The Astrophysical Journal (ASTROPHYS J )

Publisher: American Astronomical Society; University of Chicago

Description

The Astrophysical Journal is the foremost research journal in the world devoted to recent developments, discoveries, and theories in astronomy and astrophysics. Many of the classic discoveries of the twentieth century have first been reported in the Journal, which has also presented much of the important recent work on quasars, pulsars, neutron stars, black holes, solar and stellar magnetic fields, X-rays, and interstellar matter. The Astrophysical Journal Letters (http://www.journals.uchicago.edu/toc/apjl/current) is Part 2 of The Astrophysical Journal. Letters articles are published first as unpaginated papers on University of Chicago Press's Rapid Release website, then moved to a complete electronic issue, and finally are published in print with Part 1 on the 1st, 10th, and 20th of every month.

  • Impact factor
    6.73
    Show impact factor history
     
    Impact factor
  • 5-year impact
    5.95
  • Cited half-life
    7.40
  • Immediacy index
    2.05
  • Eigenfactor
    0.42
  • Article influence
    1.89
  • Website
    Astrophysical Journal, The website
  • Other titles
    The Astrophysical journal, ApJ
  • ISSN
    0004-637X
  • OCLC
    1518501
  • Material type
    Periodical, Internet resource
  • Document type
    Journal / Magazine / Newspaper, Internet Resource

Publications in this journal

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    ABSTRACT: Recent infrared spectroscopic observations have shown that proto-planetary nebulae (PPNs) are sites of active syn-thesis of organic compounds in the late stages of stellar evolution. This paper presents a study of Spitzer/Infrared Spectrograph spectra for a sample of carbon-rich PPNs, all except one of which show the unidentified 21 μm emis-sion feature. The strengths of the aromatic infrared band, 21 μm, and 30 μm features are obtained by decomposition of the spectra. The observed variations in the strengths and peak wavelengths of the features support the model that the newly synthesized organic compounds gradually change from aliphatic to aromatic characteristics as stars evolve from PPNs to planetary nebulae.
    The Astrophysical Journal 07/2016; 725:990-1001.
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    ABSTRACT: In recent years, the analysis of absorption lines in quasi-stellar object (QSO) spectra, using the many-multiplet (MM) method, has provided evidence for space–time variations in the fine-structure constant, α. Future studies aim to reduce systematic errors in these measurements by considering a greater number of transitions, but this is only possible for lines where high-precision laboratory standards exist. Two transitions of high importance for future MM analyses, but which currently lack accurately measured wavelengths, are the Ti ii transitions observed at 1910 Å. We report accurate measurements of these transitions by high-resolution Fourier transform spectroscopy, giving line wavenumbers of (52,329.889 ± 0.001) cm −1 and (52,339.240 ± 0.001) cm −1 . Lines from other important Ti ii, Mg i, Mg ii, and Zn ii transitions were measured simultaneously, minimizing their relative wavenumber uncertainties, and permitting the newly measured 1910 Å Ti ii line wavenumbers to be linked directly to lines from other studies.
    The Astrophysical Journal 07/2016; 725:424-429.
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    ABSTRACT: We have developed a computational software system to automate the process of identifying solar active regions (ARs) and quantifying their physical properties based on high-resolution synoptic magnetograms constructed from Michelson Doppler Imager (MDI; on board the SOHO spacecraft) images from 1996 to 2008. The system, based on morphological analysis and intensity thresholding, has four functional modules: (1) intensity segmentation to obtain kernel pixels, (2) a morphological opening operation to erase small kernels, which effectively remove ephemeral regions and magnetic fragments in decayed ARs, (3) region growing to extend kernels to full AR size, and (4) the morphological closing operation to merge/group regions with a small spatial gap. We calculate the basic physical parameters of the 1730 ARs identified by the auto system. The mean and maximum magnetic flux of individual ARs are 1.67 ×10 22 Mx and 1.97 ×10 23 Mx, while that per Carrington rotation are 1.83 ×10 23 Mx and 6.96 ×10 23 Mx, respectively. The frequency distributions of ARs with respect to both area size and magnetic flux follow a log-normal function. However, when we decrease the detection thresholds and thus increase the number of detected ARs, the frequency distribution largely follows a power-law function. We also find that the equatorward drifting motion of the AR bands with solar cycle can be described by a linear function superposed with intermittent reverse driftings. The average drifting speed over one solar cycle is 1. • 83 ± 0. • 04 yr −1 or 0.708 ± 0.015 m s −1 .
    The Astrophysical Journal 06/2016; 723:1006-1018.
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    ABSTRACT: We consider interactions between protons and Alfvén/ion-cyclotron (A/IC) waves in collisionless low-β plasmas in which the proton distribution function f is strongly modified by wave pitch-angle scattering. If the angle θ between the wave vector and background magnetic field is zero for all the waves, then strong scattering causes f to become approximately constant on surfaces of constant η, where η v 2 ⊥ + 1.5 v 2/3 A |v | 4/3 . Here, v ⊥ and v are the velocity components perpendicular and parallel to the background magnetic field, and v A is the Alfvén speed. If f = f (η), then A/IC waves with θ = 0 are neither damped nor amplified by resonant interactions with protons. In this paper, we argue that if some mechanism generates high-frequency A/IC waves with a range of θ values, then wave–particle interactions initially cause the proton distribution function to become so anisotropic that the plasma becomes unstable to the growth of waves with θ = 0. The resulting amplification of θ = 0 waves leads to an angular distribution of A/IC waves that is sharply peaked around θ = 0 at the large wavenumbers at which A/IC waves resonate with protons. Scattering by this angular distribution of A/IC waves subsequently causes f to become approximately constant along surfaces of constant η, which in turn causes oblique A/IC waves to be damped by protons. We calculate the proton and electron contributions to the damping rate analytically, assuming Maxwellian electrons and f = f (η). Because the plasma does not relax to a state in which proton damping of oblique A/IC waves ceases, oblique A/IC waves can be significantly more effective at heating protons than A/IC waves with θ = 0.
    The Astrophysical Journal 05/2016; 722:710-720.
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    ABSTRACT: The cross-power spectrum is a quadratic estimator between two maps that can provide unbiased estimate of the underlying power spectrum of the correlated signals, which is therefore used for extracting the power spectrum in the Wilkinson Microwave Anisotropy Probe (WMAP) data. In this paper, we discuss the limit of the cross-power spectrum and derive the residual from the uncorrelated signal, which is the source of error in power spectrum extraction. We employ the estimator to extract window functions by crossing pairs of extragalactic point sources. We demonstrate its usefulness in WMAP difference assembly maps where the window functions are measured via Jupiter and then extract the window functions of the five WMAP frequency band maps.
    The Astrophysical Journal 04/2016; 738.
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    ABSTRACT: With the development of one-dimensional stellar evolution codes including rotation and the increasing number of observational data for stars of various evolutionary stages, it becomes more and more possible to follow the evolution of the rotation profile and angular momentum distribution in stars. In this context, understanding the interplay between rotation and convection in the very extended envelopes of giant stars is very important considering that all low-and intermediate-mass stars become red giants after the central hydrogen burning phase. In this paper, we analyze the interplay between rotation and convection in the envelope of red giant stars using three-dimensional numerical experiments. We make use of the Anelastic Spherical Harmonics code to simulate the inner 50% of the envelope of a low-mass star on the red giant branch. We discuss the organization and dynamics of convection, and put a special emphasis on the distribution of angular momentum in such a rotating extended envelope. To do so, we explore two directions of the parameter space, namely, the bulk rotation rate and the Reynolds number with a series of four simulations. We find that turbulent convection in red giant stars is dynamically rich, and that it is particularly sensitive to the rotation rate of the star. Reynolds stresses and meridional circulation establish various differential rotation profiles (either cylindrical or shellular) depending on the convective Rossby number of the simulations, but they all agree that the radial shear is large. Temperature fluctuations are found to be large and in the slowly rotating cases, a dominant = 1 temperature dipole influences the convective motions. Both baroclinic effects and turbulent advection are strong in all cases and mostly oppose one another.
    The Astrophysical Journal 03/2016; 702:1078-1097.
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    ABSTRACT: White-light observations of interplanetary disturbances have been dominated by interplanetary coronal mass ejections (ICMEs). This is because the other type of disturbance, the corotating interaction region (CIR), has proved difficult to detect using white-light imagers. Recently, a number of papers have appeared presenting CIR observations using the Solar Terrestrial Relations Observatory (STEREO) Heliospheric Imagers (HIs), but have mostly only focused on a single spacecraft and imager. In this paper, we present observations of a single CIR that was observed by all three current white-light heliospheric imagers (SMEI and both STEREO HIs), as well as the in situ instruments on both STEREO satellites and ACE. We begin with a discussion of the geometry of the CIR structure, and show how the apparent leading edge structure is expected to change as it corotates relative to the observer. We use these calculations to predict elongation–time profiles for CIRs of different speeds for each of the imagers, and also to predict the arrival times at the in situ instruments. We show that although all three measured different parts, they combine to produce a self-consistent picture of the CIR. Finally, we offer some thoughts on why CIRs have proved so difficult to detect in white-light heliospheric images.
    The Astrophysical Journal 03/2016; 702:862-870.
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    ABSTRACT: We report observations of circularly polarized emission from the solar corona at 77 MHz during the periods 2006 August 11–18, 2006 August 23–29, and 2007 May 16–22 in the minimum phase between the sunspot cycles 23 and 24. The observations were carried out with the east–west one-dimensional radio polarimeter at the Gauribidanur observatory located about 100 km north of Bangalore. Two-dimensional imaging observations at 77 MHz during the same period with the radioheliograph at the same observatory revealed that the emission region co-rotated with the Sun during the three aforementioned periods. Their rotation rates, close to the central meridian on the Sun, are 4. 6, 5. 2, and 4. 9 ± 0. 5 per day, respectively. We derived the radial distance of the region from the above observed rotation rates and the corresponding values are ≈1.24 ± 0.03 R (2006 August 11–18), ≈1.40 ± 0.03 R (2006 August 23–29), and ≈1.32 ± 0.03 R (2007 May 16–22). The estimated lower limit for the magnetic field strength at the above radial distances and periods are ≈1.1, 0.6, and 0.9 G, respectively.
    The Astrophysical Journal 01/2016; 734:39-7.
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    ABSTRACT: A search for variable stars with ultra-low amplitudes (ULAs), in the millimagnitude range, has been made in the combined MACHO and OGLE databases in the broad vicinity of the Cepheid instability strip in the HR diagram. A total of 25 singly periodic and 4 multiply periodic ULA objects have been uncovered. Our analysis does not allow us to distinguish between pulsational and ellipsoidal (binary) variabilities, nor between Large Magellanic Cloud (LMC) and foreground objects. However, the objects are strongly clustered and appear to be associated with the pulsational instability strips of LMC Pop. I and II variables. When combined with the ULA variables of Buchler et al., a total of 20 objects fall close to the classical Cepheid instability strip. However, they appear to fall on parallel period–magnitude (PM) relations that are shifted to slightly higher magnitude which would confer them a different evolutionary status. Low-amplitude RV Tauri and Pop. II Cepheids have been uncovered that do not appear in the MACHO or OGLE catalogs. Interestingly, a set of binaries seem to lie on a PM relation that is essentially parallel to that of the RV Tauri/Pop. II Cepheids.
    The Astrophysical Journal 12/2015; 698:944-955.

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