arXiv subjects

Jason L. Curtis

Publications and source records attributed to Jason L. Curtis.

At least 19 recordsLinked to original sources

arXiv2026

Measuring Rotation Periods in Crowded Star Clusters with TESS: A Proof-of-Concept with NGC 3532

The Transiting Exoplanet Survey Satellite (TESS) has observed nearly the entire sky, producing full-frame images (FFIs) every 30 min (Cycles 1$-$2), 10 min (Cycles 3$-$4), and now 200 s (Cycle 5+), over 27-day sectors. Light curves extracted from FFIs can be used to measure stellar rotation periods ($P_{\rm rot}$) in nearby open clusters, and are well-suited for studying low-mass stars ($\lesssim$1.2 M$_\odot$) younger than $\approx$1 Gyr, whose $P_{\rm rot}$ are generally still $\leq$15 days. A challenge to exploiting TESS data fully is its 21$''$ pixel size, which can cause strong signals from a source to contaminate the signals of nearby sources in the crowded environments found, e.g., in the more distant and/or richest clusters. We conducted a test with the young ($\approx$350 Myr old), moderately distant (470 pc), and rich open cluster NGC 3532 ($N_\star$ > 3000), which has an extensive $P_{\rm rot}$ catalog from ground-based photometry, to examine the reliability of $P_{\rm rot}$ obtained from TESS data. We recovered 69% of the literature periods from at least one of the three TESS cycles in which NGC 3532 was observed before any quality analysis. We then used all available TESS data for low-mass members of NGC 3532 and, applying a set of quality cuts that combined information from TESS and from Gaia, measured $P_{\rm rot}$ for 885 cluster stars, adding 706 new $P_{\rm rot}$ to the existing catalog. We conclude that, when considered with appropriate caution, TESS data for stars in crowded fields can yield reliable $P_{\rm rot}$ measurements.

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arXiv2025

Evidence for a Catastrophically Disrupted Open Cluster

Of the many discoveries uncovered by the Gaia astrometric mission, some of the most exciting are related to nearby dispersed stellar structures. We analyze one such structure in the Milky Way disk, OCSN-49, a coeval stellar stream with 257 identified members spanning approximately 30$^\circ$ across the sky. We obtained high-resolution spectroscopic data for four members that span the stream's extent, finding these four stars to have solar metallicities and remarkably homogeneous chemistry. Through a combination of isochrone fitting, lithium abundance analysis, and gyrochronology, we find a consistent stellar age of 400--600 Myr. Integrating stellar orbits backwards reveals that OCSN-49 converged to a single point at a much younger age. By integrating unbound model stars forward and comparing them to the current phase-space distribution of OCSN-49, we derive a dynamical age of 83$\pm$1 Myr, inconsistent with the age of the stellar population. The discrepancy between the kinematic and stellar age indicators is naturally explained by a disruptive event that unbound OCSN-49 roughly 500 Myr into its lifetime. Based on rate estimates, disruption due to a passing giant molecular cloud (GMC) is the most likely culprit. Assuming a single encounter, we find that a nearly head-on collision with a fairly massive GMC ($\sim$10$^5$ M$_\odot$) was necessary to unbind the cluster, although encounters with multiple GMCs may be responsible. To our knowledge, OCSN-49 serves as the first known remnant of a catastrophically disrupted open cluster and therefore serves as a benchmark for further investigating cluster disruption in the Milky Way.

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arXiv2025

Signatures of Atmospheric Mass Loss and Planet Migration in the Time Evolution of Short-Period Transiting Exoplanets

Comparative studies of young and old exoplanet populations offer a glimpse into how planets may form and evolve with time. We present an occurrence rate study of short-period ($<$12 days) planets between 1.8--10 Rearth around 1374 FGK stars in nearby (200 pc) young clusters ($<$1 Gyr), utilizing data from the Transiting Exoplanet Survey Satellite (TESS) mission. These planets represent a population closer to their primordial state. We find that the occurrence rate of young planets is higher ($64^{+32}_{-22}$%) compared to the Gyr-old population observed by \kepler ($7.98^{+0.37}_{-0.35}$%). Dividing our sample into bins of young (10--100 Myr) and intermediate (100\,Myr--1 Gyr) ages, we also find that the occurrence distribution in orbital period remains unchanged while the distribution in planet radius changes with time. Specifically, the radius distribution steepens with age, indicative of a larger planet population shrinking due to the atmospheric thermal cooling and mass loss. We also find evidence for an increase (1.9$σ$) in occurrence after 100 Myr, possibly due to tidal migration driving planets inside of 12 days. While evidence suggests post-disk migration and atmospheric mass loss shape the population of short-period planets, more detections of young planets are needed to improve statistical comparisons with older planets. Detecting long-period young planets and planets $<$1.8 Rearth will help us understand these processes better. Additionally, studying young planetary atmospheres provides insights into planet formation and the efficiency of atmospheric mass loss mechanisms on the evolution of planetary systems.

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arXiv2024

Theia 456: Tidally Shredding an Open Cluster

The application of clustering algorithms to the Gaia astrometric catalog has revolutionized our census of stellar populations in the Milky Way, including the discovery of many new, dispersed structures. We focus on one such structure, Theia 456 (COIN-Gaia-13), a loosely bound collection of ~320 stars spanning ~120 pc that has previously been shown to exhibit kinematic, chemical, and gyrochronal coherency, indicating a common origin. We obtain follow-up radial velocities and supplement these with Gaia astrometry to perform an in-depth dynamical analysis of Theia 456. By integrating stellar orbits through a Milky Way potential, we find the currently dispersed structure coalesced into a small cluster in the past. Via Bayesian modeling, we derive a kinematic age of 245 +/- 3 Myr (statistical), a half-mass radius of 9 +/- 2 pc, and an initial one-dimensional velocity dispersion of 0.14 +/- 0.02 km/s. Our results are entirely independent of model isochrones, details of stellar evolution, and internal cluster dynamics, and the statistical precision in our age derivation rivals that of the most precise age-dating techniques known today, though our imperfect knowledge of the Milky Way potential and simple spherical model for Theia 456 at birth add additional uncertainties. Using posterior predictive checking, we confirm these results are robust under reasonable variations to the Milky Way potential. Such low density structures that are disrupted by the Galactic tides before virializing may be ubiquitous, signifying that Theia 456 is a valuable benchmark for studying the dynamical history of stellar populations in the Milky Way.

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arXiv2023

Wrinkles in Time -- I: Rapid Rotators Found in High Eccentricity Orbits

Recent space-based missions have ushered in a new era of observational astronomy, where high-cadence photometric light curves for thousands to millions of stars in the solar neighborhood can be used to test and apply stellar age-dating methods, including gyrochronology. Combined with precise kinematics, these data allow for powerful new insights into our understanding of the Milky Way's dynamical history. Using TESS data, we build a series of rotation period measurement and confirmation pipelines and test them on 1,560 stars across five benchmark samples: the Pleiades, Pisces--Eridanus, Praesepe, the Hyades, and field stars from the MEarth Project. Our pipelines' recovery rates across these groups are on average 89\%. We then apply these pipelines to 4,085 likely single stars with TESS light curves in two interesting regions of Galactic action space. We identify 141 unique, rapidly rotating stars in highly eccentric orbits in the disk, some of which appear as rotationally young as the 120-Myr-old Pleiades. Pending spectroscopic analysis to confirm their youth, this indicates these stars were subject to fast-acting dynamical phenomena, the origin of which will be investigated in later papers in this series.

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arXiv2023

Using Photometrically-Derived Properties of Young Stars to Refine TESS's Transiting Young Planet Survey Completeness

The demographics of young exoplanets can shed light onto their formation and evolution processes. Exoplanet properties are derived from the properties of their host stars. As such, it is important to accurately characterize the host stars since any systematic biases in their derivation can negatively impact the derivation of planetary properties. Here, we present a uniform catalog of photometrically-derived stellar effective temperatures, luminosities, radii, and masses for 4,865 young (<1 Gyr) stars in 31 nearby clusters and moving groups within 200 pc. We compared our photometrically-derived properties to a subset of those derived from spectra, and found them to be in good agreement. We also investigated the effect of stellar properties on the detection efficiency of transiting short-period young planets with TESS as calculated in Fernandes et al. 2022, and found an overall increase in the detection efficiency when the new photometrically derived properties were taken into account. Most notably, there is a 1.5 times increase in the detection efficiencies for sub-Neptunes/Neptunes (1.8-6 Re) implying that, for our sample of young stars, better characterization of host star properties can lead to the recovery of more small transiting planets. Our homogeneously derived catalog of updated stellar properties, along with a larger unbiased stellar sample and more detections of young planets, will be a crucial input to the accurate estimation of the occurrence rates of young short-period planets.

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arXiv2023

Three low-mass companions around aged stars discovered by TESS

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 $1.05\pm 0.04\ R_J$, a mass of $69.9\pm 2.3\ M_J$ and an orbital period of 7.71 days. TOI-1608b has a radius of $1.21\pm 0.06\ R_J$, a mass of $90.7\pm 3.7\ M_J$ and an orbital period of 2.47 days. TOI-2521b has a radius of $1.01\pm 0.04\ R_J$, a mass of $77.5\pm 3.3\ M_J$ and an orbital period of 5.56 days. We found all these low-mass companions are inflated. We fitted a relation between radius, mass and incident flux using the sample 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 timescales 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.

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arXiv2022

TESS Hunt for Young and Maturing Exoplanets (THYME) VII : Membership, rotation, and lithium in the young cluster Group-X and a new young exoplanet

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 F{ü}rnkranz 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 $300\pm50$ 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 $2.6\pm0.2$ \rearth\ radius planet on a 13.8-day orbit around its 300 Myr-old host star.

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arXiv2022

Examining the Rotation Period Distribution of the 40 Myr Tucana-Horologium Association with TESS

The Tucana-Horologium Association (Tuc-Hor) is a 40 Myr old moving group in the southern sky. In this work, we measure the rotation periods of 313 Tuc-Hor objects with TESS light curves derived from TESS full frame images and membership lists driven by Gaia EDR3 kinematics and known youth indicators. We recover a period for 81.4% of the sample and report 255 rotaion periods for Tuc-Hor objects. From these objects we identify 11 candidate binaries based on multiple periodic signals or outlier Gaia DR2 and EDR3 re-normalised unit weight error (RUWE) values. We also identify three new complex rotators (rapidly rotating M dwarf objects with intricate light curve morphology) within our sample. Along with the six previously known complex rotators that belong to Tuc-Hor, we compare their light curve morphology between TESS Cycle 1 and Cycle 3 and find they change substantially. Furthermore, we provide context for the entire Tuc-Hor rotation sample by describing the rotation period distributions alongside other youth indicators such as Hα and Li equivalent width, as well as near ultra-violet and X ray flux. We find that measuring rotation periods with TESS to be a fast and effective means to confirm members in young moving groups.

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arXiv2022

Bridging the gap -- the disappearance of the intermediate period gap for fully convective stars, uncovered by new ZTF rotation periods

The intermediate period gap, discovered by Kepler, is an observed dearth of stellar rotation periods in the temperature-period diagram at $\sim$ 20 days for G dwarfs and up to $\sim$ 30 days for early-M dwarfs. However, because Kepler mainly targeted solar-like stars, there is a lack of measured periods for M dwarfs, especially those at the fully convective limit. Therefore it is unclear if the intermediate period gap exists for mid- to late-M dwarfs. Here, we present a period catalog containing 40,553 rotation periods (9,535 periods $>$ 10 days), measured using the Zwicky Transient Facility (ZTF). To measure these periods, we developed a simple pipeline that improves directly on the ZTF archival light curves and reduces the photometric scatter by 26%, on average. This new catalog spans a range of stellar temperatures that connect samples from Kepler with MEarth, a ground-based time domain survey of bright M-dwarfs, and reveals that the intermediate period gap closes at the theoretically predicted location of the fully convective boundary ($G_{\rm BP} - G_{\rm RP} \sim 2.45$ mag). This result supports the hypothesis that the gap is caused by core-envelope interactions. Using gyro-kinematic ages, we also find a potential rapid spin-down of stars across this period gap.

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arXiv2022

Further Evidence of Modified Spin-down in Sun-like Stars: Pileups in the Temperature-Period Distribution

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 $\sim 5500$K. The long-period pileup is well-described by a curve of constant Rossby number, with a critical value of $\mathrm{Ro_{crit}} \lesssim 2$. The long-period pileup was predicted by van Saders et al. (2019) 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 ($\sim 2-6$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. (2020) 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. (2013a) in M-type stars. These observations provide further support for the hypothesis that the period gap is due to stellar astrophysics, rather than a non-uniform star-formation history in the Kepler field.

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arXiv2022

A Young, Low-Density Stellar Stream in the Milky Way Disk: Theia 456

Our view of the variety of stellar structures pervading the local Milky Way has been transformed by the application of clustering algorithms to the Gaia catalog. In particular, several stellar streams have been recently discovered that are comprised of hundreds to thousands of stars and span several hundred parsecs. We analyze one such structure, Theia 456, a low-density stellar stream extending nearly 200 pc and 20$^{\circ}$ across the sky. By supplementing Gaia astrometric data with spectroscopic metallicities from LAMOST and photometric rotation periods from the Zwicky Transient Facility (ZTF) and the Transiting Exoplanet Survey Satellite (TESS), we establish Theia 456's radial velocity coherence, and we find strong evidence that members of Theia 456 have a common age ($\simeq$175 Myr), common dynamical origin, and formed from chemically homogeneous pre-stellar material ([Fe/H] = $-$0.07 dex). Unlike well-known stellar streams in the Milky Way, which are in its halo, Theia 456 is firmly part of the thin disk. If our conclusions about Theia 456 can be applied to even a small fraction of the remaining $\simeq$8300 independent structures in the Theia catalog, such low-density stellar streams may be ubiquitous. We comment on the implications this has for the nature of star-formation throughout the Galaxy.

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arXiv2022

Activity and Rotation of Nearby Field M Dwarfs in the TESS Southern Continuous Viewing Zone

The evolution of magnetism in late-type dwarfs remains murky, as we can only weakly predict levels of activity for M dwarfs of a given mass and age. We report results from our spectroscopic survey of M dwarfs in the Southern Continuous Viewing Zone (CVZ) of the Transiting Exoplanet Survey Satellite (TESS). As the TESS CVZs overlap with those of the James Webb Space Telescope, our targets constitute a legacy sample for studies of nearby M dwarfs. For 122 stars, we obtained at least one $R\approx 2000$ optical spectrum with which we measure chromospheric $\mathrm{H}α$ emission, a proxy for magnetic field strength. The fraction of active stars is consistent with what is expected for field M dwarfs; as in previous studies, we find that late-type M dwarfs remain active for longer than their early type counterparts. While the TESS light curves for $\approx$20% of our targets show modulations consistent with rotation, TESS systematics are not well enough understood for confident measurements of rotation periods ($P_{\mathrm{rot}}$) longer than half the length of an observing sector. We report periods for 12 stars for which we measure $P_{\mathrm{rot}} {\lower0.8ex\hbox{$\buildrel <\over\sim$}}$ 15 d or find confirmation for the TESS-derived $P_{\mathrm{rot}}$ in the literature. Our sample of 21 $P_{\mathrm{rot}}$, which includes periods from the literature, is consistent with our targets being spun-down field stars. Finally, we examine the $\mathrm{H}α$-to-bolometric luminosity distribution for our sample. Two stars are rotating fast enough to be magnetically saturated, but are not, hinting at the possibility that fast rotators may appear inactive in $\mathrm{H}α$.

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arXiv2022

The unpopular Package: a Data-driven Approach to De-trend TESS Full Frame Image Light Curves

The majority of observed pixels on the Transiting Exoplanet Survey Satellite (TESS) are delivered in the form of full frame images (FFI). However, the FFIs contain systematic effects such as pointing jitter and scattered light from the Earth and Moon that must be removed before downstream analysis. We present unpopular, an open-source Python package to de-trend TESS FFI light curves based on the causal pixel model method. Under the assumption that shared flux variations across multiple distant pixels are likely to be systematics, unpopular removes these common (i.e., popular) trends by modeling the systematics in a given pixel's light curve as a linear combination of light curves from many other distant pixels. To prevent overfitting we employ ridge regression and a train-and-test framework where the data points being de-trended are separated from those used to obtain the model coefficients. We also allow for simultaneous fitting with a polynomial model to capture any long-term astrophysical trends. We validate our method by de-trending different sources (e.g., supernova, tidal disruption event, exoplanet-hosting star, fast rotating star) and comparing our light curves to those obtained by other pipelines when appropriate. We also show that unpopular is able to preserve sector-length astrophysical signals, allowing for the extraction of multi-sector light curves from the FFI data. The unpopular source code and tutorials are freely available online.

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arXiv2021

A Stringent Test of Magnetic Models of Stellar Evolution

Main-sequence stars with convective envelopes often appear larger and cooler than predicted by standard models of stellar evolution for their measured masses. This is believed to be caused by stellar activity. In a recent study, accurate measurements have been published for the K-type components of the 1.62 day detached eclipsing binary EPIC 219511354, showing the radii and temperatures for both stars to be affected by these discrepancies. This is a rare example of a system in which the age and chemical composition are known, by virtue of being a member of the well-studied open cluster Ruprecht 147 (age $\sim$ 3 Gyr, [Fe/H] = +0.10). Here we report a detailed study of this system with non-standard models incorporating magnetic inhibition of convection. We show that these calculations are able to reproduce the observations largely within their uncertainties, providing robust estimates of the strength of the magnetic fields on both stars: $1600 \pm 130$ G and $1830 \pm 150$ G for the primary and secondary, respectively. Empirical estimates of the magnetic field strengths based on the measured X-ray luminosity of the system are roughly consistent with these predictions, supporting this mechanism as a possible explanation for the radius and temperature discrepancies.

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arXiv2021

Eclipsing binaries in the open cluster Ruprecht 147. IV: The active triple system EPIC 219511354

We report follow-up spectroscopic observations of the 1.62 day, K-type, detached, active, near-circular, double-lined eclipsing binary EPIC 219511354 in the open cluster Ruprecht 147, identified previously on the basis of photometric observations from the Kepler/K2 mission. This is the fourth eclipsing system analyzed in this cluster. A combined analysis of the light curve and radial velocities yields accurate masses of M(Aa) = 0.912 +/- 0.013 MSun and M(Ab) = 0.822 +/- 0.010 MSun for the primary (star Aa) and secondary (Ab), along with radii of R(Aa) = 0.920 +/- 0.016 RSun and R(Ab) = 0.851 +/- 0.016 RSun, and effective temperatures of 5035 +/- 150 and 4690 +/- 130 K, respectively. Comparison with current models of stellar evolution for the known age and metallicity of the cluster reveals that both radii are larger (by 10--14%) and both temperatures cooler (by $\sim$6%) than theoretically predicted, as is often seen in M dwarfs. This is likely caused by the significant stellar activity in the system, manifested here by 6% peak-to-peak out-of-eclipse variability, a filled-in H$α$ line, and its detection as an X-ray source. We also find EPIC 219511354 to be a hierarchical triple system, with a low-mass tertiary in an eccentric 220 day orbit.

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arXiv2021

Three K2 Campaigns Yield Rotation Periods for 1013 Stars in Praesepe

We use three campaigns of K2 observations to complete the census of rotation in low-mass members of the benchmark, $\approx$670-Myr-old open cluster Praesepe. We measure new rotation periods (\prot) for 220 $\lesssim$1.3~\Msun\ Praesepe members and recover periods for $97\%$ (793/812) of the stars with a \prot\ in the literature. Of the 19 stars for which we do not recover a \prot, 17 were not observed by K2. As K2's three Praesepe campaigns took place over the course of three years, we test the stability of our measured \prot\ for stars observed in more than one campaign. We measure \prot\ consistent to within $10\%$ for $>95\%$ of the 331 likely single stars with $\geq$2 high-quality observations; the median difference in \prot\ is $0.3\%$, with a standard deviation of $2\%$. Nearly all of the exceptions are stars with discrepant \prot\ measurements in Campaign 18, K2's last, which was significantly shorter than the earlier two ($\approx$50~d rather than $\approx$75~d). This suggests that, despite the evident morphological evolution we observe in the light curves of $38\%$ of the stars, \prot\ measurements for low-mass stars in Praesepe are stable on timescales of several years. A \prot\ can therefore be taken to be representative even if measured only once.

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arXiv2021

Re-crowning The Queen: Membership, Age and Rotation Periods for the Open Cluster Coma Berenices

Coma Berenices (Coma Ber), an open cluster about the same age as Praesepe and the Hyades (700-800 Myr) is, despite being only 85 pc away, less well studied than its famous cousins. This is due principally to its sparseness and low proper motion, which together made Coma Ber's membership challenging to establish pre-Gaia. We have curated a new list of its members based on Gaia DR2 astrometry, derived its metallicity and interstellar reddening using LAMOST data, and inferred the cluster's age by fitting PARSEC isochrones to its color$-$magnitude diagram. We then measured rotation periods for Coma Ber's low-mass members using TESS and ZTF photometry. Our isochrone fitting and the TESS- and ZTF-derived rotation periods confirm that Coma Ber is coeval with the Hyades and Praesepe. This work is the first step toward re-establishing Coma Ber as another valuable benchmark cluster for age$-$rotation$-$activity studies.

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