Monthly Notices of the Royal Astronomical Society Letters

Hui (許文韜), Man-To; Kim (김윤영), Yoonyoung; Gao (高興), Xing

doi: 10.1093/mnrasl/slz112pmid: N/A

ABSTRACTMain-belt asteroid (6478) Gault was observed to show cometary features in early 2019. To investigate the cause, we conducted BVR observations at Xingming Observatory, China, from 2019 January to April. The two tails were formed around 2018 October 26–November 8, and 2018 December 29–2019 January 8, respectively, and consisted of dust grains of ≳20 $\mu$m to 3 mm in radius ejected at a speed of 0.15 ± 0.05 m s−1 and following a broken power-law size distribution bending at grain radius ∼70 $\mu$m (bulk density 1 g cm−3 assumed). The total mass of dust within a 104 km-radius aperture around Gault declined from ∼9 × 106 kg since 2019 January at a rate of 2.28 ± 0.07 kg s−1, but temporarily surged around 2019 March 25, because Earth then crossed the orbital plane of Gault, near which the ejected dust was mainly distributed. No statistically significant colour or short-term light-curve variation was seen. Nonetheless we argue that Gault is currently subjected to rotational instability. Using the available astrometry, we did not detect any non-gravitational acceleration in the orbital motion of Gault.

Fraser-McKelvie, Amelia; Merrifield, Michael; Aragón-Salamanca, Alfonso; Peterken, Thomas; Masters, Karen; Krawczyk, Coleman; Andrews, Brett; Knapen, Johan H; Kruk, Sandor; Schaefer, Adam; Smethurst, Rebecca; Riffel, Rogério; Brownstein, Joel; Drory, Niv

doi: 10.1093/mnrasl/slz085pmid:

Moradpour, H; Ziaie, A H; Ghaffari, S; Feleppa, F

doi: 10.1093/mnrasl/slz098pmid: N/A

ABSTRACTThe generalized and extended uncertainty principles affect the Newtonian gravity and also the geometry of the thermodynamic phase space. Under the influence of the latter, the energy–temperature relation of ideal gas may change. Moreover, it seems that the Newtonian gravity is modified in the framework of the Rényi entropy formalism motivated by both the long-range nature of gravity and the extended uncertainty principle. Here, the consequences of employing the generalized and extended uncertainty principles, instead of the Heisenberg uncertainty principle, on the Jeans mass are studied. The results of working in the Rényi entropy formalism are also addressed. It is shown that unlike the extended uncertainty principle and the Rényi entropy formalism that lead to the same increase in the Jeans mass, the generalized uncertainty principle can decrease it. The latter means that a cloud with mass smaller than the standard Jeans mass, obtained in the framework of the Newtonian gravity, may also undergo the gravitational collapse process.

Méndez-Abreu, J; Sánchez, S F; de Lorenzo-Cáceres, A

doi: 10.1093/mnrasl/slz103pmid: N/A

ABSTRACTThe star formation main sequence (SFMS) is a tight relation between the galaxy star formation rate (SFR) and its total stellar mass (M⋆). Early-type galaxies (ETGs) are often considered as low-SFR outliers of this relation. We study, for the first time, the separated distribution in the SFR versus M⋆ of bulges and discs of 49 ETGs from the CALIFA survey. This is achieved using c2d, a new code to perform spectrophotometric decompositions of integral field spectroscopy data cubes. Our results reflect that: (i) star formation always occurs in the disc component and not in bulges; (ii) star-forming discs in our ETGs are compatible with the SFMS defined by star-forming galaxies at z ∼ 0; (iii) the star formation is not confined to the outskirts of discs, but it is present at all radii (even where the bulge dominates the light); (iv) for a given mass, bulges exhibit lower sSFR than discs at all radii; and (v) we do not find a deficit of molecular gas in bulges with respect to discs for a given mass in our ETGs. We speculate our results favour a morphological quenching scenario for ETGs.

Keys, Peter H; Reid, Aaron; Mathioudakis, Mihalis; Shelyag, Sergiy; Henriques, Vasco M J; Hewitt, Rebecca L; Del Moro, Dario; Jafarzadeh, Shahin; Jess, David B; Stangalini, Marco

doi: 10.1093/mnrasl/slz097pmid: N/A

ABSTRACTMagnetic bright points (MBPs) are small-scale magnetic elements ubiquitous across the solar disc, with the prevailing theory suggesting that they form due to the process of convective collapse. Employing a unique full Stokes spectropolarimetric data set of a quiet Sun region close to disc centre obtained with the Swedish Solar Telescope, we look at general trends in the properties of magnetic bright points. In total we track 300 MBPs in the data set and we employ NICOLE inversions to ascertain various parameters for the bright points such as line-of-sight magnetic field strength and line-of-sight velocity, for comparison. We observe a bimodal distribution in terms of maximum magnetic field strength in the bright points with peaks at ∼480 G and ∼1700 G, although we cannot attribute the kilogauss fields in this distribution solely to the process of convective collapse. Analysis of muram simulations does not return the same bimodal distribution. However, the simulations provide strong evidence that the emergence of new flux and diffusion of this new flux play a significant role in generating the weak bright point distribution seen in our observations.

Moore, Christopher J; Gerosa, Davide; Klein, Antoine

doi: 10.1093/mnrasl/slz104pmid: N/A

ABSTRACTThe progenitors of the high-mass black-hole mergers observed by LIGO and Virgo are potential LISA sources and promising candidates for multiband GW observations. In this letter, we consider the minimum signal-to-noise ratio these sources must have to be detected by LISA bearing in mind the long duration and complexity of the signals. Our revised threshold of ρthr ∼ 15 is higher than previous estimates, which significantly reduces the expected number of events. We also point out the importance of the detector performance at high frequencies and the duration of the LISA mission, which both influence the event rate substantially.

Nordlander, T; Bessell, M S; Da Costa, G S; Mackey, A D; Asplund, M; Casey, A R; Chiti, A; Ezzeddine, R; Frebel, A; Lind, K; Marino, A F; Murphy, S J; Norris, J E; Schmidt, B P; Yong, D

doi: 10.1093/mnrasl/slz109pmid: N/A

ABSTRACTWe report the discovery of SMSS J160540.18−144323.1, a new ultra metal-poor halo star discovered with the SkyMapper telescope. We measure $\left[\rm {Fe}/\rm {H}\right]= -6.2 \pm 0.2$ (1D LTE), the lowest ever detected abundance of iron in a star. The star is strongly carbon-enhanced, $\left[\rm {C}/\rm {Fe}\right] = 3.9 \pm 0.2$, while other abundances are compatible with an α-enhanced solar-like pattern with $\left[\rm {Ca}/\rm {Fe}\right] = 0.4 \pm 0.2$, $\left[\rm {Mg}/\rm {Fe}\right] = 0.6 \pm 0.2$, $\left[\rm {Ti}/\rm {Fe}\right] = 0.8 \pm 0.2$, and no significant s- or r-process enrichment, $\left[\rm {Sr}/\rm {Fe}\right] \lt 0.2$ and $\left[\rm {Ba}/\rm {Fe}\right] \lt 1.0$ (3σ limits). Population III stars exploding as fallback supernovae may explain both the strong carbon enhancement and the apparent lack of enhancement of odd-Z and neutron-capture element abundances. Grids of supernova models computed for metal-free progenitor stars yield good matches for stars of about $10\, \rm M_\odot$ imparting a low kinetic energy on the supernova ejecta, while models for stars more massive than roughly $20\, \rm M_\odot$ are incompatible with the observed abundance pattern.

Wittkowski, David; Kampert, Karl-Heinz

doi: 10.1093/mnrasl/slz083pmid: N/A

ABSTRACTCosmogenic neutrinos originate from interactions of cosmic rays propagating through the universe with cosmic background photons. Since both high-energy cosmic rays and cosmic background photons exist, the existence of high-energy cosmogenic neutrinos is certain. However, their flux has not been measured so far. Therefore, we calculated the flux of high-energy cosmogenic neutrinos arriving at the Earth on the basis of elaborate 4D simulations that take into account three spatial degrees of freedom and the cosmological time-evolution of the universe. Our predictions for this neutrino flux are consistent with the recent upper limits obtained from large-scale cosmic-ray experiments. We also show that the extragalactic magnetic field has a strong influence on the neutrino flux. The results of this work are important for the design of future neutrino observatories, since they allow to assess the detector volume and observation time that are necessary to detect high-energy cosmogenic neutrinos in the near future. An observation of such neutrinos would push multimessenger astronomy to hitherto unachieved energy scales.

Tian (田雍), Yong; Ko (高仲明), Chung-Ming

doi: 10.1093/mnrasl/slz095pmid: N/A

ABSTRACTRecently, from the new Spitzer Photometry and Accurate Rotation Curves data, McGaugh, Lelli & Schombert reported a tight radial acceleration relation between the observed total acceleration and the acceleration produced by baryons in spiral galaxies. The relation can be fitted by different functions. However, these functions can be discerned if we express the data in the form of a halo acceleration relation. The data reveals a maximum in the halo acceleration. We examined the NFW (cusp) and Burkert (core) profiles in the context of dark matter and different parameter families of the interpolating function in the framework of modified Newtonian dynamics.

Kajava, J J E; Motta, S E; Sanna, A; Veledina, A; Del Santo, M; Segreto, A

doi: 10.1093/mnrasl/slz089pmid: N/A

ABSTRACTMAXI J1820+070, a black hole candidate first detected in early 2018 March, was observed by XMM–Newton during the outburst rise. In this letter we report on the spectral and timing analysis of the XMM–Newton X-ray and UV data, as well as contemporaneous X-ray data from the Swift satellite. The X-ray spectrum is well described by a hard thermal Comptonization continuum. The XMM–Newton X-ray light curve shows a pronounced dipping interval, and spectral analysis indicates that it is caused by a moderately ionized partial covering absorber. The XMM–Newton/OM U-filter data do not reveal any signs of the 17 h orbital modulation that was seen later on during the outburst decay. The UV/X-ray cross-correlation function shows a complex shape, with a peak at positive lags of about 4 s and a precognition dip at negative lags, which is absent during the X-ray dipping episode. Such shape could arise if the UV emission comes partially from synchrotron self-Compton emission near the black hole, as well as from reprocessing of the X-rays in the colder accretion disc further out.