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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Why Do We Find Ourselves Around a Yellow Star Instead of a Red Star?

M-dwarf stars are more abundant than G-dwarf stars, so our position as observers on a planet orbiting a G-dwarf raises questions about the suitability of other stellar types for supporting life. If we consider ourselves as typical, in the anthropic sense that our environment is probably a typical one for conscious observers, then we are led to the conclusion that planets orbiting in the habitable zone of G-dwarf stars should be the best place for conscious life to develop. But such a conclusion neglects the possibility that K-dwarfs or M-dwarfs could provide more numerous sites for life to develop, both now and in the future. In this paper we analyse this problem through Bayesian inference to demonstrate that our occurrence around a G-dwarf might be a slight statistical anomaly, but only the sort of chance event that we expect to occur regularly. Even if M-dwarfs provide more numerous habitable planets today and in the future, we still expect mid G- to early K-dwarfs stars to be the most likely place for observers like ourselves. This suggests that observers with similar cognitive capabilities as us are most likely to be found at the present time and place, rather than in the future or around much smaller stars.

anthropic principle↗
NASA NTRS2011

A Combined Subaru/VLT/MMT 1-5 Micrometer Study of Planets Orbiting HR 8799: Implications For Atmospheric Properties, Masses and Formation

We present new 1-1.25 micron (z and J band) Subaru/IRCS and 2 micron (K band) VLT/NaCo data for HR 8799 and a rereduction of the 3-5 micron MMT/Clio data first presented by Hinz et al. Our VLT/NaCo data yield a detection of a fourth planet at a projected separation of approximately 15 AU--"HR 8799e ." We also report new, albeit weak detections of HR 8799b at 1.03 micron and 3.3 micron. Empirical comparisons to field brown dwarfs show that at least HR 8799b and HR 8799c, and possibly HR 8799d, have near-to-mid-IR colors/ magnitudes significantly discrepant from the L/T dwarf sequence. Standard cloud deck atmosphere models appropriate for brown dwarfs provide only (marginally) statistically meaningful fits to HR 8799b and c for unphysically small radii. Models with thicker cloud layers not present in brown dwarfs reproduce the planets' spectral energy distributions far more accurately and without the need for resealing the planets' radii. Our preliminary modeling suggests that HR 8799b has log(g) = 4-4.5, T(sub eff) = 900 K. while HR 8799c, d, and (by inference) e have log(g) = 4-4.5, T(sub eff) = 1000-1200 K. Combining results from planet evolution models and new dynamical stability limits implies that the masses of HR 8799b, c, d, and e are 6-7 M(sub j), 7-10 M(sub j), 7-10 M(sub j), and 7-10 M(sub j). "Patchy" cloud prescriptions may provide even better fits to the data and may lower the estimated surface gravities and masses. Finally, contrary to some recent claims, forming the HR 8799 planets by core accretion is still plausible, although such systems are likely rare.

Currie, Thayne↗
DOE OSTI2025

Creation and characterization of warm dense matter isochorically heated by an intense laser-driven proton beam to temperatures exceeding 100 eV

The warm dense matter (WDM) is an exotic state of matter encountered in inertial confinement implosions for fusion energy, as well as the interiors of giant planets like Jupiter, brown dwarfs, the atmospheres of white dwarfs, neutron star crusts, and newly discovered exo-planets. One efficient way to create WDM is to use protons accelerated by a high-intensity short-pulse laser to isochorically heat dense samples to WDM states. Despite its importance, direct temperature measurements within WDM targets are scarce. This study utilizes an intense proton beam generated by the kilojoule EP laser further focused and guided by a curved foil and cone structure to efficiently heat a thin copper sample. A high-resolution streaked spectrometer tuned to copper K α fluorescence lines provided bulk temperature measurements every ~2 ps, revealing temperatures exceeding 100 eV in under 50 ps. Particle-in-cell simulations of proton transport and energy deposition closely matched the observed heating dynamics, including transverse temperature gradients revealed by the broadening of K α lines.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

True Masses of the Long-period Companions to HD 92987 and HD 221420 from Hipparcos–Gaia Astrometry

The extensive time span of modern radial velocity surveys has made the discovery of long-period substellar companions more common in recent years; however, measuring the true masses of these objects remains challenging. Astrometry from the Gaia mission is expected to provide mass measurements for many of these long-period companions, but these data are not yet available. However, combining proper-motion data from Gaia DR2 and the earlier Hipparcos mission makes it possible to measure true masses of substellar companions in favorable cases. In this work, we combine radial velocities with Hipparcos–Gaia astrometry to measure the true masses of two recently discovered long-period substellar companion candidates, HD 92987 B and HD 221420 b. In both cases, we find that the true masses are significantly higher than implied by radial velocities alone. A 2087 ± 19 m s{sup −1} astrometric signal reveals that HD 92987 B is not close to its 17 M {sub J} minimum mass but is instead a 0.2562 ± 0.0045 M {sub ⊙} star viewed at a near-polar orbital inclination, whereas the 22.9 ± 2.2 M {sub J} HD 221420 b can be plausibly interpreted as a high-mass “superplanet” or a low-mass brown dwarf. With semimajor axes of ∼10 au, both companions are interesting targets for direct imaging, and HD 221420 b in particular would be a benchmark metal-rich substellar object if it proves possible to directly detect. Our results demonstrate the power of Hipparcos–Gaia astrometry for studying long-period planet and brown dwarf candidates discovered from radial velocity surveys.

36 MATERIALS SCIENCE↗
NASA NTRS1996

A matched filter method for ground-based sub-noise detection of terrestrial extrasolar planets in eclipsing binaries: application to CM Draconis

The photometric detection of extrasolar planets by transits in eclipsing binary systems can be significantly improved by cross-correlating the observational light curves with synthetic models of possible planetary transit features, essentially a matched filter approach. We demonstrate the utility and application of this transit detection algorithm for ground-based detections of terrestrial-sized (Earth-to-Neptune radii) extrasolar planets in the dwarf M-star eclipsing binary system CM Draconis. Preliminary photometric observational data of this system demonstrate that the observational noise is well characterized as white and Gaussian at the observational time steps required for precision photometric measurements. Depending on planet formation scenarios, terrestrial-sized planets may form quite close to this low-luminosity system. We demonstrate, for example, that planets as small as 1.4 Earth radii with periods on the order of a few months in the CM Draconis system could be detected at the 99.9% confidence level in less than a year using 1-m class telescopes from the ground. This result contradicts commonly held assumptions limiting present ground-based efforts to, at best, detections of gas giant planets after several years of observation. This method can be readily extended to a number of other larger star systems with the utilization of larger telescopes and longer observing times. Its extension to spacecraft observations should also allow the determination of the presence of terrestrial-sized planets in nearly 100 other known eclipsing binary systems.

NASA Discipline Number 52-10↗
NASA NTRS2019

Development of the WFIRST CGI Integral Field Spectrograph

The principal science goal of directly imaging exoplanets is spectroscopy. Future mission concepts such as LU- VOIR and HabEx have baselined their science instruments to use an integral field spectrograph (IFS) to maximize observing efficiency. Coronagraphic imaging with an IFS has strong heritage at ground observatories, having produced planet and brown dwarf near-infrared spectra at contrast floors as low as high 1 × 10-6 levels. As a technology demonstration for future missions the WFIRST coronagraph instrument (CGI) will demonstrate the ability to measure spectra in visible light with at contrast levels sufficient for detecting Earth-like planets. The spectrograph was originally meant to match that of future missions; an independent IFS channel for wavefront control and imaging spectroscopy. Due to a series of de-scopes as the project progressed, the baseline spectroscopic capability of CGI is no longer an IFS but a zero deviation optical prism and slit used in conjunction with the direct imaging camera. Regardless, CGI advanced a lenslet IFS through the preliminary design phase of a flight project. Here we present that development as the challenges and requirements of an IFS for coronagraphy are quite unique and relevant to future missions. With that development in place, we also present the initial design of the zero optical deviation prism, highlighting the relative challenges and performance of each concept.

Tyler D Groff↗
NASA NTRS2004

The Search for Young Planetary Systems And the Evolution of Young Stars

The Space Interferometer Mission (SIM) will provide a census of planetary systems by con- ducting a broad survey of 2,000 stars that will be sensitive to the presence of planets with masses as small as approx. 15 Earth masses (1 Uranus mass) and a deep survey of approx. 250 of the nearest, stars with a mass limit of approx.3 Earth masses. The broad survey will include stars spanning a wide range of ages, spectral types, metallicity, and other important parameters. Within this larger context, the Young Stars and Planets Key Project will study approx. 200 stars with ages from 1 Myr to 100 Myr to understand the formation and dynamical evolution of gas giant planets. The SIM Young Stars and Planets Project will investigate both the frequency of giant planet formation and the early dynamical history of planetary systems. We will gain insight into how common the basic architecture of our solar system is compared with recently discovered systems with close-in giant planets by examining 200 of the nearest (less than 150 pc) and youngest (1-100 Myr) solar-type stars for planets. The sensitivity of the survey for stars located 140 pc away is shown in the planet mass-separation plane. We expect to find anywhere from 10 (assuming that only the presently known fraction of stars. 5-7%, has planets) to 200 (all young stars have planets) planetary systems. W-e have set our sensitivity threshold to ensure the detection of Jupiter-mass planets in the critical orbital range of 1 to 5 AU. These observations, when combined with the results of planetary searches of mature stars, will allow us to test theories of planetary formation and early solar system evolution. By searching for planets around pre-main sequence stars carefully selected to span an age range from 1 to 100 Myr, we will learn a t what epoch and with what frequency giant planets are found at the water-ice snowline where they are expected to form. This will provide insight into the physical mechanisms by which planets form and migrate from their place of birth, and about their survival rate. With these data in hand, we will provide data, for the first time, on such important questions as: What processes affect the formation and dynamical evolution of planets? When and where do planets form? What is initial mass distribution of planetary systems around young stars? How might planets be destroyed? What is the origin of the eccentricity of planetary orbits? What is the origin of the apparent dearth of companion objects between planets and brown dwarfs seen in mature stars? The observational strategy is a compromise between the desire to extend the planetary mass function as low as possible and the essential need to build up sufficient statistics on planetary occurrence. About half of the sample will be used to address the "where" and "when" of planet formation. We will study classical T Tauri stars (cTTs) which have massive accretion disks and post- accretion, weak-lined T Tauri stars (wTTs). Preliminary estimates suggest the sample will consist of approx. 30% cTTs and approx. 70% wTTs, driven in part by the difficulty of making accurate astrometric measurements toward objects with strong variability or prominent disks.

Beichman, Charles A.↗
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

A Decade of Radial-velocity Monitoring of Vega and New Limits on the Presence of Planets

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-amplitude of ∼10 m s{sup −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 amplitude of only 10 ppm. A comparison of the spectroscopic and photometric amplitudes 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 {sub ⊕} 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-amplitude of 6 m s{sup −1}. If caused by an orbiting companion, its minimum mass would be ∼20 M {sub ⊕}; 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.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
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↗
NASA NTRS2011

Extremely Low Mass: The Circumstellar Envelope of a Potential Proto-Brown Dwarf

What is the environment for planet formation around extremely low mass stars? Is the environment around brown dwarfs and extremely low mass stars conducive and sufficiently massive for planet production? The determining conditions may be set very early in the process of the host object's formation. IRAS 16253-2429, the source of the Wasp-Waist Nebula seen in Spitzer IRAC images, is an isolated, very low luminosity ("VeLLO") Class 0 protostar in the nearby rho Ophiuchi cloud. We present VLA ammonia mapping observations of the dense gas envelope feeding the central core accreting system. We find a flattened envelope perpendicular to the outflow axis, and gas cavities that appear to cradle the outflow lobes as though carved out by the flow and associated (apparently precessing) jet, indicating environmental disruption. Based on the NH3 (1,1) and (2,2) emission distribution, we derive the mass, velocity fields and temperature distribution for the envelope. We discuss the combined evidence for this source to be one of the youngest and lowest mass sources in formation yet known, and discuss the ramifications for planet formation potential in this extremely low mass system.

Wiseman, Jennifer↗
DOE OSTI2020

The High-energy Radiation Environment around a 10 Gyr M Dwarf: Habitable at Last?

Recent work has demonstrated that high levels of X-ray and UV activity on young M dwarfs may drive rapid atmospheric escape on temperate, terrestrial planets orbiting within the habitable zone. However, secondary atmospheres on planets orbiting older, less active M dwarfs may be stable and present more promising candidates for biomarker searches. In order to evaluate the potential habitability of Earth-like planets around old, inactive M dwarfs, we present new Hubble Space Telescope and Chandra X-ray Observatory observations of Barnard’s Star (GJ 699), a 10 Gyr old M3.5 dwarf, acquired as part of the Mega-MUSCLES program. Despite the old age and long rotation period of Barnard’s Star, we observe two FUV (δ 130 ≈ 5000 s; E 130 ≈ 10 29.5 erg each) and one X-ray (E X ≈ 10 29.2 erg) flares, and we estimate a high-energy flare duty cycle (defined here as the fraction of the time the star is in a flare state) of ~25%. A publicly available 5 Å to 10 μm spectral energy distribution of GJ 699 is created and used to evaluate the atmospheric stability of a hypothetical, unmagnetized terrestrial planet in the habitable zone (r HZ ~ 0.1 au). Both thermal and nonthermal escape modeling indicate (1) the quiescent stellar XUV flux does not lead to strong atmospheric escape: atmospheric heating rates are comparable to periods of high solar activity on modern Earth, and (2) the flare environment could drive the atmosphere into a hydrodynamic loss regime at the observed flare duty cycle: sustained exposure to the flare environment of GJ 699 results in the loss of ≈87 Earth atmospheres Gyr -1 through thermal processes and ≈3 Earth atmospheres Gyr -1 through ion loss processes. These results suggest that if rocky planet atmospheres can survive the initial ~5 Gyr of high stellar activity, or if a second-generation atmosphere can be formed or acquired, the flare duty cycle may be the controlling stellar parameter for the stability of Earth-like atmospheres around old M stars.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2019

Time Series Analysis in the Search for Other Worlds Through Transit Photometry

The Kepler Mission launched in June 2009 to commence NASA's first mission to search for potentially habitable, Earth-size planets orbiting Sun-like stars. Kepler discovered explanets via the transit method: searching for minute (100 ppm) drops in brightness lasting 1 - 13 hours corresponding to occasions where the planet crosses the face of its host star from Kepler's point of view. The exquisite precision required to carry out the Kepler mission (20 ppm in 6.5 hours) pushed astronomical time series analysis to the limits, and motivated the development of novel algorithmic approaches. Transit signatures of rocky planets are often dwarfed by the intrinsic stellar variability, which is not white noise, and often is non-stationary, and by instrumental systematic effects, which can include transients and electronic artifacts. Surmounting this challenging regime of weak, temporally compact, periodic signals in observation noise with strong systematics and other sources of variability motivated the development of 1) an overcomplete, non-decimated, wavelet-based matched filter to jointly estimate the properties of the non-stationary, non-white observation noise process, and 2) a multi-scale, maximum a posteriori (msMAP) approach to identifying and removing instrumental systematic effects. After over nine years of observations, the Kepler spacecraft finally ran out of fuel in November 2018, ending its data collection activities. Over 2300 planets were discovered by Kepler in its primary mission, and over 355 have been discovered by K2, the repurposed mission that followed Kepler's primary mission after the loss of a second reaction wheel in May 2013. We have ported the Kepler science pipeline for the Transiting Exoplanet Survey Satellite (TESS) Mission, which began science observations in July 2019, and report initial results and performance of the modified science pipeline.The Kepler and TESS Missions are supported by NASA's Science Mission Directorate.

transit surveys↗
DOE OSTI2024

Ionization by XFEL radiation produces distinct structure in liquid water

In the warm dense matter (WDM) regime, where condensed, gas, and plasma phases coexist, matter frequently exhibits unusual properties that cannot be described by contemporary theory. Experiments reporting phenomena in WDM are therefore of interest to advance our physical understanding of this regime, which is found in dwarf stars, giant planets, and fusion ignition experiments. Using 7.1 keV X-ray free electron laser radiation (nominally 5×10 5 J/cm 2 ), we produced and probed transient WDM in liquid water. Wide-angle X-ray scattering (WAXS) from the probe reveals a new ~9 Å structure that forms within 75 fs. By 100 fs, the WAXS peak corresponding to this new structure is of comparable magnitude to the ambient water peak, which is attenuated. Simulations suggest that the experiment probes a superposition of two regimes. In the first, fluences expected at the focus severely ionize the water, which becomes effectively transparent to the probe. In the second, out-of-focus pump radiation produces O 1+ and O 2+ ions, which rearrange due to Coulombic repulsion over 10 s of fs. Our simulations account for a decrease in ambient water signal and an increase in low-angle X-ray scattering but not the experimentally observed 9 Å feature, presenting a new challenge for theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Subaru Hyper Suprime-Cam Survey of Cygnus OB2 Complex – I. Introduction, photometry, and source catalogue

ABSTRACT Low-mass star formation inside massive clusters is crucial to understand the effect of cluster environment on processes like circumstellar disc evolution, planet, and brown dwarf formation. The young massive association of Cygnus OB2, with a strong feedback from massive stars, is an ideal target to study the effect of extreme environmental conditions on its extensive low-mass population. We aim to perform deep multiwavelength studies to understand the role of stellar feedback on the IMF, brown dwarf fraction and circumstellar disc properties in the region. We introduce here, the deepest and widest optical photometry of 1.5○ diameter region centred at Cygnus OB2 in r2, i2, z, and Y-filters, using Subaru Hyper Suprime-Cam (HSC). This work presents the data reduction, source catalogue generation, data quality checks, and preliminary results about the pre-main sequence sources. We obtain 713 529 sources in total, with detection down to ∼28, 27, 25.5, and 24.5 mag in r2, i2, z, and Y-band, respectively, which is ∼3 – 5 mag deeper than the existing Pan-STARRS and GTC/OSIRIS photometry. We confirm the presence of a distinct pre-main sequence branch by statistical field subtraction of the central 18 arcmin region. We find the median age of the region as ∼5 ± 2 Myr with an average disc fraction of ∼9 per cent. At this age, combined with A $_V\, \sim$ 6 – 8 mag, we detect sources down to a mass range of ∼0.01–0.17 M⊙. The deep HSC catalogue will serve as the groundwork for further studies on this prominent active young cluster.

Gupta, Saumya (ORCID:0000000161843958)↗
NASA NTRS1991

Scanning with charge-coupled devices

Results are presented of an investigation of six modes of using CCDs for searches of gamma-ray bursters, debris in geosynchronous space, satellites of asteroids, brown dwarfs, the tenth planet, comets, cometesimals, and various types of asteroids. A new discipline in astrophysics, 'scannerscopy', i.e., surveying with a CCD rather than with photography at a Schmidt telescope, is described. It uses the CCD in scanning rather than in sequencing of stare exposures as is done at most observatories, which can save telescope time and obviates the need for flat-fielding. Attention is given to the Tektronix 2048 x 2048 CCD, 38 arcmin wide, which is used to a limiting magnitude of 20.5 V. It is also shown to be successful for discovering rare and small near-earth asteroids. Possibilities with cameras on spacecraft that pass through the asteroid belt are described.

Gehrels, Tom↗
NASA NTRS1992

The use of robotic telescopes for detecting planetary systems

It is argued that increases in the precision of photometric measurements and the development of fully automatic photometric telescopes (APTs) now make possible the detection of Jupiter-size objects around other stars. The two most promising approaches are to monitor binary stars that have their orbital plane nearly in our line of sight and to measure the rotation periods of stars that are known to have dark companions and have very accurate values for Vsini. Differential photometry with APTs, based on a rapid comparison among a group of stars, provides a precision of 2 parts in 1000. Transits of solar-type stars by planets or brown dwarfs the size of Jupiter or Saturn will produce brightness variations of about 10 parts per 1000.

Borucki, William J.↗
NASA NTRS1994

The expected morphology of the solar system planetary nebula

We examine the evolution of Jupiter's orbit as the Sun evolves to form a planetary nebula. We use an orbital synchronization mechanism, which was proposed by Tassoul (1987, ApJ, 322, 856), and find that Jupiter is likely to deposit a substantial fraction of its orbital angular momentum, in spinning-up the Sun, when the latter is on the upper Asymptotic Giant Branch (AGB). This amount of angular momentum is likely to cause some small degree of axisymmetric mass loss from the Sun. In this case, the Sun will form an elliptical planetary nebula. The formation of elliptical planetary nebulae with the influence of massive planets and brown dwarfs, may explain the large fraction of elliptical planetary nebulae among the total number of planetary nebulae known today.

Soker, Noam↗