SEARCH · Search NASA

Results for “Stellar bow shocks”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

36 records · Page 2

All sources NASA NTRS DOE OSTI

NASA NTRS1994

Farby-Perot observations and new models of the HH 47A and HH 47D bow shocks

We present new models for the HH 47A and HH 47D bow shocks based on line flux and velocity maps obtained with an imaging Fabry-Perot spectrometer. We confirm that HH 47A and HH 47D each show a bow shock/Mach disk morphology, and that velocity variability in the outflow can account for the observed structures. While it was suggested a decade ago that the inner working surface HH 47A appears to be traveling into the wake of HH 47D, we find kinematic evidence that the outer bow shock HH 47D is also not the primary ejection event in the outflow but follows in the wake of previously ejected material. By comparing the observed line ratios and line profiles to those predicted by our bow shock models, we find that both bow shocks have substantially lower shock velocities than their space motions would imply, and that the emission from each bow shock is systematically blueshifted from the rest-frame velocity of the ambient emission, indicating a comoving preshock medium. We derive kinematic ages of approximately 1150 yr for HH 47D and approximately 550 yr for HH 47A, which implies that the stellar driving source may undergo repetitive eruptions similar to FU Orionis-type outbursts every several hundred years. This timescale is similar to estimates made by Reipurth and collaborators for the separation between major outbursts in the HH 34 and HH 111 stellar jets.

Morse, Jon A.↗

NASA NTRS1977

Discovering Jupiter. II

Data derived from Pioneer 10 and Pioneer 11 and other sources on the Jovian magnetosphere, the circum-Jovian radiation belts, and Jupiter's radio emission are presented at some length, descriptions are given of the principal Jovian satellites (Io, Europa, Ganymede, Callisto), and inferences are drawn on the origin of the planet and its place in the solar system. The inner, middle, and outer regions of the magnetosphere, the bow shock wave, and the particularly heavy intensity of the inner radiation belt region (within 1.44 million km of the planet) are discussed. All of the major satellites except Callisto lie immersed in the intense radiation belts. Jupiter's failure to become a stellar companion to the sun, Io's action in 'switching on' Jovian radio emission, and other Pioneer discoveries relating to asteroids, the solar system in general, and trans-Jovian space, are discussed

Source record↗

NASA NTRS1994

Shocked molecular gas around the extremely young source IRAS 03282+3035

We present observations of the shock tracers H2 and SiO around the young stellar object IRAS 03282+3035. This unusual low-luminosity (L approximately = 2 solar luminosity) source drives a strong highly collimated CO outflow, and it is one of the youngest stellar objects known so far. The near-infrared H2 emission, tracing 2000 K gas, comes from extremely high velocity CO bullets along the axis of the blueshifted lobe of the outflow. The millimeter SiO emission, tracing roughly 100 K gas, arises from lower velocity material at the end of the outflow lobe. The lack of high-temperature and high-velocity gas at the end of the outflow lobe indicates there is no not bow shock at the outflow termination. In the context of current jet models this appears to rule out a bow shock driven by a steady state jet. Possible explanations for the structure include a time-dependent jet or a jet dominated by turbulent entrainment.

Bachiller, R.↗

NASA NTRS1993

HST imaging of hydrogen-poor ejecta in Abell 30 and Abell 78 - Wind-blown cometary structures

HST Faint Object Camera images of hydrogen-poor gas in the planetary nebulae A30 and A78 have revealed remarkable 'cometary' structures in the O III 5007-A forbidden line. Most of these cometary structures, consisting of compact (0.15-0.5 arcsec) knots with radial tails several arcsec in length, are located in an equatorial plane in both nebulae. In addition, two bright, compact (0.3 arcsec) polar knots are present in A30, one of them forming a bow shock. Corresponding polar features in A78 are more diffuse. The central stars of both nebulae have energetic winds which are most likely responsible for the 'cometary' knot morphology. We interpret this morphology in terms of dense (several thousand electrons per cu cm) H-poor condensations whose outer expanding layers are swept outward by stellar winds. Photoionization modeling indicates that while dense knot cores are mostly heated by atomic photoionization, expanding tenuous gas is heated by photoelectrons ejected from abundant dust grains. Our models predict steep temperature gradients for which there is observational evidence and possible abrupt phase transitions in the expanding gas.

Borkowski, Kazimierz J.↗

NASA NTRS1992

Identification of the nebula G70.7 + 1.2 as a bow shock powered by a pulsar/Be-star binary

New data are presented here that firmly establish the nonthermal nature of the radio emission from the enigmatic radio and optical nebula G70.7 + 1.2. H-alpha and forbidden O I Fabry-Perot observations are used to argue that the extended optical emission from the nebula arises from a bow shock powered by a mass-losing luminous star moving supersonically through dense gas. The strong nonthermal radio emission from the object is then explained as the shocked relativistic wind from a pulsar, which is proposed here as a companion to the Be star. The coincidence of the optical and radio emission requires the pulsar and stellar winds to be mixed together. The system has a large overall velocity of about 60 km/s which is inexplicable in all other models but which is typical of binary pulsars.

Kulkarni, S. R.↗

NASA NTRS1993

Interaction of NGC 2276 with the NGC 2300 group - Fabry-Perot observations of the H-alpha velocity field

We report kinematic observations of H-alpha emission from the spiral galaxy NGC 2276 obtained with a Fabry-Perot Camera. The 'bow shock' appearance and enhanced star formation in NGC 2276 have been attributed by Mulchaey et al. (1993) to a ram-pressure interaction with the dense IGM detected in ROSAT observations of the NGC 2300 group of galaxies. Along the 'bow shock' limb of the galaxy, we observe strong H-alpha emission and significant kinematic perturbations located immediately interior to an abrupt decrease in the scale length of the optical disk. Although ram-pressure forces may be important in the evolution of the outer gaseous disk, the peculiar kinematics and the truncation in the stellar disk are difficult to explain in a ram-pressure model; a more likely cause is tidal interaction, probably with the elliptical galaxy NGC 2300.

Gruendl, Robert A.↗

NASA NTRS1994

Additional constraints on circumstellar disks in the Trapezium Cluster

We discuss the new constraints on the population of compact ionized sources in the Trapezium Cluster thought to arise from the ionization by the central OB stars of circumstellar disks around low-mass pre-main sequence stars. We present new Hubble Space Telescope (HST) Planetary Camera observations of two of these candidate disk sources, resolving extended nebulosity around them. One source shows a small-scale (greater than or approximately = 100 AU) bow-shock structure, previously seen on larger scales by O'Dell et al. We show that the circumstellar disk model is the most likely one for the majority of sources, although is remains plausible that some of the larger objects could be equilibrium globules. We combine the most complete censuses of compact radio sources and stars in the core region to derive the fraction of the stellar population that may be associated with a circumstellar disk. Our estimate of 25%-75% is comparable to that found for pre-main sequence (PMS) stars in the Taurus-Auriga dark clouds, indicating that the dense cluster environment of the Trapezium has not drastically reduced the frequency of disks seen around PMS stars.

Stauffer, John R.↗

NASA NTRS1994

Additional constraints on circumstellar disks in the Trapezium Cluster

We discuss new constraints on the population of compact ionized sources in the Trapezium Cluster thought to arise from the ionization by the central OB stars of circumstellar disks around low-mass pre-main sequence stars. We present new HST Planetary Camera observations of two of these candidate disk sources, resolving extended nebulosity around them. One source shows a small-scale (greater than 100 AU) bow-shock structure, previously seen on larger scales by O'Dell et al. We show that the circumstellar disk model is the most likely one for the majority of sources, although it remains plausible that some of the larger objects could be equilibrium globules. We combine the most complete censuses of compact radio sources and stars in the core region to derive the fraction of the stellar population that may be associated with a circumstellar disk. Our estimate of 25-75 percent is comparable to that found for PMS stars in the Taurus-Auriga dark clouds, indicating that the dense cluster environment of the Trapezium has not drastically reduced the frequency of disks seen around pre-main sequence stars.

Stauffer, John R.↗

NASA NTRS1998

A Radio-Jet-Galaxy Interaction in 3C441

Multi-wavelength imaging and spectroscopy of the zeta = 0.708 radio galaxy 3C441 and a red aligned optical/infrared component are used to show that the most striking aspect of the radio-optical "alignment effect" in this object is due to the interaction of the radio jet with a companion galaxy in the same group or cluster. The stellar population of the red aligned continuum component is predominately old, but with a small post-starburst population superposed, and it is surrounded by a low surface- brightness halo, possibly a face-on spiral disc. The [OIII]500.7/[OII]372.7 emission line ratio changes dramatically from one side of the component to the other, with the low-ionisation material apparently having passed through the bow shock of the radio source and been compressed. A simple model for the interaction is used to explain the velocity shifts in the emission line gas, and to predict that the ISM of the interacting galaxy is likely to escape once the radio source bow shock has passed though. We also discuss another, much fainter, aligned component, and the sub-arcsecond scale alignment of the radio source host galaxy. Finally we comment on the implications of our explanation of 3C441 for theories of the alignment effect.

Lacy, Mark↗

NASA NTRS2001

The CHANDRA HETGS X-ray Grating Spectrum of Eta Carinae

Eta Carinae may be the most massive and luminous star in the Galaxy and is suspected to be a massive, colliding wind binary system. The CHANDRA X-ray observatory has obtained a calibrated, high-resolution X-ray spectrum of the star uncontaminated by the nearby extended soft X-ray emission. Our 89 ksec CHANDRA observation with the High Energy Transmission Grating Spectrometer (HETGS) shows that the hot gas near the star is non-isothermal. The temperature distribution may represent the emission on either side of the colliding wind bow shock, effectively 'resolving' the shock. If so, the pre-shock wind velocities are approximately 700 and 1800 km/s in our analysis, and these velocities may be interpreted as the terminal velocities of the winds from 71 Carinae and from the hidden companion star. The forbidden-to-intercombination line ratios for the He-like ions of S, Si, and Fe are large, indicating that the line forming region lies far from the stellar photosphere. The iron fluorescent line at 1.93 angstroms, first detected by ASCA, is clearly resolved from the thermal iron line in the CHANDRA grating spectrum. The Fe fluorescent line is weaker in our CHANDRA observation than in any of the ASCA spectra. The CHANDRA observation also provides the first high-time resolution lightcurve of the uncontaminated stellar X-ray emission from 77 Carinae and shows that there is no significant, coherent variability during the CHANDRA observation. The 77 Carinae CHANDRA grating spectrum is unlike recently published X-ray grating spectra of single massive stars in significant ways and is generally consistent with colliding wind emission in a massive binary.

Corcoran, M. F.↗

NASA NTRS1993

Observations of entrainment and time variability in the HH 47 jet

We present new Fabry-Perot images of the HH 47 jet that show the first clear evidence for entrainment in a jet from a young star. The material in the jet moves faster down the axis of the flow and slower at the edges, similar to viscous flow in a pipe. The higher excitation lines occur along the edges of the jet, as expected if entrainment accelerates and heats the ambient material. We confirm previous observations of multiple bow shocks in this system. Together, time variability and entrainment produce much of the observed shock-excited gas in this object. Our data show that the 'wiggles' along the jet are not caused by jet material tied to a spiraling magnetic field, but instead result from time variability, variable ejection angles, or inhomogeneities in the flow. The gas entrained in the HH 47 jet may be atomic; our results do not provide direct evidence that stellar jets drive molecular outflows.

Hartigan, Patrick↗

NASA NTRS1984

A high-resolution study of Herbig-Haro objects 1 and 2

Observations have been conducted of Herbig-Haro objects 1 and 2 with high spectral and spatial resolution in order to test shock models for the line emission. A detailed bow shock model has been constructed which yields line widths and optical and UV spectra in reasonable agreement with observation for maximum shock velocities approximately 200 km/s. Such velocities are comparable to the transverse velocities of the knots in HH 1 and 2 inferred from proper motion studies. The observations suggest that HH objects are rapidly moving, dense clouds shocking with less dense interstellar medium. The large energy requirements of these objects, combined with their small apparent size as seen from the exciting star, seem to require unreasonably large stellar mass loss rates. However, it is possible that the HH objects subtended a much larger solid angle at the star when originally accelerated.

Hartmann, L.↗

NASA NTRS1992

The 0623 + 71 bow shock nebula

Deep radio continuum and deep narrow-band optical emission-line images showing the cataclysmic variable 0623 + 71 engulfed in a bow shock morphology are presented. The limb-brightened H-alpha, forbidden N II and 6 cm radio continuum emission regions define the global nebular morphology, extending to much greater spatial distances than the apex-confined forbidden O III. These morphologies are consistent with shock excitation. Complementary spectroscopy (3400-7400 A) is presented for the apex and east and west limbs of the bow shock, yielding diagnostic emission-line parameters which also indicate shock excitation. Moreover, archival IUE spectra (1200-2000 A) suggest that 06231 + 71 may be in a standstill phase. A mass-loss rate of about 1.4 x 10 exp -11 solar masses/yr and a total nebular mass of about 2.4 x 10 exp -3 solar masses are derived. Thus the nebula, by virtue of its small mass and shock excited line emission, is not a planetary nebula; it is simply a cataclysmic binary system with a strong stellar wind moving supersonically with respect to the interstellar medium.

Hollis, J. M.↗

NASA NTRS1991

Plasma wave generation near the inner heliospheric shock

There is mounting evidence that the Voyager 1 and 2 and Pioneer 11 spacecraft may approach the inner (termination) heliospheric shock near the end of this century. It is argued here, by analogy with planetary bow shocks, that energetic electrons backstreaming from the heliospheric shock along the magnetic field should be unstable to the generation of Langmuir waves by the electron beam instability. Analytic expressions for the cutoff velocity, corresponding to the beam speed of the electrons backstreaming from the shock, are derived for a standard solar wind model. At the front side of the heliosphere the maximum beam velocity is expected to be at the meridian passing through the nose of the shock, which is assumed to be aligned with the Very Local Inter-Stellar Medium flow. This foreshock region and the associated Langmuir waves are relevant to both the expected in situ observations of the heliospheric boundaries, and to the low-frequency (2-3 kHz) radio emissions observed by the Voyager spacecraft in the outer heliosphere. Provided that these radio emissions are generated by Langmuir waves, the minimum Langmuir wave electric fields at the remote source are estimated to be greater than about 3 - 30 microV/m.

Macek, W. M.↗

NASA NTRS2022

Eta Carinae: An Evolving View of the Central Binary, Its Interacting Winds and Its Foreground Ejecta

FUV spectra of η Car, recorded across two decades with HST/STIS, document multiple changes in resonant lines caused by dissipating extinction in our line of sight. The FUV flux has increased nearly tenfold, which has led to increased ionization of the multiple shells within the Homunculus and photodestruction of H 2 . Comparison of observed resonant line profiles with CMFGEN model profiles allows separation of wind–wind collision and shell absorptions from the primary wind P Cygni profiles. The dissipating occulter preferentially obscured the central binary and interacting winds relative to the very extended primary wind. We are now able to monitor changes in the colliding winds with orbital phase. High-velocity transient absorptions occurred across the most recent periastron passage, indicating acceleration of the primary wind by the secondary wind, which leads to a downstream, high-velocity bow shock that is newly generated every orbital period. There is no evidence of changes in the properties of the binary winds.

Massive stars↗

NASA NTRS1992

Herbig-Haro objects in the receding lobe of the L 1551 outflow

A spectrum has been obtained of two Herbig-Haro objects which are seen against the receding lobe of the bipolar outflow within the dark cloud Lynds 1551. Positive heliocentric velocities up to 90 km/s have been measured from the H-alpha line which point to an association of these emission knots with the embedded infrared source L 1551-IRS 5 rather than with other young stellar objects in this part of the sky. There is a velocity range of 50-100 km/s within each object. (S II) lambda 6716 is also detected at a strength of about 50 pct of H-alpha. Along the entire length of the slit there is broad H-alpha emission with strength about four times that normally seen in emission from the night sky. This feature partially resolves into two components, one of which we suggest is from the general Galactic field, and the other from extended bow-shock emission.

Graham, J. A.↗

NASA NTRS1990

Hydrodynamic simulations of stellar wind disruption by a compact X-ray source

This paper presents two-dimensional numerical simulations of the gas flow in the orbital plane of a massive X-ray binary system, in which the mass accretion is fueled by a radiation-driven wind from an early-type companion star. These simulations are used to examine the role of the compact object (either a neutron star or a black hole) in disturbing the radiatively accelerating wind of the OB companion, with an emphasis on understanding the origin of the observed soft X-ray photoelectric absorption seen at late orbital phases in these systems. On the basis of these simulations, it is suggested that the phase-dependent photoelectric absorption seen in several of these systems can be explained by dense filaments of compressend gas formed in the nonsteady accreation bow shock and wake of the compact object.

Blondin, John M.↗

NASA NTRS1995

Photoevaporating stellar envelopes observed with Rayleigh beacon adaptive optics

We present H-alpha and I-band images of a approximately 1 min diameter field centered on theta(sup 1) C Ori made with a unique adaptive optics system that uses either starlight or Rayleigh-backscattered laser light to correct for atmospheric wavefront distortion. Approximately one-half of the stars in this region are positionally associated with knots of ionized gas, which are interpreted as photoevaporating envelopes of low-mass stars. The acronyms 'partially ionized globule' (PIGs), external ionized (accretion) disks in the environs of radiation sources (EIDERs), or protoplanetary disks (ProPlyDs) all refer to these same knots. The H-alpha fluxes of the PIGs are proportional to their 2 cm radio continumm flux densities, and for nearly all the ionized knots, the 2 cm brightness temperatures are consistent with theta(sup 1) C Ori as the primary source of ionization. The comet-like morphology of the bright nebulosities is modeled as the result of an equilibrium between photoionization, recombination, and shadowing. The radii of the ionized 'head' of the cometary PIGs grow with distance from theta(sup 1) C Ori; the radii range from approximately less than or equal to 0.05 sec to approximately 0.25 sec. We interpret the size-distance relationship as evidence that the envelopes all have the same density profile and mass-loss rate within a factor of 2. Faint, arcuate wisps are observed 1 sec to 2 sec distance from some of the cometary nebulosities; these are modeled as bow shocks caused by the wind from theta(sup 1) C Ori. The positions of the stars associated with the PIGs in the observational H-R diagram indicate they are pre-main-sequence stars with masses less than approximately 3 solar mass, with approximately 1 solar mass being typical. Their medium I-K color is 2.9.

Mccullough, P. R.↗