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Li R.,Chinese Academy of Sciences | Mo H.J.,University of Massachusetts Amherst | Fan Z.,Peking University | Yang X.,Shanghai Astronomical Observatory | van den Bosch F.C.,Yale University
Monthly Notices of the Royal Astronomical Society | Year: 2013

With galaxy groups constructed from the Sloan Digital Sky Survey (SDSS), we analyse the expected galaxy-galaxy lensing signals around satellite galaxies residing in different host haloes and locatedat different halo-centric distances. We use a Markov chain Monte Carlo method to explore the potential constraints on the mass and density profile of subhaloes associated with satellite galaxies from SDSS-like surveys and surveys similar to the Large Synoptic Survey Telescope (LSST). Our results show that for SDSS-like surveys, we can only set a loose constraint on the mean mass of subhaloes. With LSST-like surveys, however, both the mean mass and the density profile of subhaloes can be well constrained. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Kopeikin S.M.,University of Missouri | Han W.-B.,Shanghai Astronomical Observatory | Han W.-B.,University of Missouri
Journal of Geodesy | Year: 2015

The Fresnel–Fizeau effect is a special relativistic effect that makes the speed of light dependent on the velocity of a transparent, moving medium. We present a theoretical formalism for discussing propagation of electromagnetic signals through the moving Earth atmosphere taking into account the Fresnel–Fizeau effect. It provides the rigorous relativistic derivation of the atmospheric time delay equation in the consensus model of geodetic VLBI observations which has never been published before. The paper confirms the atmospheric time delay of the consensus VLBI model used in IERS standards and provides a firm theoretical basis for calculation of even more subtle relativistic corrections. © 2015, Springer-Verlag Berlin Heidelberg.

Wang Z.,Shanghai Astronomical Observatory | Chakrabarty D.,Massachusetts Institute of Technology
Astrophysical Journal | Year: 2010

The X-ray source 4U 1820-30 in the globular cluster NGC 6624 is known as the most compact binary among the identified X-ray binaries (XRBs). Having an orbital period of 685.0 s, the source consists of a neutron star (NS) primary and likely a 0.06-0.08 M ⊙ white dwarf (WD) secondary. Here, we report on far-ultraviolet (FUV) observations of this XRB, made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. From our Fourier spectral analysis of the FUV timing data, we obtain a period of 693.5 ± 1.3 s, which is significantly different from the orbital period. The light curve folded at this period can be described by a sinusoid, with a fractional semiamplitude of 6.3% and the phase zero (maximum of the sinusoid) at MJD 50886.015384 ± 0.000043 (TDB). While the discovered FUV period may be consistent with a hierarchical triple system model that was previously considered for 4U 1820-30, we suggest that it could instead be the indication of superhump modulation, which arises from an eccentric accretion disk in the binary. The X-ray and FUV periods would be the orbital and superhump periods, respectively, indicating a 1% superhump excess and a WD/NS mass ratio around 0.06. Considering 4U 1820-30 as a superhump source, we discuss the implications. © 2010. The American Astronomical Society.

Han W.-B.,Shanghai Astronomical Observatory
Research in Astronomy and Astrophysics | Year: 2014

The supermassive black hole (SMBH) with a mass of 4 million Mo inside the radio source Sgr A∗ in our Galactic center is the nearest SMBH. Once S stars with a shorter period are observed, relativistic precessions especially the Lense-Thirring effect can be measured by astronomical observations at the 10 μas level in the future. An interesting but so far unaddressed problem is that the SMBH not only has spin but also spin precession like similar objects. We study the effect of such spin precession on the orbital precessions of orbiting stars. Our results show that the spin precession can produce a periodic oscillation in the precession of the star's orbital plane, but has no obvious effect on the periapse shift. For stars with an orbital period of O(0.1) yr or less, such visible oscillations occur when the SMBH's spin-precession period ranges from about a few tens of years to hundreds of years. The period of oscillation is the same as the one of the spin precession. In principle, the precession of this oscillating orbital plane can be observed and then the spin and spin precession of the nearest SMBH can be determined. © 2014 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd..

Soffel M.H.,Shanghai Astronomical Observatory | Soffel M.H.,Lohmann Observatory | Han W.-B.,Shanghai Astronomical Observatory
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2015

We calculate the time delay of light in the gravitational field of a slowly moving body with arbitrary multipoles (mass and spin multipole moments) by the Time-Transfer-Function (TTF) formalism. The parameters we use, first introduced by Kopeikin for a gravitational source at rest, make the integration of the TTF very elegant and simple. Results completely coincide with expressions from the literature. The results for a moving body (with constant velocity) with complete multipole-structure are new, according to our knowledge. © 2014 Elsevier B.V. All rights reserved.

Chen C.,Shandong University of Science and Technology | Chen C.,Key Laboratory of Surveying and Mapping Technology on Island and Reef | Li Y.,Shanghai Astronomical Observatory
Computers and Geosciences | Year: 2012

In order to avoid the ill-conditioning problem of thin plate spline (TPS), the orthogonal least squares (OLS) method was introduced, and a modified OLS (MOLS) was developed. The MOLS of TPS (TPS-M) can not only select significant points, termed knots, from large and dense sampling data sets, but also easily compute the weights of the knots in terms of back-substitution. For interpolating large sampling points, we developed a local TPS-M, where some neighbor sampling points around the point being estimated are selected for computation. Numerical tests indicate that irrespective of sampling noise level, the average performance of TPS-M can advantage with smoothing TPS. Under the same simulation accuracy, the computational time of TPS-M decreases with the increase of the number of sampling points. The smooth fitting results on lidar-derived noise data indicate that TPS-M has an obvious smoothing effect, which is on par with smoothing TPS. The example of constructing a series of large scale DEMs, located in Shandong province, China, was employed to comparatively analyze the estimation accuracies of the two versions of TPS and the classical interpolation methods including inverse distance weighting (IDW), ordinary kriging (OK) and universal kriging with the second-order drift function (UK). Results show that regardless of sampling interval and spatial resolution, TPS-M is more accurate than the classical interpolation methods, except for the smoothing TPS at the finest sampling interval of 20. m, and the two versions of kriging at the spatial resolution of 15. m. In conclusion, TPS-M, which avoids the ill-conditioning problem, is considered as a robust method for DEM construction. © 2012 Elsevier Ltd.

Hoyle F.,Pontifica University Catolica Of Ecuador | Vogeley M.S.,Drexel University | Pan D.,Drexel University | Pan D.,Shanghai Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2012

Using the sample presented by Pan et al., we analyse the photometric properties of 88794 void galaxies and compare them to galaxies that reside in higher density environments with the same absolute magnitude distribution as the void galaxies. We analysed the Sloan Digital Sky Survey Data Release 7 and found a total of 1054 dynamically distinct voids with radius larger than 10h -1Mpc. The voids are not empty, but are underdense, with δρ/ρ < -0.9 in their centres. In this paper, we study the photometric properties of these void galaxies. We look at the u - r colours as an indication of star formation activity and the inverse concentration index as an indication of galaxy type. We find that void galaxies are statistically bluer than galaxies found in higher density environments with the same magnitude distribution. We examine the colours of the galaxies as a function of magnitude, dividing the galaxies into bright, medium, faint and dwarf groups, and we fit each colour distribution with a double-Gaussian model for the red and blue subpopulations. As we move from bright to dwarf galaxies, the population of red galaxies steadily decreases and the fraction of blue galaxies increases in both voids and walls; however, the fraction of blue galaxies in the voids is always higher and bluer than in the walls. We also split the void and wall galaxies into samples depending on galaxy type, as measured by the inverse concentration index. We find that late-type void galaxies are bluer than late-type wall galaxies and the same holds for early galaxies. We also find that early-type and dwarf void galaxies are blue in colour. We also study the properties of void galaxies as a function of their distance from the centre of the void. We find very little variation in the properties, such as magnitude, colour and type, of void galaxies as a function of their location in the void. The only exception is that the dwarf void galaxies may live closer to the centres of voids. As shown by Pan et al., the centres of voids have very similar density contrast and hence all void galaxies live in very similar density environments, which may explain the lack of variation of galaxy properties with location within voids. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Guo P.,Shanghai Astronomical Observatory | Xu X.,Wenzhou University | Zhang G.X.,China Earthquake Administration
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2011

In this study, the ionospheric equivalent slab thickness is derived from the Global Ionospheric Map (GIM) and the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation (IRO) data. The spatial, diurnal, and temporal variations of the ionospheric equivalent slab thickness during the solar minimum phase (the year 2007) have been analyzed. The analytical results show diurnal and seasonal variations of the ionospheric equivalent slab thickness. © 2011.

Wang L.,CAS National Astronomical Observatories | Weinmann Simone M. S.M.,Leiden University | De Lucia Gabriella G.,National institute for astrophysics | Yang Xiaohu X.,Shanghai JiaoTong University | Yang Xiaohu X.,Shanghai Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2013

Assembly bias describes the finding that the clustering of dark matter haloes depends on halo formation time at fixed halo mass. In this paper, we analyse the influence of assembly bias on galaxy clustering using both semi-analytic galaxy formation models (SAMs) and observational data. At fixed stellar mass, SAMs predict that the clustering of central galaxies depends on the specific star formation rate (sSFR), with more passive galaxies having a higher clustering amplitude. We find similar trends using the Sloan Digital Sky Survey (SDSS) group catalogues, and verify that these are not affected by possible biases due to the group finding algorithm. Low-mass central galaxies reside in narrow bins of halo mass, so the observed trends of higher clustering amplitude for galaxies with lower sSFR is not driven by variations of the parent halo mass. We argue that the clustering dependence on sSFR represent a direct detection of assembly bias. In addition, contrary to what expected based on clustering of dark matter haloes, we find that low-mass central galaxies in SAMs with larger host halo mass have a lower clustering amplitude than their counter-parts residing in lower mass haloes. This results from the fact that, at fixed stellar mass, assembly bias has a stronger influence on clustering than the dependence on the parent halo mass. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

News Article | November 21, 2016
Site: www.eurekalert.org

An international team led by researchers from Tohoku University has found an extremely faint dwarf satellite galaxy of the Milky Way. The team's discovery is part of the ongoing Subaru Strategic Survey using Hyper Suprime-Cam. The satellite, named Virgo I, lies in the direction of the constellation Virgo. At the absolute magnitude of -0.8 in the optical waveband, it may well be the faintest satellite galaxy yet found. Its discovery suggests the presence of a large number of yet-undetected dwarf satellites in the halo of the Milky Way and provides important insights into galaxy formation through hierarchical assembly of dark matter. Currently, some 50 satellite galaxies to the Milky Way have been identified. About 40 of them are faint and diffuse and belong to the category of so-called "dwarf spheroidal galaxies". Many recently discovered dwarf galaxies, especially those seen in systematic photometric surveys such as the Sloan Digital Sky Survey (SDSS) and the Dark Energy Survey (DES) are very faint with absolute luminosity in the optical waveband below -8 magnitude. These are so-called "ultra-faint dwarf galaxies". However, previous searches made use of telescopes with a diameter of 2.5 to 4 meters, so only satellites relatively close to the Sun or those with higher magnitudes were identified. Those that are more distant or faint ones in the halo of the Milky Way are yet to be detected. The combination of the large aperture of 8.2-meter Subaru Telescope and the large field-of-view Hyper Suprime-Cam (HSC) instrument is very powerful in this study. It enables an efficient search for very faint dwarf satellites over large areas of the sky. The first step in searching out a new dwarf galaxy is to identify an over density of stars in the sky, using photometric data. Next is to assess that the over dense appearance is not due to line-of-sight or accidental juxtapositions of unrelated dense fields, but is really a stellar system. The standard method for doing this is to look for a characteristic distribution of stars in the color-magnitude diagram (comparable to the Hertzsprung-Russell diagram). Stars in a general field shows no particular patterns in this diagram. Daisuke Homma, a graduate student at Tohoku University, found Virgo I under the guidance of his advisor, Masashi Chiba, and their international collaborators. "We have carefully examined the early data of the Subaru Strategic Survey with HSC and found an apparent over density of stars in Virgo with very high statistical significance, showing a characteristic pattern of an ancient stellar system in the color-magnitude diagram," he said. "Surprisingly, this is one of the faintest satellites, with absolute magnitude of -0.8 in the optical waveband. This is indeed a galaxy, because it is spatially extended with a radius of 124 light years - systematically larger than a globular cluster with comparable luminosity." The faintest dwarf satellites identified so far was Segue I, discovered by SDSS (-1.5 mag) and Cetus II in DES (0.0 mag). Cetus II is yet to be confirmed, as it is too compact as a galaxy. Virgo I may ultimately turn out to be the faintest one ever discovered. It lies at a distance of 280,000 light years from the Sun, and such a remote galaxy with faint brightness has not been identified in previous surveys. It is beyond the reach of SDSS, which has previously surveyed the same area in the direction of the constellation Virgo. According to Chiba, the leader of this search project, the discovery has profound implications. "This discovery implies hundreds of faint dwarf satellites waiting to be discovered in the halo of the Milky Way," he said. "How many satellites are indeed there and what properties they have, will give us an important clue of understanding how the Milky Way formed and how dark matter contributed to it." Formation of galaxies like the Milky Way is thought to proceed through the hierarchical assembly of dark matter, forming dark halos, and through the subsequent infall of gas and star formation affected by gravity. Standard models of galaxy formation in the context of the so-called cold dark matter (CDM) theory predict the presence of hundreds of small dark halos orbiting in a Milky Way-sized dark halo and a comparable number of luminous satellite companions. However, only tens of satellites have ever been identified. This falls well short of a theoretical predicted number, which is part of the so-called "missing satellite problem". Astronomers may need to consider other types of dark matter than CDM or to invoke baryonic physics suppressing galaxy formation to explain the shortfall in the number of satellites. Another possibility is that they have seen only a fraction of all the satellites associated with the Milky Way due to various observational biases. The issue remains unsolved. One of the motivations for the Subaru Strategic Survey using HSC is to do increase observations in the search for Milky Way satellites. The early data from this survey is what led to the discovery of Virgo I. This program will continue to explore much wider areas of the sky and is expected to find more satellites like Virgo I. These tiny companions to be discovered in the near future may tell us much more about history of the Milky Way's formation. Daisuke Homma (Tohoku University, Japan), Masashi Chiba (Tohoku University, Japan), Sakurako Okamoto (Shanghai Astronomical Observatory, China), Yutaka Komiyama (National Astronomical Observatory of Japan (NAOJ), Japan), Masayuki Tanaka (NAOJ, Japan), Mikito Tanaka (Tohoku University, Japan), Miho N. Ishigaki (Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), University of Tokyo, Japan), Masayuki Akiyama (Tohoku University, Japan), Nobuo Arimoto (Subaru Telescope, NAOJ, USA), Jose A, Garmilla (Princeton University, USA), Robert H. Lupton (Princeton University, USA), Michael A. Strauss (Princeton University, USA), Hisanori Furusawa (NAOJ, Japan), Satoshi Miyazaki (NAOJ, Japan), Hitoshi Murayama (Kavli IPMU, WPI, University of Tokyo, Japan), Atsushi J. Nishizawa (Nagoya University, Japan), Masahiro Takada (Kavli IPMU, WPI, University of Tokyo, Japan), Tomonori Usuda (NAOJ, Japan), Shiang-Yu Wang (Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan) Leo II: An Old Dwarf Galaxy with Juvenescent Heart http://subarutelescope.

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