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1.
The radial profile of the star-formation rate (SFR) in the galaxy NGC 628 is shown to be modulated by a spiral-density wave. The radial profile of the velocity of gas inflow into the spiral arm is similar to the radial distribution of the surface density of the SFR. The position of the corotation resonance is determined along with other parameters of the spiral-density wave via a Fourier analysis of the azimuthal distribution of the observed radial velocities in annular zones of the disk of NGC 628. The radial profile of the surface density of the SFR is determined using the empirical SFR—linear size relation for star-formation complexes (giant HII regions) and measurements of the coordinates, Hα fluxes, and the sizes of HII regions in NGC 628. 相似文献
2.
E. P. Kurbatov 《Astronomy Reports》2007,51(12):957-966
We suggest a model for the star-formation function and the dissipation of turbulent energy of the interstellar medium. The star-formation function takes into account the effect of turbularization of the ISM. Applying the derived relations to a hierarchical scenario for the formation of galaxies makes it possible to explain the observed delay of star formation in the Galaxy, which corresponds to a range of stellar ages from 8–9 to 10–12 Gyr. 相似文献
3.
A number of features are detected outside the nebula NGC 6888, within 1.2° (30 pc) of the star WR 136, which can be explained in a two-phase stellar-wind model. These include regions with fine filamentary gas structure that do not contain sources of stellar wind, extended radial “streams,” ultra-compact HII regions with high-velocity gas motions, and high-velocity gas motions outside the envelope of NGC 6888. The two-phase wind consists of a rarefied component and dense compact condensations, or “bullets.” The bullets generate cylindrical shocks in the interstellar gas, resulting in the presence of high-velocity gas up 20–30 pc from the star, outside the cavity formed by the rarified component of the wind. 相似文献
4.
A. S. Gusev 《Astronomy Reports》2002,46(9):712-720
We have carried out BVRIHα CCD surface photometry of the spiral galaxy with active star formation NGC 3184 using the 1-m telescope of the Special Astrophysical Observatory. B and Hα data from the ING Archive (La Palma Observatory) were also used. We consider the structure and radial brightness distribution of the galaxy. Stellar populations in different regions of the galaxy are analyzed using two-color diagrams. We have identified and studied star-forming regions in NGC 3184 and estimated their ages based on evolutionary modeling. 相似文献
5.
A. S. Gusev V. I. Myakutin A. E. Piskunov F. K. Sakhibov M. S. Khramtsova 《Astronomy Reports》2008,52(9):714-728
We have compared the results of multicolor U BV R and Hα photometry for 169 young star-formation complexes in five galaxies using a grid of evolutionary models for young star clusters. The ages and interstellar absorptions are estimated for 102 star-formation complexes with the standard uncertainties σ t = 0.30 dex and $ \sigma _{A_V } = 0.45^m We have compared the results of multicolor U BV R and Hα photometry for 169 young star-formation complexes in five galaxies using a grid of evolutionary models for young star clusters.
The ages and interstellar absorptions are estimated for 102 star-formation complexes with the standard uncertainties σ
t
= 0.30 dex and . The accuracies of these parameters were verified using numerical simulations.
Original Russian Text ? A.S. Gusev, V.I. Myakutin, A.E. Piskunov, F.K. Sakhibov, M.S. Khramtsova, 2008, published in Astronomicheskiĭ
Zhurnal, 2008, Vol. 85, No. 9, pp. 794–809. 相似文献
6.
Seven early-type galaxies that are members of the massive X-ray group containing NGC 80 have been studied using two-dimensional spectroscopy with the 6-m telescope of the Special Astrophysical Observatory. We searched for evidence for the synchronous secular evolution of the galaxies in the group. The bulges of five of the seven galaxies appear to be old, with the average age of the bulge stars being 10–15 billion years. Signs of a relatively recent star-formation burst are observed in the small S0 galaxy IC 1548, whose average bulge age is 3 billion years and average core age is 1.5 billion years. A circumnuclear polar gas ring was also detected in this galaxy; in its outer regions, it makes a smooth transition to a gas disk that counter-rotates relative to the stars. IC 1548 probably underwent a close interaction, which resulted in its transformation from a spiral to a lenticular galaxy; the same interaction may also have induced the central burst of star formation. In the giant E0 galaxy NGC 83, a compact massive stellar-gas disk with a radius of about 2 kpc and very rapid rotation is observed, with ongoing star formation; the so-called “minor merger” is likely to have occurred there. We conclude that the NGC 80 group is in a state of formation, with the small NGC 83 subgroup “falling into” the large, old NGC 80 subgroup. 相似文献
7.
A. V. Khoperskov 《Astronomy Reports》2001,45(11):861-864
The condition for gravitational stability of the stellar disks of the galaxies NGC 936 and NGC 3198 makes maximum disk models unacceptable. We present mass estimates for these objects' spheroidal components. The mass of the dark halo of NGC 3198, within four disk radial scale lengths, exceeds its disk mass by a factor of 1.6 to 2. The masses of the disk and spheroidal subsystem (halo + bulge), within four radial scale lengths, are approximately the same for NGC 936. 相似文献
8.
The results of [O/Na] abundance modelling in globular clusters NGC 2808 and NGC 6752 are presented. An evolutionary scenario that is able to reproduce the characteristic observational peculiarities of the [O/Na] distribution function for the stars is proposed, which assumes that the source of the observed chemical anomalies is slow winds from massive rotating stars. The peculiarities of the chemical compositions of globular clusters can be explained in amodel with partialmixing of the stellar-wind material and the surrounding interstellar gas; i.e., second-generation stars are born in the vicinity of individual massive first-generation stars, from the heterogeneously distributed material ejected from their surfaces. 相似文献
9.
Astronomy Reports - We use observations of CO and HI emission in star-forming complexes (SFCs) in galaxies NGC 5457, NGC 5194, NGC 628, and NGC 6946 to search for possible correlations... 相似文献
10.
The paper reports the results of BV RI surface photometry of the giant galaxy NGC 5351 based on CCD observations obtained on the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Analysis of the structure and radial brightness distribution in the galaxy shows that NGC 5351 has a complex and, in some places, asymmetric structure. The galaxy possesses a large quantity of dust. The average internal extinction due to dust is AV=1.2m±0.4m. After correcting for the effect of this dust, the parameters of the galaxy are typical of late-type spirals. The compositions of the stellar population in various parts of the galaxy are estimated using two-color diagrams. Star-forming regions in NGC 5351 are identified and studied. Most of the star-forming regions are located in the ring of the galaxy. Evolutionary modeling is used to estimate the ages of regions of violent star formation. An elliptical companion galaxy to NGC 5351 was found. The rotation curve of the galaxy is modeled and its mass estimated. The disk of NGC 5351 is self-gravitating within its optical radius. 相似文献
11.
The parameters of the radiation of interstellar matter in star-forming complexes in the high-metallicity galaxies NGC 628, NGC 2976, and NGC 3351, which have different morphological types, are analyzed. The relationship between the emission in Hα and in lines of CO and HI is considered, as well as the relationship between Hα and the emission of dust in the infrared range (IR). The fluxes and surface brightnesses in the UV and IR correlate well with the Hα emission. The HI emission also correlates well with Hα, while the correlation between the CO and Hα emission is much weaker. The ratio of the fluxes at 8 and 24 µm decreases with increasing Hα flux. This may be due to changes in the properties of the dust ensemble (a decrease in the mass fraction of polycyclic aromatic hydrocarbons) or to changing excitation conditions. Analysis of the kinematics of the CO lines shows that the CO flux grows with increasing velocity scatter ΔV when ΔV ? 70 km/s. Preliminary evidence for the existence of star-forming complexes with higher values of ΔV is provided, when the increase in the velocity scatter is accompanied by a decrease in the CO luminosity of the complex.
相似文献12.
A. S. Gusev 《Astronomy Reports》2006,50(3):182-193
The results of multicolor surface photometry of the S0 galaxies NGC 524, NGC 1138, and NGC 7280 and the spiral galaxies NGC 532, NGC 783, and NGC 1589 are analyzed. UBVRI observations were acquired with the 1.5-m telescope of the Maidanak Observatory (Uzbekistan), while JHK data were taken from the 2MASS catalog. The brightness and color distributions in the galaxies are analyzed. Extinction in dust lanes in three spiral galaxies is estimated. The contributions of the radiation of the spherical and disk components in different photometric bands are estimated. Two-color diagrams are used to estimate the composition of the stellar populations in various galaxy components. The variations of the color characteristics in the S0 galaxies is due mostly to radial metallicity gradients. 相似文献
13.
Various origins for the formation of the heavy-element abundance gradients observed in nearly all disk galaxies are analyzed in the framework of evolutionary models. In an isolated galaxy, there is a radial gradient of the abundance of heavy elements only early in its evolution (the first several billion years), which subsequently practically disappears. The gradients of chemical compositions of young objects and the interstellar gas require that typical disk galaxies be open systems (i.e., that they eject some heavy elements into circumgalactic space and/or accrete intergalactic gas) and that the rates of both processes be dependent on galactocentric distance. 相似文献
14.
We have used 46 high-resolution echelle spectra of the Wolf-Rayet star HD 192163 taken in 2005–2009 at the Cassegrain focus of the 2-m Zeiss-2000 telescope of the Shamakha Astrophysical Observatory to study profiles of the five strongest emission lines (HeII 4859, HeII 5411, CIV 5808, HeI 5875, (HeII + Hα) 6560). We also obtained four echelle spectrograms of the Wolf-Rayet star HD 191765 for a comparative study of the NaI 5890 (D2) and NaI 5896 (D1) interstellar absorption lines. The echelle spectrograms were reduced using the DECH20 code. We determined the equivalent widths, radial velocities, central intensities, and half-widths of the emission lines. We detected variations in the violetwing of the (HeII + Hα) 6560 emission band (between λ ～ 6496 Å and λ ～ 6532 Å). Our statistical analysis of the radial velocities available for the (HeII + Hα) 6560 emission band reveals a peak at the ～1% level at the frequency ν = 0.195 d?1, corresponding to the period P = 5.128d. We also studied the NaI 5890 (D2) and NaI 5896 (D1) interstellar absorption lines, which are important for understanding the nature of the nebula NGC 6888, whose origin is related to HD 192163. Asymmetric profiles were found for the NaI 5890 and NaI 5896 interstellar absorption lines, interpreted as reflecting a contribution from NGC 6888 to these lines. We suggest that the detected profile variations of the (HeII + Hα) 6560 emission band and the periodic variations of its Doppler shifts (P = 5.128d) are due to the existence of a low-mass K-M star companion to the Wolf-Rayet star. HD 192163 is a possible evolutionary progenitor of a low-mass X-ray binary. 相似文献
15.
HST trigonometric distances, photometric metallicities, isochronic ages from the second revised version of the Geneva-Copenhagen
survey, and uniform spectroscopic Fe and Mg abundances from our master catalog are used to construct and analyze the age-metallicity
and age-relative Mg abundance relations for stars of the thin disk. The influences of selection effects are discussed in detail.
It is demonstrated that the radial migration of stars does not lead to appreciable distortions in the age dependence of the
metallicity. During the first several billion years of the formation of the thin disk, the interstellarmaterial in this disk
was, on average, fairly rich in heavy elements (〈[Fe/H]〉 ≈ −0.2) and poorly mixed. However, the metallicity dispersion continuously
decreased with age, from σ
[Fe/H] ≈ 0.22 to ≈0.13. All this time, the mean relative abundance of Mg was somewhat higher than the solar value (〈[Mg/Fe]〉 ≈ 0.1).
Roughly four to five billion years ago, the mean metallicity began to systematically increase, while retaining the same dispersion;
the mean relative Mg abundance began to decrease immediately following this. The number of stars in this subsystem increased
sharply at the same time. These properties suggest that the star-formation rate was low in the initial stage of formation
of the thin disk, but abruptly increased about four to five billion years ago. 相似文献
16.
A. V. Tutukov 《Astronomy Reports》2003,47(8):637-647
The rate of gamma-ray bursts (GRBs) in the Galaxy is estimated assuming that these events result from the formation of rapidly rotating Kerr black holes during the core collapse of massive, helium, Wolf-Rayet secondary components in very close binary systems. This process brings about rapid rotation of the cores of such Wolf-Rayet stars, inevitably resulting in the formation of Kerr black holes during type Ib,c supernovae. The current rate of formation of Kerr black holes (GRBs) in the Galaxy is about 3×10?5/year. Collimation of the gamma-ray radiation into a small solid angle (about 0.1–0.01 sr) brings this rate into consistency with the observed rate of GRBs, estimated to be 10?6–10?7/year. Possible immediate progenitors of GRBs are massive X-ray binaries with X-ray luminosities of 1038–1040 erg/s. Due to the short lifetimes of the progenitors and the very high brightnesses of GRBs, the GRB rate can provide information about the history of star formation in the Universe on the Hubble time scale. A model in which the star-formation rate is determined by the conditions for ionization of the interstellar gas, whose density and volume are determined by supernovae, yields a Galactic star-formation history that can be viewed as representing the history of star formation in the Universe. The theoretical history of star formation is in satisfactory agreement with the history reconstructed from observations. The theoretical model for the history of star formation in the Galaxy can also be used to assess the influence of dust on optical observations of supernovae and GRBs in galaxies of various ages. 相似文献
17.
The paper presents the results of monitoring the H2O maser in NGC 7538, which is associated with a star-formation region, in 1993–2003. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia). The variability of the maser emission displays a cyclic character. Two cycles of the long-term variability of the total flux were detected over the entire monitoring period (1981–2003): 1981–1993 and 1994–2003. The period of the variability is about 13 years. An anticorrelation of the emission in lateral sections of the spectra is observed, as is characteristic of protoplanetary disks. A drift in the radial velocity of the central component is observed (VLSR=?60 km/s) with a drift rate of about 0.09 km/s per year. The water-vapor maser is most likely associated with a protoplanetary disk. 相似文献
18.
Two-color photometric data obtained on the 6-m telescope of the Special Astrophysical Observatory are used to analyze the
structure of 13 large disk galaxies in the NGC 80 group. Nine of the 13 studied galaxies are classified as lenticular galaxies.
The stellar populations in the galaxies are very diverse, from old stars with ages of T > 10 billion years (IC 1541) to relatively young stars with ages of T ∼ 1–3 billion years (IC 1548, NGC 85); in one case, star formation is ongoing (UCM 0018+2216). In most of the studied galaxies,
more precisely in all of them brighter than M
B ∼ −18, two-tiered stellar disks are detected, whose radial surface-brightness profiles can be described by two exponential
segments with different characteristic scales—shorter near the center and longer at the periphery. All of the dwarf S0 galaxies
with single-tiered disks are close companions to larger galaxies. Except for this fact, no dependence of the properties of
S0 galaxies on distance from the center of the group is found. Morphological signs of a “minor merger” are found in the lenticular
galaxy NGC 85. Based on these last two results, it is concluded that the most probable mechanism for their transformation
of spiral into lenticular galaxies in groups is gravitational (minor mergers and tidal interactions). 相似文献
19.
An analysis of the H2O maser emission toward the source NGC 7538N, which is associated with an active star-forming region, is reported. The analysis is based on 24 years of monitoring in the 1.35-cm line using the the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in 1981–2005 with a spectral resolution of 0.101 km/s. Individual spectral components have been isolated, and temporal drifts in their radial velocities found. From time to time, the drifts were accompanied by velocity jumps. This can be explained if there are chains consisting of clumps of material that are elongated in the radial direction toward the star and have a radial-velocity gradient. In 1982–2005, two maser activity cycles were observed, during which the chains were activated. We propose that shocks consecutively cross the chain elements and excite maser emission in them. The longest chain, at a radial velocity of ?58 km/s, has not fewer than 15 links. For a shock velocity of 15 km/s, the chain step is estimated to be ≤1.5 AU. The chains could be located in a circumstellar disk with a width of ≤1015 cm. A structure in the form of a rotating nonuniform vortex with the rotation period of about 1.6 years has also been detected. The translational motion of the vortex may be a consequence of its orbital motion within the protoplanetary disk. 相似文献
20.
E. L. Chentsov V. G. Klochkova V. E. Panchuk M. V. Yushkin D. S. Nasonov 《Astronomy Reports》2013,57(7):527-547
The NES echelle spectrograph of the 6-m telescope of the Special Astrophysical Observatory has been used to obtain high-resolution spectra for 13 hot O3-B4 stars in the Cyg OB2 association, making it possible to study weak spectral features of stellar and interstellar origin. Velocity fields in the atmospheres and interstellar medium, characteristics of optical spectra and line profiles are investigated. The cascade star-formation scheme for the association is confirmed. Evidence is presented suggesting that the hypergiant Cyg OB2 No. 12 is an LBV object and that its anomalous reddening has a circumstellar nature. 相似文献