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1.
We present the photoionisation modelling of the intrinsic absorber in the bright quasar HS 1603 + 3820. We constructed the broad-band spectral energy distribution using the optical/UV/X-ray observations from different instruments as inputs for the photoionisation calculations. The spectra from the Keck telescope show extremely high Civ to Hi ratios, for the first absorber in system A, named A1. This value, together with high column density of Civ ion, place strong constraints on the photoionisation model. We used two photoionisation codes to derive the hydrogen number density at the cloud illuminated surface. By estimating bolometric luminosity of HS 1603 + 3820 using the typical formula for quasars, we calculated the distance to A1. We could find one photoionization solution, by assuming either a constant density cloud (which was modelled using cloudy), or a stratified cloud (which was modelled using titan), as well as the solar abundances. This model explained both the ionic column density of Civ and the high Civ to Hi ratio. The location of A1 is 0.1 pc, and it is situated even closer to the nucleus than the possible location of the Broad Line Region in this object. The upper limit of the distance is sensitive to the adopted covering factor and the carbon abundance. Photoionisation modelling always prefers dense clouds with the number density n0 = 1010 − 1012 cm−3, which explains intrinsic absorption in HS 1603 + 3820. This number density is of the same order as that in the disk atmosphere at the implied distance of A1. Therefore, our results show that the disk wind that escapes from the outermost accretion disk atmosphere can build up dense absorber in quasars.  相似文献   

2.
Among evolved massive stars likely in transition to the Wolf–Rayet phase, IRC + 10420 is probably one of the most enigmatic. It belongs to the category of yellow hypergiants and it is characterized by quite high mass loss episodes. Even though IRC + 10420 benefited of many observations in several wavelength domains, it has never been a target for an X-ray observatory. We report here on the very first dedicated observation of IRC + 10420 in X-rays, using the XMM-Newton satellite. Even though the target is not detected, we derive X-ray flux upper limits of the order of 1–3 × 10−14 erg cm−2 s−1 (between 0.3 and 10.0 keV), and we discuss the case of IRC + 10420 in the framework of emission models likely to be adequate for such an object. Using the Optical/UV Monitor on board XMM-Newton, we present the very first upper limits of the flux density of IRC + 10420 in the UV domain (between 1800 and 2250 Å and between 2050 and 2450 Å). Finally, we also report on the detection in this field of 10 X-ray and 7 UV point sources, and we briefly discuss their properties and potential counterparts at longer wavelengths.  相似文献   

3.
Here we report the serendipitous identification of a bright optical transient in the vicinity of the dwarf elliptical galaxy M 32 (NGC 221). This transient (MONS OT J004240.69+405142.0) was detected using filtered CCD imaging, about 20 arcsec southwest from the core of M 32, at equatorial coordinates α = 00:42:40.69 ± 0.05, δ = +40:51:42.0 ± 0.5, between 04:20:16 and 04:21:46 UT on June 22, 2007. A detailed analysis of the intensity profile of the feature suggests that it is of stellar nature with apparent visual magnitude 9.69 ± 0.15 which gives an absolute magnitude of ?14.7 ± 0.3 if the feature is located in M 31/M 32. Under the assumption of the event reported here being of cosmic origin and although no correlation with GRBs in time or space has been found, the behaviour of the optical transient appears to resemble that of the recently observed GRB 080319B: very fast ascent and decay of several magnitudes within a few minutes. If this interpretation is correct, the afterglow decay was extremely rapid, decreasing by more than 5 mag. in about 2 min, α = 2.4. Given its properties, the event is a possible orphan GRB optical afterglow candidate originated beyond the Local Group. Alternative explanations are also discussed.  相似文献   

4.
We report results of the observations at the Vainu Bappu Observatory and the Uttar Pradesh State Observatory of eight radio-quiet quasi-stellar objects (RQQSOs) during 1996–99. This is a part of our ongoing programme to search for intranight optical variability in RQQSOs. Additional evidence for very rapid variability in three of the five optically bright and very luminous RQQSOs we had observed earlier, 1049−006, 1444+408 and 1630+377, was found. Of the three newly observed RQQSOs, the data for 0043+039 are too noisy to allow conclusions about variability to be drawn, but 0748+294 and 0824+098 show strong hints of microvariability. We also present a summary of the results from our entire programme to date, which includes observations of 16 radio-quiet QSOs and one radio-weak QSO, and compare the general properties of rapid variability in radio-quiet versus radio-loud AGN as determined from our work and that of several other groups. Observations of this kind are likely to play a key role in understanding the relative contributions of accretion discs and relativistic plasma jets to rapid optical fluctuations of AGN.  相似文献   

5.
We present the two-dimensional distribution of the O2 a1Δ–X3Σ (0–0) band at 1.27 μm and the OH Δv = 1 Meinel airglow measured simultaneously with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board Venus Express. We show that the two emissions present very similar spatial structures. A cross-correlation analysis indicates that the highest level of correlation is reached with only very small relative shifts of the pairs of images. In spite of the strong spatial correlation between the morphology of the bright spots in the two emissions, we also show that their relative intensity is not constant, in agreement with earlier statistical studies of their limb profiles. We conclude that the two emissions have a common precursor that controls the production of both excited species. We argue that atomic oxygen, which produces O2 (1Δ) molecules by three-body recombination and is the precursor of ozone formation, also governs to a large extent the OH airglow morphology through the H + O3 → OH* + O2 reaction.  相似文献   

6.
Building upon previous studies, we re-investigated the ethane spectrum between 1330 and 1610 cm?1 by combining unapodized spectra obtained at room temperature with a Bruker Fourier transform spectrometer (FTS) in Brussels and at 131 K with a Bruker FTS in Pasadena. The maximum optical path differences (MOPD) of the two datasets were 450 and 323.7 cm, corresponding to spectral resolutions of 0.0020 and 0.0028 cm?1, respectively. Of the 15,000 lines observed, over 4592 transitions were assigned to the ν6 (at 1379 cm?1), ν8 (at 1472 cm?1), ν4+ν12 (at 1481 cm?1) and 2ν4+ν9 (at 1388 cm?1) bands, and another 1044 transitions were located for the ν4+ν8?ν4 hot band (at 1472 cm?1). Our new analysis included an improved implementation of the Hamiltonian calculation needed to interpret the complex spectral structures caused by numerous interactions affecting these four modes of vibration. From these results, we created the first line-by-line database containing the molecular parameters for over 20,000 12C2H6 transitions at 7 μm.  相似文献   

7.
Kathryn Volk  Renu Malhotra 《Icarus》2012,221(1):106-115
The Haumea family is currently the only identified collisional family in the Kuiper belt. We numerically simulate the long-term dynamical evolution of the family to estimate a lower limit of the family’s age and to assess how the population of the family and its dynamical clustering are preserved over Gyr timescales. We find that the family is not younger than 100 Myr, and its age is at least 1 Gyr with 95% confidence. We find that for initial velocity dispersions of 50–400 m s?1, approximately 20–45% of the family members are lost to close encounters with Neptune after 3.5 Gyr of orbital evolution. We apply these loss rates to two proposed models for the formation of the Haumea family, a graze-and-merge type collision between two similarly sized, differentiated KBOs or the collisional disruption of a satellite orbiting Haumea. For the graze-and-merge collision model, we calculate that >85% of the expected mass in surviving family members within 150 m s?1 of the collision has been identified, but that one to two times the mass of the known family members remains to be identified at larger velocities. For the satellite-break-up model, we estimate that the currently identified family members account for ～50% of the expected mass of the family. Taking observational incompleteness into account, the observed number of Haumea family members is consistent with either formation scenario at the 1σ level, however both models predict more objects at larger relative velocities (>150 m s?1) than have been identified.  相似文献   

8.
Based on the latest release of the SGP4/SDP4 (Simplified General Perturbation Version 4/ Simplified Deep-space Perturbation Version 4) model, in this paper we have designed an orbit determination program. Through calculations for the 1120 objects with various types and orbital elements selected from the space objects database, we have obtained the accuracies of the orbit determination prediction dealt with various types of space objects by the SGP4/SDP4 model. The results show that the accuracies of the near-earth objects are in the order of magnitude of 100 meters; the averages of the orbit determination accuracies of the semi-synchronous and geosynchronous orbits are, respectively, 0.7 and 1.9 km. The orbit determination accuracies of the elliptical orbit objects are related to their eccentricities. Except for few elliptical orbit objects with e > 0.8, the orbit determination errors of the vast majority of the elliptical orbit objects are all less than 10 km. By using the SGP4/SDP4 model to make 3 days predictions for near-earth objects, 30 days for semi-synchronous orbit objects, 15 days for geosynchronous orbit objects and 1 day for elliptical orbit objects, the errors of prediction generally don’t exceed 40 km.  相似文献   

9.
The EGRET observations have confirmed and proposed the new isotropically distributed γ-ray background, but the known objects radiating γ-rays can not supply so much radiation. Meanwhile, EGRET also reveals a population of γ-ray sources with no radio counterparts which are isotropically distributed in the sky, indicating their possible cosmological origins. Wang et al.[13] proposed a new γ-ray radiation process driven by the radiation feedback of AGNs. The energy of the radiation peaks around 1 GeV—0.1 TeV with the typical luminosity of 1042—1043 ergs · s?1. This kind of radiation process in the radio quiet quasars make them the potential γ-ray radiation sources as well as the contributors to the γ-ray background. We consider two cases in which the seed photons in the inverse-Compton processes are from the accretion disks of quasars and cosmic microwave background (CMB), respectively. We find that the former contributes 78%—92% of the background radiation around 1 GeV, while the contribution from the latter is negligible. The radio quiet quasars are highly likely to become the objects which contribute the most energy to the γ-ray background around 1 GeV.  相似文献   

10.
Observations of Venus using the ultraviolet filter of the Venus Monitoring Camera (VMC) on ESA’s Venus Express Spacecraft (VEX) provide the best opportunity for study of the spatial and temporal distribution of the venusian unknown ultraviolet absorber since the Pioneer Venus (PV) mission. We compare the results of two sets of 125 radiative transfer models of the upper atmosphere of Venus to each pixel in a subset of VMC UV channel images. We use a quantitative best fit criterion based upon the notion that the distribution of the unknown absorber should be independent of the illumination and observing geometry. We use the product of the cosines of the incidence and emission angles and search for absorber distributions that are uncorrelated with this geometric parameter, finding that two models can describe the vertical distribution of the unknown absorber. One model is a well-mixed vertical profile above a pressure level of roughly 120 mb (～63 km). This is consistent with the altitude of photochemical formation of sulfuric acid. The second model describes it as a thin layer of pure UV absorber at a pressure level roughly around 24 mb (～71 km) and this altitude is consistent with the top of upper cloud deck. We find that the average abundance of unknown absorber in the equatorial region is 0.21 ± 0.04 optical depth and it decreases in the polar region to 0.08 ± 0.05 optical depth at 365 nm.  相似文献   

11.
We suggest that planets, brown dwarfs, and even low mass stars can be formed by fragmentation of protoplanetary disks around very massive stars (M ? 100 M⊙). We discuss how fragmentation conditions make the formation of very massive planetary systems around very massive stars favorable. Such planetary systems are likely to be composed of brown dwarfs and low mass stars of ～0.1–0.3 M⊙, at orbital separations of ～ few × 100–104 AU. In particular, scaling from solar-like stars suggests that hundreds of Mercury-like planets might orbit very massive stars at ～103 AU where conditions might favor liquid water. Such fragmentation objects can be excellent targets for the James Webb Space Telescope and other large telescopes working in the IR bands. We predict that deep observations of very massive stars would reveal these fragmentation objects, orbiting in the same orbital plane in cases where there are more than one object.  相似文献   

12.
Determining the optical constants of Titan aerosol analogues, or tholins, has been a major concern for the last three decades because they are essential to constrain the numerical models used to analyze Titan’s observational data (albedo, radiative transfer, haze vertical profile, surface contribution, etc.). Here we present the optical constant characterization of tholins produced with an RF plasma discharge in a (95%N2–5%CH4) gas mixture simulating Titan’s main atmospheric composition, and deposited as a thin film on an Al–SiO2 substrate. The real and imaginary parts, n and k, of the tholin complex refractive index have been determined from 370 nm to 900 nm wavelength using spectroscopic ellipsometry. The values of n decrease from n = 1.64 (at 370 nm) to n = 1.57 (at 900 nm) as well as the values of k which feature two behaviors: an exponential decay from 370 nm to 500 nm, with k = 12.4 × e?0.018λ (where λ is expressed in nm), followed by a plateau, with k = (1.8 ± 0.2) × 10?3. The trends observed for the PAMPRE tholins optical constants are compared to those determined for other Titan tholins, as well as to the optical constants of Titan’s aerosols retrieved from observational data.  相似文献   

13.
P. Abolmasov 《New Astronomy》2011,16(7):421-429
Using the archives of the American Association of Variable Stars Observers and our own data, we analyse the long-term variability of several well-studied luminous blue variables (LBVs) aiming on a general picture of stochastic variability of these objects. The power density spectra of all the selected objects may be generally described by a single power law contaminated by observational noise at higher frequencies. The slopes of the power-law component are close to p = 2 (where PDS ∝ f?p, and f is frequency) for strongly variable flaring objects like AG Car and significantly smaller (p ～ 1.3) for P Cyg where brightness variation amplitude is ? 1m and dominated by slow low-amplitude variability. The slope holds for about two orders of magnitude in the frequency domain, though peaks and curvatures are present at f ? 10?2–10?3 d?1. We show that pseudo-photosphere approach to variability may explain the power-law shape of the variability spectrum at higher frequencies. However, the observed spectra are actually rather “red” than “brown”: flux variations are correlated up to tens of years that is much longer than the characteristic refreshment time scales of the pseudo-photosphere. We propose that several stochastic noise components produce the power spectra of LBVs.  相似文献   

14.
《Astroparticle Physics》2006,24(6):537-542
The AMANDA neutrino telescope has recently reported the detection of high-energy neutrinos spatially and temporally coincident with the flaring of the TeV blazar 1ES 1959 + 650. If high-energy neutrinos are in fact generated by this blazar, it would be the first strong evidence for the hadronic acceleration of cosmic rays. At present, the statistical significance of this observation cannot be reliably assessed, however. In this letter, we investigate whether circumstances exist where the source can produce the flux implied by the coincident events. We show that if the TeV gamma-ray emission observed from 1ES 1959 + 650 or other nearby TeV blazars is the result of accelerated protons interacting with nucleons, it is reasonable that AMANDA could detect several events during a flaring period. Such rates require that the spectral index of the source be rather high (for instance ∼2.8 for 1ES 1959 + 650) and that the Lorentz factor of the jet be fairly small (Γ ∼ 1).  相似文献   

15.
《New Astronomy》2007,12(7):556-561
The results of a long-term UBV photometric monitoring of the red supergiant (RSG) star V424 Lac are presented. V424 Lac shows multiperiodic brightness variations which can be attributed to pulsational oscillations. A much longer period (P = 1601 d), that allows us to classify this star as a long secondary period variable star (LSPV) has been also detected. The B − V and U − B color variations related to the long secondary period (LSP) are similar to those related to the shorter periods, supporting the pulsational nature of LSP. The long period brightness variation of V424 Lac is accompanied by a near-UV (NUV) excess, which was spectroscopically detected in a previous study [Massey, P., Plez, B., Levesque, E.M., et al., 2005. ApJ 634, 1286] and which is now found to be variable from photometry. On the basis of the results found for V424 Lac, the NUV excess recently found in a number of RSGs may be due not solely to circumstellar dust but may also have a contribution from a still undetected LSP variability.  相似文献   

16.
We present the 2005–2010 outburst history of the SU UMa-type dwarf HS 0417+7445, along with a detailed analysis of extensive time-series photometry obtained in March 2008 during the second recorded superoutburst of the system. The mean outburst interval is 197 ± 59 d, with a median of 193 d. The March 2008 superoutburst was preceded by a precursor outburst, had an amplitude of 4.2 magnitudes, and the whole event lasted about 16 days. No superhumps were detected during the decline from the precursor outburst, and our data suggests instead that orbital humps were present during that phase. Early superhumps detected during the rise to the superoutburst maximum exhibited an unusually large fractional period excess of ? = 0.137 (Psh = 0.0856(88) d). Following the maximum, a linear decline in brightness followed, lasting at least 6 days. During this decline, a stable superhump period of Psh = 0.07824(2) d was measured. Superimposed on the superhumps were orbital humps, which allowed us to accurately measure the orbital period of HS 0417+7445, Porb = 0.07531(8) d, which was previously only poorly estimated. The fractional superhump period excess during the main phase of the outburst was ? = 0.037, which is typical for SU UMa dwarf novae with similar orbital period. Our observations are consistent with the predictions of the thermal-tidal instability model for the onset of superoutbursts, but a larger number of superoutbursts with extensive time-series photometry during the early phases of the outburst would be needed to reach a definite conclusion on the cause of superoutbursts.  相似文献   

17.
《New Astronomy》2007,12(2):146-160
We point out that although conventional stars are primarily fed by burning of nuclear fuel at their cores, in a strict sense, the process of release of stored gravitational energy, known as, Kelvin–Helmholtz (KH) process is either also operational albeit at an arbitrary slow rate, or lying in wait to take over at the disruption of the nuclear channel. In fact, the latter mode of energy release is the true feature of any self-gravity bound object including stars. We also highlight the almost forgotten fact that Eddington was the first physicist to introduce special relativity into the problem and correctly insist that, actually, total energy stored in a star is not the mere Newtonian energy but the total mass energy (E = Mc2). Accordingly, Eddington defined an “Einstein time scale” of Evolution where the maximum age of the Sun turned out to be tE ≈ 1.4 × 1013 yr. This concept has a fundamental importance though we know now that Sun in its present form cannot survive for more than 10 billion years. We extend this concept by introducing general relativity and show that the minimum value of depletion of total mass–energy is tE = ∞ not only for Sun but for and sufficiently massive or dense object. We propose that this time scale be known in the name of “Einstein–Eddington”. We also point out that, recently, it has been shown that as massive stars undergo continued collapse to become a Black Hole, first they become extremely relativistic radiation pressure supported stars. And the life time of such relativistic radiation pressure supported compact stars is indeed dictated by this Einstein–Eddington time scale whose concept is formally developed here. Since this observed time scale of this radiation pressure supported quasistatic state turns out to be infinite, such objects are called eternally collapsing objects (ECO). Further since ECOs are expected to have strong intrinsic magnetic field, they are also known as “Magnetospheric ECO” or MECO.  相似文献   

18.
We present the ensemble properties of 31 comets (27 resolved and 4 unresolved) observed by the Sloan Digital Sky Survey (SDSS). This sample of comets represents about 1 comet per 10 million SDSS photometric objects. Five-band (u, g, r, i, z) photometry is used to determine the comets’ colors, sizes, surface brightness profiles, and rates of dust production in terms of the Afρ formalism. We find that the cumulative luminosity function for the Jupiter Family Comets in our sample is well fit by a power law of the form N(<H) ∝ 10(0.49±0.05)H for H < 18, with evidence of a much shallower fit N(<H) ∝ 10(0.19±0.03)H for the faint (14.5 < H < 18) comets. The resolved comets show an extremely narrow distribution of colors (0.57 ± 0.05 in g ? r for example), which are statistically indistinguishable from that of the Jupiter Trojans. Further, there is no evidence of correlation between color and physical, dynamical, or observational parameters for the observed comets.  相似文献   

19.
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20.
《Planetary and Space Science》2007,55(11):1541-1556
The exosphere of Mercury has been the object of many investigations and speculations regarding its composition, formation, depletion and dynamics. While vapourization of Mercurian surface materials by meteorite impacts has been often considered to be a less important contributor to the exosphere than other potential processes, larger objects coming from the Main Asteroid Belt could cause high local and transient enhancements in the density of the exosphere. Vapourization by such impacts is an almost stoichiometric process, and thus would contain valuable information about the surface composition. We investigate some exospheric effects of impact vapourization for meteorites with radii of 1, 10 cm, and 1 m, with particular reference to the missions that will explore Mercury during the next decade (MESSENGER and BepiColombo). Because of their higher probabilities, impacts of objects in the two smaller size ranges will surely occur during the lifetimes of the two missions. The enhancement of the exospheric density on the dayside of Mercury would be appreciable for the 10-cm and 1-m meteorites (some orders of magnitude, especially for Al, Mg, Si, and Ca). Such events could allow detection, for the first time, of refractory species like Al, Mg, and Si, which are expected to exist on the surface but have not yet been detected in the exosphere. Ca could be detectable in all cases, even if produced by impacting objects as small as 1 cm in radius. The lower exospheric background on the night side should allow easier identification of Na and K produced by impulsive events, even if their generally high background values make this eventuality less likely.  相似文献   

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