All-sky census of galactic open cluster stars
We present the results of a systematic study of the wider neighbourhoods of 520 Galactic open clusters from data of the all-sky high-precision homogeneous catalogue ASCC-2.5. About 30 000 members have been selected on the basis of proper motion, photometric and spatial criteria. Angular and linear s...
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| Published in: | Кинематика и физика небесных тел |
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| Date: | 2005 |
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Головна астрономічна обсерваторія НАН України
2005
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| Cite this: | All-sky census of galactic open cluster stars / N.V. Kharchenko, A.E. Piskunov, S. Roser, E. Schilbach, R.-D. Scholz // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 381-384. — Бібліогр.: 5 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860207850058416128 |
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| author | Kharchenko, N.V. Piskunov, A.E. Roser, S. Schilbach, E. Scholz, R.-D. |
| author_facet | Kharchenko, N.V. Piskunov, A.E. Roser, S. Schilbach, E. Scholz, R.-D. |
| citation_txt | All-sky census of galactic open cluster stars / N.V. Kharchenko, A.E. Piskunov, S. Roser, E. Schilbach, R.-D. Scholz // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 381-384. — Бібліогр.: 5 назв. — англ. |
| collection | DSpace DC |
| container_title | Кинематика и физика небесных тел |
| description | We present the results of a systematic study of the wider neighbourhoods of 520 Galactic open clusters from data of the all-sky high-precision homogeneous catalogue ASCC-2.5. About 30 000 members have been selected on the basis of proper motion, photometric and spatial criteria. Angular and linear sizes of cluster cores and coronas, mean cluster proper motions in the Hipparcos system, distances and ages are derived for all clusters, including some 200 clusters, for which distances and ages have been obtained for the first time. Mean radial velocities are computed for about 300 clusters (for about 100 clusters for the first time). The typical cluster radii are found to be more than two times larger than previously published values. The catalogue of cluster parameters is supplemented by a catalogue of 171 000 stars located in 520 cluster areas and by an atlas of diagrams for each individual cluster.
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| first_indexed | 2025-12-07T18:13:00Z |
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ALL-SKY CENSUS OF GALACTIC OPEN CLUSTER STARS
N. V. Kharchenko1, A. E. Piskunov2, S. Röser3, E. Schilbach3, R.-D. Scholz4
1Main Astronomical Observatory, NAS of Ukraine
27 Akademika Zabolotnoho Str., 03680 Kyiv, Ukraine
e-mail: nkhar@mao.kiev.ua
2Institute of Astronomy, Russian Academy Sci.
48 Pjatnitskaya Str., Moscow Zh-17, Russia
email: piskunov@inasan.rssi.ru
3Astronomisches Rechen-Institut
12–14 Mönchhofstraße, D–69120 Heidelberg, Germany
email: elena@ari.uni-heidelberg.de
4Astrophysikalisches Institut Potsdam
16 An der Sternwarte, D–14482 Potsdam, Germany
email: rdscholz@aip.de
We present the results of a systematic study of the wider neighbourhoods of 520 Galactic open clus-
ters from data of the all-sky high-precision homogeneous catalogue ASCC-2.5. About 30 000 mem-
bers have been selected on the basis of proper motion, photometric and spatial criteria. Angular
and linear sizes of cluster cores and coronas, mean cluster proper motions in the Hipparcos system,
distances and ages are derived for all clusters, including some 200 clusters, for which distances
and ages have been obtained for the first time. Mean radial velocities are computed for about
300 clusters (for about 100 clusters for the first time). The typical cluster radii are found to be
more than two times larger than previously published values. The catalogue of cluster parameters
is supplemented by a catalogue of 171 000 stars located in 520 cluster areas and by an atlas of
diagrams for each individual cluster.
INTRODUCTION
Open clusters (OCs) are typical representatives of the Galactic disc population. Since each cluster includes up to
several hundred stars, its age, spatial coordinates and velocities can be determined much more accurately than
for other Population I objects. The principal drawback of using clusters as objects for such studies is the con-
tamination of cluster areas with fore- and background stars as well as inhomogeneity, and incompleteness of
stellar data. This makes rather difficult the correct separation of cluster members and field stars. The uncer-
tainty of this procedure influences the estimates of the principal parameters of the cluster: its stellar content,
structure, space velocity, colour-magnitude diagram, and age.
So far, about 1700 open clusters have been discovered in the Galaxy. However, only after the Hipparcos
mission had been successfully completed it became possible to create catalogues of open-cluster parameters
determined in reference systems that are uniform over the entire sky in terms of the observational material
and/or methods used.
The study of the nearest clusters was among the primary tasks of the Hipparcos [6] mission. Robichon
et al. [13], Baumgardt et al. [3], and Loktin and Beshenov [11] determined the trigonometric parallaxes of 50,
205, and 45 open clusters based on pre-selected lists of 550, 715, and 638 members, respectively. Robichon
et al. [13] and Baumgardt et al. [3] obtained the mean proper motions of the open clusters in the Hipparcos
reference frame. Dias et al. [4, 5] determined these parameters for 205 clusters using data for about 5900 Tycho-2
stars selected as cluster members by the statistical method of Sanders [14]. As a common feature, these papers
are aiming at the study of kinematics of open clusters. Kharchenko et al. [8] determined structural (cluster
radii), and kinematic (average proper motions) parameters for 401 open clusters. A more complete set of cluster
parameters (proper motions, sizes, distances, and sometimes ages) was determined for a few tens of objects by
Platais et al. [12] and Alessi et al. [1] as a result of searching new clusters in the Hipparcos and Tycho-2
catalogues.
Our study is based on the All Sky Compiled Catalogue of about 2.5 Million Stars [7], called hereafter
ASCC-2.5. This catalogue is based on Tycho-2 data, but is supplemented with some specific Hipparcos data
sets, as well as with some ground-based catalogues. Thus, the stellar content and data quality is improved in
comparison to other Hipparcos-family catalogues. The ultimate goal of the current project is the determination
c© N. V. Kharchenko, A. E. Piskunov, S. Röser, E. Schilbach, R.-D. Scholz, 2004
381
Figure 1. ASCC-2.5 is constructed from catalogues of the Hipparcos family and ground based (PPM, CMC11) catalogues
and is complete down to V ≈ 11.5 (Vlim ≈ 14). All known clusters including stars brighter than Vlim are identified
of unbiased spatio-kinematic parameters of open clusters obtained from the spatially unlimited and uniform
data extracted from the Hipparcos-based all-sky catalogue ASCC-2.5.
THE ASCC-2.5
The ASCC-2.5 is the result of a cross-identification of stars from large high-precision catalogues from space
(Hipparcos and Tycho family: Hipparcos main catalogue with the Multiple System Annex, Tycho-1, Tycho-2,
ACT-RC, TRC) and from ground-based (CMC11, PPM-N, PPM-S, PPM-add) observations and their reduction
to standard systems of corresponding stellar data (see [7] or the ASCC-2.5 ReadMe file at the CDS for more
details on the references and for a detailed description of the ASCC-2.5). The main stellar data presented
in the ASCC-2.5 are the equatorial coordinates (taken from the source catalogues in the order given above,
reflecting a priority in the accuracy of coordinates), weighted mean proper motions, B and V stellar magnitudes.
Additionally, the trigonometric parallaxes, spectral types in the MK or HD system, multiplicity and variability
flags as well as the Hipparcos, Tycho-2, HD, and DM designations are given (if available).
All data in the ASCC-2.5 are reduced to the Hipparcos proper motions and Johnson photometric systems.
The catalogue provides the most complete list of stars having uniform data down to about V = 14, with a com-
pleteness limit at about V = 11.5. The ASCC-2.5 is a full-sky catalogue which is important for an unbiased
determination of the cluster sizes, and contains an extended set of stellar data which allows to carry out the se-
lection of cluster members in a multidimensional space of spatial coordinates, proper motions, and photometric
data. Additionally, the ASCC-2.5 was recently cross-identified by Kharchenko et al. [9] with the General Cata-
logue of Radial Velocities [2] and can be used for the calculation of 3D velocities of open clusters.
SELECTION OF OPEN CLUSTER MEMBERS
Unbiased determination of cluster parameters is only possible if the cluster members are correctly separated
from field stars. The most objective methods of membership evaluation are based on kinematic parameters,
first and foremost on proper motions as the most complete kinematic data sets.
Since the publication of the paper by Sanders [14] describing a statistical method of separation of cluster
members, there have been many examples of successful implementations of this technique to various clusters.
This method, however, is only efficient if the sample under study is kinematically uniform (with respect to
the accuracy of proper motion) and representative enough (enabling to construct and analyze the corresponding
distribution functions). Generally, for poor samples, the method of Sanders produces an unstable separation.
Due to the bright limiting magnitude, Hipparcos-based catalogues are biased to small samples of open cluster
members, and using Sanders’ technique, one therefore could meet difficulties. For example, applying this
method to the Tycho-2 data, Dias et al. [4, 5] only succeeded to determine the membership for less than half of
the clusters contained in the Tycho-2 catalogue.
In the current study (see Kharchenko et al. [10] for details), we use spatial (location with respect to the cluster
centre) and kinematic (proper motions) criteria for the selection of cluster members, and photometric constraints
to clear the cluster member sample from co-moving field stars located in the cluster colour-magnitude diagram
(CMD) beyond major sequences of the cluster.
382
Figure 2. Illustration of the applied iterative member-selection algorithm. Arrows indicate a sequence of basic selection
phases shown as rectangles. Iterations are performed until the list of 1σ-members is no more changing
The membership probabilities are determined as:
Pμ = exp
{
− 1
4
[(
μx−μx
εμi
x
+δε
)2
+
(
μy−μy
εμy +δε
)2
]}
, (proper motion probability)
Pph = exp
{
− 1
2
[
Δ(B−V )
ε(B−V )
]2
}
, (photometric probability)
Pc =
{
min{Pμ, Pph}, r ≤ rcl ,
0, r > rcl ,
(combined probability)
here μ is the average proper motion of the most probable cluster members, Δ(B − V ) is the distance of a star
from the main sequence borders (for stars residing within the MS strip Δ(B − V ) = 0), ε corresponds to
the rms error of the respective parameters. Both membership probabilities and corresponding cluster average
parameters were determined with the help of an iterative procedure shown in Fig. 2. The same and uniform
membership selection procedure has been applied to all clusters. This yields complete set of cluster parameters
(core and corona sizes, proper motions, radial velocities, distances, and ages) all over the sky.
SUMMARY OF THE DERIVED RESULTS
Due to its origin from the all-sky space-based experiment Hipparcos, the member sample presented here has
two important features: (i) accurate and homogeneous data, which served as the basis for a consistent approach
for the identification of open cluster membership regardless of the cluster position at the sky, and (ii) unlimited
areas for searching possible cluster members. This allow to determine the cluster parameters free from a spatial
bias. The applied cluster member selection criteria considerably clear off the cluster neighbourhoods, and
improve the conditions for the determination of cluster sizes, which are strongly affected by contaminating field
stars.
In Fig. 3 and in Table 1 we show a few results based on the cluster parameters derived after a new membership
determination. Figure 3 confirms, that young clusters avoid the inter-arm regions, whereas the older clusters
are distributed more uniformly. Table 1 shows that cluster radii for cleared samples are as a rule 2–3 times
larger than published in the literature from the counts contaminated with field stars. Linear cluster radii are
also much larger, and at the upper limit approach association sizes.
Table 1. Typical radii (in pc) of clusters (Rcl) and associations (Rass). Standard deviations are given in brackets
Value New Previous
Core Corona
Rcl (10 min) 0.5 (0.2) 0.9 (0.2) 0.5 (0.3)
Rcl (10 max) 6.4 (2.4) 17.2 (2.2) 6.7 (4.5)
Rcl (all) 2.0 (3.2) 5.0 (1.3) 2.7 (2.7)
Rass (all) 6.6 (2.6) 21.9 (11.7) –
383
Figure 3. Distribution of open clusters in the Galactic disc plane. Filled dots are clusters younger than log t = 7.4,
pluses – those with log t = 7.4...8.4, and stars are clusters with log t > 8.4. The shaded curves are the Perseus, Local,
and Carina–Sagittarius spiral arms (from top to bottom)
Acknowledgements. This work was supported by the DFG grant 436 RUS 113/757/0–1, RFBR grant 03–
02–04028, and by FCNTP “Astronomy”.
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Astrophys.–2003.–410, N 2.–P. 565–575.
[2] Barbier-Brossat M., Figon P. Mean radial velocities of galactic stars // Astron. and Astrophys. Suppl. Ser.–2000.–
142, N 2.–P. 217–223.
[3] Baumgardt H., Dettbarn C., Wielen R. Open clusters absolute proper motions. I. Observational data // Astron.
and Astrophys. Suppl. Ser.–2000.–146, N 2.– P. 251–258.
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[6] The Hipparcos and Tycho Catalogues.–Noordwijk: ESA SP-1200, 1997.–Vol. 1–4.
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384
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| id | nasplib_isofts_kiev_ua-123456789-79681 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0233-7665 |
| language | English |
| last_indexed | 2025-12-07T18:13:00Z |
| publishDate | 2005 |
| publisher | Головна астрономічна обсерваторія НАН України |
| record_format | dspace |
| spelling | Kharchenko, N.V. Piskunov, A.E. Roser, S. Schilbach, E. Scholz, R.-D. 2015-04-03T18:43:31Z 2015-04-03T18:43:31Z 2005 All-sky census of galactic open cluster stars / N.V. Kharchenko, A.E. Piskunov, S. Roser, E. Schilbach, R.-D. Scholz // Кинематика и физика небесных тел. — 2005. — Т. 21, № 5-додаток. — С. 381-384. — Бібліогр.: 5 назв. — англ. 0233-7665 https://nasplib.isofts.kiev.ua/handle/123456789/79681 We present the results of a systematic study of the wider neighbourhoods of 520 Galactic open clusters from data of the all-sky high-precision homogeneous catalogue ASCC-2.5. About 30 000 members have been selected on the basis of proper motion, photometric and spatial criteria. Angular and linear sizes of cluster cores and coronas, mean cluster proper motions in the Hipparcos system, distances and ages are derived for all clusters, including some 200 clusters, for which distances and ages have been obtained for the first time. Mean radial velocities are computed for about 300 clusters (for about 100 clusters for the first time). The typical cluster radii are found to be more than two times larger than previously published values. The catalogue of cluster parameters is supplemented by a catalogue of 171 000 stars located in 520 cluster areas and by an atlas of diagrams for each individual cluster. This work was supported by the DFG grant 436 RUS 113/757/0–1, RFBR grant 03–02–04028, and by FCNTP “Astronomy”. en Головна астрономічна обсерваторія НАН України Кинематика и физика небесных тел MS4: Positional Astronomy and Global Geodynamics All-sky census of galactic open cluster stars Article published earlier |
| spellingShingle | All-sky census of galactic open cluster stars Kharchenko, N.V. Piskunov, A.E. Roser, S. Schilbach, E. Scholz, R.-D. MS4: Positional Astronomy and Global Geodynamics |
| title | All-sky census of galactic open cluster stars |
| title_full | All-sky census of galactic open cluster stars |
| title_fullStr | All-sky census of galactic open cluster stars |
| title_full_unstemmed | All-sky census of galactic open cluster stars |
| title_short | All-sky census of galactic open cluster stars |
| title_sort | all-sky census of galactic open cluster stars |
| topic | MS4: Positional Astronomy and Global Geodynamics |
| topic_facet | MS4: Positional Astronomy and Global Geodynamics |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79681 |
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