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The Astrophysical Journal
Published by the University of Chicago Press for the American Astronomical Society
The Astrophysical Journal

Published by the University of Chicago Press for the American Astronomical Society

0067-0049

The Astrophysical Journal/Journal The Astrophysical Journal
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    A MeerKAT 1.28 GHz Atlas of Southern Sources in the IRAS Revised Bright Galaxy Sample

    Condon, J. J.Cotton, W. D.Jarrett, T.Marchetti, L....
    23页
    查看更多>>摘要：The IRAS Revised Bright Galaxy Sample (RBGS) comprises galaxies and unresolved mergers stronger than S=5.24 Jy at lambda=60 mu m with galactic latitudes vertical bar b vertical bar > 5 degrees. Nearly all are dusty star-forming galaxies whose radio continuum and far-infrared luminosities are proportional to their current rates of star formation. We used the MeerKAT array of 64 dishes to make 5 x 3 min snapshot observations at nu = 1.28 GHz covering all 298 southern (J2000 delta < 0 degrees) RBGS sources identified with external galaxies. The resulting images have theta approximate to 7'''.5 arcsec FHWM resolution and rms fluctuations sigma approximate to 20 mu Jy beam(-1)approximate to 0.26 K low enough to reveal even faint disk emission. The rms position uncertainties are sigma(alpha) approximate to sigma(delta) approximate to 1 '' arcsec relative to accurate near-infrared positions, and the image dynamic ranges are DR greater than or similar to 10(4):1. Cropped MeerKAT images of all 298 southern RBGS sources are available in FITS format from 10.48479/dnt7-6q05.
      原文链接:
    • NSTL

    Optical Variability of a Newly Discovered Blazar Sample from the BZCAT Catalog

    Kalita, NibeditaGupta, Alok C.Gu, Minfeng
    14页
    查看更多>>摘要：In an optical monitoring program to characterize the variability properties of blazars, we observed 10 sources from the Roma-BZCAT catalog for 26 nights in V and R bands during 2014 October to 2015 June with two telescopes located in India. The sample includes mainly newly discovered BL Lacertae objects (BL Lacs) for which the redshift of some sources is not yet known. We present the results of flux and color variations of the sample on intraday and short timescales obtained by using the power-enhanced F-test and the nested-ANOVA tests, along with their spectral behavior. We find significant intraday variability in the single flat-spectrum radio quasar in our sample, having an amplitude of variation similar to 12%. Although a few of the BL Lacs showed probable variation in some nights, none of them passed the variability tests at 99.9% significance level. We find that 78% of the sample showed significant negative color-magnitude correlations, i.e., a redder-when-brighter spectral evolution. Those that do not show strong or clear chromatism predominantly exhibit a redder-when-brighter trend. Unlike on hourly timescales, the high-synchrotron-peaked blazars in the sample (BZGJ0656+4237, BZGJ0152+0147, and BZBJ1728+5013) show strong flux variation on timescales of days to months, where again we detect a decreasing trend of the spectral slope with brightness. We observe a global steepening of the optical spectrum with increasing flux on the intranight timescale for the entire blazar sample. The nonvariability in the BL Lacs in our sample might be caused by the distinct contribution from the disk as well as from other components in the studied energy range.
      原文链接:
    • NSTL

    Magnetohydrodynamic Modeling of the Solar Corona with an Effective Implicit Strategy

    Feng, XueshangWang, HaopengXiang, ChangqingLiu, Xiaojing...
    23页
    查看更多>>摘要：In this paper, we design an effective and robust model to solve the 3D single-fluid solar wind plasma magnetohydrodynamics (MHD) problem of low plasma beta. This MHD model is formulated on a six-component composite grid system free of polar singularities. The computational domain ranges from the solar surface to the super-Alfvenic region. As common to all MHD codes, this code must handle the physical positivity-preserving property, time-step enlargement, and magnetic field divergence-free maintenance. To maintain physical positivity, we employ a positivity-preserving Harten-Lax-van Leer Riemann solver and take a self-adjusting and positivity-preserving method for variable reconstruction. To loosen the time-step limitation, we resort to the implicit lower-upper symmetric Gauss-Seidel method and keep the sparse Jacobian matrix diagonally dominant to improve the convergence rate. To deal with the constant theme of a magnetic field that is divergence-free, we adopt a globally solenoidality-preserving approach. After establishing the solar wind model, we use its explicit and implicit versions to numerically investigate the steady-state solar wind in Carrington rotations (CRs) 2172 and 2210. Both simulations achieve almost the same results for the two CRs and are basically consistent with solar coronal observations and mapped in situ interplanetary measurements. Furthermore, we use the implicit method to conduct an ad hoc simulation by multiplying the initial magnetic field of CR 2172 with a factor of 6. The simulation shows that the model can robustly and efficiently deal with the problem of a plasma beta as low as about 5 x 10(-7). Therefore, the established implicit solar wind MHD model is very promising for simulating complex and strong magnetic environments.
      原文链接:
    • NSTL

    On the Origin of Gamma-Ray Flares from Bright Fermi Blazars

    Paliya, Vaidehi S.Bottcher, M.Gurwell, MarkStalin, C. S....
    6页
    查看更多>>摘要：The origin of gamma-ray flares observed from blazars is one of the major mysteries in jet physics. We have attempted to address this problem following a novel spectral energy distribution (SED) fitting technique that explored the flaring patterns identified in the broadband SEDs of two gamma-ray bright blazars, 3C 279 (z = 0.54) and 3C 454.3 (z = 0.86), using near-simultaneous radio-to-gamma-ray observations. For both sources, the gamma-ray flux strongly correlates with the separation of the SED peaks and the Compton dominance. We propose that spectral hardening of the radiating electron population and/or enhancement of the Doppler factor can naturally explain these observations. In both cases, magnetic reconnection may play a pivotal role in powering the luminous gamma-ray flares.
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    • NSTL

    The mini-JPAS: A Study of the Wavelength Dependence of the Photon Response Nonuniformity of the JPAS-Pathfinder Camera

    Xiao, KaiYuan, HaiboVarela, J.Zhan, Hu...
    11页
    查看更多>>摘要：Understanding the origins of small-scale flats of CCDs and their wavelength-dependent variations plays an important role in high-precision photometric, astrometric, and shape measurements of astronomical objects. Based on the unique flat data of 47 narrowband filters provided by JPAS-Pathfinder, we analyze the variations of small-scale flats as a function of wavelength. We find moderate variations (from about 1.0% at 390 nm to 0.3% at 890 nm) of small-scale flats among different filters, increasing toward shorter wavelengths. Small-scale flats of two filters close in central wavelengths are strongly correlated. We then use a simple physical model to reproduce the observed variations to a precision of about +/- 0.14% by considering the variations of charge collection efficiencies, effective areas, and thicknesses between CCD pixels. We find that the wavelength-dependent variations of the small-scale flats of the JPAS-Pathfinder camera originate from inhomogeneities of the quantum efficiency (particularly charge collection efficiency), as well as the effective area and thickness of CCD pixels. The former dominates the variations in short wavelengths, while the latter two dominate at longer wavelengths. The effects on proper flat-fielding, as well as on photometric/flux calibrations for photometric/slitless spectroscopic surveys, are discussed, particularly in blue filters/wavelengths. We also find that different model parameters are sensitive to flats of different wavelengths, depending on the relations between the electron absorption depth, photon absorption length, and CCD thickness. In order to model the wavelength-dependent variations of small-scale flats, a small number (around 10) of small-scale flats with well-selected wavelengths are sufficient to reconstruct small-scale flats in other wavelengths.
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    • NSTL

    KAPPA: A Package for the Synthesis of Optically Thin Spectra for the Non-Maxwellian kappa-distributions. II. Major Update to Compatibility with CHIANTI Version 10

    Dzifcakova, ElenaDudik, JaroslavZemanova, AlenaLorincik, Juraj...
    11页
    查看更多>>摘要：KAPPA is a database and software for the calculation of the optically thin spectra for the non-Maxwellian kappa-distributions that were recently diagnosed in the plasma of solar coronal loops, flares, as well as in the transition region. KAPPA is based on the widely used CHIANTI database and reproduces many of its capabilities for kappa-distributions. Here we perform a major update of the KAPPA database, including a near-complete recalculation of the ionization, recombination, excitation, and deexcitation rates for all ions in the database, as well as an implementation of the two-ion model for calculations of relative-level populations (and intensities) if these are modified by ionization and recombination from or to excited levels. As an example of KAPPA usage, we explore novel diagnostics of kappa, and show that O iii lines near 500 and 700 angstrom provide a strong sensitivity to kappa, with some line intensity ratios changing by a factor of up to 2-4 compared to Maxwellian. This is much larger than previously employed diagnostics of kappa.
      原文链接:
    • NSTL

    A Catalog of 323 Cataclysmic Variables from LAMOST DR6

    Sun, YongkangCheng, ZhenghaoYe, ShuoDing, Ruobin...
    13页
    查看更多>>摘要：In this work, we present a catalog of cataclysmic variables (CVs) identified from the sixth data release (DR6) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). To single out the CV spectra, we introduce a novel machine-learning algorithm called UMAP to screen out a total of 169,509 H alpha emission spectra, and obtain a classification accuracy of the algorithm of over 99.6% from the cross-validation set. We then apply the template-matching program PyHammer v2.0 to the LAMOST spectra to obtain the optimal spectral type with metallicity, which help us identify the chromospherically active stars and potential binary stars from the 169,509 spectra. After visually inspecting all of the spectra, we identify 323 CV candidates from the LAMOST database, among them 52 objects are new. We further classify the new CV candidates in subtypes based on their spectral features, including five DN subtypes during outbursts, five NL subtypes, and four magnetic CVs (three AM Her type and one IP type). We also find two CVs that have been previously identified by photometry and confirm their previous classification with the LAMOST spectra.
      原文链接:
    • NSTL

    The Simons Observatory Large Aperture Telescope Receiver (vol 256, 23, 2021)

    Sierra, CarlosSonka, RitaSpisak, JacobSutariya, Shreya...
    2页
      原文链接:
    • NSTL

    Benchmarking Multiconfiguration Dirac-Hartree-Fock Calculations for Astrophysics: Si-like Ions from Cr xi to Zn xvii

    Zhang, X. H.Del Zanna, G.Wang, K.Rynkun, P....
    18页
    查看更多>>摘要：The multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction methods are used to provide excitation energies, lifetimes, and radiative transition data for the 604 (699, 702, 704, 704, 704, and 699) lowest levels of the 3s (2)3p (2), 3s3p (3), 3s (2)3p3d, 3p (4), 3s3p (2)3d, 3s (2)3d (2), 3p (3)3d, 3s3p3d (2), 3s3d (3), 3p3d (3), 3p (2)3d (2), 3s (2)3p4s, 3s (2)3p4p, 3s (2)3p4d, 3s (2)3p4f, 3s3p (2)4s, 3s3p (2)4p, 3s3p (2)4d, 3s3p (2)4f, 3s (2)3d4s, 3s (2)3d4p, 3p (3)4s, 3p (3)4p, 3s3p3d4s, 3s (2)3p5s, and 3s (2)3p5p configurations in Cr xi, (Mn xii, Fe xiii, Co xiv, Ni xv, Cu xvi, and Zn xvii). Previous line identifications of Fe xiii and Ni xv in the EUV and X-ray wavelength ranges are reviewed by comprehensively comparing the MCDHF theoretical results with available experimental data. Many recent identifications of Fe xiii and Ni xv lines are confirmed, and several new identifications for these two ions are proposed. A consistent atomic data set with spectroscopic accuracy is provided for the lowest hundreds of levels for Si-like ions of iron-group elements of astrophysical interest, for which experimental values are scarce. The uncertainty estimation method suggested by Kramida, applied to the comparison of the length and velocity line strength values, is used for ranking the transition data. The correlation of the latter with the gauge dependency patterns of the line strengths is investigated.
      原文链接:
    • NSTL

    Multiwavelength Properties of Miras

    Iwanek, PatrykKozlowski, SzymonGromadzki, MariuszSoszynski, Igor...
    22页
    查看更多>>摘要：We comprehensively study the variability of Miras in the Large Magellanic Cloud by simultaneously analyzing light curves in 14 bands in the range of 0.5-24 mu m. We model over 20 yr long, high-cadence I-band light curves collected by the Optical Gravitational Lensing Experiment (OGLE) and fit them to light curves collected in the remaining optical/near-infrared/mid-infrared bands to derive both the variability amplitude ratio and phase lag as a function of wavelength. We show that the variability amplitude ratio declines with increasing wavelength for both oxygen-rich (O-rich) and carbon-rich (C-rich) Miras, while the variability phase lag increases slightly with increasing wavelength. In a significant number of Miras, mostly the C-rich ones, the spectral energy distributions (SEDs) require the presence of a cool component (dust) in order to match the mid-IR data. Based on SED fits for a golden sample of 140 Miras, we calculated synthetic period-luminosity relations (PLRs) in 42 bands for the existing and future sky surveys that include OGLE, the VISTA Near-Infrared YJK (s) Survey of the Magellanic Clouds System, Legacy Survey of Space and Time, Gaia, Spitzer, the Wide-field Infrared Survey Explorer, the James Webb Space Telescope, the Nancy Grace Roman Space Telescope (formerly WFIRST), and the Hubble Space Telescope. We show that the synthetic PLR slope decreases with increasing wavelength for both the O-rich and C-rich Miras in the range of 0.1-40 mu m. Finally, we show the location and motions of Miras on the color-magnitude and color-color diagrams.
      原文链接:
    • NSTL