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1.
The open star cluster NGC 6067 was investigated by the strip method on charts of photographs with different exposure times taken with the 1-m Schmidt telescope of the European Southern Observatory. Because of the large distance (1820 pc) of the cluster its luminosity function is known up to date only betweenM v =–4.5 andM v =+1.5. In this paper it is continued toM v =4.4 and further extrapolated by means of 2 variants. The cluster contains 419 respectively 476 stars with total masses of 1453 resp. 1483. On account of its radius of 5.9 pc the cluster is a rather extended object, which can be described by the generalized density law of Schuster withn=4.42 and the central star density 8.9 stars pc–3. The mean velocity of the stars amounts to 1.03 km s–1, the massbrightness relation is 0.031 in solar units.

Mitteilungen Serie A.  相似文献   

2.
The young open star cluster M25 (IC 4725) is located in the direction of the galactic center, near much irregular absorption features on Sagittarius arm. This system is found to be at a distance of 600 pc, with a median age of 9.45 × 107 years and a distance from the galactic plane of –52.82 pc The mass data available in the literature has been gathered and many statistical methods have been applied for this cluster. Depending only on these methods, the stellar density, the distribution of dark matter, the luminosity and the mass functions have been estimated. The center of the cluster has been defined, it is shifted by 45 arc sec in the northeast direction. The radius of the cluster is found to be 4 pc. More than 220 stars with mean reddening of 0.50 mag and absorption of 1.62mag are found inside this aria. The total mass of the cluster has been estimated with the mass of the interstellar matter (gas and dust). It is found to be 1937 M ⊙, whereas about 24% of the material mass of the cluster has remained as interstellar matter after the processes of formation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
The dependence of interstellar extinction on distance in the direction of the dark cloud south of Merope is determined using photoelectric photometry of 93 stars in the Vilnius photometric system. The cloud front edge is detected at 120–130 pc from the Sun and the distance of the Pleiades cluster is found to be 127 pc. Mean extinctionA V in the Merope cloud is of the order of 1.0 mag. There is no evidence of extinction at distances exceeding the Merope cloud distance. Variable extinction method yieldsR=A V/EB-V=3.6, while the maximum polarization wavelength method gives the value 3.4. Some Pleiades stars are suspected to be unresolved binaries.  相似文献   

4.
The first results of the construction of a three-dimensional reddening map for stars within 1600 pc of the Sun are presented. Analysis of the distribution of 70 million stars from the 2MASS catalog with the most accurate photometry on the (J-Ks)-Ks diagram supplemented with Monte Carlo simulations has shown that one of the maxima of this distribution corresponds to F-type dwarfs and subgiants with a mean absolute magnitude M Ks = 2⊙ m 5. The shift of this maximum toward large J-Ks with increasing Ks reflects the reddening of these stars with increasing heliocentric distance. The distribution of the sample of stars over Ks, l, and b cells with a statistically significant number of stars in each cell corresponds to their distribution over three-dimensional spatial cells. As a result, the reddening E(J-Ks) has been determined with an accuracy of 0· m 03 for spatial cells with a side of 100 pc. All of the known large absorbing clouds within 1600 pc of the Sun have manifested themselves in the results obtained. The distances to the near and far edges of the clouds have been determined with a relative accuracy of 15%. The cases where unknown clouds are hidden behind known ones on the same line of sight have been found. The distance dependence of reddening is considered for various Galactic latitudes and longitudes. The absorbing matter of the Gould Belt is shown to manifest itself at latitudes up to 40° and within 600 pc of the Sun. The size and influence of the Gould Belt may have been underestimated thus far. The absorbing matter at latitudes up to 60° and within 1600 pc of the Sun has been found to be distributed predominantly in the first and second quadrants in the southern hemisphere and in the third and fourth quadrants in the northern hemisphere. The warping of the absorbing layer in the near Galaxy apparently manifests itself in this way. A nonrandom orientation of the clouds relative to the Sun is possible. The mass of the baryonic dark matter in solar neighborhoods can then be considerably larger than is generally believed.  相似文献   

5.
In the open cluster NGC 752, 89 stars are observed in the Vilnius seven-colour photometric system, including probable members fainter than observed hitherto. Spectral classification of observed stars are made and individual reddening values are determined. The mean reddening of the cluster stars is equivalentE(B - V) = 0 . m 025. By fitting on colour index-magnitude diagrams the cluster Main Sequence with the Hyades one the distance modulus (m - M)0 = 8 . m 15 ± 0 . m 15 is found. For 11 red giant members of the cluster absolute magnitudes are derived and compared with ones of the standard calibration. It is obtained that the cluster giants are in mean 0 . m 6 fainter than giants of corresponding spectral class in the solar vicinity.  相似文献   

6.
The Ophiuchus molecular cloud complex has produced in Lynds 1688 the richest known embedded cluster within ∼300 pc of the Sun. Unfortunately, distance estimates to the Oph complex vary by nearly ∼40% (∼120–165 pc). Here I calculate a new independent distance estimate of 135±8 pc to this benchmark star‐forming region based on Hipparcos trigonometric parallaxes to stars illuminating reflection nebulosity in close proximity to Lynds 1688. Combining this value with recent distance estimates from reddening studies suggests a consensus distance of 139±6 pc (4% error), situating it within ∼11 pc of the centroid of the ∼5 Myr old Upper Sco OB subgroup of Sco OB2 (145 pc). The velocity vectors for Oph and Upper Sco are statistically indistinguishable within ∼1 km s–1 in each vector component. Both Oph and Upper Sco have negligible motion (<1 km s–1) in the Galactic vertical direction with respect to the Local Standard of Rest, which is inconsistent with the young stellar groups having formed via the high velocity cloud impact scenario. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
Photoelectric Vilnius seven-color photometry is presented and analyzed for a sample of 24 red giant branch and clump stars in the open cluster NGC 7789. For each star we have determined photometric spectral type, absolute magnitude, interstellar reddening, effective temperature, metallicity, and surface gravity. From averages over the stars in the sample we find the mean reddening to the cluster E Y−V = 0.21± 0.02 (s.d.), or E B−V = 0.25, and the apparent distance modulus (m−M) V = 12.21± 0.10 (s.d.), which yield a distance of 1840 pc. The mean overall metallicity is found to be [Fe/H] = −0.18± 0.09 (s.d.). The clump stars, on average, appear to be slightly more metal-rich than the other red giants, which is most probably caused by evolutionary changes of carbon and nitrogen molecular bands falling in the photometric passbands. A difference in mass between the two groups of stars has also been detected, which suggests that the clump stars might have undergone extra mass loss before reaching their core He-burning phase of evolution.  相似文献   

8.
Existing photometry for NGC 2264 tied to the Johnson & Morgan (1953) UBV system is reexamined and, in the case of the original observations by Walker (1956), reanalyzed in order to generate a homogeneous data set for cluster stars. Color terms and a Balmer discontinuity effect in Walker's observations were detected and corrected, and the homogenized data were used in a new assessment of the cluster reddening, distance, and age. Average values of EB – V = 0.075 ± 0.003 s.e. and V0 –MV = 9.45 ± 0.03 s.e. (d = 777 ± 12 pc) are obtained, in conjunction with an inferred cluster age of ∼5.5 × 106 yr from pre‐main‐sequence members and the location of the evolved, luminous, O7 V((f)) dwarf S Mon relative to the ZAMS. The cluster main sequence also contains gaps that may have a dynamical origin. The dust responsible for the initial reddening towards NGC 2264 is no more than 465 pc distant, and there are numerous, reddened and unreddened, late‐type stars along the line of sight that are difficult to separate from cluster members by standard techniques, except for a small subset of stars on the far side of the cluster embedded in its gas and dust and background B‐type ZAMS members of Mon OB2. A compilation of likely NGC 2264 members is presented. Only 3 of the 4 stars recently examined by asteroseismology appear to be likely cluster members. NGC 2264 is also noted to be a double cluster, which has not been mentioned previously in the literature (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
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   

10.
For at all 24 stars in the field of the heavity reddened open cluster NGC 1502 we obtained UBV and uvby photometry. 19 of these stars we classified definitely as members. From the photometric results we derived 1·1 × 107 years as the cluster age, 960 pc as its distance, and <E(B—V)> = 0·78 mag as mean reddening of the cluster. From the reddening of the foreground stars we evaluated that the intracluster reddening has to be smaller than 0·2 mag. The value of the colour excess ratio E(b—y)/E(B—V) = 0·770 leads us to the conclusion that in the spectra of the cluster stars a very broadband structure (VBS) with a central depth of about 0·04 mag is present.  相似文献   

11.
Cr 135 revisited     
In this paper we combine information on photometry, radial velocities and proper motions to study the nature of the suspected open cluster Cr 135. For the first time we introduce proper motions of a large number of stars in the region of Cr 135 into the discussion. The proper motions taken from the PPM catalogue favour the hypothesis that Cr 135 is a real open cluster with at least 12 members at a distance of 300 pc having a space motion U, V, W of (−11, −13, −15) km s−1. But still more accurate observations are needed to separate it from the field stars without any doubt.  相似文献   

12.
A sample of O- and B-type stars with Hipparcos astrometric data, ages computed from Strömgren photometry and radial velocities, has been used to characterize the structure, age and kinematics of the Gould Belt system. The local spiral structure of our galaxy is determined from this sample, and also from a sample of Hipparcos Cepheid stars. The Gould Belt, with an orientation with respect to the galactic plane ofi G = 16-22° and ΩG =275-295°, extends up to a distance of 600 pc from the Sun. Roughly the 60-65% of the O and B stars younger than 60 Myr in the solar neighbourhood belong to this structure. Our results indicate that the kinematical behaviour of this system is complex, with an expansion motion in the solar neighbourhood (R<300 pc).In the frame of the Lin's theory, and analysing the O and B stars further than 600 pc and the Cepheids, we found a galactic spiral structure characterized by a 4-arm spiral pattern with the Sun located atψ⊙ = 350-355 ± 30° – near the Sagittarius-Carina arm– and outside the corotation circle. The angular rotation speed of the spiral pattern was found to be Ωp = 31-32 ± 4 kms-1 kpc-1.  相似文献   

13.
We review different surveys, in the optical and infrared, conducted in the very young (age 1–8 Myr), nearby (d ～ 350 pc) σ Orionis cluster aimed to characterize the substellar population. We describe spectral characteristics of very low mass stars, brown dwarfs and planetary mass objects in the cluster with spectral types from K7 to T6. We study the spatial distribution of the substellar population detected in a IZJ survey covering an area of 1.12 deg.2 We find that the radial distribution of substellar objects can be well fitted by an exponential law (ρ = ρo e ?r/ro ), with a central density (ρ o ) of 0.26 ± 0.03 objects/arcmin2 and a characteristic radius (r o) of 8.8 arcmin ± 0.6 (equivalent to 0.90 ± 0.06 pc at the distance of the cluster). We discuss the presence of possible inhomogeneities in this distribution due to the existence of subclustering. We also compare the spatial distribution of the substellar population with previously known stars in the cluster. We report the initial mass spectrum in the substellar domain.  相似文献   

14.
A study of four open clusters in the direction of the Galactic anticentre (l = 186°, b = +2°) is presented. In a field of 8.32 square degrees proper motions and B magnitudes for about 79 000 stars down to 19.5 were determined on Tautenburg Schmidt plates. For more than 15 500 of them U magnitudes down to 17.3 could be obtained. Additionally, OCA Schmidt plates were used to determine V, R magnitudes in a larger field of 24.45 square degrees for 271 000 stars down to V = 18.2. For stars brighter than V = 15.5 an accuracy of about 1.5 mas/yr has been estimated for proper motions. The rms errors of stellar magnitudes and colour indices are 0.09 – 0.12 mag. Several open clusters have been already known in this direction of the sky, e.g. NGC 2168 or M 35 (C 0605+243), NGC 2158 (C 0604+241) and IC 2157 (C 0601+240). Inspecting the plates and analysing the colour-magnitude diagrams and published data, we could identify an additional anonymous cluster C 0605+242 with a projection on the sky near the centre of M 35 but at a larger distance from the Sun. The cluster membership determination was carried out using information on spatial and proper motion distributions of stars in the field. The colour-magnitude diagrams were derived down to the limiting stellar magnitude. For each cluster the interstellar extinction Av, the diameters of the core and corona, the ages and spatial velocity components (V,W) relative to the LSR in the Y,Z – Galactic directions were determined. The distances to the clusters of 960 pc, 2 600 pc, 2 520 pc and 3 700 pc were obtained for M 35, IC 2157, C 0605+242 and NGC 2158. They show the loci of the clusters in the Local and Perseus spiral arms and at external border of Perseus arm, respectively.  相似文献   

15.
A study of four open clusters on Tautenburg Schmidt plates in the direction to the Galactic Centre (l = 17.0°, b = +0.8°) is presented. In a field of 8.95 square degrees proper motions and B, V magnitudes were determined for about 36 500 stars up to the limiting magnitudes B = 17m.9, V = 16m.8. For stars brighter than B = 16m an accuracy of about 3 mas/year has been estimated for proper motions. The rms errors of stellar magnitudes and (B—V) colours is about 0.1 mag. There are two open clusters already known in this sky area: Trumpler 32 (C 1814-133) and NGC 6611 (C 1816-138). By the inspection of the plates two additional anonymous clusters were identified near the double star ADS 11285 or BD −14°5014 (C 1819-146) and near the star BD −14°5016 (C 1820-146). The cluster membership determination was carried out using information on spatial and proper motion distributions of stars in the field. The colour-magnitude diagrams up to the limiting stellar magnitude were constructed. For each cluster interstellar extinction AV, diameters of the core and corona, ages and spatial velocity components (V, W) relative to the LSR in the Y, Z-galactic directions were derived. The distances to the clusters were obtained to 1720 pc, 2260 pc, 2130 pc and 2130 pc for Trumpler 32, NGC 6611, C 1819-146 and C 1820-146, respectively. All clusters are situated in the Sagittarius-Carina spiral arm. Their spatial location confirms the assumption that galactic spiral arms are close to logarithmic spirals with a characteristic angle of about 20 degrees.  相似文献   

16.
This paper deals with the determination of the three-dimensional distribution of flare stars in the Pleiades cluster. For this purpose a one-dimensional distribution is first constructed from the observed two-dimensional distribution of the stars. It is shown that reliable construction of one dimensioned distribution requires solution of the Abel equation. The last one used to determine the dependence of the true three-dimensional distribution of the density of flare stars on distance from the center of the cluster. This reveals a spherical layer of width 0.5 pc (2.8 R 3.5 pc) with a deficit in the number of flare stars. A profile of the three-dimensional density distribution of flare stars is constructed in the region of deficit. The characteristics of this region are described.  相似文献   

17.
With an apparent cluster diameter of 1.5° and an age of 4 Myr, Trumpler 37 is an ideal target for photometric monitoring of young stars as well as for the search of planetary transits, eclipsing binaries and other sources of variability. The YETI consortium has monitored Trumpler 37 throughout 2010 and 2011 to obtain a comprehensive view of variable phenomena in this region. In this first paper we present the cluster properties and membership determination as derived from an extensive investigation of the literature. We also compared the coordinate list to some YETI images. For 1872 stars we found literature data. Among them 774 have high probability of being member and 125 a medium probability. Based on infrared data we re‐calculate a cluster extinction of 0.9–1.2 mag. We can confirm the age and distance to be 3–5 Myr and870 pc. Stellar masses are determined from theoretical models and the mass function is fitted with a power‐law index of α = 1.90 (0.1–0.4 M⊙) and α = 1.12 (1–10 M⊙). (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
While implementing the first stage of the Pulkovo program of research on stars with large proper motions, we determined the trigonometric parallaxes of 29 stars (12 m < V < 16 m ) based on CCD observations with a 26-inch refractor. The mean standard error was 3.7 mas. Comparison of the Pulkovo parallaxes with those obtained at the Observatory of the Yale University and the US Naval Observatory (USNO) has shown that the parallax differences (Pulkovo-Yale/USNO) lie within the limits of their measurement errors in an overwhelming majority of cases. On average, they are −0.6 ± 1.0 mas. No systematic dependences on stellar distance, magnitude, and color in this set of differences have been found. Our comparisons show that the observing and data reduction techniques used in the Pulkovo program of research on fast stars allow highly accurate trigonometric parallaxes of these objects to be obtained. All program stars are within 50 pc of the Sun; most of them belong to the immediate solar neighborhood (D < 25 pc). For two stars (J0522+3814 and J1202+3636), the trigonometric parallaxes have been determined for the first time.  相似文献   

19.
Photometric data inuvbyß system from 3713 stars is used to map the distribution of colour excesses up to 500 parsec from the Sun, producing diagrams for a series of layers aligned with the galactic plane. Individual clouds are detected, with a mean diameter of 6 parsecs, while cloud complexes have a mean diameter of 100 pc. From the maps it seems that the interstellar medium near the Sun presents regions of non-negligible extinction, while the Sun itself is enbedded in a diffuse cloud, or slightly off its border. The large scatter in the distribution ofE(b-) is confirmed, with a mean extinction ofA v=0 . m 38 up to 500 pc.  相似文献   

20.
We study the spatial structure and sub‐structure of regions rich in Hipparcos stars with blue BT – VT colours. These regions, which comprise large stellar complexes, OB associations, and young open clusters, are tracers of on‐going star formation in the Galaxy. The DBSCAN (Density‐Based Spatial Clustering of Applications with Noise) data clustering algorithm is used to look for spatial overdensities of early‐type stars. Once an overdensity, “agglomerate”, is identified, we carry out a data and bibliographic compilation of their star member candidates. The actual membership in agglomerate of each early‐type star is studied based on its heliocentric distance, proper motion, and previous spectro‐photometric information. We identify 35 agglomerates of early‐type Hipparcos stars. Most of them are associated to previously known clusters and OB associations. The previously unknown P Puppis agglomerate is subject of a dedicated study with Virtual Observatory tools. It is actually a new, nearby, young open cluster (d ∼ 470 pc, age ∼ 20 Ma) with a clear radial density gradient.We list P Puppis and other six agglomerates (including NGC 2451 A, vdBH 23, and Trumpler 10) as new sites for substellar searches because of their youth, closeness, and spatial density. We investigate in detail the sub‐structure in the Orion, CMa‐Pup and Pup‐Vel OB complexes (“super‐agglomerates”). We confirm or discover some stellar overdensities in the Orion complex, like the 25 Ori group, the Horsehead region (including the σ Orionis cluster), and the η Orionis agglomerate. Finally, we derive accurate parallactic distances to the Pleiades, NGC 2451 A, and IC 2391, describe several field early‐type stars at d < 200 pc, and discuss the incompleteness of our search. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

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