Other
Scientific paper
Jan 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005esasp.576..105k&link_type=abstract
"Proceedings of the Gaia Symposium "The Three-Dimensional Universe with Gaia" (ESA SP-576). Held at the Observatoire de Paris-Me
Other
Gaia Photometry, Visual Absorptions, Accuracy, Star Forming Regions, Cloud Distances
Scientific paper
A reason for correcting the obscuring effect of the interstellar medium is of course to obtain individual intrinsic astrophysical stellar parameters. Another useful application of the distance-extinction information is the potential to localize molecular clouds and star forming regions in three-dimensional space. The distance to a star forming region is a necessity for deriving all sorts of physical parameters needed for protostellar modelling. The reddening correction is mainly a problem for the Gaia medium band photometry systems to solve. A main goal of the Gaia mission is to determine ages better than 10%. General accuracy conditions for the sample termed scientific targets (ST, Jordi et al. (2003a)) are detailed in Jordi et al. (2003b) where a weighting scheme was also introduced. Since Gaia was conceived as a Galactic mission less emphasis has been put on some stellar types and chemical elements implying the resulting set of STs and a corresponding weighting scheme. The weights are to a large extent determined from the targets relevant for Galactic studies. So it is important that the final photometric system (PS henceforth) is able to provide extinctions for the highest weighted Galactic tracers. If a PS does not succeed in this the astrophysical parameters may not be derived. An extinction correction is considered to be acceptable when σAV ≤ 0.09 mag. We use simulated data from the X2MX2B system which at the moment of writing showed the best overall figure of merit. The results are not too encouraging and show some unpleasant tendencies e.g., that some STs with the highest weighting do not perform quite well at the larger distances. A general result of the test is that scientific targets with the highest priority have a success rate of about 50% at a distance of ≈ 5 kpc. In order to demonstrate what may be done for the molecular clouds / star forming regions we use an intrinsic calibration of the 2MASS JHK photometry to probe in the direction of some intermediate velocity gas and in the direction of the star forming cloud MBM 12. The intermediate velocity gas is interesting to probe for dust because it may possess a non-standard gas/dust ratio. We introduce a new concept for estimating cloud distances by only accepting a cloud distance, not only when we see an extinction jump at a well defined distance, but also require that the projected extinction contours show a high degree of continuity. Such a procedure is only possible from sky surveys with a sufficiently high stellar density. This way we derive distances to two features in the intermediate velocity cloud IV Arch of 0.3 and 1.5 kpc and confine the MBM 12 distance to the range from 200 to 300 pc.
Fabricius Claus
Knude Jens
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