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1.
Coolingflows, cluster mergers, and the motions of galaxies through cluster gas with supersonic and sonic velocities must lead to large scale motions of the intracluster medium (ICM). A high-resolution numerical simulation of X-ray cluster formation by Norman and Bryan (1999) predicts cluster-wide turbulence with νturb ≈300–600 km s?1 and eddy scales louter ≈100–500 kpc, the larger numbers being characteristic of turbulence near the virial radius, while the smaller numbers pertain to the core. The simulation also predicts the existence of ordered bulk flows in the core with v≈400 km s?1 on scales of several hundred kpc. In this paper, we consider the observability of such fluid motions via the distortions they induce in the CMB via the kinematic SZ effect, as well as via Doppler broadening and shifting of metal lines in the X-ray spectrum. We estimate |ΔT/T|kinematic?6—at or below current limits of detectability. However, we find that an energy resolution of a few eV is sufficient to detect several Doppler shifted components in the 6.7 keV Fe line in the cluster core.  相似文献   

2.
We have measured the interstellar extinction in the region of ultradeep Galactic-field observations by the Chandra telescope (l II, b II) ≈ 0.1–1.42 using photometric data from the 2MASS infrared allsky survey. The angular resolution of our interstellar extinction map is 1′.8. We show that the interstellar extinction has a minimum, A V ～ 3.4, near the center of the Chandra field of view and increases to A V ～ 5.8–6 at the edge of the field of view. In addition, we show that the bulk of the extinction is gained in the Galactic disk and is approximately the same for all bulge stars. Our results will be subsequently used to process the Chandra data and to estimate the properties of the stellar population in this region.  相似文献   

3.
During the GRIF experiment onboard the Mir orbiting station, the sky was monitored with a PX-2 wide-field (～1 sr) scintillation X-ray spectrometer to detect bursts in the photon energy range 10–300 keV. Because of the comprehensive instrumentation, which, apart from the X-ray and gamma-ray instruments, also included charged-particle detectors, the imitations of astrophysical bursts by magnetospheric electron precipitations and strongly ionizing nuclei were effectively filtered out. It was also possible to separate solar and atmospheric events. Several tens of bursts interpreted as being astrophysical were detected in the experiment at sensitivity levels S～10?7 erg cm?2 (for bursts whose spectra were characterized by effective temperatures kT～100 keV) and S～3×10?8 erg cm?2 (for bursts with kT～25 keV). Some of the soft gamma-ray or hard X-ray bursts with kT～10–50 keV were identified with the bursting pulsar GRO J1744-28. Our estimate of the detection rate for cosmological soft gamma-ray or hard X-ray bursts from the entire sky suggests that the distributions of long-duration (>1 s) gamma-ray bursts (GRBs) in characteristic energy kT and duration are inconsistent with the steady-state cosmological model in which the evolution of burst sources is disregarded. Based on GRIF and BATSE/CGRO data, we conclude that most of the GRB sources originate at redshifts 1<z<5.  相似文献   

4.
We measured the radial velocity of the star θ1 Ori D from IUE spectra and used published observations. Based on these data, we determined the period of its radial-velocity variations, P=20.2675±0.0010 days, constructed the phase radial-velocity curve, and solved it by least squares. The spectroscopic orbital elements were found to be the following: the epoch of periastron passage Ep=JD 2430826.6±0.1, the system's center-of-mass velocity /Gg=32.4±1.0 km s?1, K=14.3±1.5 km s?1, Ω=3.3±0.1 rad, e=0.68±0.09, a1 sin i = 3 × 1010 km, and f1 = 0.0025M⊙. Twice the period, P=40.528±0.002 days, is also consistent with the observations.  相似文献   

5.
Based on an analogy between stellar and solar flares, we investigate the ten-second oscillations detected in the U and B bands on the star EV Lac. The emission pulsations are associated with fast magnetoacoustic oscillations in coronal loops. We have estimated the magnetic field, B ≈ 320 G; the temperature, T ≈ 3.7 × 107 K; and the plasma density, n ≈ 1.6 × 1011 cm?3, in the region of energy release. We provide evidence suggesting that the optical emission source is localized at the loop footpoints.  相似文献   

6.
While analyzing the archival data of the INTEGRAL observatory, we detected and localized a cosmic gamma-ray burst recorded on April 28, 2006, by the IBIS/ISGRI and SPI telescopes in their fields of view. Since the burst was not revealed by the INTEGRAL burst alert system (IBAS), information about its coordinates was not distributed in time and no search for its afterglow was conducted. The burst was recorded by the KONUS/WIND and RHES SI satellites. Its 20–200-keV fluence was 2.3 × 10?6 erg cm?2, the peak flux was 3.6 × 10?7 erg cm?2 s?1 (3.9 phot. cm?2 s?1). The burst had a complex multipeaked profile and stood out among typical bursts by an increase in its hardness with time. At the flux peak, the spectrum was characterized by a photon index α ? ?1.5 and a peak energy E p ? 95 keV. The burst lasted for ～12 s, after which its afterglow decaying as a power law with an index γ ～ ?4.5 was observed at energies 15–45 keV. The spectral hardness decreased noticeably during the afterglow.  相似文献   

7.
We analyze in detail the ASCA observations of the hard X-ray source IGR J16318-4848, which was recently discovered by the INTEGRAL observatory (Courvoisier et al. 2003). The source has an anomalously hard spectrum in the energy range 0.5–10 keV and is virtually undetectable below 4 keV because of strong photoabsorption (n H L>4×1023 cm?2). The Kα line of neutral or weakly ionized iron with an equivalent width of ～2.5 keV dominates in the energy range 4–10 keV. There is also evidence for the presence of a second line at energy ～7 keV. Our analysis of archival observational data for the infrared counterpart of IGR J16318-4848 that was discovered by Foschini et al. (2003) revealed the source in the wavelength range 1–15 µm. Available data suggest that the object can be an X-ray binary system surrounded by a dense envelope. The source may be a high-mass X-ray binary similar to GX 301-2. We believe that IGR J16318-4848 can be the first representative of a hitherto unknown population of strongly absorbed Galactic X-ray sources that could not be detected by previous X-ray observatories.  相似文献   

8.
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   

9.
We have analyzed the Hubble Space Telescope spectrum of the young star FU Ori in the range 2300–3100 Å. The long-wavelength part of the spectrum is similar to the spectrum of a supergiant with T eff ? 5000–6000 K, but the range of wavelengths shorter than ?2600 Å is dominated by radiation from a region with T eff ? 9000 K. We discuss the possibility of explaining these peculiarities of the spectrum, the Al II] 2669.2 emission line profile, and the results of X-ray observations for FU Ori in terms of an accretion disk model whose thickness increases as the star is approached starting from distances ?1012 cm. Near the star, the disk has the shape of a cone in which only the part of its surface on the far (from the observer) side is visible. The suggested model is a kind of a compromise between the models of a thin α-disk and a supergiant: basically, this is an accretion model, but it resembles a supergiant in observational manifestations. Numerous absorption lines originating in the disk wind are superimposed on the disk spectrum. The wind is a cold (T ? 5000 K), dense (N e ? 1011 cm?3) gas. The number of wind absorption lines in the ultraviolet spectrum of FU Ori increases with decreasing wavelength. This causes a rapid decline in intensity in the short-wavelength part of the spectrum. As a result, the maximum temperature in the disk estimated from low-resolution IUE spectra has been underestimated.  相似文献   

10.
We present the JHKLM photometry for five close (W Ser) binary systems obtained in the period 1996–2004. Positive phase shifts (with respect of the adopted ephemerides) have been found in the orbital infrared light curves for three binaries, RX Cas, KX And, and β Lyr; the rates of increase in their periods are ～3.5 × 10?4, ～1.6 × 10?3, and ～1.4 × 10?4 days yr?1, respectively. We have performed the spectral classification of the components of the binaries under study and estimated their parameters.  相似文献   

11.
We present the results of our hydrodynamic calculations of radial pulsations in helium stars with masses 1 M⊙ ≤ M ≤ 10 M⊙, luminosity-to-mass ratios 1 × 103L⊙/M⊙ ≤ L/M ≤ 2 × 104L⊙/M⊙, and effective temperatures 2 × 104 K ≤ Teff ≤ 105 K for mass fractions of helium Y=0.98 and heavy elements Z=0.02. We show that the lower boundary of the pulsation-instability region corresponds to L/M ～ 103L⊙/M⊙ and that the instability region for L/M ? 5 × 103L⊙/M⊙ is bounded by effective temperatures Teff ? 3 × 104 K. As the luminosity rises, the instability boundary moves into the left part of the Hertzsprung-Russell diagram and radial pulsations can arise in stars with effective temperatures Teff ? 105 K at L/M ? 7 × 103L⊙/M⊙. The velocity amplitude for the outer boundary of the hydrodynamic model increases with L/M and lies within the range 200 ? ΔU ? 700 km s?1 for the models under consideration. The periodic shock waves that accompany radial pulsations cause a significant change of the gas-density distribution in the stellar atmosphere, which is described by a dynamic scale height comparable to the stellar radius. The dynamic instability boundary that corresponds to the separation of the outer stellar atmospheric layers at a superparabolic velocity is roughly determined by a luminosity-to-mass ratio L/M ～ 3 × 104L⊙/M⊙.  相似文献   

12.
We have performed hydrodynamic calculations of the radial pulsations of helium stars with masses 10M⊙ ≤ M ≤ 50M⊙, luminosity-to-mass ratios 5 × 103L⊙/M⊙ ≤ L/M ≤ 2.5 × 104L⊙/M⊙, and effective temperatures 2 × 104 K ≤ Teff ≤ 105 K for helium and heavy-element mass fractions of Y=0.98 and Z=0.02, respectively. We show that the high-temperature boundary of the instability region for radial pulsations at L/M ? 104L⊙/M⊙ extends to Teff≈105 K. The amplitude of the velocity variations for outer layers is several hundred km s?1, while the brightness variations in the B band of the UBV photometric system are within the range from several hundredths to half a magnitude. At constant luminosity-to-mass ratio, the radial pulsation period is determined only by the effective temperature of the star. In the ranges of luminosity-to-mass ratios 104L⊙/M⊙ ≤ L/M ≤ 2 × 104L⊙/M⊙ and effective temperatures 5 × 104 K ≤ Teff ≤ 9 × 104 K, the periods of the radial modes are within 6 min ?Π?103 min.  相似文献   

13.
We obtained constraints on the luminosity of the central source in SNR 1987 A using XMM-Newton and INTEGRAL data. XMM-Newton yields an upper limit on the SNR luminosity in the 2–10 keV energy band, LX ? 5 × 1034 erg s?1. Since the optical depth of the envelope is still large in the XMM-Newton energy band, this constraint carries no useful information about the luminosity of the central source. The optical depth is expected to be small in the hard (20–200 keV) X-ray band of the IBIS telescope aboard the INTEGRAL observatory. We detected no statistically significant emission from SNR 1987 A in the INTEGRAL data and obtained an upper limit of LX ? 1.1 × 1036 erg s?1 on the luminosity of the central source in the 20–60 keV band. We also obtained an upper limit on the mass of radioactive 44Ti, M(44Ti) ? 10?3M⊙.  相似文献   

14.
We systematically investigate the evolution of low-mass (0.35, 0.40, and 0.65M ⊙) helium donors in semidetached binaries with white-dwarf accretors. The initial periods of the binaries are chosen in such a way that the helium abundance in the center of the models at the time of Roche lobe overflow varies between Y c = 0.98 and Y c ? 0.1. The results of our calculations can be used to analyze the formation scenarios and evolutionary status of AM CVn stars. We show that the minimum orbital periods of the semidetached binaries depend weakly on the total mass of the components and the evolutionary phase of the donor at the time of Roche lobe overflow and are 9–10 min. The differences in the mass transfer rates after P orb reaches its minimum in the range P orb ≈ 10–40 min do not exceed a factor of ～2.5. For P orb ? 20 min, the mass-losing stars are weakly degenerate homogeneous cooling objects; the He, C, N, O, and Ne abundances depend on the evolutionary phase at which Roche lobe overflow occurred. For the binaries that are currently believed to be the most probable candidates for AM CVn stars with helium donors, Y ? 0.4, X C ? 0.3, X O ? 0.25, and X N ? 0.5 × 10?2. In the binaries under consideration, once P orb ≈ 40 min has been reached, the mass loss time scale begins to exceed the thermal time scale of the donors, the latter begin to contract, their matter becomes degenerate, and the populations of AMCVn stars with white-dwarf and helium-star progenitors of their donors probably merge together.  相似文献   

15.
We present the results of solving the radiative transfer equation for the Stokes vector in the case of light scattering by spherical forsterite dust particles in an axisymmetric circumstellar envelope of a red giant. We have assumed that the surfaces of constant scattering-particle density are prolate or oblate spheroids, the particle density decreases with radius as N d ∝ r −2, and the dust particles at the inner boundary of the envelope are in thermal equilibrium with the stellar emission at solid-phase evaporation temperature T ev = 800 K. In the wavelength range 0.27 μm ≤ λ ≤ 1 μm, particles with radii 0.03 μm ≲ a ≲ 0.2 μm make a major contribution to the linear polarization of the stellar emission. The increase in scattering efficiency factor with decreasing wavelength λ is mainly responsible for the growth of polarization toward the short wavelengths known from observations. However, at a mean number of scatterings 1.2 ≤ N sca ≤ 1.6, the polarization ceases to grow due to depolarization effects and decreases rapidly as the wavelength decreases further. The wavelength of the polarization maximum is determined mainly by two quantities: the particle radius and the mass loss rate. The upper limits for the degree of linear polarization in the case of light scattering in circumstellar dust envelopes with the geometries of prolate and oblate spheroids are p ≈ 3 and 5%, respectively. The polarization for light scattering by enstatite particles is higher than that for light scattering by forsterite particles approximately by 0.3%. Original Russian Text ? Yu.A. Fadeyev, 2007, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2007, Vol. 33, No. 2, pp. 123–133.  相似文献   

16.
We have analysed 64 flares observed with GOES and RHESSI in the 3.1?–?24.8 keV band (0.5?–?4 Å). Flares were randomly chosen to represent different GOES classes, between B1 and M6. RHESSI was used to image the flaring region on the surface of the Sun. We derived the spatial area of the flare on the surface of the Sun from the imaging observations, scaled it dimensionally to volume, and used the spectroscopically derived emission measure to obtain several flare parameters. We experimented with several imaging methods and selected the use of 50% maximum image photon flux contours to define the flare area (F 50%). Most of the flares showed a single spherical loop-top source. The volume measurement for V, temperature T, and electron density N produced power indices that showed no correlation within the boundaries of error. Larger flares by loop-top source volume are thus neither hotter nor denser. The background-subtracted GOES flux?–?RHESSI Total Emission Measure (TEM RHESSI) and TEM GOES?–?TEM RHESSI dependencies were in agreement with the instrument characteristics and earlier studies. Nonthermal flux was noticed to increase with thermal energy and TEM, which can be said to agree with the “Big Flare Syndrome,” with nonthermal photon flux being considered as one flare manifestation.  相似文献   

17.
Highly accurate W BV R photometric measurements of the eclipsing binary HP Aur were performed in 2002–2003 with the 48-cm AZT-14 reflector at the Tien-Shan High-Altitude Observatory to determine the rate of apsidal motion. A consistent system of physical and geometrical parameters of the components and the binary as a whole has been constructed for the first time by analyzing these new measurements together with other published data: we determined their radii (R1 = 1.05R⊙, R2 = 0.82R⊙) and luminosities (L1 = 1.10L⊙, L2 = 0.46L⊙), spectral types (G2V + G8V) and surface gravities (log g1 = 4.38, log g2 = 4.51), age (t = 9.5 × 109 yr), and the distance to the binary (d = 197 pc). We detected an ultraviolet excess in the spectra of both components, \(\Delta (W - B) \simeq - 0\mathop .\limits^m 25\), that is probably attributable to a metal deficiency in the atmospheres of these stars. In this system of two solar-type stars, we found a third body with the mass M3 sin i 3 3 = 0.17M⊙ that revolved with the period P3 = 13.7 yr around the eclipsing binary in a highly eccentric elliptical orbit: e3 = 0.70 and A3 sin i3 ? 7 AU. The orbit of the eclipsing binary itself was shown to be also elliptical, but with a low eccentricity (e = 0.0025(5)), while apsidal motion with a period Uobs > 80 yr was observed at a theoretically expected period Uth ≈ 92 yr. At least 20 to 30 more years of photoelectric measurements of this star will be required to reliably determine Uobs.  相似文献   

18.
We analyzed the chemical composition of the chemically peculiar (CP) star HD 0221=43 Cas using spectra taken with the NES spectrograph of the 6-m telescope with a spectral resolution of 45 000. The Hβ line profile corresponds most closely to Teff = 11 900 K and log g = 3.9. The rotational velocity is ve sin i = 27 ± 2 km s?1, and the microturbulence is ξt = 1 km s?1. The results of our abundance determination by the method of synthetic spectra show that the star has chemical anomalies typical of SrCrEu stars, although its effective magnetic field is weak, Be < 100 G. For silicon, we obtained an abundance distribution in atmospheric depth with a sharp jump of 1.5 dex at an optical depth of log τ5000 = ?0.3 and with silicon concentration in deep atmospheric layers. Similar distributions were found in the atmospheres of cooler stars with strong and weak magnetic fields. A comparison of the chemical peculiarities in HD 10221 with known CP stars with magnetic fields of various strengths leads us to conclude that a low rotational velocity rather than amagnetic field is the determining factor in the formation mechanism of chemical anomalies in the atmospheres of CP stars.  相似文献   

19.
We present our long-term photometric and spectroscopic observations of a high-latitude B supergiant with an infrared excess—the protoplanetary nebula IRAS 18062+2410. OurU BV observations in 2000–2006 have confirmed the rapid irregular photometric variability of the star with a maximum amplitude as high as 0 . m 4 in V that we found previously. The B—V and U—B color indices vary with amplitudes as high as 0 . m 10 and 0 . m 25, respectively, and show no clear correlation with the brightness. Our V-band CCD observations on 11 nights in 2006 have revealed brightness trends during the night. The variability of IRAS18062+2410 is similar in pattern to the light variations in other hot post-AGB objects and some of the nuclei of young planetary nebulae. We assume that pulsations and a variable stellar wind can be responsible for the variability of these stars. In addition to the rapid variability, our 12-year-long observations have revealed a systematic decline in the mean brightness of IRAS 18062+2410. This may be related to a rise in the temperature of the star at constant luminosity as a result of its evolution. Low-resolution spectroscopic observations have shown a systematic increase in the equivalent widths of the Hα, Hβ, [NII]λ6584 Å, OI λ8446 Å, and [OII] λ7320–7330 Å emission lines. The changes in the star’s emission line spectrum are probably caused by an increase in the degree of ionization of the gas shell due to a rise in the temperature of the ionizing star. Our photometric and spectroscopic observations of IRAS 18062+2410 confirm the previously made assumptions that the star evolves very rapidly to the region of planetary nebulae.  相似文献   

20.
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   

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