51 research outputs found
Corotation: its influence on the chemical abundance pattern of the Galaxy
A simple theory for the chemical enrichment of the Galaxy which takes into
account the effects of spiral arms on heavy elements output was developed. In
the framework of the model with the corotation close to the position of the Sun
in the Galaxy the observed abundance features are explained.Comment: LaTeX, 6 pages, 5 jpg figures, uses aastex.sty, submitted to ApJ Let
Is it possible to reveal the lost siblings of the Sun?
We present the results of our numerical experiments on stellar scattering in
the galactic disc under the influence of the perturbed galactic gravitation
field connected with the spiral density waves and show that the point of view
according to which stars do not migrate far from their birthplace, in general,
is incorrect. Despite close initial locations and the same velocities after 4.6
Gyrs members of an open cluster are scattered over a very large part of the
galactic disc. If we adopt that the parental solar cluster had
stars, it is unlikely to reveal the solar siblings within 100 pc from the Sun.
The problem stands a good chance to be solved if the cluster had
stars.
We also demonstrate that unbound open clusters disperse off in a short period
of time under the influence of spiral gravitation field. Their stars became a
part of the galactic disc. We have estimated typical times of the cluster
disruption in radial and azimuth directions and the corresponding diffusion
coefficients.Comment: 7 pages, 12 figure
A New Model for the Spiral Structure of the Galaxy. Superposition of 2+4-armed patterns
We investigate the possibility of describing the spiral pattern of the Milky
Way in terms of a model of superposition 2- and 4-armed wave harmonics (the
simplest description, besides pure modes). Two complementary methods are used:
a study of stellar kinematics, and direct tracing of positions of spiral arms.
In the first method, the parameters of the galactic rotation curve and the free
parameters of the spiral density waves were obtained from Cepheid kinematics,
under different assumptions. To turn visible the structure corresponding to
these models, we computed the evolution of an ensemble of N-particles,
simulating the ISM clouds, in the perturbed galactic gravitational field. In
the second method, we present a new analysis of the longitude-velocity (l-v)
diagram of the sample of galactic HII regions, converting positions of spiral
arms in the galactic plane into locii of these arms in the l-v diagram. Both
methods indicate that the ``self-sustained'' model, in which the 2-armed and
4-armed mode have different pitch angles (6 arcdeg and 12 arcdeg, respectively)
is a good description of the disk structure. An important conclusion is that
the Sun happens to be practically at the corotation circle. As an additional
result of our study, we propose an independent test for localization of the
corotation circle in a spiral galaxy: a gap in the radial distribution of
interstellar gas has to be observed in the corotation region.Comment: 17 pages, 9 figures, Latex, uses aas2pp4.st
A New Method of the Corotation Radius Evaluation in our Galaxy
We propose a new method for determination of the rotation velocity of the
galactic spiral density waves, correspondingly, the corotation radius, ,
in our Galaxy by means of statistical analysis of radial oxygen distribution in
the galactic disc derived over Cepheids. The corotation resonance happens to be
located at kpc, depending on the rate of gas infall on to
the galactic disc, the statistical error being kpc.
Simultaneously, the constant for the rate of oxygen synthesis in the galactic
disc was determined.
We also argue in favour of a very short time-scale formation of the galactic
disc, namely: Gyr. This scenario enables to solve the problem of
the lack of intergalactic gas infall.Comment: 5 pages, 5 figure, 1 tabl
Periodic Pattern in the Residual-Velocity Field of OB Associations
An analysis of the residual-velocity field of OB associations within 3 kpc of
the Sun has revealed periodic variations in the radial residual velocities
along the Galactic radius vector with a typical scale length of
lambda=2.0(+/-0.2) kpc and a mean amplitude of fR=7(+/-1) km/s. The fact that
the radial residual velocities of almost all OB-associations in rich
stellar-gas complexes are directed toward the Galactic center suggests that the
solar neighborhood under consideration is within the corotation radius. The
azimuthal-velocity field exhibits a distinct periodic pattern in the region
0<l<180 degrees, where the mean azimuthal-velocity amplitude is ft=6(+/-2)
km/s. There is no periodic pattern of the azimuthal-velocity field in the
region 180<l<360 degrees. The locations of the Cygnus arm, as well as the
Perseus arm, inferred from an analysis of the radial- and azimuthal-velocity
fields coincide. The periodic patterns of the residual-velocity fields of
Cepheids and OB associations share many common features.Comment: 21 page
Galactic constraints on supernova progenitor models
Aims. To estimate the mean masses of oxygen and iron ejected per each type of supernovae (SNe) event from observations of the elemental abundance patterns in the Galactic disk and constrain the relevant SNe progenitor models.
Methods. We undertake a statistical analysis of the radial abundance distributions in the Galactic disk within a theoretical framework for Galactic chemical evolution which incorporates the influence of spiral arms. This framework has been shown to recover the non-linear behaviour in radial gradients, the mean masses of oxygen and iron ejected during SNe explosions to be estimated, and constraints to be placed on SNe progenitor models.
Results. (i) The mean mass of oxygen ejected per core-collapse SNe (CC SNe) event (which are concentrated within spiral arms) is similar to 0.27 M-circle dot; (ii) the mean mass of iron ejected by tardy Type Ia SNe (SNeIa, whose progenitors are older/longer-lived stars with ages greater than or similar to 100 Myr and up to several Gyr, which do not concentrate within spiral arms) is similar to 0.58 M-circle dot; (iii) the upper mass of iron ejected by prompt SNeIa (SNe whose progenitors are younger/shorter-lived stars with ages less than or similar to 100 Myr, which are concentrated within spiral arms) is <= 0.23 M-circle dot per event; (iv) the corresponding mean mass of iron produced by CC SNe is <= 0.04 M-circle dot per event; (v) short-lived SNe (core-collapse or prompt SNeIa) supply similar to 85% of the Galactic disk's iron.
Conclusions. The inferred low mean mass of oxygen ejected per CC SNe event implies a low upper mass limit for the corresponding progenitors of similar to 23 M-circle dot, otherwise the Galactic disk would be overabundant in oxygen. This inference is the consequence of the non-linear dependence between the upper limit of the progenitor initial mass and the mean mass of oxygen ejected per CC SNe explosion. The low mean mass of iron ejected by prompt SNeIa, relative to the mass produced by tardy SNeIa (similar to 2.5 times lower), prejudices the idea that both sub-populations of SNeIa have the same physical nature. We suggest that, perhaps, prompt SNeIa are more akin to CC SNe, and discuss the implications of such a suggestion
A Mechanism for the Oxygen and Iron Bimodal Radial Distribution Formation in the Disc of our Galaxy
Recently it has been proposed that there are two types of SN Ia progenitors
-- short-lived and long-lived. On the basis of this idea, we develope a theory
of a unified mechanism for the formation of the bimodal radial distribution of
iron and oxygen in the Galactic disc. The underlying cause for the formation of
the fine structure of the radial abundance pattern is the influence of spiral
arms, specifically, the combined effect of the corotation resonance and
turbulent diffusion. From our modelling we conclude that to explain the bimodal
radial distributions simultaneously for oxygen and iron and to obtain
approximately equal total iron output from different types of supernovae, the
mean ejected iron mass per supernova event should be the same as quoted in
literature if maximum mass of stars, that eject heavy elements, is . For the upper mass limit of the production of iron
by a supernova II explosion should be increased by about 1.5 times.Comment: 7 pages, 6 figures, MNRAS submitte
Direct determination of the spiral pattern rotation speed of the Galaxy
The rotation velocity of the spiral pattern of the Galaxy is determined by
direct observation of the birthplaces of open clusters of stars in the galactic
disk as a function of their age. Our measurement does not depend on any
specific model of the spiral structure, like the existence of a given number of
spiral arms, or the presence of a bar in the central regions. This study became
possible due to the recent completion of a large database on open clusters by
our group. The birthplaces of the clusters are determined by two methods, one
that assumes that the orbits are circular, and the other by integrating the
orbits in the Galactic potential for a time equal to the age of the clusters.
We selected in the database a sample of 212 clusters for which proper motions,
radial velocities, distances and ages are available, or of 612 clusters that
have ages and distances available. We tested different assumptions concerning
the rotation curve and the radius of the solar orbit. Our results confirm
that a dominant fraction of the open clusters are formed in spiral arms, and
that the spiral arms rotate like a rigid body, as predicted by the classical
theory of spiral waves. We find that the corotation radius is close to
the solar galactic orbit (). This proximity has many
potentially interesting consequences, like a better preservation of life on the
Earth, and a new understanding of the history of star formation in the solar
neighborhood, and of the evolution of the abundance of elements in the galactic
disk.Comment: 9 pages, 5 figures, submitted to Ap
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