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http://hdl.handle.net/20.500.12386/23313
Title: | The Gaia-ESO Survey: Chromospheric emission, accretion properties, and rotation in γ Velorum and Chamaeleon I | Authors: | FRASCA, Antonio BIAZZO, Katia Lanzafame, Alessandro Carmelo ALCALA', JUAN MANUEL Brugaletta, Elisa Klutsch, A. STELZER, BEATE SACCO, GIUSEPPE GERMANO Spina, L. Jeffries, R. D. Montes, D. Alfaro, E. J. Barentsen, G. Bonito, Rosaria Gameiro, J. F. López-Santiago, J. Pace, G. Pasquini, L. PRISINZANO, Loredana Sousa, S. G. Gilmore, G. RANDICH, Maria Sofia MICELA, Giuseppina BRAGAGLIA, Angela FLACCOMIO, Ettore Bayo, A. Costado, M. T. FRANCIOSINI, Elena Hill, V. Hourihane, A. Jofré, P. Lardo, C. Maiorca, E. Masseron, T. MORBIDELLI, LORENZO Worley, C. C. |
Issue Date: | 2015 | Journal: | ASTRONOMY & ASTROPHYSICS | Number: | 575 | First Page: | A4 | Abstract: | Aims: One of the goals of the Gaia-ESO Survey (GES), which is conducted with FLAMES at the VLT, is the census and the characterization of the low-mass members of very young clusters and associations. We conduct a comparative study of the main properties of the sources belonging to γ Velorum (γ Vel) and Chamaeleon I (Cha I) young associations, focusing on their rotation, chromospheric radiative losses, and accretion. Methods: We used the fundamental parameters (effective temperature, surface gravity, lithium abundance, and radial velocity) delivered by the GES consortium in the first internal data release to select the members of γ Vel and Cha I among the UVES and GIRAFFE spectroscopic observations. A total of 140 γ Vel members and 74 Cha I members were studied. The procedure adopted by the GES to derive stellar fundamental parameters also provided measures of the projected rotational velocity (vsini). We calculated stellar luminosities through spectral energy distributions, while stellar masses were derived by comparison with evolutionary tracks. The spectral subtraction of low-activity and slowly rotating templates, which are rotationally broadened to match the vsini of the targets, enabled us to measure the equivalent widths (EWs) and the fluxes in the Hα and Hβ lines. The Hα line was also used for identifying accreting objects, on the basis of its EW and the width at the 10% of the line peak (10%W), and for evaluating the mass accretion rate (Ṁ<SUB>acc</SUB>). Results: The distribution of vsini for the members of γ Vel displays a peak at about 10 km s<SUP>-1</SUP> with a tail toward faster rotators. There is also some indication of a different vsini distribution for the members of its two kinematical populations. Most of these stars have Hα fluxes corresponding to a saturated activity regime. We find a similar distribution, but with a narrower peak, for Cha I. Only a handful of stars in γ Vel display signatures of accretion, while many more accretors were detected in the younger Cha I, where the highest Hα fluxes are mostly due to accretion, rather than to chromospheric activity. Accreting and active stars occupy two different regions in a T<SUB>eff</SUB>-flux diagram and we propose a criterion for distinguishing them. We derive Ṁ<SUB>acc</SUB> in the ranges 10<SUP>-11</SUP>-10<SUP>-9</SUP> M<SUB>☉</SUB> yr<SUP>-1</SUP> and 10<SUP>-10</SUP>-10<SUP>-7</SUP> M<SUB>☉</SUB> yr<SUP>-1</SUP> for γ Vel and Cha I accretors, respectively. We find less scatter in the Ṁ<SUB>acc</SUB> - M<SUB>⋆</SUB> relation derived through the Hα EWs, when compared to the Hα10%W diagnostics, in agreement with other authors. <P />Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002.Tables 5, 6, and Appendix A are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201424409/olm">http://www.aanda.org</A>Tables 2-4 are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/575/A4">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/575/A4</A> | Acknowledgments: | The authors are grateful to the referee for carefully reading the paper and for the useful remarks. This work was partly supported by the European Union FP7 program through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell’Istruzione, dell’ Università e della Ricerca (MIUR) in the form of the grant “Premiale VLT 2012”. The results presented here benefit from discussions held during the Gaia -ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Program. S.G.S. acknowledge the support from the Fundação para a Ciência e Tecnologia, FCT (Portugal) in the form of the fellowship SFRH/BPD/47611/2008. This research also made use of the SIMBAD database, operated at the CDS (Strasbourg, France) and of the Deep Near Infrared Survey of the Southern Sky (DENIS) database. | URI: | http://hdl.handle.net/20.500.12386/23313 | URL: | https://www.aanda.org/articles/aa/pdf/2015/03/aa24409-14.pdf https://arxiv.org/pdf/1412.4153.pdf |
ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201424409 | Bibcode ADS: | 2015A&A...575A...4F | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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aa24409-14.pdf | pdf editoriale | 1.37 MB | Adobe PDF | View/Open |
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