Spotting stellar activity cycles in Gaia astrometry

Morris, Brett M.; Agol, Eric; Davenport, James R. A.; Hawley, Suzanne L.

doi:10.1093/mnras/sty568

Cited by 19 publications

(17 citation statements)

References 58 publications

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“…First, we assume that the stellar inclination is i = 90 • , which may be a good approximation since each of these systems host (often multiple) transiting exoplanets. Next, we fix the spot contrast to c = 0.7; this is compatible with the area-weighted spot coverage of sunspots, the starspot contrasts of HAT-P-11 (Morris et al 2017), and a valid approximation to the observed spot contrasts of several stars extrapolated into the Kepler and TESS bandpasses (Morris et al 2018). We also place a uniform bounded prior on the spot latitudes | | < 60 • .…”

Section: Comparison With Observations Of Planet-hosting Starsmentioning

confidence: 94%

“…One difficulty in comparing photometry across two telescopes is that Kepler, TESS, and Gaia all have a slightly different bandpasses. Fortunately, the effect of the slightly different bandpasses on the scale of rotational modulation is small (see Figure 2 of Morris et al 2018). Future catalogs of photometry from the Gaia mission may also prove useful in measuring the photometric variability of young stars due to starspots.…”

Section: Comparing Rotational Modulation Across Bandpassesmentioning

confidence: 99%

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A Relationship between Stellar Age and Spot Coverage

Morris

2020

ApJ

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We investigate starspot distributions consistent with space-based photometry of F, G, and K stars in six stellar associations ranging in age from 10 Myr to 4 Gyr. We show that a simple light curve statistic called the "smoothed amplitude" is proportional to stellar age as t −1/2 , following a Skumanich-like spin-down relation. We marginalize over the unknown stellar inclinations by forward modeling the ensemble of light curves for direct comparison with the Kepler, K2 and TESS photometry. We sample the posterior distributions for spot coverage with Approximate Bayesian Computation. We find typical spot coverages in the range 1-10% which decrease with increasing stellar age. The spot coverage is proportional to t n where n = −0.37 ± 0.16, also statistically consistent with a Skumanich-like t −1/2 decay of starspot coverage with age. We apply two techniques to estimate the spot coverage of young exoplanet-hosting stars likely to be targeted for transmission spectroscopy with the James Webb Space Telescope, and estimate the bias in exoplanet radius measurements due to varying starspot coverage.

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Section: Comparison With Observations Of Planet-hosting Starsmentioning

confidence: 94%

Section: Comparing Rotational Modulation Across Bandpassesmentioning

confidence: 99%

A Relationship between Stellar Age and Spot Coverage

Morris

2020

ApJ

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“…More recently, Morris et al (2018) compared the effects of stellar magnetic activity with the precision of Gaia's astrometry. By simulating Gaia observations on stars, accounting for shifts in the photocenter due to just dark starspots, they found that Gaia's precision is likely sufficient to detect the astrometric effects of magnetic activity in nearby active stars.…”

Section: Introductionmentioning

confidence: 99%

Multiwavelength Mitigation of Stellar Activity in Astrometric Planet Detection

Kaplan-Lipkin,

Macintosh,

Madurowicz

et al. 2021

Preprint

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Astrometric detection of exoplanets by stellar reflex motion will be made possible for giant planets by the recent Gaia mission and for Earth-like planets by proposed missions such as LUVOIR. At the theoretical limits, astrometry would allow for the detection of smaller planets than previously seen by current exoplanet search methods, but stellar activity may make these theoretical limits unreachable. Astrometric jitter of a Sun-like star due to magnetic activity in its photosphere induces apparent variability in the photocenter of order 0.5 mR . This jitter creates a fundamental astrophysical noise floor preventing detection of lower mass planets in a single spectral band. By injecting planet orbits into simulated solar data at five different passbands, we investigate mitigation of this fundamental astrometric noise using correlations across passbands. For a true solar analog and a planet at 1 au semi-major axis, the 5-sigma detection limit set by stellar activity for an ideal telescope at the best single passband is 0.01 Earth masses. We found that pairs of passbands with highly correlated astrometric jitter due to stellar activity but with less motion in the redder band enable higher precision measurements of the common signal from the planet. Using this method improves detectable planet masses at 1 au by up to a factor of 8, corresponding to at best 0.004 Earth masses for a Sun-like star with a perfect telescope. Given these results, we recommend that future astrometry missions consider proceeding with two or more passbands to reduce noise due to stellar activity.

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“…The second release of Gaia astrometric data (Lindegren et al 2018) has led to a renewed interest in exploring the impact of starspot jitter on the astrometric signal from a planet. Recently, Morris et al (2018) developed a simple model to show that the precision of Gaia astrometry is insufficient to detect starspot-induced jitter from stars with near-solar activity levels, though it is sufficient to detect jitter of nearby active stars. Meunier et al (2019) proposed a model to simulate astrometric time series for solar-type stars.…”

Section: Introductionmentioning

confidence: 99%

Predictions of Astrometric Jitter for Sun-like Stars. II. Dependence on Inclination, Metallicity, and Active-Region Nesting

Sowmya,

Nèmec,

Shapiro

et al. 2021

Preprint

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Ultra-precise astrometry from the Gaia mission is expected to lead to astrometric detections of more than 20,000 exoplanets in our Galaxy. One of the factors that could hamper such detections is the astrometric jitter caused by the magnetic activity of the planet host stars. In our previous study, we modeled astrometric jitter for the Sun observed equator-on. In this work, we generalize our model and calculate the photocenter jitter as it would be measured by the Gaia and Small-JASMINE missions for stars with solar rotation rate and effective temperature, but with various values of the inclination angle of the stellar rotation axis. In addition, we consider the effect of metallicity and of nesting of active regions (i.e. the tendency of active regions to emerge in the vicinity of each other). We find that, while the jitter of stars observed equator-on does not have any long-term trends and can be easily filtered out, the photocenters of stars observed out of their equatorial planes experience systematic shifts over the course of the activity cycle. Such trends allow the jitter to be detected with continuous measurements, in which case it can interfere with planet detectability. An increase in the metallicity is found to increase the jitter caused by stellar activity. Active-region nesting can further enhance the peak-to-peak amplitude of the photocenter jitter to a level that could be detected by Gaia.

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Spotting stellar activity cycles in Gaia astrometry

Cited by 19 publications

References 58 publications

A Relationship between Stellar Age and Spot Coverage

A Relationship between Stellar Age and Spot Coverage

Multiwavelength Mitigation of Stellar Activity in Astrometric Planet Detection

Predictions of Astrometric Jitter for Sun-like Stars. II. Dependence on Inclination, Metallicity, and Active-Region Nesting

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