17 research outputs found
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
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 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
Galactic restrictions on iron production by various Types of supernovae
We propose a statistical method for decomposition of contributions to iron
production from various sources: supernovae Type II and the subpopulations of
supernovae Type Ia -- prompt (their progenitors are short-lived stars of ages
less then 100 Myr) and tardy (whose progenitors are long-lived stars of
ages 100 Myr). To do that, we develop a theory of oxygen and iron synthesis
which takes into account the influence of spiral arms on amount of the above
elements synthesized by both the supernovae Type II and prompt supernovae Ia.
We solve this task without of any preliminary suppositions about the ratio
among the portions of iron synthesized by the above sources.
The relative portion of iron synthesized by tardy supernovae Ia for the
life-time of the Galaxy is 35 per cent (in the present ISM this portion
is 50 per cent). Correspondingly, the total portion of iron supplied to
the disc by supernovae Type II and prompt supernovae Ia is 65 per cent
(in the present ISM this portion is 50 per cent).
The above result slightly depends on the adopted mass of oxygen and iron
synthesized during one explosion of supernovae and the shape (bimodal or
smooth) of the so-called Delay Time Distribution function.
The portions of iron mass distributed between the short-lived supernovae are
usually as follows: depending on the ejected masses of oxygen or iron during
one supernovae Type II event the relative portion of iron, supplied to the
Galactic disc for its age, varies in the range 12 - 32 per cent (in the present
ISM 9-25 per cent); the portion supplied by prompt supernovae Ia to the
Galactic disc is 33 - 53 per cent (in ISM 26 - 42 per cent).Comment: 16 pages, 8 figures, 2 tables accepted to Mon. Not. R. Astron. So
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
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
Polygonal Structures in the Gaseous Disk: Numerical Simulations
The results of numerical simulations of a gaseous disk in the potential of a
stellar spiral density wave are presented. The conditions under which
straightened spiral arm segments (rows) form in the gas component are studied.
These features of the spiral structure were identified in a series of works by
A.D. Chernin with coauthors. Gas-dynamic simulations have been performed for a
wide range of model parameters: the pitch angle of the spiral pattern, the
amplitude of the stellar spiral density wave, the disk rotation speed, and the
temperature of the gas component. The results of 2D- and 3D-disk simulations
are compared. The rows in the numerical simulations are shown to be an
essentially nonstationary phenomenon. A statistical analysis of the
distribution of geometric parameters for spiral patterns with rows in the
observed galaxies and the constructed hydrodynamic models shows good agreement.
In particular, the numerical simulations and observations of galaxies give
for the average angles between straight segments.Comment: 22 pages, 10 figure