This programme aims at obtaining optical spectra of a large sample of
young
stars in the L1630 and L1641 clouds in Orion. These two clouds have been
imaged in excellent quality with the IRAC camera onboard Spitzer Space
Telescope at 3.6, 4.5, 5.8 and 8.0 micron, in total the infrared observations
cover several square degrees. Based on the infrared colors, we have identified
hundreds of YSO candidates in both clouds. Judging from IR fluxes, there are
stars present in various stages of their evolution. These range from very young
(embedded, still heavily accreting, "class I") objects, through intermediate age
YSOs (still harboring a massive disk but no longer accreting stronger, "class II"),
to more evolved objects that appear to have already lost at least the inner parts
of their disks ("class III").
Due to the large number of detected sources, the Spitzer observations allow
statistical studies of the disk properties and evolution. We wish to study how
the disk properties relate to those of the central star. Thus it is essential to
have well determined stellar parameters, which can be obtained only through
spectroscopy. This is the purpose of the VIMOS observations: we have selected
the most promising fields in the Spitzer data (those with most YSO candidates),
obtained VIMOS pre-imaging and correlated optically visible stars with the
disks seen in the Spitzer images.
This programme has a somewhat confusing history, and I will therefore briefly
sketch a "sequence of events" that should take away possible confusion.
The programme was rated as being of high scientific value, but the OPC
expressed some doubts concerning its feasibility. Therefore, it was split
up in two parts: a high priority "pilot" study of 1 field to demonstrate
feasibility (spectroscopy has recently been performed), and a reduced
priority part containing the bulk of the sample. Thus, the programme
*should* have been assigned 4 subruns (A: pre-imaging for the pilot field,
B: MOS for the pilot field, C: pre-imaging for the bulk sample, D: MOS for
the bulk sample). Originally however, there was only an A and a B subrun.
Run C and D have been added in later.
Further, we were still in the process of analyzing the IR (Spitzer) data
while the phase 1 proposal was being written. The original proposal had
many more different fields, all with only 1 pointing per field. Afterward,
we found that the quality of the IR data varied strongly, and that the data
of the L1630 and L1641 fields were highly superior compared to the rest of
the sample. Thus, we decided to omit a number of sources, and do more pointings
in the L1630 and L1641 (named L1630_1, L1630_2, etc). The target list for the
C+D runs is different from the original phase 1 list (waiver was submitted and
approved).
Note that L1641_2 has already been done (this was the "pilot" field), and
L1641_4 had so few optically visible sources in the pre-imaging that we
dropped this one (it had many interesting IR sources but these all turned
out embedded).
Thus, we are left with the following (with priorities, which are also indicated
in the OBs themselves):
field prior
L1641_1 2
L1641_3 5
L1641_5 7
L1641_6 1
L1630_1 4
L1630_2 3
L1630_3 6
Due to the relatively late submission of the OBs (an unfortunate coincidence of
a number of practical constrains on my side), the other field in the programm
(HD245185, with 2 subfields), is no longer feasible during this semester (and
the L16## fields have higher priority anyway) and have not been included.
Thus, the total execution time is 7.3 hours shorter than allocated).
That's, we hope everything is clear, especially the skies ;-)
good luck!