Strömgren and Hβ photometry of O and B type stars in star-forming regions - III. Carina Spiral Feature

Astronomy and Astrophysics Supplement Series, Jul 2018

Strömgren and Hβ photometry of O and B type stars, generally brighter than 9.5 mag is reported for the field of the Carina Spiral Feature. The observations are based on the PPM catalogue identifications and are designed to improve the completeness of the existing data for the bright early-type stars in the field. We present new uvby photometry for 283 stars and Hβ photometry for 225 of them. These observations are part of an ongoing effort to study the structure of selected star-forming regions in the Milky Way by means of photometry. A comparison of the new data to other data sets for this field is presented.

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Strömgren and Hβ photometry of O and B type stars in star-forming regions - III. Carina Spiral Feature

Astron. Astrophys. Suppl. Ser. photometry of O and B type stars in Str¨omgren and H star-forming regions III. Carina Spiral Feature? N.T. Kaltcheva 0 1 E.H. Olsen 0 J.V. Clausen 0 0 Niels Bohr Institute for Astronomy , Physics and Geophysics, Juliane Maries Vej 30, DK-2100 Copenhagen , Denmark 1 Department of Astronomy, University of So a , 5 James Bourchier Avenue, 1164 So a , Bulgaria Str¨omgren and H photometry of O and B type stars, generally brighter than 9.5 mag is reported for the eld of the Carina Spiral Feature. The observations are based on the PPM catalogue identi cations and are designed to improve the completeness of the existing uvby data for the bright early-type stars in the eld. We present new uvby photometry for 283 stars and H photometry for 225 of them. These observations are part of an ongoing effort to study the structure of selected star-forming regions in the Milky Way by means of uvby photometry. A comparison of the new data to other uvby data sets for this eld is presented. stars; early type | and associations; Carina Spiral Feature - open clusters 1. Introduction The importance of the Carina Spiral Feature in understanding the structure of our own Galaxy has been stressed by Bok (1932) and has since then been emphasized by many others. As pointed out by Graham 30 years ago, the Carina section of the MW is the most promising of all elds for the optical study of a single large scale feature of the Galaxy (Graham 1970) . The Carina Feature is spread out over a distance of several Send o print requests to: N. Kaltcheva ? Based on data from the Stro¨mgren Automatic Telescope of the Copenhagen University Observatory, La Silla. ?? Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html kiloparsecs along the line of sight and may either be part of a major spiral arm, or may represent a strong inter-arm link. A large number of prominent young open clusters and OB associations are found over a wide range of distances and have also been intensively investigated. The Feature is situated beyond 500 pc, i.e. beyond the limits of the Hipparcos survey (ESA, 1997) , and so far photometry remains the most e cient tool to study its characteristics. The observations presented in this paper are aimed at improving the completeness of the Str¨omgren and H data of O and B type stars, generally brighter than 9.5 mag. The eld under consideration is within 5 degrees from the Galactic plane, bounded between l = 285o and l = 295o. 2. Observations and reductions The observations were performed with the Str¨omgren Automatic Telescope (SAT) of the Copenhagen University Observatory at La Silla. The vast majority of the photometry was obtained during 20 nights in December 1997 { January 1998. Several stars, omitted during this run were included in our list of targets during December 1998. The selection of the targets is based on the PPM catalogueSouth (Bastian & Ro¨ser 1993) , including all stars of spectral types O and B in the eld. The uvby compilation of Hauck & Mermilliod (1998) was used to exclude from the list of targets stars with already existing data. Since it would be of interest to compare the new data to other data sets, some stars in common with previous observations were, however, left in the list. In this way, 283 stars for uvby photometry and 225 for H photometry were included. 77 stars in the nal sample are intrinsically luminous stars (Stephenson & Sanduleak 1971). The selection of standard stars, observing procedures and transformations to the standard systems for the two observing runs are described in detail in Kaltcheva & Olsen (1999) and Kaltcheva et al. (1999) (Papers I and II). All observations in the present catalogue were made by the SAT in its fully-automatic mode. Details about the spectrometer, the observing procedure, and the fullyautomatic mode are given by Olsen (1993, 1994). A circular diaphragm of 1700 was used. The number of photo-electrons counted was 100 000 in the y-channel and 70 000 in the narrow-channel, except for a few of the faintest stars. The background was measured at each program star at a xed o set. Before reductions, several sky measurements from a small area of the sky, and contiguous in time, were combined and then used on all stars in the area. Sky measurements contaminated by faint stars were eliminated in this process. 3. Results In Table 1, the catalogue of Str¨omgren uvby photometry for 283 program stars is presented. The PPM identi cations are given in the rst column. Columns 2, 4, 6 and 8 give V , b − y, m1 and c1. Columns 3, 5, 7 and 9 present the internal rms errors of one observation (weight 1). In Cols. 10 and 11 the weight of V and the indices are listed. Column 12 gives the number of nights for each star. Table 2 gives H photometry for 225 program stars. The PPM identi cations are given in the rst column, and the photometry, the internal rms errors of one observation (weight 1), the weight of the H indices and the number of the nights for each star follow. The cross-identi cation with the HD and LS numbers is available in the last two columns of the tables. 4. Comparison of the new data to other data sets Good agreement between photometric data coming from di erent observers is an essential issue when studying the structure and characteristics of star-forming regions, both on the basis of photometric diagrams or via the photometry-derived physical stellar parameters. Observing stars from previous lists helps to get more clear insight on the homogeneity of the existing photometric data sets. This allows one to evaluate the errors in the derived stellar parameters when using photometry from di erent sources. Furthermore, it will eventually permit to homogenize to some extent the existing uvby photometric data for the eld under investigation. In this paragraph we compare our data to other sources. Tables 3 and 4 present this comparison for the H photometry and for the V uvby photometry, respectively. The tables give the mean di erences between the individual sources and the new data, together with the corresponding standard deviations (from the mean di erence) in , V , b − y, m1 and c1 for each source. The rst columns show the number of stars in common involved in the comparison. The sources of the corresponding photometric data sets are listed in the last columns. The comparison of the new data to the homogenized data from the Hauck & Mermilliod (1998) compilation in the sense (HM minus this paper) is given in Fig. 1. Figures 2 to 5 present the comparison of the data obtained in this paper to the individual sources used in the HM compilation for the considered eld, in the sense (others minus this paper). The agreement between H photometry from HM and the present paper is in general good (Fig. 1). The mean di erences Delta = H − H (SAT) listed in Table 3 are below 0.010 mag for the majority of the sources and the comparison to the individual sources present small systematic trends of 0:03 mag only in two cases. For some sources the V magnitudes show a systematic shift in the zero point of as much as 0.03 mag (Fig. 2). This shift is more signi cant towards the brightest stars (V < 7 mag) and does not obviously depend of the colour term (b − y) (Fig. 3). The largest disagreements are with Hill & Perry (1969) and Eggen (1983) : 0.032 and 0.019 mag, respectively. The agreement in (b − y) is within the photometric errors, although for some sources a systematic di erence of 0.01 mag may exist (Fig. 4). The m1 and c1 colour di erences obtained in the present paper show a good agreement with Crawford et al. (1971) , Schneider & Weiss (1988) and Kaltcheva & Georgiev (1994) (Fig. 5). There is a discrepancy of up to −0.02 in m1 and up to 0.02 mag in c1 with the other sources. Dealing with O and B luminous stars, one should keep in mind the variability in light among them (Abt 1957) , which also contributes to the scatter between the di erent sets. Spectral anomalies can also cause large mean errors in magnitude or colour indices (Young 1974; Manfroid 1985; Franco 1994). The comparisons in Tables 3 and 4 suggest di erences in the precision and accuracy of the di erent data sets. The consistency of di erent uvby data sets has been already discussed by Manfroid & Sterken (1987), who stressed the need for a more strictly de ned standard system and for closely matching instrumental system. The indication of a small systematic di erence in m1 and c1 is slightly worrying. A similar di erence in c1 in a large data set has been previously noticed by Franco (1994). Recently, Crawford (1999a) also presented a comparison between uvby data from di erent publications, showing di erences in m1 and c1 up to 0:05 mag. He also pointed out the reasons that can lead to systematic errors (Crawford 1999b) . An additional source may be not applying a correction of −0.008 in c1 to a large set of the southern standards (cf. Olsen 1983). In the case of photometry in star-forming regions, the discrepancy may also 2.6 2.7 beta (SAT) (mag) 7 8 V (SAT) (mag) 9 10 -0.1 0 0.1 0.2 (b-y) (SAT) (mag) 0.3 0.4 The systematic di erences between the existing data sets lead to systematic di erences in the photometryderived stellar parameters. The ideal case to compare data only internally is often not possible. In this event the possible inconsistence should be carefully estimated. If the photometric diagrams including c1 and m1 are used, the di erences in the photometry, mentioned above, can be easily misinterpreted in terms of luminosity or metallicity. In case of calculating the reddening, a systematic di erences of 0.01 in b − y and 0.02 in c1 lead to a di erence of 0.01 in E(b − y). In calculating the absolute magnitude MV , which is a function of and c0, the indices are the most critical parameter. A systematic di erence 2 3 8 11 13 12 7 8 V (SAT) (mag) 9 10 5 6 7 8 V (SAT) (mag) 9 10 0.1 0.2 0.3 0.4 -0.1 0 0.1 0.2 0.3 0.4 -0.1 0 0.1 0.2 0.3 0.4 -0.1 0 0.1 0.2 0.3 0.4 -0.1 0 0.1 0.2 0.3 0.4 -0.1 0 0.1 0.2 0.3 0.4 -0.1 0 0.1 0.2 0.3 0.4 -0.1 0 0.1 0.2 0.3 0.4 -0.1 0 0.1 0.2 0.3 0.4 -0.1 0 fFoirg.t5h.eTshouerdcieselriesntecdesinDTelatablme41., Tc1heeqiunadlivtioduma1l −soumr1c(eSs AoTf)th(ecrpohssoetso)maentdryc1ar−e csh1(oSwAnTa)t(tohpeenpasnyemlsbols) plotted vs. b − y(SAT) 12 −0.007 0.024 12 0.019 0.012 of 0.03 mag in , leads to a systematic di erences in the corresponding MV values of 0.3 mag. A systematic di erence from the standard system of +0.02 0.02 mag in c1 alone leads to overestimation of MV of 0.15 mag and to overestimation of the distance of about 5%. The structure of the Carina Spiral Feature eld based on photometry presented here will be discussed in a forthcoming paper. Acknowledgements. This research has been supported by the Danish Natural Science Research Council. This research has made use of the Simbad database, operated at CDS, Strasbourg, France. Franco G.A.P., 1994, A&AS 104, 9 Manfroid J., Sterken C., 1987, A&AS 71, 539 Hauck B., Mermilliod M., 1998, A&AS 129, 143 Olsen E.H., 1983, A&AS 54, 55 Hill G., Perry C.L., 1969, AJ 74, 1011 Olsen E.H., 1993, A&AS 102, 89 Kaltcheva N.T., Georgiev L.N., 1994, MNRAS 269, 289 Olsen E.H., 1994, A&AS 106, 257 Kaltcheva N.T., Olsen E.H., 1999, A&A 352, 600 (Paper I) Schneider H., Weiss W.W., 1988, A&AS 75, 353 Kaltcheva N.T., Olsen E.H., Clausen J.V., 1999, A&A 352, 605 Stephenson C.B., Sanduleak N., 1971, Luminous Stars in the (Paper II) Southern Milky Way, Publ. Warner Swasey Obs. 1, 1 Manfroid J., 1985, Traitement Numerique des Donnees Young A.T., 1974, in Methods of Experimental Physics 12A, Photometriques, Universite de Liege Carleton N. (ed.). Academic Press, NY, p. 123 Abt H. , 1957 , ApJ 126 , 138 Bastian U. , Ro¨ser S., 1993 , Catalogue of Positions and Proper Motions - South, Astronomisches Rechen-Institut, Heidelberg Bok B.J. , 1932 , Harvard Repr ., No. 77 Crawford D.L. , 1999a , in Craine D., Tucker R. , Barnes J . (eds.), ASP Conf. Ser. 189, Astron. Soc. Pac ., San Francisco, p. 6 Crawford D.L. , 1999b , in Craine, D., Tucker R. , Barnes J . (eds), ASP Conf. Ser. 189, Astron. Soc. Pac ., San Francisco, p. 3 Crawford D.L. , Barnes J.V. , Golson J.C. , 1971 , AJ 76 , 621 Graham J.A. , 1970 , IAU Symp . 38 , 262 Eggen O.J. , 1983 , MNRAS 204 , 377 ESA 1997 , The Hipparcos Catalogue , ESA SP-1200


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N. T. Kaltcheva, E. H. Olsen, J. V. Clausen. Strömgren and Hβ photometry of O and B type stars in star-forming regions - III. Carina Spiral Feature, Astronomy and Astrophysics Supplement Series, 365-372, DOI: 10.1051/aas:2000364