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1.
Slitless spectroscopy is used to discover 22 emission stars in the central and northwest regions of the cluster located in the NGC 7129 nebula. 16 of them are found for the first time. This sample is essentially complete up to V 20.0. The emission stars are distributed nonuniformly over the field of the cluster and are concentrated toward its center. Photometry in the V, R, and I bands is conducted on more than a hundred stars in the cluster. This yields an average absorption coefficient A V=1.7±0.27 for this region. Based on their positions in color diagrams for the optical and near IR ranges, most of the emission stars can be regarded as T Tau objects.  相似文献   

2.
From a new infrared photometry of the globular cluster M10 its interstellar extinction and distance modulus are discussed. This is done by comparison with the well-studied clusters M3, M13, and M92. Final values ofE(B-V)=0.17±0.05 and (M v-V)=14.0±0.3 are proposed. The dependence on metallicity of these values is briefly discussed.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   

3.
We obtained the luminosity function from the Main-Sequence turnoff region to the subgiants for M15 (V=17.0–19.6), using plates taken by the Kitt Peak 4 m reflector. The measured region isr=2.5–8.0 zone. We extrapolated the star counts to the cluster center and to the tidal limit, using King's (1966) photometry, Kinget al.'s (1968) counts, Peterson and King's (1975) result, and Simoda and Iben's (1970) theoretical results.The comparison of the observed function with the theoretical ones by Simoda and Iben (1970) indicates that the observation is consistent with the theory forX0.9±0.1, thus marginally inconsistent with the Big Bang cosmology value (X=0.76). The comparison with Bertelliet al. (1970) theoretical ones gives contradictory results. Possible causes of this problem are the improper extrapolation of star counts to the cluster center and/or the inaccuracies of the theoretical luminosity functions so far published, and/or the impropriety of the canonical structure and evolution theory of Population II stars. In the last two cases, the ages and the helium abundances of globular clusters may vary.We also obtained the luminosity function for blue horizontal branch stars fromV=17.0 to 19.6.Kitt Peak National Observatory, U.S.A., which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.  相似文献   

4.
Thirty stars in the direction of the open cluster NGC 6996 are measured in the Vilnius photometric system. Photometric spectral types, absolute magnitudes, interstellar reddenings, extinctions, and distances are determined for most of them. Fifteen stars are suspected to be cluster members. Their mean distance is 620±30 pc and mean extinctionA v is 1.74 mag. The extinction within the cluster is variable. The age of the cluster is of the order of 108 yr and this excludes the possibility that it is evolutionary related with the North America and Pelican Nebulae complex. The distance of this complex 550 pc is confirmed.  相似文献   

5.
Using a method which will be explained in detail by Steenman and Thé (1989) the extinction law towards several stars indicating the distance of the Chamaeleon dark cloud was determined. This has also been done for HD 97048 and HD 97300, which turn out to be anomalous with a ratio of total to selective extinctionR5.0. In studies involving the distance of the Chamaeleon dark cloud we propose to use 150±15 pc. The extinction-free spectral energy distribution of HD 97300 does not show the presence of a hot dust shell of 2750 K, which was found by Théet al. (1986) in a previous study.Based in part on observations made at the ESO, La Silla, Chile.  相似文献   

6.
Results ofUBV photoelectric photometry in NGC 5138 are presented for 50 stars brighter than 14.0 mag. In addition, four probable red giants were also observed in the DDO system. Sixteen stars previously considered members by Lindoff (1972), were found not to be physically connected with the cluster. NGC 5138 is located 1.80 kpc from the Sun and the visual interstellar absorption determined from the reddenedB stars amounts toA v =0.75 mag. Three of the four red stars observed in the DDO system were found to be cluster members. The mean cyanogen anomaly is CN=0.043±0.018 (m.e.), which implies that NGC 5138 is richer in CN than the field K giants in the solar neighbourhood, but poorer than the Hyades giants. The cluster age is estimated to be 1.5×108 yr.Member of the Carrera del Investigador Cientifico del Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, and visiting astronomer, Cerro Tololo Inter-American Observatory, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.  相似文献   

7.
The stellar field centred close to theh and Per double cluster is one of the 123 fields recorded in the galactic plane at 2000 Å by the balloon-borne stratospheric gondola of the SCAP-2000 programme. The analysis of the frame allows us to determine an ultraviolet colour indexU 1-V for more than 600 stars. Among these are stars belonging to theh and Per and Tr 2 clusters and to the PER OB1 association. The prevailing extinction law is found to produce greater extinction at 1965 Å than predicted by the mean extinction law. Moreover, the clouds responsible for the extinction are situated in the local arm and distributed in two layers with a very transparent interval. The comparison of theA v extinction and theHI and CO abundances leads us to assume the presence of a H2 cloud in front ofh and Per, in the second absorbing layer and, therefore, in the local arm. The two absorbing layers and the molecular cloud are perhaps in the plane of the Gould belt and associated with the expanding gas detected by Lindblad. A group of hot stars centred at the same distance as this molecular cloud has been detected and could form an association of OB stars in the local arm. Other, much more distant OB stars belonging to the Perseus arm of Efremov's list. Several stars which must have a very hot companion are detected in the field.  相似文献   

8.
Interstellar extinction curves obtained from the ‘extinction without standard’ method were used to constrain the dust characteristics in the mean ISM (R V = 3.1), along the lines of sight through a high latitude diffuse molecular cloud towards HD 210121 (R V = 2.1) and in a dense interstellar environment towards the cluster NGC 1977 (R V = 6.42). We have used three-component dust models comprising silicate, graphite and very small carbonaceous grains (polycyclic aromatic hydrocarbons) following the grain size distributions introduced by Li & Draine in 2001. It is shown that oxygen, carbon and silicon abundances derived from our models are closer with the available elemental abundances for the dust grains in the ISM if F & G type stars atmospheric abundances are taken for the ISM than the solar. The importance of very small grains in modelling the variation of interstellar extinction curves has been investigated. Grain size distributions and elemental abundances locked up in dust are studied and compared at different interstellar environments using these three extinction curves. We present the albedo and the scattering asymmetry parameter evaluated from optical to extreme-UV wavelengths for the proposed dust models.  相似文献   

9.
A study of the background corona near solar minimum   总被引：2，自引：0，他引：2  
The white light coronagraph data from Skylab is used to investigate the equatorial and polarK andF coronal components during the declining phase of the solar cycle near solar minimum. Measurements of coronal brightness and polarization brightness product between 2.5 and 5.5R during the period of observation (May 1973 to February 1974) lead to the conclusions that: (1) the equatorial corona is dominated by either streamers or coronal holes seen in projections on the limb approximately 50% and 30% of the time, respectively; (2) despite the domination by streamers and holes, two periods of time were found which were free from the influences of streamers or holes (neither streamers nor holes were within 30° in longitude of the limb); (3) the derived equatorial background density model is less than 15% below the minimum equatorial models of Newkirk (1967) and Saito (1970); (4) a spherically symmetric density model for equatorial coronal holes yields densities one half those of the background density model; and (5) the inferred brightness of theF-corona is constant to within ±10% and ±5% for the equatorial and polar values, respectively, over the observation period. While theF-corona is symmetric at 2R it begins to show increasing asymmetry beyond this radius such that at 5R the equatorialF-coronal brightness is 25% greater than the polar brightness.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

10.
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11.
RecentUBV photometry of the RS CVn binary CF Tuc is discussed and analysed. If we combine the results with previously published spectroscopy we find radii of 1.63R for the hotter (6000 K) and 3.11R for the cooler (4500 K) component; both stars having a mass of about 1.3M . The distance to the system is put at 86±15 pc.Though the photometric data is incomplete in the coverage of some regions out of the minima, there is no significant evidence of the wave-type distortions — a known hallmark of RS CVn stars — and the data can be modeled by a standard eclipsing binary system in which the statistical test of goodness-of-fit (2) produces quite acceptable values for reasonable estimates of observational accuracy (0.01 mag). We, therefore, have no need to postulate any additional photometric complications, and feel entitled to some confidence in the reliability of the derived parameter set.  相似文献   

12.
R. P. Kane 《Solar physics》1989,122(1):175-185
The 12-month running mean of the geomagnetic index aa seems to have attained a minimum value of 17.5 centered at December 1986. The fresh estimate of R z (max) is now 165 ± 35. Also, if R z (min) is taken into consideration, the R z (max) estimate will drop to 130. Details of the methodology and the data used are presented.  相似文献   

13.
Physical parameters and radial pulsation modes are determined for three Delta Scuti stars in the Praesepe cluster: HD 73345, HD 73712, and HD 73746. Their agest and evolutionary massesM eare interpolated in the track systems of Iben (1967) and Paczyski (1970). By combining these age estimates with our previous results for nine other Delta Scuti-stars in the Praesepe cluster (Tsvetkov, 1989), the following weighted mean age estimates of this cluster are obtained: (14.2 ± 1.3) × 108 yr (Iben) and (5.4 ± 0.4) × 108 yr (Paczyski). Age and evolutionary mass estimates of the twelve cluster variables are also obtained in the modern track system of Maeder and Meynet (1988), in which the weighted mean cluster age is (15.3 ± 1.0) × 108 yr.Pulsation massesM Qcalculated from the fitting formulae of Faulkner (1977) and Fitch (1981) as well as massesM g=gR 2 / G were evaluated for the twelve cluster variables by Tsvetkov (1990) or in the present paper. In most cases there is a satisfactory agreement between our estimates of massesM e,M g, andM Q.Due to a large disagreement between the long period and low luminosity of the star HD 73746, its radial pulsation mode and pulsation massM Qcannot be evaluated.  相似文献   

14.
Summary Binary stars are the main source of fundamental data on stellar masses and radii (M, R). Considerable progress has been made in recent years in the quality and quantity of such data, and stellar masses and radii of high accuracy have led to a number of qualitatively new and interesting results on the properties and evolution of normal stars. This paper reviews the current status of fundamentalM andR determinations which (i) have errors 2%, the limit for non-trivial results in many applications, and (ii) can be presumed valid for single stars. These two conditions limit the discussion to data fromdetached, doublelined eclipsing binary systems.After a brief discussion (Sect. 2) of the main tests for accuracy and consistency which must be met for observational data to be included in the sample, data for 45 binary systems (90 single stars) are presented in Sect. 3 (Table 1 and Figs. 2–5). Spectral types are O8-M1 on the main sequence, with only two stars clearly in the red-giant region. From the review by Popper (1980), data for only 6 systems survive unchanged in the present list, while improved data are given for 18 systems; 21 systems are new additions. Broadband colours, effective temperatures, and luminosities are also given, but are scale-dependent and considerably less reliably determined thanM andR.The observed ranges inM andR for a given colour far exceed the observational errors, primarily due to evolutionary effects within the main sequence. For this reason, single-parameter relations used to predictM andR for single stars are limited to an accuracy of some ±15% inM and ±50% inR, basically independent of the number and accuracy of the data used to establish the relations. Two-parameter calibrations are discussed (Sect. 4) which can eventually reduce these errors to & 5% in bothM andR. At this level, abundance effects become significant and presumably account for the residual scatter.Comparison of the data with stellar evolution models is the topic of Sect. 5. Characteristic features of the data which are crucial in such work are emphasized, rather than attempts to prove the validity of any particular set of models. Already fromM andR alone, some significant constraints can be derived (Fig. 4). When bothM, R, andT e are known, the initial helium abundanceY can be estimated if the metal-abundance parameter Z is assumed or determined. Studies in which binaries with accurate values ofM, R, and Z are fit by models calculated for the precise observed masses, and withY and mixing length constrained to solar values, provide the most stringent tests of the models. Probing further model refinements such as convective overshooting requires full use of the potential of the data. For example, models may yield general main-sequence limits which are consistent with the observations, but still be unable to fit any single system to the precision of the data. Conditions for critical, informative tests are discussed. Tidal effects in binaries are briefly discussed in Sect. 6. As tidal forces are extremely sensitive to the dimensions and internal structure of the stars, the present sample is well suited for such studies. Recent success in matching computed and observed apsidal-motion parameters for early-type binaries is mentioned. Finally, main priorities for future work are outlined.  相似文献   

15.
The ratio of total to selective absorbtion,R, has been found to remain constant as dust is processed in clouds from low to high density, through Hii regions and open clusters, and returned to the interstellar medium.R has the same value in dense dust clouds as it has in Hii regions of different ages. Variations inR values obtained from stars in Hii regions may be due to errors in special type classification. Globular cluster diameters show no tendency to increase with distance from the Sun whenR=3.2 is used. Large grains evidently do not exist in the interstellar medium. There is no evidence for neutral extinction in the Galaxy at large.  相似文献   

16.
Photographicuvby photometry of 15 stars in the open cluster M52 (NGC 7654) has been obtained. The distance modulusV o–M v=11.3±0.1 and mean cluster reddeningE(B–V)=0.57 are determined. Some basic physical characteristics of 30 stars with observeduvby values are obtained as well as a numerical estimation of the open cluster age 9.6×107 yr is made.  相似文献   

17.
Using the discrete dipole approximation, we have calculated the extinction efficiency of hollow spherical particles of graphite as a possible constituent of interstellar grains. The particles had a shell structure with the basal plane perpendicular to the radius. The calculations were made on the particles having the outer radiusR 0=10 and 5nm in the wave number region from 0.8 to 8.0 m–1 using the anisotropic optical constants. It was found that the hollow particles with the inner radiusR 10.65R 0 yield an extinction feature at 4.6 m–1, which fits fairly well to one observed in the interstellar extinction.  相似文献   

18.
Preliminary results on new CCD photometry inV andB bands of approximately 5000 stars in four overlapping fields in the globular cluster M3 are presented. The colour-magnitude diagram shows a very well-defined sequence with a small scatter, going fainter than previously published work on this cluster. The turn-off point found atV=19.1±0.2 mag and (B-V)=0.445±0.01, is slightly redder than those obtained in previous studies.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   

19.
Because of the bimodal distribution of sunspot cycle periods, the Hale cycle (or double sunspot cycle) should show evidence of modulation between 20 and 24 yr, with the Hale cycle having an average length of about 22 yr. Indeed, such a modulation is observed. Comparison of consecutive pairs of cycles strongly suggests that even-numbered cycles are preferentially paired with odd-numbered following cycles. Systematic variations are hinted in both the Hale cycle period and R sum (the sum of monthly mean sunspot numbers over consecutively paired sunspot cycles). The preferred even-odd cycle pairing suggests that cycles 22 and 23 form a new Hale cycle pair (Hale cycle 12), that cycle 23 will be larger than cycle 22 (in terms of R M, the maximum smoothed sunspot number, and of the individual cycle value of R sum), and that the length of Hale cycle 12 will be longer than 22 yr. Because of the strong correlation (r = 0.95) between individual sunspot cycle values of R sum and R M, having a good estimate of R Mfor the present sunspot cycle (22) allows one to predict its R sum, which further allows an estimation of both R Mand R sum for cycle 23 and an estimation of R sum for Hale cycle 12. Based on Wilson's bivariate fit (r = 0.98), sunspot cycle 22 should have an R Mequal to 144.4 ± 27.3 (at the 3- level), implying that its R sum should be about 8600 ± 2200; such values imply that sunspot cycle 23 should have an R sum of about 10500 ± 2000 and an R Mof about 175 ± 40, and that Hale cycle 12 should have an R sum of about 19100 ± 3000.  相似文献   

20.
Pioneer 11 magnetic field data at 20 AU are analysed by the computational method of Moussas, Quenby, and Webb (1975), Moussas and Quenby (1978), and Moussas, Quenby, and Valdes-Galicia (1982a, b) to obtain the parallel mean free path , and the diffusion coefficient parallel to the magnetic field line K . This method is the most appropriate for the mean free path calculation at large heliodistances since the alternative method which is based on fitting of energetic particle intensities cannot be easily and accurately be used because the association of energetic particles with their parent flares is not precise. The results show that the mean free path has values between 0.85 and 0.98 AU, linearly increasing with energy according to (Tkinetic) = + MT, where = 0.846 AU and M = 4.44 × 10 –5 AU MeV–1 for energies between 10 MeV and 3 GeV for protons. These values of the parallel mean free path are much larger than the values estimated by previous studies up to 6 AU. The diffusion coefficient dependence upon energy follows a relation which simply reflects an almost constant mean free path and a linear dependence on the velocity of the particle, so that at 20 AU heliodistance K (T kin) = K , 1 MeV(T kin)T kinetic , with = 1/2. The distance dependence of the parallel diffusion mean free path follows a power law, (R) = , 1 AU R , where is 1 ± 0.1. While the parallel diffusion coefficient obeys a power-law relation with heliodistance R, K (R, T kin) = K , 1 AU(T kin)R , with = 1 ± 0.1. The radial diffusion coefficient of cosmic rays is not expected to strongly depend upon the parallel diffusion coefficient because the nominal magnetic field at these large heliodistances (20 AU) is almost perpendicular to the radial direction and the contribution of the diffusion coefficient perpendicular to the magnetic field is expected to play a dominant role. However, the actual garden hose angle varies drastically and for long time periods and hence the contribution of the diffusion parallel to the field may continue to be important for the small scale structure of intensity gradients.  相似文献   

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