Publication: Quantifying the contamination by old main-sequence stars in young moving groups: the case of the Local Association
Loading...
Official URL
Full text at PDC
Publication Date
2009-05
Authors
Advisors (or tutors)
Editors
Journal Title
Journal ISSN
Volume Title
Publisher
EDP Sciencies
Citations
Exportar
Abstract
Context. The associations and moving groups of young stars are excellent laboratories for investigating stellar formation in the solar neighborhood. Previous results have confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of possible members of young stellar kinematic groups. A detailed study of the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, and identify the origin of these structures. Aims. Our intention is to characterize members of the young moving groups, determine their age distribution, and quantify the contamination by old main-sequence stars, in particular, for the Local Association. Methods. We used stars possible members of the young (~10-650 Myr) moving groups from the literature. To determine the age of the stars, we used several suitable age indicators for young main sequence stars, i.e., X-ray fluxes from the Rosat All-sky Survey database, photometric data from the Tycho-2, Hipparcos, and 2MASS database. We also used spectroscopic data, in particular the equivalent width of the lithium line Li I λ6707.8 Å and H_α, to constrain the range of ages of the stars. Results. By combining photometric and spectroscopic data, we were able to separate the young stars (10-650 Myr) from the old (> 1 Gyr) field ones. We found, in particular, that the Local Association is contaminated by old field stars at the level of ~30%. This value must be considered as the contamination for our particular sample, and not of the entire Local Association. For other young moving groups, it is more difficult to estimate the fraction of old stars among possible members. However, the level of X-ray emission can, at least, help to separate two age populations: stars with <200 Myr and stars older than this. Conclusions. Among the candidate members of the classical moving groups, there is a non-negligible fraction of old field stars that should be taken into account when studying the stellar birthrate in the solar neighborhood. Our results are consistent with a scenario in which the moving groups contain both groups of young stars formed in a recent star-formation episode and old field stars with similar space motion. Only by combining X-ray and optical spectroscopic data is it possible to distinguish between these two age populations.
Description
© ESO 2009. J. López Santiago acknowledges financial support by the Marie Curie Fellowship contract No. MTKD-CT-2004-002769 and financial contribution by MERG-CT-2007-046535. The Madrid group acknowledges financial contribution by the Universidad Complutense de Madrid and the Programa Nacional de Astronomía y Astrofísica of the Spanish Ministerio de Educación y Ciencia (MEC), under grants AYA2005–02750 and AYA2008- 000695 and to the PRICIT project S-0505/ESP-0237 (ASTROCAM) of the Comunidad de Madrid. G. Micela acknowledges financial contribution from contract ASI-INAF I/088/06/0. We thanks the referee for useful comments that allowed to improve our manuscript. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research made use of the SIMBAD database, operated at the CDS, Strasbourg, France.
UCM subjects
Unesco subjects
Keywords
Citation
Affer, L., Micela, G., & Morel, T. 2008, A&A, 490, 601
Antoja, T., Figueras, F., Fernández, D., & Torra, J. 2008, A&A, 490, 135
Asiain, R., Figueras, F., Torra, J., & Chen, B. 1999, A&A, 341, 427
Barrado y Navascués, D. 1998, A&A, 339, 831
Bertout, C., & Genova, F. 2006, A&A, 460, 499
Bessell, M. S., & Brett, M. 1988, PASP, 100, 113
Bubar, E. J., King, J. R., Soderblom, D. R., Deliyannis, C. P., & Boesgaard, A. M. 2007, AJ, 134, 2328
Daemgen, S., Siegler, N., Reid, I. N., & Close, L. M. 2007, ApJ, 654, 558
Eggen, O. J. 1991, AJ, 102, 2028
Eiroa, C., Garzón, F., Alberdi, A., et al. 2001, A&A, 365, 110
ESA 1997, The Hipparcos and Tycho Catalogues, ESA SP-1200
Famaey, B., Jorissen, A., Luri, X., et al. 2005, A&A, 430, 165
Famaey, B., Pont, F., Luri, X., et al. 2007, A&A, 461, 957
Famaey, B., Siebert, A., & Jorissen, A. 2008, A&A, 483, 453
Favata, F., Barbera, M., Micela, G., & Sciortino, S. 1993, A&A, 277, 428
Fernández, D., Figueras, F., & Torres, J. 2008, A&A, 480, 735
Francis, C., & Anderson, E. 2009, in press [arXiv:0901.3503]
Guillout, P., Sterzik, M. F., Schmitt, J. H. M. M., et al. 1998, A&A, 334, 540
Herbig, G. H. 1978, in Problems of Physics and Evolution of the Universe, ed. L. V. Mirzoyan (Yerevan: Publishing House of the Armenian Academy of Sciences), 171
Hg, E., Fabricius, C., Makarov, V. V., et al. 2000, A&A, 355, L27
Hünsch, M., Schmitt, J. H. M. M., Schroeder, K. P., & Reimers, D. 1996, A&A, 310, 801
King, J. R., Villarreal, A. R., Soderblom, D. R., Gulliver, A. F., & Adelman, S. J. 2003, AJ, 125, 1980
Klement, R., Fuchs, B., & Rix, H.-W. 2008, ApJ, 685, 261
López Santiago, J. 2005, Ph.D. Thesis, Universidad Complutense de Madrid, Spain
López Santiago, J., Montes, D., Crespo Chacón, I., & Fernández Figueroa, M. J. 2006, ApJ, 643, 1160
López Santiago, J., Micela, G., Sciortino, S., et al. 2007, A&A, 463, 165
López Santiago, J., Montes D., Gálvez M. C., et al. 2009, A&A, in preparation
Makarov, V. V. 2007, ApJS, 169, 105
Mamajek, E. E., & Feigelson, E. D. 2001, ASP Conf. Ser. 244, Young Stars Near Earth: Progress and Prospects, ed. R. Jayawardhana, & Th. Greene, 104
Micela, G., Affer, L., Favata, F., et al. 2007, A&A, 461, 977
Montes, D., López Santiago, J., Gálvez, M. C., et al. 2001a, MNRAS, 328, 45
Montes, D., López Santiago, J., Fernández Figueroa, M. J., & Gálvez, M. C. 2001b, A&A, 379, 976
Montes, D., López Santiago, J., Martínez Arnáiz, R. M., et al. Proceedings of the The 15th Cool Stars, Stellar Systems and the Sun workshop, held in St Andrews, Scotland, UK, July 21–25, 2008, ed. E. Stempels, Conf. Proc. Ser. Amer. Inst. Phys. (AIP), 1094, 943
Orlov, V. V., Panchenko, I. E., Rastorguev, A. S., & Yatsevich, A. V. 1995, Astron. Zh., 72, 495
Schmitt, J. H. M. M., Fleming, T. A., & Giampapa, M. S. 1995, ApJ, 450, 392
Sciortino, S., Favata, F., & Micela, G. 1995, A&A, 296, 370
Siess, L., Duffour, E., & Forestini, M. 2000, A&A, 358, 593
Skuljan, J., Hearnshaw, J. B., & Cottrell, P. L. 1999, MNRAS, 308, 731
Soderblom, D. R., & Mayor, M. 1993, ApJ, 402, 5
Soderblom, D. R., Jones, B. F., Balachandran, S., et al. 1993, AJ, 106, 1059
Soderblom, D. R., King, J. R., Siess, L., et al. 1998, ApJ, 498, 385
Torres, C. A. O., Quast, G. R., da Silva, L., et al. 2006, A&A, 460, 695
Torres, C. A. O., Quast, G. R., Melo, C. H. F., & Sterzik, M. F. 2008, ASP Monogr. Public., 5, 757
Xu, Y., Reid, M. J., Zheng, X. W., & Menten, K. M. 2006, Science, 311, 54
Zhao, J., Zhao, G., & Chen, Y. 2009, ApJ, in press [arXiv:0902.1370]
Zickgraf, F.-J., Krautter, J., Reffert, S., et al. 2005, A&A, 433, 151
Zuckerman, B., & Song, I. 2004, ARA&A, 42, 685