ORCID Profile
0000-0002-2792-134X
Current Organisation
Columbia University
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Publisher: American Astronomical Society
Date: 29-03-2018
Publisher: American Astronomical Society
Date: 28-02-2023
Publisher: American Astronomical Society
Date: 30-08-2022
Abstract: The public, all-sky surveys Gaia and TESS provide the ability to identify new young associations and determine their ages. These associations enable study of planetary evolution by providing new opportunities to discover young exoplanets. A young association was recently identified by Tang et al. and Fürnkranz et al. using astrometry from Gaia (called “Group-X” by the former). In this work, we investigate the age and membership of this association, and we validate the exoplanet TOI 2048 b, which was identified to transit a young, late G dwarf in Group-X using photometry from TESS. We first identified new candidate members of Group-X using Gaia EDR3 data. To infer the age of the association, we measured rotation periods for candidate members using TESS data. The clear color–period sequence indicates that the association is the same age as the 300 ± 50 Myr old NGC 3532. We obtained optical spectra for candidate members that show lithium absorption consistent with this young age. Further, we serendipitously identify a new, small association nearby Group-X, which we call MELANGE-2. Lastly, we statistically validate TOI 2048 b, which is a 2.1 ± 0.2 R ⊕ radius planet on a 13.8-day orbit around its 300 Myr old host star.
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: Zenodo
Date: 2016
DOI: 10.5281/ZENODO.58758
Publisher: American Astronomical Society
Date: 15-10-2018
Publisher: American Astronomical Society
Date: 14-01-2021
Publisher: American Astronomical Society
Date: 16-12-2019
Publisher: American Astronomical Society
Date: 24-06-2020
Publisher: American Astronomical Society
Date: 06-07-2018
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: 25-10-2022
Abstract: Stellar positions and velocities from Gaia are yielding a new view of open cluster dispersal. Here we present an analysis of a group of stars spanning Cepheus ( l = 100°) to Hercules ( l = 40°), hereafter the Cep-Her complex. The group includes four Kepler objects of interest: Kepler-1643 b ( R p = 2.32 ± 0.13 R ⊕ , P = 5.3 days), KOI-7368 b ( R p = 2.22 ± 0.12 R ⊕ , P = 6.8 days), KOI-7913 Ab ( R p = 2.34 ± 0.18 R ⊕ , P = 24.2 days), and Kepler-1627 Ab ( R p = 3.85 ± 0.11 R ⊕ , P = 7.2 days). The latter Neptune-sized planet is in part of the Cep-Her complex called the δ Lyr cluster. Here we focus on the former three systems, which are in other regions of the association. Based on kinematic evidence from Gaia, stellar rotation periods from TESS, and spectroscopy, these three objects are also ≈40 million years (Myr) old. More specifically, we find that Kepler-1643 is 46 − 7 + 9 Myr old, based on its membership in a dense subcluster of the complex called RSG-5. KOI-7368 and KOI-7913 are 36 − 8 + 10 Myr old, and are in a diffuse region that we call CH-2. Based on the transit shapes and high-resolution imaging, all three objects are most likely planets, with false-positive probabilities of 6 × 10 −9 , 4 × 10 −3 , and 1 × 10 −4 for Kepler-1643, KOI-7368, and KOI-7913, respectively. These planets demonstrate that mini-Neptunes with sizes of ≈2 Earth radii exist at ages of 40 Myr.
Publisher: American Astronomical Society
Date: 29-06-2023
Publisher: Oxford University Press (OUP)
Date: 15-06-2023
Abstract: We report the discovery of three transiting low-mass companions to aged stars: a brown dwarf (TOI-2336b) and two objects near the hydrogen burning mass limit (TOI-1608b and TOI-2521b). These three systems were first identified using data from the Transiting Exoplanet Survey Satellite (TESS). TOI-2336b has a radius of 1.05 ± 0.04 RJ, a mass of 69.9 ± 2.3 MJ and an orbital period of 7.71 d. TOI-1608b has a radius of 1.21 ± 0.06 RJ, a mass of 90.7 ± 3.7 MJ and an orbital period of 2.47 d. TOI-2521b has a radius of 1.01 ± 0.04 RJ, a mass of 77.5 ± 3.3 MJ, and an orbital period of 5.56 d. We found all these low-mass companions are inflated. We fitted a relation between radius, mass, and incident flux using the s le of known transiting brown dwarfs and low-mass M dwarfs. We found a positive correlation between the flux and the radius for brown dwarfs and for low-mass stars that is weaker than the correlation observed for giant planets. We also found that TOI-1608 and TOI-2521 are very likely to be spin-orbit synchronized, leading to the unusually rapid rotation of the primary stars considering their evolutionary stages. Our estimates indicate that both systems have much shorter spin-orbit synchronization time-scales compared to their ages. These systems provide valuable insights into the evolution of stellar systems with brown dwarf and low-mass stellar companions influenced by tidal effects.
Location: United States of America
Location: United States of America
No related grants have been discovered for Jason Curtis.