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Título de Acceso Abierto
The Astrophysical Journal (ApJ)
Resumen/Descripción – provisto por la editorial en inglés
The Astrophysical Journal is an open access journal devoted to recent developments, discoveries, and theories in astronomy and astrophysics. Publications in ApJ constitute significant new research that is directly relevant to astrophysical applications, whether based on observational results or on theoretical insights or modeling.Palabras clave – provistas por la editorial
astronomy; astrophysics
Disponibilidad
Institución detectada | Período | Navegá | Descargá | Solicitá |
---|---|---|---|---|
No detectada | desde jul. 1995 / hasta dic. 2023 | IOPScience |
Información
Tipo de recurso:
revistas
ISSN impreso
0004-637X
ISSN electrónico
1538-4357
Editor responsable
American Astronomical Society (AAS)
Idiomas de la publicación
- inglés
País de edición
Reino Unido
Información sobre licencias CC
Cobertura temática
Tabla de contenidos
Eta Carinae: A Tale of Two Periastron Passages
Theodore R. Gull; Felipe Navarete; Michael F. Corcoran; Augusto Damineli; David Espinoza; Kenji Hamaguchi; Henrik Hartman; D. John Hillier; Thomas Madura; Anthony F. J. Moffat; Patrick Morris; Krister Nielsen; Julian M. Pittard; Andrew M. T. Pollock; Noel D. Richardson; Christopher M. P. Russell; Ian R. Stevens; Gerd Weigelt
<jats:title>Abstract</jats:title> <jats:p>Since 2002, the far-ultraviolet (FUV) flux (1150–1680 Å) of Eta Carinae, monitored by the Hubble Space Telescope/Space Telescope Imaging Spectrograph, has increased by an order of magnitude. This increase is attributed to partial dissipation of a line-of-sight (LOS) occulter that blocks the central core of the system. Across the 2020 February periastron passage, changes in the FUV emission show a stronger wavelength dependence than occurred across the 2003 July periastron passage. Across both periastron passages, most of the FUV spectrum dropped in flux then recovered a few months later. The 2020 periastron passage included enhancements of FUV flux in narrow spectral intervals near periastron followed by a transient absorption and recovery to pre-periastron flux levels. The drop in flux is due to increased absorption by singly ionized species as the secondary star plunges deep into the wind of the primary star, which blocks the companion’s ionizing radiation. The enhanced FUV emission is caused by the companion’s wind-blown cavity briefly opening a window to deeper layers of the primary star. This is the first time transient brightening has been seen in the FUV comparable to transients previously seen at longer wavelengths. Changes in resonance line-velocity profiles hint that the dissipating occulter is associated with material in LOS moving at −100 to −300 km s<jats:sup>−1</jats:sup>, similar in velocity of structures previously associated with the 1890s lesser eruption.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 102
Evidence of X-Ray Plateaus Driven by the Magnetar Spindown Winds in Gamma-Ray Burst Afterglows
Shu-Jin Hou; Shuang Du; Tong Liu; Hui-Jun Mu; Ren-Xin Xu
<jats:title>Abstract</jats:title> <jats:p>The central engine of gamma-ray bursts (GRBs) remains an open and cutting-edge topic in the era of multimessenger astrophysics. X-ray plateaus appear in some GRB afterglows, which are widely considered to originate from the spindown of magnetars. According to the stable magnetar scenario of GRBs, an X-ray plateau and a decay phase ∼<jats:italic>t</jats:italic> <jats:sup>−2</jats:sup> should appear in X-ray afterglows. Meanwhile, the “normal” X-ray afterglow is produced by the external shock from a GRB fireball. We analyze the Neil Gehrels Swift GRB data, then find three gold samples that have an X-ray plateau and a decay phase ∼<jats:italic>t</jats:italic> <jats:sup>−2</jats:sup> superimposed on the jet-driven normal component. Based on these features of the lightcurves, we argue that the magnetars should be the central engines of these three GRBs. Future joint multimessenger observations might further test this possibility, which can then be beneficial to constrain GRB physics.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 102
Dynamics of Langmuir Wave Spectra in Randomly Inhomogeneous Solar Wind Plasmas
C. Krafft; A. S. Volokitin
<jats:title>Abstract</jats:title> <jats:p>Solar coronal and wind plasmas often contain density fluctuations of various scales and amplitudes. The scattering of Langmuir wave turbulence on these inhomogeneities modifies the properties of the radiated electromagnetic emissions traveling from the Sun to the Earth. This paper shows the similarities between the physical results obtained by (i) a model based on the Zakharov equations, describing the self-consistent dynamics of Langmuir wave turbulence spectra in a plasma with external density fluctuations, and (ii) a modeling, within the framework of geometric optics approximation, of quasi-particles (representing plasmon quanta) moving in a fluctuating potential. It is shown that the dynamics of the Langmuir spectra is governed by anomalous diffusion processes, as a result of multiple scattering of waves on the density fluctuations; the same dynamics are observed in the momenta distributions of quasi-particles moving in potential structures with random inhomogeneities. These spectra and distributions are both characterized by a fast broadening during which energy is transported to larger wavevectors and momenta, exhibiting nonlinear time dependence of the average squares of wavevectors and quasi-particle momenta as well as non-Gaussian tails in the asymptotic stage. The corresponding diffusion coefficients depend on the time and are proportional to the square of the average level of density (or potential) fluctuations. It appears that anomalous transport and superdiffusion phenomena are responsible for the spectral broadening.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 103
Ultimate Fast Gyrosynchrotron Codes
Alexey A. Kuznetsov; Gregory D. Fleishman
<jats:title>Abstract</jats:title> <jats:p>The past decade has seen a dramatic increase in practical applications of microwave gyrosynchrotron emission for plasma diagnostics and three-dimensional modeling of solar flares and other astrophysical objects. This breakthrough became possible due to an apparently minor, technical development of fast gyrosynchrotron codes, which enormously reduced the computation time needed to calculate a single spectrum, while preserving the accuracy of the computation. However, the available fast codes are limited in that they can only be used for a factorized distribution over the energy and pitch angle, while the distribution of electrons over energy or pitch angle is limited to a number of predefined analytical functions. In realistic simulations, these assumptions do not hold; thus, the codes free from the mentioned limitations are called for. To remedy this situation, we extended our fast codes to work with an arbitrary input distribution function of radiating electrons. We accomplished this by implementing fast codes for a distribution function described by an arbitrary numerically defined array. In addition, we removed several other limitations of the available fast codes and improved treatment of the free–free component. The ultimate fast codes presented here allow for an arbitrary combination of the analytically and numerically defined distributions, which offers the most flexible use of the fast codes. We illustrate the code with a few simple examples.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 103
Magnetic Archaeology of Early-type Stellar Dynamos
Adam S. Jermyn; Matteo Cantiello
<jats:title>Abstract</jats:title> <jats:p>Early-type stars show a bimodal distribution of magnetic field strengths, with some showing very strong fields (≳1 kG) and others very weak fields (≲10 G). Recently, we proposed that this reflects the processing or lack thereof of fossil fields by subsurface convection zones. Stars with weak fossil fields process these at the surface into even weaker dynamo-generated fields, while in stars with stronger fossil fields magnetism inhibits convection, allowing the fossil field to remain as is. We now expand on this theory and explore the timescales involved in the evolution of near-surface magnetic fields. We find that mass loss strips near-surface regions faster than magnetic fields can diffuse through them. As a result, observations of surface magnetism directly probe the frozen-in remains of the convective dynamo. This explains the slow evolution of magnetism in stars with very weak fields: these dynamo-<jats:italic>generated</jats:italic> magnetic fields evolve on the timescale of the mass loss, not that of the dynamo.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 104
Testing for Dark Matter in the Outskirts of Globular Clusters
Raymond G. Carlberg; Carl J. Grillmair
<jats:title>Abstract</jats:title> <jats:p>The proper motions of stars in the outskirts of globular clusters are used to estimate cluster velocity dispersion profiles as far as possible within their tidal radii. We use individual color–magnitude diagrams to select high-probability cluster stars for 25 metal-poor globular clusters within 20 kpc of the Sun, 19 of which have substantial numbers of stars at large radii. Of the 19, 11 clusters have a falling velocity dispersion in the 3–6 half-mass radii range, 6 are flat, and 2 plausibly have a rising velocity dispersion. The profiles are all in the range expected from simulated clusters that started at high redshift in a zoom-in cosmological simulation. The 11 clusters with falling velocity dispersion profiles are consistent with no dark matter above the Galactic background. The six clusters with approximately flat velocity dispersion profiles could have local dark matter, but are ambiguous. The two clusters with rising velocity dispersion profiles are consistent with a remnant local dark matter halo, but need membership confirmation and detailed orbital modeling to further test these preliminary results.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 104
Solar Wind Anomalies at 1 au and Their Associations with Large-scale Structures
Yan Li; Shaosui Xu; Janet G. Luhmann; Benoit Lavraud
<jats:title>Abstract</jats:title> <jats:p>We study solar wind anomalies and their associations with solar wind structures using the STEREO solar wind and suprathermal electron (STE) data from IMPACT and PLASTIC. We define solar wind anomalies as temporary and local excursions from the average solar wind state, regardless of their origins, for six anomalies: sunward strahls, counterstreaming suprathermal electrons, suprathermal electron depletions, nearly radial magnetic field episodes, anomalously low proton temperatures, and anomalously low proton beta. We first establish the solar wind synoptic contour displays, which show the expected variations in solar wind structure during the solar cycle: recurrent corotating heliospheric magnetic field (HMF) and stream structures are dominant during solar quiet times around the solar minimum (2008 December) preceding cycle 24, while complex structures characterize solar active times around the solar maximum (2014 April). During the declining phase of the cycle (2016–2019), the stream structures remain complex, but the HMF sectors show the structures of the solar minimum. We then systematically study the six anomalies by analyzing the STE data using automated procedures. All anomalies present some degree of dependence on the large-scale solar wind structure, especially around the solar minimum, implying that the solar wind structure plays a role in either the generation or transportation of these anomalies. One common feature of all of the anomalies is that the distributions of the durations of the anomalous episodes all peak at the 1 hr data resolution, but monotonically decrease over longer durations, which may arguably imply that solar anomalies occur on a continuum of temporal and spatial scales.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 105
Tracing the Origin of Moving Groups. III. Detecting Moving Groups in LAMOST DR7
Yong Yang; Jingkun Zhao; Jiajun Zhang; Xianhao Ye; Gang Zhao
<jats:title>Abstract</jats:title> <jats:p>We revisit the moving groups (MGs) in the solar neighborhood with a sample of 91,969 nearby stars constructed from LAMOST DR7. Using the wavelet technique and Monte Carlo simulations, five MGs together with a new candidate located at <jats:italic>V</jats:italic>≃−130 km s<jats:sup>−1</jats:sup> are detected simultaneously in <jats:inline-formula> <jats:tex-math> <?CDATA $V-\sqrt{{U}^{2}+2{V}^{2}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>V</mml:mi> <mml:mo>−</mml:mo> <mml:msqrt> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>U</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>+</mml:mo> <mml:mn>2</mml:mn> <mml:msup> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:msqrt> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac289eieqn1.gif" xlink:type="simple" /> </jats:inline-formula> space. Taking into account the other known MGs, we conclude that MGs in the Galactic disk are spaced by approximately 15–25 km s<jats:sup>−1</jats:sup> along <jats:italic>V</jats:italic> velocity. The origin of detected MGs is analyzed through the distributions of [Fe/H]−[Mg/Fe] and ages. Our results support attributing the origin to the continuous resonant mechanisms probably induced by the bar or spiral arms of the Milky Way.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 105
Fermi-LAT Detection of Extended Gamma-Ray Emission in the Vicinity of SNR G045.7-00.4: Evidence of Escaping Cosmic Rays Interacting with the Surrounding Molecular Clouds
Hai-Ming Zhang; Ruo-Yu Liu; Yang Su; Hui Zhu; Shao-Qiang Xi; Xiang-Yu Wang
<jats:title>Abstract</jats:title> <jats:p>We present an analysis of Fermi Large Area Telescope data of the gamma-ray emission in the vicinity of a radio supernova remnant (SNR), G045.7-00.4. To study the origin of the gamma-ray emission, we also make use of the CO survey data of Milky Way Imaging Scroll Painting to study the massive molecular gas complex that surrounds the SNR. The whole size of the gigaelectronvolt emission is significantly larger than that of the radio morphology. Above 3 GeV, the gigaelectronvolt emission is resolved into two sources: one is spatially consistent with the position of the SNR with a size comparable to that of the radio emission, and the other is located outside of the western boundary of the SNR and spatially coincident with the densest region of the surrounding molecular cloud. We suggest that the gigaelectronvolt emission of the western source may arise from cosmic rays (CRs) that have escaped the SNR and illuminated the surrounding molecular cloud. We find that the gamma-ray spectra of the western source can be consistently explained by this scenario with a total energy of ∼10<jats:sup>50</jats:sup> erg in escaping CRs assuming the escape is isotropic.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 106
Methanol at the Edge of the Galaxy: New Observations to Constrain the Galactic Habitable Zone
J. J. Bernal; C. D. Sephus; L. M. Ziurys
<jats:title>Abstract</jats:title> <jats:p>The Galactic Habitable Zone (GHZ) is a region believed hospitable for life. To further constrain the GHZ, observations have been conducted of the <jats:italic>J</jats:italic> = 2 → 1 transitions of methanol (CH<jats:sub>3</jats:sub>OH) at 97 GHz, toward 20 molecular clouds located in the outer Galaxy (<jats:italic>R</jats:italic> <jats:sub>GC</jats:sub> = 12.9–23.5 kpc), using the 12 m telescope of the Arizona Radio Observatory. Methanol was detected in 19 out of 20 observed clouds, including sources as far as <jats:italic>R</jats:italic> <jats:sub>GC</jats:sub> = 23.5 kpc. Identification was secured by the measurement of multiple asymmetry and torsional components in the <jats:italic>J</jats:italic> = 2 → 1 transition, which were resolved in the narrow line profiles observed (Δ<jats:italic>V</jats:italic> <jats:sub>1/2</jats:sub> ∼ 1–3 km s<jats:sup>−1</jats:sup>). From a radiative transfer analysis, column densities for these clouds of <jats:italic>N</jats:italic> <jats:sub>tot</jats:sub> = 0.1–1.5 × 10<jats:sup>13</jats:sup> cm<jats:sup>−2</jats:sup> were derived, corresponding to fractional abundances, relative to H<jats:sub>2</jats:sub>, of <jats:italic>f</jats:italic> (CH<jats:sub>3</jats:sub>OH) ∼ 0.2–4.9 × 10<jats:sup>−9</jats:sup>. The analysis also indicates that these clouds are cold (<jats:italic>T</jats:italic> <jats:sub>K</jats:sub> ∼ 10–25 K) and dense (n(H<jats:sub>2</jats:sub>) ∼ 10<jats:sup>6</jats:sup> cm<jats:sup>−3</jats:sup>), as found from previous H<jats:sub>2</jats:sub>CO observations. The methanol abundances in the outer Galaxy are comparable to those observed in colder molecular clouds in the solar neighborhood. The abundance of CH<jats:sub>3</jats:sub>OH therefore does not appear to decrease significantly with distances from the Galactic Center, even at <jats:italic>R</jats:italic> <jats:sub>GC</jats:sub> ∼ 20–23 kpc. Furthermore, the production of methanol is apparently not affected by the decline in metallicity with galactocentric distance. These observations suggest that organic chemistry is prevalent in the outer Galaxy, and methanol and other organic molecules may serve to assess the GHZ.</jats:p>
Palabras clave: Space and Planetary Science; Astronomy and Astrophysics.
Pp. 106