Numerical Study of Statistical Properties of the Galactic Center Distance Estimate from the Geometry of Spiral Arm Segments     

I. I. Nikiforov  A. V. Veselova 《Astronomy Letters》2018,44(11):699-719

The influence of various factors on the statistical properties of the Galactic center distance (R₀) estimate obtained by solving the general problem of determining the geometric parameters of a Galactic spiral arm from its segment with the inclusion of the distance to the spiral pole, i.e., R₀, in the set of parameters has been studied by the Monte Carlo method. Our numerical simulations have been performed for the model segments representing the Perseus and Scutum arms based on masers in high-mass star forming regions. We show that the uncertainty in the present-day parallax measurements for these objects systematically decreases (!) with increasing heliocentric distance, while the relative uncertainty in the parallaxes is, on average, approximately constant. This lucky circumstance increases significantly (by a factor of 1.4–1.7) the accuracy of estimating R₀ from the arm segment traced by masers. Our numerical experiments provide evidence for the consistency of the R₀ estimate from the spiral-segment geometry. The significant biases of the estimate detected only for the Scutum arm are caused mainly by the random parallax errors, the small angular extent of the segment, and the small number of objects representing it. The dispersion of the R₀ estimate depends most strongly on the angular extent of the segment and the parallax uncertainty if the latter, on average, does not depend on the distance. The remaining parameters, except for the pitch angle, exert an equally significant, but weaker influence on the statistical accuracy of the estimate. When the data on 3–8 segments are processed simultaneously, the predicted standard error of the final estimate is σR₀ ? 0.5?0.3 kpc, respectively. The accuracy can be improved by increasing the extent of the identified segments and the number of objects belonging to them. The method of determining R₀ from spiral segments has turned out to be operable for a wide set of possible parameters even when using an L-estimator (median). This makes the development of a more complex method based on an M-estimator, which allows one to properly take into account the measuring and natural dispersions of objects relative to the arm center line and, thus, to avoid the biases of the parameter estimates, meaningful.  相似文献   

First Analysis of Ground-Level Enhancement (GLE) 72 on 10 September 2017: Spectral and Anisotropy Characteristics     

A. Mishev  I. Usoskin  O. Raukunen  M. Paassilta  E. Valtonen  L. Kocharov  R. Vainio 《Solar physics》2018,293(10):136

Using data obtained with neutron monitors and space-borne instruments, we analyzed the second ground-level enhancement (GLE) of Solar Cycle 24, namely the event of 10 September 2017 (GLE 72), and derived the spectral and angular characteristics of associated GLE particles. We employed a new neutron-monitor yield function and a recently proposed model based on an optimization procedure. The method consists of simulating particle propagation in a model magnetosphere in order to derive the cutoff rigidity and neutron-monitor asymptotic directions. Subsequently, the rigidity spectrum and anisotropy of GLE particles are obtained in their dynamical evolution during the event on the basis of an inverse-problem solution. The derived angular distribution and spectra are discussed briefly.  相似文献   

Phytocenoses of the Ob Estuary and Kara Sea Shelf in the Late Spring Season     

Sukhanova  I. N.  Flint  M. V.  Sakharova  E. G.  Fedorov  A. V.  Makkaveev  P. N.  Nedospasov  A. A. 《Oceanology》2018,58(6):802-816

Oceanology - Based on the material obtained in the spring–summer season of 2016, the composition and quantitative distribution of phytoplankton in the Ob estuary and over the Kara Sea shelf...  相似文献   

Probing Twisted Magnetic Field Using Microwave Observations in an M Class Solar Flare on 11 February, 2014     

I. N. Sharykin  A. A. Kuznetsov  I. I. Myshyakov 《Solar physics》2018,293(2):34

This work demonstrates the possibility of magnetic-field topology investigations using microwave polarimetric observations. We study a solar flare of GOES M1.7 class that occurred on 11 February, 2014. This flare revealed a clear signature of spatial inversion of the radio-emission polarization sign. We show that the observed polarization pattern can be explained by nonthermal gyrosynchrotron emission from the twisted magnetic structure. Using observations of the Reuven Ramaty High Energy Solar Spectroscopic Imager, Nobeyama Radio Observatory, Radio Solar Telescope Network, and Solar Dynamics Observatory, we have determined the parameters of nonthermal electrons and thermal plasma and identified the magnetic structure where the flare energy release occurred. To reconstruct the coronal magnetic field, we use nonlinear force-free field (NLFFF) and potential magnetic-field approaches. Radio emission of nonthermal electrons is simulated by the GX Simulator code using the extrapolated magnetic field and the parameters of nonthermal electrons and thermal plasma inferred from the observations; the model radio maps and spectra are compared with observations. We have found that the potential-magnetic-field approach fails to explain the observed circular polarization pattern; on the other hand, the Stokes-\(V\) map is successfully explained by assuming nonthermal electrons to be distributed along the twisted magnetic structure determined by the NLFFF extrapolation approach. Thus, we show that the radio-polarization maps can be used for diagnosing the topology of the flare magnetic structures where nonthermal electrons are injected.  相似文献   

Implementation of the Concept for Creating a Spacecraft Double-Launch System as a Part of the Upper Stages of the Fregat Family     

Ishin  S. V.  Vikulenkov  V. P.  Fedoskin  D. I.  Poreshnev  A. Yu.  Jumahanov  N. B.  Yakovlev  B. D. 《Solar System Research》2020,54(7):690-698

Solar System Research - Abstract—Results of the implementation of a single concept for the development of the double launch system (SDZ) are presented, in particular the SDZ-La5 for the...  相似文献   

Study of the Galactic Rotation Based on Masers and Radio Stars with VLBI Measurements of Their Parallaxes     

Bobylev  V. V.  Krisanova  O. I.  Bajkova  A. T. 《Astronomy Letters》2020,46(7):439-448

Astronomy Letters - Based on published data, we have produced a sample of 256 radio sources whose trigonometric parallaxes and proper motions were measured by VLBI. This sample contains Galactic...  相似文献   

Recent Tectonic Rupturing on the Mud Volcano of Mount Karabetova,Taman Peninsula     

Ovsyuchenko  A. N.  Larkov  A. S.  Sysolin  A. I.  Rogozhin  E. A.  Sobisevich  A. L.  Chen  J.  Liu  J.  Qin  J. 《Doklady Earth Sciences》2020,492(1):361-365

Doklady Earth Sciences - In October 2019, extremely impressive, fresh ruptures of the surface on the mud volcano of Mount Karabetova were discovered. The ruptures are represented by all the main...  相似文献   

First Find of Platinum in Cosmogenic Spherules of Ferromanganese Crusts (Fedorov Guyot,Magellan Seamounts,Pacific Ocean)     

Savelyev  D. P.  Khanchuk  A. I.  Savelyeva  O. L.  Moskaleva  S. V.  Mikhailik  P. E. 《Doklady Earth Sciences》2020,491(2):199-203

Doklady Earth Sciences - More than 250 magnetic spherules 40–200 µm in size were mechanically separated from a ferromanganese crust sample of Fedorov Guyot in the Magellan Seamounts. The...  相似文献   

Mesoscale Variability of the Ocean in the Northern Part of the Weddell Sea     

Morozov  E. G.  Frey  D. I.  Polukhin  A. A.  Krechik  V. A.  Artemiev  V. A.  Gavrikov  A. V.  Kasian  V. V.  Sapozhnikov  F. V.  Gordeeva  N. V.  Kobylyansky  S. G. 《Oceanology》2020,60(5):573-588

Oceanology - Results of a mesoscale survey in the Powell Basin in the northern part of the Weddell Sea are analyzed. The survey included 24 CTD casts (6 × 4) with an interval of six nautical...  相似文献   

Nothrotheriops sp. (Mammalia,Xenarthra) from the Late Pleistocene of Argentina: implications for the dispersion of ground sloths during the Great American Biotic Interchange     

Diego Brandoni  Raúl I. Vezzosi 《Boreas: An International Journal of Quaternary Research》2019,48(4):879-890

The aim of this contribution is to describe a femur (MCRS 199) assigned to Nothrotheriops sp. from the Late Pleistocene of Santa Fe Province (Argentina), and discuss the implications of this find in the context of the dispersal of ground sloths during the Great American Biotic Interchange. The specimen MCRS 199 is smaller than the femora referred to the North American species Nothrotheriops texanus and Nothrotheriops shastensis but shares several features with these species: (i) shape and position of the greater trochanter, (ii) development of the lesser trochanter, (iii) presence of connection between the third trochanter and the ectepicondyle, (iv) distal third of the femur wider, with ML/DW index of 1.93, and (v) location and relationship of the distal condyles. These similarities allow us to assign MCRS 199 to Nothrotheriops sp. The record of Nothrotheriops sp. from Santa Fe Province chronologically coincides with the earliest records of Nothrotheriops shastensis suggesting a broad geographical distribution of Nothrotheriops during the Late Pleistocene, ranging from 33–36°N (e.g. states of California and Arizona, USA) to 31°S (northern Salado River, Santa Fe Province, Argentina). Thus, Nothrotheriops have dispersed from North America (where Nothrotheriops has early records, Calabrian–Middle Pleistocene) to South America where localities bearing Nothrotheriops are Late Pleistocene in age. In addition, once in South America and probably during the Middle Pleistocene, Nothrotheriops probably gave rise to its sister taxon, Nothrotherium, with records from the Middle Pleistocene (e.g. 223 ka BP, northeastern Brazil) to the Late Pleistocene (e.g. 15 ka BP).  相似文献