New catalogue of optically visible open clusters and candidates
1
1
1
2,3
Wilton S. Dias , Bruno S. Alessi , Jacques Lépine and André Moitinho
1- Instituto Astronômico e Geofísico da Universidade de São Paulo - Brazil
2- Observatório Astronômico Nacional, UNAM, Apdo. Postal 877, C.P. 22800, Ensenada B.C., México
3- CAAUL, Observatório Astronômico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
We have compiled a new catalogue of open clusters in the Galaxy which updates the previous catalogues of Lynga (1987) and Mermilliod (1995) (included in the WEBDA database). New objects
and new data, in particular, data on kinematics (proper motions) that were not present in the old catalogues, have been included. Virtually all the clusters (1627) presently known were included,
which represents an increment of about 380 objects relative to the Lynga (1987) catalogue. The catalogue is presented in a single table containing all the important data (positions, reddenings,
distances, ages, kinematics) which makes it easy to use. The catalogue presents mean absolute proper motions for hundreds of open clusters and membership probabilities for individual stars
(Dias et al. 2001, 2002) obtained using the Tycho 2 proper motions. Unpublished mean radial velocities of several dozens clusters are also presented. The catalogue is being constantly updated and
the latest version (1.0) can be accessed on line at http://www.astro.iag.usp.br/~wilton.
Mean proper motion and Membership
The selected clusters where searched in the Tycho2 Catalogue, using the central coordinates and the radius taken
from the WEBDA database. In many cases the central coordinates of the cluster are different from those given in
ESO Catalogue (Lauberts 1982); in these cases we adopted the ESO coordinates. All the stars situated within the
limits of the clusters were investigated (Dias et al. 2001 and 2002).
For open clusters with an apparent diameter less than 15' we searched for stars in an area 4 times the
cluster area, and if D > 15' we used the area covered by the cluster. From a total of hundreds clusters initially
selected, we obtained satisfactory results for 205.
The methods were those described by Vasilevskis and Rach (1957) and Sanders (1971), also discussed by
Slovak (1977). The method of Vasilevskis and Rach was used to estimate the initial values of the parameters
used in the method of Sanders.
As a final result, the parameters provided by the method of Sanders are given. The mean proper motions of
the clusters macosd, md, s and the results of the two-dimensional Gaussian fit to the population of field stars
are given. With the frequency function parameters we could determine the individual membership
probabilities for each cluster star.
Our results can be compared to those in the literature and the differences between literature and our work
are within the precision of our measurements, in most cases. The mean of the differences in the comparison
with the results of Baumgardt et al. (2000) show that there are no systematic trends, and the small value of the
mean square difference assures that both sets of measurements are in agreement (the mean difference of 0.1
mas/yr in macosd and 0 mas/yr in md were obtained; the root mean square differences are 1.2 mas/yr in macosd
and 1.3 mas/yr in md).
A New Open Cluster Catalogue: 2002 edition
The catalogue presents a compilation of published fundamental parameters (coordinates, distances, ages,
velocities) obtained from old and recent catalogues and papers.
This new edition contains 1627 objects versus 1181 catalogued by Lynga (1987). The catalogue is made up
of one list giving all important global parameter for each object.
The file is self-explanatoy and fully documental internally. The parameters of the open clusters included
are the following : cluster name - equatorial coordinates (in J2000.0) - estimates of angular apparent diameter
- distances - color excess - age - mean proper motions (pm) and their errors - stars used in the pm computation
- individual reference for pm - mean radial velocities (rv) and their errors - stars used in the rv computation individual reference for rv - estimates of the metallicities and errors - stars used (when available).
* All objects were visually checked in the DSS and in many cases the central coordinates of the clusters
were corrected (eg.Lynga 8, Stock 12, and Stock 15)
* We added flags for POCR (Probable Open Cluster Remnants) (Bica et al. 2001)
* New open clusters discovered were inserted in the catalogue (eg. Platais 1998, Chereul et al. 1999,
Alessi et al. 2002 )
* New flags and Trumpler types were inserted to classify the objects
* A complementary table with available photometric data is also supplied.
With mean radial velocity
With both mean proper motion and
mean radial velocity
With mean proper motion
- Near all the clusters (95%) have
estimates of their apparent diameter
- 37% have distances, E(B-V) and age
determinations
- 18% have mean proper motions
determinations
- 12% have mean radial velocities
determinations
With apparent diameter estimated
The differences between Baumgardt et al. (2000) and our work are
within the precision of our measurements, in most cases. The mean
of the differences (0.1 mas/yr) show that there are no systematic
trends and the small value of the mean square difference (1.3
mas/yr) assures that both sets of measurements are in agreement.
Comparison of our results with
those provided by Robichon et al.
(1999). Note that represents the
values in macosd and * in md
- 9% have both kinematical information
simultaneously
With distance, E(B-V) and age determined
.
Mean radial velocities
We used the membership results published by Baumgardt et al. (2000) and Dias et al (2001 and 2002) to
investigate the radial velocities of hundreds clusters. We performed a systematic search for radial velocities for
all stars in the main catalogues in the literature (eg. HIC, GCRV, WEB Catalogue of mean Radial velocities,
among others).
The table below shows an example of the catalogue:
Cluster
NGC 6087
NGC 6124
NGC 6134
Rup 119
NGC 6167
NGC 6204
16
16
16
16
16
16
alfa
18 51
25 20
27 47
28 15
34 35
46 10
delta
-57 56
-40 39
-49 9
-51 30
-49 46
-47 1
D(')
14
39
6
8
7
5
d(pc)
866
466
1001
1046
1029
1126
m-M E(B-V) log t
10.26 0.18 7.91
10.77 0.76 8.00
11.22 0.38 9.21
11.99 0.59 7.16
12.59 0.79 7.59
11.63 0.43 7.92
ma*
-2.35
-1.26
-0.86
-1.15
-0.83
-0.02
err
1.83
2.03
3.30
1.54
0.76
1.58
md
-3.90
-3.00
-4.60
-1.80
-4.52
-0.01
err
1.83
2.03
3.30
1.54
0.59
1.17
nc
30
60
15
14
2
2
ref RV
TYC 5.7
TYC
TYC -26
TYC
BDW
BDW -53
err
0.2
nc
ref
RGDZ
0.2
14
CM92
6
RGDZ
Data search and analysis strategy
First we used SIMBAD to produce a cross-identifications for each star;
Then each star was searched in the selected catalogues. Identification of the stars was based on their
coordinates (all given in J2000.0) and on the cross-identifications.
The result was one file containing all identified stars in all catalogues searched. Note that since each star
can appear more than once a cleaning process was necessary. This step was performed by inspection of the
files and eliminating dubious identifications, identifications that did not present a radial velocity value (these
cases were almost non existent)
The adopted radial velocities were obtained by the simple mean derived using all returned ones.
Based on the membership probability of each star we calculated the mean radial velocity of the cluster.
When the number of the stars used was more than 10 we adopted a gaussian fit, when not we used a simple
mean computation.
Results:
180 clusters with mean radial velocity determined
56 clusters with the mean radial velocity determined for the first time
In the figure below we present the differences relative to results from the literature for the common clusters.
Comparison of our results with those obtained from the literature. In the left we present the histogram of the
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differences of mean radial velocities: mean RV= 2.5 km.s and a standard deviation of 5.5 km.s (using members
stars from Dias et al. 2001 and 2002).
We also presented the individual differences for the same sample. As the figures show, no systematic differences are
found.
In the right site we present the figures with the comparison of results using stars members from Baumgardt et al.
(2000) with those obtained from the literature.
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The gaussian fit to the histogram of differences give the mean radial velocity difference of 0.8 km.s and a standard
deviation of 5.6 km.s-1 .
Future work
The catalogue is being continuously updated with new results from the literature. Besides maintaining
the catalogue, our group is actively producing new results such as:
The analysis of 13 newly discovered open clusters (Alessi 1-13) in the solar vicinity (Alessi, Moitinho
and Dias 2002).
New fundamental parameters of dozens open clusters in the solar vicinity obtained using Tycho2 data
(Moitinho, Dias and Alessi 2003).
On the observational side we are presently reducing photometric and spectroscopic observations
obtained at the LNA Observatory (Brazil), San Pedro Martir (Mexico), and CTIO.
Our main use of the catalogue will be in galactic structure studies: investigate the orbits of these
systems, study the motion of spiral arms and of moving groups, large scale star formation, etc.
References
Acknowledgements:
Alessi B. S., Moitinho A. and Dias W. S,2002, submitted to A&A
Baumgardt H., Dettbarn C. and Wielen R., 2000, A&AS 146, 251
Bica E., Santiago B. X., Dutra C. M., 2001, A&A 366, 827
Dias W. S. & Lépine J., 2003, in preparation
Dias W. S., Alessi B. S., Motinho A. and Lépine J. R. D. 2002, A&A 389, 871
Dias W. S., Lépine J. R. D. and Alessi B. S. 2002, A&A 388, 168
Dias W. S., Lépine J. R. D. and Alessi B. S. 2001, A&A 376, 441
ESA, 1997, The Hipparcos and TYCHO Catalogues, ESA SP- 1200
Hog, E. Fabricius, C. Makarov, V. V. et al., 2000, A&A 355, 27
Robichon, N., Arenou, F., Mermilliod, J.-C., Turon, C., 1999, A&A 345, 471
Moitinho A., Dias W. S. And Alessi B. S., In preparation
Sanders W.L., 1971, A&A 14, 226
Vasilevskis S., Rach R.A., 1957, AJ 62, 175
Extensive
Zhao J.L., He Y.P., 1990, A&A 237, 54
We thank Dr. J-C Mermilliod, Dr. Holger Baumgardt, Dr. Elena
Glushkova and all the people that have helped with their comments
and discussions about this work and the catalogue..
use has been made of the SIMBAD and WEBDA databases.
Project supported by FAPESP (number 99/11781- 4)