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1.
The advanced Russian project Laplace-P is aimed at developing and launching two scientific spacecraft (SC)—Laplace-P1 (LP1 SC) and Laplace-P2 (LP2 SC)—designed for remote and in-situ studies of the system of Jupiter and its moon Ganymede. The LP1 and LP2 spacecraft carry an orbiter and a lander onboard, respectively. One of the orbiter’s objectives is to map the surface of Ganymede from the artificial satellite’s orbit and to acquire the data for the landing site selection. The main objective of the lander is to carry out in-situ investigations of Ganymede’s surface. The paper describes the scientific goals and objectives of the mission, its special features, and the LP1 and LP2 mission profiles during all of the phases—from the launch to the landing on the surface of Ganymede.  相似文献   

2.
The data acquired by the Vega and Giotto spacecraft, while investigating comet 1Р/Halley in 1986, are compared to the results of the first phase of exploration of the nucleus of comet 67P/Churyumov–Gerasimenko performed with the Rosetta and Philae modules. The course of the Rosetta mission activity and the status of the modules after the Philae probe landing on the comet’s nucleus are overviewed. Since some elements of the touchdown equipment failed, a number of in-situ experiments on the comet’s nucleus were not carried out.  相似文献   

3.
The paper contains the data on the thermal and physical characteristic of the surface regolith of the Martian satellite Phobos obtained from the spaceborne remote sensing (with the Mariner 9, Viking, and Mars Global Surveyor orbiters and the Phobos-2 spacecraft) and the results of the numerical modeling of the thermal regime in the surface regolith (on diurnal and seasonal scales) performed for the prospective landing site in the Lagado Planitia region located in the anti-Martian hemisphere of Phobos.  相似文献   

4.
Three three-component (bulge, disk, halo) model Galactic gravitational potentials differing by the expression for the dark matter halo are considered. The central (bulge) and disk components are described by the Miyamoto–Nagai expressions. The Allen–Santillán (I), Wilkinson–Evans (II), and Navarro–Frenk–White (III) models are used to describe the halo. A set of present-day observational data in the range of Galactocentric distances R from 0 to 200 kpc is used to refine the parameters of thesemodels. For the Allen–Santillán model, a dimensionless coefficient γ has been included as a sought-for parameter for the first time. In the traditional and modified versions, γ = 2.0 and 6.3, respectively. Both versions are considered in this paper. The model rotation curves have been fitted to the observed velocities by taking into account the constraints on the local matter density ρ ⊙ = 0.1 M ⊙ pc?3 and the force K z =1.1/2πG = 77 M ⊙ pc?2 acting perpendicularly to the Galactic plane. The Galactic mass within a sphere of radius 50 kpc, M G (R ≤ 50 kpc) ≈ (0.41 ± 0.12) × 1012 M ⊙, is shown to satisfy all three models. The differences between the models become increasingly significant with increasing radius R. In model I, the Galactic mass within a sphere of radius 200 kpc at γ = 2.0 turns out to be greatest among the models considered, M G (R ≤ 200 kpc) = (1.45 ±0.30)× 1012 M ⊙, M G (R ≤ 200 kpc) = (1.29± 0.14)× 1012 M ⊙ at γ = 6.3, and the smallest value has been found in model II, M G (R ≤ 200 kpc) = (0.61 ± 0.12) × 1012 M ⊙. In our view, model III is the best one among those considered, because it ensures the smallest residual between the data and the constructed model rotation curve provided that the constraints on the local parameters hold with a high accuracy. Here, the Galactic mass is M G (R ≤ 200 kpc) = (0.75 ± 0.19) × 1012 M ⊙. A comparative analysis with the models by Irrgang et al. (2013), including those using the integration of orbits for the two globular clusters NGC 104 and NGC 1851 as an example, has been performed. The third model is shown to have subjected to a significant improvement.  相似文献   

5.
We consider a spherically symmetric general relativistic perfect fluid in its comoving frame. It is found that, by integrating the local energy momentum conservation equation, a general form of g 00 can be obtained. During this study, we get a cue that an adiabatically evolving uniform density isolated sphere having ρ(r,t)=ρ 0(t), should comprise “dust” having p 0(t)=0; as recently suggested by Durgapal and Fuloria (J. Mod. Phys. 1:143, 2010) In fact, we offer here an independent proof to this effect. But much more importantly, we find that for the homogeneous and isotropic Friedmann-Robertson-Walker (FRW) metric having p(r,t)=p 0(t) and ρ(r,t)=ρ 0(t), \(g_{00} = e^{-2p_{0}/(p_{0} +\rho_{0})}\). But in general relativity (GR), one can choose an arbitrary t→t ?=f(t) without any loss of generality, and thus set g 00(t ?)=1. And since pressure is a scalar, this implies that p 0(t ?)=p 0(t)=0 in the Big-Bang model based on the FRW metric. This result gets confirmed by the fact the homogeneous dust metric having p(r,t)=p 0(t)=0 and ρ(r,t)=ρ 0(t) and the FRW metric are exactly identical. In other words, both the cases correspond to the same Einstein tensor \(G^{a}_{b}\) because they intrinsically have the same energy momentum tensor \(T^{a}_{b}=\operatorname {diag}[\rho_{0}(t), 0,0, 0]\).  相似文献   

6.
Based on CCD observations with the Pulkovo 26-inch refractor in 2003–2018, we have obtained the orbit of the visual double star ADS 2668 AB (P = 947 yr, a = 2.9″, e = 0.41, ω = 246°, Ω = 131°, i = 114°, T = 1456 yr) for the first time by the apparent motion parameter (AMP) method, which is consistent with the inner orbit of ADS 2668 Aa-Ab, and improved the orbit of ADS 8236 AB (P = 1996 yr, a = 4.69″, e = 0.39, ω = 201°, Ω = 166°, i = 110°, T = 1246 yr). The inner orbit of the photocenter of ADS 8236 with a period of 4.627 yr has been calculated from the residuals. This orbit of ADS 8236 Ba–Bb supplements the spectroscopic orbit by the elements specifying the orbital plane (i and Ω). In both cases, the planes of the inner and outer orbits are noncoplanar. The presence of an additional companion in the system ADS 2668 is discussed.  相似文献   

7.
Based on our UBV RI observations and X-ray data from the RXTE satellite, we have investigated the variability of the galaxy 3C 120 over the period 1996–2008. The relative variability amplitude in the U and B bands without any subtraction of the contribution from the underlying galaxy is 23 and 22%, respectively, against 21% in the X-ray band. The autocorrelation function based on the B-band data is considerably wider than that based on the X-ray data. The structure functions on a time scale from 1 to ～100–300 days in the X-ray and optical spectral ranges have the form of a power law (SF ～ τ b ). However, their indices differ significantly: b = 0.42 in the X-ray band and b = 1.36 in the B band. Considering the X-ray and optical variabilities as a superposition of independent flares in a wide range of durations, we may conclude that the amplitudes of short flares in the X-ray band are higher than those in the optical one and, conversely, the relative amplitudes of long flares in the X-ray band are slightly lower than those in the optical one, i.e., short events dominate in the X-ray band. The optical flux variations in the R c and I c bands lag significantly behind those in the B band, by 3.9 ?0.7 +1.0 and 6.2 ?0.6 +1.1 days, respectively, if the lag is estimated from the centroid of the cross-correlation function. The X-ray variability on a time scale of about 1800 days (～5 yr) lags behind the B-band variations by 5.3 ?3.3 +2.7 days, but the confidence level of this estimate is only 87%. A more detailed analysis of the correlation between the X-ray and optical emissions has revealed a fairly complex picture: different degrees of correlation between the optical and X-ray fluxes are observed at different times.  相似文献   

8.
Small tidal forces in the Earth–Moon system cause detectable changes in the orbit. Tidal energy dissipation causes secular rates in the lunar mean motion n, semimajor axis a, and eccentricity e. Terrestrial dissipation causes most of the tidal change in n and a, but lunar dissipation decreases eccentricity rate. Terrestrial tidal dissipation also slows the rotation of the Earth and increases obliquity. A tidal acceleration model is used for integration of the lunar orbit. Analysis of lunar laser ranging (LLR) data provides two or three terrestrial and two lunar dissipation parameters. Additional parameters come from geophysical knowledge of terrestrial tides. When those parameters are converted to secular rates for orbit elements, one obtains dn/dt = \(-25.97\pm 0.05 ''/\)cent\(^{2}\), da/dt = 38.30 ± 0.08 mm/year, and di/dt = ?0.5 ± 0.1 \(\upmu \)as/year. Solving for two terrestrial time delays and an extra de/dt from unspecified causes gives \(\sim \) \(3\times 10^{-12}\)/year for the latter; solving for three LLR tidal time delays without the extra de/dt gives a larger phase lag of the N2 tide so that total de/dt = \((1.50 \pm 0.10)\times 10^{-11}\)/year. For total dn/dt, there is \(\le \)1 % difference between geophysical models of average tidal dissipation in oceans and solid Earth and LLR results, and most of that difference comes from diurnal tides. The geophysical model predicts that tidal deceleration of Earth rotation is \(-1316 ''\)/cent\(^{2}\) or 87.5 s/cent\(^{2}\) for UT1-AT, a 2.395 ms/cent increase in the length of day, and an obliquity rate of 9 \(\upmu \)as/year. For evolution during past times of slow recession, the eccentricity rate can be negative.  相似文献   

9.
In this paper, we investigate the model with a new type of interaction between generalized Chaplygin gas (GCG) and dark matter. It is shown that there exists a stable scaling attractor, which provides the possibility to alleviate the coincidence problem. The equation of state (EoS) of GCG approaches the attractor phase from either w g >?1 or w g w g w g w g >?1), and next cross again the phantom divide (the transition from w g >?1 to w g Q can change its sign from Q<0 to Q>0 as the universe expands, which is different from the usual interaction. Moreover, we investigate the model from statefinder viewpoint. The statefinder diagnostic can not only discriminate the model with different coupling constant but also distinguish the model from other dark energy models.  相似文献   

10.
We show that including the recoil upon scattering in the Ly-α line can lead to a noticeable acceleration of the primordial hydrogen recombination. Thus, for example, for the ΛCDM model, the decrease in the degree of ionization exceeds 1% at redshifts z = 800–1050, reaching ≈1.3% at z = 900. The corresponding corrections to the calculated cosmic microwave background power spectra reach 1.1% and 1.7% for TT and EE spectra, respectively. The radiative transfer in these calculations was treated in the quasi-stationary approximation.We have also obtained numerical solutions (in the diffusion approximation) to the nonstationary problem of radiative transfer in the Ly-α line for a partial frequency redistribution with recoil. We trace the evolution of the local line profile and the relative number of uncompensated transitions from the 2p state to the 1s state. We show that including the nonstationarity of the Ly-α line radiative transfer can lead to an additional acceleration of the primordial hydrogen recombination.  相似文献   

11.
EChO is a three-modules (VNIR, SWIR, MWIR), highly integrated spectrometer, covering the wavelength range from 0.55 μ m to 11.0 μ m. The baseline design includes the goal wavelength extension to 0.4 μ m while an optional LWIR module extends the range to the goal wavelength of 16.0 μ m. An Instrument Control Unit (ICU) is foreseen as the main electronic subsystem interfacing the spacecraft and collecting data from all the payload spectrometers modules. ICU is in charge of two main tasks: the overall payload control (Instrument Control Function) and the housekeepings and scientific data digital processing (Data Processing Function), including the lossless compression prior to store the science data to the Solid State Mass Memory of the Spacecraft. These two main tasks are accomplished thanks to the Payload On Board Software (P-OBSW) running on the ICU CPUs.  相似文献   

12.
In this paper we study the relations between the main characteristics of groups and clusters of galaxies using the archival data of the SDSS and 2MASX catalogs. We have developed and implemented a new method of determining the size of galaxy systems and their effective radius which contains half of the galaxies and not half the luminosity, since the luminosity of the brightest galaxy in a group can account for over 50% of the total luminosity of the group. The derived parameters (log LK, logRe, and log σ200) for 94 systems of galaxies (0.0038 < z < 0.09) determine the Fundamental Plane (FP), which, with a scatter of 0.15, is similar in form to the FP of galaxy clusters obtained by Schaeffer et al. (1993) and D’Onofrio et al. (2013) with other methods and for different bands. We show that the FP in the near-infrared region (NIR) for 94 galaxy systems has the form of LK ∝ \(R_e^{0.70 \pm {{0.13}_\sigma }1.34 \pm 0.13}\), whereas in x-rays it has the form of—LX ∝ \(R_e^{1.15 \pm {{0.39}_\sigma }2.56 \pm 0.40}\). The form of the FP for groups and clusters is consistent with the FP for early-type galaxies determined in the same way. The form of the FP for galaxy systems deviates from the shape that one would expect from virial predictions. Adding the mass-to-light ratio as a fourth independent parameter has little effect on this deviation, but decreases the scatter of the FP for a sample of rich galaxy clusters by 12%.  相似文献   

13.
In this paper, we consider the inverse problem of central configurations of n-body problem. For a given \({q=(q_1, q_2, \ldots, q_n)\in ({\bf R}^d)^n}\), let S(q) be the admissible set of masses denoted \({ S(q)=\{ m=(m_1,m_2, \ldots, m_n)| m_i \in {\bf R}^+, q}\) is a central configuration for m}. For a given \({m\in S(q)}\), let S m (q) be the permutational admissible set about m = (m 1, m 2, . . . , m n ) denoted
$S_m(q)=\{m^\prime | m^\prime\in S(q),m^\prime \not=m \, {\rm and} \, m^\prime\,{\rm is\, a\, permutation\, of }\, m \}.$
The main discovery in this paper is the existence of a singular curve \({\bar{\Gamma}_{31}}\) on which S m (q) is a nonempty set for some m in the collinear four-body problem. \({\bar{\Gamma}_{31}}\) is explicitly constructed by a polynomial in two variables. We proved:
  1. (1)
    If \({m\in S(q)}\), then either # S m (q) = 0 or # S m (q) = 1.
     
  2. (2)
    #S m (q) = 1 only in the following cases:
    1. (i)
      If s = t, then S m (q) = {(m 4, m 3, m 2, m 1)}.
       
    2. (ii)
      If \({(s,t)\in \bar{\Gamma}_{31}\setminus \{(\bar{s},\bar{s})\}}\), then either S m (q) = {(m 2, m 4, m 1, m 3)} or S m (q) = {(m 3, m 1, m 4, m 2)}.
       
     
  相似文献   

14.
We have compiled a catalog of 903 candidates for type 1 quasars at redshifts 3 < z < 5.5 selected among the X-ray sources of the “serendipitous” XMM-Newton survey presented in the 3XMMDR4 catalog (the median X-ray flux is ≈5 × 10?15 erg s?1 cm?2 in the 0.5–2 keV energy band) and located at high Galactic latitudes |b| > 20° in Sloan Digital Sky Survey (SDSS) fields with a total area of about 300 deg2. Photometric SDSS data as well infrared 2MASS and WISE data were used to select the objects. We selected the point sources from the photometric SDSS catalog with a magnitude error δ mz′ < 0.2 and a color i′ ? z′ < 0.6 (to first eliminate the M-type stars). For the selected sources, we have calculated the dependences χ2(z) for various spectral templates from the library that we compiled for these purposes using the EAZY software. Based on these data, we have rejected the objects whose spectral energy distributions are better described by the templates of stars at z = 0 and obtained a sample of quasars with photometric redshift estimates 2.75 < z phot < 5.5. The selection completeness of known quasars at z spec > 3 in the investigated fields is shown to be about 80%. The normalized median absolute deviation (Δz = |z spec ? z phot|) is σ Δz /(1+z spec) = 0.07, while the outlier fraction is η = 9% when Δz/(1 + z спек.) > 0.2. The number of objects per unit area in our sample exceeds the number of quasars in the spectroscopic SDSS sample at the same redshifts approximately by a factor of 1.5. The subsequent spectroscopic testing of the redshifts of our selected candidates for quasars at 3 < z < 5.5 will allow the purity of this sample to be estimated more accurately.  相似文献   

15.
We investigate the variation of the fraction of galaxies with suppressed star formation (MK < ?21 . m 5) and early-type galaxies (fracE) of the “red sequence” along the projected radius in six galaxy clusters:Coma (A1656), A1139, and A1314 in the Leo supercluster region (z ≈ 0.037) and A2040, A2052, A2107 in the Hercules supercluster region (z ≈ 0.036). According to SDSS (DR10) data, fracE is the highest in the central regions of galaxy clusters and it is, on the average, equal to 0.62 ± 0.03, whereas in the 2–3R/R200c interval and beyond the Rsp ≈ 0.95 ± 0.04 R200m radius that we inferred from the observed profile fracE is minimal and equal to 0.25 ± 0.02. This value coincides with the estimate fracE = 0.24 ± 0.01 that we inferred for field galaxies located between the Hercules and Leo superclusters at the same redshifts. We show that the fraction of galaxies with suppressed star formation decreases continuously with cluster radius from 0.87 ± 0.02 in central regions down to 0.43 ± 0.03 in the 2–3 R/R200c interval and beyond Rsp, but remains, on the average, higher than 26% than the corresponding fraction for field objects. This decrease is especially conspicuous in the galaxy mass interval log M* [M⊙] = 9.5–10. We found that galaxies with ongoing star formation have average clustercentric distances 1.5–2.5 R/R200c and that their radial-velocity dispersions are higher than those of galaxies with suppressed star formation.  相似文献   

16.
The present paper is devoted to the construction of a catalog of isolated galaxy pairs extracted from the HyperLEDA extragalactic database. The radial velocities of the galaxies in the pairs are in the range [3000, 16000] km s?1. In order to get an unbiased pair catalog as complete as possible, we have limited the absolute magnitude of the galaxies to M ≤ ?18.5. The criteria used to define the isolated galaxy pairs are the following: 1) velocity criterion: radial velocity difference between the pair members ΔV < 500 kms?1; 2) interdistance criterion: projected distance between the members rp < 1 Mpc; 3) reciprocity criterion: each member is the closest galaxy to the other one, which excludes multiplets; 4) isolation criterion: we define a pair as isolated if the ratio ρ = r3/rp of the projected distance of the pair to its closest galaxy (this one having a velocity difference lower than 500 km s?1 with respect to the pair) and the members projected interdistance rp is larger than 2.5.We have searched for these closest galaxies first in HyperLEDA M-limited source catalog, then in the full one.We have managed not to suppress the small number of pairs having close-by but faint dwarf galaxy companions. The galaxy pair catalog lists the value of ρ for each isolated pair. This method allows the user of the catalog to select any isolation level (beyond the chosen limit ρ > 2.5). Our final catalog contains 13 114 galaxy pairs, of which 57% are fairly isolated withρ > 5, and 30% are highly isolated with ρ ≥ 10.  相似文献   

17.
We present the results of multicolor (UBV JHKLM) photometry (2009–2017) and low-resolution spectroscopy (2016–2017) of the semi-regular variable V1427 Aql = HD 179821, a yellow supergiant with gas-dust envelope. The star displays low-amplitude (ΔV<0 . m 2) semi-periodic brightness variations superimposed on a long-term trend. The light curve shape and timescale change from cycle to cycle. There are temperature variations characteristic for pulsations; brightness oscillations with no significant change of color are also observed. The UBV data for the 2009–2011 interval are well reproduced by a superposition of two periodic components with P = 170d and 141d (or P = 217d—the one year alias of P = 141d). The variation became less regular after 2011, the timescale increased and exceeded 250d. Unusual photometric behavior was seen in 2015 when the star brightness increased by 0 . m 25 in the V filter in 130 days and reached the maximum value ever observed in the course of our monitoring since 1990. In 2009–2016 the annual average brightness monotonically increased in V, J, K, whereas it decreased in U and B. The annual average U ? B, B ? V, and J ? K colors grew, the star was getting redder. The cooling and expanding of the star photosphere along with the increasing of luminosity may explain the long-term trend in brightness and colors. Based on our photometric data we suppose that the photosphere temperature decreased by ~400 K in the 2008–2016 interval, the radius increased by ~24%, and the luminosity grew by ~19%. We review the change of annual average photometric data for almost 30 years of observations. Low-resolution spectra in the λ4000?9000 Å wavelength range obtained in 2016–2017 indicate significant changes in the spectrum of V1427 Aql as compared with the 1994–2008 interval, i.e., the Ba II and near-infraredCa II triplet absorptions have gotten stronger while the OI λ7771-4 triplet blend has weakened that points out the decrease of temperature in the region where the absorptions are formed. The evolutionary stage of the star is discussed. We also compare V1427 Aql with post-AGB stars and yellow hypergiants.  相似文献   

18.
We determine the color excesses, photometric distances, ages, astrometric parallaxes and proper motions for 94 open clusters in the northern part of the Milky Way. We estimate the color excesses and photometric distances based on the data from IPHAS photometric survey of the northern Galactic plane using individual total-to-selective extinction ratios Rr = Ar/Er?i for each cluster computed via the color-difference method based on IPHAS r, i, and Hα-band, 2MASS J-, H-, and Ks-band, WISE W1-band, and Pan-STARRS i-, z-, and y-band data. The inferred Rr values vary significantly from cluster to cluster spanning the Rr = 3.1–5.2 interval with a mean and standard deviation equal to 〈Rr〉 = 3.99 and σRr = 0.34, respectively.We identified cluster members using (1) absolute proper motions determined from individual-epoch positions of stars retrieved from IPHAS, 2MASS,URAT1, ALLWISE,UCAC5, and Gaia DR1 catalogs and positions of stars on individual Palomar Sky Survey plates reconstructed based on the data provided in USNO-B1.0 catalog and (2) absolute proper motions provided in Gaia DR2 catalog, and computed the averageGaia DR2 trigonometric parallaxes and propermotions of the clusters. Themean formal error of the inferred astrometric parallaxes of clusters is of about 7 μas, however, a comparison of astrometric and photometric parallaxes of our cluster sample implies that Gaia DR2 parallaxes are, on the average, systematically underestimated by 45 ± 9 μas. This result agrees with estimates obtained by other authors using other objects. At the same time, we find our photometric distance scale to be correct within the quoted errors (the inferred correction factor is equal to unity to within a standard error of 0.025).  相似文献   

19.
The processing of the plates of the Kitab part of the FON project has been completed. In total, 1963 plates were processed. The catalog of equatorial coordinates α, δ, and B-magnitudes for 13 413268 stars and galaxies up to B ≤ 17.5 m for the epoch 1984.97 is compiled. The Epson Expression 10000XL scanner with a 1200 dpi scanning mode and a plate size of 30 × 30 cm or 13000 × 13000 pel was used to digitize astronegatives. Coordinates of stars and galaxies are obtained in the Tycho-2 catalog system and B-magnitudes are obtained in the photovoltaic system. The catalog internal accuracy for all objects is σα,δ = 0.23" and σ B = 0.15 m (for stars in the range B = 5 m …14 m , errors are σα,δ = 0.085" and σ B = 0.054 m ) for equatorial coordinates and stellar B-magnitudes, respectively. Convergence between the calculated and reference positions is σα,δ = 0.042", and convergence between photoelectric B-magnitudes is σ B = 0.16 m . Coordinate errors with respect to the UCAC-4 catalog are σα,δ = 0.26" (9892697 or 73.75% of stars and galaxies were identified).  相似文献   

20.
We have estimated the dark matter content in galaxy pairs and triplets selected from SDSS DR5 by a higher-order Voronoi tesseleration method. Specifically, the median mass-to-light ratios M vir/L are 12 M ⊙/L ⊙ for isolated pairs, 44 M ⊙/L ⊙ for isolated triplets, and 7 (8) M ⊙/L ⊙ for compact pairs (triplets) with a characteristic distance between the galaxies of R < 50 (100) kpc. We show that the less isolated a system, the larger its mass-to-light ratio. This suggests that galaxy groups in a denser environment have a higher velocity dispersion.  相似文献   

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