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1.
The size distribution of dark clouds and of H II regions were used to derive a distance of 440±22 kpc for M31. Some galactic H II regions and dark clouds were combined with the same ingredients in M31 to study the mass spectrum of both phenomena. A gas to dust ratio of 10001 has been derived for M31. Radii of the classical H II regions as derived in this work using distance of 440 kpc agrees with the galactic classical H II region radii.  相似文献   

2.
The first observations of the 2(20)-2(11) transition of cyclopropenylidene (C3H2) at 21.6 GHz are described. In all cases where it has been detected, the line appears in absorption, showing that this transition is "refrigerated" (i.e., Tex < 2.7 K) in cold dust clouds. These results are compared with those for the 1(10)-1(01) transition of C3H2, and the consequences for the excitation of C3H2 qualitatively discussed.  相似文献   

3.
From a new mosaic image in the Hα line of the complete disc of the spiral galaxy M100, a catalogue is composed listing 1948 individual H II regions. I give details of the data collection and reduction procedure, and of the production of the H II region catalogue. For each H II region, the catalogue gives its position relative to the centre of the galaxy, its deprojected distance to the centre, its radius and its calibrated luminosity. An indication is included as to whether the H II region is located in the arms, between them, or in the circumnuclear star-forming region. I present the results of a statistical study of properties of the H II regions. The luminosity function of the complete ensemble of H II regions shows a characteristic shape well fitted by a power-law slope in the higher luminosity range, and complying with literature values for galaxies like M100. Luminosity function slopes for arm and interarm H II region populations separately are found to be equal within the errors of the fits, indicating that whereas the density wave accumulates material into the arm regions, and may trigger star formation there, it does not in fact change the mass distribution of the star-forming clouds, nor the statistical properties of the H II region population. Diameter distributions and the radial number density distribution are discussed. The latter indicates those areas where most star formation occurs: the circumnuclear region and the spiral arms. The huge number of H II regions allowed the construction of a number of independent luminosity functions at different distances to the nucleus. The slope of the luminosity function shows a marginal decrease with increasing distance from the centre, which could indicate a gradual change towards shallower IMF slopes with increasing galactocentric distance, or an evolutionary effect.  相似文献   

4.
We study the properties of the He I 10830 (A) line in nine selected solar flares, using spectral data obtained with the Multi-channel Infrared Solar Spectrograph (MISS) at Purple Mountain Observatory (PMO) and photospheric images from the Michelson Doppler Imager (MD1) onboard the Solar and Heliospheric Observatory (SOHO). Our results indicate that, over an area of 3"- 8", the He I 10830 (A) line shows emission exceeding the continuum in nearby quiet region when the Geostationary Operations Environmental Satellite (GOES) X-ray class of the flare reaches a threshold value (C4.5). The He I 10830A line emission is detected only in the kernels of the Hα brightenings, but is not associated with the size of the flare. It is found that, whenever the He I 10830(A) line shows excess emission over the nearby continuum both the Hα and the Ca II 8542 (A) lines display enhanced intensities exceeding their preflare intensities. The He I 10830(A) line emission can occasionally extend into the umbra of the involved sunspot, which is inconsistent with previous studies. The weak com-ponent of He I 10830(A) line changes from emission to absorption earlier than does the main component. Our results favor the photoionization-reconnection mechanism for the excitation of the He I 10830(A) line.  相似文献   

5.
We examined the Sloan Digital Sky Survey (SDSS) spectra of the H II regions in the disk of the spiral galaxy M101 (NGC 5457), and 17 H II regions with the auroral oxygen line [O III] λ 436.3 nm in their spectra were selected for line intensity measurements. The measurement data were used to determine the oxygen abundance in the H II region sample. We demonstrate that the spectral SDSS data supplemented with the information on the nebular oxygen line [O II] λ 372.7 nm based on the recently found ff-relation between the oxygen line intensities in the spectra of H II regions allow the oxygen abundance to be determined as accurately as in the standard T e method. The parameters of the radial oxygen abundance distribution in the M101 disk (the abundance at the galactic center and the radial gradient) are estimated.  相似文献   

6.
CCD spectra taken with the PFES and CEGS echelle spectrographs attached to the 6-m Special Astrophysical Observatory (Russian Academy of Sciences) telescope and the 2-m Shamakha Astrophysical Observatory (National Academy of Sciences of Azerbaijan) telescope, respectively, were used to study the line-profile variations in the spectrum of the hot supergiant α Cam. No fast (≤1.5 h) line-profile and radial-velocity variations were found. Some of the systematic effects that cause spurious variability are considered. The Hα-profile variability appears symmetric relative to the radial velocity of the star’s center of mass and is attributable to variable blueshifted and redshifted emission and/or absorption components superimposed on a variable photospheric profile. The Hα line shows evidence of a large-scale mass ejection from the stellar surface, which is also traceable in other spectral lines. The He II 4686 line exhibits an inverse P Cyg profile, while the red wing of the He I 5876 line shows weak and variable emission. The fast (on characteristic time scales of shorter than an hour) variability of the He II 4686 profile that was previously revealed by our observations (Kholtygin et al. 2000) is called into question. A comparison of the observational data on the variability of ultraviolet and optical line profiles for the supergiant αCam suggests that nonradial motions are mainly responsible for the radial-velocity and line-profile variability.  相似文献   

7.
We report the astronomical detections of several ammonia inversion transitions involving nonmetastable levels with energies as high s 1090 K above the ground state. The (J, K) = (9, 6) inversion transition shows maser-like emission in the directions of W51, NGC 7538, W49, and DR 21(OH). The NH3 (6, 3) line exhibits similar characteristics in W51 but is seen in absorption in NGC 7538. These are the first definite detections of ammonia masers in space. The intensities and narrow line widths (0.5-1.5 km s-1) for the emission features are in contrast to the previously detected broad, weak, nonmetastable lines attributed to thermal emission in these sources. Temporal variability appears to be evident in the (9, 6) emission in W49 over a 4 month period. The highly excited (J, K) = (9, 6) and (6, 3) ammonia lines are found in regions containing compact H II regions and strong infrared sources with associated H2O and OH masers; i.e., in regions of active star formation.  相似文献   

8.
The J = 2-1 transition of SiO has been searched for toward both hot and cold molecular gas. SiO was not detected toward the dark clouds TMC-1, L134 N, and B335, down to column density upper limits of N < 2-4 x 10(10) cm-2. The species, however, has been observed toward all sources with a kinetic temperature greater than or equal to 30 K, with the largest column densities (N approximately 10(13)-10(17) cm-2) measured in the warmest (TK > or = 100 K) material. The abundance of SiO, relative to HCN, is found to be approximately 0.1-1 in the massive star-forming regions toward Orion and NGC 7538; toward the dark clouds, the upper limits to this ratio is less than 0.0002-0.004. A similar enhancement in the warmer regions is reflected in the SiO/H2 ratio as well. A linear relation was found between the natural log of the SiO concentration and 1/TK, suggesting that the species' formation involves a chemically specific process that contains an activation barrier of approximately 90 K. SiO was also found to be underabundant with respect to SO in cold clouds, with SiO/SO < 1/1000, versus SiO/SO > or =, measured in Orion-KL. The formation of SiO is therefore linked closely to the local gas kinetic temperature, rather than the oxygen abundance, and its synthesis is likely to involve high-temperature gas-phase reactions. The species thus may serve as an unambiguous indicator of high-temperature or "shock" chemistry.  相似文献   

9.
Based on far-infrared spectroscopy of a small sample of nearbyinfrared-bright and ultraluminous infrared galaxies (ULIRGs) with theISO Long Wavelength Spectrometer we find adramatic progression in ionic/atomic fine-structure emission line andmolecular/atomic absorption line characteristics in these galaxiesextending from strong [O III]52,88 m and [N III]57 m lineemission to detection of only faint [C II]158 m line emissionfrom gas in photodissociation regions in the ULIRGs. The molecularabsorption spectra show varying excitation as well, extending fromgalaxies in which the molecular population mainly occupies the groundstate to galaxies in which there is significant population in higherlevels. In the case of the prototypical ULIRG, the merger galaxy Arp220, the spectrum is dominated by absorption lines of OH, H2O, CH,and [O I]. Low [O III]88 m line flux relative to the integratedfar-infrared flux correlates with low excitation and does not appear tobe due to far-infrared extinction or to density effects. A progressiontoward soft radiation fields or very dusty H II regions may explainthese effects.  相似文献   

10.
The large backscattering cross section of the particles composing the upper clouds on Venus suggests that a small quantity of high refractive index material is present in the clouds. We propose that this material is elemental sulfur and that sulfur also accounts for the absorption of uv-visible radiation at wavelengths outside of the SO2 absorption bands. A physical-chemical model of the clouds shows that sulfur, with a mass comparable to that of the observed Mode 1 particles, can be produced in oxygen-poor regions of the upper clouds and in rising air columns. Sulfur production from SO2 can be rapid, which explains the observed correlation between SO2 and the uv absorber. The sulfur is properly located to be the uv absorber uv absorber since its calculated concentration rapidly increases with depth in the upper clouds, but it is largely absent in the middle and lower clouds. Sulfur nucleation provides a means of generating the observed bimodal particle size distribution in the upper clouds. Chemical modeling shows that the sulfur vapor is rich in short-chain allotropes such as S3 and S4. These allotropes have absorption bands centered near 4000 and 5300 Å, respectively. We suggest that the sulfur particles on Venus are largely composed of S8, but also contain a few percent of S3 and S4. Such particles could account for the wavelength dependence of the albedo of Venus and for the solar energy deposition profile in the clouds. These allotropes are metastable and relax to S8 over periods of hours to days, providing a simple explanation for the relatively short lifetime of the uv absorber.  相似文献   

11.
H. Zirin 《Solar physics》1974,38(1):91-108
High resolution filtergrams made with a 0.3 Å K line filter at Big Bear are discussed. The dark K3 clouds noted in spectra by Bappu and Sivaraman (1971) are confirmed; they cover about 1/3 of the inside of supergranule cells, and oscillate (mainly horizontally) with 3–4 min period. Their vertical extent of about 3000 km produces a sharp broadening of K3 at the extreme limb and obscuration of bright features. Spicules also produce K3 absorption, but they occur in emission more often than in Hα, particularly near the limb. Apart from these differences the structures seen in Hα and K generally correspond. A fine structure of granule size, also oscillating with 3–4 min period, is seen in K1. This structure is also obscured near the extreme limb, possibly by the same clouds seen in K1. The bright K232 network does not appear to oscillate significantly in brightness, except through covering and uncovering by the overlying dark clouds. Some bright spicules, and many dark ones, are seen over all elements of the K network, as in Hα. In active regions the structure in K is very close to Hα; all plagettes and plages are bounded by systems of strongly inclined bright and dark fibrils apparently marking the lines of force. The fibrils are the same (bright or dark) in Hα and K3; they are not seen in K2. Umbral flashes are much less visible in Hα. There is, however, a finer, granular umbral structure in Hα which does not oscillate. Running penumbral waves are not seen in K. The penumbra and surrounding areas are bright in K3. Every bright point in K3 corresponds to a magnetic field spot, except for the intranetwork area, where the magnetograms cannot detect possible fields. Flares are the same in K and Hα. The formation of the K double reversal at the limb is exhaustively discussed.  相似文献   

12.
We report the first detection of a sharp spectral feature in a narrow-line Seyfert 1 galaxy. Using XMM-Newton we have observed 1H     and find a drop in flux by a factor of more than 2 at a rest-frame energy of ∼ 7 keV without any detectable narrow Fe K α line emission. The energy of this feature suggests a connection with the neutral iron K photoelectric edge, but the lack of any obvious absorption in the spectrum at lower energies makes the interpretation challenging. We explore two alternative explanations for this unusual spectral feature: (i) partial-covering absorption by clouds of neutral material; and (ii) ionized disc reflection with lines and edges from different ionization stages of iron blurred together by relativistic effects. We note that both models require an iron overabundance to explain the depth of the feature. The X-ray light curve shows strong and rapid variability, changing by a factor of 4 during the observation. The source displays modest spectral variability which is uncorrelated with flux.  相似文献   

13.
Several interstellar molecules have been detected toward the highly perturbed B and G clouds associated with the supernova remnant IC 443 via their 3 mm transitions, including N2H+, SiO, SO, CN, HNC, and H13CO+. The (J, K) = (1, 1) and (2, 2) inversion lines of metastable ammonia have also been observed, as well as the J = 3-2 transition of HCO+ at 1.2 mm. Analysis of the (1, 1) and (2, 2) inversion lines of NH3 indicates minimum gas kinetic temperatures of TK = 70 K toward cloud B, and TK = 33 K in cloud G. Modeling of the J = 1-0 and J = 3-2 transitions of HCO+ implies densities greater than 10(5) cm-3 toward both positions. These data clearly show that hot and dense material is present in IC 443, and they suggest the presence of shocks in both regions. A careful analysis of the HCO+ lines indicates that the HCO+ abundance is at most enhanced by factors of a few over that found in cold, quiescent gas. This conclusion contradicts past claims of HCO+ abundance enhancements of several orders of magnitude in the perturbed regions. The N2H+ abundance was also found to be similar to that in cold gas, suggesting that there is no increase in ionization in the clouds. The abundances of SO and CS, as well as CN and NH3, do not appear to differ significantly from those found in cold dark clouds, although chemistry models predict sulfur-containing species to undergo high-temperature enhancements. SiO, however, is found to have an abundance in the perturbed gas 100 times larger than the upper limits observed in the dark cloud TMC 1, a result in agreement with high temperature chemistry models. In addition, the HNC/HCN ratio in both IC 443 B and G was found to be approximately 0.1--far from the ratio of 1 predicted by low-temperature ion-molecule chemistry, but similar to the values observed in clouds where elevated temperatures are present.  相似文献   

14.
There are relatively few H2CO mappings of large-area giant molecular cloud (GMCs). H2CO absorption lines are good tracers for low-temperature molecular clouds towards star formation regions. Thus, the aim of the study was to identify H2CO distributions in ambient molecular clouds. We investigated morphologic relations among 6-cm continuum brightness temperature (CBT) data and H2CO (111−110; Nanshan 25-m radio telescope), 12CO (1–0; 1.2-m CfA telescope) and midcourse space experiment (MSX) data, and considered the impact of background components on foreground clouds. We report simultaneous 6-cm H2CO absorption lines and H110α radio recombination line observations and give several large-area mappings at 4.8 GHz toward W49 (50′×50′), W3 (70′×90′), DR21/W75 (60′×90′) and NGC2024/NGC2023 (50′×100′) GMCs. By superimposing H2CO and 12CO contours onto the MSX color map, we can compare correlations. The resolution for H2CO, 12CO and MSX data was ∼10′, ∼8′ and ∼18.3″, respectively. Comparison of H2CO and 12CO contours, 8.28-μm MSX colorscale and CBT data revealed great morphological correlation in the large area, although there are some discrepancies between 12CO and H2CO peaks in small areas. The NGC2024/NGC2023 GMC is a large area of HII regions with a high CBT, but a H2CO cloud to the north is possible against the cosmic microwave background. A statistical diagram shows that 85.21% of H2CO absorption lines are distributed in the intensity range from −1.0 to 0 Jy and the ΔV range from 1.206 to 5 km s−1.  相似文献   

15.
We present the results of spectroscopy of 39 H II regions in the spiral galaxy NGC 6946. The spectral observations were carried out at the 6-m BTA telescope of the SAO RAS with the SCORPIO focal reducer in the multi-slit mode with the dispersion of 2.1 Å/px and spectral resolution of 10 Å. The absorption estimates for 39 H II regions were obtained. Using the “strong line” method (NS-calibration) we determined the electron temperature, and the abundances of oxygen and nitrogen for 30 H II regions. The radial gradients of O/H and N/H were constructed.  相似文献   

16.
The method of determination of heavy element abundances in H II regions (the strong-line method) uses the assumption that some combinations of strong emission line intensities in spectra of H II regions can serve as indicators of metallicities and electron temperatures in nebulosities. Three sets of strong lines are considered, namely, A (R 3, R 2, N 2, S 2 lines), B (R 3, R 2, N 2 lines), and C (R 3, N 2, S 2 lines). Strong line intensities are normalized to the H ?? intensity). We searched for an unambiguous relationship between strong emission line intensities of these line sets in spectra of H II regions and their compositions. The extensive model grid for H II regions is computed. Chemical compositions of nebulosities and intensities of A and C lines are shown to be related unambiguously. For the B line set, 5% of model H II regions do not have any unambiguous relationship, namely, the models with appreciably different oxygen and nitrogen abundances in H II regions can have similar intensities of the B set lines. The versions of strong-line method (calibrations) using the A and C lines are more reliable than those based on the B lines.  相似文献   

17.
We have imaged a region of ∼ 5′ extent surrounding Sgr A* in the HI 21 cm-line absorption using the Very Large Array. A Gaussian decomposition of the optical depth spectra at positions within ∼ 2′ (∼ 5 pc at 8.5 kpc) of Sgr A* detects a wide line underlying the many narrow absorption lines. The wide line has a mean peak optical depth of 0.32 ± 0.12 centered at a mean velocity of V1sr = −4 ± 15 km s{−1}. The mean full width at half maximum is 119 ± 42 km s−1. Such a wide line is absent in the spectra at positions beyond ∼ 2′ from Sgr A*. The position-velocity diagrams in optical depth reveal that the wide line originates in various components of the circumnuclear disk (radius ∼ 1.3′ ) surrounding Sgr A*. These components contribute to the optical depth of the wide line in different velocity ranges. The position-velocity diagrams do not reveal any diffuse feature which could be attributed to a large number of HI clouds along the line of sight to Sgr A*. Consequently, the wide line has no implications either to a global population of shocked HI clouds in the Galaxy or to the energetics of the interstellar medium as was earlier thought.  相似文献   

18.
The 1667-MHz ground-state hydroxyl (OH) line has been observed towards positions on Puppis A as well as in the immediate vicinity of this supernova remnant (SNR). The spectra at two positions on Puppis A show absorption lines at velocities less than +7.6 km s1, and emission lines above this velocity. Analysis of all four 18 cm OH lines indicates that Puppis A must lie between the OH clouds seen in absorption and emission, giving it a v lsr of +7.6 km s1. This implies that the kinematic distance to Puppis A is The OH clouds in front of Puppis A are slightly anomalously excited, as shown by analysis of the four 18 cm OH lines at the two observed positions on Puppis A. There is no evidence of any interaction of the SNR with the clouds in front of and behind it.  相似文献   

19.
Using proxy data for the occurrence of those mass ejections from the solar corona which are directed earthward, we investigate the association between the post-1970 interplanetary magnetic clouds of Klein and Burlaga (1982) and coronal mass ejections. The evidence linking magnetic clouds following shocks with coronal mass ejections is striking; six of nine clouds observed at Earth were preceded an appropriate time earlier by meter-wave type II radio bursts indicative of coronal shock waves and coronal mass ejections occurring near central meridian. During the selected control periods when no clouds were detected near Earth, the only type II bursts reported were associated with solar activity near the limbs. Where the proxy solar data to be sought are not so clearly suggested, that is, for clouds preceding interaction regions and clouds within cold magnetic enhancements, the evidence linking the clouds and coronal mass ejections is not as clear; proxy data usually suggest many candidate mass-ejection events for each cloud. Overall, the data are consistent with and support the hypothesis suggested by Klein and Burlaga that magnetic clouds observed with spacecraft at 1 AU are manifestations of solar coronal mass ejection transients.  相似文献   

20.
We compare the line-of-sight velocities of stars in OB associations within 3 kpc of the Sun and the molecular clouds closest to them. The Perseus arm is used as an example to show that the line-of-sight velocity ranges in which OB-association stars, molecular clouds, and H II regions ionized by these association stars are observed overlap. The streaming motions produced by density waves in the (l, VLSR) plane were found to lead to an inversion of the distances to objects of the Perseus arm and the interarm space beyond this arm.  相似文献   

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