Optical monitoring of the central region of the globular cluster M 15 = NGC 7078: New variable stars     

A. P. Zheleznyak  V. V. Kravtsov 《Astronomy Letters》2003,29(9):599-611

We obtained a series of more than two hundred R-band CCD images for the crowded central (115″×77″) region of the metal-poor globular cluster M 15 with an angular resolution of \(0\mathop .\limits^{''} 5 - 0\mathop .\limits^{''} 9\) in most images. Optimal image subtraction was used to identify variable stars. Brightness variations were found in 83 stars, 55 of which were identified with known cluster variables and the remaining 28 are candidates for new variables. Two of them are most likely SX Phe variables. The variability type of two more stars is uncertain. The remaining stars were tentatively classified as RR Lyrae variables. A preliminary analysis of published data and our results shows that the characteristics of RR Lyrae variables in the densest part (r<35″) of the cluster probably change. More specifically, the maximum of the period distribution of first-and second-overtone (RR1, RR2) pulsating stars shifts toward shorter periods; i.e., there is an increase in the fraction of stars pulsating with periods \( < 0\mathop .\limits^d 3\) and a deficiency of stars with \(0\mathop .\limits^d 35 - 0\mathop .\limits^d 40\). The ratio of the number of these short-period RR Lyrae variables to the number of fundamental-tone (RR0) pulsating variables changes appreciably. We found and corrected the error of transforming the coordinates of variables V128–155 in M 15 into the coordinate system used in the catalog of variable stars in globular clusters.  相似文献   

Present Observational Status of High Mass Pulsating Stars     

Peter De Cat 《Astrophysics and Space Science》2003,284(1):37-44

In this short review we present the current observationalstatus of high mass pulsating stars.We give an overview of the results of the first asteroseismicstudies performed for some of the best known Cepheiand slowly pulsating B stars and discuss the asteroseismicpotential of these pulsators for future ground-and space-based data-sets.  相似文献   

Characterization of intermittent chaos and oscillating frequencies in some pulsating stars     

Fusheng Chen  Jiulin Du  Shiyang Jiang 《Astrophysics and Space Science》1994,218(1):101-111

If one zone models are available for some pulsating stars and the motion remains close to adiabaticity, we show the existence of odd frequencies in the power spectrum of these pulsating variable stars, and the frequency of free oscillation thus becomes dependent on the amplitude. We find 3 appearing in the power spectrum of the white dwarf PG 1351+489. Furthermore, the intrinsic stochasticity in the basic equations describing the structure of stars is discussed in this paper. We found that the pulsation of intermittent chaos can occur spontaneously in the basic equations of a star within certain intervals of values of its control parameters, and the intermittency can be used as an interpretation of pulsation in variable stars.  相似文献   

EXOTIME: searching for planets around pulsating subdwarf B stars     

Sonja Schuh  Roberto Silvotti  Ronny Lutz  Björn Loeptien  Elizabeth M. Green  Roy H. Østensen  Silvio Leccia  Seung-Lee Kim  Gilles Fontaine  Stéphane Charpinet  Myriam Francœur  Suzanna Randall  Cristina Rodríguez-López  Valerie van Grootel  Andrew P. Odell  Margit Paparó  Zsófia Bognár  Péter Pápics  Thorsten Nagel  Benjamin Beeck  Markus Hundertmark  Thorsten Stahn  Stefan Dreizler  Frederic V. Hessman  Massimo Dall’Ora  Dario Mancini  Fausto Cortecchia  Serena Benatti  Riccardo Claudi  Rimvydas Janulis 《Astrophysics and Space Science》2010,329(1-2):231-242

In 2007, a companion with planetary mass was found around the pulsating subdwarf B star V391 Pegasi with the timing method, indicating that a previously undiscovered population of substellar companions to apparently single subdwarf B stars might exist. Following this serendipitous discovery, the EXOTIME (http://www.na.astro.it/~silvotti/exotime/) monitoring program has been set up to follow the pulsations of a number of selected rapidly pulsating subdwarf B stars on time scales of several years with two immediate observational goals:

1. determine $\dot{P}$ of the pulsational periods P
2. search for signatures of substellar companions in O–C residuals due to periodic light travel time variations, which would be tracking the central star’s companion-induced wobble around the centre of mass

These sets of data should therefore, at the same time, on the one hand be useful to provide extra constraints for classical asteroseismological exercises from the $\dot{P}$ (comparison with “local” evolutionary models), and on the other hand allow one to investigate the preceding evolution of a target in terms of possible “binary” evolution by extending the otherwise unsuccessful search for companions to potentially very low masses. While timing pulsations may be an observationally expensive method to search for companions, it samples a different range of orbital parameters, inaccessible through orbital photometric effects or the radial velocity method: the latter favours massive close-in companions, whereas the timing method becomes increasingly more sensitive toward wider separations. In this paper we report on the status of the on-going observations and coherence analysis for two of the currently five targets, revealing very well-behaved pulsational characteristics in HS?0444+0458, while showing HS?0702+6043 to be more complex than previously thought.  相似文献   

δ Scuti Pulsations in Pre-main Sequence Stars     

Claude Catala 《Astrophysics and Space Science》2003,284(1):53-60

Intermediate mass pre-main sequence stars (1.5 to 5 M )cross the instability strip on their way to the main sequence.They are therefore expected to be pulsating in a similar way as the Scuti stars. In this review, I present the status of observational studies ofpulsations in these stars, and comment on prospects for futureinvestigations of these pulsations from the ground and from space.  相似文献   

Nonlinear pulsations of red supergiants     

Yu. A. Fadeyev 《Astronomy Letters》2012,38(4):260-270

Excitation of radial oscillations in population I (X = 0.7, Z = 0.02) red supergiants is investigated using the solution of the equations of radiation hydrodynamics and turbulent convection. The core helium burning stars with masses 8M _⊙ ≤ M ≤ 20M _⊙ and effective temperatures T _eff < 4000 K are shown to be unstable against radial pulsations in the fundamental mode. The oscillation periods range between 45 and 1180 days. The pulsational instability is due to the κ-mechanism in the hydrogen and heliumionization zones. Radial pulsations of stars with mass M < 15M _⊙ are strictly periodic with the light amplitude ΔM _bol ≤ 0?5. The pulsation amplitude increases with increasing stellar mass and for M > 15M _⊙ the maximum expansion velocity of outer layers is as high as one third of the escape velocity. The mean radii of outer Lagrangean mass zones increase due to nonlinear oscillations by ≤30% in comparison with the initial equilibrium. The approximate method (with uncertainty of a factor of 1.5) to evaluate the mass of the pulsating red supergiant with the known period of radial oscillations is proposed. The approximation of the pulsation constant Q as a function of the mass-to-radius ratio is given. Masses of seven galactic red supergiants are evaluated using the period-mean density relation.  相似文献   

Population i pulsating stars     

Ts. G. Tsvetkov 《Astrophysics and Space Science》1989,151(1):47-71

On the basis of our age estimations of Population I pulsating stars in our Galaxy (Tsvetkov, 1986a), the mean ages of 6 open star clusters containing 21 Delta Scuti-variables and of 8 star clusters and associations containing 13 classical cepheids, have been evaluated. These mean cluster age estimations weighted according to the probabilities for different evolutionary phases of the pulsating stars, are obtained in the evolutionary track systems of Iben (1967) and Paczyski (1970); the cluster ages are larger in the former system. Our results are compared with those obtained from various methods by other authors. Clusters with classical cepheids and with Delta Scuti-stars have ages, respectively, in the ranges 10⁷–10⁸ years and 10⁶–10⁹ years. It is shown that the use of simple period-age(-colour) relations for Population I pulsating stars gives sufficiently accurate cluster age estimations. By use of our period-age relations for classical cepheids (Tsvetkov, 1986a), the mean ages of 56 other star clusters and associations in our Galaxy, the Magellanic Clouds, and M 31 galaxy have been estimated in both systems of tracks. The results are generally in agreement with those obtained from various methods by other authors. The use of Population I pulsating stars in star clusters and associations is one of the simplest and most easily applied methods for determining cluster ages; but there are some limitations in its application.  相似文献   

Population I pulsating stars     

Ts. G. Tsvetkov 《Astrophysics and Space Science》1985,117(2):227-243

Luminosities of Population I pulsating stars (Delta Scuti variables and classical cepheids) are investigated. From data for 80 Delta Scuti stars, semi-empirical period-luminosity-colour (P-L-C) relations and period-luminosity (P-L) relations are obtained for the four lowest modes of radial pulsations. The improvement of the accuracy of the stellar luminosity is determined when a P-L-C relation is used instead of the corresponding P-L relation. From data for 155 classical cepheids, empirical P-L relations are derived for short-period stars (logP1.1), long-period stars (logP>1.1), and s-cepheids. The comparison of the P-L relations for the two types of variable stars shows good agreement, but between them there is a gap with a dim nature.  相似文献   

Amplitude variations in pulsating sdB stars     

David Kilkenny 《Astrophysics and Space Science》2010,329(1-2):175-181

Frequency analyses over two or more seasons are presented for several pulsating sdB stars. These results indicate that amplitude variations in sdBV stars might be common and occur on timescales from less than a day to years. It is not clear whether such variations are a result of real amplitude modulation or of the fact that very close frequencies have not all been resolved. In either case, it would appear to be necessary to carry out reasonably extensive studies before one can claim to have resolved “all” frequencies, and to exhibit care before selecting frequencies for ‘ $\dot{P}$ ’ studies.  相似文献   

Two-dimensional high-resolution spectroscopy of quiet regions on the sun     

D. Bonaccini  G. Cauzzi  A. Falchi  R. Falciani  L. A. Smaldone 《Astrophysics and Space Science》1990,169(1-2):117-119

In this communication we briefly review the content of Cephei pulsating stars in young open clusters. The actual metallicity differences between clusters are suggested to be detectable as variations of the location of these stars in the photometric diagrams. We make a quantitative estimate of these differences and comment on the connections with the existence and possible determination of a metallicity gradient in the galactic plane.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

Population I pulsating stars     

Ts. G. Tsvetkov 《Astrophysics and Space Science》1986,128(2):319-339

Evolutionary masses corresponding to various evolutionary phases of Population I pulsating stars (89 Delta Scuti variables and 155 classical cepheids) are interpolated in the systems of tracks of Iben (1967) and Paczyski (1970). The evolutionary masses are larger in the latter system than in the former one. The uncertainty of the evolutionary mass of a star is estimated, when various evolutionary phases are possible for this star (a smaller evolutionary mass corresponds to a later phase). Semi-empirical period-evolutionary mass-colour (P-M _e -C) and period-evolutionary mass (P-M _e ) relations are derived for various modes, groups of stars, colour indices (and effective temperature), and evolutionary phases. For Delta Scuti stars, the uncertainty of evolutionary masses calculated from theP-M _e relations for different modes, is estimated. The improvement of the evolutionary mass accuracy is estimated, when aP-M _e -C relation is used instead of the correspondingP-M _e relation. The theoretical and semi-empirical period ratios of radial pulsations derived from theP-M _e relations for Delta Scuti stars, are compared. There is a relatively good agreement between theP-M _e relations for the two types of Population I pulsating stars, but a gap exists between them. The evolutionary masses of these stars are closer in the two systems of tracks and are derived with a relatively higher accuracy in comparison with their ages.  相似文献   

Period distributions in pulsating and binary stars     

R. J. Quiroga  J. C. Mello 《Astrophysics and Space Science》1992,193(2):247-267

We analyze the hypothesis of quantization in bands for the angular momenta of binary systems and for the maount of actionA _c in stable and pulsating stars. This parameter isA _c=Mv _eff R _eff, where the effective velocity corresponds to the kinetic energy in the stellar interior and the effective radius corresponds to the potential energyGM ²/R _eff. Analogous parameters can be defined for a pulsating star withm=M where is the rate of the massm participating in the oscillation to the total massM andv _osc,R _osc the effective velocity and oscillation radius.From an elementary dimensional analysis one has thetA _c (energy x time) (period)^1/3 independently ifA _c corresponds to the angular momentum in a binary system, or to the oscillation in a pulsating star or the inner energy and its time-scaleP _eff in a stable star.From evolving stellar models one has that P _effP _eff(solar)1.22 hr a near-invariant for the Main Sequence and for the range of masses 0.6M <M<1.6M .With this one can give scalesn _k=kn ₁ withk integers andn ₁=(P/P ₁)^1/3 withP ₁=P _eff1.22 hr. In these scales proportional toA _c, one sees that the periods in binary and pulsating stars are clustered in discrete unitsn ₁,n ₂,n ₃, etc.This can be seen in pulsating Scuti, Cephei, RR Lyrae, W Virginis, Cephei, semi-regular variables, and Miras and in binary stars as cataclysmic binaries, W Ursa Majoris, Algols, and Lyrae with the corresponding subgroups in all these materials. Phase functions (n _k) in RR Lyrae and Cephei are also associated with discrete levelsn _k.the suggested scenario is that the potential energies and the amounts of actionE _p(t), A_c(t) are indeed time-dependent, but the stars remain more time in determinated most proble states. The Main Sequence itself is an example of this. These most probable states in binary systems, or pulsating or stable stars, must be associated with velocities sub-multiplesc/ _F , given by the velocity of light and the fine structure constant.Additional tests for such a hypothesis are suggested when the sufficient amount of observational data are available. They can made with oscillation velocities in pulsating stars and velocity differences of pairs of galaxies.  相似文献   

Photoelectric radial velocities, Paper XVI 625 ninth-magnitude K0 stars in the six southern Clube Selected Areas     

R. F. Griffin  A. P. Cornell 《Monthly notices of the Royal Astronomical Society》2006,371(3):1140-1158

Paper XIII of this series presented radial velocities for 406 stars in certain of the Clube Selected Areas, a set of areas systematically arranged in Galactic coordinates. We now complete the survey by providing the radial velocities, mostly obtained at the European Southern Observatory (ESO), of 625 stars in the six southernmost Areas. Each star has been measured at least twice; the mean velocities have standard errors typically of 0.2–0.3 km s⁻¹. Additional observations made from Haute-Provence of many of the stars that are observable from there have helped to identify, and in some instances to characterize, the ∼70 spectroscopic binaries discovered in this programme. The final results of the programme, complementing those given in table 3 of Paper XIII, are summarized in Table 12 , which presents the mean velocities and velocity dispersions in the six southern Areas. It is noted that the difference between Paper XIII and this one as regards the provenance of the radial velocities has led to a small difference in zero-points, which is discussed in Section 3 and needs to be taken into account in any analysis of the combined data.