_1998jad.....4....6f

1998: The Journal of Astronomical Data 4, 6.All rights reserved. c©S. Frandsen and T. Arentoft. Published by Twin Press, Vledder, The Nether-lands

The STACC Open Cluster Target List

S. Frandsen (1) [[email protected]]T. Arentoft (1,2) [[email protected]]

(1) Institute of Physics and Astronomy, Aarhus University, Bygn. 520, DK-8000 Aarhus C

(2) Astronomy, University of Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium

Received date; accepted date

Abstract

Observations of variable stars offer a potential to test stellar structure and evolution. Theobservations can be either of single, isolated stars, or of variable stars in clusters. TheSTACC group (Frandsen 1992) has for the last several years searched for open clusters witha population of δ Scuti stars. To make this search more efficient, we have produced a targetlist with a number of promising open clusters. The list includes parameters, finding charts,Colour-Magnitude diagrams (CM diagrams) and references for the clusters. This target listis presented here, and is thus made available to observers interested in participating in thesearch for variable stars in open clusters.In this paper we describe the motivation, contents and use of the STACC Open ClusterTarget List. We also give some guidelines on how to make CCD observations of openclusters in order to search for variable stars.

Keywords: Open clusters – stars: variable – stars: δ Scuti

1 Introduction

In a number of open clusters a population of δ Scuti stars is found. The advantage ofanalysing a group of stars with similar properties is obvious. Praesepe is a very good clusterin this sense with more than a dozen δ Scuti members (Rodriguez et al. 1994). In orderto get good frequency spectra long network observations are necessary (in the case of FGVir, which is not a cluster star, more than 600 hours have been accumulated, see Bregeret al. 1995). In the Hyades, a fair number of δ Scuti stars have been found as well. Butin both cases only one or two variables can be observed simultaneously, which means thatlong observing runs are necessary to get a good frequency spectrum for each variable in thecluster. Such a process is under way for Praesepe (e.g. Belmonte et al. 1994, Arentoft etal. 1998). In more distant clusters several variables can be observed simultaneously withinthe field of view of a CCD.STACC (Small Telescope Array with CCD Cameras, Frandsen 1992) is a group of observerssearching for and making observations of variable stars in the more distant open clusters.

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1.1 Open clusters for CCD observations

In the Lund catalog (Lynga 1987) a few clusters are mentioned with δ Scuti members(NGC 752 has 1, Melotte 20 has 3 and NGC 2264 has 2). But very few clusters with a richpopulation of such variables are known.

Although a number of people and groups have shown interest in participating in observingcampaigns to measure light curves of δ Scuti stars in open clusters, we have so far not locatedthe ideal target in the northern sky for a large campaign, though promising results have beenobtained for the cluster NGC 1817 (see the section on NGC 1817 later in this paper, or seeFrandsen and Arentoft 1998). We are particular interested in finding targets in the northernsky, since most suitable telescopes are located in the northern hemisphere. The ideal targetwould be a cluster which has at least 5 δ Scuti stars in the field of view of the telescopestypically to be used in a campaign. This means a diameter of 0.5m to 1.5m and a CCD witha sensitive area between 1 and 25 cm2. Quite a large range in equipment! In the southerncluster NGC 6134, where we have detected 6 δ Scuti stars (Frandsen et al. 1996), the rangein colours and absolute magnitudes is

0.25 < (B − V )0 < 0.35 (1)

0.5 < MV < 2.0 (2)

The distance to this cluster is close to 1 Kpc and the reddening is EB−V = 0.46. Thesenumbers may be useful for estimating the probability of locating δ Scuti stars in the clustersdescribed in the present publication.

1.2 Why such a cluster?

The reason why these clusters are such important targets is that by having a small set ofvariables, be it δ Scuti or β Cepheid stars, in a cluster, the tests of stellar evolutionarymodels become much more stringent. It is difficult to fit isochrones to the region of theCM diagram, where stars have convective cores, without using non-standard models, whichchange the core by introducing overshooting (Maeder and Meynet 1989) or diffusion (as inthe case of the Sun, Christensen-Dalsgaard et al. 1993, 1996). The idea is to search for waysto calibrate such enhancements to the standard model for stars, where the changes relativeto the standard model have one, if not more, free parameter. We believe that variable starsoffer such a potential. Thus we need to search for clusters with variables.

1.3 Other considerations

The advantage of analysing δ Scuti stars in a cluster is that one has additional constraintscompared to the study of single stars. The disadvantage is the faintness of the stars, whichmakes spectral work very difficult. This prevents the use of advanced techniques for pulsa-tion mode identification that can be applied to bright stars.If a cluster contains other interesting targets such as eclipsing binaries or other useful vari-ables, then it is even a better target. In the case of eclipsing binaries, values of stellarmasses and radii may be obtained for the components to a precision better than 1% (Ander-sen 1995). The more independent information that can be obtained, the stronger constraintscan be put on the modelling of the stars.

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2 The STACC Open Cluster Target List

In order to make the search for targets more efficient, we have produced a target list ofsuitable open clusters, mainly in the northern hemisphere. Each cluster is described in aseparate section, which has the following content:

• A table with coordinates (J2000), distance, age and reddening EB−V .

• A short description of the cluster, including known variables and other information asfar as we find it of immediate relevance for judging the importance of a cluster as atarget.

• A colour-magnitude diagram (V, B − V ).

• A finding chart, typically covering 10 × 10 arcminutes on the sky. Most of these chartsare from the Digitized Sky Survey.

• A list of relevant references from the SIMBAD database.

The information comes from several sources, where the more important one is the SIM-BAD database in Strasbourg. The clusters have been found in the Lund catalog or simplyin the list of open clusters in the Astronomical Almanac. Photometric data come from thedatabase by Mermilliod (1986, 1992) for open clusters, or from newer observations (Viskumet al. 1997, Frandsen and Arentoft 1998). The clusters have been selected on the basis oftheir age, distance (brightness and angular extent on the sky) and field of view. The clustersshould be dense, but not crowded. Age seems to be the most important parameter. Thechances of locating δ Scuti stars in clusters are highest when the turn-off from the main se-quence is located near the δ Scuti instability strip. This corresponds to an age slightly below1 Gyr. In such clusters, the potential variables are found among the brightest members ofthe cluster, and enough photons can be collected from the variables without overexposingother stars on the CCD.

Estimating the ages of clusters it may be helpful to have a look at Fig. 1, taken fromJanes and Adler (1982), which relates the (B −V )t turn-off colour to the age of the cluster.

The angular extent on the sky should not be much larger than approximately 10′× 10′.

For open clusters this typically corresponds to a distance of about 1 Kpc. The clustersshould not be too distant, since the stars then will be too faint, and spectroscopic andprecise photometric measurements will only be possible with large telescopes. Spectroscopyis needed to determine precise parameters for the stars, e.g. effective temperature, metallicityand rotational velocity v sin i.

2.1 Errors on the basic parameters

The basic parameters for the selected clusters (age, distance and reddening) are compiledfrom various catalogs. The question is how well we can trust these values. This will dependon the quality of the CM diagram, and on the models and methods used for determiningthe parameters.On the basis of 120 clusters for which two or more estimates exist, Janes and Adler (1982)gives a rms-variation on the reddening, distance modulus and turnoff colour of ± 0.07 mag,± 0.55 mag and ± 0.07 mag, respectively. For determining the age from the turnoff coloursee Fig. 1, and for a discussion see Janes and Adler (1982). In a recent paper by Viskum etal. (1997), isochrone fitting to CCD data is used for determining reddening, distance and agefor four open clusters. They find the uncertainty on the reddening to be 0.02–0.03 mag, and

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Figure 1: Turnoff colour - age relation, from Janes and Adler, 1982

the uncertainty on the distance to be 15% corresponding to an uncertainty in the distancemodulus of ± 0.30 mag. Carraro and Chiosi (1994) gives ages for 26 open clusters, withδt/t≈ 0.13–0.22 on ages between 450 Myr and 5.46 Gyr. The problem of determining thebasic parameters of open clusters from CM diagrams is also discussed in Janes and Phelps(1994).The various estimates given above for the uncertainty of the age for a cluster represent theconversion of observational errors into an error in age, given a set of isochrones. On topof that comes a systematic error. Models with different metallicity, different amount ofconvective overshoot and other changes in input physics lead to differences as large or largerthan the pure observational errors. Comparing cluster ages one should make sure that theages are derived in a consistent way.

2.2 Use of the target list

As can be seen in this publication, the existing CM-diagrams for this type of clusters areoften of a very poor quality. The first step is therefore to produce new and better CM-diagrams from CCD photometry. From these diagrams better estimates of age and distancecan be made, and the selection of good candidates becomes easier. After a cluster has beenselected from the criteria described above, the next step is CCD time series observationsduring preferably two nights (but not necessarily more), in order to locate variables anddetermine their type. As the clusters lie in the galactic plane, one should be aware thatdetected variable stars might be foreground or background objects. A way of confirmingcluster membership is by measuring radial velocities.Once the right cluster has been found, a network-campaign can be organized, involvingphotometry and spectroscopy from several sites.

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2.3 Establishing variability

From the time series observations, the variable stars are found by examining the light curves.This can be very time consuming, as several hundreds of stars can be observed at the sametime in these clusters. A way of excluding a number of stars as constant is by looking at thepulsation parameter d (Kjeldsen and Frandsen 1992). d is calculated as the ratio betweenthe total rms scatter of the time series and the internal (point-to-point) scatter. A variablestar will, if the time between successive data points is short compared to the period of thevariability, have a high d-value, while a constant star will have a d-value close to 1. We do,however, suggest that the light curves of all stars within the instability strip are examinedvisually.A more robust and versatile technique to look for variability is described by Welch andStetson (1993). For pairs of frames in different (or the same) passbands, changes relativeto a mean magnitude will be correlated for variable stars, and not for constant stars. Thetechnique is less sensitive to spurious data points than methods based on excess scatter.

2.4 Preparing the observations

We include a Section with advice on how to proceed when picking a target from this collectionand when planning and performing observations. Part of this Section will be familiar to manyreaders, but still it might serve as a reminder.

In order to make this description more specific we have selected a target from the list,NGC 1907, for which we have no further information than what is presented in the targetlist. We also make some assumptions about the instrumentation we plan to use, but theseassumptions do not correspond to an instrument, which is actually available to us. It ismore an idea about the typical instrument to be used for this type of observations.

2.4.1 The CM diagram and the basic parameters

A quick look at the CM diagram for NGC 1907 (Fig. 2) shows that the quality is notgood enough to give good basic parameters for the cluster. The scatter is high, and it isdifficult to determine the turn-off from the main sequence. If the reddening given is correct(EB−V = 0.45), the cluster is a bit too young to make it a good target for a search forδ Scuti stars. They would be located at rather faint magnitudes close to the main sequence.Generally that also signifies that their oscillation amplitudes are small (a few mmag).

But the age could be underestimated, as appears from the fact that there are a fairnumber of giants in the cluster. It is thus necessary to get a better CM diagram and toconfirm the reddening. With CCD photometry the biggest problem is the reddening dueto the lack of sensitivity of the detector in the U band. This problem can be solved usingStromgren photometry including the β index, given that these filters are available.

Now, assume that reliable parameters have been obtained and the parameters listed forNGC 1907 have been confirmed. What would the brightness of the δ Scuti stars be? WithEB−V = 0.45 the brightest variables would be around B − V = 0.7 and the stars will havemagnitudes V = 14 or fainter. The stars would also be non-evolved.

2.5 Time series photometry

2.5.1 Telescope size

The first question we must address is whether the telescope at hand is of large enough (ormaybe too large) aperture. To detect oscillations in δ Scuti stars we will demand that a

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Figure 2: CM diagram for NGC 1907 (Mermilliod 1986). ∗ are photoelectric data, and •

are photographic measurements

noise level in the amplitude spectrum of at least 400 ppm (0.4 mmag) is reached in half anight (4 hours). Experience has shown that a S/N ≈ 5 is needed for detection. We takeconservative parameters for the performance of the instrumentation: passband of 100 nmin the V band, a total quantum efficiency of 20% and a 60% duty cycle. In Fig. 3 one canfind the necessary telescope size as function of the brightness of the stars to be searched forvariability. At some level photons do not matter any more but scintillation will dominatethe error budget. This limit is not very relevant in the present context, but it becomesimportant in observations of bright objects. In NGC 1907 (see Sec. 2.2) we can search forδ Scuti stars among most of the candidates, if the faint limit for measuring oscillations at2 mmag is V = 15. In this case we need a telescope with diameter D > 0.6m. To measure1 mmag oscillations one would need a D > 1 m telescope.

2.5.2 Exposure time and duty cycle

In order to make the best out of the observing time we need to check a few other details.For NGC 1907 a field of view of 6′ × 6′ is recommended to get enough stars to analyse

(see the finding chart in the Section on NGC 1907). If we assume the maximum exposurelevel (CCD well capacity) to be 150000 e−, we can calculate the maximum exposure time fora given magnitude to avoid overexposed images. If we have an overhead for a frame of 30 s,then we can plot the duty cycle as function of magnitude. We can now find the brighteststar we can study by asking for a duty cycle above, say, 50%. We can tolerate a moderate

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Figure 3: Telescope size to detect an oscillation with amplitude 0.5 mmag, 1 mmag and 2mmag (left to right in the figure) in 4 hours (see text). The dotted line defines the limitwhere scintillation noise is comparable to photon noise.

number of overexposed images up to 1 to 2 magnitudes brighter than the saturation level(but this depends on the CCD chip). Again for the cluster used as a model (NGC 1907)the situation is such that we would get into problems if we saturate for stars fainter thanV = 10 (Fig. 2).

The question can now be answered: can we hope to detect δ Scuti stars in NGC 1907 ordo we have technical problems with the setup parameters we have assumed? The answer inthe case of NGC 1907 is that one would be able to do an efficient search for variables with atelescope not much smaller than D = 1m. The duty cycle would be acceptable even whenthe exposure time has to be adjusted not to overexpose the bright stars.

3 Observing guidelines

Since we are searching for variations at a millimagnitude level, the telescope must, besideshaving the right size, possess a few more qualities:

• A good guiding system must be installed to keep the image drift below at least 10pixels and preferably within 2–3 pixels.

• A low level of scattered light/straylight. A good description of how to measure theamount of straylight and the source of this straylight is given by Grundahl and Sørensen(1996).

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Figure 4: Duty cycle for different telescope sizes. A pixel size of 0.33 arcseconds has beenassumed and a seeing of 2 arcseconds (see text for more details). The horizontal line givesthe maximum duty cycle achievable for a readout time of 30 s, while exposures longer than5 min would not be recommended in a search for variables.

If a very accurate calibration exists for the pixel sensitivity (a high-quality flat-field), therequirements on the guiding could be relaxed. We are looking into techniques for using timeseries of CCD frames obtained with telescopes that do not guide very well. But normallyflat field problems will prevent detection of millimagnitude oscillations if the guiding is bad.One suggestion for a technique to determine the sensitivity has been described by Kuhnet al. (1991).

Even using an advanced flat-field technique, straylight adds an additional source of com-plication and should be reduced as much as possible in order to reach the precision aimedat, even for small guiding errors.

Finally, if all prerequisites have been mastered, the observations can be started. Use awide-band filter: photons are the most precious item in this game of high precision.

We do not want to explain in great detail the story of how CCD images are taken andreduced. But we do give a short summary to remind observers about some of the calibrationsthat are needed. For an observing run in addition to the science frames a set of calibrationexposures are needed:

1. Linearity tests (no CCD is a real linear device at the low level of variability we arelooking at). Do it before or after the observing run. It can be done in several ways,but we have mostly used a technique of multiple exposures using a stable source ofillumination. Most systems provide an option for taking multiple exposures beforereading out, as this is quite useful for focus determination. Shutter effects are elimi-

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nated with this method. First one defines a unit exposure time to give the smallestexposure level. Then record a series of frames: bias, 1, 2, 1, 3, 1, 4, 1, 5, 1, 6, 1, 7,1, 8, 1, 9, 1, 10, 1, bias. This is just one of several possible schemes. A simple lineardrift in illumination can be tolerated. The accuracy of the test is determined by thestability of the light source and the repeatability of the shutter.

2. Batches of bias frames (16 frames) to decide on the way to do the bias subtraction.For a good system one needs only to subtract the mean level in a rectangle in theoverscan area, which is included with most CCD systems. But sometimes drift is seenduring readout and a more complicated scheme is needed.

3. Flat fields are needed each night. Take enough (10–20 frames) so that photon statisticsare eliminated and use a light source with a spectrum as close to the spectra of thestars as possible: scattered sunlight is one possibility. Take dome flats at the beginningand at the end of the night, and try to get some twilight flats as well.

4. Normally, dark exposures are not needed, but if you are using a CCD system withPeltier cooling, take a dark exposure and repeat it once a day, in case of a significantsignal.

5. Depending on the field, a small defocusing of the telescope might be a good idea touse, in order to smooth out the effect of flat-field errors, and to increase the dutycycle. But, as the seeing changes, the defocusing or the exposure time might have tobe adjusted from time to time. Monitor the images to make sure the right exposurelevels are reached.

6. If you have a large CCD, consider whether you need the whole field or whether awindow is sufficient. Binning is normally not recommended as the exposure levels areclose to maximum well-capacity and binning easily leads to overflow in the registers.Check that the gain setting is such that the maximum signal is not limited by a smallconversion factor, but by the well capacity of the CCD.

7. Register all household data (temperatures, seeing monitor values etc.). They mightbe useful if drift problems occur.

8. Check that you get timing information. Make sure you know what the informationwritten in the image header files mean. Set the computer clocks if needed. Check thetiming each night and do not forget to reset the clocks after system crashes.

9. Use wideband filters.

Further instructions can be obtained from the authors. We have several instructionmanuals for various observing runs that are available on request.

3.1 Data reduction

The reduction of the images to obtain light curves for the set of stars in the field of viewcan be done using most standard photometry packages like DAOPHOT, ROMAFOT orDOPHOT. A special package MOMF has been developed (Kjeldsen and Frandsen, 1992).MOMF deals with series of CCD frames in an efficient way. It should compile and installon most UNIX systems with a FORTRAN compiler. A new version has been produced thatruns more easily on groups of workstations. It makes use of environment variables to makeit easier to switch between workstations.

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In the following sections we present The STACC Open Cluster Target List. Each cluster isdescribed in a separate section.

Acknowledgements

This research has made use of the Simbad database, operated at CDS, Strasbourg, France,and of The Digitized Sky Survey, both for southern declinations:

Based on photographic data obtained using The UK Schmidt Telescope. The UK SchmidtTelescope was operated by the Royal Observatory Edinburgh, with funding from the UKScience and Engineering Research Council, until 1988 June, and thereafter by the Anglo-Australian Observatory. Original plate material is copyright the Royal Observatory Edin-burgh and the Anglo-Australian Observatory. The plates were processed into the presentcompressed digital form with their permission. The Digitized Sky Survey was produced atthe Space Telescope Science Institute under US Government grant NAG W-2166.

and for northern declinations:

Based on photographic data obtained using Oschin Schmidt Telescope on Palomar Moun-tain. The Palomar Observatory Sky Survey was funded by the National Geographic Society.The Oschin Schmidt Telescope is operated by the California Institute of Technology andPalomar Observatory. The plates were processed into the present compressed digital formatwith their permission. The Digitized Sky Survey was produced at the Space Telescope Sci-ence Institute under US Government grant NAG W-2166.

T. Arentoft acknowledges financial support from the Belgian Fund for Scientific Research(FWO) under contract number G.0265.97.

References

Andersen J. 1995, in Highlights of Astronomy, Vol. 10, Ed. I. Appenzeller. Kluwer, Dordrecht, 419.

Arentoft T., Kjeldsen H., Nuspl J. et al. 1998, A&A, in press.

Belmonte J.A., Michel E., Alvarez M. et al. 1994, A&A, 283, 121.

Breger M., Handler G., Nather R.E. et al. 1995, A&A, 297, 473.

Carraro G., Chiosi C. 1994, A&A, 287, 761.

Christensen-Dalsgaard J., Proffitt C.R. and Thompson M.J. 1993, ApJ, 403, L75.

Christensen-Dalsgaard J. Dappen W., Ajukov S.V. et al. 1996, Science, 272, 1286.

Frandsen S. 1992, Delta Scuti Star Newsletter, Vienna Observatory (Ed. M. Breger), 5, 12.

Frandsen S., Arentoft T. 1998, A&A, 333, 524.

Frandsen S. Balona L.A., Viskum M. et al. 1996, A&A, 308, 132.

Grundahl F., Sørensen A. 1996, A&ASS, 116, 367.

Janes K., Phelps R.L. 1994, AJ, 108, 1773.

Janes K., Adler D. 1982, ApJS, 49, 425.

Kjeldsen H., Frandsen S. 1992, PASP, 104, 413.

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Kuhn J.R., Lin H. and Loranz D. 1991, PASP, 103, 1097

Lynga G. 1987, Catalogue of open cluster data, Lund Observatory.

Maeder A., Meynet G. 1989, A&A, 210, 155.

Mermilliod J.C. 1992, Bull. inf. Centre Donnees Stellaires, 40, 115.

Mermilliod J.C. 1986, Bull. inf. Centre Donnees Stellaires, 31, 175.

Rodriguez E. Lopez de Coca P., Rolland R. et al. 1994, A&ASS, 106, 21.

Viskum M., Hernandez M.M., Belmonte J.A. and Frandsen S. 1997, A&A, in press.

Welch D. L., Stetson P.B. 1993, AJ, 105, 1813.

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4 The open cluster list

In this Section we present the individual clusters. The basic data of the clusters can be seen inTable 1, after which each cluster is described in a separate section. The finding charts are mostlyfrom The Digitized Sky Survey, and the references are from the SIMBAD database.

Table 1: Basic data for the open clusters included in the target list. The age is given aslog(t), with t in years, and the distance is given in parsec. For a discussion of errors, seeSection 2.1.

Cluster α2000 δ2000 Distance Age

NGC 559 01 29 21 63 17 1100 8.66NGC 744 01 58 24 55 29 1400 8.30NGC 1245 03 14 42 47 15 2200 9.03NGC 1342 03 31 36 37 20 540 8.80NGC 1513 04 10 00 49 31 820 8.63NGC 1528 04 15 24 51 14 750 8.34NGC 1664 04 51 06 43 42 1100 8.38NGC 1817 05 12 06 16 42 1800 8.90NGC 1907 05 28 05 35 19 1300 8.11NGC 2099 05 52 19 32 33 1300 8.30NGC 2194 06 13 42 12 48 2700 8.57NGC 2215 06 21 00 -07 17 980 8.80NGC 2251 06 34 42 08 22 1600 8.66NGC 2324 07 04 12 01 03 2900 8.82NGC 2360 07 17 42 -15 38 1100 9.00NGC 2489 07 56 12 -30 04 1200 8.50NGC 6811 19 38 12 46 34 1100 8.92NGC 6866 20 03 42 44 10 1300 8.75NGC 6939 20 31 24 60 38 1200 9.20NGC 7062 21 23 18 46 23 1700 8.69NGC 7209 22 05 12 46 30 900 8.59NGC 7226 22 10 30 55 25 2150 8.70NGC 7245 22 15 18 54 20 2800 8.50NGC 7654 23 24 12 61 35 1400 8.20NGC 7762 23 49 48 68 02 1020 8.90

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4.1 NGC 559

Basic Cluster data:

Coordinates Distance Age Reddeningα2000 δ2000 parsec log(t) in y EB−V

01 29 21 +63 17 1100 8.66 0.9

This cluster has the right angular extent, and the right distance. It may be a bit too young,but as the reddening is high, the age is probably quite uncertain. The cluster has a dense centralregion, so if the age is correct, it may represent a good target. The cluster contains blue stragglers.

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Figure 5: V , B − V diagram for NGC 559, ∗ are photoelectric measurements, and • photo-graphic.

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Figure 6: Finding chart for NGC 559

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References

[1991] Strobel A. 1991, A&A 247, 35: An observational age-metallicity relation for the galaxy.

[1991] Strobel A. 1991, Astron. Nachr. 312, 177: Metallicities of open clusters.

[1989] Ejgenson A.M. and Yatsyk O.S. 1989, Astrofizika 31, 37–48: Component analysis of openclusters.

[1989] Strobel A. 1989, Astron. Nachr. 310, 367–373: Two populations of open clusters.

[1988] Janes K.A., Tilley C. and Lynga G. 1988, AJ 95, 771-784: Properties of the open clustersystem.

[1988] Ejgenson A.M., Yatzyk O.S. and Khomik S.I. 1988, Astron. Zh. 65, 730–740: Classificationof open clusters by centroid method of taxonomical analysis.

[1987] Sowell J.R. 1987, ApJS 64, 241–267: Yellow evolved stars in open clusters.

[1987] Danilov V.M., Seleznev A.F., Gurto E.Yu. and Lapina E.A. 1987, Kinematika Fiz. Nebesn.

Tel. 3, 77–83: The study of structural and dynamical characteristics of open clusters (OCL). I.The results of star counts in 50 OCLs.

[1986] Mermilliod J.C. 1986, Bull. Inf. Centre Donnees Stellaires 31, 175–182: Catalogue of UBV

photometry and MK spectral types in open clusters (Third edition).

[1985] Sagar R. 1985, Astrophys. Space Sci. 113, 171–180: The effect of main-sequence stars onage estimates of open clusters.

[1985] van Leeuwen F. 1985, IAU Symp. 113, Ed. by J. Goodman and P. Hut. Dynamics of star

clusters, 579–606: Proper motion studies of stars in and around open clusters.

[1984] Bolte M.J. and Mateo M. 1984, Bull. American Astron. Soc. 16, 947: A radial velocity studyof open clusters containing blue stragglers.

[1982] Janes K. and Adler D. 1982, ApJS 49, 425-446: Open clusters and galactic structure.

[1982] Cardon de Lichtbuer P. 1982, Vatican Obs. Publ. 2, 1–13: Photoelectric sequences for threeopen clusters: CO 126+630 (NGC 559), C 2137+572(TR 37) and C 2152+623 (NGC 7160).

[1980] Piskunov A. 1980, Bull. Inf. Centre Donnees Stellaires 19, 67–70: Catalogue of masses andages of stars in 68 open clusters.

[1979] De Graeve E. 1979, Vatican Obs. Publ. 1, 283–306: Astrometric criteria for selecting physicalmembers of open clusters with low astrometric precision. Application to NGC 559.

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4.2 NGC 744

Basic Cluster data:


01 58 24 +55 29 1400 8.30 0.38

This cluster seems to be too young, but again, the age estimate is probably uncertain. Althoughrather distant, the angular extent is good. New UBV measurements are needed.

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Figure 7: (V, B − V ) diagram for NGC 744, ∗ are photoelectric measurements, • photo-graphic.

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References


[1988] Ejgenson A.M. and Yatsyk O.S. 1988, Astron. Zh. 65, 330–340: Cluster analysis of openclusters.


[1987] Danilov V.M., Seleznev A.F., Gurto E.YU. and Lapina E.A. 1987, Kinematika Fiz. Nebesn.

Tel. 3, 77–83: The study of structural and dynamical characteristics of open clusters (OCL). I.The results of star counts in 50 OCLs.

[1986] Mermilliod J.C. 1986, Bull. Inf. Centre Donnees Stellaires 31, 175–182: Catalogue of UBV


[1985] Danilov V.M., Seleznev A.F., Orekhova L.K., Matkin N.V., Kuznetzova E.F., Agisheva M.S.and Danilova L.V. 1985, Astron. Tsirk. 1365, 1–4: Star count integral characteristics for 22 openstar clusters.

[1983] Bruch A. and Sanders W.L. 1983, A&A 121, 237–240: The absolute masses of 72 galacticclusters and 12 OB associations.

[1982] Janes K. and Adler D. 1982, ApJS 49, 425–446: Open clusters and galactic structure.

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4.3 NGC 1245

Basic Cluster data:


03 14 42 +47 15 2200 9.03 0.27

NGC 1245 is a bit distant, but the angular extent is still about 10 arcmin. It may be too old, asindicated by the colour-magnitude diagram, but Carraro et al. (1994) finds the age to be about 800Myr. The cluster has received some attention, and the CM-diagram is based on CCD measurements.It has a rich central core, which could make it a nice target for an observing campaign. NGC 1245contains red giants.

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Figure 9: (V, B − V ) diagram for NGC 1245, CCD data

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References

[1995] Carraro G., Vallenari A. and Ortolani S. 1995, A&A 300, 128–133 CCD photometry of thefaint old open clusters ESO 96–SC04 and ESO 92–SC18.

[1995] Patat F. and Carraro G. 1995, MNRAS 272, 507–512 : A photometric study of the opencluster Haffner 6.

[1994] Carraro G. and Patat F. 1994, A&A 289, 397–403: CCD BV photometry of the intermediateage open cluster NGC 1245.

[1994] Phelps R.L., Janes K.A. and Montgomery K.A. 1994, AJ. 107, 1079–1096: Development ofthe galactic disk: a search for the oldest open clusters.

[1994] Janes K.A. and Phelps R.L. 1994, AJ 108, 1773–1785: The galactic system of old starclusters: the development of the galactic disk.

[1991] Strobel A. 1991, A&A 247, 35: An observational age-metallicity relation for the galaxy.

[1991] Strobel A. 1991, Astron. Nachr. 312, 177: Metallicities of open clusters.

[1989] Pandey A.K., Bhatt B.C., Mahra H.S. and Sagar R. 1989, MNRAS 236, 263–276: Integratedparameters of open clusters.


[1989] Strobel A. 1989, Astron. Nachr. 310, 367–373: Two populations of open clusters.


[1987] Sowell J.R. 1987, ApJS 64, 241–267: Yellow evolved stars in open clusters.

[1986] Mermilliod J.C. 1986, Bull. Inf. Centre Donnees Stellaires, 31, 175–182: Catalogue of UBV


[1985] Sagar R. 1985, Astrophys. Space Sci. 113, 171–180: The effect of main-sequence stars onage estimates of open clusters.

[1984] Barbaro G. and Pigatto L. 1984, A&A 136, 355–362: Red giants in old open clusters. A testfor stellar evolution.

[1983] Bruch A. and Sanders W.L. 1983, A&A, 121, 237–240: The absolute masses of 72 galacticclusters and 12 OB associations.


[1980] Piskunov A. 1980, Bull. Inf. Centre Donnees Stellaires, 19, 67–70: Catalogue of masses andages of stars in 68 open clusters.

24

4.4 NGC 1342

Basic Cluster data:


03 31 36 +37 20 540 8.80 0.27

This nearby cluster is probably too close and spreads too much for CCD photometry. The age isdifficult to determine from the CM-diagram, and different estimates have been suggested: log(t) =8.48 − 8.80. New UBV photometry is needed.

25

Figure 11: (V, B − V ) diagram for NGC 1342. ∗ are photoelectric measurements, • photo-graphic.

26


27

References

[1994] Pena J.H., Peniche R., Bravo H. and Yam O. 1994, Rev. Mex. Astron. Astrofis., 28, 7–16:

uvbyβ photometry of open clusters. II. NGC 1342.

[1994] Pena J.H. and Peniche R. 1994, Rev. Mex. Astron. Astrofis., 29, 125–128: uvbyβ photometryof the open clusters NGC 1662 and NGC 2129.

[1991] Strobel A. 1991, A&A, 247, 35: An observational age-metallicity relation for the galaxy.

[1991] Strobel A. 1991, Astron. Nachr., 312, 177: Metallicities of open clusters.

[1991] Glushlova E.V. and Rastorgouev A.S. 1991, Pis’ma Astron. Zh., 17, 30: The radial velocitiesof stars in open clusters.

[1990] Renson P. 1990, Bull. Inf. Centre Donnees Stellaires, 38, 151: Liste des etoiles Ap et Amdans les amas ouverts.

[1989] Francic S.P. 1989, AJ, 98, 888–925: Mass functions for eight nearby galactic clusters.

[1989] Strobel A. 1989, Astron. Nachr., 310, 367–373: Two populations of open clusters.

[1988] Ejgenson A.M. and Yatsyk O.S. 1988, Astron. Zh., 65, 330–340: Cluster analysis of openclusters.



[1985] Cameron L.M. 1985, A&A, 147, 39–46: Metallicities and distances of galactic clusters asdetermined from UBV -data. II. The metallicities and distances of 38 open clusters.

[1985] Cameron L.M. 1985, A&A, 147, 47–53: Metallicities and distances of galactic clusters asdetermined from UBV -data. III. Ages and abundance gradients of open clusters.

[1984] Bolte M. and Mateo M. 1984, PASP., 96, 784: A radial-velocity study of open clusterscontaining blue stragglers.


[1982] Mermilliod J.C. 1982, Bull. Inf. Centre Donnees Stellaires, 22, 70–74: Analysis of UBV

data in open clusters.

28

4.5 NGC 1513

Basic Cluster data:


4 10.0 +49 31 820 8.63 0.58

This cluster is probably too young to contain any developed δ Scuti stars, as the new CM-diagram (with the CCD data added to the photoelectric data), indicates that we are looking at ayoung cluster. The age in the table above is certainly an overestimate. But the field is nice withmany isolated stars. Thus we have included it anyway.

29

NGC 1513

0.0 0.5 1.0 1.5 2.0B-V

18

16

14

12

10

V

Figure 13: (V, B − V ) diagram for NGC 1513, + are our own CCD measurements, ⋄ arephotoelectric measurements.

30


31

References

[1995] Subramaniam A., Gorti U., Sagar R. and Bhatt H.C. 1995, A&A 302, 86–89 Probablebinary open star clusters in the Galaxy.

[1988] Del Rio G. and Huestamendia G. 1988, A&AS 73, 425–435 Photoelectric UBV and photo-graphic RGU photometry of the open clusters NGC 1496 and NGC 1513.

32

4.6 NGC 1528

Basic Cluster data:


04 15 24 +51 14 750 8.34 0.29

NGC 1528 is a large cluster, but the density of stars in the center is quite large. It seems a littleyoung, but this is, again, uncertain. Two variables has been detected in the cluster by Bruegman(1989).

33


34


35

References


[1989] Francic S.P. 1989, AJ, 98, 888–925: Mass functions for eight nearby galactic clusters.

[1989] Popova M. and Kraicheva Z. 1989, Astrofisik. Issledovanija – Sofia, 5, 43–50: TheoreticalC-M diagrams of open clusters.

[1989] Bruegman O. 1989 The Observatory, 109, 95–98: Three new variable stars and eight newfaint standard stars.


Tel., 3, 77–83: The study of structural and dynamical characteristics of open clusters (OCL). I.The results of star counts in 50 OCLs




[1985] Cameron L.M. 1985, A&A, 147, 47–53: Metallicities and distances of galactic clusters asdetermined from UBV -data. III. Ages and abundance gradients of open clusters.

[1985] Danilov V.M., Seleznev A.F., Orekhova L.K., Matkin N.V., Kuznetzova E.F., Agisheva M.S.and Danilova L.V. 1985, Astron. Tsirk., 1365, 1–4: Star count integral characteristics for 22open star clusters.



36

4.7 NGC 1664

Basic Cluster data:


04 51 06 +43 42 1100 8.38 0.32

NGC 1664 is an extended cluster, but the central region is quite rich. The cluster looks too young,but the age is difficult to estimate from the existing CM-diagram. The cluster has been subject tostudies of proper motions, and it contains blue stragglers.

37


38


39

References


[1990] Missana M. and Missana N. 1990, AJ, 100, 1850: A new method for deriving stellar mem-bership with an application to the open cluster NGC 1664.

[1990] Renson P. 1990, Bull. Inf. Centre Donnees Stellaires, 38, 151: Liste des etoiles Ap et Amdans les amas ouverts.





[1986] Berdnikov L.N. 1986, Perem. Zvezdy, 22, 369–400: Photoelectric observations of classicalcepheids.

[1985] Abt H.A. 1985, ApJ 294, L103–L106: The spectra and ages of blue stragglers.

[1985] Zhao J.-L. and Tian K.-P. 1985, Acta Astron. Sinica, 26, 152–161: On determining mem-bership of open clusters from relative proper motions.

[1985] Spassova N.M. and Baev P.V. 1985, Astrophys. Space Sci., 112, 111–123: Integrated mag-nitudes and colors of open clusters.

[1985] van Leeuwen F. 1985, IAU Symp., 113, Ed. by J. Goodman and P. Hut. Dynamics of star



[1983] Babu G.S.D. 1983, J. Astrophys. Astron., 4, 235–252: Membership of stars in faint galacticopen clusters.

[1973] Kerridge S.J., Nelson R.M. and Mesrobian W.S., 1973, AJ., 78, 53: Relative proper motionsin the region of the open cluster NGC 1664.

40

4.8 NGC 1817

Basic Cluster data:


05 12 06 +16 42 1800 8.90 0.33

According to The Astronomical Almanac, NGC 1817 has the right age, and this is in agreementwith the CM diagram. The angular extent of the cluster is quite large, and some very bright starsare present near the center. These stars can be avoided by observing the outer parts of the cluster.NGC 1817 was observed by T. Arentoft and M. Viskum, using the 80 cm telescope at Izana,Tenerife, in February 1996. Time-series CCD-photometry was performed during two nights, andthe light curves of 176 stars were analysed. Several stars were found to show variability (Frandsenand Arentoft 1998). The periods ly in the range of 0.7 to 2 hours, with amplitudes of a few mmag.(2.5–6.5mmag.). Seven of the variable stars ly within or very near the δ Scuti instability strip inthe CM diagram, and have thus been classified as being δ Scuti stars. If the colour is correct, oneof the found variables is much too red to be a δ Scuti star. Further observations of the clusteris needed, but NGC 1817 is certainly a very interesting cluster. The cluster has been subject tostudies of proper motion.

41

Figure 19: (V, B − V ) diagram for NGC 1817, photoelectric measurements.

42


43

References

[1998] Frandsen S. and Arentoft T. 1998, accepted by A&A:, The search for δ Scuti stars in openclusters.

[1994] Carraro G. and Chiosi C. 1994, A&A, 287, 761–768: The Galactic system of old openclusters: age calibration and age-metallicity relation.

[1994] Phelps R.L., Janes K.A. and Montgomery K.A. 1994, AJ 107, 1079–1096: Development ofthe galactic disk: a search for the oldest open clusters.

[1994] Janes K.A. and Phelps R.L. 1994, AJ, 108, 1773–1785: The galactic system of old starclusters: the development of the galactic disk.

[1994] Carraro G. 1994, Mem. Soc. Astron. Ital., 65, 685–688: Properties of the galactic old openclusters system.

[1993] Friel E.D. and Janes K.A. 1993, A&A, 267, 75–91: Metallicities and radial velocities of oldopen clusters.



[1989] Friel E.D., Liu T. and Janes K.A. 1989, PASP 101, 1105–1112: Radial velocities of moreold open clusters.


[1988] Ejgenson A.M., Yatzyk O.S. and Khomik S.I. 1988, Astron. Zh., 65, 730–740: Classificationof open clusters by centroid method of taxonomical analysis.

[1987] Zhao J.-L. and He Y.-P. 1987, Acta Astron. Sinica, 28, 374–379: Uncertainties of member-ship parameters of open clusters.





[1985] van Leeuwen F. 1985, IAU Symp., 113, Ed. J. Goodman and P. Hut. Dynamics of star


[1984] Barbaro G. and Pigatto L. 1984, A&A, 136, 355–362: Red giants in old open clusters. Atest for stellar evolution.


44

4.9 NGC 1907

Basic Cluster data:


05 28 05 +35 19 1300 8.11 0.45

NGC 1907 looks like a very young cluster, but the reddening is high, so the age is probably uncertain.The center is quite crowded, and some of the stars lie too close to be resolved. But since the numberof stars is high, NGC 1907 could still be an interesting object.

45

Figure 21: (V, B − V ) diagram for NGC 1907, photoelectric (*) and photographic (•) mea-surements.

46


47

References

[1995] Subramaniam A., Gorti U., Sagar R. and Bhatt H.C. 1995, A&A 302, 86–89: Probablebinary open star clusters in the Galaxy.

[1994] Battinelli P., Brandimarti A. and Capuzzo-Dolcetta R. 1994, A&AS 104, 379–390: Inte-grated photometric properties of open clusters.





[1989] Pavlovskaya E.D. and Filippova A.A. 1989, Astron. Zh., 66, 12–21: The groups of openclusters with common motion in the galaxy.



[1987] Barkhatova K.A., Kutuzov S.A. and Ossipkov L.P. 1987, Astron. Tsirk., 1508, 6: A possiblerotation of the system of open cluster complexes.


Tel., 3, 77–83: The study of structural and dynamical characteristics of open clusters (OCL). I.The results of star counts in 50 OCLs.



[1985] Danilov V.M., Seleznev A.F., Orekhova L.K., Matkin N.V., Kuznwrzova E.F., Agisheva M.S.and Danilova L.V. 1985, Astron. Tsirk., 1365, 1–4: Star count integral characteristics for 22 openstar clusters.

[1985] Danilov V.M., Matkin N.V. and Pylskaya O.P. 1985, Astron. Zh., 62, 1065–1072: Methodeof estimate of diameters and of reality of open star clusters.



48

4.10 NGC 2099

Basic Cluster data:


05 52 19 +32 33 1300 8.30 0.32

NGC 2099 is a large cluster (23 arcmin.), but with a very rich center which can be covered on oneCCD-frame. There are different estimates of the age, log(t) = 8.30−8.50, in any case, it is probablya bit too young. Still it might serve as an interesting target. The cluster contains blue stragglers,and has been subject to studies of proper motion.

49


50


51

References

[1994] Battinelli P., Brandimarti A. and Capuzzo-Dilcetta R.I 1994, A&AS 104, 379–390: Inte-grated photometric properties of open clusters.





[1989] Barkhatova K.A., Ossipkov L.P. and Kutuzov S.A. 1989, Astron. Zh., 66, 1154–1164: Someproperties of open star cluster complexes.


[1989] Ling A. 1989, Astronomy, 17, part no 1, 98–103: Standout winter star clusters.

[1988] Mohan V., Bijaoui A., Creze M. and Robin A.C. 1988, A&AS 73, 85–102: UBV photometryin two fields in anticentre direction.



[1987] Pandey A.K., Bhatt B.C. and Mahra H.S. 1987, Astrophys. Space Sci., 129, 293–302: Agedistribution of open clusters as a function of their linear diameter and age-dependence of clustermasses.



[1985] Abt H.A. 1985, ApJ., 294, L103–L106: The spectra and ages of blue stragglers.







52

4.11 NGC 2194

Basic Cluster data:


06 13 42 +12 48 2700 8.57

NGC 2194 is a nice, dense (and distant) cluster, but the information on it is sparse. The Colour-Magnitude diagram looks a little odd, and since it is based on only photographic measurements,it should probably not be trusted too much. The reddening is unknown, making it even harder toextract any information from the CM diagram. New UBV observations are needed for this cluster.

53

Figure 25: (V, B − V ) diagram for NGC 2194, photographic measurements.

54


55

References


[1994] Janes K.A. and Phelps R.L. 1994, AJ, 108, 1773–1785: The galactic system of old starclusters: the development of the galactic disk.

[1988] Danilov V.M. and Seleznev A.F. 1988, Kinematika Fiz. Nebesn. Tel., 4, 51–58: Studyof structural and dynamical characteristics of open clusters (OCL). II. The effects of non-stationarity.


Tel., 3, 77–83: The study of structural and dynamical characteristics of open clusters (OCL). I.The results of star counts in 50 OCLs

56

4.12 NGC 2215

Basic Cluster data:


06 21.0 -07 17 980 8.80 0.31

NGC 2215 seems like a very nice target, though it is probably a bit too young. It has the rightangular extent on the sky, and a very nice field for CCD photometry.NGC 2215 was observed during one night in February 1996, by M. Viskum and T. Arentoft. Inthese observations, no variables were found at a detection level of a few mmag. This seems tosuggest that the cluster is, in fact, too young.

57


58


59

References


[1989] Ejgenson A.M. and Yatsyk O.S. 1989, Astrofizika, 31, 37–48: Component analysis of openclusters.



60

4.13 NGC 2251

Basic Cluster data:


06 34 42 +08 22 1600 8.66 0.23

From the CM diagram, NGC 2251 looks very promising, with a lot of stars in the region of theinstability strip. But the problem is the same as in the case of NGC 1817, with a few very brightstars, which will set limits to the exposure time. These bright stars should be avoided in the searchfor variable stars in the cluster.

61


62


63

References

[1995] Subramaniam A., Gorti U., Sagar R. and Bhatt H.C. 1995, A&A, 302, 86–89: Probablebinary open star clusters in the Galaxy.





[1987] Jura M. 1987, ApJ 313, 743–749: Mass-losing red giants in open clusters.



[1987] Ostonen R. 1987, Publ. Tartuskoj Astrofiz. Obs., 52, 329–331: Photographic light curve ofeclipsing binary GO Mon.



[1985] Danilov V.M., Seleznev A.F., Orekhova L.K., Matkin N.V., Kuznetzova E.F., Agisheva M.S.and Danilova L.V. 1985, Astron. Tsirk., 1365, 1–4: Star count integral characteristics for 22open star clusters.

[1984] Mermilliod J.C. 1984, Bull. Inf. Centre Donnees Stellaires, 26, 9–15: Bibliography of indi-vidual radial velocities for stars in open cluster. II. NGC and IC clusters.


[1982] Janes K. and Adler D. 1982, ApJS, 49, 425–446: Open clusters and galactic structure.

[1978] Van Rensbergen W., Hammerschlag-Hensberge G. and van den Heuvel E.P.J., 1978, A&A,

64, 131–137: Spectroscopic studies of open clusters - A search for Ap stars.

64

4.14 NGC 2324

Basic Cluster data:


7 4.2 +1 3 2900 8.82 0.11

This seems to be a cluster of the right age with a rich population of stars in the unstable areaof the HR-diagram. New CCD data give a better definition of the main sequence and indicate thatsome of the stars in the CM-diagram are binaries or non-members. The field is somewhat crowded,but the cluster has the advantage of being observable from the north and the south. We considerthis a very promising target.

65

NGC 2324

0.0 0.5 1.0 1.5 2.0B-V

18

16

14

12

10

V

Figure 31: (V, B − V ) diagram for NGC 2324. + are new CCD data, ⋄ are photoelectricdata.

66


67

References

[1993] Marie M. 1993, Astrophys. Space Sci., 201, 71–77: Astrometry of the open cluster NGC2324.

[1993] White J.R. and Friel E.D. 1993, BAAS, 25, 1455: CCD photometry of the open clusterNGC 2324.

[1993] Geisler D., Claria J.J. and Minniti D. 1993, Rev. Mex. Astron. Astrofis., 26, 102: Metallici-ties of old open clusters located in the third galactic quadrant.

[1992] Geisler D., Claria J.J. and Minniti D. 1992, AJ, 104, 1892–1905: Washington photometryof open cluster giants: nine old disk clusters in the third galactic quadrant.


[1985] Cameron L.M. 1985, A&A, 147, 47–53: Metallicities and distances of galactic clusters asdetermined from UBV -data. III. Ages and abundance gradients of open clusters. Methode ofestimate of diameters and of reality of open star clusters.

68

4.15 NGC 2360

Basic Cluster data:


07 17.7 -15 38 1100 9.00 0.06

NGC 2360 is a southern cluster, but it can, of course, still be observed from the northernhemisphere. The central region is dense, without being crowded, and with an age around 1 Gyr(Meynet et. al. 1993), this cluster could be a very interesting target. Based on CCD-observationsmade by M. Gelbmann and U. Heiter, University of Vienna, a new CM-diagram has been produced.The observations were made with the Danish 1.54 m telescope at La Silla, and for the reductionthe photometric package MOMF (Kjeldsen and Frandsen 1992) was applied. The CM-diagram hasbeen published by Frandsen and Arentoft (1998). The main sequence is rather broad (scatter anddouble stars), but the diagram is not inconsistent with an age around 1 Gyr. The cluster containsred giants and blue stragglers.

69

Figure 33: Colour-Luminosity diagram for NGC 2360, CCD data.

70


71

References

[1998] Frandsen S., Arentoft T. 1998, accepted by A&A: The search for δ Scuti stars in open clusters.

[1996] Mermilliod J.-C., Huestamendia G., Del Rio G. and Mayor M. 1996, A&A 307, 80–87: Redgiants in open clusters. V. NGC 2099.

[1994] Raboud D. and Mermilliod J.-C. 1994, A&A 289, 121–126: The apparent distribution ofred giant spectroscopic binaries in open clusters.


[1994] Milone A.A.E. and Latham D.W. 1994, AJ 108, 1828-1833: Radial velocities of blue strag-glers. I. A catalog of candidates in six open clusters.

[1993] Friel E.D. and Janes K.A. 1993, A&A 267, 75–91: Metallicities and radial velocities of oldopen clusters.

[1993] Meynet G., Mermilliod J.-C. and Maeder A. 1993, A&AS 98, 477–504: New dating ofgalactic open clusters.

[1992] Mukherjee K., Anthony-Twarog B.J. and Twarog B.A. 1992, PASP 104, 561: uvby CCDphotometry of the upper main sequence in omega Centauri.

[1992] Milone A.A.E. 1992, PASP 104, 1268–1268: The blue stragglers of M 67 and other openclusters.

[1992] Kjeldsen H., Frandsen S. 1992, PASP 104, 413–434: High-precision time-resolved CCDphotometry


[1990] Mermilliod J.-C. and Mayor M. 1990, A&A 237, 61: Red giants in open clusters. III. Binarityand stelllar evolution in five intermediate-age clusters: NGC 2360, 2423, 5822, 6811 and IC 4756.


[1988] Murray R.L., Anthony-Twarog B.J. and Twarog B.A. 1988, BAAS 20, 717: A BV photo-graphic survey of the open cluster NGC 2360.

[1985] Cameron L.M. 1985, A&A 147, 39–46: Metallicities and distances of galactic clusters asdetermined from UBV -data. II. The metallicities and distances of 38 open clusters.

[1985] Cameron L.M., A&A 147, 47–53: Metallicities and distances of galactic clusters as deter-mined from UBV -data. III. Ages and abundance gradients of open clusters.

72

4.16 NGC 2489

Basic Cluster data:


07 56.2 -30 04 1200 8.50 0.34

NGC 2489 cannot be observed from the northern hemisphere. Again, the field is dense, but notcrowded, making it a nice target. The cluster is, however, possibly too young, but it still containssome stars in the instability strip. The CM-diagram is produced on the basis of CCD observationsmade by M. Gelbmann and U. Heiter, University of Vienna, using the 1.54 m. Danish telescope atLa Silla, and the photometric reduction was done using the reduction-package MOMF (Kjeldsenand Frandsen 1992). The CM-diagram has been published by Frandsen and Arentoft (1998).

73

Figure 35: Colour-Luminosity diagram for NGC 2489, CCD data.

74


75

References

[1998] Frandsen S., Arentoft T. 1998, accepted by A&A: The search for δ Scuti stars in open clusters.

[1992] Ramsay G. and Pollacco D.L. 1992, A&AS 94, 73–102: CCD observations in 7 open clusters:NGC 2421, NGC 2439, NGC 2567, NGC 2627, NGC 2658 and NGC 2910.

[1992] Kjeldsen H. and Frandsen S. 1992, PASP 104, 413–434: High-precision time-resolved CCDphotometry



76

4.17 NGC 6811

Basic Cluster data:


19 38 12 +46 34 1100 8.92 0.14

New UBV measurements are needed on the stars in NGC 6811. But if the few photoelectric andthe many photographic data points can be trusted, the cluster looks promising. The cluster seemsto have the right age, the right distance, and a lot of stars in the instability strip. The field doesnot pose any problems, so NGC 6811 could be a good candidate for locating δ Scuti stars. Thecluster has been subject to studies of proper motion.

77

Figure 37: (V, B − V ) diagram for NGC 6811. ∗ are photoelectric measurements, • photo-graphic.

78


79

References

[1995] Dambis A.K., Melnik A.M. and Rastorguev A.S. 1995, Pis’ma Astron. Zh., 21, 331–347:

Rotation curve of the system of classical Cepheids and the distance to the Galactic Center.

[1990] Mermilliod J.-C. and Mayor M. 1990, A&A, 237, 61: Red giants in open clusters. III.Binarity and stelllar evolution in five intermediate-age clusters: NGC 2360, 2423, 5822, 6811 andIC 4756.









[1985] Sagar R. 1985, Astrophys. Space Sci., 113, 171–180: The effect of main-sequence stars onage estimates of open clusters.






[1978] Barkhatova K.A., Zakharova P.E., Shaskina L.P., Stellar Clusters and double systems, 1978,

Ural State University: The photographic UBV -photometry in the field of the open cluster NGC6811.

[1972] Lindoff U. 1972, A&A, 16, 315–321: The open cluster NGC 6811.

[1971] Sanders W.L. 1971, A&A, 15, 368–373: Membership of the open cluster NGC 6811.

80

4.18 NGC 6866

Basic Cluster data:


20 03 42 +44 10 1300 8.75 0.13

This cluster resembles somewhat NGC 6811. Maybe it is a little younger, but it is still a goodcandidate, for the same reasons as for NGC 6811. Also for NGC 6866, new UBV data is needed.The cluster has been subject to studies of proper motion.

81


82


83

References

[1989] Pavlovskaya E.D. and Filippova A.A. 1989, Astron. Zh., 66, 12–21: The groups of openclusters with common motion in the galaxy.


[1988] Danilov V.M. and Seleznev A.F. 1988, Kinematika Fiz. Nebesn. Tel., 4, 51–58: Studyof structural and dynamical characteristics of open clusters (OCL). II. The effects of non-stationarity.

[1987] Barkhatova K.A., Kutuzov S.A. and Ossipkov L.P. 1987, Astron. Tsirk., 1508, 6: A possiblerotation of the system of open cluster complexes.

[1987] Barkhatova K.A., Kutuzov S.A. and Osipkov L.P. 1987, Astron. Zh., 64, 956–964: A cata-logue of some observational data and elements of galactic orbits of open star clusters.







[1985] Sagar R. 1985, Astrophys. Space Sci., 113, 171–180: The effect of main-sequence stars onage estimates of open clusters.






84

4.19 NGC 6939

Basic Cluster data:


20 31 24 +60 38 1200 9.20 0.47

NGC 6939 is a bit old, but as the reddening is high, this is uncertain. With EB−V around 0.5, thestars seem to have the right position in the CM-diagram, though new photoelectric or CCD datacertainly are needed. The field looks nice, and the cluster may be a good candidate. The clustercontains Blue Stragglers and Red Giants, and has been subject to studies of proper motion.

85


86


87

References

[1994] Carraro G. and Chiosi C. 1994, A&A, 287, 761–768: The Galactic system of old openclusters: age calibration and age-metallicity relation.


[1994] Milone A.A.E. and Latham D.W. 1994, AJ, 108, 1828–1833: Radial velocities of blue strag-glers. I. A catalog of candidates in six open clusters.

[1994] Milone A.A.E. 1994, PASP, 106, 1085–1090: The mean radial velocity of the open clusterNGC 6939.

[1994] Piersimoni A., Brocato E. and Castellani V. 1994, Mem. Soc. Astron. Ital., 65, 765–768:

CCD observations of young and intermediate age clusters.

[1993] Thogersen E.N., Friel E.D. and Fallon B.V. 1993, PASP 105, 1253–1259: Metallicities andvelocities of old open clusters.

[1991] Manteiga M., Martinez Roger C., Morales C. and Sabau L. 1991, A&A, 251, 49: Bluestragglers: a search for binaries in the infrared.

[1991] Glushkova E.V. and Rastorgouev A.S. 1991, Pis’ma Astron. Zh., 17, 149: The proper motionand radial velocity measurements of stars in the open cluster NGC 6939.

[1990] Mateo M., Harris H.C., Nemec J. and Olszewski E.W. 1990, AJ, 100, 469: Blue stragglersas remnants of stellar mergers: the discovery of short-period eclipsing binaries in globular clusterNGC 5466.

[1989] Manteiga M., Pickles A.J. and Martinez Roger C. 1989, A&A, 210, 66–77: Blue stragglersand the binary hypothesis.

[1989] Popova M. and Antov A. 1989, Astrofisik. Issledovanija - Sofia, 5, 36–42: Investigation ofthe structure of the open cluster NGC 6939.

[1989] Manteiga M., Martinez Roger C. and Pickles A.J. 1989, Astrophys. Space Sci., 156, 169–171:

The contribution to population in ellipticals of blue stragglers: a test of their origin.

[1988] Geisler D. 1988, PASP 100, 338–343: Radial velocities of stars in five old open clusters.




88

4.20 NGC 7062

Basic Cluster data:


21 23.3 +46 23 1700 8.69 0.48

This cluster has a small, but fairly concentrated part, which should fit within the field of view ofmost CCD cameras. UBV and uvbyβ photometry exists. The instability strip contains mainlystars in the range V = 13 − 15. Peniche et al. (1990) find three potential variables with r.m.s.fluctuations at 2–3%, whereas other stars have r.m.s. fluctuations at 0.5%. In the same paper anage of 7 × 108 y is given. There are red giants and blue stragglers in the cluster.

Newer observations (Viskum et al. 1997) only consist in a small set of CCD frames. Starting with5 potential variables (Fig. 45), only 1 seems to be significant. A new colour magnitude diagramfrom Viskum et al. (1997) is presented. In addition we show the field with the position of thesuspected variables, as well as the image from The Digitized Sky Survey. The conclusion is thatbetter data are needed before the presence of variables can be decided on.

89

NGC 7062

Figure 43: (V, B−V ) diagram for NGC 7062 from Viskum et al. (1997), with the instabilitystrip indicated

90


91

Figure 45: The position of the variables in NGC 7062. The variable stars are labeled witha running number. X,Y-coordinates are in pixels.

92

References

[1997] Viskum M., Hernandez M.M., Belmonte J.A. and Frandsen S. 1997, A&A, in press: A searchfor δ Scuti stars in northern open clusters. I. CCD photometry of NGC 7245, NGC 7062, NGC7226 and NGC 7654.

[1993] Nelson M.J. and Kreidl T.J. 1993, AJ, 105, 1903–1914: A seven-year northern sky surveyof Ap stars for rapid variability.

[1990] Peniche R., Pena J.H., Diaz Martinez S.H. and Gomez T. 1990, Rev. Mex. Astron. Astrofis.,

20, 127: uvbyβ photoelectric photometry of the open cluster NGC 7062.

[1990] Tignanelli H., Vazquez R.A., Mostaccio C., Gordillo S., Feinstein A. and Plastino A. 1990,Rev. Mex. Astron. Astrofis., 21, 305 Numerical taxonomy for open clusters.

[1987] Peniche R. and Pena J.H. 1987, Rev. Mex. Astron. Astrofis., 14, 420–422 A photometricstudy of short period variable stars in open clusters.

[1984] Barbaro G. and Pigatto L. 1984, A&A, 136, 355–362 Red giants in old open clusters. Atest for stellar evolution.

[1984] Bolte M. and Mateo M. 1984, PASP, 96, 784 A radial-velocity study of open clusterscontaining blue stragglers.

[1973] Hassan S.M. 1973, A&AS 9, 261–287 Three colour photometry of the five open clustersNGC 7039,NGC 7062, NGC 7067, NGC 7082, IC 1369.

[1970] Jones B.F. and Van Altena W.F. 1970, A&A, 9, 86–94 Membership in the open clusterNGC 7062.

93

4.21 NGC 7209

Basic Cluster data:


22 05.2 +46 30 900 8.5 0.20

The cluster is very large, too large to observe on one CCD frame, at least for most telescopes.The density of stars is large enough to make it a reasonable target. It may be a bit too young forδ Scuti stars to be easily observed. The cluster has been subject to studies of proper motions. TheCM diagram is very poorly determined.

94


95


96

References

[1992] Platais I. 1992, Bull. Inf. Centre Donnees Stellaires, 40, 7–8: Catalogue of proper motionsin NGC 7209.

[1992] Platais I. 1991, A&AS 87, 577: The studies of proper motions in the regions of open clusters.III. NGC 7209.

[1992] Zakirov M.M. and Azimov A.A. 1990, IAU Inform. Bull. Var. Stars, 3487, 1: The disap-pearance of minima of eclipsing binary SSry SS Lac in open cluster NGC 7209.



[1988] Ejgenson A.M. and Yatsyk O.S. 1988, Astron. Zu., 65, 330–340: Cluster analysis of openclusters.

[1988] Ejgenson A.M., Yatzyk O.S. and Khomik S.I. 1988, Astron. Zu., 65, 730–740: Classificationof open clusters by centroid method of taxonomical analysis.

[1987] Jura M. 1987, ApJ 313, 743–749: Mass-losing red giants in open clusters.








[1976] Harris G.L.H. 1976, ApJS 30, 451–490: Evolved stars in open clusters.

[1966] Van Schewick H. 1966, Mitteil. Astron. Gesellschaft, 21, 123: Die Eigenbewegungen offenerSternhaufen.

[1966] Van Schewick H. 1966, Veroeff. Astron. Inst. Bonn, 74, 1–44: Untersuchungen uber dieEigenbewegungen von Sternhaufen.

[1961] Hoag A.A. 1961, Vistas in Astronomy, 8, 139–148: Open cluster distance moduli.

[1940] Mavers F.W. 1940, Astron. Abh. Hamburg. Sternw., 5, 85–103: Untersuchungen der offenenSternhaufen NGC 7092 (M 39), NGC 7209 und NGC 7243.

97

4.22 NGC 7226

Basic Cluster data:


22 10.5 +55 25 2150 8.7 0.47

The cluster has been observed by Viskum et al. (1997). There are different estimates for the age:log t = 8.4 − 8.7. The cluster is distant, and not much is known about it. So in addition to timeseries photometry it would be wise to do UBV or uvbyβ photometry as well.

There are three suspected variables in the cluster. The data from Viskum et al. (1997) covertoo short a time interval to classify the variables, but it looks as two δ Scuti stars and one eclipsingbinary. It might also be three δ Scuti stars or there could be two eclipsing binaries. However, acloser look at the light curves shows that the variability is ambiguous. The HR-diagram is new anda figure indicating the position of the suspected variables is included (Fig. 50).

The cluster is situated in a crowded area with many foreground or background stars.

98

NGC 7226

Figure 48: Colour-Magnitude diagram for NGC 7226 from Viskum et al. (1997)

99


100

Figure 50: Frame giving the positions of the variables in NGC 7226. The variables arelabeled with a running number. X and Y-coordinates are in pixels.

101

References


[1990] Tignanelli H., Vazquez R.A., Mostaccio C., Gordillo S., Feinstein A. and Plastino 1990, A.

Rev. Mex. Astron. Astrofis., 21, 305: Numerical taxonomy for open clusters.



102

4.23 NGC 7245

Basic Cluster data:


22 15.3 +54 20 2800 8.5 0.40

One can add the same comments as for the nearby cluster NGC 7226. There are different estimatesfor the age: log t = 8.2− 8.6. The cluster is distant and does not come out so well on the DigitizedSky Survey map. Not much is known about this cluster, so in addition to time series photometryit would be wise to do UBV or uvbyβ photometry as well.

Viskum et al. (1997) find four variables: 2 δ Scuti stars, one eclipsing binary and possibly a WUMA star. The presence of two δ Scuti stars and one EB makes this cluster a very interesting one.

103

NGC 7245

Figure 51: (V, B − V ) diagram for NGC 7245, CCD-data

104


105

Figure 53: The variables in NGC 7245, 456 and 493 are the δ Scuti stars (running number).X and Y-coordinates are in pixels.

106

References


[1992] Petry C.E. and Degioia-Eastwood K. 1992, BAAS 24, 1235: New color magnitude diagramsfor NGC 637 and NGC 7245.





107

4.24 NGC 7654 (M52)

Basic Cluster data


23 24.2 +61 35 1400 8.2 0.58

Even though this cluster is a bit too young to represent an ideal target, it has been included, becauseit is a very rich cluster. Furthermore, the field seems to contain two clusters superimposed. Thisexplains the difference in age determinations given in in the literature. The bright B stars presentin this cluster pose a problem, if one wants to study the fainter A and F stars.

Three stars are potential variables, one δ Scuti, one β Cephei and one eclipsing binary. Thiswas later modified to two variables both of type δ Scuti (215 and 501). The positions are shown inthe figures from Viskum et al. (1997).

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NGC 7654

Figure 54: (V, B − V ) diagram for NGC 7654, photographic data.

109


110

Figure 56: Position of variables in NGC 7654, 501 the δ Scuti, 471 the β Cephei and 215the eclipsing binary. X and Y-coordinates in pixels.

111

References

[1997] Viskum M., Hernandez M.M., Belmonte J.A. and Frandsen S. 1997, A&A, in press: A searchfor delta Scuti stars in northern open clusters. I. CCD photometry of NGC 7245, NGC 7062,NGC 7226 and NGC 7654.

[1991] Battinelli P. and Capuzzo-Dolcetta R. 1991, MNRAS 249, 76: Formation and evolutionaryproperties of the galactic open cluster system.

[1990] Arellano Ferro A. and Parrao L. 1990, A&A, 239, 205–213: Colour excesses and absolutemagnitudes for non-cepheid F-G supergiants from uvbyβ photometry.

[1990] Kaltcheva N.T. 1990, Astrophys. Space Sci., 173, 69 : Photographic uvby photometry of theopen cluster M 52.

[1987] Sowell J.R. 1987, ApJS 64, 241–267 : Yellow evolved stars in open clusters.

[1985] Fenkart R.P. and Schroder A. 1985, A&AS 59, 83–86: UBV three-colour photometric pa-rameters of four galactic clusters near Cassiopeia.

[1984] Schmidt E.G. 1984, ApJS 55, 455–463: Yellow giants in young clusters. I. Photometricobservations.

[1981] Danford S.C. and Thomas J. 1981, PASP., 93, 447–452: uvbyβ photometry of the opencluster M 52.

[1960] Pesch P. 1960, ApJ 132, 689: The galactic cluster NGC 7654 (M 52).

112

4.25 NGC 7762

Basic Cluster data


23 49.8 +68 02 1020 8.9 0.98

NGC 7762 is not a cluster which has received much attention. Consequently the data for this clusterare sparse and the parameters not too well determined. It is old, maybe too old, but as the ageis often quite uncertain for these clusters with only few photometric measurements, it has beenincluded as one of the targets anyway. The reddening is quite high in the direction of this clusterand the uncertainty in the reddening transfers to an uncertainty in the colour of the turnoff.

113

Figure 57: Colour-Magnitude diagram for NGC 7762, ∗ are photoelectric measurements, •photographic.

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115

References




[1966] Chincarini G. 1966, Mem. Soc. Astron. Ital., 37, 423–425 : The galactic cluster NGC 7762.

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Documents

open clusters stars

number of open clusters

distant open clusters

group of stars

distant clusters

isolated stars

fair number of scuti

light curves of scuti