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Astronomie, Physik
Institute of Physics Publishing IOP
0004-637X
jährlich 36 mal
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Electron Densities and Nitrogen Abundances in Ionized Gas Derived Using [N ii ] Fine-structure and Hydrogen Recombination Lines
We present a method for deriving the electron density of ionized gas using the ratio of the intensity of the [N ii ] 205 μ m line to that of hydrogen radio recombination lines (RRLs). We use this method to derive electron densities of 21 velocity components in 11 lines of sight through the Galaxy, including the Galactic center. We observed, at high spectral resolution, the [N ii ] 205 μ m with the Herschel /HIFI and SOFIA/GREAT instruments and the RRLs with the Green Bank Telescope and the NASA Deep Space Network Deep Space Station 43 (DSS-43) telescope. We find typical electron densities between 8 and 170 cm −3 , which are consistent with those derived at low spectral resolution using the [N ii ] 205 μ m/122 μ m ratio with Herschel /PACS on a larger sample of sight lines in the Galactic plane. By matching the electron densities derived from the [N
Determination of Transport Coefficients by Coronal Seismology of Flare-induced Slow-mode Waves: Numerical Parametric Study of a 1D Loop Model
Recent studies of a flaring loop oscillation event on 2013 December 28 observed by the Atmospheric Imaging Assembly of the Solar Dynamics Observatory have revealed the suppression of thermal conduction and significant enhancement of compressive viscosity in hot (∼10 MK) plasma. In this study we aim at developing a new coronal seismology method for determining the transport coefficients based on a parametric study of wave properties using a 1D nonlinear magnetohydrodynamics (MHD) loop model in combination with the linear theory. The simulations suggest a two-step scheme: we first determine the effective thermal conduction coefficient from the observed phase shift between temperature and density perturbations as this physical parameter is insensitive to the unknown viscosity; then from the loop model with the obtained thermal conduction coefficient, we determine the effective viscosity coefficient from the observed decay time using the parametric modeling. With this new sei...
Rankine–Hugoniot Shock Conditions for Space and Astrophysical Plasmas Described by Kappa Distributions
This paper provides the set of Rankine–Hugoniot (R–H) jump conditions for shocks in space and astrophysical plasmas described by kappa, distributions. The characteristic result is the development of a new R–H condition that transforms the values of kappa upstream and downstream the shock. The kappa index parameterizes and labels kappa distributions, and it is necessary for characterizing the thermodynamics of space plasmas. This first approach is restricted to non-magnetized plasmas, and the whole achievement is derived by following first principles of statistical mechanics and thermodynamics. The results show that, depending on the shock strength, the kappa indices across the shock may decrease or increase, indicating cases of shock acceleration or deceleration, respectively.
Can Neutron-star Mergers Explain the r -process Enrichment in Globular Clusters?
Star-to-star dispersion of r -process elements has been observed in a significant number of old, metal-poor globular clusters (GCs). We investigate early-time neutron-star mergers as the mechanism for this enrichment. Through both numerical modeling and analytical arguments, we show that neutron-star mergers cannot be induced through dynamical interactions early in the history of the cluster, even when the most liberal assumptions about neutron-star segregation are assumed. Therefore, if neutron-star mergers are the primary mechanism for r -process dispersion in GCs, they likely result from the evolution of isolated, primordial binaries in the clusters. Through population modeling of double neutron-star progenitors, we find that most enrichment candidates are fast-merging systems that undergo a phase of mass transfer involving a naked He-star donor. Only models where a significant number of double neutron-star progenitors proceed through this evolutionary phase give ...
The First Day in the Life of a Magnetar: Evolution of the Inclination Angle, Magnetic Dipole Moment, and Braking Index of Millisecond Magnetars during Gamma-Ray Burst Afterglows
The afterglow emission of some gamma-ray bursts (GRBs) shows a shallow decay (plateau) phase implying continuous injection of energy. The source of this energy is very commonly attributed to the spin-down power of a nascent millisecond magnetar. The magnetic dipole radiation torque is considered to be the mechanism causing the spin-down of the neutron star. This torque has a component working for the alignment of the angle between rotation and the magnetic axis, i.e., the inclination angle, which has been neglected in modeling GRB afterglow light curves. Here, we demonstrate the evolution of the inclination angle and magnetic dipole moment of nascent magnetars associated with GRBs. We constrain the initial inclination angle, magnetic dipole moment, and rotation period of seven magnetars by modeling the seven long-GRB afterglow light curves. We find that, in its first day, the inclination angle of a magnetar decreases rapidly. The rapid alignment of the magnetic and rotation axis...
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. I. Identifying and Characterizing the Protostellar Content of the OMC-2 FIR4 and OMC-2 FIR3 Regions
We present Atacama Large Millimeter/submillimeter Array (0.87 mm) and Very Large Array (9 mm) observations toward OMC-2 FIR4 and OMC-2 FIR3 within the Orion integral-shaped filament, thought to be two of the nearest regions of intermediate-mass star formation. We characterize the continuum sources within these regions on ∼40 au (0.″1) scales and associated molecular line emission at a factor of ∼30 better resolution than previous observations at similar wavelengths. We identify six compact continuum sources within OMC-2 FIR4, four in OMC-2 FIR3, and one additional source just outside OMC-2 FIR4. This continuum emission is tracing the inner envelope and/or disk emission on less than 100 au scales. HOPS-108 is the only protostar in OMC-2 FIR4 that exhibits emission from high-excitation transitions of complex organic molecules (e.g., methanol and other lines) coincident with the continuum emission. HOPS-370 in OMC-2 FIR3, with L ∼ 360 L ⊙ , also exhibits emi...
Uncertainty Quantification in Sunspot Counts
Observing and counting sunspots constitutes one of the longest-running scientific experiments, with first observations dating back to Galileo (around 1610). Today the sunspot number (SN) time series acts as a benchmark of solar activity in a large range of physical models. An appropriate statistical modeling, adapted to the time series’ complex nature, is, however, still lacking. In this work, we provide the first comprehensive uncertainty quantification analysis of sunspot counts. We study three components: the number of sunspots ( N s ), the number of sunspot groups ( N g ), and the composite N c , defined as {${N}_{c}:= {N}_{s}+10{N}_{g}$} . Those are reported by a network of observatories around the world and are corrupted by errors of various types. We use a multiplicative framework to provide, for these thr...
Bottom-up Acceleration of Ultra-high-energy Cosmic Rays in the Jets of Active Galactic Nuclei
It has been proposed that ultra-high-energy cosmic rays (UHECRs) up to 10 20 eV could be produced in the relativistic jets of powerful active galactic nuclei (AGNs) via a one-shot reacceleration of lower-energy CRs produced in supernova remnants (the espresso mechanism). We test this theory by propagating particles in realistic 3D magnetohydrodynamic simulations of ultrarelativistic jets and find that about 10% of the CRs entering the jet are boosted by at least a factor of ∼Γ 2 in energy, where Γ is the jet’s effective Lorentz factor, in agreement with the analytical expectations. Furthermore, about 0.1% of the CRs undergo two or more shots and achieve boosts well in excess of Γ 2 . Particles are typically accelerated up to the Hillas limit, suggesting that the espresso mechanism may promote galactic-like CRs to UHECRs even in AGN jets with moderate Lorentz factors, and not in powerful blazars only. Finally, we find that the sign of th...
Multiwavelength Stereoscopic Observation of the 2013 May 1 Solar Flare and CME
A M-class behind-the-limb solar flare on 2013 May 1 (SOL2013-05-01T02:32), accompanied by a (∼400 km s −1 ) coronal mass ejection (CME), was observed by several space-based observatories with different viewing angles. We investigated the RHESSI -observed occulted hard X-ray (HXR) emissions that originated at least 0.1 {${R}_{{\rm{S}}}$} above the flare site. Emissions below ∼10 keV revealed a hot, extended (11 MK, >60″) thermal source from the escaping CME core, with densities around 10 9 cm −3 . In such a tenuous hot plasma, ionization times scales are several minutes, consistent with the nondetection of the hot CME core in SDO /AIA’s 131 Å filter. The nonthermal RHESSI source originated from an even larger area (∼100″) at lower densities (10 8 cm −3 ) located above the hot core, but still behind the CME front. This i...
Dwarfs or Giants? Stellar Metallicities and Distances from ugrizG Multiband Photometry
We present a new fully data-driven algorithm that uses photometric data from the Canada–France Imaging Survey (CFIS; u ), Pan-STARRS 1 (PS1; griz ), and Gaia ( G ) to discriminate between dwarf and giant stars and to estimate their distances and metallicities. The algorithm is trained and tested using the Sloan Digital Sky Survey (SDSS)/SEGUE spectroscopic data set and Gaia photometric/astrometric data set. At [Fe/H] < −1.2, the algorithm succeeds in identifying more than 70% of the giants in the training/test set, with a dwarf contamination fraction below 30% (with respect to the SDSS/SEGUE data set). The photometric metallicity estimates have uncertainties better than 0.2 dex when compared with the spectroscopic measurements. The distances estimated by the algorithm are valid out to a distance of at least ∼80 kpc without requiring any prior on the stellar distribution and have fully independent uncertainties that take into account both random ...
The MOSDEF Survey: A Census of AGN-driven Ionized Outflows at z = 1.4–3.8
Using data from the MOSFIRE Deep Evolution Field (MOSDEF) survey, we present a census of active galactic nucleus (AGN)–driven ionized outflows in a sample of 159 AGNs at1.4 ≤ z ≤ 3.8. The sample spans AGN bolometric luminosities of 10 44–47 erg s −1 and includes both quiescent and star-forming galaxies extending across 3 orders of magnitude in stellar mass. We identify and characterize outflows from the H β , [O iii ], H α , and [N ii ] emission line spectra. We detect outflows in 17% of the AGNs, seven times more often than in a mass-matched sample of inactive galaxies in MOSDEF. The outflows are fast and galaxy-wide, with velocities of ∼400–3500 km s {${}^{-1}$} and spatial extents of 0.3–11.0 kpc. The incidence of outflows among AGNs is independent of the stellar mass of the host galaxy, with outf...
Search for Sources of Astrophysical Neutrinos Using Seven Years of IceCube Cascade Events
Low-background searches for astrophysical neutrino sources anywhere in the sky can be performed using cascade events induced by neutrinos of all flavors interacting in IceCube with energies as low as ∼1 TeV. Previously we showed that, even with just two years of data, the resulting sensitivity to sources in the southern sky is competitive with IceCube and ANTARES analyses using muon tracks induced by charge current muon neutrino interactions—especially if the neutrino emission follows a soft energy spectrum or originates from an extended angular region. Here, we extend that work by adding five more years of data, significantly improving the cascade angular resolution, and including tests for point-like or diffuse Galactic emission to which this data set is particularly well suited. For many of the signal candidates considered, this analysis is the most sensitive of any experiment to date. No significant clustering was observed, and thus many of the resulting constraints are the ...
UVIT Open Cluster Study. II. Detection of Extremely Low Mass White Dwarfs and Post–Mass Transfer Binaries in M67
A detailed study of the UV-bright stars in the old open star cluster M67 is presented based on the far-UV observations using the Ultra Violet Imaging Telescope (UVIT) on ASTROSAT . The UV and UV–optical color–magnitude diagrams (CMDs), along with overlaid isochrones, are presented for the member stars, which include blue straggler stars (BSSs), triple systems, white dwarfs (WDs), and spectroscopic binaries. The CMDs suggest the presence of excess UV flux in many members, which could be extrinsic or intrinsic to them. We construct multiwavelength spectral energy distributions (SEDs) using photometric data from the UVIT , Gaia DR2, Two Micron All Sky Survey, and Wide-Field Infrared Survey Explorer surveys, along with optical photometry. We fitted model SEDs to seven WDs and find that four of them have mass >0.5 M ⊙ and cooling age of less than 200 Myr, thus demanding BSS progenitors. SED fits to 23 stars detect extremely low mass (ELM) WD co...
An ALMA View of Molecular Filaments in the Large Magellanic Cloud. I. The Formation of High-mass Stars and Pillars in the N159E-Papillon Nebula Triggered by a Cloud–Cloud Collision
We present ALMA observations of CO isotopes and 1.3 mm continuum emission toward the N159E-Papillon Nebula in the Large Magellanic Cloud (LMC). The spatial resolution is 0.″25–0.″28 (0.06–0.07 pc), which is a factor of 3 higher than previous ALMA observations in this region. The high resolution allowed us to resolve highly filamentary CO distributions with typical widths of ∼0.1 pc (full width half maximum) and line masses of a few 100 M ⊙ pc −1 . The filaments (more than ten in number) show an outstanding hub-filament structure emanating from the nebular center toward the north. We identified for the first time two massive protostellar outflows of ∼10 4 yr dynamical age along one of the most massive filaments. The observations also revealed several pillar-like CO features around the Nebula. The H ii region and the pillars have a complementary spatial distribution and the column density of the pillars is an order of m...
An ALMA View of Molecular Filaments in the Large Magellanic Cloud. II. An Early Stage of High-mass Star Formation Embedded at Colliding Clouds in N159W-South
We have conducted ALMA CO isotopes and 1.3 mm continuum observations toward filamentary molecular clouds of the N159W-South region in the Large Magellanic Cloud with an angular resolution of ∼0.″25 (∼0.07 pc). Although the previous lower-resolution (∼1″) ALMA observations revealed that there is a high-mass protostellar object at an intersection of two line-shaped filaments in 13 CO with the length scale of ∼10 pc, the spatially resolved observations, in particular, toward the highest column density part traced by the 1.3 mm continuum emission, the N159W-South clump, show complicated hub-filamentary structures. We also discovered that there are multiple protostellar sources with bipolar outflows along the massive filament. The redshifted/blueshifted components of the 13 CO emission around the massive filaments/protostars have complementary distributions, which is considered to be possible evidence for a cloud–cloud collision. We propose a new scenario in which...
Habitability and Spectroscopic Observability of Warm M-dwarf Exoplanets Evaluated with a 3D Chemistry-Climate Model
Planets residing in circumstellar habitable zones offer us the best opportunities to test hypotheses of life’s potential pervasiveness and complexity. Constraining the precise boundaries of habitability and its observational discriminants is critical to maximizing our chances at remote life detection with future instruments. Conventionally, calculations of the inner edge of the habitable zone (IHZ) have been performed using both 1D radiative-convective and 3D general circulation models. However, these models lack interactive 3D chemistry and do not resolve the mesosphere and lower thermosphere region of the upper atmosphere. Here, we employ a 3D high-top chemistry-climate model (CCM) to simulate the atmospheres of synchronously rotating planets orbiting at the inner edge of habitable zones of K- and M-dwarf stars (between T eff = 2600 and 4000 K). While our IHZ climate predictions are in good agreement with general circulation model studies, we find noteworthy ...
Intensity Gradients Technique: Synergy with Velocity Gradients and Polarization Studies
Magnetic fields are ubiquitous in the interstellar medium but notoriously difficult to study through observation. Making use of the advances in our understanding of MHD turbulence and turbulent reconnection, the velocity gradients technique (VGT) was suggested and successfully applied to study magnetic fields utilizing spectroscopic data. Applying the tools developed for the VGT to intensity statistics, we introduce the intensity gradients technique (IGT) as a complementary tool that can be used synergistically with the VGT. In this paper, we apply the IGT to a diffuse H i region selected from the GALFA-H i survey and compare the intensity gradient (IG) maps with those obtained using velocity gradients, as well as Planck polarization measurements. We demonstrate the possibility of using the IGT and VGT for both studying the magnetic field and identifying shocks in the diffuse interstellar medium. We also explore the ability of th...
Sunspot Characteristics at the Onset of the Maunder Minimum Based on the Observations of Hevelius
An analysis of the sunspot observations made by Hevelius during 1642–1645 is presented. These records are the only systematic sunspot observations just before the Maunder Minimum (MM). We have studied different phenomena meticulously recorded by Hevelius after translating the original Latin texts. We reevaluate the observations of sunspot groups by Hevelius during this period and obtain an average value 7% greater than that calculated from his observations given in the current group database. Furthermore, the average of the active day fraction obtained in this work from Hevelius’s records previous to the MM is significantly greater than the solar activity level obtained from Hevelius’s sunspot observations made during the MM (70% versus 30%). We also present the butterfly diagram obtained from the sunspot positions recorded by Hevelius for the period 1642–1645. It can be seen that no hemispheric asymmetry exists during this interval, in contrast with the MM. Hevelius noted a ∼3-...
Ly α Observations of High Radial Velocity Low-mass Stars Ross 1044 and Ross 825
The discovery of habitable zone (HZ) planets around low-mass stars has highlighted the need for a comprehensive understanding of the radiation environments in which such planets reside. Of particular importance is knowledge of the far-ultraviolet (FUV) radiation, as low-mass stars are typically much more active than solar-type stars and the proximity of their HZs can be one-tenth the distance. The vast majority of the flux emitted by low-mass stars at FUV wavelengths occurs in the Ly α line at 1216 Å. However, measuring a low-mass star’s Ly α emission directly is almost always impossible because of the contaminating effects of interstellar hydrogen and geocoronal airglow. We observed Ross 825 (K3) and Ross 1044 (M0), two stars with exceptional radial velocities, with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope . Their radial velocities resulted in significant line shifts, allowing for a more complete view of their Ly α lin...
Bayesian Time-resolved Spectroscopy of GRB Pulses
We performed time-resolved spectroscopy on a sample of 38 single pulses from 37 gamma-ray bursts detected by the Fermi /Gamma-ray Burst Monitor during the first 9 yr of its mission. For the first time a fully Bayesian approach is applied. A total of 577 spectra are obtained and their properties studied using two empirical photon models, namely the cutoff power law (CPL) and Band model. We present the obtained parameter distributions, spectral evolution properties, and parameter relations. We also provide the result files containing this information for usage in further studies. It is found that the CPL model is the preferred model, based on the deviance information criterion and the fact that it consistently provides constrained posterior density maps. In contrast to previous works, the high-energy power-law index of the Band model, β , has in general a lower value for the single pulses in this work. In particular, we investigate the individual spectrum in each pulse...
Stellar Dynamos in the Transition Regime: Multiple Dynamo Modes and Antisolar Differential Rotation
Global and semi-global convective dynamo simulations of solar-like stars are known to show a transition from an antisolar (fast poles, slow equator) to solar-like (fast equator, slow poles) differential rotation (DR) for increasing rotation rate. The dynamo solutions in the latter regime can exhibit regular cyclic modes, whereas in the former one, only stationary or temporally irregular solutions have been obtained so far. In this paper we present a semi-global dynamo simulation in the transition region, exhibiting two coexisting dynamo modes, a cyclic and a stationary one, both being dynamically significant. We seek to understand how such a dynamo is driven by analyzing the large-scale flow properties (DR and meridional circulation) together with the turbulent transport coefficients obtained with the test-field method. Neither an α Ω dynamo wave nor an advection-dominated dynamo are able to explain the cycle period and the propagation direction of the mean magnetic field....
Evolution of ONeMg Core in Super-AGB Stars toward Electron-capture Supernovae: Effects of Updated Electron-capture Rate
Stars with∼8–10 M ⊙ evolve to form a strongly degenerate ONeMg core. When the core mass becomes close to the Chandrasekhar mass, the core undergoes electron captures on 24 Mg and 20 Ne that induce an electron-capture supernova (ECSN). In order to clarify whether the ECSN leads to a collapse or thermonuclear explosion, we calculate the evolution of an 8.4 M ⊙ star from the main sequence until the oxygen ignition in the ONeMg core. We apply the latest electron-capture rate on 20 Ne, including the second forbidden transition, and investigate how the location of the oxygen ignition (center or off-center) and the Y e distribution depend on the input physics and the treatment of the semiconvection and convection. The central density when the oxygen deflagration is initiated, ρ c,def , can be significantly higher than that of the oxygen ignition thanks to the convection, and w...
A Two-zone Model for Blazar Emission: Implications for TXS 0506+056 and the Neutrino Event IceCube-170922A
A high-energy muon neutrino event, IceCube-170922A, was recently discovered in both spatial and temporal coincidence with a gamma-ray flare of the blazar TXS 0506+056. It has been shown with standard one-zone models that neutrinos can be produced in the blazar jet via hadronic interactions, but with a flux that is mostly limited by the X-ray data. In this work, we explore the neutrino production from TXS 0506+056 by invoking two physically distinct emission zones in the jet, with an inner blob inside of or close to the broad-line region (BLR) and an outer one well beyond the BLR. Using the Doppler-boosted radiation of the BLR as the target photon field, the inner zone accounts for the neutrino and gamma-ray emission via pγ interactions and inverse Compton scattering, respectively, while the outer zone produces the optical and X-ray emission via synchrotron and synchrotron self-Compton processes. The different conditions of the two zones allow us to suppress the X-ray emis...
A Search for Late-time Radio Emission and Fast Radio Bursts from Superluminous Supernovae
We present results of a search for late-time radio emission and fast radio bursts (FRBs) from a sample of type-I superluminous supernovae (SLSNe-I). We used the Karl G. Jansky Very Large Array to observe 10 SLSN-I more than 5 yr old at a frequency of 3 GHz. We searched fast-sampled visibilities for FRBs and used the same data to perform a deep imaging search for late-time radio emission expected in models of magnetar-powered supernovae. No FRBs were found. One SLSN-I, PTF10hgi, is detected in deep imaging, corresponding to a luminosity of 1.2 × 10 28 erg s −1 . This luminosity, considered with the recent 6 GHz detection of PTF10hgi in Eftekhari et al., supports the interpretation that it is powered by a young, fast-spinning (∼ms spin period) magnetar with ∼15 M ⊙ of partially ionized ejecta. Broadly, our observations are most consistent with SLSNe-I being powered by neutron stars with fast spin periods, although most require more free–free ab...
Constraining the Fraction of Binary Black Holes Formed in Isolation and Young Star Clusters with Gravitational-wave Data
Ten binary black hole mergers have already been detected during the first two observing runs of advanced LIGO and Virgo, and many more are expected to be observed in the near future. This opens the possibility for gravitational-wave (GW) astronomy to better constrain the properties of black hole binaries—not only as single sources, but as a whole astrophysical population. In this paper, we address the problem of using GW measurements to estimate the proportion of merging black holes produced either via isolated binaries or binaries evolving in young star clusters. To this end, we use a Bayesian hierarchical modeling approach applied to catalogs of merging binary black holes generated using state-of-the-art population synthesis and N -body codes. In particular, we show that, although current advanced LIGO/Virgo observations only mildly constrain the mixing fraction {${f}\in [0,1]$}
The Atmospheric Circulation of Ultra-hot Jupiters
Recent observations of ultra-hot Jupiters with dayside temperatures in excess of 2500 K have found evidence for new physical processes at play in their atmospheres. In this work, we investigate the effects of the dissociation of molecular hydrogen and recombination of atomic hydrogen on the atmospheric circulation of ultra-hot Jupiters. To do so, we incorporate these effects into a general circulation model (GCM) for hot Jupiter atmospheres and run a large suite of models varying the incident stellar flux, rotation period, and strength of frictional drag. We find that including hydrogen dissociation and recombination reduces the fractional day-to-night temperature contrast of ultra-hot Jupiter atmospheres and causes the speed of the equatorial jet to decrease in simulations with fixed rotation. This is because the large energy input required for hydrogen dissociation cools the dayside of the planet, and the energy released due to hydrogen recombination warms the nightside. The r...
Type IIP Supernova Progenitors and Their Explodability. I. Convective Overshoot, Blue Loops, and Surface Composition
We present the evolution of massive star progenitors of supernovae of type IIP. We take the example of the nearby and well-studied SN 2013ej. We explore how convective overshoot affects the stellar structure, surface abundances, and effective temperature of massive stars, using the Modules for Experiments in Stellar Astrophysics. In particular, models with moderate overshoot ( f = 0.02–0.031) show the presence of blue loops in the Hertzsprung–Russell diagram with a red to blue excursion (log 10 [ T eff /K] from <3.6 to >4.0) and transition back to red, during the core helium-burning phase. Models with overshoot outside this range of f values kept the star in the red supergiant state throughout the post-helium-ignition phases. The surface CNO abundance shows enrichment post-main-sequence and again around the time when helium is exhausted in the core. These evolutionary changes in surface CNO abundance are indistinguishable in the curren...
Understanding the Discrepancy between IRX and Balmer Decrement in Tracing Galaxy Dust Attenuation
We compare the infrared excess (IRX) and Balmer decrement ( {${\rm{H}}\alpha /{\rm{H}}\beta $} ) as dust attenuation indicators in relation to other galaxy parameters using a sample of ∼32,000 local star-forming galaxies (SFGs) carefully selected from the Sloan Digital Sky Survey, the Galaxy Evolution Explorer , and the Wide-field Infrared Survey Explore . While at fixed {${\rm{H}}\alpha /{\rm{H}}\beta $} , IRX turns out to be independent on galaxy stellar mass, the Balmer decrement does show a strong mass dependence at fixed IRX. We find the discrepancy, parameterized by the color excess ratio {${R}_{\mathrm{EBV}}\equiv E{(B-V)}_{\mathrm{IRX}}/E{(B-V)}_{{\rm{H}}\alpha /{\rm{H}}\beta }$} , i...
Fast Outflows Identified in Early Star-forming Galaxies at z = 5–6
We present velocities of galactic outflows in seven star-forming galaxies at z = 5–6 with stellar masses of M * ∼ 10 10.1 {${M}_{\odot }$} . Although it is challenging to observationally determine the outflow velocities, we overcome this by using ALMA [C ii ] 158 μ m emission lines for systemic velocities and deep Keck spectra with metal absorption lines for velocity profiles available to date. We construct a composite Keck spectrum of the galaxies at z = 5–6 with the [C ii ]-systemic velocities, and fit outflow-line profiles to the Si ii λ 1260, C ii λ 1335, and Si iv λλ 1394,1403 absorption lines in the composite spectrum. We measure the maximum (90%) and central outflow velocities to be ##IMG##
A Carbon-rich Hot Bubble in the Planetary Nebula NGC 5189
We present the discovery of extended X-ray emission from the planetary nebula (PN) NGC 5189 around the [WO1]-type WD 1330−657 with XMM-Newton . The X-ray-emitting gas fills the cavities detected in the Hubble Space Telescope [O iii ] narrowband image and presents a limb-brightened morphology toward the outer edges of the east and west lobes. The bulk of the X-ray emission is detected in the soft (0.3–0.7 keV) band with the XMM-Newton EPIC spectra dominated by the C vi Ly α line at 0.37 keV (=33.7 Å). Spectral analysis resulted in carbon and neon abundances 38 and 6 times their solar values, with a plasma temperature of kT = 0.14 ± 0.01 keV ( T = 1.6 × 10 6 K) and X-ray luminosity of L X = (2.8 ± 0.8) × 10 32 erg s −1 . NGC 5189 is an evolved and extended PN (≲0.70 pc in radius), thus, we suggest that the origin of its X-ray emission is consistent...
The Mass–Metallicity Relation at z ∼ 0.8: Redshift Evolution and Parameter Dependency
The spectra of emission-line galaxies from the extended Baryon Oscillation Spectroscopic Survey of the Sloan Digit Sky Survey (SDSS) are used to study the mass–metallicity relation (MZR) at z ∼ 0.8. The selected sample contains about 180,000 massive star-forming galaxies with0.6 < z < 1.05 and {$9\lt \mathrm{log}({M}_{\star }/{M}_{\odot })\lt 12$} . The spectra are stacked in bins of different parameters including redshift, stellar mass, star formation rate (SFR), specific star formation rate (sSFR), half-light radius, mass density, and optical color. The average MZR at z ∼ 0.83 has a downward evolution in the MZR from the local to high-redshift universe, which is consistent with previous works. At a specified stellar mass, galaxies with higher SFR/sSFR and larger half-light radius have systematically lower metallicity. This behavior is reversed for galaxies ...
Frequency Distribution of Acoustic Oscillation in the Solar Atmosphere During Flare Event
We present a study of multi-wavelength observations, of a C 2.3 solar flare in Active Region NOAA 12353, observed on 2015 May 23, which reveal new properties of acoustic waves in the flaring region. The space-, and ground-based data measured by the HELioseismological Large Regions Interferometric Device, operating at the Vacuum Tower Telescope, the Atmospheric Imaging Assembly (AIA), and Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory , were used in this paper. First, using power spectra of solar oscillations, we identified the dominant frequencies and their location at seven different atmospheric levels before and after the flare event. Second, based on AIA observations taken in six Extreme Ultraviolet filters, we derived Differential Emission Measure (DEM) profiles and DEM maps of the flare. Finally, we confirm the sigma shape of the magnetic field in the active area, directly related to the flare. Our results are as follows: the high-frequency wa...
Mid-IR Variability and Dust Reverberation Mapping of Low- z Quasars. I. Data, Methods, and Basic Results
The continued operation of the Wide-field Infrared Survey Explorer ( WISE ), combined with several ground-based optical transient surveys (e.g., CRTS, ASAS-SN, and PTF), offers an unprecedented opportunity to explore the dust structures in luminous active galactic nuclei (AGNs). We use these data for a mid-IR dust reverberation mapping (RM) study of 87 archetypal Palomar–Green quasars at z ≲ 0.5. To cope with various contaminations of the photometry data and the sparse time sampling of the light curves, procedures to combine these data sets and retrieve the dust RM signals have been developed. We find that ∼70% of the sample (with a completeness correction up to 95%) has convincing mid-IR time lags in the WISE W1 (∼3.4 μ m) and W2 (∼4.5 μ m) bands, and they are proportional to the square root of the AGN luminosity. Combined with previous K -band (∼2.2 μ m) RM results in the literature, the inferred dust emission size ratio...
Origin of the Short-lived Radionuclide 10 Be and Its Implications for the Astronomical Setting of CAI Formation in the Solar Protoplanetary Disk
We report Li–Be–B and Al–Mg isotopic compositions of Ca-Al-rich inclusions (CAIs) in Sayh al Uhaymir 290 (CH) and Isheyevo (CH/CB) metal-rich carbonaceous chondrites. All CAIs studied here do not show resolvable excesses in 26 Mg, a decay product of the short-lived radionuclide 26 Al, which suggests their formation occurred prior to the injection of 26 Al into the solar system from a nearby stellar source. The inferred initial 10 Be/ 9 Be ratios obtained for these CAIs range from 0.17 × 10 −3 to 6.1 × 10 −3 , which tend to be much higher and more variable than those of CAIs in CV3 chondrites. The high 10 Be/ 9 Be ratios suggest that 10 Be was most likely synthesized through solar cosmic-ray irradiation. The lithium isotopic compositions of these CAIs are nearly chondritic, independent of their initial 10 Be/ 9 Be ratios. This can be explained by the irradiation tar...
Age Determination of Galactic B-type Stars in Double-lined Eclipsing Binaries
We present the results of age determination for galactic B-type main-sequence stars that are components of double-lined eclipsing binaries. Only detached systems are considered. We analyze 38 binary systems that meet such criteria. The analysis is based on evolutionary computations, and we consider that the age is determined if there is a common value from the radius–age diagrams and the agreement in the position of both components in the Hertzsprung–Russell diagram. In some cases, to meet these two conditions, it was necessary to adjust the value of the metallicity, Z , or/and the parameter of overshooting from the convective core, α ov . We determine a consistent age for 33 of the 38 binaries. Additionally, we completed extensive computations, and for each system, we give the range of α ov and Z for which a consistent solution exists. The age of the studied B-type main-sequence stars ranges, as counted from the Zero Age Main Sequ...
ALMA Observations of Fragmentation, Substructure, and Protostars in High-mass Starless Clump Candidates
The initial physical conditions of high-mass stars and protoclusters remain poorly characterized. To this end, we present the first targeted ALMA Band 6 1.3 mm continuum and spectral line survey toward high-mass starless clump candidates, selecting a sample of 12 of the most massive candidates ( {$4\times {10}^{2}\,{M}_{\odot }\lesssim {M}_{\mathrm{cl}}\lesssim 4\times {10}^{3}\,{M}_{\odot }$} ) within {${d}_{\odot }\lt 5\,\mathrm{kpc}$} . The joint {$12+7\,{\rm{m}}$} array maps have a high spatial resolution of {$\lesssim 3000\,\mathrm{au}$} ( {$0.015\,\mathrm{pc}$}
Black Hole Spin and Accretion Disk Magnetic Field Strength Estimates for More Than 750 Active Galactic Nuclei and Multiple Galactic Black Holes
Black hole systems, composed of a black hole, accretion disk, and collimated outflow, are studied here. Three active galactic nucleus (AGN) samples including 753 AGNs and 102 measurements of four stellar-mass galactic black holes (GBHs) are studied. Applying the theoretical considerations described by Daly, general expressions for the black hole spin function and accretion disk magnetic field strength are presented and applied to obtain the black hole spin function, spin, and accretion disk magnetic field strength in dimensionless and physical units for each source. Relatively high spin values are obtained; spin functions indicate typical spin values of about 0.6–1 for the sources. The distributions of accretion disk magnetic field strengths for the three AGN samples are quite broad and have mean values of about 10 4 G, while those for individual GBHs have mean values of about 10 8 G. Good agreement is found between spin values obtained here and published val...
The Infall Motion in the Low-mass Protostellar Binary NGC 1333 IRAS 4A1/4A2
We report ALMA observations of NGC 1333 IRAS 4A, a young low-mass protostellar binary, whose components are referred to as 4A1 and 4A2. With multiple H 2 CO transitions and HNC (4−3) observed at a resolution of 0.″25 (∼70 au), we investigate the gas kinematics of 4A1 and 4A2. Our results show that on the large angular scale (∼10″), 4A1 and 4A2 each display a well-collimated outflow along the N–S direction, and an S-shaped morphology is discerned in the outflow powered by 4A2. On the small scale (∼0.″3), 4A1 and 4A2 exhibit distinct spectral features toward the continuum centroid, with 4A1 showing simple symmetric profiles predominantly in absorption and 4A2 demonstrating rather complicated profiles in emission as well as in absorption. Based on radiative transfer modeling exercises, we find that the physical parameters inferred from earlier low-resolution observations cannot be directly extrapolated down to the inner region of 4A1. Possible reasons for the discrepancies...
Possible Contribution of Magnetized White Dwarf Binaries to Type Ia Supernova Populations
The evolution of an accreting white dwarf (WD) with a strong magnetic field toward a Type Ia supernova (SN Ia) may differ from the classical single-degenerate (SD) channel. In this paper, we perform binary population synthesis simulations for the SD channel with a main-sequence (MS) companion, including the strongly magnetized WD accretion. Under a reasonable assumption that the fraction of such systems is ∼15%, the resulting delay-time distribution roughly follows the t −1 power-law distribution. Within the (WD/MS) SD channel, the contribution from the highly magnetized WD is estimated to be comparable to that from the classical, non-magnetized WD channel. The contribution of the SD channel toward SNe Ia can be at least ∼30% among the whole SN Ia population. We suggest that the SNe Ia resulting from the highly magnetized WD systems would not share the observational properties expected for the classical SD channel; for every (potentially peculiar) SN observatio...
Evolution of the Stellar Mass–Metallicity Relation. II. Constraints on Galactic Outflows from the Mg Abundances of Quiescent Galaxies
We present the stellar mass–[Fe/H] and mass–[Mg/H] relation of quiescent galaxies in two galaxy clusters at z ∼ 0.39 and z ∼ 0.54. We derive the age, [Fe/H], and [Mg/Fe] for each individual galaxy using a full-spectrum fitting technique. By comparing with the relations for z ∼ 0 Sloan Digital Sky Survey galaxies, we confirm our previous finding that the mass–[Fe/H] relation evolves with redshift. The mass–[Fe/H] relation at higher redshift has lower normalization and possibly steeper slope. However, based on our sample, the mass–[Mg/H] relation does not evolve over the observed redshift range. We use a simple analytic chemical evolution model to constrain the average outflow that these galaxies experience over their lifetime, via the calculation of mass-loading factor. We find that the average mass-loading factor η is a power-law function of galaxy stellar mass, {$\eta \propto {M}_{* }^{-0.21\pm 0.09}$}
Coronal Cooling as a Result of Mixing by the Nonlinear Kelvin–Helmholtz Instability
Recent observations show cool, oscillating prominence threads fading when observed in cool spectral lines and appearing in warm spectral lines. A proposed mechanism to explain the observed temperature evolution is that the threads were heated by turbulence driven by the Kelvin–Helmholtz instability that developed as a result of wave-driven shear flows on the surface of the thread. As the Kelvin–Helmholtz instability is an instability that works to mix the two fluids on either side of the velocity shear layer, in the solar corona it can be expected to work by mixing the cool prominence material with that of the hot corona to form a warm boundary layer. In this paper, we develop a simple phenomenological model of nonlinear Kelvin–Helmholtz mixing, using it to determine the characteristic density and temperature of the mixing layer. For the case under study, with constant pressure across the two fluids, these quantities are ##IMG## {${\rho }_{\mathrm{mixed}}=\sqrt{{...}
Chemical Cartography. II. The Assembly History of the Galactic Stellar Halo Traced by Carbon-enhanced Metal-poor Stars
We present an analysis of the kinematic properties of stellar populations in the Galactic halo, making use of over 100,000 main-sequence turnoff (MSTO) stars observed in the Sloan Digital Sky Survey. After dividing the Galactic halo into an inner-halo region (IHR) and outer-halo region (OHR), based on the spatial variation of carbon-to-iron ratios in the sample, we find that stars in the OHR exhibit a clear retrograde motion of −49 ± 4 km s −1 and a more spherical distribution of stellar orbits, while stars in the IHR have zero net rotation (−3 ± 1 km s −1 ) with a much more radially biased distribution of stellar orbits. Furthermore, we classify the carbon-enhanced metal-poor (CEMP) stars among the MSTO sample in each halo component into CEMP-no and CEMP- s subclasses, based on their absolute carbon abundances, A (C), and examine the spatial distributions and kinematics associated with each subclass. The CEMP-no stars are the majority subclass of ...
Double-detonation Models for Type Ia Supernovae: Trigger of Detonation in Companion White Dwarfs and Signatures of Companions’ Stripped-off Materials
We have studied double-detonation explosions in double-degenerate (DD) systems with different companion white dwarfs (WDs) for modeling Type Ia supernovae (SNe Ia) by means of high-resolution smoothed particle hydrodynamics (SPH) simulations. We have found that only the primary WDs explode in some of the DD systems, while the explosions of the primary WDs induce the explosions of the companion WDs in the other DD systems. The former case is a so-called dynamically-driven double-degenerate double-detonation (D 6 ) explosion, or helium-ignited violent merger explosion. The SN ejecta of the primary WDs strip materials from the companion WDs, whose mass is ∼10 −3 M ⊙ . The stripped materials contain carbon and oxygen when the companion WDs are carbon–oxygen (CO) WDs with He shells ≲0.04 M ⊙ . Since they contribute to low-velocity ejecta components as observationally inferred for iPTF14atg, D 6 explosions can be counterpa...
The Initial Physical Conditions of the Orion BN/KL Fingers
Orion BN/KL is an example of a poorly understood phenomena in star-forming regions involving the close encounters of young stellar objects. The explosive structure, the great variety of molecules observed, the energy involved in the event, and the mass of the region suggest a contribution to the chemical diversity of the local interstellar medium. Nevertheless, the frequency and duration of other, similar events have not been determined. In this paper, we explore a recent analytic model that takes into account the interaction of a clump with its molecular environment. We show that the widespread kinematic ages of the Orion fingers—500 to 4000 yr—are a consequence of the interaction of the explosion debris with the surrounding medium. This model explains satisfactorily the age discrepancy of the Orion fingers, and infers the initial conditions together with the lifetime of the explosion. Moreover, our model can explain why some CO streamers do not have an associated H 2 ...
Runaway O-star Bow Shocks as Particle Accelerators? The Case of AE Aur Revisited
We present results of our Chandra /ACIS observations of the field centered on the fast, runaway O star AE Aur and its bow shock. Previous XMM-Newton observations revealed an X-ray “blob” near the IR arc tracing the bow shock, possibly a nonthermal source consistent with models of Inverse Compton scattering of dust IR photons by electrons accelerated at the shock. The new, subarcsecond-resolution Chandra data, while confirming the presence of the XMM-Newton source, clearly indicate that the latter is neither extended nor coincident with the IR arc and strongly suggest it is a background active galactic nucleus. Motivated by results published for the bow shock of BD+43°3654, we extended our study to the radio domain by analyzing archival EVLA data. We find no radio emission from the AE Aur bow shock either. The corresponding upper limits for the absorbed (unabsorbed) X-ray flux of 5.9(7.8) × 10 −15 erg cm −2 s −1 (3 σ )...
Characterizing Magnetic Field Morphologies in Three Serpens Protostellar Cores with ALMA
With the aim of characterizing the dynamical processes involved in the formation of young protostars, we present high-angular-resolution ALMA dust polarization observations of the Class 0 protostellar cores Serpens SMM1, Emb 8(N), and Emb 8. With spatial resolutions ranging from 150 to 40 au at 870 μ m, we find unexpectedly high values of the polarization fraction along the outflow cavity walls in Serpens Emb 8(N). We use 3 mm and 1 mm molecular tracers to investigate outflow and dense-gas properties and their correlation with the polarization. These observations allow us to investigate the physical processes involved in the radiative alignment torques (RATs) acting on dust grains along the outflow cavity walls, which experience irradiation from accretion processes and outflow shocks. The inner core of SMM1-a presents a polarization pattern with a poloidal magnetic field at the bases of the two lobes of the bipolar outflow. To the south of SMM1-a we see two polarized filam...
Searching for the Magnetized Tidal Dwarf Galaxies in Hickson Compact Groups: HCG 26, 91, and 96
In this work, archive 1.4 and 4.86 GHz radio continuum data from the Very Large Array were re-reduced and, together with the 1.4 GHz maps from the NRAO VLA Sky Survey, investigated for the presence of detectable, nonthermal continuum radio emission that could be associated with the tidal dwarf galaxy (TDG) candidates in HCG 26, 91, and 96. Radio emission highly coincident with the optical and H α emission maxima of the TDG candidate HCG 91i (estimated physical separation of less than 150 pc) was revealed. Should this emission be intrinsic to this object, it would imply the presence of a magnetic field as strong as 11–16 μ G—comparable to that found in the most radio-luminous, star-forming dwarf galaxies of non-tidal origin. However, the star formation rate derived for this object using the radio flux is about two orders of magnitude higher than the one estimated from the H α data. Analysis of the auxiliary radio, ultraviolet, and infra...
Evidence for a Massive Warm–Hot Circumgalactic Medium around NGC 3221
We report a 3.4 σ detection of the warm–hot, massive, extended circumgalactic medium (CGM) around an L ⋆ star-forming spiral galaxy NGC 3221, using deep Suzaku observations. The temperature of the gas is 10 6.1 K, comparable to that of the Milky Way CGM. The spatial extent of the gas is at least 150 kpc. For a β -model of density profile with solar abundance, the central emission measure is EM = (3 ± 1) × 10 −5 cm −6 kpc and the central electron density is n eo = (4 ± 1) × 10 −4 cm −3 , with a slope of β = 0.56. We investigate a range of β values and find that the details of the density profile do not change our results significantly. The mass of the warm–hot gas, assuming a metallicity of {$\tfrac{1}{3}$} Z ⊙ , is (16 ± 3) × 10 10 M <...
Chemical Abundances in a Turbulent Medium–H 2 , OH + , H 2 O + , ArH +
Supersonic turbulence results in strong density fluctuations in the interstellar medium (ISM), which have a profound effect on the chemical structure. Particularly useful probes of the diffuse ISM are the ArH + , OH + , H 2 O + molecular ions, which are highly sensitive to fluctuations in the density and the H 2 abundance. We use isothermal magnetohydrodynamic simulations of various sonic Mach numbers, {${{ \mathcal M }}_{{\rm{s}}}$} , and density decorrelation scales, y dec , to model the turbulent density field. We post process the simulations with chemical models and obtain the probability density functions (PDFs) for the H 2 , ArH + , OH + , and H 2 O + abundances. We find that the PDF dispersions increases with increasing ##IMG## {${{ \mathcal M }}_{{\rm{s}...}
An Unusual Mid-infrared Flare in a Type 2 AGN: An Obscured Turning-on AGN or Tidal Disruption Event?
We report the discovery of an exceptional MIR flare in a Type 2 AGN, SDSS J165726.81+234528.1, at z = 0.059. This object brightened by 3 mag in the Wide-field Infrared Survey Explorer ( WISE ) W 1 and W 2 bands between 2015 and 2017 (and has been fading since 2018), without significant changes (≲0.2 mag) in the optical over the same period of time. Based on the WISE light curves and near-IR imaging, the flare is more significant at longer wavelengths, suggesting an origin of hot dust emission. The estimated black hole mass (∼10 6.5 M ⊙ ) from different methods places its peak bolometric luminosity around the Eddington limit. The high luminosity of the MIR flare and its multiyear timescale suggest that it most likely originated from reprocessed dust radiation in an extended torus surrounding the AGN, instead of from stellar explosions. The MIR color variability is consistent with known changing-look AGN and tidal di...
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