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Active regions and the large-scale magnetic field of solar cycle 24
No full textContext. Most of the intracyclic variability in the large-scale solar magnetic field comes from the equatorial dipole component of the solar magnetic field. The equatorial dipole component is highly sensitive to the longitude distribution of the active regions.
Aims. We quantify the effect of individual active regions on the large-scale solar magnetic field of the solar cycle 24. We study the effect of the longitude distribution of active regions on the strength of the large-scale dipole component.
Methods. We used a surface flux transport (SFT) model to simulate the evolution of individual active regions and quantified their effect on the large-scale magnetic field using the recently developed vector sum method. We took advantage of the longitudinal translational invariance of the SFT model and compared the observed solar cycle 24 to the 10 000 simulations of the solar cycle 24 using randomized longitudinal source locations, but otherwise identical flux emergence.
Results. We find that taking into account both the axial and equatorial components of the vector sum characterizing the global solar magnetic field sets better constraints on the parameter space of the SFT model than, for example, using the axial dipole moment alone as an optimization metric. We studied the maximum of cycle 24 and identified the recurrent and localized flux emergence in the southern hemisphere as the main culprit behind the rapid strengthening of the large-scale magnetic field in late 2014. We find that during the declining phase of the solar cycle, the strength of the large-scale magnetic field stayed above the median level of randomized simulations (p < 0.027) for 42 subsequent rotations (from September 2014 to November 2017). This indicates that the longitudinal distribution of active regions is not random and, rather, that it demonstrates a tendency for some regions to emerge at longitudes where their equatorial components reinforce the large-scale equatorial field
ExoNAMD: Leveraging the spin–orbit angle to constrain the dynamics of multi-planet systems
No full textMulti-planet systems are excellent laboratories for studying the formation and evolution of exoplanets inside the same stellar environment. The number of known multi-planet systems is expected to skyrocket with the advent of PLATO and the Roman space telescope. The spin–orbit angle is a key context information for the systems’ dynamical history, and in recent years a growing number of planets had their spin–orbit angles measured, revealing a large diversity in orbital configurations, from well-aligned to polar, and even retrograde, orbits. Still, observers lack a robust tool with which to compare the dynamical state of different systems and to select the most suitable ones for future avenues of exploration, such as investigating the evolutionary pathways and their links to the atmospheric composition. Here, we present ExoNAM
Beyond the Clouds: S3 as the most distant extended Milky Way stream, not of LMC origin
No full textContext. While the influence of the LMC on Milky Way (MW) stellar streams has been extensively studied, streams associated with the Clouds have received far less attention. Beyond the Magellanic Stream, only four stream candidates (S1–S4) have been reported.
Aims. We focus on the S3 stream, a long (~30°) and narrow (~1.2°) structure at 60–80 kpc that is nearly aligned with the LMC. Our goals are: (1) to validate the stream through a kinematic analysis of S3 candidates with Gaia DR3 data; (2) to enlarge the sample of potential members with machine-learning methods; and (3) to model the stream in order to test its association with either the MW or the LMC.
Methods. We selected new S3 candidates with a supervised neural network classifier trained on Gaia DR3 astrometry and photometry, and further reduced contamination through a polygon cut in the proper-motion space. To investigate the origin of S3, we evolved stream models within time-dependent, deforming MW and LMC halos, thereby accounting for possible effects of the MW–LMC interaction.
Results. We identify 1542 high-confidence new S3 stream candidates and find that the stream’s apparent width has grown from ~1.2° to ~3–4° compared to previous studies. We also present a list of 440 potential S3 red clump stars, which are valuable targets for spectroscopic follow-up thanks to their well-defined luminosities and ability to yield precise distances. Both modelling and a comparison of S3 stars’ closest approach distance and velocity with the LMC’s escape velocity indicate that S3 likely does not originate from the LMC and instead represents a distant (~75 kpc) MW stream.
Conclusions. S3 is the most distant (~75 kpc) extended (~30° long, ~3–4° thick) MW stream known, offering a unique probe of the outer halo and the LMC’s recent influence. Its angular width corresponds to a physical thickness of ~4–5 kpc, making S3 among the thickest streams discovered
Double-hump spectrum, pulse profile dip, and pulsed fraction spectra from the low-accretion regime in the X-ray pulsar MAXI J0655-013
No full textContext. Accreting X-ray pulsars (XRPs) undergo different physical regimes depending on different mass accretion rates, with related changes in the emitted X-ray spectral properties. Recent observations have shown a dramatic change in the emission properties of this class of sources observed at low luminosity.
Aims. We explore the timing and spectral properties of the XRP MAXI J0655-013 observed in the low-luminosity regime (about 5 × 1033 erg s−1) to witness the corresponding spectral shape and pulse profiles.
Methods. We employed recent XMM-Newton and NuSTAR pointed observations of the MAXI J0655-013 X-ray activity during the low-luminosity stage. We explored several spectral models to fit the data and test theoretical expectations of the dramatic transition of the spectral shape compared to the higher luminosity regime. We studied the pulsating nature of the source and found a precise timing solution. We explored the energy-resolved pulse profiles and the derived energy dependence of different pulsed fraction estimators (PFminmax and PFrms). We also obtained NuSTAR pulsed fraction spectra (PFS) at different luminosity regimes.
Results. The MAXI J0655-013 spectrum is well fit by a double Comptonization model, in agreement with recent observational results and theoretical expectations that explain the observed spectrum as being composed of two distinct bumps, each dominated by different polarization modes. We measured a spin period of 1081.86 ± 0.02 s, consistent with the source spinning up compared to previous observations, yielding an upper limit for the magnetic field strength of B ≲ 9 × 1013 G. The pulse profiles show a single broad peak interrupted by a sharp dip that coincides with an increase in the hardness ratio, and thus likely due to absorption. For the low-luminosity observation, the PFminmax increases with energy up to ∼100% in the 10–30 keV band, while the PFrms remains steady at ∼60%. The PFS obtained at high luminosity shows evidence of an iron Kα emission line but no indications of a cyclotron line
Heavy-nucleus-acoustic solitary modes in a thermally degenerate quantum plasma
No full textA rigorous theoretical study on the formation and propagation properties of nucleus-acoustic solitary waves has been carried out via the fluid dynamical approach. A three-component thermally degenerate relativistic quantum plasma (TDRQP) system is considered, composed of thermally degenerate relativistic non-inertial electrons and non-inertial non-relativistic degenerate light nuclei (the combined degenerate and thermal pressure of electrons and light nuclei provide the restoring force) and inertial non-degenerate heavy nucleus species (whose mass density provides the inertia). The nonlinear properties of heavy-nucleus-acoustic solitary waves (HNASWs) in such a thermally degenerate quantum plasma are analyzed in detail, via the solitary wave solution of KdV equation. The fundamental characteristics of small-amplitude thermal and degenerate pressure-driven HNASWs in different thermally degenerate plasma medium are analyzed, and the effect of non-relativistically light nucleus and non/ultra-relativistically electron degeneracies, the heavy nucleus temperature effect, the influence of light and heavy nuclei number densities and masses on the propagation dynamics of HNASWs are also examined. It is investigated that the presence of mobile heavy nuclei forms a new waves “heavy-nucleus-acoustic waves (HNAWs)” in TDRQP. It is found that the phase velocity increases with the density of heavy nuclei species, while the increase in mass of heavy nuclei species may lead to the propagation of taller and steeper solitons in TDRQP. It is predicted that the amplitude and the width of the solitary waves increases for ultra-relativistic case. It is also examined that the amplitude and width of HNASWs increases with the decrease in heavy nuclei temperature, while the amplitude (width) increases (decreases) with the increase (decrease) in heavy (light) nuclei number density. The implications of our results for nonlinear structures in astrophysical, space, and laboratory plasma environments are briefly discussed
Effects of genotypes and sowing date on seed yield, oil content, and fatty acid profile of camelina (
No full textDetermining the appropriate sowing date can have a significant impact on increasing the yield potential of alternative crops such as camelina in semiarid agricultural ecosystems. This study aimed to determine the effects of sowing date and genotype on yield components, seed yield, oil yield, oil content and fatty acid profile of camelina. A split-plot experimental design using sowing dates (30–31 March, 5–8 April, 15–17 April, 25–28 April and 6–7 May) as main plot and genotypes as subplots was adopted during two growing seasons (2021–2022). The results of the present study showed that delaying sowing exposed the seed-filling period to high temperatures, which resulted in significant decreases in seed yield and oil content of camelina. Thus, the most positive results in terms of yield and yield components were obtained from the first and second sowing dates. In this respect, the highest seed yield (1982 kg ha−1), oil yield (797 kg ha−1) and seed oil content (40.2%) were obtained from the Arslanbey genotype. In addition, while the rates of linolenic acid (36.75%), palmitic acid (5.12%), stearic acid (2.55%), arachidic acid (1.55%) and eicosenoic acid (16.58%) in camelina seed showed high values at the first and second sowing times, these rates relatively decreased as the sowing time was delayed. On the contrary, the highest values in terms of linoleic acid and oleic acid were observed in the fourth sowing date. As a result, although the ecological conditions of the region are suitable for camelina cultivation, significant decreases in camelina seed yield and oil content were observed with the delay of sowing. In this context, it was determined that the suitable sowing time for spring camelina cultivation in the Muş province located in the east of Türkiye is the last week of March and the first week of April. However, further research is needed to optimize other agricultural inputs for camelina production in the region
Spiral galaxies with flat radial abundance gradients at large radii
No full textWe consider the oxygen abundance distributions for a sample of massive (log(M★/M⊙) ≳ 10) spiral galaxies from the Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey in which the radial abundance gradient flattens to a constant value outside of the outer break radius, Rb, outer. The outer break radius can be considered as a dividing radius between the galaxy and the circumgalactic medium (CGM). The values of the Rb, outer range from ∼0.8 R25 to ∼1.45 R25, where R25 is the optical (isophotal) radius of the galaxy. The oxygen abundances in the CGM range from 12+log(O/H) ∼8.0 to ∼8.5. The oxygen abundance distribution in each of our galaxies also shows the inner break in the radial abundance profile at the radius Rb, inner. The metallicity gradient in the outer part of the galaxy (Rb, inner < R < Rb, outer) is steeper than in the inner part (R < Rb, inner). The behaviour of the radial abundance distributions in these galaxies can be explained by assuming an interaction with (capture of the gas from) a small companion and adopting the model for the chemical evolution of galaxies with a radial gas flow. The interaction with a companion results in the mixing of gas and a flat metallicity gradient in the CGM. The capture of the gas from a companion increases the radial gas inflow rate and changes the slope of the radial abundance gradient in the outer part of the galaxy
Infrared emission from
No full textQuasars at the dawn of cosmic time (z > 6) are fundamental probes for investigating the early coevolution of supermassive black holes and their host galaxy. Nevertheless, their infrared spectral energy distribution currently remains poorly constrained because the photometric coverage that probes the far-infrared wavelength range in which the dust modified blackbody is expected to peak (∼80 μm) is limited. We studied the high-frequency dust emission via a dedicated ALMA Band 8 (∼400 GHz) campaign targeting 11 quasar host galaxies at 6 < z < 7. Combined with archival observations in other ALMA bands, this program enables a detailed characterization of their infrared emission, which allowed us to derive dust masses (Md), dust emissivity indexes (β), dust temperatures (Td), infrared luminosities (LIR), and associated star formation rates (SFRs). Our analysis confirmed that dust temperature is higher in this sample (34−65 K) than in local main-sequence galaxies, and this finding can be linked to the increased star formation efficiency we derived, as also suggested by the [CII]158 μm deficit. Most remarkably, we note that the average value of Td of this sample does not differ from the one that is observed in luminous, ultraluminous and hyperluminous infrared galaxies at different redshifts that show no signs of hosting a quasar. Finally, our findings suggest that the presence of a bright AGN does not significantly bias the derived infrared properties, although further high frequency observations with a high spatial resolution might reveal more subtle effects on subkiloparsec scales
Coherent bulk motions in a weakly turbulent merging Coma cluster
No full textThe hot gas permeating galaxy clusters – the intracluster medium (ICM) – is a key tracer of their assembly history and internal dynamics. Understanding the motion of this gas provides critical insight into processes such as mergers, turbulence, and energy dissipation in the largest gravitationally bound structures in the Universe. The Coma cluster is a nearby, massive system long suspected to be dynamically disturbed. Previous high-resolution X-ray spectroscopy with the XRISM mission revealed bulk motions in the cluster core and southern regions. Here we present new XRISM Resolve observations of a northern region in Coma, which reveal a coherent velocity gradient of nearly 530 km/s across the cluster from south to north. We find that the hot gas in this northern region exhibits modest line-of-sight motions and uniform thermodynamic properties, indicating relatively mild local disturbances. The consistent levels of turbulence throughout the cluster suggest that the energy from a past merger has been distributed on large scales. These findings provide compelling evidence for an off-axis merger event and demonstrate how high-resolution X-ray spectroscopy can uncover subtle dynamical signatures in the ICM, offering important constraints for simulations of cluster evolution
Holiday in a black hole
No full textA “blackholonaut” making a tour through a black hole can go out by using his engines; when the black hole is charged, this typically occurs automatically. The tour takes a finite proper time. For an ingoing Painlevé-Gullstrand observer, the ingoing part also lasts a finite time; for an outgoing one, the outgoing part does so. These observers outside the black hole can communicate with each other and with a stationary observer. For the latter, the tour also lasts a finite time, even though signals emitted during the entrance to the black hole will reach him forever. On his clock, the blackholonaut comes out of the black hole in the infinte past. Cross-horizon communication with the blackholonaut is possible. Closed time-like curves occur for a stationary observer, but not for a pair of moving observers. If crossing points occur, they are peculiarities in the mathematical description by the observer, which do not relate to physical events