
University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Edward Schmidt Publications Research Papers in Physics and Astronomy 4-1982 Intermediate-Band Photometry of the Open Cluster NGC 3114 Edward G. Schmidt University of Nebraska at Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/physicsschmidt Part of the Physics Commons Schmidt, Edward G., "Intermediate-Band Photometry of the Open Cluster NGC 3114" (1982). Edward Schmidt Publications. 41. https://digitalcommons.unl.edu/physicsschmidt/41 This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Edward Schmidt Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. PUBLICATIONSOF THE AS~ONOMICALSOCIETY OF THE PACIFIC 94:232-238, April 1982 INTERMEDIATE-BAND PHOTOMETRY OF THE OPEN CLUSTER NGC 3114 EDWARD G. SCHMIDT" Department of Physics and Astronomy, University of Nebraskh-Lincoln, Lincoln, Nebraska 68588-0111 Received 1981 Nocember 9 Four-color and HP photometry has been obtained of 33 stars in the southern galactic cluster NGC 3114. This cluster contains many interesting stars including blue stragglers, red giants, and stars with spectral peculiarities. The distance modulus was found to be V, - Mv = 10.26 which corresponds to 1130 pc. The color excess is E(b -y) = O'?'060. The cluster appears to be slightly older than the Pleiades. There are two extreme blue stragglers and six additional stars which might be considered milder cases of the same phenomenon. The distance moduli of the stars with peculiar spectra and the blue stragglers inferred from the photometry agree with those of the normal cluster stars and we conclude that this strengthens the view that the photometric indices of such stars are not affected significantly by their peculiarities. Key words: open clusters-uvbyp photometry-stellar evolution-blue stragglers-peculiar stars I. Introduction ther information about the properties of peculiar stars in NGC 3114 (a = 10h02", 6 = -60°00'(1975), P = the uvbyP system. Additionally, the relatively large number of red giants can be used to study the evolution 238", b = -4") is a rich open cluster situated in a re- gion of Carina which has relatively low obscuration. of stars off of the main sequence. Basic to such studies This cluster has nearly 200 stars brighter than V = 12 are the distance, age, and color excess of the cluster. In within its boundaries and is about half a degree across. this paper the results of a four-color and HP study of the The richness of the cluster and its small absorption make B stars in NGC 3114 are reported. it a useful object for studies of cluster properties and 11. The Observations studies of various types of stars which might be mem- bers. The star numbers used by Lyngi and Jankowitz and Lyngi (1959, 1962) and Jankowitz and McCosh (1963) McCosh are listed in the first two columns of Table I have published UBV studies of stars in NGC 3114. They and the spectral types are given in the following two derived a distance of about 900 pc and a color excess in columns. The V magnitudes are the averages of those (B- V) between OW4 and OW9. However, the distance from Lyngi, Jankowitz and McCosh, and the present is somewhat difficult to determine due to the presence of photometry. numerous field stars which are confused with the cluster The four-color and HP photometry was obtained at stars. Lyngi estimated the age of this object at 200 to Cerro Tololo Inter-American Observatory during March 500 million years while Jankowitz and McCosh found a 1980 and May 1981 with the 0.91-meter telescope. A slightly smaller age of 100 to 200 million years. On the two-channel photometer was used with one channel other hand, Harris's (1976) discussion implies an age of serving to monitor the stability of the transparency. The about 30 million years and Mermilliod (1981) places it in photometric indices are given in the sixth through the an age class slightly older than the Pleiades (perhaps 60 ninth columns while the tenth column gives the number million years). of nights on which each star was observed. It can be seen Spectral types have been published for stars in that most of the stars were observed three or more times. NGC 3114 by Frye, MacConnell, and Humphreys The observations were made with standard four-color (1970), Levato and Malaroda (1975) and Harris (1976). and HP filters. They were reduced to the standard sys- Of the 42 stars classified by one or more of these in- tem using secondary standards which were in turn re- vestigators, there are ten with peculiar spectra. Four are ferred to the four-color and HP standards of Crawford silicon stars, one is a Hg-Mn star, one is a Be star, one and Mander (1966) and Crawford and Barnes (1970). These secondary standard data will be published and dis- has enhanced N 11 lines, one has enhanced 0 11 lines and two of the red giants have abnormal CN strengths. cussed elsewhere. In the reduction of HP photometry it The presence of so many interesting stars in this clus- is necessary to consider the possibility of color terms ter made it a prime candidate for intermediate-band (Muzzio 1978; Schmidt and Taylor 1979). However, in photometry. This photometry will serve to provide fur- both observing seasons a filter set was used which has very well matched wide and narrow filters and no cor- rection was necessary. The internal errors of the indices "Visiting Astronomer, Cerro Tololo Inter-American Observatory, supported by the National Science Foundation under contract No. (standard deviation of a single measurement) are as fol- AST 74-04128. lows: (b- y), OW09; m,, 0W11; c,, Om013; P, 0W10. PHOTOMETRY OF NGC 3114 233 TABLE I Photometry of Early-Type Stars in NGC 3114 Designation Spectral Type Levato and Frye n E(b-y) Vo- M,, ~yng; JM Malaroda et al. V b-Y '-"l 1 F B81 I I B8.5IVp B9IV B8.5111~ B2IVp B8III B9.5IV B9IV B9III B4Vn B8IVp B8Vn B9III-IVp B 7V'n AOVn - B2Vnne B8III:p - - - - - - - - - - - - - B9.5V:* - * Classification from Harris (1976). Therefore, all of the mean indices in Table I (except a 111. The Distance and Reddening few marked as uncertain by a colon) should be accurate Because NGC 3114 is located in a crowded field of the to better than 0W10. Milky Way, there are likely to be a significant number All the stars with spectral types in Table I except of field stars in our sample. To study the membership of number 33 are B stars. Rough spectral types can also be a cluster, proper motions of the individual stars are inferred from the four-color indices; for example, the needed. Since these are lacking for NGC 3114, we will [m,],[c,]diagram is useful in this regard. This test in- resort to the photometric indices to remove obviously dicated that all stars in Table I are B stars including discordant stars. Figures 1, 2, 3, and 4 are useful in this those with no assigned spectral types. Therefore, we regard. In the first three diagrams we have marked those have applied Crawford's (1978) B-star calibration to points which seem to deivate from the group of cluster each star to obtain the color excess and true distance data points. If we form the mean distance modulus modulus. These are listed in the last two columns of the omitting these deviant points, we obtain V, - M, = table. In these calculations we have assumed that A, = 10.41 + 0.70 (standard deviation for a single star). In 4.28 E(b - y) (Crawford and Mandwewala 1976). Figure 4 it appears that there is a grouping of points be- EDWARD G. SCHMIDT FIG. 1-The V - cl diagram for the stars from Table I. In this diagram and in the other figures the solid curve is the zero-age main-sequence relation from Crawford (1978) adjusted to a color excess of E(b- y) = 0.060 and a distance modulus of V, - Jf, = 10.26. Deviant stars are identified by number. FIG. 2-The V - P diagram of the stars from Table I. PHOTOMETRY OF NGC 3114 FIG. 3-The /3 - c, diagram of the stars from Table I FIG. 4-The color excesses plotted against the true distance moduli for all the stars from Table I except star 47. tween V,, - MV = 9.7 and 10.8. If we assume that the There is little reddening in this field and the mean stars in this range are all members and reject the remain- reddening is not affected by our choice of member stars. der, we obtain a mean distance modulus of 10.27 f The mean for the stars which appear to be members in 0.28. Applying both criteria reduces the sample to 14 Figures 1, 2, and 3 is E(b- y) = 0.060 + 0.009 and we stars but is likely to be the best estimate because it adopt this as the cluster color excess. should contain few field stars. We therefore adopt that One star in Table I, number 47, deserves special men- value which is 10.26 + 0.10 (standard error of the tion. The derived distance modulus of this object, 16.97, mean). This corresponds to a distance of 1130 f 50 pc. implies the implausibly large distance of nearly 25 kpc. The error quoted is the internal error and does not in- However, one of the spectral types indicates emission in clude uncertainties due to the calibration and possibly this star and it is likely that there is some filling in of the due to selection effects in the rejection of stars as non- HP line.
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