Galactic studies with GSC-II GSC-II Annual Meeting Barolo, Italy, October 2001 Alessandro Spagna Osservatorio Astronomico di Torino

Galactic structure: all-sky starcounts Cumulative Starcounts for F  18 and J  19 (|b|>20  ) predicted by the Mendez’s Galaxy model extended to the GSC-II photometric system.

Galactic structure: all-sky starcounts

Starcount Distribution

Proper motion distribution GSC2 Proper motion vs. distribution predicted by the Besancon model for 17<V<17.5 and 0.5<B-V<0.9 (blue peak)

Kinematics of Pre-MS population in the Chamaeleon Star Forming Region The Chamaeleon region is one of the most active SFR near the Sun, including 3 large dark clouds (Cha I, Cha II and Cha III) and several small isolated clouds with 100<r<400 pc. A large population of Pre-MS stars (cTTs with strong H  emission lines, infrared sources, Herbig-Haro objects) is associated to the Cha I and Cha II clouds. In addition, a large number of wTTs with faint H  emission line, but strong Li I absorption line (as cTTs) plus strong X-ray activity has been revealed by the ROSAT All Sky Survey, spread over an area of 160 sq-deg around the clouds. We used GSC-II material for deriving proper motions of about 140 PMS stars, in order to: Identify the various kinematic groups of PMS stars associated with the SFR complex Perform a kinematical membership of the PMS candidates to these groups Infer information on the dynamical local mechanics and the scenario of global evolution of the whole SFR

Kinematics of Pre-MS stars in the Chamaleleon SFR Molecular clouds of the SFR cloud complex in Cha, derived from COBE 100  m maps. The rectangle indicates the S039 plate.  Cha Cha II Cha I Spatial distribution and proper motions of 140 PMS stars (bona fide PMS, wTTs, cTTs) over about 150 sq-deg.

Kinematics of Pre-MS stars in the Chamaleleon SFR Two main kinematic populations have been identified: the PMS stars (cTTs, wTTs, IR) associated to Cha I with  (l)  -20 mas/yr, at a distance of  pc The dispersed wTTs, with  (l)  -40 mas/yr, associated to a newly discovered population at a smaller distance of  100 pc In addition,the dispersed wTTs are older (10-30 Myr) than the cTTs in Cha I (a few Myr).

Kinematics of Pre-MS stars in the Chamaleleon SFR Note that the Chamaeleon SFR is not far from several other SFRs, OB associations and young cluster, such as the Upper Scorpius, Lupus, Low Centaurus Crux, etc, which are correlated to the Gould Belt, the asymmetric structure in the galactic plane including both a stellar component (Pop.I, t<80 Myr) and associated interstellar matter.

Kinematics of Pre-MS stars in the Chamaleleon SFR The formation of the Gould Belt is still controversial. One hypothesis claims an expanding ring produced by collisions of high velocity clouds or supernova explosions (Moreno et al, 1999, 522, 276). Guillout et al (1998, 337, 113) pointed out that in this scenario the belt should actually a thick ring, and that star forming activity starts in the front of the expanding ring while older SFRs are found in the inner parts.

Kinematics of Pre-MS stars in the Chamaleleon SFR Cha Lupus Gould Belt The expanding ring scenario is well supported by our data, after deriving 3D velocities based on proper motions, radial velocity and estimated distances: Cha-I cTTs and molecular clouds are located on the ring front, while the older wTTs are located in the intermediate regions. (Terranegra et al., 2001, in preparation)

Check of astrometric systematic errors which affect proper motions Residuals XS018 vs. S018:  T=16 yr Residuals XS038 vs. ESO blue:  T=4 yr