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At least 127 records · Page 7
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DOE OSTI2023

Hours-long Near-UV/Optical Emission from Mildly Relativistic Outflows in Black Hole–Neutron Star Mergers

The ongoing LIGO–Virgo–KAGRA observing run O4 provides an opportunity to discover new multimessenger events, including binary neutron star (BNS) mergers such as GW170817 and the highly anticipated first detection of a multimessenger black hole–neutron star (BH–NS) merger. While BNS mergers were predicted to exhibit early optical emission from mildly relativistic outflows, it has remained uncertain whether the BH–NS merger ejecta provides the conditions for similar signals to emerge. We present the first modeling of early near-ultraviolet/optical emission from mildly relativistic outflows in BH–NS mergers. Adopting optimal binary properties, a mass ratio of q = 2, and a rapidly rotating BH, we utilize numerical relativity and general relativistic magnetohydrodynamic (GRMHD) simulations to follow the binary's evolution from premerger to homologous expansion. We use an M1 neutrino transport GRMHD simulation to self-consistently estimate the opacity distribution in the outflows and find a bright near-ultraviolet/optical signal that emerges due to jet-powered cocoon cooling emission, outshining the kilonova emission at early time. The signal peaks at an absolute magnitude of ~–15 a few hours after the merger, longer than previous estimates, which did not consider the first principles–based jet launching. By late 2024, the Rubin Observatory will have the capability to track the entire signal evolution or detect its peak up to distances of ≳1 Gpc. In 2026, ULTRASAT will conduct all-sky surveys within minutes, detecting some of these events within ~200 Mpc. The BH–NS mergers with higher mass ratios or lower BH spins would produce shorter and fainter signals.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1981

Did ice streams carve Martian outflow channels

Outflow channels on Mars are long sinuous linear depressions that occur mostly in the equatorial area (+ or - 30 deg latitude). They differ from small valley networks by being larger and arising full-born from chaotic terrains. Outflow channels resemble terrestrial stream beds, and their origin has generally been attributed to water in catastrophic floods or mudflows. The problem of channel origin is examined here from the perspective of erosional characteristics and the resultant landforms created by former and present-day ice streams and glaciers on earth. From morphologic comparisons, an ice-stream origin seems equally well suited to explain the occurrences and form of the outflow channels on Mars, and in contrast with the hydraulic hypothesis, ice streams and ice sheets produce terrestrial features of the same scale as those observed on Mars.

Lucchitta, B. K.↗
NASA NTRS1982

High velocity gas outflow from the nova-like variable LSI 55 deg -8

Low and high dispersion International Ultraviolet Explorer observations and measurements of the optical brightness of LSI 55-8 taken on 5 December, 1981 are analyzed. The presence of the C IV resonance doublet showing a variable P Cygni type of profile with a blue shifted absorption component along with the blue shifted absorption features of the high temperature ions indicate the existence of outflowing hot plasma (i.e., a wind). An upper limit of the mass outflow rate was established from the shot wavelength edge of the C IV absorption. The normalized C IV profile is shown o be variable with the largest changes occurring in the relative strength and shape of the emission component. These changes appear to be systematic, and may be associated with the changing projection of the outflowing hot plasma against the disk as a function of orbital motion. LSI 55-8 demonstrates most of the spectral and photometric characteristics exhibited by the nova like, UX UMa type variables, as well as with the dwarf novae in outburst or standstill. The high accretion rate inferred from fitting the Williams theoretical disk model fluxes to IUE data support the hypothesis that LSI 55-8 and related nova like systems are in a state of prolonged outburst.

Guinan, E. F.↗
NASA NTRS1982

The energetic molecular outflow near AFGL 961 - Millimeter-wave and infrared observations

Sensitive millimeter-wave C-12O line observations and near-infrared hydrogen recombination line observations of AFGL 961 are reported and analyzed. The observations show that the high-velocity flow has a maximum extent of at least six arcmin or 1.9 pc at the distance of AFGL 961. The flow is anisotropic and the emission profiles are asymmetric in velocity. The mass of the gas involved in the flow is determined to be approximately 19 solar masses, and the kinetic energy of this gas is estimated to be about 8 x 10 to the 46th ergs. These observations are interpreted as evidence that an energetic bipolar outflow of molecular gas is occurring near AFGL 961. Comparison of infrared recombination line data, radio continuum, and CO observations shows that a strong, ionized, stellar wind would not be a sufficient force to drive the outflow. The effects of the outflow on the surrounding molecular cloud was also investigated.

Lada, C. J.↗
NASA NTRS1984

Superthermal ionospheric outflows

In recent years observations have shown that the terrestrial ionosphere serves as a significant source of the hot plasma in the magnetosphere. These findings imply that cold plasma flows upward to great altitudes and at some point along the way gains energies much larger than typical ionospheric values. The present investigation is mainly concerned with observations of ionospheric outflows at energies higher than those predicted by ambipolar wind models but lower than those associated with keV auroral ion acceleration, giving particular attention to the energy range from a few to a few hundred electron volts. The ion flows in the energy range intermediate between polar wind and keV auroral ion beams are called superthermal ion outflows. It is shown that recent observations of superthermal ion outflows from the terrestrial ionosphere are related to theoretical models of the topside ionosphere.

Moore, T. E.↗
NASA NTRS1985

Condensation onto grains in the outflows from mass-losing red giants

In the outflows from red giants, grains are formed which are driven by radiation pressure. For the development of a model of the outflows, a detailed understanding of the interaction between the gas and dust is critical. The present investigation is concerned with condensation processes which occur after the grains nucleate near the stars. A physical process considered results from the cooling of the grains as they flow away from the star. Molecules which initially do not condense onto the grains can do so far from the star. It is shown that for some species this effect can be quite important in determining their gas-phase abundances in the outer circumstellar envelope. One of the major motivations of this investigation was provided by the desire to understand the physical conditions and molecular abundances in the outflows from the considered stars.

Jura, M.↗
NASA NTRS1985

Energetic auroral and polar ion outflow at DE 1 altitudes Magnitude, composition, magnetic activity dependence, and long-term variations

Data acquired from the Dynamics Explorer I Energetic Ion Composition Spectrometer in the period from September 1981 to May 1984 are used to determine the magnitude of the terrestrial ion outflow in the 0.01-17 keV/el range. The data are also employed to investigate the mass composition and topology (local time and invariant latitude distributions) of the ion outflow, as well as the outflow's magnetic activity dependence and long-term variation. The relative importance of auroral versus polar cap upflowing ions as a source of energetic plasma for various parts of the magnetosphere is examined.

Yau, A. W.↗
NASA NTRS1986

Evidence of high densities and ion outflows in the polar cap during the recovery phase

The composition and characteristics of the polar cap plasma for an Oct. 14, 1981 outflow of polar wind ions are examined using data from the DE 1 satellite. The on-board instruments included a plasma wave instrument, a retarding ion mass spectrometer (RIMS) and a high altitude plasma instrument (HAPI). The outflow took place at an altitude of about 19,000 km at a magnetic local time of about midnight. The total plasma density measured was about 50/cu cm, which was an order of magnitude higher than normally recorded at that location and altitude. The background hydrogen plasma was disturbed by highly collimated flows of hydrogen and oxygen ions. The H(+) ions had a mean energy of 0.15 eV and a density of 6-10/cu cm. The O(+) ions had an average density of 20/cu cm and a temperature of 0.26 eV. The total flux of outflowing H(+) and O(+) was about 10 million/sq cm per sec. The HAPI data indicated that the O(+) ions appeared in the dayside ionosphere and the H(+) ions detected by the RIMS originated in the nightside polar cap.

Gallagher, D. L.↗
NASA NTRS1986

Jets, mass outflows and disks associated with young stellar objects

Over the past 3 years, a series was obtained of the CCD images of regions surrounding young stellar objects (YSO's) located in a variety of environments with the goal of providing a census of the properties of mass outflows associated these objects. A catalog describing the optical morphology and kinematics of 38 mass outflows associated with young stellar objects (YSOs) was completed. The direct detection was reported of disks surrounding HL Tau and LI551/IRS 5 -- both sources of optical jets and large-scale mass outflows. In each case, the disk dimensions are on the order of several hundred astronomical units and the disk dust masses approximately 10 to the -7th power solar masses. A program aimed at indirect detection of circumstellar disks associated with YSOs was started. The technique involves comparison of an observed bolometric luminosity (L(bol)) with an independent measure of the true luminosity (L(spec)) of a YSO which derives from the observed strengths of surface-gravity-sensitive spectral features.

Strom, S. E.↗
NASA NTRS1986

Accelerated auroral and polar-cap ions - Outflow at DE-1 altitudes

Observations of terrestrial-ion outflow obtained at 0.01-17 keV with the DE-1 energetic-ion composition spectrometer during 1981-1984 are compiled in graphs and analyzed. Long-term variations of the O(+) outflow rate - but not of the H(+) rate - at both magnetically active and quiet times are shown to be well correlated with the declining solar radio flux, the rate in 1983-1984 being only about half that for 1981-1982. Both outflow rates are found to increase exponentially with the Kp index, being 30 and 5 times greater, respectively, at Kp = 6 or more than at Kp = 0. The role of perpendicular ion-acceleration mechanisms at low altitudes is discussed.

Yau, A. W.↗
NASA NTRS1987

Kinematic properties of the neutral gas outflow from comet P/Halley

High-resolution infrared spectra of H2O in Comet Halley, obtained by the Kuiper Airborne Observatory, were used to characterize the dynamics of the neutral gas outflow from the comet. The spatial distribution and the expansion velocity of the H2O molecules were deduced from the positions, widths, and shapes of the H2O lines. The character of line profiles suggested that the H2O distribution was anisotropic in the circular field-of-view of aproximately 10,000 radius centered on the nucleus. Direct observations of the H2O spatial brightness distribution showed that the outflow was concentrated in the sunward direction (although some H2O emission was also detected in the tail). An obvious property of the gas outflow from the Comet P/Halley was its variability. The specific intensities of the H2O lines demonstrated that the gas production from the comet varied significantly on many time scales; there were pre- and postperihelion asymmetries, day-to-day variations, and outbursts.

Larson, H. P.↗
NASA NTRS1988

An unusual outflow around IRAS 16293-2422

The dense dusty molecular cloud core associated with the unusual protostellar source IRAS 16293-1422 (IRAS 1629A) was observed in the J = 2-1 transition of (C-12)O and (C-13)O. These observations indicate that IRAS 1629A is a source of an unusual high-velocity molecular outflow with four separate emission lobes. The morphology and velocity structure of the lobes may suggest the presence of a dual jet or double bipolar outflow system originating from the vicinity of IRAS 1269A. These observations resolve the outflowing gas into numerous high-velocity clumps which are either being continuously accelerated from low to high velocity along the entire length of the flow or are undergoing free-flow expansion.

Walker, Christopher K.↗
NASA NTRS1988

Molecular outflows in the Monoceros OB1 molecular cloud

Observations of J = 1-0 emission from CO in nine suspected molecular outflows in the Monoceros OB1 molecular cloud are presented. It is found that, if the five sources which are confirmed to be outflows conserve momentum as they evolve, they will sweep up at least 0.6 percent of the mass of the entire cloud before coming into pressure equilibrium with the ambient gas. This number indicates that it should take at most 160 episodes of similar outflow activity in order to sweep up the bulk of the Mon OB1 cloud to highly supersonic speeds.

Margulis, Michael↗
NASA NTRS1989

Time dependent inflow-outflow boundary conditions for 2D acoustic systems

An analysis of the number and form of the required inflow-outflow boundary conditions for the full two-dimensional time-dependent nonlinear acoustic system in subsonic mean flow is performed. The explicit predictor-corrector method of MacCormack (1969) is used. The methodology is tested on both uniform and sheared mean flows with plane and nonplanar sources. Results show that the acoustic system requires three physical boundary conditions on the inflow and one on the outflow boundary. The most natural choice for the inflow boundary conditions is judged to be a specification of the vorticity, the normal acoustic impedance, and a pressure gradient-density gradient relationship normal to the boundary. Specification of the acoustic pressure at the outflow boundary along with these inflow boundary conditions is found to give consistent reliable results. A set of boundary conditions developed earlier, which were intended to be nonreflecting is tested using the current method and is shown to yield unstable results for nonplanar acoustic waves.

Watson, Willie R.↗
NASA NTRS1989

The outflow speed of the coma of Halley's comet

Data concerning the outflow speed of the coma of Comet Halley are studied in relation to a generalization of the coupled pure-gas-dynamic/Monte Carlo model of Combi and Smyth (1988) to include the dusty-gas dynamics of the inner coma. Measurements made by the Giotto neutral-gas spectrometer, IR water observations from the Kuiper Airborne Observatory, and Doppler radio line profiles of HCN and OH are used to examine the radial dependence of the outflow speed, the asymmetry in the outflow speed, and the overall heliocentric distance dependence of the Doppler profiles, respectively. The results suggest that the model makes it possible to understand the gross long-term behavior and radial structure of the dynamics of the cometary coma.

Combi, Michael R.↗
NASA NTRS1990

Images of shock-excited molecular hydrogen in young stellar outflows

High-angular resolution molecular hydrogen (H2) v = 1-0 S(1) line images of several well-known molecular outflow sources (DR 21, NGC 2071, HH 7-11, and HH 12) are presented. It is found that all of the outflow sources possess highly collimated jets of shock-excited gas that are extremely clumpy and often consist of bright knots that are placed periodically along the jet axis. The H2 emission-line jets are significantly more collimated than their corresponding CO outflows and remain collimated to large distances from their driving source. In DR 21 and NGC 2071, the H2 jets appear to become more collimated with increasing distance from the central source, suggesting that they are pressure-confined by the ambient cloud medium. In HH 7-11 and HH 12 the shock-excited ionized and molecular components are spatially coincident and appear to be of comparable shape and size; this suggests that the shocked gas is highly mixed on scales significantly smaller than the current spatial resolution.

Garden, Rognvald P.↗
NASA NTRS1990

Starburst outflows from nearby galaxies

Starburst outflows from NGC 5461, 1569 and M82 are discussed. The Sc I galaxy, M101, is reknowned for the kpc-size superassociations of star clusters and HII regions that dominate its spiral arms. NGC 5461 is one of the brightest of these superassociations, rivaling the Large Magellanic Cloud in H alpha luminosity. The NGC 5461 superassociation is dominated by a single unresolved HII region of outstanding luminosity (approx. 1000 Orion nebulae). Detailed examination of corresponding continuum images indicates that only the southern plume has any sort of stellar counterpart. The other plumes are clearly diffuse with no underlying hot stars. An image of NGC 1569 is discussed. Besides showing the peculiar arm noted by Zwicky (1971) and the filamentary extensions to the North and South (as noted by Hodge 1974), this image also reveals two arc-like features of diffuse ionized gas to the South. Both arcs are concentric with the bright center of the galaxy - where the super star clusters, A and B are located. The inner arc (Arc 1) appears to follow the same curve as the SW arm thus suggesting that the two features represent limb-brightened fragments of vast superbubble that was blown out by a central starburst sometime in the past. As the classic starburst galaxy, M82 displays all the luminous hallmarks of intense high-mass star formation and outflow activity. The diffuse H alpha and x ray emitting gas along the minor axis provides especially good evidence for a bipolar outflow of hot gas which is shock heating the swept-up interstellar medium (ISM) to temperatures of approx. 10(exp 4) K. An image shows the H alpha emission within the disk and along the minor axis. Another image shows the same field in the light of near-infrared. Both figures are based on charge coupled device images taken with the McGraw-Hill 1.3 m telescope (Waller 1989). The longer wavelength emission clearly shows a more extended morphology along the major axis. The morphological discrepancy is most likely due to the greater obscuration by dust suffered by the H alpha photons. A third image shows the map of visual extinction that researchers derive from a pixel-by-pixel comparison of the (SIII) and H alpha fluxes. The greatest extinctions are evident along an arc that includes two especially obscured regions on opposite sides of the bursting nucleus.

Waller, William H.↗
NASA NTRS1991

Vorticity-streamfunction formulation of unsteady incompressible flow past a cylinder - Sensitivity of the computed flow field to the location of the outflow boundary

The influence of the location of the outflow computational boundary on the unsteady incompressible flow past a circular cylinder at Reynolds number 100 is examined. The vorticity-streamfunction formulation of the Navier-Stokes equations is used in all computations. Two types of outflow boundary conditions are subjected to a series of tests in which the domain length is gradually reduced. The traction-free condition performs well in most cases and allows the outflow boundary to be located as close as 6.5 cylinder diameters from the body. The other boundary condition type is not as forgiving, but has the advantage of being simpler to implement and can still provide reasonably accurate solutions. It is also observed that both condition types can influence the flow field strongly and globally when the boundary is brought closer than 2.5 diameters from the body. In such cases the temporal periodicity of the solution is lost.

Behr, M.↗