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At least 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

US 943 - A 19th mag eclipsing cataclysmic variable with a period of 2 hr 3.8 min

The high-latitude, V equals about 19.5, blue variable star US 943 is found to be an eclipsing binary with an orbital period of 2.06 hr. The light curve is dominated by an orbital hump which has an amplitude of 0.9 mag in V and is centered about 0.17 orbital cycles before the 1.5-mag deep eclipse. There is evidence that the eclipse has at least two components. The overall appearance of the star is that of a dwarf nova in quiescence, a conclusion that is supported by the observation of a subsequent bright state (V equals about 15) suggesting a dwarf nova outburst.

Howell, S. B.↗
DOE OSTI2020

First discovery of an ultra-cool white dwarf benchmark in common proper motion with an M dwarf

Ultra-cool white dwarfs are among the oldest stellar remnants in the Universe. Their efficient gravitational settling and low effective temperatures are responsible for the smooth spectra they exhibit. For that reason, it is not possible to derive their radial velocities or to find the chemistry of the progenitors. The best that can be done is to infer such properties from associated sources, which are coeval. The simplest form of such a system is a common proper motion pair where one star is an evolved degenerate and the other a main-sequence star. Herein, we present the discovery of the first of such a system, the M dwarf LHS 6328 and the ultra-cool white dwarf PSO J1801+625, from the Pan-STARRS 1 3π survey and the Gaia Data Release 2. Follow-up spectra were collected covering a usable wavelength range of 3750–24 500 Å. Their spectra show that the white dwarf has an effective temperature of 3550 K and surface gravity of log $g$ = 7.45 ± 0.13 or log $g$ = 7.49 ± 0.13 for a CO or He core, respectively, when compared against synthetic spectra of ultra-cool white dwarf atmosphere models. The system has slightly subsolar metallicity with -0.25 < [Fe/H] < 0.0, and a spatial velocity of (U, V, W) = (-114.26 ± 0.24, 222.94 ± 0.60, 10.25 ± 0.34) km s -1 , the first radial velocity and metallicity measurements of an ultra-cool white dwarf. This makes it the first and only benchmark of its kind to date.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2026

X-Ray Polarization From the Atoll 4U 1735−44 Suggests a Low Inclination

X-ray polarimetry is a new tool capable of probing the geometry of accretion onto weakly magnetized neutron stars. Here we present the first X-ray spectro-polarimetric results from coordinated observations of the atoll source 4U 1735−44, conducted with the Imaging X-ray Polarimetry Explorer (IXPE), NICER, and NuSTAR . Over the 2–8 keV energy range, we obtained a marginal detection of polarization with the polarization degree of 1.4% ± 0.7% and polarization angle of −29◦ ± 14◦, corresponding to a 3σ upper limit on the polarization degree of 3.5%. The best-fit model to describe the spectrum comprises a thermal component associated with the accretion disk, a Comptonized black body component, and a relativistic reflection component. From the reflection model, we infer a disk inclination of ∼40◦. The spectroscopic and polarimetric properties of 4U 1735−44 are consistent with those observed in other atoll sources studied by IXPE, with its low polarization likely due to its low inclination

X-rays: binaries↗
NASA NTRS1989

Is 4U 2129 + 47 (= V1727 Cygni) a triple system?

Surprising observations of radial velocity variations and spectral type of the low-mass X-ray binary (LMXRB) 4U 2129 + 47 made from June 1987 to October 1988 are reported. Shifts in the mean radial velocity, the lack of variations in the orbital period, and the anomalous spectral type suggest that this system is a hierarchical triple with an inner boundary consisting of an LMXRB with a 5.24 hr period and an F7 V star in a much larger orbit around the inner binary. A necessary consequence of such a triple would be a cycle of about 45 yr in the mean eccentricity of the inner binary, which is consistent with the pattern of on and off states that have been observed since the 1930s.

Garcia, Michael R.↗
NASA NTRS2009

Kepler Data Validation and Follow-up Programs

The approach that the Kepler Mission uses to remove false positive events and to validate the discoveries consists of two parts; data validation (DPI) and follow up observations program (FOP). DV consists of several methods of examining the data from the spacecraft observations. First, to rule out statistical fluctuations in the data, accept only signals that show 3 or more transits and that have a total signal-to-noise ratio that exceeds 7 sigma. Second. to identify small stellar companions to the target star, we check for secondary eclipses and determine if the transit characteristics are appropriate for a planetary companion. Third, check for background binaries that are in the target aperture. Here we measure the movement of the image centroid before, during, and after the transit. If the target is producing the signal, a dimming wi11 move the image centroid in a known direction and magnitude. If the signal comes from a nearby star, the amplitude and direction of the motion wi11 be different, This test is expected to rule out the hundreds of binary signals expected from background stars. The precision of the measurement depends on the stellar fluxes and positions but can be better than 0.01 pixel; i.e., 0.04". Those candidates that pass these tests are examined using ground-based telescopes and radial velocity spectrometers. First medium precision RV is used to rule out any remaining stellar companions. Then high spatial resolution imaging is used to check for nearby stars that are in the aperture- (The Kepler apertures depend on magnitude but are of order 36 sq are sec in area.) If no stars are present that quid generate the observed signal, then the candidate goes to a large telescope such as Keck, HET, or Wi1lilam Herschel for high precision observations to get the planet mass or an upper limit to it, if there are some stars in the aperture, then the photometric observations are employed to look for the transit by cane of the confounding stars. If none are seen, then the candidate is sent to a large telescope such as Keck

William, Borucki J.↗
NASA NTRS1982

Einstein observations of BY Draconis variables and RS CVn binaries

Observations of five BY Draconis variables and four RS Canum Venaticorum systems with the Einstein Observatory are presented. All nine stars were detected. Although the BY Draconis stars have an average X-ray luminosity one to two orders of magnitude lower than the RS CVn binaries, at least three of these systems fit the X-ray/bolometric luminosity ratio-vs-period relation first described by Walter and Bowyer (1981) for RS CVn's. Since one of the BY Draconis stars is almost certainly single, this result lends strong support to the suggestion that rapid rotation, and not duplicity, is the determining factor in defining the level of stellar activity in such stars. In addition, the X-ray data are consistent with the suggestion, made by Vogt and Fekel (1979), that the BY Draconis stars are in the final stages of pre-main-sequence evolution.

Caillault, J.-P.↗
NASA NTRS1988

IUE observations of X-ray-selected stars

UV spectra for four X-ray-selected bright (V less than 10) late-type (F and G) stars have been obtained in both the long- and short-wavelength cameras of the IUE satellite. The stars were selected because they had the largest ratios of X-ray to optical luminosity for their spectral type, with known binaries being eliminated from the sample in order to determine if other mechanisms for extreme X-ray emission are present. Three of the four stars in the sample have since been observed to be binaries with radial-velocity variations consistent with periods of a few days. The fourth star, HD 142361 is a pre-main-sequence star based on the detection of Li I at a wavelength of 6707 A in absorption.

Bergoffen, Martin J.↗
DOE OSTI2024

The Evolution of Accreting Binaries: From Brown Dwarfs to Supermassive Black Holes

Circumbinary accretion occurs throughout the universe, from the formation of stars and planets to the aftermath of major galactic mergers. We present an extensive investigation of circumbinary accretion disks, studying circular binaries with mass ratios (q ≡ M 2 /M 1 ) from 0.01 to 1 and at each mass ratio probing the effects of disk thickness and viscosity. We study disks with aspect ratios H/r $\in$ {0.1, 0.05, 0.03} and vary both the magnitude and spatial dependence of viscosity. Although thin accretion disks have previously been found to promote rapid inspirals of equal-mass binaries, we find that gravitational torques become weaker at lower mass ratios and most binaries with 0.01 ≤ q ≤ 0.04 outspiral, which may delay the coalescence of black hole binaries formed from minor mergers and cause high-mass exoplanets to migrate outward. However, in a number of cases, the disks accreting onto binaries with mass ratios ~0.07 fail to develop eccentric modes, leading to extremely rapid inspirals. Variability in black hole accretion correlates with disk eccentricity, and we observe variability above the ~10% level even for mass ratios of 0.01. We demonstrate that the spatial dependence of the viscosity (e.g., α vs. constant ν) significantly affects the degree of preferential accretion onto the secondary, resolving discrepancies between previous studies. Colder circumbinary disks remain eccentric even at q ~ 0.01 and sustain deep, asymmetric cavities.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2021

The orbit and stellar masses of the archetype colliding-wind binary WR 140

We present updated orbital elements for the Wolf–Rayet (WR) binary WR 140 (HD 193793; WC7pd + O5.5fc). The new orbital elements were derived using previously published measurements along with 160 new radial velocity measurements across the 2016 periastron passage of WR 140. Additionally, four new measurements of the orbital astrometry were collected with the CHARA Array. With these measurements, we derive stellar masses of M(WR)=10.31±0.45Mꙩ and M(O)=29.27±1.14Mꙩ⁠. We also include a discussion of the evolutionary history of this system from the Binary Population and Spectral Synthesis model grid to show that this WR star likely formed primarily through mass-loss in the stellar winds, with only a moderate amount of mass lost or transferred through binary interactions.

Joshua D. Thomas↗
DOE OSTI2024

Insights from binary pulsars and laboratories into baryon number violation: Implications for GeV dark matter

Rare processes in laboratory and within astrophysical environments can be highly sensitive probes of baryon-number-violating interactions at the TeV scale. We demonstrate the power of neutron stars to constrain baryon-number violation by considering a minimal extension of the standard model involving a TeV-mass scalar mediator and a GeV scale Majorana fermion ψ . We find that a Δ B = 2 mass-loss process in binary pulsar systems via n → γ ψ and the subsequent scattering ψ n → π − K + places stringent constraints on the model parameter space. These limits will become much stronger, due to the possibility of Λ → γ ψ decays at the tree level, if the neutron star equation of state is hyperonic. We compare these constraints with ongoing and future collider experiments, n − n ¯ oscillations, and dinucleon decay searches at future large-scale neutrino experiments, finding that the binary pulsars bounds on couplings are significantly tighter for specific flavor combinations. Published by the American Physical Society 2024

baryons↗
NASA NTRS1994

HST photometry of the trapezium cluster

We have obtained images of 11 fields in the Trapezium cluster with the Planetary Camera (PC) of the Hubble Space Telescope (HST) in order to extend Herbig & Terndrup's (1986) study of this prototype, dense embedded cluster to fainter magnitudes than is possible from the ground. Using these images, we have identified 319 stars within an area of approximately 12 sq arc min corresponding roughly to a volume of approximately 0.065 cu pc assuming the cluster is approximately spherically symmetric. Our completeness limits for star identification in V-band and I-band images are V approximately = 20 and I(sub c) approximately = 19 respectively, corresponding to a mass limit of approximately 0.15 solar mass if the faintest stars have the same average A(sub v) as that estimated for the brighter stars in the cluster. We have compared the V versus V-I color-magnitude diagram derived from the HST photometry to new theoretical isochrones. Star formation in the Trapezium appears to be remarkably coeval, with greater than or = 80% of the stars having inferred ages less than 1 Myr. Over the somewhat limited mass range of the observations, there is no evidence for 'bimodal' star formation-the high- and low-mass stars appear to have the same ages. The sharp cores of the HST images and the small angular size of the PC pixels has allowed us to identify 35 new visual binaries in the cluster with separations from approximately 0.06 arc sec (approximately 26 AU) to approximately 1.0 arc sec (approximately 440 AU). For the range of binary separations that we are sensitive to, the observed binary frequency for the Trapezium is essentially identical to that estimated for field low-mass stars by Duquennoy & Mayor (1991). The most straightfoward inference from this result is that binaries in this separation are unlikely to be formed by a tidal capture process. We have also identified three stars which have associated compact nebulosity visible in the HST images. One of these star + nebulosity cases was previously identified by O'Dell, Wen, & Hu (1993)-these objects appear to form a class of objects whose circumstellar matter is being 'lit up', most likely by Theta(sup 1) Ori C, enabling the gas to be observable at both optical and radio wavelengths (Felli et al. 1993a, b). We provide a brief summary of the optical properties of the other radio sources which appear in our PC images.

Prosser, Charles F.↗
NASA NTRS1975

X-ray binaries in globular clusters

It appears to be very unlikely that primordial binaries in globular clusters have evolved to produce high-luminosity X-ray sources like the four variable sources detected by the Uhuru and OSO-7 satellites. It is suggested that the cluster X-ray sources are binaries formed by capture from the remnants of massive single stars that exploded with sufficient isotropy to remain bound in the cluster. These remnants have lurked near the centers of the clusters where the high stellar densities have favored their capture of field stars which eventually turn the remnants on as X-ray sources when the captives enter the post-main-sequence expansion phase of their evolution. A case is made for the conclusion that there is approximately one potential binary X-ray source near the center of each of the globular clusters.

Clark, G. W.↗
DOE OSTI2022

Jets from main sequence and white dwarf companions during common envelope evolution

ABSTRACT It has long been speculated that jet feedback from accretion on to the companion during a common envelope (CE) event could affect the orbital evolution and envelope unbinding process. We present global 3D hydrodynamical simulations of CE evolution (CEE) that include a jet subgrid model and compare them with an otherwise identical model without a jet. Our binary consists of a 2-M⊙ red giant branch primary and a 1- or 0.5-M⊙ main sequence (MS) or white dwarf (WD) secondary companion modelled as a point particle. We run the simulations for 10 orbits (40 d). Our jet model adds mass at a constant rate $\dot{M}_\mathrm{j}$ of the order of the Eddington rate, with maximum velocity vj of the order of the escape speed, to two spherical sectors with the jet axis perpendicular to the orbital plane. We explore the influence of the jet on orbital evolution, envelope morphology and envelope unbinding, and assess the dependence of the results on the jet mass-loss rate, launch speed, companion mass, opening angle, and accretion rate. In line with our theoretical estimates, jets are choked around the time of first periastron passage and remain choked thereafter. Subsequent to choking, but not before, jets efficiently transfer energy to bound envelope material. This leads to increases in unbound mass of up to $\sim 10{{\ \rm per\ cent}}$, as compared to the simulations without jets. We also estimate the cumulative effects of jets over a full CE phase, finding that jets launched by MS and WD companions are unlikely to dominate envelope unbinding.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

How negative feedback and the ambient environment limit the influence of recombination in common envelope evolution

ABSTRACT We perform 3D hydrodynamical simulations to study recombination and ionization during the common envelope (CE) phase of binary evolution, and develop techniques to track the ionic transitions in time and space. We simulate the interaction of a $2\, \mathrm{M_\odot }$ red giant branch primary and a $1\, \mathrm{M_\odot }$ companion modelled as a particle. We compare a run employing a tabulated equation of state (EOS) that accounts for ionization and recombination, with a run employing an ideal gas EOS. During the first half of the simulations, ∼15 per cent more mass is unbound in the tabulated EOS run due to the release of recombination energy, but by simulation end the difference has become negligible. We explain this as being a consequence of (i) the tabulated EOS run experiences a shallower inspiral and hence smaller orbital energy release at late times because recombination energy release expands the envelope and reduces drag, and (ii) collision and mixing between expanding envelope gas, ejecta and circumstellar ambient gas assists in unbinding the envelope, but does so less efficiently in the tabulated EOS run where some of the energy transferred to bound envelope gas is used for ionization. The rate of mass unbinding is approximately constant in the last half of the simulations and the orbital separation steadily decreases at late times. A simple linear extrapolation predicts a CE phase duration of ${\sim}2\, {\rm yr}$, after which the envelope would be unbound.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Blue Straggler Population of the Open Clusters Trumpler 5, Trumpler 20, and NGC 2477

We present a study based on Gaia DR2 of the population of blue straggler stars in the open clusters Trumpler 5, Trumpler 20, and NGC 2477. All candidates were selected according to their position in the color–magnitude diagram, their proper motion components, and their parallax. We also looked for yellow stragglers, i.e., possible evolved blue stragglers. We found that Trumpler 5 hosts a large blue straggler star population, which allowed us to analyze their radial distribution as a probe of the cluster’s dynamical status. The blue straggler star distribution was compared with that of red giant branch stars to evaluate mass segregation. Our results indicate that blue straggler stars are not more centrally concentrated than red giant branch stars stars in any of the clusters. The radial distribution of blue straggler stars in Trumpler 5 is flat. Additionally, using a multi-epoch radial velocity survey conducted with the high-resolution spectrograph FLAMES/GIRAFFE at the Very Large Telescope, we measured the radial velocities of a sample of stragglers to compare with the mean radial velocity and velocity dispersion of the clusters. Based on the radial velocity variations for different epochs, we roughly classified these stars as possible close or long-period binaries.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Stellar and Accretion Disk Parameters of the Close Binary HD 50526

We present a photometric and spectroscopic study of HD 50526, an ellipsoidal binary member of the group Double Periodic Variable stars. Performing data mining in photometric surveys and conducting new spectroscopic observations with several spectrographs during 2008–2015, we obtained orbital and stellar parameters of the system. The radial velocities were analyzed with the genetic PIKAIA algorithm, whereas Doppler tomography maps for the Hα and Hβ lines were constructed with the Total Variation Minimization code. An optimized simplex algorithm was used to solve the inverse problem adjusting the light curve with the best stellar parameters for the system. We find an orbital period of 6.ͩ701 ± 0.ͩ001 and a long photometric cycle of 191 ± 2 days. We detected the spectral features of the coldest star and modeled it with a logg=2.79±0.02 dex giant of mass 1.13 ± 0.02 M {sub ⊙} and effective temperature 10500 ± 125 K. In addition, we determine a mass ratio q = 0.206 ± 0.033 and that the hot star is a B-type dwarf of mass 5.48 ± 0.02 M {sub ⊙}. The V-band orbital light curve can be modeled including the presence of an accretion disk around the hotter star. This fills the Roche lobe of the hotter star and has a radius 14.74 ± 0.02 R {sub ⊙} and the temperature at the outer edge is 9400 K. Two bright spots located in the disk account for the global morphology of the light curve. The Doppler tomography maps of Hα and Hβ reveal complex structures of mass fluxes in the system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Orbital Modulation of Gamma Rays from PSR J2339-0533

In this work, we report on orbital modulation of the 100–600 MeV gamma-ray emission of the P B = 4.6 hr millisecond pulsar binary PSR J2339-0533 using 11 yr of Fermi Large Area Telescope data. The modulation has high significance (chance probability p ≈ 10 -7 ), is approximately sinusoidal, peaks near pulsar superior conjunction, and is detected only in the low-energy 100–600 MeV band. The modulation is confined to the on-pulse interval, suggesting that the variation is in the 2.9 ms pulsed signal itself. Additionally, this contrasts with the few other known systems exhibiting GeV orbital modulations, as these are unpulsed and generally associated with beamed emission from an intrabinary shock. The origin of the modulated pulsed signal is not yet clear, although we describe several scenarios, including Compton upscattering of photons from the heated companion. This would require high coherence in the striped pulsar wind.

79 ASTRONOMY AND ASTROPHYSICS↗