Bow Shock Nebula Research Articles

Discovery of a Bow-shock Nebula Around the Z Cam-type Cataclysmic Variable SY Cancri

We report the serendipitous discovery of a bow-shock nebula around the cataclysmic variable (CV) SY Cancri. In addition, SY Cnc lies near the edge of a faint Hα-emitting nebula with a diameter of about 15′ . The orientation of the bow shock is consistent with the direction of SY Cnc’s proper motion. Nebulae are extremely rare around CVs, apart from those known to have undergone classical-nova (CN) outbursts; bow shocks and off-center nebulae are even more unusual. Nevertheless, the properties of SY Cnc and its nebulosity are strikingly similar to those of V341 Ara, another CV that is also associated with a bow shock and is likewise off-center with respect to its faint Hα nebula. Both stars are binaries with optically thick accretion disks, belonging to the classes of Z Cam CVs or nova-like variables. We discuss three scenarios to explain their properties. They may have resulted from chance encounters with interstellar gas clouds, with the stars leaving in their wakes material that is recombining after being photoionized by ultraviolet radiation from the CVs. Alternatively, the large nebulae could be ejecta from unobserved CN outbursts in the recent past, which have been decelerated through collisions with the interstellar medium (ISM), while the stars continue to snowplow through the gas. Or the faint Hα nebulae may be ambient ISM that was flash-ionized by a CN outburst in the past and is now recombining.

TYC 3340-2437-1: A Quadruple System with a Massive Star

Hierarchical massive quadruple systems are ideal laboratories for examining the theories of star formation, dynamical evolution, and stellar evolution. The successive mergers of hierarchical quadruple systems might explain the mass gap between neutron stars and black holes. Looking for light curves of O-type binaries identified by LAMOST, we find a (2+2) quadruple system: TYC 3340-2437-1, located in the stellar bow-shock nebula (SBN). It has a probability of over 99.99% being a quadruple system derived from the surface density of the vicinity stars. Its inner orbital periods are 3.390602(89) days and 2.4378(16) days, respectively, and the total mass is about (11.47 + 5.79) + (5.2 + 2.02) = 24.48 M ⊙. The line-of-sight inclinations of the inner binaries, B1 and B2, are 55.°94 and 78.°2, respectively, indicating that they are not coplanar. Based on observations spanning 34 months and the significance of the astrometric excess noise (D > 2) in Gaia Data Release 3 data, we guess that its outer orbital period might be a few years. If it were true, the quadruple system might form through the disk fragmentation mechanism with outer eccentric greater than zero. This eccentricity could be the cause of both the arc-like feature of the SBN and the noncoplanarity of the inner orbit. The outer orbital period and outer eccentric could be determined with the release of future epoch astrometric data of Gaia.

MUSE observations of the optical nebula surrounding the central compact object in the Vela Junior supernova remnant

ABSTRACT Central compact objects (CCOs), neutron stars found near the centre of some supernova remnants (SNRs), have been almost exclusively studied in X-rays and are thought to lack the wind nebulae typically seen around young, rotation-powered pulsars. We present the first, spatially resolved, morphological and spectroscopic study of the optical nebula observed at the location of CXOU J085201.4−461753, the CCO in the heart of the Vela Junior SNR. It is currently the only Galactic CCO with a spatially coincident nebula detected at optical wavelengths, whose exact nature remains uncertain. New Multi Unit Spectroscopic Explorer integral field spectroscopy data confirm that the nebula, shaped like a smooth blob extending 8 arcsec in diameter, is dominated by [N ii]${\lambda } {\lambda }$6548, 6583 emission. The data reveal a distinct and previously unobserved morphology of the H ${\alpha }$ emission, exhibiting an arc-like shape reminiscent of a bow shock nebula. We observe a significantly strong [N ii] emission relative to H ${\alpha }$, with the [N ii]${\lambda } {\lambda }$6548, 6583 up to 34 times the intensity of the H ${\alpha }$ emission within the optical nebula environment. Notably, the [N ii] and H ${\alpha }$ structures are not spatially coincident, with the [N ii] nebula concentrated to the south of the CCO and delimited by the H ${\alpha }$ arc-like structure. We detect additional emission in [N i], He i, [S ii], [Ar iii], [Fe ii], and [S iii]. We discuss our findings in the light of a photoionization or Wolf–Rayet nebula, pointing to a very massive progenitor and further suggesting that very massive stars do not necessarily make black holes.

The Spatial and Emission Properties of the Large [O iii] Emission Nebula Near M31

Drechsler et al. reported the unexpected discovery of a 1.°5 long [O iii] emission nebula 1.°2 southeast of the M31 nucleus. Here we present additional images of this large emission arc, called the Strottner–Drechsler–Sainty Object (SDSO), along with radial velocity and flux measurements from low-dispersion spectra. Independent sets of [O iii] images show SDSO to be composed of broad streaks of diffuse emission aligned northeast–southwest. Deep Hα images reveal no strong coincident emission suggesting a high [O iii]/Hα ratio. We also find no other [O iii] emission nebulosity as bright as SDSO within several degrees of M31 and no filamentary Hα emission connected to SDSO. Optical spectra taken along the nebula’s northern limb reveal [O iii] λ λ4959, 5007 emissions matching the location and extent seen in our [O iii] images. The heliocentric velocity of this [O iii] nebulosity is −9.8 ± 6.8 km s−1 with a peak surface brightness of (4 ± 2) × 10−18 erg s−1 cm−2 arcsec−2 (∼0.55 Rayleigh). We discuss SDSO as a possible unrecognized supernova remnant, a large and unusually nearby planetary nebula, a stellar bow shock nebula, or an interaction of M31's outer halo with Local Group circumgalactic gas. We conclude that galactic origins for SDSO are unlikely and favor instead an extragalactic M31 halo–circumgalactic cloud interaction scenario, despite the nebula’s low radial velocity. We then describe new observations that may help resolve the nature and origin of this large nebulosity so close to M31 in the sky.

Discovery of a Filamentary Synchrotron Structure Connected to the Coherent Magnetic Field in the Outer Galaxy

Using data from the Galactic Arecibo L-band Feed Array Continuum Transit Survey, we report the discovery of two previously unidentified, very compressed, thin, and straight polarized filaments approximately centered at Galactic coordinates, (l, b) = (182.°5, − 4.°0), which we call G182.5–4.0. Using data from the Isaac Newton Telescope Galactic Plane Survey, we also find straight, long, and extremely thin Hα filaments coincident with the radio emission. These filaments are positioned in projection at the edge of the Orion-Eridanus superbubble and we find evidence indicating that the filaments align with the coherent magnetic field of the outer Galaxy. We find a lower limit on the total radio flux at 1.4 GHz to be 0.7 ± 0.3 Jy with an average linearly polarized fraction of . We consider various scenarios that could explain the origin of these filaments, including a shell-type supernova remnant (SNR), a bow shock nebula associated with a pulsar, or relic fragments from one or more supernova explosions in the adjacent superbubble, with a hybrid scenario being most likely. This may represent an example of a new class of objects that is neither an SNR nor a bow shock. The highly compressed nature of these filaments and their alignment with the Galactic plane suggests a scenario where this object formed in a magnetic field that was compressed by the expanding Orion-Eridanus superbubble, suggesting that the object is related to this superbubble and implying a distance of ∼400 pc.

Wray 15-811: An unusual runaway star

We investigate Wray 15-811, a poorly studied object of controversial nature. We present for the first time spectroscopic observations (at low, medium, and high resolution), together with deep narrow-band images. These original data are combined with data from public surveys, to infer the nature of this object.We conclude that Wray 15-811 is indeed a carbon star with an optical bow-shock nebula associated. Its spectrum displays a split Hα emission, and its SED indicates the presence of silicates features. The light curve is similar to the expected for a Mira variable with a 504-day period. Its proper motion is compatible with that of a runaway star, consistent with the presence of the observed bow-shock nebula.

Kinematics of the Central Stars Powering Bowshock Nebulae and the Large Multiplicity Fraction of Runaway OB Stars

OB stars powering stellar bowshock nebulae (SBNe) have been presumed to have large peculiar velocities. We measured peculiar velocities of SBN central stars to assess their kinematics relative to the general O-star population using Gaia EDR3 data for 267 SBN central stars and a sample of 455 Galactic O stars to derive projected velocities v 2D. For a subset of each sample, we obtained new optical spectroscopy to measure radial velocities and identify multiple-star systems. We find a minimum multiplicity fraction of 36% ± 6% among SBN central stars, consistent with >28% among runaway Galactic O stars. The large multiplicity fraction among runaways implicates very efficient dynamical ejection rather than binary-supernova origins. The median v 2D of SBN central stars is v 2D = 14.6 km s−1, larger than the median v 2D = 11.4 km s−1 for non-bowshock O stars. Central stars of SBNe have a runaway (v 2D > 25 km s−1) fraction of 24%, consistent with the % for control-sample O stars. Most (76%) SBNe central stars are not runaways. Our analysis of alignment (ΔPA) between the nebular morphological and v 2D kinematic position angles reveals two populations: a highly aligned (σ PA = 25°) population that includes stars with the largest v 2D (31% of the sample) and a random (nonaligned) population (69%). SBNe that lie within or near H ii regions comprise a larger fraction of this latter component than SBNe in isolated environments, implicating localized ISM flows as a factor shaping their orientations and morphologies. We outline a new conceptual approach to computing the solar local standard of rest motion, yielding [U ⊙, V ⊙, W ⊙] = [5.5, 7.5,4.5] km s−1.

3D MHD astrospheres: applications to IRC-10414 and Betelgeuse

ABSTRACT A significative fraction of all massive stars in the Milky Way move supersonically through their local interstellar medium (ISM), producing bow shock nebulae by wind-ISM interaction. The stability of these observed astrospheres around cool massive stars challenges precedent 2D (magneto-)hydrodynamical (MHD) simulations of their surroundings. We present 3D MHD simulations of the circumstellar medium of runaway M-type red supergiant stars moving with velocity $v_{\star }=50\, \rm km\, \rm s^{-1}$. We treat the stellar wind with a Parker spiral and assume a $7\, \rm \mu G$ magnetization of the ISM. Our free parameter is the angle θmag between ISM flow and magnetization, taken to 0°, 45°, and 90°. It is found that simulation dimension, coordinate systems, and grid effects can greatly affect the development of the modelled astrospheres. Nevertheless, as soon as the ISM flow and magnetization directions differs by more than a few degrees (θmag ≥ 5°), the bow shock is stabilized, most clumpiness and ragged structures vanishing. The complex shape of the bow shocks induce important projection effects, e.g. at optical H α line, producing complex of astrospheric morphologies. We speculate that those effects are also at work around earlier-type massive stars, which would explain their diversity of their observed arc-like nebula around runaway OB stars. Our 3D MHD models are fitting well observations of the astrospheres of several runaway red supergiant stars. The results interpret the smoothed astrosphere of IRC-10414 and Betelgeuse (αOri) are stabilized by an organized non-parallel ambient magnetic field. Our findings suggest that IRC-10414 is currently in a steady state of its evolution, and that Betelgeuse’s bar is of interstellar origin.

X-Ray Jet, Counter-jet, and Trail of the Fast-moving Pulsar PSR B2224+65

Abstract I report the detection of linear X-ray features associated with PSR B2224+65, based on a new Chandra observation, plus two obtained ∼6 and 12 yr earlier. This mid-aged pulsar is known for its extreme proper motion and its associated guitar-shaped optical nebula in the opposite direction. The main jet-like feature with the same proper motion is ∼ 2 .′ 4 long and directed 62° away from the nebula, which is associated with a faint X-ray tail detected for the first time. Also now clearly revealed are the sharp forward edge and epoch-dependent substructures of the feature and its curvature near the pulsar, as well as a much fainter/shorter counter-jet. Magnetic field appears to play a central role in the formation of the features, which represent the synchrotron radiation of energetic particles leaked out from the bow shock nebula through small holes, produced probably by localized magnetic reconnection, and streaming along interstellar magnetic field lines.

Probing the star formation origin of gamma-rays from 3FHL J1907.0+0713

ABSTRACT Star-forming (SF) regions embedded inside giant molecular clouds (GMCs) are potential contributors to Galactic gamma-rays. The gamma-ray source 3FHL J1907.0+0713 is detected with a significance of roughly 13σ in the 0.2–300 GeV energy range after the removal of gamma-ray pulsation periods of PSR J1906+0722 from the Fermi-LAT data set of about 10 yr. The energy spectrum of 3FHL J1907.0+0713 is best-fitted to a power-law model with a spectral index of 2.26 ± 0.05. The CO(J = 1−0) data taken by NANTEN2 revealed that 3FHL J1907.0+0713 is overlapping with a GMC having a peak velocity of about 38 km s−1. The best-fitting location of 3FHL J1907.0+0713 is measured to be approximately 0.13 deg away from the Galactic supernova remnant (SNR) 3C 397 and it overlaps with a star that is associated with a bow-shock nebula. We show that there is no physical connection between 3FHL J1907.0+0713, 3C 397, as well as any positional coincidence with the pulsar. The spectrum of 3FHL J1907.0+0713 is fitting to both hadronic and leptonic gamma-ray emission models and the total luminosity at a distance of 2.6 kpc is calculated to be 1.1 × 1034 erg s−1. We also discuss possible SF origins of gamma-rays from 3FHL J1907.0+0713, where SNRs, massive protostar outflows, stellar winds from runaway stars, colliding wind binaries, and young stellar clusters are considered as candidate sources.

The Wind beneath My Wings. I. Spectral Types and Multiplicity of the Central Stars Supporting Stellar Bow Shock Nebulae

The Wind beneath My Wings. I. Spectral Types and Multiplicity of the Central Stars Supporting Stellar Bow Shock Nebulae

Magnetised gas nebulae of evolved massive stars

AbstractMassive stars are amongst the rarest but also most intriguing stars. Their extreme, magnetised stellar winds induce, by wind-ISM interaction, famous multi-wavelengths circumstellar gas nebulae of various morphologies, spanning from large-scale wind bubbles to stellar wind bow shocks, rings and bipolar shapes. We present two- and three-dimensional magneto-hydrodynamical (MHD) simulations of the circumstellar medium of such massive stars at different phase of their evolution. Particularly, we investigate the stability properties of 3D MHD bow shock nebulae around the runaway red supergiant stars IRC-10414 and Betelgeuse. Our results show that their astrospheres are stabilised by an organised, non-parallel ambient magnetic field. These findings suggest that Betelgeuse’s bar is of interstellar origin. Last, we explore the circular aspect of the young nebula around the Wolf-Rayet stars. It is found that Wolf-Rayet nebulae are not affected by the ISM gas distribution in which the stellar objects lie, even in the case of fast stellar motion: as testifies the ring-like surroundings of the Milky Way’s fastest Wolf-Rayet star, WR124. The morphology of these nebulae is tightly related to their pre-Wolf-Rayet wind geometry and to their phase evolution transition properties, which can generate bipolar shapes. We will further discuss their diffuse projected emission by means of radiative transfer calculations and show that the projected diffuse emission can appear as bipolar structures as in NGC6888.

Fast-moving pulsars as probes of interstellar medium

ABSTRACT Pulsars moving through interstellar medium (ISM) produce bow shocks detected in hydrogen H α line emission. The morphology of the bow shock nebulae allows one to probe the properties of ISM on scales ∼0.01 pc and smaller. We performed 2D relativistic magnetohydrodynamic modelling of the pulsar bow shock and simulated the corresponding H α emission morphology. We find that even a mild spatial inhomogeneity of ISM density, δρ/ρ ∼ 1, leads to significant variations of the shape of the shock seen in H α line emission. We successfully reproduce the morphology of the Guitar Nebula. We infer quasi-periodic density variations in the warm component of ISM with characteristic length of ∼0.1 pc. Structures of this scale might be also responsible for the formation of the fine features seen at the forward shock of Tycho supernova remnant (SNR) in X-rays. Formation of such short periodic density structures in the warm component of ISM is puzzling, and bow-shock nebulae provide unique probes to study this phenomenon.

A deep X-ray spectral imaging of the bow-shock pulsar wind nebula associated with PSR B1929+10

In this work, we study the X-ray bow-shock nebula powered by the mature pulsar PSR B1929+10 using data from XMM-Newton, with an effective exposure of ∼300 ks, offering the deepest investigation of this system thus far. We found the X-ray axial outflow extends as long as ∼8 arc minute behind the proper motion direction, which is a factor of two longer than the result reported in the previous study. Furthermore, we found evidence of two faint lateral outflows extending laterally with respect to the proper motion. We also found indications of spectral hardening along the axial outflow, suggesting that certain acceleration processes might occur along this feature.

Wind nebulae and supernova remnants of very massive stars

ABSTRACT A very small fraction of (runaway) massive stars have masses exceeding $60\!-\!70\, \rm M_{\odot }$ and are predicted to evolve as luminous blue variable and Wolf–Rayet stars before ending their lives as core-collapse supernovae. Our 2D axisymmetric hydrodynamical simulations explore how a fast wind ($2000\, \rm km\, \rm s^{-1}$) and high mass-loss rate ($10^{-5}\, \rm M_{\odot }\, \rm yr^{-1}$) can impact the morphology of the circumstellar medium. It is shaped as 100 pc-scale wind nebula that can be pierced by the driving star when it supersonically moves with velocity $20\!-\!40\, \rm km\, \rm s^{-1}$ through the interstellar medium (ISM) in the Galactic plane. The motion of such runaway stars displaces the position of the supernova explosion out of their bow shock nebula, imposing asymmetries to the eventual shock wave expansion and engendering Cygnus-loop-like supernova remnants. We conclude that the size (up to more than $200\, \rm pc$) of the filamentary wind cavity in which the chemically enriched supernova ejecta expand, mixing efficiently the wind and ISM materials by at least $10{{\ \rm per\ cent}}$ in number density, can be used as a tracer of the runaway nature of the very massive progenitors of such $0.1\, \rm Myr$ old remnants. Our results motivate further observational campaigns devoted to the bow shock of the very massive stars BD+43°3654 and to the close surroundings of the synchrotron-emitting Wolf–Rayet shell G2.4+1.4.

Modelling of far ultraviolet emission of pulsar wind nebulae with bow shocks

The kinetic modelling of electron and positron acceleration in the colliding shock flows of pulsar wind nebulae with bow shocks allows to explain the nature of their hard particle spectra. The hard synchrotron emission produced by the accelerated particles can reach the far ultraviolet range (1250 — 2000 Å) providing the maximal luminosity of the bow shock nebulae in this range. In this paper the results of modelling of pulsar wind particles transport in the colliding shock flows in the bow shock nebulae of PSRs J1741-2054 and B1929+10 are presented. The results of the synchrotron emission modelling are confronted to the observations in order to estimate possible far ultraviolet luminosities of the discussed objects.

Mass-loss Rates for O and Early B Stars Powering Bow Shock Nebulae: Evidence for Bistability Behavior

Abstract Second only to initial mass, the rate of wind-driven mass loss determines the final mass of a massive star and the nature of its remnant. Motivated by the need to reconcile observational values and theory, we use a recently vetted technique to analyze the mass-loss rates in a sample of OB stars that generate bow shock nebulae. We measure peculiar velocities from new Gaia parallax and proper motion data and their spectral types from new optical and infrared spectroscopy. For our sample of 70 central stars in morphologically selected bow shock nebulae, 67 are OB stars. The median peculiar velocity is 11 km s−1, significantly smaller than classical “runaway star” velocities. Mass-loss rates for these O and early B stars agree with recently lowered theoretical predictions, ranging from ≃10−7 M ⊙ yr−1 for mid-O dwarfs to 10−9 M ⊙ yr−1 for late O dwarfs—a factor of about 2.7 lower than the often-used Vink et al. formulation. Our results provide the first observational mass-loss rates for B0–B3 dwarfs and giants—10−9 to 10−8 M ⊙ yr−1. We find evidence for an increase in the mass-loss rates below a critical effective temperature, consistent with predictions of the bistability phenomenon in the range T eff = 19,000–27,000 K. The sample exhibits a correlation between modified wind momentum and luminosity, consistent in slope but lower by 0.43 dex in magnitude compared to canonical wind–luminosity relations. We identify a small subset of objects deviating most significantly from theoretical expectations as probable radiation-driven bow wave nebulae by virtue of their low stellar-to-nebular luminosity ratios. For these, the inferred mass-loss rates must be regarded as upper limits.

From outburst to quiescence: spectroscopic evolution of V1838 Aql imbedded in a bow-shock nebula

We analyse new optical spectroscopic, direct-image and X-ray observations of the recently discovered a high proper motion cataclysmic variable V1838 Aql. The data were obtained during its 2013 superoutburst and its subsequent quiescent state. An extended emission around the source was observed up to 30 days after the peak of the superoutburst, interpreted it as a bow--shock formed by a quasi-continuous outflow from the source in quiescence. The head of the bow--shock is coincident with the high--proper motion vector of the source ($v_{\perp}=123\pm5$ km s$^{-1}$) at a distance of $d=202\pm7$ pc. The object was detected as a weak X-ray source ($0.015\pm0.002$ counts s$^{-1}$) in the plateau of the superoutburst, and its flux lowered by two times in quiescence (0.007$\pm$0.002 counts s$^{-1}$). Spectroscopic observations in quiescence we confirmed the orbital period value $P_{\rm{orb}}=0.0545\pm 0.0026$ days, consistent with early-superhump estimates, and the following orbital parameters: $\gamma= -21\pm3$ km s$^{-1}$ and $K_1 = 53\pm3$ km s$^{-1}$. The white dwarf is revealed as the system approaches quiescence, which enables us to infer the effective temperature of the primary $T_{eff}=11,600\pm400$K. The donor temperature is estimated $\lesssim 2200$K and suggestive of a system approaching the period minimum. Doppler maps in quiescence show the presence of the hot spot in HeI line at the expected accretion disc-stream shock position and an unusual structure of the accretion disc in H$\alpha$.

Discovery of a pulsar-powered bow shock nebula in the Small Magellanic Cloud supernova remnant DEM S5

We report the discovery of a new Small Magellanic Cloud Pulsar Wind Nebula (PWN) at the edge of the Supernova Remnant (SNR)-DEM S5. The pulsar powered object has a cometary morphology similar to the Galactic PWN analogs PSR B1951+32 and 'the mouse'. It is travelling supersonically through the interstellar medium. We estimate the Pulsar kick velocity to be in the range of 700-2000 km/s for an age between 28-10 kyr. The radio spectral index for this SNR PWN pulsar system is flat (-0.29 $\pm$ 0.01) consistent with other similar objects. We infer that the putative pulsar has a radio spectral index of -1.8, which is typical for Galactic pulsars. We searched for dispersion measures (DMs) up to 1000 cm/pc^3 but found no convincing candidates with a S/N greater than 8. We produce a polarisation map for this PWN at 5500 MHz and find a mean fractional polarisation of P $\sim 23$ percent. The X-ray power-law spectrum (Gamma $\sim 2$) is indicative of non-thermal synchrotron emission as is expected from PWN-pulsar system. Finally, we detect DEM S5 in Infrared (IR) bands. Our IR photometric measurements strongly indicate the presence of shocked gas which is expected for SNRs. However, it is unusual to detect such IR emission in a SNR with a supersonic bow-shock PWN. We also find a low-velocity HI cloud of $\sim 107$ km/s which is possibly interacting with DEM S5. SNR DEM S5 is the first confirmed detection of a pulsar-powered bow shock nebula found outside the Galaxy.

3D dynamics and morphology of bow-shock pulsar wind nebulae

Bow-shock pulsar wind nebulae (PWNe) show a variety of morphological shapes. We attribute this diversity to the geometrical factors: relative orientations of the pulsar rotation axis, proper velocity, and the line of sight (magnetic inclination angle may also have a certain influence on the morphology). We identify three basic types of bow-shock nebulae: (i) a "Rifle Bullet" (pulsar spin axis and proper velocity are aligned); (ii) a "Frisbee" (pulsar spin axis and proper velocity are orthogonal with the spin axis lying in the plane of the sky), and (iii) a Cart Wheel" (like frisbee but the spin axis is perpendicular to the plane of the sky). Using 3D RMHD simulations, as well as analytical calculations, we reproduce the key morphological features of the bow-shock PWNe, as well as variations, are seen across different systems. magnetic stresses within the shocked pulsar wind affect the overall structure strongly, producing "whiskers", "tails", "filled-in" and "mushroom" shapes, as well as non-symmetric morphologies. On the other hand, the interstellar medium inhomogeneities and the anisotropy of the energy flux in the pulsar wind have only a mild impact of the PWN morphology. In a few cases, when we clearly identify specific morphological structures, our results do not favor alignment of the pulsar spin axis and proper velocity. Our calculations of the underlying emission processes explain the low synchrotron X-ray efficiency (in terms of the spin-down luminosity) and imply an energetical subdominant contribution of the inverse Compton process.