Precision Space Astrometry as a Tool to Find Earth-like Exoplanets

Shao, Michael; Turyshev, Slava G.; Bendek, Eduardo; Fischer, Debra; Guyon, Olivier; McArthur, B.; Muterspaugh, Matthew W.; Zhai, Chengxing; Bœhm, Céline

doi:10.48550/arxiv.1803.03732

Cited by 3 publications

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“…We assume their orbits can be predicted, based on data from either multi-epoch direct imaging, radial velocity, 3 or astrometry. The Keplerian orbital fits from these observations are adequate for us to target the wanderers at gibbous phase outside the IWA (Shao et al 2018;Butler et al 2017;Ranalli et al 2017).…”

Section: An Observation Flowchartmentioning

confidence: 96%

“…We consider two possible routes to constraining planetary albedo (figure 7). One route is to choose targets whose masses are known from radial velocity or astrometry surveys (Plavchan et al 2018;Shao et al 2018;Bendek et al 2015;Fischer et al 2016;Weiss et al 2016). We can use a mass-radius relation (e.g., Chen & Kipping 2017) to estimate the planet's radius from its mass.…”

Section: Breaking the Radius-albedo Degeneracymentioning

confidence: 99%

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The Direct Imaging Search for Earth 2.0: Quantifying Biases and Planetary False Positives

Guimond

Cowan

2018

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Direct imaging is likely the best way to characterize the atmospheres of Earth-sized exoplanets in the habitable zone of Sun-like stars. Previously, Stark et al. (2014, 2015 estimated the Earth twin yield of future direct imaging missions, such as LUVOIR and HabEx. We extend this analysis to other types of planets, which will act as false positives for Earth twins. We define an Earth twin as any exoplanet within half an e-folding of 1 AU in semi-major axis and 1 R ⊕ in planetary radius, orbiting a G-dwarf. Using Monte Carlo analyses, we quantify the biases and planetary false positive rates of Earth searches. That is, given a pale dot at the correct projected separation and brightness to be a candidate Earth, what are the odds that it is, in fact, an Earth twin? Our notional telescope has a diameter of 10 m, an inner working angle of 3λ/D, and an outer working angle of 10λ/D (62 mas and 206 mas at 1.0 µm). With no precursor knowledge and one visit per star, 77% of detected candidate Earths are actually un-Earths; their mean radius is 2.3 R ⊕ , a sub-Neptune. The odds improve if we image every planet at its optimal orbital phase, either by relying on precursor knowledge, or by performing multi-epoch direct imaging. In such a targeted search, 47% of detected Earth twin candidates are false positives, and they have a mean radius of 1.7 R ⊕ . The false positive rate is insensitive to stellar spectral type and the assumption of circular orbits. and HabEx are being motivated based on their ability to characterize Earth twins.Brown (2005) presented a "photometric and obscurational single-visit completeness" method to estimate the chance, for a particular star, that a companion exoplanet is detectable during one visit given that the planet exists. In their model, "photometric" refers to the condition that the planet/star contrast must exceed the inherent instrument floor in photon counting. "Obscurational" refers to how the planet and its star must be positioned in the sky plane, such that the planet is outside the inner obscuring disk of the coronagraph or starshade. This inner working angle (IWA) is defined technically as the angle at which transmission decreases by 50%. Coronagraphs may also have an outer working angle (OWA), beyond which starlight is no longer ade-

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Section: An Observation Flowchartmentioning

confidence: 96%

Section: Breaking the Radius-albedo Degeneracymentioning

confidence: 99%

The Direct Imaging Search for Earth 2.0: Quantifying Biases and Planetary False Positives

Guimond

Cowan

2018

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“…Modern astrometric catalogs (i.e., the Gaia Catalogue of Nearby Stars; Smart et al 2021) are at the few tens of microarcseconds level accuracy (Lindegren et al 2021) that is needed to predict likely stellar conjunctions. Ongoing technology developments may may soon be available for an astrometric search for Earth-like exoplanets (Shao et al 2018(Shao et al , 2022Ji et al 2022).…”

Section: Estimating the Occurrence Ratementioning

confidence: 99%

Evolving Morphology of Resolved Stellar Einstein Rings

Turyshev

Toth²

2023

ApJ

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We consider strong gravitational lensing by nearby stars. Using our wave-optical treatment of lensing phenomena, we study Einstein rings that may form around nearby stellar lenses. It is remarkable that these rings are bright and large enough to be detected and resolved by existing instruments. Such lensing events have durations of hours or days, with peak light amplification lasting for several minutes. Many such events may be predicted using the Gaia astrometric catalog. Serendipitous discoveries are also possible. Fortuitous alignments can be used to confirm or discover and study exoplanets. For lenses that have dense stellar regions in their background, these events may occur several time a year, warranting their continuous or recurrent monitoring. Resolved imaging and spectroscopy of the evolving morphology of an Einstein ring offers knowledge about both the lens and the source. The angular size of the Einstein ring amounts to a direct measurement of the lens mass. The changing orientation of the major and minor images of the source offers astrometric information related to the mutual orientation of the objects. The event duration, when the full ring is present, helps to determine the source’s size. The sky position of planetary lensing events constrains the planet’s orbit. Spectroscopy of the ring allows for direct investigations of the source. The frequency and predictability of these events and the wealth of information that can be obtained by imaging motivate observational campaigns using existing facilities and/or construction of new instruments dedicated to the search and study of Einstein rings that are forming around nearby stars. As a specific example, we consider a predicted 2028 lensing of a red giant by α Centauri A and discuss the relevant science campaign.

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“…5 https://exoplanetarchive.ipac.caltech.edu/ radial velocity surveys targeting Earth analogs in that (1) astrometric measurements can break the mass-inclination degeneracy inherent in radial velocity observations without the geometric and observational requirements inherent in transit observations, (2) astrometric measurements, which are more sensitive to longer periods, complement RV observations, which are more sensitive to shorter periods, and (3) astrometric observations could allow us to marginalize over stellar noise in the RV data, as astrometry is less sensitive to stellar noise than the Doppler method (Makarov et al 2009;Shao et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Detecting Solar System Analogs through Joint Radial Velocity/Astrometric Surveys

Yahalomi,

Angus,

Spergel

et al. 2023

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Earth-mass exoplanets on year-long orbits and cool gas giants (CGG) on decade-long orbits lie at the edge of current detection limits. The Terra Hunting Experiment (THE) will take nightly radial velocity (RV) observations on HARPS3 of at least 40 bright nearby G and K dwarfs for 10 yr, with a target 1σ measurement error of ∼0.3 m s−1, in search of exoplanets that are Earth-like in mass and temperature. However, RV observations can only provide minimum mass estimates, due to the mass–inclination degeneracy. Astrometric observations of these same stars, with sufficient precision, could break this degeneracy. Gaia will soon release ∼100–200 astrometric observations of the THE stars with a 10 yr baseline and ∼34.2 μas 1σ along-scan measurement error. The Nancy Grace Roman Space Telescope will be capable of precision astrometry using its wide field imager (target ∼5–20 μas 1σ measurement error for bright stars) and could extend the astrometric observational baseline to ∼25 yr. We simulate and model an observing program that combines data from these three telescopes. We find that (1) THE RVs and Gaia astrometry can detect Earth-like and CGG-like exoplanets around bright Sun-like stars at 10 pc and that (2) adding Roman astrometry improves the detection precision for CGG masses and periods by respective factors up to ∼10 and ∼4. Such a survey could provide insight into the prevalence of Solar System analogs, exoplanet architectures reminiscent of the mass and orbital separation hierarchy of our Solar System, for the nearest Sun-like stars.

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Precision Space Astrometry as a Tool to Find Earth-like Exoplanets

Cited by 3 publications

References 0 publications

The Direct Imaging Search for Earth 2.0: Quantifying Biases and Planetary False Positives

The Direct Imaging Search for Earth 2.0: Quantifying Biases and Planetary False Positives

Evolving Morphology of Resolved Stellar Einstein Rings

Detecting Solar System Analogs through Joint Radial Velocity/Astrometric Surveys

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