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GSC-II Annual Meeting Barolo, Italy, 22-23
October 2001
Galactic studies with GSC-II
Alessandro Spagna Osservatorio Astronomico di
Torino
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Galactic structure all-sky starcounts
Cumulative Starcounts for F ? 18 and J ? 19
(bgt20?) predicted by the Mendezs Galaxy model
extended to the GSC-II photometric system.
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Galactic structure all-sky starcounts
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Starcount Distribution
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Proper motion distribution
GSC2 Proper motion vs. distribution predicted by
the Besancon model for 17ltVlt17.5 and 0.5ltB-Vlt0.9
(blue peak)
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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 100ltrlt400 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

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Kinematics of Pre-MS stars in the Chamaleleon SFR
Cha I
Cha II
? Cha
Molecular clouds of the SFR cloud complex in Cha,
derived from COBE 100 ?m maps. The rectangle
indicates the S039 plate.
Spatial distribution and proper motions of 140
PMS stars (bona fide PMS, wTTs, cTTs) over about
150 sq-deg.
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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 ?160-170
  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).

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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, tlt80 Myr) and associated interstellar
matter.
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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.
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Kinematics of Pre-MS stars in the Chamaleleon SFR
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)
Cha
Lupus
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Check of astrometric systematic errors which
affect proper motions
Residuals XS038 vs. ESO blue ?T4 yr
Residuals XS018 vs. S018 ?T16 yr