 Subjects -> ASTRONOMY (Total: 94 journals)
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- Interactions of a shock with a molecular cloud at various stages of its
evolution due to thermal instability and gravity- Authors: Kupilas M; Wareing C, Pittard J, et al.
Pages: 3137 - 3154
Abstract: ABSTRACTUsing the adaptive mesh refinement code mg, we perform hydrodynamic simulations of the interaction of a shock with a molecular cloud evolving due to thermal instability (TI) and gravity. To explore the relative importance of these processes, three case studies are presented. The first follows the formation of a molecular cloud out of an initially quiescent atomic medium due to the effects of TI and gravity. The second case introduces a shock whilst the cloud is still in the warm atomic phase, and the third scenario introduces a shock once the molecular cloud has formed. The shocks accelerate the global collapse of the clouds with both experiencing local gravitational collapse prior to this. When the cloud is still atomic, the evolution is shock dominated and structures form due to dynamical instabilities within a radiatively cooled shell. While the transmitted shock can potentially trigger the TI, this is prevented as material is shocked multiple times on the order of a cloud-crushing time-scale. When the cloud is molecular, the post-shock flow is directed via the pre-existing structure through low-density regions in the inter-clump medium. The clumps are accelerated and deformed as the flow induces clump–clump collisions and mergers that collapse under gravity. For a limited period, both shocked cases show a mixture of Kolmogorov and Burgers turbulence-like velocity and logarithmic density power spectra, and strongly varying density spectra. The clouds presented in this work provide realistic conditions that will be used in future feedback studies.
PubDate: Thu, 07 Jan 2021 00:00:00 GMT
DOI: 10.1093/mnras/staa3889
Issue No: Vol. 501, No. 3 (2021)
- Erratum: Spectropolarimetric observations of the CIZA J2242.8+5301
northern radio relic: no evidence of high-frequency steepening- Authors: Loi F; Murgia M, Vacca V, et al.
Pages: 3183 - 3183
Abstract: errata, addendapolarizationgalaxies: clusters: individual: CIZA J2242.8+5301radio continuum: general
PubDate: Sat, 09 Jan 2021 00:00:00 GMT
DOI: 10.1093/mnras/staa3947
Issue No: Vol. 501, No. 3 (2021)
- Feedback-limited accretion: variable luminosity from growing planets
- Authors: Gárate M; Cuadra J, Montesinos M, et al.
Pages: 3113 - 3121
Abstract: ABSTRACTPlanets form in discs of gas and dust around stars, and continue to grow by accretion of disc material while available. Massive planets clear a gap in their protoplanetary disc, but can still accrete gas through a circumplanetary disc. For high enough accretion rates, the planet should be detectable at infrared wavelengths. As the energy of the gas accreted on to the planet is released, the planet surroundings heat up in a feedback process. We aim to test how this planet feedback affects the gas in the coorbital region and the accretion rate itself. We modified the 2D code FARGO-AD to include a prescription for the accretion and feedback luminosity of the planet and use it to model giant planets on 10 au circular and eccentric orbits around a solar mass star. We find that this feedback reduces but does not halt the accretion on to the planet, although this result might depend on the near-coincident radial ranges where both recipes are implemented. Our simulations also show that the planet heating gives the accretion rate a stochastic variability with an amplitude $\Delta \dot{M}_p \sim 0.1 \dot{M}_p$. A planet on an eccentric orbit (e = 0.1) presents a similar variability amplitude, but concentrated on a well-defined periodicity of half the orbital period and weaker broad-band noise, potentially allowing observations to discriminate between both cases. Finally, we find that the heating of the co-orbital region by the planet feedback alters the gas dynamics, reducing the difference between its orbital velocity and the Keplerian motion at the edge of the gap, which can have important consequences for the formation of dust rings.
PubDate: Wed, 16 Dec 2020 00:00:00 GMT
DOI: 10.1093/mnras/staa3860
Issue No: Vol. 501, No. 3 (2020)
- The delay time distribution of supernovae from integral-field spectroscopy
of nearby galaxies- Authors: Castrillo A; Ascasibar Y, Galbany L, et al.
Pages: 3122 - 3136
Abstract: ABSTRACTConstraining the delay time distribution (DTD) of different supernova (SN) types can shed light on the time-scales of galaxy chemical enrichment and feedback processes affecting galaxy dynamics, and SN progenitor properties. Here, we present an approach to recover SN DTDs based on integral-field spectroscopy (IFS) of their host galaxies. Using a statistical analysis of a sample of 116 SNe in 102 galaxies, we evaluate different DTD models for SN types Ia (73), II (28), and Ib/c (15). We find the best SN Ia DTD fit to be a power law with an exponent α = −1.1 ± 0.3 (50 per cent confidence interval (C.I.)), and a time delay (between star formation and the first SNe) $\Delta = 50^{+100}_{-35}~\mathrm{Myr}$ (50 per cent C.I.). For core collapse (CC) SNe, both of the Zapartas et al. DTD models for single and binary stellar evolution are consistent with our results. For SNe II and Ib/c, we find a correlation with a Gaussian DTD model with $\sigma = 82^{+129}_{-23}~\mathrm{Myr}$ and $\sigma = 56^{+141}_{-9}~\mathrm{Myr}$ (50 per cent C.I.), respectively. This analysis demonstrates that IFS opens a new way of studying SN DTD models in the local Universe.
PubDate: Thu, 17 Dec 2020 00:00:00 GMT
DOI: 10.1093/mnras/staa3876
Issue No: Vol. 501, No. 3 (2020)
- Galactic and cosmological fast radio bursts as scaled-up solar radio
bursts- Authors: Wang F; Zhang G, Dai Z.
Pages: 3155 - 3161
Abstract: ABSTRACTFast radio bursts (FRBs) are bright milliseconds radio transients with large dispersion measures. Recently, FRB 200428 was detected in temporal coincidence with a hard X-ray flare from the Galactic magnetar SGR 1935+2154, which supports that at least some FRBs are from magnetar activity. Interestingly, a portion of X-ray flares from magnetar XTE J1810−197 and the Sun are also accompanied by radio bursts. Many features of Galactic FRB 200428 and cosmological FRBs resemble solar radio bursts. However, a common physical origin among FRBs, magnetar radio pulses, and solar radio bursts has not yet been established. Here, we report a universal correlation between X-ray luminosity and radio luminosity over 20 orders of magnitude among solar type III radio bursts, XTE J1810−197 and Galactic FRB 200428. This universal correlation reveals that the energetic electrons that produce the X-ray flares and those that cause radio emissions have a common origin, which can give stringent limits on the generation process of radio bursts. Moreover, we find similar occurrence frequency distributions of energy, duration, and waiting time for solar radio bursts, SGR 1935+2154 and repeating FRB 121102, which also support the tight correlation and the X-ray flares temporally associated with radio bursts. All of these distributions can be understood by avalanche models of self-organized criticality systems. The universal correlation and statistical similarities indicate that the Galactic FRB 200428 and FRBs seen at cosmological distances can be treated as scaled-up solar radio bursts.
PubDate: Wed, 23 Dec 2020 00:00:00 GMT
DOI: 10.1093/mnras/staa3912
Issue No: Vol. 501, No. 3 (2020)
- Testing the intrinsic scatter of the asteroseismic scaling relations with
Kepler red giants- Authors: Li Y; Bedding T, Stello D, et al.
Pages: 3162 - 3172
Abstract: ABSTRACTAsteroseismic scaling relations are often used to derive stellar masses and radii, particularly for stellar, exoplanet, and Galactic studies. It is therefore important that their precisions are known. Here we measure the intrinsic scatter of the underlying seismic scaling relations for Δν and νmax, using two sharp features that are formed in the H–R diagram (or related diagrams) by the red giant populations. These features are the edge near the zero-age core-helium-burning phase, and the strong clustering of stars at the so-called red giant branch bump. The broadening of those features is determined by factors including the intrinsic scatter of the scaling relations themselves, and therefore it is capable of imposing constraints on them. We modelled Kepler stars with a Galaxia synthetic population, upon which we applied the intrinsic scatter of the scaling relations to match the degree of sharpness seen in the observation. We found that the random errors from measuring Δν and νmax provide the dominating scatter that blurs the features. As a consequence, we conclude that the scaling relations have intrinsic scatter of $\sim 0.5$ (Δν), $\sim 1.1$ (νmax), $\sim 1.7$ (M), and $\sim 0.4{{\ \rm per\ cent}}$ (R), for the SYD pipeline measured Δν and νmax. This confirms that the scaling relations are very powerful tools. In addition, we show that standard evolution models fail to predict some of the structures in the observed population of both the HeB and RGB stars. Further stellar model improvements are needed to reproduce the exact distributions.
PubDate: Mon, 21 Dec 2020 00:00:00 GMT
DOI: 10.1093/mnras/staa3932
Issue No: Vol. 501, No. 3 (2020)
- A two-component Comptonization model for the type-B QPO in MAXI
J1348−630- Authors: García F; Méndez M, Karpouzas K, et al.
Pages: 3173 - 3182
Abstract: ABSTRACTSpectral-timing analysis of the fast variability observed in X-rays is a powerful tool to study the physical and geometrical properties of the accretion/ejection flows in black hole (BH) binaries. The origin of type-B quasi-periodic oscillations (QPO), predominantly observed in BH candidates in the soft-intermediate state, has been linked to emission arising from the relativistic jet. In this state, the X-ray spectrum is characterized by a soft-thermal blackbody-like emission due to the accretion disc, an iron emission line (in the 6–7 keV range), and a power-law-like hard component due to inverse-Compton scattering of the soft-photon source by hot electrons in a corona or the relativistic jet itself. The spectral-timing properties of MAXI J1348−630 have been recently studied using observations obtained with the NICER observatory. The data show a strong type-B QPO at ∼4.5 Hz with increasing fractional rms amplitude with energy and positive lags with respect to a reference band at 2–2.5 keV. We use a variable-Comptonization model that assumes a sinusoidal coherent oscillation of the Comptonized X-ray flux and the physical parameters of the corona at the QPO frequency, to fit simultaneously the energy-dependent fractional rms amplitude and phase lags of this QPO. We show that two physically connected Comptonization regions can successfully explain the radiative properties of the QPO in the full 0.8–10 keV energy range.
PubDate: Sat, 26 Dec 2020 00:00:00 GMT
DOI: 10.1093/mnras/staa3944
Issue No: Vol. 501, No. 3 (2020)
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