scholarly journals Bow shocks, nova shells, disc winds and tilted discs: the nova-like V341 Ara has it all

2021 ◽  
Vol 501 (2) ◽  
pp. 1951-1969
Author(s):  
N Castro Segura ◽  
C Knigge ◽  
J A Acosta-Pulido ◽  
D Altamirano ◽  
S del Palacio ◽  
...  
Keyword(s):  
Mass Loss Rate ◽  
Cataclysmic Variables ◽  
Accretion Disc ◽  
Bow Shock ◽  
High Mass ◽  
Characteristic Time Scale ◽  
Spatially Resolved ◽  
Unique System ◽  
Bow Shocks ◽  
Nova Shells

ABSTRACT V341 Ara was recently recognized as one of the closest (d ≃ 150 pc) and brightest (V ≃ 10) nova-like cataclysmic variables. This unique system is surrounded by a bright emission nebula, likely to be the remnant of a recent nova eruption. Embedded within this nebula is a prominent bow shock, where the system’s accretion disc wind runs into its own nova shell. In order to establish its fundamental properties, we present the first comprehensive multiwavelength study of the system. Long-term photometry reveals quasi-periodic, super-orbital variations with a characteristic time-scale of 10–16 d and typical amplitude of ≃1 mag. High-cadence photometry from theTransiting Exoplanet Survey Satellite (TESS) reveals for the first time both the orbital period and a ‘negative superhump’ period. The latter is usually interpreted as the signature of a tilted accretion disc. We propose a recently developed disc instability model as a plausible explanation for the photometric behaviour. In our spectroscopic data, we clearly detect antiphased absorption and emission-line components. Their radial velocities suggest a high mass ratio, which in turn implies an unusually low white-dwarf mass. We also constrain the wind mass-loss rate of the system from the spatially resolved [O iii] emission produced in the bow shock; this can be used to test and calibrate accretion disc wind models. We suggest a possible association between V341 Ara and a ‘guest star’ mentioned in Chinese historical records in AD 1240. If this marks the date of the system’s nova eruption, V341 Ara would be the oldest recovered nova of its class and an excellent laboratory for testing nova theory.

scholarly journals On the formation of wind bow-shocks around OB runaway stars

1999 ◽  
Vol 193 ◽  
pp. 316-324 ◽  
Author(s):  
Lex Kaper ◽  
Fernando Comerón ◽  
Orly Barziv
Keyword(s):  
Massive Star ◽  
Large Fraction ◽  
Space Velocity ◽  
Bow Shock ◽  
High Mass ◽  
Bow Shocks ◽  
Local Sound ◽  
Infrared Wavelengths ◽  
Hydrodynamical Simulations ◽  
Runaway Stars

The interaction of the stellar wind of a supersonically moving massive star with its surrounding interstellar medium can result in the formation of an observable bow-shock. Recent studies at optical and infrared wavelengths indicate the presence of wind bow-shocks around several OB runaways, including the high-mass X-ray binary system Vela X-1. A large fraction of runaway stars do not seem to form wind bow-shocks. Obviously, when the local sound speed is high (∼ 100 km s−1), as is the case e.g., inside a hot superbubble, the (subsonic) space velocity would not be sufficient to form a bow-shock. Two-dimensional time-dependent hydrodynamical simulations indicate that the bow-shock is generally unstable; for certain combinations of ISM and wind parameters a bow-shock is not formed at all. The runaway nature of Wolf-Rayet stars in relation to the formation of wind bow-shocks is also discussed.

scholarly journals Wind nebulae and supernova remnants of very massive stars

2020 ◽  
Vol 493 (3) ◽  
pp. 3548-3564 ◽  
Author(s):  
D M-A Meyer ◽  
M Petrov ◽  
M Pohl
Keyword(s):  
Supernova Remnants ◽  
Galactic Plane ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Supernova Explosion ◽  
Bow Shock ◽  
High Mass ◽  
Fast Wind ◽  
High Mass Loss ◽  
Hydrodynamical Simulations

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.

Formation of the SMC WO+O binary AB8

2018 ◽  
Vol 14 (S346) ◽  
pp. 78-82
Author(s):  
Chen Wang ◽  
Norbert Langer ◽  
Götz Gräfener ◽  
Pablo Marchant
Keyword(s):  
Binary Systems ◽  
Mass Loss Rate ◽  
Vital Role ◽  
Least Square ◽  
High Mass ◽  
Stellar Winds ◽  
High Mass Loss ◽  
Low Metallicity ◽  
Binary Evolution ◽  
Oxygen Ratio

AbstractWolf-Rayet (WR) stars are stripped stellar cores that form through strong stellar wind or binary mass transfer. It is proposed that binary evolution plays a vital role in the formation of WR stars in low metallicity environments due to the metallicity dependance of stellar winds. However observations indicate a similar binary fraction of WR stars in the Small Magellanic Cloud (SMC) compared to the Milky Way. There are twelve WR stars in the SMC and five of them are members of binary systems. One of them (SMC AB8) harbors a WO type star. In this work we explore possible formation channels of this binary. We use the MESA code to compute large grids of binary evolution models, and then use least square fitting to compare our models with the observations. In order to reproduce the key properties of SMC AB8, we require efficient semiconvection to produce a sufficiently large convective core, as well as a longer He-burning lifetime. We also need a high mass loss rate during the WN stage to assist the removal of the outer envelope. In this way, we can reproduce the observed properties of AB8, except for the surface carbon to oxygen ratio, which requires further investigation.

scholarly journals Systematic search for very-high-energy gamma-ray emission from bow shocks of runaway stars

2018 ◽  
Vol 612 ◽  
pp. A12 ◽  
Author(s):  
◽  
H. Abdalla ◽  
A. Abramowski ◽  
F. Aharonian ◽  
F. Ait Benkhali ◽  
...  
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Bow Shock ◽  
Systematic Search ◽  
Upper Limits ◽  
Very High Energy ◽  
Bow Shocks ◽  
Gamma Ray Emission ◽  
Runaway Stars ◽  
Very High

Context. Runaway stars form bow shocks by ploughing through the interstellar medium at supersonic speeds and are promising sources of non-thermal emission of photons. One of these objects has been found to emit non-thermal radiation in the radio band. This triggered the development of theoretical models predicting non-thermal photons from radio up to very-high-energy (VHE, E ≥ 0.1 TeV) gamma rays. Subsequently, one bow shock was also detected in X-ray observations. However, the data did not allow discrimination between a hot thermal and a non-thermal origin. Further observations of different candidates at X-ray energies showed no evidence for emission at the position of the bow shocks either. A systematic search in the Fermi-LAT energy regime resulted in flux upper limits for 27 candidates listed in the E-BOSS catalogue.Aim. Here we perform the first systematic search for VHE gamma-ray emission from bow shocks of runaway stars.Methods. Using all available archival H.E.S.S. data we search for very-high-energy gamma-ray emission at the positions of bow shock candidates listed in the second E-BOSS catalogue release. Out of the 73 bow shock candidates in this catalogue, 32 have been observed with H.E.S.S.Results. None of the observed 32 bow shock candidates in this population study show significant emission in the H.E.S.S. energy range. Therefore, flux upper limits are calculated in five energy bins and the fraction of the kinetic wind power that is converted into VHE gamma rays is constrained.Conclusions. Emission from stellar bow shocks is not detected in the energy range between 0.14 and 18 TeV.The resulting upper limits constrain the level of VHE gamma-ray emission from these objects down to 0.1–1% of the kinetic wind energy.

scholarly journals 1.16. 4.5 to 11.7 microns spectrophotometric observations of the Galactic bulge by the MIRS/IRTS

1998 ◽  
Vol 184 ◽  
pp. 47-47
Author(s):  
Kin-Wing Chan ◽  
T. L. Roellig ◽  
T. Onaka ◽  
I. Yamamura ◽  
T. Tanabé
Keyword(s):  
Interstellar Medium ◽  
Mass Loss Rate ◽  
Life Time ◽  
High Mass ◽  
Galactic Latitude ◽  
Galactic Bulge ◽  
Stellar Content ◽  
Mid Infrared ◽  
Evolved Stars ◽  
Infrared Background

Using the Mid-Infrared (MIRS) on board the Infrared Telescope in Space (IRTS) we obtained the 4.5 to 11.7 μm spectra of the stellar populations and diffuse interstellar medium in the Galactic bulge (l ≈ 8.7°, b ≈ 2.9, 4.0, 4.7, and 5.7°). Below galactic latitute of 4.0° the mid-infrared background spectra in the bulge are similar to the spectrum of M and K giants. The UIR bands (6.2, 7.7, 8.6, and 11.3 μm) are also detected in these regions and they are likely arising from the diffuse interstellar medium in the bulge. Above galactic latitude of 4.0°, the mid-infrared background spectra are similar to the spectrum of those evolved stars with high mass-loss rate detected by IRAS. One likely interpretation is that this background emission arises predominantly from these stars with very low luminosities that have not been detected by IRAS. The main-sequence life time for such low luminosity evolved stars is at least 10 Gyr, even in the metal poor cases. If these low luminosity evolved stars are metal-rich then the age would be much older. Thus, the existence of a large number (~ 75) of such low luminosity evolved stars in a small region (8′ × 8′) in the bulge would have significant impact on our understanding of the stellar content and the age of the Galactic bulge.

scholarly journals Global 3D radiation magnetohydrodynamic simulations for FU Ori’s accretion disc and observational signatures of magnetic fields

2020 ◽  
Vol 495 (3) ◽  
pp. 3494-3514 ◽  
Author(s):  
Zhaohuan Zhu ◽  
Yan-Fei Jiang ◽  
James M Stone
Keyword(s):  
Magnetic Fields ◽  
Accretion Rate ◽  
Mass Loss Rate ◽  
Global Radiation ◽  
Surface Region ◽  
Accretion Disc ◽  
Near Ir ◽  
Mhd Simulations ◽  
Fu Ori ◽  
Magnetohydrodynamic Simulations

ABSTRACT FU Ori is the prototype of FU Orionis systems that are outbursting protoplanetary discs. Magnetic fields in FU Ori’s accretion discs have previously been detected using spectropolarimetry observations for Zeeman effects. We carry out global radiation ideal MHD simulations to study FU Ori’s inner accretion disc. We find that (1) when the disc is threaded by vertical magnetic fields, most accretion occurs in the magnetically dominated atmosphere at z ∼ R, similar to the ‘surface accretion’ mechanism in previous locally isothermal MHD simulations. (2) A moderate disc wind is launched in the vertical field simulations with a terminal speed of ∼300–500 km s−1 and a mass-loss rate of 1–10 per cent the disc accretion rate, which is consistent with observations. Disc wind fails to be launched in simulations with net toroidal magnetic fields. (3) The disc photosphere at the unit optical depth can be either in the wind launching region or the accreting surface region. Magnetic fields have drastically different directions and magnitudes between these two regions. Our fiducial model agrees with previous optical Zeeman observations regarding both the field directions and magnitudes. On the other hand, simulations indicate that future Zeeman observations at near-IR wavelengths or towards other FU Orionis systems may reveal very different magnetic field structures. (4) Due to energy loss by the disc wind, the disc photosphere temperature is lower than that predicted by the thin disc theory, and the previously inferred disc accretion rate may be lower than the real accretion rate by a factor of ∼2–3.

scholarly journals Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Doradus

2018 ◽  
Vol 609 ◽  
pp. A63 ◽  
Author(s):  
M. Van de Sande ◽  
L. Decin ◽  
R. Lombaert ◽  
T. Khouri ◽  
A. de Koter ◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Central Star ◽  
High Mass ◽  
Circumstellar Envelope ◽  
Gaussian Profile ◽  
Macro Scale ◽  
Abundance Profile ◽  
Envelope Model

Context. The stellar outflows of low- to intermediate-mass stars are characterised by a rich chemistry. Condensation of molecular gas species into dust grains is a key component in a chain of physical processes that leads to the onset of a stellar wind. In order to improve our understanding of the coupling between the micro-scale chemistry and macro-scale dynamics, we need to retrieve the abundance of molecules throughout the outflow. Aims. Our aim is to determine the radial abundance profile of SiO and HCN throughout the stellar outflow of R Dor, an oxygen-rich AGB star with a low mass-loss rate. SiO is thought to play an essential role in the dust-formation process of oxygen-rich AGB stars. The presence of HCN in an oxygen-rich environment is thought to be due to non-equilibrium chemistry in the inner wind. Methods. We analysed molecular transitions of CO, SiO, and HCN measured with the APEX telescope and all three instruments on the Herschel Space Observatory, together with data available in the literature. Photometric data and the infrared spectrum measured by ISO-SWS were used to constrain the dust component of the outflow. Using both continuum and line radiative transfer methods, a physical envelope model of both gas and dust was established. We performed an analysis of the SiO and HCN molecular transitions in order to calculate their abundances. Results. We have obtained an envelope model that describes the dust and the gas in the outflow, and determined the abundance of SiO and HCN throughout the region of the stellar outflow probed by our molecular data. For SiO, we find that the initial abundance lies between 5.5 × 10-5 and 6.0 × 10-5 with respect to H2. The abundance profile is constant up to 60 ± 10 R∗, after which it declines following a Gaussian profile with an e-folding radius of 3.5 ± 0.5 × 1013 cm or 1.4 ± 0.2 R∗. For HCN, we find an initial abundance of 5.0 × 10-7 with respect to H2. The Gaussian profile that describes the decline starts at the stellar surface and has an e-folding radius re of 1.85 ± 0.05 × 1015 cm or 74 ± 2 R∗. Conclusions. We cannot unambiguously identify the mechanism by which SiO is destroyed at 60 ± 10 R∗. The initial abundances found are higher than previously determined (except for one previous study on SiO), which might be due to the inclusion of higher-J transitions. The difference in abundance for SiO and HCN compared to high mass-loss rate Mira star IK Tau might be due to different pulsation characteristics of the central star and/or a difference in dust condensation physics.

Modeling of hydrodynamic processes within high-mass X-ray binaries

2018 ◽  
Vol 14 (S346) ◽  
pp. 197-201
Author(s):  
Petr Kurfürst ◽  
Jiří Krtička
Keyword(s):  
Mass Loss Rate ◽  
Compact Object ◽  
Supernova Explosion ◽  
High Mass ◽  
Be Stars ◽  
X Ray ◽  
Hydrodynamic Processes ◽  
Hydrodynamic Structure ◽  
X Ray Binaries ◽  
Circumstellar Environment

AbstractHigh-mass X-ray binaries belong to the brightest objects in the X-ray sky. They usually consist of a massive O or B star or a blue supergiant while the compact X-ray emitting component is a neutron star (NS) or a black hole. Intensive matter accretion onto the compact object can take place through different mechanisms: wind accretion, Roche-lobe overflow, or circumstellar disk. In our multi-dimensional models we perform numerical simulations of the accretion of matter onto a compact companion in case of Be/X-ray binaries. Using Bondi-Hoyle-Littleton approximation, we estimate the NS accretion rate. We determine the Be/X-ray binary disk hydrodynamic structure and compare its deviation from isolated Be stars’ disk. From the rate and morphology of the accretion flow and the X-ray luminosity we improve the estimate of the disk mass-loss rate. We also study the behavior of a binary system undergoing a supernova explosion, assuming a blue supergiant progenitor with an aspherical circumstellar environment.

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