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1.
We have used the Ultra-High-Resolution Facility (UHRF) at the AAT, operating at a resolution of 0.35 km s−1 (FWHM), to observe K  i and C2 absorption lines arising in the circumstellar environment of the post-AGB star HD 56126. We find three narrow circumstellar absorption components in K  i , two of which are also present in C2. We attribute this velocity structure to discrete shells resulting from multiple mass-loss events from the star. The very high spectral resolution has enabled us to resolve the intrinsic linewidths of these narrow lines for the first time, and we obtain velocity dispersions ( b -values) of 0.2–0.3 km s−1 for the K  i components, and 0.54±0.03 km s−1 for the strongest (and best defined) C2 component. These correspond to rigorous kinetic temperature upper limits of 211 K for K  i and 420 K for C2, although the b -value ratio implies that these two species do not co-exist spatially. The observed degree of rotational excitation of C2 implies low kinetic temperatures ( T k≈10 K) and high densities ( n ≈106 to 107 cm−3) within the shell responsible for the main C2 component. Given this low temperature, the line profiles then imply either mildly supersonic turbulence or an unresolved velocity gradient through the shell.  相似文献   

2.
We report new calculations of the cooling rate of primordial gas by the HD molecule, taking into account its ro-vibrational structure. The HD cooling function is calculated including radiative and collisional transitions for   J ≤ 8  rotational levels, and for the vibrational levels v = 0, 1, 2 and 3. The ro-vibrational level population is calculated from the balance equation assuming steady state. The cooling function is evaluated in the ranges of the kinetic temperatures, T k, from 102 to  2 × 104 K  and the number densities, n H, from 1 to  108 cm−3  . We find that the inclusion of collisional ro-vibrational transitions increases significantly the HD cooling efficiency, in particular for high densities and temperatures. For   n H≳ 105  and   T k∼ 104 K  the cooling function becomes more than an order of magnitude higher than previously reported. We give also the HD cooling rate in the presence of the cosmic microwave radiation field for radiation temperatures of 30, 85 and 276 K (redshifts of 10, 30 and 100). The tabulated cooling functions are available at http://www.cifus.uson.mx/Personal_Pages/anton/DATA/HD_cooling/HD_cool.html . We discuss the relevance to explore the effects of including our results into models and simulations of galaxy formation, especially in the regime when gas cools down from temperatures above ∼3000 K.  相似文献   

3.
Absorption lines of MgH and CaH N  = 1 − 0 transitions were searched for in foreground molecular clouds towards the continuum sources associated with Sgr B2 (M) and W49A (N). None of these lines was detected with our sensitivity level of ∼20 mK. Millimetric absorption lines of MgO, MgOH, CaO and CaOH were also searched for towards Sgr B2 (M) without success. The fractional abundances relative to molecular hydrogen are ≲ 1.0 × 10−11 for MgH, ≲ 7.9 × 10−13 for MgO, ≲ 1.6 × 10−10 for MgOH, ≲ 1.6 × 10−9 for CaH, ≲ 2.0 × 10−12 for CaO, and ≲ 2.5 × 10−10 for CaOH, respectively. The low abundances measured in absorption indicate that a significant fraction of interstellar magnesium and calcium cannot be tied up in their monohydrides, monoxides and monohydroxides. The low abundance of MgH also implies that grain-surface chemistry involving magnesium is not efficient and that magnesium is depleted on to grains to a factor of ≳ 102.5 in well-shielded molecular clouds.  相似文献   

4.
We have detected the   v = 1 → 0 S(1) (λ= 2.1218 μm)  and   v = 2 → 1 S(1) (λ= 2.2477 μm)  lines of H2 in the Galactic Centre, in a  90 × 27 arcsec2  region between the north-eastern boundary of the non-thermal source Sgr A East, and the giant molecular cloud (GMC)  M−0.02 − 0.07  . The detected  H2 v = 1 → 0  S(1) emission has an intensity of  1.6–21 × 10−18 W m−2 arcsec−2  and is present over most of the region. Along with the high intensity, the large linewidths  (FWHM = 40–70 km s−1)  and the  H2 v = 2 → 1 S(1)  to   v = 1 → 0 S(1)  line ratios (0.3–0.5) can be best explained by a combination of C-type shocks and fluorescence. The detection of shocked H2 is clear evidence that Sgr A East is driving material into the surrounding adjacent cool molecular gas. The H2 emission lines have two velocity components at ∼+50 and  ∼0 km s−1  , which are also present in the NH3(3, 3) emission mapped by McGary, Coil & Ho. This two-velocity structure can be explained if Sgr A East is driving C-type shocks into both the  GMC M−0.02 − 0.07  and the northern ridge of McGary et al.  相似文献   

5.
We present a new determination of the local volume-averaged star formation rate from the 1.4-GHz luminosity function of star forming galaxies. Our sample, taken from the   B ≤12  Revised Shapley–Ames catalogue (231 normal spiral galaxies over an effective area of 7.1 sr) has ≃100 per cent complete radio detections and is insensitive to dust obscuration and cirrus contamination. After removal of known active galaxies, the best-fitting Schechter function has a faint-end slope of  −1.27±0.07  in agreement with the local H α luminosity function, characteristic luminosity   L ∗=(2.6±0.7)×1022 W Hz−1  and density   φ ∗=(4.8±1.1)×10−4 Mpc−3.  The inferred local radio luminosity density of  (1.73±0.37±0.03)×1019 W Hz−1 Mpc−3  (Poisson noise, large-scale structure fluctuations) implies a volume-averaged star formation rate ∼2 times larger than the Gallego et al. H α estimate, i.e.   ρ 1.4 GHz=(2.10±0.45±0.04)×10−2 M⊙ yr−1 Mpc−3  for a Salpeter initial mass function from  0.1–125 M⊙  and Hubble constant of 50 km s−1 Mpc−1. We demonstrate that the Balmer decrement is a highly unreliable extinction estimator, and argue that optical–ultraviolet (UV) star formation rates (SFRs) are easily underestimated, particularly at high redshift.  相似文献   

6.
We have detected the Sunyaev–Zel'dovich (SZ) increment at 850 μm in two galaxy clusters (Cl 0016+16 and MS 1054.4−0321) using the Submillimetre Common User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope. Fits to the isothermal β model yield a central Compton y parameter of  (2.2 ± 0.7) × 10−4  and a central 850-μm flux of  Δ I 0= 2.2 ± 0.7 mJy beam−1  in Cl 0016. This can be combined with decrement measurements to infer   y = (2.38 ±0.360.34) × 10−4  and   v pec= 400±19001400 km s−1  . In MS 1054 we find a peak 850-μm flux of  Δ I 0= 2.0 ± 1.0 mJy beam−1  and   y = (2.0 ± 1.0) × 10−4  . To be successful such measurements require large chop throws and non-standard data analysis techniques. In particular, the 450-μm data are used to remove atmospheric variations in the 850-μm data. An explicit annular model is fit to the SCUBA difference data in order to extract the radial profile, and separately fit to the model differences to minimize the effect of correlations induced by our scanning strategy. We have demonstrated that with sufficient care, SCUBA can be used to measure the SZ increment in massive, compact galaxy clusters.  相似文献   

7.
The 'Carina Flare' supershell, GSH 287+04−17, is a molecular supershell originally discovered in  12CO( J = 1–0)  with the NANTEN 4 m telescope. We present the first study of the shell's atomic ISM, using H  i 21-cm line data from the Parkes 64-m telescope Southern Galactic Plane Survey. The data reveal a gently expanding,  ∼230 × 360  pc H  i supershell that shows strong evidence of Galactic Plane blowout, with a break in its main body at   z ∼ 280  pc and a capped high-latitude extension reaching   z ∼ 450  pc. The molecular clouds form comoving parts of the atomic shell, and the morphology of the two phases reflects the supershell's influence on the structure of the ISM. We also report the first discovery of an ionized component of the supershell, in the form of delicate, streamer-like filaments aligned with the proposed direction of blowout. The distance estimate to the shell is re-examined, and we find strong evidence to support the original suggestion that it is located in the Carina Arm at a distance of  2.6 ± 0.4 kpc  . Associated H  i and H2 masses are estimated as   M H I≈ 7 ± 3 × 105 M⊙  and     , and the kinetic energy of the expanding shell as   E K ∼ 1 × 1051  erg. We examine the results of analytical and numerical models to estimate a required formation energy of several 1051 to  ∼1052  erg, and an age of  ∼107 yr  . This age is compatible with molecular cloud formation time-scales, and we briefly consider the viability of a supershell-triggered origin for the molecular component.  相似文献   

8.
We report further UKIRT spectroscopic observations of Sakurai's object (V4334 Sgr) made in 1999 April/May in the 1–4.75 μm range, and find that the emission is dominated by amorphous carbon at T d~600 K. The estimated maximum grain size is 0.6 μm, and the mass lower limit is 1.7±0.2×10−8 M⊙ to 8.9±0.6×10−7 M⊙ for distances of 1.1–8 kpc. For 3.8 kpc the mass is 2.0±0.1×10−7 M⊙.
We also report strong He  i emission at 1.083 μm, in contrast to the strong absorption in this line in 1998. We conclude that the excitation is collisional, and is probably caused by a wind, consistent with the P Cygni profile observed by Eyres et al. in 1998.  相似文献   

9.
High-resolution spectroscopic observations around the Hα line and BVRI photometry of the eclipsing short-period RS CVn star UV Leo are presented. The simultaneous light-curve solution and radial velocity-curve solution led to the following values of the global parameters of the binary: temperatures   T 1= 6000 ± 100 K  and   T 2= 5970 ± 20 K  ; masses   M 1= 0.976 ± 0.067 M⊙  and   M 2= 0.931 ± 0.052 M⊙  ; separation   a = 3.716 ± 0.048 R⊙  ; orbital inclination     ; radii   R 1= 1.115 ± 0.052 R⊙  and   R 2= 1.078 ± 0.051 R⊙  ; equatorial velocities   V 1= 98.8 ± 2.3 km s−1  and   V 2= 89.6 ± 2.7 km s−1  . These results lead to the conclusion that the two components of UV Leo are slightly oversized for their masses and lie within the main-sequence band on the mass–radius diagram, close to the isochrone 9 × 1010 yr.  相似文献   

10.
An analysis of the spatial fluctuations in 15 deep ASCA SIS0 images has been conducted in order to probe the 2–10 keV X-ray source counts down to a flux limit ∼ 2 × 10−14 erg cm−2 s−1. Special care has been taken in modelling the fluctuations in terms of the sensitivity maps of every one of the 16 regions (5.6 × 5.6 arcmin2 each) into which the SIS0 has been divided, by means of ray-tracing simulations with improved optical constants in the X-ray telescope. The very extended 'sidelobes' (extending up to a couple of degrees) exhibited by these sensitivity maps make our analysis sensitive to both faint on-axis sources and brighter off-axis ones, the former being dominant. The source counts in the range (2−12) × 10−14 erg cm−2 s−1 are found to be close to a Euclidean form which extrapolates well to previous results from higher fluxes and are in reasonable agreement with some recent ASCA surveys. However, our results disagree with the deep survey counts by Georgantopoulos et al. The possibility that the source counts flatten to a sub-Euclidean form, as is observed at soft energies in ROSAT data, is only weakly constrained to happen at a flux < 1.8 × 10−12 erg cm−2 s−1 (90 per cent confidence). Down to the sensitivity limit of our analysis, the integrated contribution of the sources the imprint of which is seen in the fluctuations amounts to ∼ 35 ± 13 per cent of the extragalactic 2–10 keV X-ray background.  相似文献   

11.
We present 13 CO J  = 1 − 0 line observations of the H  ii region complex W51B located in the high-velocity (HV) stream. These observations reveal a filamentary and clumpy structure in the molecular gas. The mean local standard of rest (LSR) velocity ∼ + 65 km s−1 of the molecular gas in this region is greater than the maximum velocities allowed by kinematic Galactic rotation curves. The size and mass of the molecular clouds are ∼ 48 × 17 pc2 and ∼ 2.4 × 105 M⊙ respectively. In a position–velocity diagram, molecular gas in the southern part comprises a redshifted ring structure with v LSR=+ 60 to +73 km s−1. The velocity gradient of this ring is ∼ 0.5 km s−1 pc−1, and the mass is ∼ 6.2 × 104 M⊙. If we assume that the ring is expanding with a uniform velocity, the expansion velocity, radius and kinetic energy are ∼ 7 km s−1, ∼ 13 pc and ∼ 3.0 × 10 49 erg respectively. The kinetic energy and mass spectrum of the ring could be explained by an expanding cylindrical cloud with a centrally condensed mass distribution. The locations of two compact H  ii regions, G49.0−0.3 and G48.9−0.3, coincide with the two molecular clumps in this ring. We discuss star formation, and the mechanism that produced the ring structure.  相似文献   

12.
We have derived the angular correlation function of a sample of 2096 sources detected in the ROSAT All-Sky Survey (RASS) Bright Source Catalogue, in order to investigate the clustering properties of active galactic nuclei (AGN) in the local Universe. Our sample is constructed by rejecting all known stars, as well as extended X-ray sources. Areas with | b |<30° and declination δ <−30° are also rejected owing to the high or uncertain neutral hydrogen absorption. Cross-correlation of our sample with the Hamburg/RASS optical identification catalogue suggests that the vast majority of our sources are indeed AGN. A 4.1 σ correlation signal between 0° and 8° was detected with w ( θ <8°)=2.5±0.6×10−2. Assuming a two-point correlation function of the form w ( θ )=( θ θ 0)−0.8, we find θ 0=0062. Deprojection on three dimensions, using Limber's equation, yields a spatial correlation length of r 0≈6.0±1.6  h −1 Mpc. This is consistent with the AGN clustering results derived at higher redshifts in optical surveys and suggests a comoving model for the clustering evolution.  相似文献   

13.
We calculate the expected mid-infrared (MIR) molecular hydrogen line emission from the first objects in the Universe. As a result of their low masses, the stellar feedback from massive stars is able to blow away their gas content and collect it into a cooling shell where H2 rapidly forms and IR roto-vibrational (as for example the rest-frame 2.12 μm) lines carry away a large fraction (up to 10 per cent) of the explosion energy. The fluxes from these sources are in the range 10−21–10−17 erg s−1 cm−2 . The highest number counts are expected in the 20-μm band, where about 105 sources deg−2 are predicted at the limiting flux of 3×10−18 erg s−1 cm−2. Among the planned observational facilities, we find that the best detection perspectives are offered by the Next Generation Space Telescope ( NGST ), which should be able to reveal about 200 first objects in one hour observation time at its limiting flux in the above band. Therefore, mid-IR instruments appear to represent perfect tools to trace star formation and stellar feedback in the high ( z ≳5) redshift Universe.  相似文献   

14.
The cluster 3C 129 is classified as a rich cluster. An analysis of the properties of the cluster 3C 129 from ROSAT PSPC and HRI, Einstein IPC, and EXOSAT ME observations is presented. The mean temperature from a joint fit of the ROSAT PSPC and EXOSAT ME data is 5.5(±0.2) keV. The luminosity is 0.6×1044 erg s−1 in 0.2–2.4 keV and 2.7×1044 erg s−1 in 0.2–10 keV. We find a cooling flow with a rate of ∼84 M⊙ yr−1. The central gas density is 6×10−3 cm−3, and the ICM mass is 3.6×1013 M⊙. The total cluster mass is ∼5×1014 M⊙. The X-ray morphology shows an east–west elongation, which is evidence for a recent merger event. The radio source 3C 129.1 is located near the X-ray centre. Another cluster member galaxy (the radio galaxy 3C 129) is a prototype of head-tailed radio galaxies, and is located in the west part of the cluster. The tail points along the gradient of intracluster gas pressure. There are no significant point X-ray sources associated with the AGNs of the two radio galaxies.  相似文献   

15.
The rate coefficients for the formation of carbon monophosphide (CP) and silicon monophosphide (SiP) by radiative association are estimated for temperatures ranging from 300 to 14 100 K. In this temperature range, the radiative association rate coefficients are found to vary from  1.14 × 10−18  to  1.62 × 10−18 cm3 s−1  and from  3.73 × 10−20  to  7.03 × 10−20 cm3 s−1  for CP and SiP, respectively. In both cases, rate coefficients increase slowly with the increase in temperature.  相似文献   

16.
An algorithm of the ensemble pulsar time based on the optimal Wiener filtration method has been constructed. This algorithm allows the separation of the contributions to the post-fit pulsar timing residuals of the atomic clock and the pulsar itself. Filters were designed using the cross- and auto-covariance functions of the timing residuals. The method has been applied to the timing data of millisecond pulsars PSR B1855+09 and B1937+21 and allowed the filtering out of the atomic-scale component from the pulsar data. Direct comparison of the terrestrial time TT(BIPM06) and the ensemble pulsar time PTens revealed that the fractional instability of TT(BIPM06)−PTens is equal to  σ z = (0.8 ± 1.9) × 10−15  . Based on the  σ z   statistics of TT(BIPM06)−PTens, a new limit of the energy density of the gravitational wave background was calculated to be equal to  Ωg h 2∼ 3 × 10−9  .  相似文献   

17.
We present BeppoSAX observations of Nova Velorum 1999 (V382 Vel), carried out in a broad X-ray band covering 0.1–300 keV only 15 d after the discovery and again after 6 months. The nova was detected at day 15 with the BeppoSAX instruments which measured a flux F x≃1.8×10−11 erg cm−2 s−1 in the 0.1–10 keV range and a 2 σ upper limit F x<6.7×10−12 erg cm−2 s−1 in the 15–60 keV range. We attribute the emission to shocked nebular ejecta at a plasma temperature kT ≃6 keV . At six months no bright component emerged in the 15–60 keV range, but a bright central supersoft X-ray source appeared. The hot nebular component previously detected had cooled to a plasma temperature kT <1 keV . There was strong intrinsic absorption of the ejecta in the first observation and not in the second, because the column density of neutral hydrogen decreased from N (H)≃1.7×1023 to N (H)≃1021 cm−2 (close to the interstellar value). The unabsorbed X-ray flux also decreased from F x=4.3×10−11 to F x≃10−12 erg cm−2 s−1 .  相似文献   

18.
We discuss the evolution of the magnetic flux density and angular velocity in a molecular cloud core, on the basis of three-dimensional numerical simulations, in which a rotating magnetized cloud fragments and collapses to form a very dense optically thick core of  >5 × 1010 cm−3  . As the density increases towards the formation of the optically thick core, the magnetic flux density and angular velocity converge towards a single relationship between the two quantities. If the core is magnetically dominated its magnetic flux density approaches  1.5( n /5 × 1010 cm−3)1/2 mG  , while if the core is rotationally dominated the angular velocity approaches  2.57 × 10−3 ( n /5 × 1010 cm−3)1/2 yr−1  , where n is the density of the gas. We also find that the ratio of the angular velocity to the magnetic flux density remains nearly constant until the density exceeds  5 × 1010 cm−3  . Fragmentation of the very dense core and emergence of outflows from fragments will be shown in the subsequent paper.  相似文献   

19.
The multi-transitional observations of CS molecules towards the NGC 2071 core have been re-analysed by using a tri-dimensional Monte Carlo radiative transfer code. Better agreement with the observations is made by an introduction of clumpiness to this model than by smoothly varying density to the 1D microturbulent one. The best-fitting model shows that, when a unique density is assumed for clumps, the volume filling factor of the clumps varies as r −2 with an average of ∼5 per cent over the entire core, and that the H2 number density and the CS abundance of the clump relative to H2 are ∼ 2 × 106 cm−3 and ∼ 6 × 10−10, respectively. The radial density gradient ∝ r −2 obtained from our clumpy core model is steeper than that (∝ r −1.3) obtained from the microturbulent model. Since all clumps are subject to random bulk motions in this 3D clumpy macroturbulent model, synthesized line profiles do not show self-absorption dips even for opaque transitions and the resulting linewidth is in good accordance with the observations.  相似文献   

20.
The recent cratering record of the surface of the Earth is re-examined using a new technique that concentrates on estimating the mean areas occupied by individual craters, together with the gradients of linear plots of crater numbers versus crater ages. This analysis indicates that the lower limit of the rate at which craters have been produced over the last 125±20 Myr is, for example, (12.0±0.7)×10−15 km−2 yr−1 for D 2.4 km craters, (9.5±0.6)×10−15 km−2 yr−1 for D 5.0 km craters, (6.5±0.5)×10−15 km−2 yr−1 for D 12 km craters, and (3.0±0.3)×10−15 km−2 yr−1 for D 22 km craters. These figures indicate that previous researchers have considerably overestimated the rate at which small (2.4< D <20 km) craters are being produced. It is also found that the relationship between crater production rate and crater diameter is not a simple power law in the 2.4< D <40 km diameter range. On the most stable areas of the Earth's continents, and over the last 125±20 Myr it seems that the rate at which craters are eroded below the detection limit does not depend on crater diameter throughout the above size range.  相似文献   

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