ORCID Profile
0000-0003-4540-5661
Current Organisations
Flatiron Institute
,
American Museum of Natural History
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Publisher: American Astronomical Society
Date: 07-2022
Abstract: Stellar variability is driven by a multitude of internal physical processes that depend on fundamental stellar properties. These properties are our bridge to reconciling stellar observations with stellar physics and to understand the distribution of stellar populations within the context of galaxy formation. Numerous ongoing and upcoming missions are charting brightness fluctuations of stars over time, which encode information about physical processes such as the rotation period, evolutionary state (such as effective temperature and surface gravity), and mass (via asteroseismic parameters). Here, we explore how well we can predict these stellar properties, across different evolutionary states, using only photometric time-series data. To do this, we implement a convolutional neural network, and with data-driven modeling we predict stellar properties from light curves of various baselines and cadences. Based on a single quarter of Kepler data, we recover the stellar properties, including the surface gravity for red giant stars (with an uncertainty of ≲0.06 dex) and rotation period for main-sequence stars (with an uncertainty of ≲5.2 days, and unbiased from ≈5 to 40 days). Shortening the Kepler data to a 27 days Transiting Exoplanet Survey Satellite–like baseline, we recover the stellar properties with a small decrease in precision, ∼0.07 for log g and ∼5.5 days for P rot , unbiased from ≈5 to 35 days. Our flexible data-driven approach leverages the full information content of the data, requires minimal or no feature engineering, and can be generalized to other surveys and data sets. This has the potential to provide stellar property estimates for many millions of stars in current and future surveys.
Publisher: American Astronomical Society
Date: 20-05-2022
Abstract: The majority of observed pixels on the Transiting Exoplanet Survey Satellite (TESS) are delivered in the form of full-frame images (FFIs). However, the FFIs contain systematic effects such as pointing jitter and scattered light from the Earth and Moon that must be removed (i.e., “detrended”) before downstream analysis. We present unpopular , an open-source Python package to obtain detrended TESS FFI light curves optimized for variable sources. The unpopular package implements a variant of the causal pixel model to remove systematics and allows for simultaneous fitting with a polynomial component to capture nontransit astrophysical variations, such as supernova signals or stellar variability, that tend to be removed in techniques optimized for exoplanet detection. We validate our method by detrending different sources (e.g., supernovae, tidal disruption events (TDEs), exoplanet-hosting stars, fast-rotating stars) and comparing our light curves to those obtained by other pipelines when appropriate. Our supernova and TDE light curves are visually similar to those obtained by others using the ISIS image subtraction package, indicating that unpopular can be used to extract multisector light curves by preserving astrophysical signals on timescales of a TESS sector (∼27 days). We note that our method contains tuning parameters that are currently set heuristically, and that the optimal set of tuning parameters will likely depend on the particular signal the user is interested in obtaining. The unpopular source code and tutorials are freely available online.
Publisher: American Astronomical Society
Date: 10-01-2022
Abstract: While the population of confirmed exoplanets continues to grow, the s le of confirmed transiting planets around evolved stars is still limited. We present the discovery and confirmation of a hot Jupiter orbiting TOI-2184 (TIC 176956893), a massive evolved subgiant ( M ⋆ = 1.53 ± 0.12 M ⊙ , R ⋆ = 2.90 ± 0.14 R ⊙ ) in the Transiting Exoplanet Survey Satellite (TESS) Southern Continuous Viewing Zone. The planet was flagged as a false positive by the TESS Quick-Look Pipeline due to periodic systematics introducing a spurious depth difference between even and odd transits. Using a new pipeline to remove background scattered light in TESS Full Frame Image data, we combine space-based TESS photometry, ground-based photometry, and ground-based radial velocity measurements to report a planet radius of R p = 1.017 ± 0.051 R J and mass of M p = 0.65 ± 0.16 M J . For a planet so close to its star, the mass and radius of TOI-2184b are unusually well matched to those of Jupiter. We find that the radius of TOI-2184b is smaller than theoretically predicted based on its mass and incident flux, providing a valuable new constraint on the timescale of post-main-sequence planet inflation. The discovery of TOI-2184b demonstrates the feasibility of detecting planets around faint (TESS magnitude 12) post-main-sequence stars and suggests that many more similar systems are waiting to be detected in the TESS FFIs, whose confirmation may elucidate the final stages of planetary system evolution.
Publisher: American Astronomical Society
Date: 07-2022
Abstract: We combine stellar surface rotation periods determined from NASA’s Kepler mission with spectroscopic temperatures to demonstrate the existence of pileups at the long-period and short-period edges of the temperature–period distribution for main-sequence stars with temperatures exceeding ∼5500 K. The long-period pileup is well described by a curve of constant Rossby number, with a critical value of Ro crit ≲ Ro ⊙ . The long-period pileup was predicted by van Saders et al. as a consequence of weakened magnetic braking, in which wind-driven angular momentum losses cease once stars reach a critical Rossby number. Stars in the long-period pileup are found to have a wide range of ages (∼2–6 Gyr), meaning that, along the pileup, rotation period is strongly predictive of a star’s surface temperature but weakly predictive of its age. The short-period pileup, which is also well described by a curve of constant Rossby number, is not a prediction of the weakened magnetic braking hypothesis but may instead be related to a phase of slowed surface spin-down due to core-envelope coupling. The same mechanism was proposed by Curtis et al. to explain the overlapping rotation sequences of low-mass members of differently aged open clusters. The relative dearth of stars with intermediate rotation periods between the short- and long-period pileups is also well described by a curve of constant Rossby number, which aligns with the period gap initially discovered by McQuillan et al. in M-type stars. These observations provide further support for the hypothesis that the period gap is due to stellar astrophysics, rather than a nonuniform star formation history in the Kepler field.
Publisher: American Astronomical Society
Date: 10-01-2023
Abstract: The fate of planets around rapidly evolving stars is not well understood. Previous studies have suggested that, relative to the main-sequence population, planets transiting evolved stars ( P 100 days) tend to have more eccentric orbits. Here we present the discovery of TOI-4582 b, a 0.94 − 0.12 + 0.09 R J , 0.53 ± 0.05 M J planet orbiting an intermediate-mass subgiant star every 31.034 days. We find that this planet is also on a significantly eccentric orbit ( e = 0.51 ± 0.05). We then compare the population of planets found transiting evolved (log g 3.8) stars to the population of planets transiting main-sequence stars. We find that the rate at which median orbital eccentricity grows with period is significantly higher for evolved star systems than for otherwise similar main-sequence systems. In general, we observe that mean planet eccentricity 〈 e 〉 = a + b log 10 ( P ) for the evolved population with significant orbital eccentricity where a = −0.18 ± 0.08 and b = 0.38 ± 0.06, significantly distinct from the main-sequence planetary system population. This trend is seen even after controlling for stellar mass and metallicity. These systems do not appear to represent a steady evolution pathway from eccentric, long-period planetary orbits to circular, short-period orbits, as orbital model comparisons suggest that inspiral timescales are uncorrelated with orbital separation or eccentricity. Characterization of additional evolved planetary systems will distinguish effects of stellar evolution from those of stellar mass and composition.
Publisher: American Astronomical Society
Date: 09-02-2022
Abstract: Giant planets on short-period orbits are predicted to be inflated and eventually engulfed by their host stars. However, the detailed timescales and stages of these processes are not well known. Here, we present the discovery of three hot Jupiters ( P 10 days) orbiting evolved, intermediate-mass stars ( M ⋆ ≈ 1.5 M ⊙ , 2 R ⊙ R ⋆ 5 R ⊙ ). By combining TESS photometry with ground-based photometry and radial velocity measurements, we report masses and radii for these three planets of between 0.4 and 1.8 M J and 0.8 and 1.8 R J . TOI-2337b has the shortest period ( P = 2.99432 ± 0.00008 days) of any planet discovered around a red giant star to date. Both TOI-4329b and TOI-2669b appear to be inflated, but TOI-2337b does not show any sign of inflation. The large radii and relatively low masses of TOI-4329b and TOI-2669b place them among the lowest density hot Jupiters currently known, while TOI-2337b is conversely one of the highest. All three planets have orbital eccentricities of below 0.2. The large spread in radii for these systems implies that planet inflation has a complex dependence on planet mass, radius, incident flux, and orbital properties. We predict that TOI-2337b has the shortest orbital decay timescale of any planet currently known, but do not detect any orbital decay in this system. Transmission spectroscopy of TOI-4329b would provide a favorable opportunity for the detection of water, carbon dioxide, and carbon monoxide features in the atmosphere of a planet orbiting an evolved star, and could yield new information about planet formation and atmospheric evolution.
Publisher: American Astronomical Society
Date: 02-03-2021
Abstract: We present an analysis of 1524 spectra of Vega spanning 10 yr, in which we search for periodic radial-velocity variations. A signal with a periodicity of 0.676 day and a semi- litude of ∼10 m s −1 is consistent with the rotation period measured over much shorter time spans by previous spectroscopic and spectropolarimetric studies, confirming the presence of surface features on this A0 star. The activity signal appears to evolve on long timescales, which may indicate the presence of failed fossil magnetic fields on Vega. TESS data reveal Vega’s photometric rotational modulation for the first time, with a total litude of only 10 ppm. A comparison of the spectroscopic and photometric litudes suggests that the surface features may be dominated by bright plages rather than dark spots. For the shortest orbital periods, transit and radial-velocity injection recovery tests exclude the presence of transiting planets larger than 2 R ⊕ and most non-transiting giant planets. At long periods, we combine our radial velocities with direct imaging from the literature to produce detection limits for Vegan planets and brown dwarfs out to distances of 15 au. Finally, we detect a candidate radial-velocity signal with a period of 2.43 days and a semi- litude of 6 m s −1 . If caused by an orbiting companion, its minimum mass would be ∼20 M ⊕ because of Vega’s pole-on orientation, this would correspond to a Jovian planet if the orbit is aligned with the stellar spin. We discuss the prospects for confirmation of this candidate planet.
Publisher: American Astronomical Society
Date: 08-2021
Location: United Kingdom of Great Britain and Northern Ireland
Location: United States of America
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Ruth Angus.