Cosmochemical and spectroscopic properties of Northwest Africa 7325—A consortium study          下载免费PDF全文

I. Weber  A. Morlok  A. Bischoff  H. Hiesinger  D. Ward  K. H. Joy  S. A. Crowther  N. D. Jastrzebski  J. D. Gilmour  P. L. Clay  R. A. Wogelius  R. C. Greenwood  I. A. Franchi  C. Münker 《Meteoritics & planetary science》2016,51(1):3-30

This work is part of a project to build an infrared database in order to link IR data of planetary materials (and therefore possible Mercury material) with remote sensing observations of Mercury, which will probably be obtained by the MERTIS instrument on the forthcoming BepiColombo mission. The unique achondrite Northwest Africa (NWA) 7325, which has previously been suggested to represent the first sample from Mercury, was investigated by optical and electron microscopy, and infrared and Raman spectroscopy. In addition, the oxygen, strontium, xenon, and argon isotopes were measured and the abundance of selected trace elements determined. The meteorite is a cumulate rock with subchondritic abundances of HFSE and REE and elevated Sr contents, which underwent a second heating and partial remelting process. Oxygen isotope measurements show that NWA 7325 plots in the ureilite field, close to the ALM‐A trachyandesitic fragment found in the unique Almahata Sitta meteorite breccia. On the other hand, mineralogical investigations of the pyroxenes in NWA 7325 provide evidence for similarities to the lodranites and acapulcoites. Furthermore, the rock is weakly shocked and argon isotope data record ancient (~4.5 Ga) plateau ages that have not been reset. The sample records a cosmogenic exposure age of ~19 Ma. Systematics of Rb‐Sr indicate an extreme early volatile depletion of the precursor material, similar to many other achondrite groups. However, despite its compositional similarities to other meteorite groups, our results suggest that this meteorite is unique and unrelated to any other known achondrite group. An origin for NWA 7325 as a sample from the planet Mercury is not supported by the results of our investigation. In particular, the evidence from infrared spectroscopy indicates that a direct relationship between NWA 7325 and the planet Mercury can be ruled out: no acceptable spectral match between laboratory analyses and remote sensing observations from Mercury has been obtained. However, we demonstrate that infrared spectroscopy is a rapid and nondestructive method to characterize mineral phases and thus an excellent tool for planetary surface characterization in space missions.  相似文献   

Power Spectrum Density of Stochastic Oscillating Accretion Disk     

G.?B.?Long  J.?W.?Ou  Y.?G.?ZhengEmail author 《Journal of Astrophysics and Astronomy》2016,37(2):10

In this paper, we employ a stochastic oscillating accretion disk model for the power spectral index and variability of BL Lac object S5 0716+714. In the model, we assume that there is a relativistic oscillation of thin accretion disks and it interacts with an external thermal bath through a friction force and a random force. We simulate the light curve and the power spectrum density (PSD) at (i) over-damped, (ii) critically damped and (iii) under-damped cases, respectively. Our results show that the simulated PSD curves depend on the intrinsic property of the accretion disk, and it could be produced in a wide interval ranging from 0.94 to 2.05 by changing the friction coefficient in a stochastic oscillating accretion disk model. We argue that accretion disk stochastic oscillating could be a possible interpretation for observed PSD variability.  相似文献   

Line-of-Sight Anisotropies in the Cosmic Dawn and Epoch of Reionization 21-cm Power Spectrum     

Suman?MajumdarEmail authorView author&#;s OrcID profile  Kanan?K.?Datta  Raghunath?Ghara  Rajesh?Mondal  T.?Roy?Choudhury  Somnath?Bharadwaj  Sk.?Saiyad?Ali  Abhirup?Datta 《Journal of Astrophysics and Astronomy》2016,37(4):32

The line-of-sight direction in the redshifted 21-cm signal coming from the cosmic dawn and the epoch of reionization is quite unique in many ways compared to any other cosmological signal. Different unique effects, such as the evolution history of the signal, non-linear peculiar velocities of the matter etc. will imprint their signature along the line-of-sight axis of the observed signal. One of the major goals of the future SKA-LOW radio interferometer is to observe the cosmic dawn and the epoch of reionization through this 21-cm signal. It is thus important to understand how these various effects affect the signal for its actual detection and proper interpretation. For more than one and half decades, various groups in India have been actively trying to understand and quantify the different line-of-sight effects that are present in this signal through analytical models and simulations. In many ways the importance of this sub-field under 21-cm cosmology have been identified, highlighted and pushed forward by the Indian community. In this article, we briefly describe their contribution and implication of these effects in the context of the future surveys of the cosmic dawn and the epoch of reionization that will be conducted by the SKA-LOW.  相似文献   

A Stringent Limit on Variation of the Fine-Structure Constant Using Absorption Line Multiplets in the Early Universe     

T. D. Le 《Astrophysics》2016,59(2):285-291

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Predicting Changes in the Radio Emission Fluxes of Extragalactic Sources     

A. L. Sukharev  M. I. Ryabov  G. I. Donskikh 《Astrophysics》2016,59(2):213-226

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Distribution of Pulsars in the Galaxy     

H. A. Andreasyan  R. R. Andreasyan  G. M. Paronyan 《Astrophysics》2016,59(1):57-67

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Fractality of Isotherms of the Cosmic Microwave Background Based on Data from the Planck Spacecraft     

A. A. Mylläri  A. A. Raikov  V. V. Orlov  P. A. Tarakanov  V. N. Yershov  M. Y. Yezhkov 《Astrophysics》2016,59(1):31-37

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Possible Reasons for the Slow Rotation of BF Ori     

S. G. Shulman 《Astrophysics》2016,59(1):20-30

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Isentropic “Shock Waves” in Numerical Simulations of Astrophysical Problems     

G. S. Bisnovatyi-Kogan  S. G. Moiseenko 《Astrophysics》2016,59(1):1-10

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Orbital motions and light curves of young binaries XZ Tau and VY Tau     

A. V. Dodin  N. V. Emelyanov  A. V. Zharova  S. A. Lamzin  E. V. Malogolovets  J. M. Roe 《Astronomy Letters》2016,42(1):29-40

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