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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Cluster Difference Imaging Photometric Survey. II. TOI 837: A Young Validated Planet in IC 2602

We report the discovery of TOI 837b and its validation as a transiting planet. We characterize the system using data from the NASA Transiting Exoplanet Survey Satellite mission, the ESA Gaia mission, ground-based photometry from El Sauce and ASTEP400, and spectroscopy from CHIRON, FEROS, and Veloce. We find that TOI 837 is a T = 9.9 mag G0/F9 dwarf in the southern open cluster IC 2602. The star and planet are therefore 35(sup +11)(sub -5) million years old. Combining the transit photometry with a prior on the stellar parameters derived from the cluster color–magnitude diagram, we find that the planet has an orbital period of 8.3 days and is slightly smaller than Jupiter (R(sub p) = 0.77(sup + 0.09)(sub -0.07) R(sub Jup)). From radial velocity monitoring, we limit M(sub p) sin i to less than 1.20 M(sub Jup) (3σ). The transits either graze or nearly graze the stellar limb. Grazing transits are a cause for concern, as they are often indicative of astrophysical false-positive scenarios. Our follow-up data show that such scenarios are unlikely. Our combined multicolor photometry, high-resolution imaging, and radial velocities rule out hierarchical eclipsing binary scenarios. Background eclipsing binary scenarios, though limited by speckle imaging, remain a 0.2% possibility. TOI 837b is therefore a validated adolescent exoplanet. The planetary nature of the system can be confirmed or refuted through observations of the stellar obliquity and the planetary mass. Such observations may also improve our understanding of how the physical and orbital properties of exoplanets change in time.

Exoplanets↗
NASA NTRS2019

A High Binary Fraction for the Most Massive Close-in Giant Planets and Brown Dwarf Desert Members

Stellar multiplicity is believed to influence planetary formation and evolution, although the precise nature and extent of this role remain ambiguous. We present a study aimed at testing the role of stellar multiplicity in the formation and/or evolution of the most massive, close-in planetary and substellar companions. Using past and new direct imaging observations, as well as the Gaia DR2 catalogue, we searched for wide binary companions to 38 stars hosting massive giant planets or brown dwarfs (M > 7 MJup) on orbits shorter than ∼1 au. We report the discovery of a new component in the WASP-14 system, and present an independent confirmation of a comoving companion to WASP-18. From a robust Bayesian statistical analysis, we derived a binary fraction of per cent between 20 and 10 000 au for our sample, twice as high as for field stars with a 3σ significance. This binary frequency was found to be larger than for lower-mass planets on similar orbits, and we observed a marginally higher binary rate for inner companions with periods shorter than 10 d. These results demonstrate that stellar companions greatly influence the formation and/or evolution of these systems, suggesting that the role played by binary companions becomes more important for higher-mass planets, and that this trend may be enhanced for systems with tighter orbits. Our analysis also revealed a peak in binary separation at 250 au, highlighting a shortfall of close binaries among our sample. This indicates that the mechanisms affecting planet and brown dwarf formation or evolution in binaries must operate from wide separations, although we found that the Kozai–Lidov mechanism is unlikely to be the dominant underlying process. We conclude that binarity plays a crucial role in the existence of very massive short-period giant planets and brown dwarf desert inhabitants, which are almost exclusively observed in multiple systems.

C Fontanive↗
NASA NTRS1992

Water masers in W49N - The youngest stellar jet?

Observations by Gwinn et al. (1992) of the proper motions of water masers in W49N show that they have an elongated distribution expanding from a common center. Features with high space velocity only occur far from the center, while low-velocity features occur at all distances. It is proposed that water masers in star-forming regions occur in expanding shells swept up by high-velocity winds from young, massive stars during the early phases of the expansion. In W49N, confinement of the bubble by a density distribution with an axial cavity can explain both the velocity field and the shape of the maser distribution. A fully dynamical calculation of the expanding bubble is presented which provides a satisfactory fit for the observations and suggests that this system is only about 250 yr old. Thus these observations may show the very first stages of the formation of a jet from a young stellar object.

Mac Low, MORDECAI-M.↗
NASA NTRS2013

High-Resolution Near-Infrared Spectroscopy of an Equivalent Width-Selected Sample of Starbursting Dwarf Galaxies

Spectroscopic observations from the Large Binocular Telescope and the Very Large Telescope reveal kinematically narrow lines (approx. 50 km/s) for a sample of 14 Extreme Emission Line Galaxies (EELGs) at redshifts 1.4 < zeta < 2.3. These measurements imply that the total dynamical masses of these systems are low ( 3 × 10(exp 9) M). Their large [O III]5007 equivalent widths (500 − 1100 A) and faint blue continuum emission imply young ages of 10−100 Myr and stellar masses of 10(exp 8)−10(exp 9) M, confirming the presence of a violent starburst. The stellar mass formed in this vigorous starburst phase thus represents a large fraction of the total (dynamical) mass, without a significantly massive underlying population of older stars. The occurrence of such intense events in shallow potentials strongly suggests that supernova-driven winds must be of critical importance in the subsequent evolution of these systems.

Spectroscopy↗
NASA NTRS2016

SEEDS Direct Imaging of the RV-Detected Companion to V450 Andromedae, and Characterization of the System

We report the direct imaging detection of a low-mass companion to a young, moderately active star V450 And, that was previously identified with the radial velocity (RV) method. The companion was found in high-contrast images obtained with the Subaru Telescope equipped with the HiCIAO camera and AO188 adaptive optics system. From the public ELODIE and SOPHIE archives we extracted available high-resolution spectra and RV measurements, along with RVs from the Lick planet search program. We combined our multi-epoch astrometry with these archival, partially unpublished RVs, and found that the companion is a low-mass star, not a brown dwarf, as previously suggested. We found the best-fitting dynamical masses to be m(sub 1) = 1.141(sup + 0.037, sub - 0.091) and m(sub 2) = 0.279(sup + 0.023, sub - 0.020) solar mass. We also performed spectral analysis of the SOPHIE spectra with the iSpec code. Hipparcos time-series photometry shows a periodicity of P = 5.743 day, which is also seen in the SOPHIE spectra as an RV modulation of the star A. We interpret it as being caused by spots on the stellar surface, and the star to be rotating with the given period. From the rotation and level of activity, we found that the system is 380(sup + 220, sub -100) Myr old, consistent with an isochrone analysis (220 (sup +2120, sub -90) Myr). This work may serve as a test case for future studies of low mass stars, brown dwarfs, and exoplanets by combination of RV and direct imaging data.

direct imaging detection of a low-mass companion↗
NASA NTRS1972

Measured physical and optical properties of the passive geodetic satellite /Pageos/ and Echo 1.

Two satellites used for geodesy, Pageos and Echo 1, have been observed in a continuing program since 1966 to determine the stability of their physical and optical properties. Measurements are made in the UBVRI spectral system. The amount of solar radiation reflected from a satellite's surface is measured photoelectrically and is calibrated against known stellar magnitudes by standard astronomical techniques. The calibrated satellite magnitudes are analyzed with respect to the sun-satellite-observer phase angle to infer the shape and size of the satellite and the reflective properties of the satellite's surface material. The physical and optical properties are used to determine proper position of the solar image on the satellite's surface, resulting in more precise geometric geodesy. Quantitative results from five observing periods indicate that, although local structural anomalies appear to exist, both satellites essentially maintained their nominal average 30.48-meter (50-ft) radius of curvature and specular reflecting characteristics.

Mcdougal, D. S.↗
NASA NTRS1978

Observation of X-ray eclipses from LMC X-4

Observations made with the Rotation Modulation Collimator system (RMC) have revealed that X-ray source X-4 in the Large Magellanic Cloud (LMC X-4) is most likely part of a binary system. An analysis of the star's coordinates is presented, with attention given to orbital period and flux intensity variations. Stellar mass and orbital inclination angle are estimated for both X-4 and its companion star.

Li, F.↗
NASA NTRS1982

Fiducial reference for the Hipparcos reference system

Means of determining the Hipparcos satellite instrumental system rotation and for tying Hipparcos system coordinates to a fundamental coordinate system are discussed. Observational characteristics requirements for radio sources and stars, for a Hipparcos-Space Telescope reference tie are given. Rotation of the Hipparcos system with respect to the extragalactic system can be derived from observations of the relative radial positions and motions of selected Hipparcos stars and quasi-stellar objects.

Hemenway, D.↗
NASA NTRS1985

Observational studies of the symbiotic stars. III High-dispersion IUE and H-alpha observations of EG Andromedae

High-dispersion IUE and optical spectra are presented for the symbiotic star EG Andromedae (HD 4174). Remarkable emission-line strength and profile variations are confirmed for the S IV, O IV, C IV, and He II ultraviolet lines as well as H-alpha. Accurate cross-correlation absorption-line velocities determined from Ti I, Ca I, and Fe I features convincingly demonstrate that EG And is a single-lined spectroscopic binary. The velocity curve suggests that the photometric ephemeris reported by Smith in 1980 should be revised by a redefinition of zero phase by about 0.08 of a period. The primary of the system may be similar to the central star of a planetary nebula embedded in a dense nebula with a mild stellar wind. The behavior of the emission lines is interpreted to indicate that the primary and its surrounding nebula suffer a partial eclipse by the cool giant secondary.

Oliversen, N. A.↗
NASA NTRS1995

EUV spectroscopy of 3 RSCVn binaries

The extreme ultraviolet (EUV) spectroscopy of several binary stars containing cool components is used to define the high temperature plasma structure of these stars and their stellar atmospheres. Different line emission spectra are reported, along with a spectrum analysis of Capella, a nearby bright multiple star system, using data from the EUVE satellite.

Dupree, A. K.↗
NASA NTRS1995

Chemical evolution of circumstellar matter around young stellar objects

Recent observational studies of the chemical composition of circumstellar matter around both high- and low-mass young stellar objects are reviewed. The molecular abundances are found to be a strong function of evolutionary state, but not of system mass or luminosity. The data are discussed with reference to recent theoretical models.

Non-NASA Center↗
NASA NTRS1999

Kinematics in the Interacting, Star-Forming Galaxies NGC 3395/3396 and NGC 3991/3994/3995

It has been suggested that induced star formation is more sensitive to galaxy dynamics than to local phenomena and that enhanced star formation is found in galaxies with disturbed velocity structures. We are studying the stellar populations of several UV-bright, interacting galaxies to try to understand the detailed star formation process in these systems. We present preliminary results of an investigation of the kinematics of star-forming regions in the interacting systems NGC 3395/3396 and NGC 3991/3994/3995. Regions of powerful star formation are observed throughout these galaxies. The observatation will be used to investigate rotation curves in the galaxies and motion in the tidal tails.

Weistrop, Donna↗
NASA NTRS1995

Astrophysics with Pulsar/Main Sequence Star Binaries

Until very recently, all known radio pulsars in binary orbits had as companions old, degenerate stars, either neutron stars or white dwarfs. In this talk we introduce a new class of binary radio pulsars having as companions young, massive stars. Concentrating on one system in particular, we show that these systems open a new phase space for studying a variety of physical phenomena, including post-Keplerian dynamics, physics of stellar winds and interiors, and binary evolution theory.

Arecibo Telescope↗
NASA NTRS2003

The Micro-Arcsecond Metrology Testbed

The Micro-Arcsecond Metrology (MAM) testbed is a ground-based system of optical and electronic equipment for testing components, systems, and engineering concepts for the Space Interferometer Mission (SIM) and similar future missions, in which optical interferometers will be operated in outer space. In addition, the MAM testbed is of interest in its own right as a highly precise metrological system. The designs of the SIM interferometer and the MAM testbed reflect a requirement to measure both the position of the starlight central fringe and the change in the internal optical path of the interferometer with sufficient spatial resolution to generate astrometric data with angular resolution at the microarcsecond level. The internal path is to be measured by use of a small metrological laser beam of 1,319-nm wavelength, whereas the position of the starlight fringe is to be estimated by use of a charge-coupled-device (CCD) image detector sampling a large concentric annular beam. For the SIM to succeed, the optical path length determined from the interferometer fringes must be tracked by the metrological subsystem to within tens of picometers, through all operational motions of an interferometer delay line and siderostats. The purpose of the experiments performed on the MAM testbed is to demonstrate this agreement in a large-scale simulation that includes a substantial portion of the system in the planned configuration for operation in outer space. A major challenge in this endeavor is to align the metrological beam with the starlight beam in order to maintain consistency between the metrological and starlight subsystems at the system level. The MAM testbed includes an optical interferometer with a white light source, all major optical components of a stellar interferometer, and heterodyne metrological sensors. The aforementioned subsystems are installed in a large vacuum chamber in order to suppress atmospheric and thermal disturbances. The MAM is divided into two distinct subsystems: the test article (TA), which is the interferometer proper, and the inverse interferometer pseudo-star (IIPS), which synthesizes the light coming from a distant target star by providing spatially coherent wavefronts out of two mirrors, separated by the MAM baseline, that feed directly into two siderostats that are parts of the TA. The two feed mirrors of the IIPS are articulated (in translation and tilt) in order to simulate stars located at different orientations in space, while still illuminating the TA siderostats. The spectrum of the simulated starlight of the IIPS corresponds to that of a blackbody at a temperature of about 3,100 K.

Goullioud, Renaud↗
NASA NTRS2017

Utilizing Stable Isotopes and Isotopic Anomalies to Study Early Solar System Formation Processes

Chondritic meteorites contain a diversity of particle components, i.e., chondrules and calcium-, aluminum-rich refractory inclusions (CAIs), that have survived since the formation of the Solar System. The chemical and isotopic compositions of these materials provide a record of the conditions present in the protoplanetary disk where they formed and can aid our understanding of the processes and reservoirs in which solids formed in the solar nebula, an important step leading to the accretion of planetesimals. Isotopic anomalies associated with nucleosynthetic processes are observed in these discrete materials, and can be compared to astronomical observations and astrophysical formation models of stars and more recently proplyds. The existence and size of these isotopic anomalies are typically thought to reflect a significant state of isotopic heterogeneity in the earliest Solar System, likely left over from molecular cloud heterogeneities on the grain scale, but some could also be due to late stellar injection. The homogenization of these isotopic anomalies towards planetary values can be used to track the efficiency and timescales of disk wide mixing,

Simon, Justin↗
NASA NTRS2019

The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁ'hòmdímà (229762 2007 UK126)

We present high spatial resolution images of the binary transneptunian object Gǃkúnǁ'hòmdímà (229762 2007 UK126) obtained with the Hubble Space Telescope and with the Keck observatory on Mauna Kea to determine the orbit of Gǃò'é ǃhúGǃò'é ǃhú, the much smaller and redder satellite. Gǃò'é ǃhú orbits in a prograde sense, on a circular or near-circular orbit with a period of 11.3 days and a semimajor axis of 6000 km. Tidal evolution is expected to be slow, so it is likely that the system formed already in a low-eccentricity configuration, and possibly also with the orbit plane of the satellite in or close to the plane of Gǃkúnǁ'hòmdímà's equator. From the orbital parameters we can compute the system mass to be 1.4 × 1020 kg. Combined with estimates of the size of Gǃkúnǁ'hòmdímà from thermal observations and stellar occultations, we can estimate the bulk density as about 1 g cm−3. This low density is indicative of an ice-rich composition, unless there is substantial internal porosity. We consider the hypothesis that the composition is not unusually ice-rich compared with larger TNOs and comet nuclei, and instead the porosity is high, suggesting that mid-sized objects in the 400 to 1000 km diameter range mark the transition between small, porous objects and larger objects that have collapsed their internal void space as a result of their much higher internal pressures and temperatures.

W M Grundy↗
NASA NTRS1971

Cosmic rays from supernovae and comments on the Vela X pre-supernova

A possible history of the production of elements in the galaxy is presented, based on assumptions about the end points of stellar evolution and of the general evolution of the galaxy. A wide range of quantities involving the relative abundances of nucleosynthesis products observed in the solar system, and various galactic quantities such as the current rate of supernova production and the present gas content of the galaxy, were considered. These assumptions were utilized in a computer program in which the gas content of the galaxy is gradually turned into stars. The stars are continually enriched in the products of nucleosynthesis as they approach the ends of their evolutionary lifetimes. It is suggested that supernova explosions are associated with the mass range of about 4-8 solar masses. Possible theories on the type of stellar explosive event represented by the Vela supernova are discussed.

Cameron, A. G. W.↗