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PMS stars and young BDs in Star Forming Regions

Within a collaboration with E. Covino and J.M. Alcalá of INAF-Napoli Observatory, A. Frasca and L. Spezzi have developed strategies for the identification of low-mass Pre-Main Sequence (PMS) stars, young Brown Dwarfs (BDs) and free-floating planet candidates using wide-field imaging techniques in star forming regions (). In particular, they present preliminary results on the identification of low-mass Pre-Main Sequence stars and young brown dwarf candidates in the star forming regions L1616, Chamaeleon II (Fig. 1.20) and the Southern Cross. Spectroscopic follow-up observations in L1616 show that some of the candidates are very likely young brown dwarfs ().

Figure 1.20: Dereddened $I_C$ versus $(I_C-z)$ diagram for the point-like objects extracted from WFI images in the Cha II field. The lines in the plot represent the theoretical PMS isochrones for 1 (dashed line), 5 (full line) and 10 Myr (dash-dotted line), respectively, shifted to the distance modulus of Cha II (6.25 mag). The previously known PMS stars are indicated with squares. The big dots represent the objects above the 5-Myr isochrone, i.e. the "photometrically-selected" candidates. The big blue dots represent the BD candidates with $H\alpha$ emission.
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They have also reported new photometric observations and a new dermination of the fundamental stellar parameters for the low-mass pre-main sequence eclipsing system RX J0529.4+0041A based on high-precision, near-IR ($JHK$) differential photometry obtained using adaptive optics at the ESO-La Silla 3.6m telescope, and $UBV(RI)_C$ CCD photometry performed with the OIG camera at TNG (). The new photometric data, in combination with the existing information from radial velocity curves, yield a more precise determination of the absolute dimensions and masses as well as of other basic physical properties of the components of the inner binary, as well as of the tertiary companion (Fig. 1.21).

Figure 1.21: Upper panel: Spectral energy distribution (SED) of RX J0529.4+0041 A as deduced from observed $UBV(RI)_C JHK$ fluxes (dots) compared with calculated ones (triangles) obtained from a combination of two synthetic Next-Generation spectra with effective temperatures of 5200K and 4200K (continuous thin lines). Lower panel: comparison between observed (dots) and computed (squares) SED of RX J0529.4+0041 B, superimposed to the synthetic Next-Generation spectrum (thin continuous line) for $T_{\rm eff}=4400$K.
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Within the above mentioned collaboration with INAF-Napoli Observatory, E. Marilli, A. Frasca and S. Catalano have also presented the results of an extensive photometric monitoring on 26 solar-mass weak-line T Tauri stars (WTTs) in the Orion clouds (). Photometric $B$ and $V$ data were collected from 1999 to 2004 at Catania Astrophysical Observatory. From the observed rotational modulation, induced by starspots, they derived the rotation periods, using both the Lomb-Scargle periodogram and the CLEAN deconvolution algorithms. The rotation periods range from about 0.5 to 13 days, with a major concentration around 1-2 days, giving further evidences for the spin up of solar-mass stars predicted by models of angular momentum evolution of pre-main sequence (PMS) stars. Though some of these stars have been found to be spectroscopic binaries, only a few of them are synchronized.


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Innocenza Busa' 2005-11-14