More Like this

1. Localizing Sources of Variability in Crowded TESS Photometry

   https://doi.org/10.3847/1538-3881/acb20c  

   Higgins, Michael E. ; Bell, Keaton J. ( March 2023 , The Astronomical Journal)

   The Transiting Exoplanet Survey Satellite (TESS) has an exceptionally large plate scale of 21″ px⁻¹, causing most TESS light curves to record the blended light of multiple stars. This creates a danger of misattributing variability observed by TESS to the wrong source, which would invalidate any analysis. We developed a method that can localize the origin of variability on the sky to better than one fifth of a pixel. Given measured frequencies of variability (e.g., from periodogram analysis), we show that the best-fit sinusoid amplitudes to raw light curves extracted from each pixel are distributed in the same way as light from the variable source. The primary assumption of this method is that other nearby stars are not variable at the same frequencies. Essentially, we are using the high frequency resolution of TESS to overcome limitations from its low spatial resolution. We have implemented our method in an open-source Python package,TESS_localize(github.com/Higgins00/TESS-Localize), that determines the location of a variable source on the sky and the most likely Gaia source given TESS pixel data and a set of observed frequencies of variability. Our method utilizes models of the TESS pixel response function, and we characterize systematics in themore »residuals of fitting these models to data. We find that even stars more than three pixels outside a photometric aperture can produce significant contaminant signals in the extracted light curves. Given the ubiquity of source blending in TESS light curves, verifying the source of observed variability should be a standard step in TESS analyses.

   « less
2. A Dynamical Systems Approach to the Theory of Circumbinary Orbits in the Circular Restricted Problem

   https://doi.org/10.3847/1538-3881/acb7df  

   Langford, Andrew ; Weiss, Lauren M. ( March 2023 , The Astronomical Journal)

   To better understand the orbital dynamics of exoplanets around close binary stars, i.e., circumbinary planets (CBPs), we applied techniques from dynamical systems theory to a physically motivated set of solutions in the Circular Restricted Three-Body Problem (CR3BP). We applied Floquet theory to characterize the linear dynamical behavior—static, oscillatory, or exponential—surrounding planar circumbinary periodic trajectories (limit cycles). We computed prograde and retrograde limit cycles and analyzed their geometries, stability bifurcations, and dynamical structures. Orbit and stability calculations are exact computations in the CR3BP and reproducible through the open-source Python packagepyraa. The periodic trajectories (doi.org/10.5281/zenodo.7532982) produce a set of noncrossing, dynamically cool circumbinary orbits conducive to planetesimal growth. For mass ratiosμ∈ [0.01, 0.50], we found recurring features in the prograde families. These features include (1) an innermost near-circular trajectory, inside which solutions have resonant geometries, (2) an innermost stable trajectory (a_c≈ 1.61 − 1.85a_bin) characterized by a tangent bifurcating limit cycle, and (3) a region of dynamical instability (a≈ 2.1a_bin; Δa≈ 0.1a_bin), the exclusion zone, bounded by a pair of critically stable trajectories bifurcating limit cycles. The exterior boundary of the exclusion zone is consistent with prior determinations ofa_caround a circular binary. We validate our analytic results withN-body simulations and applymore »them to the Pluto–Charon system. The absence of detected CBPs in the inner stable region, between the prograde exclusion zone anda_c, suggests that the exclusion zone may inhibit the inward migration of CBPs.

   « less
3. SALT3-NIR: Taking the Open-source Type Ia Supernova Model to Longer Wavelengths for Next-generation Cosmological Measurements

   https://doi.org/10.3847/1538-4357/ac93f9  

   Pierel, J. D. R. ; Jones, D. O. ; Kenworthy, W. D. ; Dai, M. ; Kessler, R. ; Ashall, C. ; Do, A. ; Peterson, E. R. ; Shappee, B. J. ; Siebert, M. R. ; et al ( October 2022 , The Astrophysical Journal)

   A large fraction of Type Ia supernova (SN Ia) observations over the next decade will be in the near-infrared (NIR), at wavelengths beyond the reach of the current standard light-curve model for SN Ia cosmology, SALT3 (∼2800–8700 Å central filter wavelength). To harness this new SN Ia sample and reduce future light-curve standardization systematic uncertainties, we train SALT3 at NIR wavelengths (SALT3-NIR) up to 2μm with the open-source model-training softwareSALTshaker, which can easily accommodate future observations. Using simulated data, we show that the training process constrains the NIR model to ∼2%–3% across the phase range (−20 to 50 days). We find that Hubble residual (HR) scatter is smaller using the NIR alone or optical+NIR compared to optical alone, by up to ∼30% depending on filter choice (95% confidence). There is significant correlation between NIR light-curve stretch measurements and luminosity, with stretch and color corrections often improving HR scatter by up to ∼20%. For SN Ia observations expected from the Roman Space Telescope, SALT3-NIR increases the amount of usable data in the SALT framework by ∼20% at redshiftz≲ 0.4 and by ∼50% atz≲ 0.15. The SALT3-NIR model is part of the open-sourceSNCosmoandSNANASN Ia cosmology packages.
4. MESA Models with Magnetic Braking

   https://doi.org/10.3847/1538-4357/abebdf  

   Gossage, Seth ; Dotter, Aaron ; Garraffo, Cecilia ; Drake, Jeremy J. ; Douglas, Stephanie ; Conroy, Charlie ( May 2021 , The Astrophysical Journal)

   Two magnetic braking models are implemented inMESAfor use in theMISTstellar model grids. Stars less than about 1.3 solar masses are observed to spin down over time through interaction with their magnetized stellar winds (i.e., magnetic braking). This is the basis for gyrochronology and is fundamental to the evolution of lower-mass stars. The detailed physics behind magnetic braking are uncertain, as are 1D stellar evolution models. Thus, we calibrate our models and compare to data from open clusters. Each braking model tested here is capable of reproducing aspects of the data, with important distinctions; neither fully accounts for the observations. The Matt et al. prescription matches the slowly rotating stars observed in open clusters but tends to overestimate the presence of rapidly rotating stars. The Garraffo et al. prescription often produces too much angular momentum loss to accurately match the observed slow sequence for lower-mass stars but reproduces the bimodal nature of slowly and rapidly rotating stars observed in open clusters fairly well. Our models additionally do not reproduce the observed solar lithium depletion, corroborating previous findings that effects other than rotation may be important. We find additional evidence that some level of mass dependency may be missing in thesemore »braking models to match the rotation periods observed in clusters older than 1 Gyr better.

   « less
5. Modules for Experiments in Stellar Astrophysics (MESA): Time-dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure

   https://doi.org/10.3847/1538-4365/acae8d  

   Jermyn, Adam S. ; Bauer, Evan B. ; Schwab, Josiah ; Farmer, R. ; Ball, Warrick H. ; Bellinger, Earl P. ; Dotter, Aaron ; Joyce, Meridith ; Marchant, Pablo ; Mombarg, Joey S. G. ; et al ( February 2023 , The Astrophysical Journal Supplement Series)

   We update the capabilities of the open-knowledge software instrument Modules for Experiments in Stellar Astrophysics (MESA). The newauto_diffmodule implements automatic differentiation inMESA, an enabling capability that alleviates the need for hard-coded analytic expressions or finite-difference approximations. We significantly enhance the treatment of the growth and decay of convection inMESAwith a new model for time-dependent convection, which is particularly important during late-stage nuclear burning in massive stars and electron-degenerate ignition events. We strengthenMESA’s implementation of the equation of state, and we quantify continued improvements to energy accounting and solver accuracy through a discussion of different energy equation features and enhancements. To improve the modeling of stars inMESA, we describe key updates to the treatment of stellar atmospheres, molecular opacities, Compton opacities, conductive opacities, element diffusion coefficients, and nuclear reaction rates. We introduce treatments of starspots, an important consideration for low-mass stars, and modifications for superadiabatic convection in radiation-dominated regions. We describe new approaches for increasing the efficiency of calculating monochromatic opacities and radiative levitation, and for increasing the efficiency of evolving the late stages of massive stars with a new operator-split nuclear burning mode. We close by discussing major updates toMESA’s software infrastructure that enhance source code development and communitymore »engagement.

   « less