ABSTRACT
A characteristic feature that is frequently found in nearby supernova remnants (SNRs) is the existence of two antisymmetric, local protrusions that are projected as two ‘ears’ in the ...morphology of the nebula. In this paper, we present a novel scenario for the ‘ear’ formation process, according to which the two lobes are formed through the interaction of the SNR with a bipolar circumstellar medium (CSM) that was surrounding the explosion’s centre. We conduct two-dimensional hydrodynamic simulations and we show that the SNR shock breakout from the bipolar CSM triggers the inflation of two opposite protrusions at the equator of the remnant, which retain their size and shape from several hundreds up to a few thousand years of the SNR evolution. We run a set of models by varying the supernova (SN) and CSM properties and we demonstrate that the extracted results reveal good agreement with the observables, regarding the sizes, lifespan, morphology and kinematics of the ‘ears’. We discuss the plausibility of our model in nature and we suggest that the most likely progenitors of the ‘ear-carrying’ SNRs are the luminous blue variables or the red/yellow supergiants for the SNRs resulting from core collapse SN events, and the symbiotic binaries or the planetary nebulae for the SNRs formed by Type Ia SNe. Finally, we compare our model with other ‘ear’ formation models found in the literature and we show that there are distinctive differences among them, concerning the orientation of the ‘ears’ and the phase in which the ‘ear’ formation process occurs.
Abstract
The bipolar collimated outflows of the Hb4 planetary nebula (PN) exhibit an evident decrease in their expansion velocity with respect to the distance from the central star. So far, similar ...velocity law has also been found in Herbig–Haro objects. The interpretation of this peculiar velocity law and the classification of the outflows is the main focal point of this paper. High-dispersion long-slit echelle spectra along with high-resolution images from the Hubble Space Telescope (HST) are applied in the astronomical code shape in order to reproduce a three-dimensional morpho-kinematical model for the core and the bipolar outflows. Its central part shows a number of low-ionization filamentary structures (knots and jets) indicative of common-envelope PN evolution and it is reconstructed assuming a toroidal structure. The high-resolution HST N ii image of Hb4 unveils the fragmented structure of outflows. The northern and southern outflows are composed of four and three knots, respectively, and each knot moves outwards with its own expansion velocity. These are reconstructed as a string of knots rather than jets.This string of knots is formed by ejection events repeated every 200–250 yr. Hb4 displays indirect evidence of a binary central system with a Wolf–Rayet companion evolved through the common envelopes channel. The observed deceleration of the knots is likely to be associated with shock collisions between the knots and the interstellar medium or nebular material.
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.
ABSTRACT
We present a systematic study of the supernova remnant (SNR) populations in the nearby galaxies NGC 45, NGC 55, NGC 1313, and NGC 7793 based on deep H $\rm {\alpha }$ and S ii imaging. We ...find 42 candidate and 51 possible candidate SNRs based on the S ii/H $\rm {\alpha }$>0.4 criterion, 81 of which are new identifications. We derive the H $\rm {\alpha }$ and the joint S ii–H $\rm {\alpha }$ luminosity functions after accounting for incompleteness effects. We find that the H $\rm {\alpha }$ luminosity function of the overall sample is described with a skewed Gaussian with a mean equal to $\rm \log (L_{H\alpha }/10^{36}\, erg\, s^{-1})=0.07$ and $\rm \sigma (\log (L_{H\alpha }/10^{36}\, erg\, s^{-1}))=0.58$. The joint S ii–H $\rm {\alpha }$ function is parametrized by a skewed Gaussian along the log(S ii$\rm /10^{36}\, erg\, s^{-1}) = 0.88 \times \log (L_{H\alpha }/10^{36}\, erg\, s^{-1}) - 0.06$ line and a truncated Gaussian with $\rm \mu (\log (L_{S\, II}/10^{36})) = 0.024$ and $\rm \sigma (\log (L_{S\, II}/10^{36})) = 0.14$, on its vertical direction. We also define the excitation function as the number density of SNRs as a function of their S ii/H $\rm {\alpha }$ ratios. This function is represented by a truncated Gaussian with a mean at −0.014. We find a sub-linear S ii–H $\rm {\alpha }$ relation indicating lower excitation for the more luminous objects.
ABSTRACT
Many binary companions to the central stars of planetary nebulae (PNe) are found to be inflated, perhaps indicating that accretion onto the central star might occur during the planetary ...nebula (PN) phase. The discovery of a handful of nova eruptions and supersoft X-ray sources inside PNe supports this hypothesis. In this paper, we investigate the impact that hosting a steadily accreting white dwarf (WD) would have on the properties and evolution of a PN. By pairing the published accreting nuclear-burning WD models with radiation transfer simulations, we extract the time evolution of the emission line spectra and ionization properties of a PN that surrounds a 0.6$\, \rm M_{\odot }$ steadily nuclear-burning WD as a function of the mass accretion rate. We find that accreting WDs are able to form very extended, high excitation, ${\rm O\, \small {\rm III}}$-bright PNe, which are characterized by high nebular electron temperatures. Their properties remain almost invariant with time and their visibility time can be much longer compared to PNe powered by single WDs. We discuss the implications of our findings in explaining specific characteristics observed in PNe. Finally, we examine how accreting WDs affect the planetary nebula luminosity function (PNLF) by covering WD masses in the range of 0.5–0.8$\, \rm M_{\odot }$ and for various accretion rates within the steady accretion regime. We find that for all but the lowest accretion rates, the ${\rm O\, \small {\rm III}}$ luminosities are almost constant and clustered very close to the PNLF cut-off value. Our results suggest that mass-accreting WDs in interacting binaries might play a role in understanding the invariant cut-off of the PNLF.
Since the start of the Wide-angle Search for Planets (WASP) program, more than 160 transiting exoplanets have been discovered in the WASP data. In the past, possible transit-like events identified by ...the WASP pipeline have been vetted by human inspection to eliminate false alarms and obvious false positives. The goal of this paper is to assess the effectiveness of machine learning as a fast, automated, and reliable means of performing the same functions on ground-based wide-field transit-survey data without human intervention. To this end, we have created training and test data sets made up of stellar light curves showing a variety of signal types including planetary transits, eclipsing binaries, variable stars, and non-periodic signals. We use a combination of machine-learning methods including Random Forest Classifiers (RFCs) and convolutional neural networks (CNNs) to distinguish between the different types of signals. The final algorithms correctly identify planets in the test data ∼90 per cent of the time, although each method on its own has a significant fraction of false positives. We find that in practice, a combination of different methods offers the best approach to identifying the most promising exoplanet transit candidates in data from WASP, and by extension similar transit surveys.
ABSTRACT
We carry out an advanced morpho-kinematic analysis of the Planetary Nebula (PN) NGC 2818, whose complex morphology is described by a basic bipolar component, filamentary structures and a ...knotty central region. We performed an upgrated 3D Morpho-kinematic (MK) model by employing the shape software, combining for the first time in PNe optical 2D spatially resolved echelle spectra and Fabry–Perot data cubes. The best-fitting 3D model of NGC 2818 successfully reconstructs the main morphology, considering one bipolar component, radial filamentary structures, and an equatorial component as the geometrical locus of the group of cometary knots. The model shows that the equatorial component has the lower expansion velocity of the system at 70 ± 20 km s−1. The velocity of the bipolar component is 120 ± 20 km s−1, while all the filamentary structures were found to expand at higher velocities of 180 ± 20 km s−1. Moreover, Fabry–Perot data revealed for the first time a north-eastern filament expanding at a mean velocity of 80 ± 20 km s−1, while its equivalent counterpart in the south-western region was confirmed by a new detected substructure in the echelle data. A new detected knotty structure at velocity −40 ± 20 km s−1 is also reported, as expelled material from the fragmented eastern lobe of the nebula. We interpret the overall structure of NGC 2818 as the result of the evolution of a binary system that underwent the common envelope phase, in conjunction with the ejections of a magnetized jet, misaligned with respect to the symmetry axis of the bipolar/elliptical shell.
We present results of high-cadence monitoring of the optical light curve of the nearby, Type Ia SN 2014J in M 82, using the 2.3 m Aristarchos telescope. B and V-band photometry on days 15–18 after ...tmax(B) was obtained with a cadence of 2 min per band, revealing evidence for rapid variability at the 0.02–0.05 mag level on timescales of 15–60 min on all four nights. The decline slope was measured as steeper in the B-band than in the V-band, and to steadily decrease in both bands from 0.15 mag day-1 (night 1) to 0.04 mag day-1 (night 4) in V, and from 0.19 mag day-1 (night 1) to 0.06 mag day-1 (night 4) in B, corresponding to the onset of the secondary maximum. We propose that rapid variability could be due to one or a combination of the following scenarios: the clumpiness of the ejecta, their interaction with circumstellar material, the asymmetry of the explosion, or the mechanism causing the secondary maximum in the near-infrared light curve. We encourage the community to undertake high-cadence monitoring of future, nearby and bright supernovae to investigate the intraday behaviour of their light curves.
To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets' mass and radius with a good precision (≲10%) is essential. To achieve this purpose the ...discovery of transiting exoplanets around bright stars is of prime interest. In this paper, we report the discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15%. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31−0.03+0.04 MJ$0.31_{-0.03}^{+0.04}\,{M_{\textrm{J}}}$0.31−0.03+0.04 MJ, 1.13−0.03+0.03 RJ$1.13_{-0.03}^{+0.03}\,{R_{\textrm{J}}}$1.13−0.03+0.03 RJ, 0.22−0.02+0.03 ρJ$0.22_{-0.02}^{+0.03}\,\rho_{\mathrm{J}}$0.22−0.02+0.03 ρJ and 1290−10+20 K$1290_{-10}^{+20}~\mathrm{K}$1290−10+20 K, and 0.39−0.02+0.02 MJ$0.39_{-0.02}^{+0.02}\,{M_{\textrm{J}}}$0.39−0.02+0.02 MJ, 1.55−0.08+0.10 RJ$1.55_{-0.08}^{+0.10}\,{R_{\textrm{J}}}$1.55−0.08+0.10 RJ, 0.11−0.02+0.02 ρJ$0.11_{-0.02}^{+0.02}\,\rho_{\mathrm{J}}$0.11−0.02+0.02 ρJ and 1700−0.40+0.40 K$1700_{-40}^{+40}~\mathrm{K}$1700−40+40 K, respectively. Their host stars are early G type stars (with mag V ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a super-Neptune orbiting a K type star (mag V = 11.6). It has a mass of $0.128_{-0.009}^{+0.010}\,{M_{\rm J}}$0.128−0.009+0.010 MJ0.128-0.009+0.010MJ, a radius of $0.51_{-0.02}^{+0.02}\,{R_{\rm J}}$0.51−0.02+0.02 RJ0.51-0.02+0.02RJ, a density of 1.0−0.1+0.1 ρJ$1.0_{-0.1}^{+0.1}\,\rho_{\mathrm{J}}$1.0−0.1+0.1 ρJ, an equilibrium temperature of 970−20+30 K$970_{-20}^{+30}~\mathrm{K}$970−20+30 K and an orbital period of 3.83 days. The radius of WASP-151b appears to be only slightly inflated, while WASP-153b presents a significant radius anomaly compared to a recently published model. WASP-156b, being one of the few well characterized super-Neptunes, will help to constrain the still debated formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms an already observed tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behavior for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population.
Aims. The shaping mechanisms of old nova remnants are probes for several important and unexplained processes, such as dust formation and the structure of evolved star nebulae. To gain a more complete ...understanding of the dynamics of the GK Per (1901) remnant, an examination of symmetry of the nova shell is explored, followed by a kinematical analysis of the previously detected jet-like feature in the context of the surrounding fossil planetary nebula. Methods. Faint-object high-resolution echelle spectroscopic observations and imaging were undertaken covering the knots which comprise the nova shell and the surrounding nebulosity. New imaging from the Aristarchos telescope in Greece and long-slit spectra from the Manchester Echelle Spectrometer instrument at the San Pedro Mártir observatory in Mexico were obtained, supplemented with archival observations from several other optical telescopes. Position-velocity arrays are produced of the shell, and also individual knots, and are then used for morpho-kinematic modelling with the shape code. The overall structure of the old knotty nova shell of GK Per and the planetary nebula in which it is embedded is then analysed. Results. Evidence is found for the interaction of knots with each other and with a wind component, most likely the periodic fast wind emanating from the central binary system. We find that a cylindrical shell with a lower velocity polar structure gives the best model fit to the spectroscopy and imaging. We show in this work that the previously seen jet-like feature is of low velocity. Conclusions. The individual knots have irregular tail shapes; we propose here that they emanate from episodic winds from ongoing dwarf nova outbursts by the central system. The nova shell is cylindrical, not spherical, and the symmetry axis relates to the inclination of the central binary system. Furthermore, the cylinder axis is aligned with the long axis of the bipolar planetary nebula in which it is embedded. Thus, the central binary system is responsible for the bipolarity of the planetary nebula and the cylindrical nova shell. The gradual planetary nebula ejecta versus sudden nova ejecta is the reason for the different degrees of bipolarity. We propose that the “jet” feature is an illuminated lobe of the fossil planetary nebula that surrounds the nova shell.
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