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1.
Observations of the K2 mission (continuing the program of the Kepler Space Telescope) are used to estimate the spot coverage S (the fractional area of spots on the surface of an active star) for stars of the Hyades cluster. The analysis is based on data on the photometric variations of 47 confirmed single cluster members, together with their atmospheric parameters, masses, and rotation periods. The resulting values of S for these Hyades objects are lower than those stars of the Pleiades cluster (on average, by ΔS ~ 0.05?0.06). A comparison of the results of studies of cool, low-mass dwarfs in the Hyades and Pleiades clusters, as well as the results of a study of 1570 M stars from the main field observed in the Kepler SpaceMission, indicates that the Hyades stars are more evolved than the Pleiades stars, and demonstrate lower activity. The activity of seven solar-type Hyades stars (S = 0.013 ± 0.006) almost approaches the activity level of the present-day Sun, and is lower than the activity of solar-mass stars in the Pleiades (S = 0.031 ± 0.003). Solar-type stars in the Hyades rotate faster than the Sun (〈P〉 = 8.6 d ), but slower than similar Pleiades stars.  相似文献   

2.
The spottedness parameters S (the fraction of the visible surface of the star occupied by spots) characterizing the activity of 674 stars in the Beehive Cluster (age 650 Myr) are estimated, together with variations of this parameter as a function of the rotation period, Rossby number Ro and other characteristics of the stars. The activity of the stars in this cluster is lower than the activity of stars in the younger Pleiades (125 Myr). The average S value for the Beehive Cluster stars is 0.014, while Pleiades stars have the much higher average value 0.052. The activity parameters of 61 solar-type stars in the Beehive Cluster, similar Hyades stars (of about the same age), and stars in the younger Pleiades are compared. The average S value of such objects in the Beehive Cluster is 0.014± 0.008, nearly coincident with the estimate obtained for solar-type Hyades stars. The rotation periods of these objects are 9.1 ± 3.4 day, on average, in agreement with the average rotation period of the Hyades stars (8.6 d ). Stars with periods exceeding 3–4 d are more numerous in the Beehive Cluster than in the Pleiades, and their periods have a larger range, 3–30 d . The characteristic dependence with a kink at Ro (saturation) = 0.13 is not observed in the S–Rossby number diagram for the Beehive and Hyades stars, only a clump of objects with Rossby numbers Ro > 0.7. The spottedness data for the Beehive Cluster and Hyades stars are in good agreement with the S values for dwarfs with ages of 600–700 Myr. This provides evidence for the reliability of the results of gyrochronological calibrations. The data for the Beehive and Pleiades stars are used to analyze variations in the spot-forming activity for a large number of stars of the same age that are members of a single cluster. A joint consideration of the data for two clusters can be used to draw conclusions about the time evolution of the activity of stars of different masses (over a time interval of the order of 500 Myr).  相似文献   

3.
We have modeled the dynamical evolution of small groups of N=3–18 stars in the framework of the gravitational N-body problem, taking into account possible coalescences of stars and the ejection of single and binary stars from the system. The distribution of states is analyzed for a time equal to 300 initial crossing times of the system. The parameters of the binaries and stable triple systems formed, as well as those of ejected single stars, are studied. In most cases, the evolution of the group results in the formation of a binary or stable triple system. The orbital eccentricities of the binaries formed are distributed according to the law f(e)=2e. As a rule, stable triple systems display pronounced hierarchy (the mean ratio of the semimajor axes of the outer and inner binaries is about 20:1). Stars are ejected with velocities from several km/s to several tens of km/s. The results of the modeling are compared with the parameters of observed wide binaries and triple systems.  相似文献   

4.
Various mechanisms for the loss of angular momentum of neutron stars are analyzed. Theoretical predictions about the evolution of the period are compared with the observed distribution of pulsars on the log\(\dot P\)log(P) diagram. Pulsars with short periods (P≤0.1 s) cannot be fit well by any of the models considered. Their braking index is n=?1, which requires the development of a new braking mechanism. The evolution of pulsars with P>1.25 s is described by the law \(\dot P \propto P^2\), probably due to processes internal to the neutron stars. The observational data for pulsars with 0.1<P≤1.25 s can be fit with a hybrid model incorporating internal processes and magnetic-dipole losses. The magnetic fields in pulsar catalogs should be recomputed in accordance with the results obtained. For example, the magnetic fields obtained for two magnetars with P=5.16 s and P=7.47 s are B s =1.7×1013 and 2.9×1013 G, which are lower than the critical field Bcr=4.4×1013 G. For a substantial fraction of pulsars, their characteristic ages \(\tau = P/2\dot P\) cannot serve as measures of their real ages.  相似文献   

5.
We have carried out numerical simulations of the dynamical evolution of galaxy clusters taking into account merging when the relative velocities of the colliding galaxies are low. In particular, we study the evolution of the structure, mass spectrum, and velocity spectrum of a cluster of a thousand galaxies, as well as the growth of the central supermassive cD galaxy. The initial velocity dispersion of the galaxies and the rotation of the cluster were taken into account. The observed logarithmic spectrum dN ～ \(\tfrac{{dM}}{M}\) was adopted as the initial mass spectrum. The dynamical evolution of galaxy clusters, allowing for the possible merging of colliding galaxies, results in the emergence of a central supermassive galaxy, whose mass continuously increases due to mergers. This occurs only if the mass of the central galaxy becomes greater than ～0.1 of the total mass of the cluster. The observation of cD galaxies with relative masses of ～0.01 suggests that they initially formed in the cluster core, merged with nearby galaxies, and accreted intergalactic gas. The model indicates that a logarithmic galaxy mass spectrum is preserved during the cluster evolution, despite the substantial decrease in the number of galaxies in the cluster with time. The model can also reproduce the observed mass distribution with distance from the cluster center, M r ～ r 1.7.  相似文献   

6.
Lower limits for the percentages of stars with various luminosities in the cores of six globular clusters are derived using stellar spatial density distributions f(r) to deep limiting B magnitudes obtained earlier. For NGC 6535 and NGC 5466, the logarithmic density range and Kholopov parameters Df and Dr are also determined. These two parameters are correlated with the mean masses of stars of various subsystems and the total mass (number) of stars in the cluster.  相似文献   

7.
We have modeled the dynamical evolution of small stellar groups with N=6 components in the framework of the gravitational N-body problem, taking into account possible mergers of stars and ejection of single and binary stars. We study the influence of the initial global parameters of the systems (the mass spectrum, average size, virial factor) on their dynamical evolution. The distribution over states is analyzed for a time equal to 300 initial crossing times of the system. The parameters of binary and stable triple systems that form are studied, as well as the properties of ejected single and binary stars. The rate of dynamical evolution in both expanding and contracting groups is higher than in systems in a state of virial equilibrium. The dynamical evolution is more intense in the case of unequal masses than when the system initially consists of equal-mass stars. In most cases, the evolution of a group ends with the formation of a binary or stable triple system. The semimajor axes of the binaries range from several hundredths to several times the initial size of the system. The distribution of the eccentricities of the binaries formed is consistent with an f(e)=2e law. When the initial size of the group is small, the number of final binaries with large eccentricities, and also of stable triple systems with elongated inner-binary orbits, decreases due to merging. As a rule, stable triple systems are substantially hierarchical (the average ratio of the semimajor axes of the inner and outer binaries is 1: 20). On average, the eccentricities of the inner binaries exceed those of the outer binaries: they are equal to \(\overline {e_{in} } \approx 0.7\) and \(\overline {e_{ex} } \approx 0.5\), respectively. The velocities of ejected stars are from several to several tens of km/s, and tend to increase as the initial size of the system, and hence its virial coefficient, decreases.  相似文献   

8.
A CCD BV R photometric study of the central region (15″ ≤ r ≤ 100″) of the globular cluster NGC 7006 based on color-magnitude diagrams is presented. We find for the main parameters of the cluster [Fe/H] = ?1.62, Y = 0.21, E B?V = 0.15 m , V HB = 18.84 m , M V HB =+0.56 m , R ⊙ = 37.1 kpc). Two previously unknown RR Lyr variables were discovered in the central region of the cluster. The morphological index of the horizontal branch for the entire region studied indicates that the red stellar population dominates, consistent with previous studies: HB mi = ?0.13. Such anomalously negative morphological indices are possessed by a whole group of Ool clusters with intermediate metallicities, which also display a characteristic distribution of stars along the horizontal branch. There is a radial dependence for the horizontal-branch morphology, with the color becoming primarily blue with approach toward the cluster center. One possible origin for this behavior could be the effect of inner dynamical processes on the spatial distribution of hot stars.  相似文献   

9.
The non-LTE sodium abundances of 100 stars with metallicities ?3<[Fe/H]<0.3 are determined using high-dispersion spectra with high signal-to-noise ratios. The sodium abundances [Na/Fe] obtained are close to the solar abundance and display a smaller scatter than values published previously. Giants (logg<3.8) with [Fe/H]g>3.8) with metallicities ?2<[Fe/H]相似文献   

10.
Spectroscopic and photometric data for the two rapidly rotating members of the α Persei cluster He 373 and AP 225 are analyzed. Improved estimates have been obtained for the projected equatorial rotation velocities: v sin i = 164 km/s for He 323 and v sin i = 129 km/s for AP 225. Multi-band photometric mapping is used to map the spot distributions on the surfaces of the two stars. The fractional spotted areas S and mean temperature difference ΔT between the unspotted photosphere and the spots are estimated (S = 7% and ΔT = 1000 K for He 373; S = 9% and ΔT = 800 K for AP 225). The H α line profiles of both stars have variable emission components whose widths are used to deduce the presence of extended regions of emission reaching the corotation radius.  相似文献   

11.
Observations of the K2 continuation of Kepler Space Telescope program are used to estimate the spot coverage S (the fractional spotted area on the surface of an active star) for stars of the Pleiades cluster. The analysis is based on data on photometric variations of 759 confirmed clustermembers, together with their atmospheric parameters, masses, and rotation periods. The relationship between the activity (S) of these Pleiades stars and their effective temperatures shows considerable change in S for stars with temperatures T eff less than 6100 K (this can be considered the limiting value for which spot formation activity begins) and a monotonic increase in S for cooler objects (a change in the slope for stars with Teff ~ 3700 K). The scatter in this parameter ΔS about its mean dependence on the (V ?Ks)0 color index remains approximately the same over the entire (V?K s )0 range, including cool, fully convective dwarfs. The computated S values do not indicate differences between slowly rotating and rapidly rotating stars with color indices 1.1 < (V?K s )0 < 3.7. The main results of this study include measurements of the activity of a large number of stars having the same age (759 members of the Pleiades cluster), resulting in the first determination of the relationship between the spot-forming activity and masses of stars. For 27 stars with masses differing from the solarmass by nomore than 0.1M⊙, themean spot coverage is S = 0.031±0.003, suggesting that the activity of candidate young Suns is more pronounced than that of the present-day Sun. These stars rotate considerably faster than the Sun, with an average rotation period of 4.3d. The results of this study of cool, low-mass dwarfs of the Pleiades cluster are compared to results from an earlier study of 1570 M stars.  相似文献   

12.
Equations of motion containing a small parameter μ are derived for stars at the peripheries of open star clusters. The parameter μ is obtained for six numerical open-cluster models. The general analytical solution of these equations of motion for μ = 0 is found. An iterative method is used to derive the frequencies of the stellar motions for first-order expansions in μ of the solutions of the equations of motion for stars at the cluster periphery. Applications of the results are discussed.  相似文献   

13.
We analyze the distribution of close binary stars in the orbital semimajor axis—primary mass plane. The reduced spatial density of stars with semimajor axes below 10R⊙ is confirmed. We identify the area in this plane occupied by precursors of W UMa stars, assuming that the driving force causing the components to approach each other is their magnetic stellar wind. This scenario enables us to estimate the rate of formation (0.02/year) and lifetime (108 yr) of W UMa stars. We derive a theoretical estimate of the ratio of the number of blue stragglers, N BS , and of horizontal-branch stars, N HB , in globular clusters based on the hypothesis that all blue stragglers are the result of component mergers in W UMa contact binaries. This ratio is N BS /N HB =0.4, close to the observed value for 62 Galactic globular clusters. We discuss possible reasons for the considerable dispersion of the observed estimates of this ratio for different clusters in our Galaxy.  相似文献   

14.
A dynamical estimate of the mass of the black hole in the LMC X-1 binary system is obtained in the framework of a Roche model for the optical star, based on fitting of the He I 4471 Å and He II 4200 Å absorption lines assuming LTE. The mass of the black hole derived from the radial-velocity curve for the He II 4200 Å line is mx = 10.55 M⊙, close to the value found earlier based on a model with two point bodies [1].  相似文献   

15.
The space velocities from the catalog of Nordstr?m et al. (2004) are used to trace variations of a number of kinematic parameters of single F and G dwarfs as a function of their age. The vertex deviation of disk stars increases from 7° ± 1° to 15° ± 2° as the mean age decreases from 4.3 to 1.5 Gyr. The two-dimensional velocity distributions in the UV, UW, and VW planes are analyzed. The evolution of the main peaks in the velocity distributions can be followed to an average age of ≈9 Gyr. We find that: (1) in the distributions of the UV velocity components, stars of different types are concentrated toward several stable peaks (the Hyades, Pleiades, and Sirius Cluster), suggesting that the stars belonging to these formations did not form simultaneously; (2) the peak associated with the Hyades Cluster dominates in all age intervals; and (3) the Hyades peak is strongest for stars with an average age of 1.5 Gyr, suggesting that this peak contains a considerable fraction of stars from the Hyades cluster. The age dependences of the kinematic parameters exhibit a break near ≈4–5 Gyr, which can be explained as an effect of the different contributions of stars of the thin and thick disks. The Stromberg relation yields a solar LSR velocity of V ⊙LSR = (8.7, 6.2, 7.2) ± (0.5, 2.2, 0.8) km/s.  相似文献   

16.
We have obtained the stellar velocity dispersion in three mutually perpendicular directions in the halos and cores of clusters as a function of time for several non-stationary open-cluster models. During the dynamical evolution of the open-cluster models, the velocity dispersions undergo oscillations that do not decay during 5–10 violent-relaxation timescales, τ vr . We estimated the time for synchronization of the rotation of the open-cluster models and their motion around the center of the Galaxy, t s , which, depending on the model parameters, is t s ? (5–27)τ vr . Synchronization mechanisms for the models are discussed. The disruption of the systems in the force field of the Galaxy is strongly affected by tidal friction. We have also estimated the time for the formation of a spherical stellar-velocity distribution in the cluster models, t σ ? (6 ? 25)τ vr . The impact of instability in the stellar motions in a cluster on the formation of a spherical velocity distribution in the open-cluster models is discussed. We have noted a tendency for a weakening of the dependence of the coarse phase density of the cluster on small initial perturbations of the stellar phase coordinates in the model cluster cores for times about five times longer than the violent-relaxation time.  相似文献   

17.
The dynamical stability of 16 multiple stars is analyzed using Monte Carlo simulations with allowance for the errors in the observational data. The analysis was carried out by varying the uncertainties in the initial observational data. Six different stability criteria were considered, and the dynamical evolution was studied using numerical simulations. Eleven of the systems are probably stable, whereas five systems (HD 40887, HD 136176, HD 150680, HD 217675, and HD 222326) are probably unstable (the probability that they are unstable is 0.94 or more accordingt o the results of forward and backward simulations over intervals of 106 yr). The results of the simulations were most consistent with the criteria of Mardling-Aarseth (the correlation coefficient between the probabilities of disruption inferred from the stability criterion and numerical integration was r = 0.998), Valtonen-Karttunen (r = 0.998), and Eggleton-Kiseleva (r = 0.997). In about 92–93% of all cases, these criteria yield results that are consistent with the numerical simulations. These criteria also yield high disruption probabilities for the unstable systems. Scenarios for the formation of such systems are discussed: temporary capture of a field star by a close binary, perturbation of a stable multiple system by a massive field object, and disruption of small stellar groups or clusters. The probabilities that these scenarios are realized are analyzed.  相似文献   

18.
The sequence of events determining the initial stages of star formation is analyzed in framework of the self-enrichment scenario. The computations are based on a single-zone chemo-dynamical model. It is shown that the first episode of star formation was characterized by an initial mass function shifted toward massive stars (M ≥ 8M⊙). We argue that the transition to a star formation with a normal (Salpeter) initial mass function was due to more efficient radiative cooling of the proto-globular cluster gas after its enrichment to a metallicity of Z ～ 0.02 Z⊙ in agreement with those observed in globular clusters.  相似文献   

19.
We have modeled the magnetic fields of the slowly rotating stars HD 116458 and HD 126515 using the “magnetic charge” technique. HD 116458 has a small angle between its rotation axis and dipole axis (β = 12°), whereas this angle is large for HD 126515 (β = 86°). Both stars can be described with a decentered-dipole model, with the respective displacements being r = 0.07 and r = 0.24 in units of the stellar radius. The decentered-dipole model is able to satisfactorily explain the phase relations for the effective field, Be(P), and the mean surface field, Bs(P), for both stars, along with the fact that the Be(P) phase relation for HD 126515 is anharmonic. We discuss the role of systematic measurement errors possibly resulting from instrumental or methodical effects in one or both of the phase relations. The displacement of the dipole probably reflects real asymmetry of the stellar field structure, and is not due to measurement errors. Using both phase relations, Be(P) and Bs(P), in the modeling considerably reduces the influence of the nonuniform distribution of chemical elements on the stellar surface.  相似文献   

20.
A method for estimating the spottedness parameter S (the spotted area as a fraction of the surface of an active star) proposed earlier is applied to an analysis of activity in 1570 M dwarf stars. The analysis is based on observational material obtained with the Kepler Space Telescope, as well as data on the fluxes of the studied objects in the near and far ultraviolet (NUV and FUV) based on data from the GALEX space telescope. The variations of S with the ages of the stars are studied (four groups with different ages are distinguished), as well as variations of S with their rotational periods. A diagram characterizing the relationship between S and the Rossby number Ro resembles the classical dependence of the X-ray luminosities of active stars on Ro, and a saturation regime is attained at the same value, Ro = 0.13. Moreover, objects with ages of more than 100 million years do not form a single sequence (and stars older than 900 million years possess surface spottednesses of order 1%). The S?Ro dependence obtained could expand possibilities for analyzing the dependence of the X-ray luminosities of active stars on their Rossby numbers, and could also be applied to refine parameters characterizing the action of dynamo mechanisms, such as the dynamo number N D . A comparison of the GALEX NUV and FUV brightness estimates with the activity parameters of the stars suggests that younger, more rapidly rotating active stars are brighter in the NUV, and that the FUV flux grows and the difference of the FUV and NUV brightnesses decreases with increasing spottedness S.  相似文献   

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