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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Analysis of Early Science observations with the CHaracterising ExOPlanets Satellite ( CHEOPS ) using pycheops

ABSTRACT CHEOPS (CHaracterising ExOPlanet Satellite) is an ESA S-class mission that observes bright stars at high cadence from low-Earth orbit. The main aim of the mission is to characterize exoplanets that transit nearby stars using ultrahigh precision photometry. Here, we report the analysis of transits observed by CHEOPS during its Early Science observing programme for four well-known exoplanets: GJ 436 b, HD 106315 b, HD 97658 b, and GJ 1132 b. The analysis is done using pycheops, an open-source software package we have developed to easily and efficiently analyse CHEOPS light-curve data using state-of-the-art techniques that are fully described herein. We show that the precision of the transit parameters measured using CHEOPS is comparable to that from larger space telescopes such as Spitzer Space Telescope and Kepler. We use the updated planet parameters from our analysis to derive new constraints on the internal structure of these four exoplanets.

Maxted, P. F. L. (ORCID:0000000337941317)↗
DOE OSTI2021

NEMESIS: Exoplanet Transit Survey of Nearby M-dwarfs in TESS FFIs. I

In this work, we present an analysis of 33,054 M-dwarf stars, located within 100 parsecs, via the Transiting Exoplanet Survey Satellite (TESS) full-frame images (FFIs) of observed sectors 1–5. We present a new pipeline called NEMESIS, developed to extract detrended photometry, and to perform transit searches of single-sector data in TESS FFIs. As many M-dwarfs are faint, and are not observed with a two-minute cadence by TESS, FFI transit surveys can provide an empirical validation of how many planets are missed, using the 30-minute cadence data. In this work, we detect 183 threshold crossing events, and present 29 candidate planets for sectors 1–5, 24 of which are new detections. Our sample contains orbital periods ranging from 1.25 to 6.84 days, and planetary radii from 1.26 to 5.31 R {sub ⊕}. With the addition of our new planet candidate detections, along with detections previously observed in sectors 1–5, we calculate an integrated occurrence rate of 2.49 ± 1.58 planets per star, for the period range ∈ [1, 9] days, and planet radius range ∈ [0.5,11] R {sub ⊕}. We project an estimated yield of 122 ± 11 transit detections of nearby M-dwarfs. Of our new candidates, 23 have signal-to-noise ratios >7, transmission spectroscopy metrics >38, and emission spectroscopy metrics >10. We present all of our data products for our planet candidates via the Filtergraph data visualization service, located at https://filtergraph.com/NEMESIS.

47 OTHER INSTRUMENTATION↗
NASA NTRS1998

Obtaining the Mass and Radius of Extra-Solar Giant Planets

The scientific utility and feasibility of detecting transits of the 9 known extrasolar planets is explored. A transit of a solar-like star by a Jupiter mass planet produces a 1% decrease in the amount of light received from the star. Transit observation will remove the ambiguity in the measurement of the planetary mass inherent in the radial velocity method and confirm the planet's existence. The 9 known planets have a 33% chance of producing at least one observable transit. Additional extrasolar planet detections from the radial velocity surveys will increase this probability to greater than 90%. The radius of the planet can be determined by the fractional decrease in light received during transit. The mass and radius may distinguish rocky or gas giant planets from brown dwarfs. The probability of detection, the transit signal size and duration, and predictions of the transit times (including errors) are calculated for circular and elliptical orbits. Observational limits are investigated and it is shown that small telescopes and existing detectors are adequate enough to achieve the 0.1% photometry necessary to detect transits of the known extrasolar planets.

Castellano, Tim↗
DOE OSTI2021

EXPRES. II. Searching for Planets around Active Stars: A Case Study of HD 101501

By controlling instrumental errors to below 10 cm s{sup −1}, the EXtreme PREcision Spectrograph (EXPRES) allows for a more insightful study of photospheric velocities that can mask weak Keplerian signals. Gaussian processes (GP) have become a standard tool for modeling correlated noise in radial velocity data sets. While GPs are constrained and motivated by physical properties of the star, in some cases they are still flexible enough to absorb unresolved Keplerian signals. We apply GP regression to EXPRES radial velocity measurements of the 3.5 Gyr old chromospherically active Sun-like star, HD 101501. We obtain tight constraints on the stellar rotation period and the evolution of spot distributions using 28 seasons of ground-based photometry, as well as recent Transiting Exoplanet Survey Satellite data. Light-curve inversion was carried out on both photometry data sets to reveal the spot distribution and spot evolution timescales on the star. We find that the >5 m s{sup −1} rms radial velocity variations in HD 101501 are well modeled with a GP stellar activity model without planets, yielding a residual rms scatter of 45 cm s{sup −1}. We carry out simulations, injecting and recovering signals with the GP framework, to demonstrate that high-cadence observations are required to use GPs most efficiently to detect low-mass planets around active stars like HD 101501. Sparse sampling prevents GPs from learning the correlated noise structure and can allow it to absorb prospective Keplerian signals. We quantify the moderate to high-cadence monitoring that provides the necessary information to disentangle photospheric features using GPs and to detect planets around active stars.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2005

A Search for Transiting Neptune-Mass Extrasolar Planets in High-Precision Photometry of Solar-Type Stars

Tennessee State University operates several automatic photometric telescopes (APTs) at Fairborn Observatory in southern Arizona. Four 0.8 m APTs have been dedicated to measuring subtle luminosity variations that accompany magnetic cycles in solar-type stars. Over 1000 program and comparison stars have been observed every clear night in this program for up to 12 years with a precision of approximately 0.0015 mag for a single observation. We have developed a transit-search algorithm, based on fitting a computed transit template for each trial period, and have used it to search our photometric database for transits of unknown companions. Extensive simulations with the APT data have shown that we can reliably recover transits with periods under 10 days as long as the transits have a depth of at least 0.0024 mag, or about 1.6 times the scatter in the photometric observations. Thus, due to our high photometric precision, we are sensitive to transits of possible short-period Neptune-mass planets that likely would have escaped detection by current radial velocity techniques. Our search of the APT data sets for 1087 program and comparison stars revealed no new transiting planets. However, the detection of several unknown grazing eclipsing binaries from among our comparison stars, with eclipse depths of only a few millimags, illustrates the success of our technique. We have used this negative result to place limits on the frequency of Neptune-mass planets in close orbits around solar-type stars in the Sun's vicinity.

Henry, Stephen M.↗
DOE OSTI2020

The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b

Using radial velocity data from the Habitable Zone Planet Finder, we have measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity of its M4.5 dwarf host star in the 600–800 Myr Hyades cluster. This is one of the youngest planetary systems for which both of these quantities have been measured and one of the very few M dwarfs with a measured obliquity. Based on a joint analysis of the radial velocity data, time-series photometry from the K2 mission, and new transit light curves obtained with diffuser-assisted photometry, the planet’s radius and mass are 3.44 ± 0.12 R {sub ⊕} and 24.5{sub −5.2}{sup +5.7}M{sub ⊕}. These properties are compatible with a rocky core enshrouded by a thin hydrogen–helium atmosphere (5% by mass). We measure an orbital eccentricity of e = 0.43 ± 0.05. The sky-projected stellar obliquity is λ = 3° ± 16°, compatible with spin–orbit alignment, in contrast to other “hot Neptunes” that have been studied around older stars.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2023

JWST NIRCam Defocused Imaging Photometric Stability Performance and How It Can Sense Mirror Tilts

We use JWST NIRCam short-wavelength photometry to capture a transit lightcurve of the exoplanet HAT-P-14 b to assess performance as part of instrument commissioning. The short-wavelength precision is 152 ppm per 27 s integration as measured over the full time series compared to a theoretical limit of 107 ppm, after corrections to spatially correlated 1/f noise. Persistence effects from charge trapping are well fit by an exponential function with short characteristic timescales, settling on the order of 5–15 minutes. The short-wavelength defocused photometry is also uniquely well suited to measure the real-time wave-front error of JWST. Analysis of the images and reconstructed wave-front maps indicates that two different hexagonal primary mirror segments exhibited “tilt events,” where they changed orientation rapidly in less than ∼1.4 s. In some cases, the magnitude and timing of the flux jumps caused by tilt events can be accurately predicted with a telescope model. These tilt events can be sensed by simultaneous longer-wavelength NIRCam grism spectral images alone in the form of changes to the point-spread function, diagnosed from the full width at half maximum. They can also be sensed with the fine guidance sensor instrument from difference images. Tilt events possibly from sudden releases of stress in the backplane structure behind the mirrors were expected during the commissioning period because they were found in ground-based testing. Tilt events have shown signs of decreasing in frequency but have not disappeared completely. The detectors exhibit some minor (less than 1%) deviations from linear behavior in the first few groups of each integration, potentially impacting absolute fluxes and transit depths on bright targets, where only a handful of groups are possible. Overall, the noise is within 50% of the theoretical photon noise and read noise. This bodes well for high-precision measurements of transiting exoplanets and other time variable targets.

Everett Schlawin↗
NASA NTRS2000

Processing CCD Images to Detect Transits of Earth-Sized Planets: Maximizing Sensitivity While Achieving Reasonable Downlink Requirements

We have performed end-to-end laboratory and numerical simulations to demonstrate the capability of differential photometry under realistic operating conditions to detect transits of Earth-sized planets orbiting solar-like stars. Data acquisition and processing were conducted using the same methods planned for the proposed Kepler Mission. These included performing aperture photometry on large-format CCD images of an artificial star fields obtained without a shutter at a readout rate of 1 megapixel/sec, detecting and removing cosmic rays from individual exposures and making the necessary corrections for nonlinearity and shutterless operation in the absence of darks. We will discuss the image processing tasks performed `on-board' the simulated spacecraft, which yielded raw photometry and ancillary data used to monitor and correct for systematic effects, and the data processing and analysis tasks conducted to obtain lightcurves from the raw data and characterize the detectability of transits. The laboratory results are discussed along with the results of a numerical simulation carried out in parallel with the laboratory simulation. These two simulations demonstrate that a system-level differential photometric precision of 10-5 on five- hour intervals can be achieved under realistic conditions.

Earth-size planets↗
NASA NTRS2004

Photometric Detection of Extra-Solar Planets

This NASA Origins Program grant supported the TEMPEST Texas McDonald Photometric Extrasolar Search for Transits) program at McDonald Observatory, which searches for transits of extrasolar planets across the disks of their parent stars. The basic approach is to use a wide-field ground-based telescope (in our case the McDonald Observatory 0.76m telescope and it s Prime Focus Corrector) to search for transits of short period (1-15 day orbits) of close-in hot-Jupiter planets in orbit around a large sample of field stars. The next task is to search these data streams for possible transit events. We collected our first set of test data for this program using the 0.76 m PFC in the summer of 1998. From those data, we developed the optimal observing procedures, including tailoring the stellar density, exposure times, and filters to best-suit the instrument and project. In the summer of 1999, we obtained the first partial season of data on a dedicated field in the constellation Cygnus. These data were used to develop and refine the reduction and analysis procedures to produce high-precision photometry and search for transits in the resulting light curves. The TeMPEST project subsequently obtained three full seasons of data on six different fields using the McDonald Observatory 0.76m PFC.

Hatzes, Artie P.↗
NASA NTRS2022

TOI-3757 b: A Low-density Gas Giant Orbiting a Solar-metallicity M Dwarf

We present the discovery of a new Jovian-sized planet, TOI-3757 b, the lowest-density transiting planet known to orbit an M dwarf (M0V). This planet was discovered around a solar-metallicity M dwarf, using Transiting Exoplanet Survey Satellite photometry and confirmed with precise radial velocities from the Habitable-zone Planet Finder (HPF) and NEID. With a planetary radius of 12.0 (+0.4 -0.5) R ⊕ and mass of 85.3 (+8.8 -8.7)M ⊕ , not only does this object add to the small sample of gas giants (∼10) around M dwarfs, but also its low density (ρ=0.27 +0.05 -0.04 g) provides an opportunity to test theories of planet formation. We present two hypotheses to explain its low density; first, we posit that the low metallicity of its stellar host (∼0.3 dex lower than the median metallicity of M dwarfs hosting gas giants) could have played a role in the delayed formation of a solid core massive enough to initiate runaway accretion. Second, using the eccentricity estimate of 0.14 ± 0.06, we determine it is also plausible for tidal heating to at least partially be responsible for inflating the radius of TOI-3757b b. The low density and large scale height of TOI-3757 b makes it an excellent target for transmission spectroscopy studies of atmospheric escape and composition (transmission spectroscopy measurement of ∼ 190). We use HPF to perform transmission spectroscopy of TOI-3757 b using the helium 10830 Å line. Doing this, we place an upper limit of 6.9% (with 90% confidence) on the maximum depth of the absorption from the metastable transition of He at ∼10830 Å, which can help constraint the atmospheric mass-loss rate in this energy-limited regime.

Exoplanet astronomy↗
NASA NTRS2000

A Search for Planetary Transits of the Star HD 187123 by Spot Filter CCD Differential Photometry

A novel method for performing high precision, time series CCD differential photometry of bright stars using a spot filter, is demonstrated. Results for several nights of observing of the 51 Pegasi b-type planet bearing star HD 187123 are presented. Photometric precision of 0.0015 - 0.0023 magnitudes is achieved. No transits are observed at the epochs predicted from the radial velocity observation. If the planet orbiting HD 187123 at 0.0415 AU is an inflated Jupiter similar in radius to HD 209458b it would have been detected at the greater than 6(sigma), level if the orbital inclination is near 90 degrees and at the greater than 3(sigma), level if the orbital inclination is as small as 82.7 degrees.

Castellano, T.↗
DOE OSTI2020

Photometric detection of internal gravity waves in upper main-sequence stars

Massive stars are predicted to excite internal gravity waves (IGWs) by turbulent core convection and from turbulent pressure fluctuations in their near-surface layers. These IGWs are extremely efficient at transporting angular momentum and chemical species within stellar interiors, but they remain largely unconstrained observationally. In this work, we aim to characterise the photometric detection of IGWs across a large number of O and early-B stars in the Hertzsprung–Russell diagram, and explain the ubiquitous detection of stochastic variability in the photospheres of massive stars. Furthermore, we combined high-precision time-series photometry from the NASA Transiting Exoplanet Survey Satellite with high-resolution ground-based spectroscopy of 70 stars with spectral types O and B to probe the relationship between the photometric signatures of IGWs and parameters such as spectroscopic mass, luminosity, and macroturbulence.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The TESS-Keck Survey. II. An Ultra-short-period Rocky Planet and Its Siblings Transiting the Galactic Thick-disk Star TOI-561

We report the discovery of TOI-561, a multiplanet system in the galactic thick disk that contains a rocky, ultra-short-period planet. This bright (V = 10.2) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P = 0.44 days, R {sub p} = 1.45 ± 0.11 R {sub ⊕}), c (TOI-561.01, P = 10.8 days, R {sub p} = 2.90 ± 0.13 R {sub ⊕}), and d (TOI-561.03, P = 16.3 days, R {sub p} = 2.32 ± 0.16 R {sub ⊕}). The star is chemically ([Fe/H] = −0.41 ± 0.05, [α/Fe] = +0.23 ± 0.05) and kinematically consistent with the galactic thick-disk population, making TOI-561 one of the oldest (10 ± 3 Gyr) and most metal-poor planetary systems discovered yet. We dynamically confirm planets b and c with radial velocities from the W. M. Keck Observatory High Resolution Echelle Spectrometer. Planet b has a mass and density of 3.2 ± 0.8 M {sub ⊕} and 5.5{sub −1.6}{sup +2.0} g cm{sup −3}, consistent with a rocky composition. Its lower-than-average density is consistent with an iron-poor composition, although an Earth-like iron-to-silicates ratio is not ruled out. Planet c is 7.0 ± 2.3 M {sub ⊕} and 1.6 ± 0.6 g cm{sup −3}, consistent with an interior rocky core overlaid with a low-mass volatile envelope. Several attributes of the photometry for planet d (which we did not detect dynamically) complicate the analysis, but we vet the planet with high-contrast imaging, ground-based photometric follow-up, and radial velocities. TOI-561 b is the first rocky world around a galactic thick-disk star confirmed with radial velocities and one of the best rocky planets for thermal emission studies.

47 OTHER INSTRUMENTATION↗
NASA NTRS2017

Stellar and Planetary Parameters for K2's Late-Type Dwarf Systems from C1 to C5

The NASA K2 (Kepler-2) mission uses photometry to find planets transiting stars of various types. M dwarfs are of high interest since they host more short-period planets than any other type of main-sequence star and transiting planets around M dwarfs have deeper transits compared to other main-sequence stars. In this paper, we present stellar parameters from K and M dwarfs hosting transiting planet candidates discovered by our team. Using the SOFI (Son OF Isaac - ESA's earlier, similar instrument) spectrograph on the European Southern Observatory's New Technology Telescope, we obtained R approximately equal to 1000 J-, H-, and K-band (0.95-2.52 micron) spectra of 34 late-type K2 planet and candidate planet host systems and 12 bright K4-M5 dwarfs with interferometrically measured radii and effective temperatures. Out of our 34 late-type K2 targets, we identify 27 of these stars as M dwarfs. We measure equivalent widths of spectral features, derive calibration relations using stars with interferometric measurements, and estimate stellar radii, effective temperatures, masses, and luminosities for the K2 planet hosts. Our calibrations provide radii and temperatures with median uncertainties of 0.059 solar radii (16.09 percent) and 160 degrees Kelvin (4.33 percent), respectively. We then reassess the radii and equilibrium temperatures of known and candidate planets based on our spectroscopically derived stellar parameters. Since a planet's radius and equilibrium temperature depend on the parameters of its host star, our study provides more precise planetary parameters for planets and candidates orbiting late-type stars observed with K2. We find a median planet radius and an equilibrium temperature of approximately 3 solar radii and 500 degrees Kelvin, respectively, with several systems (K2-18b and K2-72e) receiving near-Earth-like levels of incident irradiation.

Martinez, Arturo O.↗
NASA NTRS2023

TOI-5344 b: A Saturn-like Planet Orbiting a Super-solar Metallicity M0 Dwarf

We confirm the planetary nature of TOI-5344 b as a transiting giant exoplanet around an M0-dwarf star. TOI-5344 b was discovered with the Transiting Exoplanet Survey Satellite photometry and confirmed with ground-based photometry (the Red Buttes Observatory 0.6 m telescope), radial velocity (the Habitable-zone Planet Finder), and speckle imaging (the NN-Explore Exoplanet Stellar Speckle Imager). TOI-5344 b is a Saturn-like giant planet (ρ = 0.80 +0.17 −0.15 g cm −3 ) with a planetary radius of 9.7 ± 0.5 R⊕ (0.87 ± 0.04 R Jup ) and a planetary mass of 135 +17 −18 M⊕ (0.42 +0.05 −0.06 M Jup ). It has an orbital period of 3.792622 +0.000010 −0.000010 days and an orbital eccentricity of 0.06 +0.07 −0.04 . We measure a high metallicity for TOI-5344 of [Fe/H] = 0.48 ± 0.12, where the high metallicity is consistent with expectations from formation through core accretion. We compare the metallicity of the M-dwarf hosts of giant exoplanets to that of M-dwarf hosts of nongiants (≲8 R⊕). While the two populations appear to show different metallicity distributions, quantitative tests are prohibited by various sample caveats.

Te Han↗
DOE OSTI2020

A White Dwarf with Transiting Circumstellar Material Far outside the Roche Limit

We report the discovery of a white dwarf exhibiting deep, irregularly shaped transits, indicative of circumstellar planetary debris. Using Zwicky Transient Facility DR2 photometry of ZTF J013906.17+524536.89 and follow-up observations from the Las Cumbres Observatory, we identify multiple transit events that recur every ≈107.2 days, much longer than the 4.5–4.9 hr orbital periods observed in WD 1145+017, the only other white dwarf known with transiting planetary debris. The transits vary in both depth and duration, lasting 15–25 days and reaching 20%–45% dips in flux. Optical spectra reveal strong Balmer lines, identifying the white dwarf as a DA with ${T}_{\mathrm{eff}}=10,530\pm 140\,{\rm{K}}$ and $\mathrm{log}(g)=7.86\pm 0.06$. A Ca ii K absorption feature is present in all spectra both in and out of transit. Spectra obtained during one night at roughly 15% transit depth show increased Ca ii K absorption with a model atmospheric fit suggesting [Ca/H] = –4.6 ± 0.3, whereas spectra taken on three nights out of transit have [Ca/H] of –5.5, –5.3, and –4.9 with similar uncertainties. While the Ca ii K line strength varies by only 2σ, we consider a predominantly interstellar origin for Ca absorption unlikely. Here, we suggest a larger column density of circumstellar metallic gas along the line of site or increased accretion of material onto the white dwarf's surface are responsible for the Ca absorption, but further spectroscopic studies are required. In addition, high-speed time series photometry out of transit reveals variability with periods of 900 and 1030 s, consistent with ZZ Ceti pulsations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2022

TESS Revisits WASP-12: Updated Orbital Decay Rate and Constraints on Atmospheric Variability

After observing WASP-12 in the second year of the primary mission, the Transiting Exoplanet Survey Satellite (TESS) revisited the system in late 2021 during its extended mission. In this paper, we incorporate the new TESS photometry into a reanalysis of the transits, secondary eclipses, and phase curve. We also present a new Ks-band occultation observation of WASP-12b obtained with the Palomar/Wide-field Infrared Camera instrument. The latest TESS photometry spans three consecutive months, quadrupling the total length of the TESS WASP-12 light curve and extending the overall time baseline by almost two years. Based on the full set of available transit and occultation timings, we find that the orbital period is shrinking at a rate of −29.81 ± 0.94 ms yr−1. The additional data also increase the measurement precision of the transit depth, orbital parameters, and phase-curve amplitudes. We obtain a secondary eclipse depth of 466 ± 35 ppm, a 2σ upper limit on the nightside brightness of 70 ppm, and a marginal 6°.2 ± 2°.8 eastward offset between the dayside hotspot and the substellar point. The voluminous TESS data set allows us to assess the level of atmospheric variability on timescales of days, months, and years. We do not detect any statistically significant modulations in the secondary eclipse depth or day–night brightness contrast. Likewise, our measured Ks-band occultation depth of 2810 ± 390 ppm is consistent with most ∼2.2 μm observations in the literature.

Ian Wong↗
NASA NTRS2019

A Super-Earth and Sub-Neptune Transiting the Late-type M Dwarf LP 791-18

Planets occur most frequently around cool dwarfs, but only a handful of specific examples are known to orbit the latest-type M stars. Using TESS photometry, we report the discovery of two planets transiting the low-mass star called LP 791-18 (identified by TESS as TOI 736). This star has spectral type M6V, effective temperature 2960 K, and radius 0.17 Rꙩ, making it the third-coolest star known to host planets. The two planets straddle the radius gap seen for smaller exoplanets; they include a 1.1Rꚛ planet on a 0.95 day orbit and a 2.3Rꚛ planet on a 5 day orbit. Because the host star is small the decrease in light during these planets' transits is fairly large (0.4% and 1.7%). This has allowed us to detect both planets' transits from ground-based photometry, refining their radii and orbital ephemerides. In the future, radial velocity observations and transmission spectroscopy can both probe these planets' bulk interior and atmospheric compositions, and additional photometric monitoring would be sensitive to even smaller transiting planets.

Ian J. M. Crossfield↗