighting the critical hardware, algorithms, and operations being demonstrated. We also describe several exoplanet and circumstellar disk science cases enabled by these capabilities. A competitively selected Community Participation Program team will be an integral part of the technology demonstration and could perform additional CGI observations beyond the initial tech demo if the instrument performance warrants it.
The Nancy Grace Roman Space Telescope (Roman) is an observatory for both wide-field observations and coronagraphy that is scheduled for launch in the mid 2020s. Part of the planned survey is a deep, cadenced field or fields that enable cosmological measurements with type Ia supernovae (SNe Ia). With a pixel scale of 0.11, the Wide Field Instrument will be undersampled, presenting a difficulty for precisely subtracting the galaxy light underneath the SNe. We use simulated data to validate the ability of a forward-model code (such codes are frequently also called scene-modeling codes) to perform precision supernova photometry for the Nancy Grace Roman Space Telescope SN survey. Our simulation includes over 760,000 image cutouts around SNe Ia or host galaxies (~ 10% of a full-scale survey). To have a realistic 2D distribution of underlying galaxy light, we use the VELA simulated high-resolution images of galaxies. We run each set of cutouts through our forward-modeling code which automatically measures time-dependent SN fluxes. Given our assumed inputs of a perfect model of the instrument PSFs and calibration, we find biases at the millimagnitude level from this method in four red filters (Y106, J129, H158, and F184), easily meeting the 0.5% Roman inter-filter calibration requirement for a cutting-edge measurement of cosmological parameters using SNe Ia. Simulated data in the bluer Z087 filter shows larger ~ 2--3 millimagnitude biases, also meeting this requirement, but with more room for improvement. Our forward-model code has been released on Zenodo.
Reflected starlight measurements will open a new path in the characterization of directly imaged exoplanets. However, we still lack a population study of known targets amenable to this technique. Here, we investigate which of the about 4300 exoplanets confirmed to date are accessible to the Roman Space Telescopes coronagraph (CGI) in reflected starlight at reference wavelengths $lambda$=575, 730 and 825 nm. We carry out a population study and also address the prospects for phase-curve measurements. We used the NASA Exoplanet Archive as a reference for planet and star properties, and explored the impact of their uncertainties on the exoplanets detectability by applying statistical arguments. We define a planet as Roman-accessible on the basis of the instrument inner and outer working angles and its minimum planet-to-star constrast (IWA, OWA, $C_{min}$). We adopt for these technical specifications three plausible configurations labeled as pessimistic, intermediate and optimistic. Our key outputs for each exoplanet are its probability of being Roman-accessible ($P_{access}$), the range of observable phase angles, the evolution of its equilibrium temperature, the number of days per orbit that it is accessible and its transit probability. In the optimistic scenario, we find 26 Roman-accessible exoplanets with $P_{access}$>25% and host stars brighter than $V$=7 mag. This population is biased towards planets more massive than Jupiter but also includes the super-Earths tau Cet e and f which orbit near their stars habitable zone. A total of 13 planets are part of multiplanet systems, 3 of them with known transiting companions, offering opportunities for contemporaneous characterization. The intermediate and pessimistic scenarios yield 10 and 3 Roman-accessible exoplanets, respectively. We find that inclination estimates (e.g. with astrometry) are key for refining the detectability prospects.
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