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RevMexAA (Serie de Conferencias), 26, 64–65 (2006) M. Altmann,1 R. A. M´endez,1 W. van Altena,2 V. Korchargin,2 M. T. Ruiz,1 and the MUSYC collaboration Presentamos resultados preliminares del programa gal´actico como parte de la colaboraci´on MUSYC. Utilizandola fotometr´ıa multicolor de MUSYC, podemos clasificar objetos y seleccionar muestras de un tipo dado. Apli-camos la selecci´on de color para establecer una muestra de estrellas M en el campo de MUSYC CDFS-E, quefue utilizado para estudiar la distribuci´on a lo largo del rayo de haz. La distribuci´on muestra tres componentespara los cuales hemos derivado alturas de escala que indican que estos componentes son el disco delgado, eldisco grueso y el halo.
We present some preliminary results of the Galactic program within the MUSYC collaboration. Using themulti-colour photometry of MUSYC we are able to classify objects and select samples of a given type. Weapply colour selection to establish a sample of M-stars in the MUSYC field CDFS-E which was then used tostudy the distribution along the pencil beam. The distribution shows three components for which we derivedscale heights indicating that these components are the Thin and Thick Disk and the Halo.
Key Words: GALAXY: DISK — GALAXY: STELLAR CONTENT — GALAXY: STRUCTURE — The MUltiwavelength Survey Yale Chile (Ga- (which was used to extract sources from the images).
For our purposes a limiting value of 0.85 was suffi- yale.edu/MUSYC) is a one square degrees deep multi- cient. Note however that CLASS becomes increas- passband survey. Like most, MUSYC’s main aim ingly less reliable for objects fainter than 25 mag.
is extragalactic research. However MUSYC was de- However a large fraction of these selected sources signed from the beginning with Galactic research in will still be extragalactic. To separate these from the mind - it is one of the very few which has a proper stars and also to classify the objects in the sample we developed a SED fitting routine which compares in- The Galactic program mainly aims at the detec- tegrated template fluxes, which were convolved with tion of faint objects, such as white and brown dwarfs the filter transmission, detector function and atmo- (see Altmann et al. 2005) but also aims at studies spheric throughput, with the optical data. The com- of stellar statistics. The colour selection routines de- parison is done using the minimisation of chi2. Hatz- Ed. Leopoldo Infante, Monica Rubio & Silvia Torres-Peimbert veloped to select these dwarfs can also be used to iminaoglou et al. (2002) and Groenewegen et al.
harvest samples of more common objects which can (2002) used a similar approach on the same field.
then be used to study the Galaxy and it’s substruc- As templates we currently use various extragalactic tures. Here we show some preliminary results of such and stellar model spectra. To accomodate redshift, a study in one of the fields (CDFS-E); the full results the extragalactic model spectra were redshifted in on all 4 fields will be published in a later stage.
2006: Instituto de Astronomía, UNAM - XI IAU Regional Latin American Meeting of Astronomy steps of 0.1 within reasonable redshift ranges.
To select the point sources from the catalog we used the CLASS parameter of SEXTRACTOR While this routine allows a relatively precise clas- sification of objects, there are some object types 1 Departamento de Astronom´ıa, Universidad de Chile, which are ambiguous, such as QSOs and A- stars.
Camino del Observatorio 1515, Las Condes, Santiago, Chile.
Another contaminant are elliptical galaxies. It was 2 Department of Astronomy, Yale University, New Haven, found that K and M stars are quite free of con- 3 Unfortunately due to persistent adverse weather condi- tamination, which is also supported by the spec- tion or technical problems the data acquisition for the second troscopy.Another reason for using K and M stars as epoch has been delayed for most fields. Moreover the MUSYC a probe in this analysis is that they are the most proper motion program extends to fields of a previous effort, numerous stars and their absolute magnitude range the CYDER (Calan Yale Deep Extragalactic Research) sur-vey, extending the total area for this part to three square fits perfectly to MUSYC’s magnitude range., i.e. the MUSYC M stars cover the whole Galactic extent.
A better method is to use two or three component distribution for the fit4. The resulting scale heightvalues for the 2-component fits are for both samples 800 pc for the middle component and 9300 pc for theshallow part, while the 3-component fit delivers 400 pc, 1060 pc and 16000 pc for our M-starsample, and150 pc , 780 pc and 9300 pc for the K-sample. The discrepancy in the latter fit is due to the issues con-cerning the bins closest to us. We therefore consider the 2-component fits to be more reliable, and come to the conclusion that the middle component, repre- senting the Galactic Thick Disk has a scale height ofabout 800 pc. The Halo (the shallow distribution), Fig. 1. The z distribution of M stars in the MUSYC which does not have an exponential distribution - field CDFS and various functions fitted to represent thescaleheights of different components. Two components therefore the fit can only be a crude approximation - can be clearly seen, the third can be glimpsed at the left.
has a value of 9000 pc. The steep component, featur-ing the Thin Disk has a value of 150-400 pc, clearlythe issues concerning this part need to be resolved.
Distances of the objects were determined by first Compared with the results of other work, we find deriving a quadratic relation between R − I (this that Altmann et al. (2004) arrive at 900 pc for the colour was used to ensure maximum accuracy in the Thick Disk and 7500 pc for the Halo. Especially the colours even for the faintest stars) and the abso- Thick Disk value is very close to ours - which is strik- lute V magnitude, based on data taken from Cox ing, since that study used both completely different (2000). From this the absolute V magnitude for each stars and methods. Another study concerning the star was computed. The distribution of the stars scale height of M stars (Phleps et al. 2000), leads to with distance was then transformed into a histogram a somewhat larger result of about 1200-1300 pc.
which was then normalised by the volume covered by Given that these are preliminary results, they each bin to give the volume density. Finally, assum- further constrain the scale height of the Thick Disk ing an exponential distribution we took the natural to be ≤ 1 kpc. This analysis is currently being done logarithm of the volume densities. Finally the dis- for all 4 fields and we will then be able to draw fur- tribution was corrected for Galactic latitude.
ther conclusions about the structure of our Galaxy.
The resulting logarithmic distribution does not show a uniform slope, as would be expected if there was only one population of stars (Figure 1); there Altmann, M., Edelmann, H., & de Boer, K. S. 2004, are most likely two to three components with a very Ed. Leopoldo Infante, Monica Rubio & Silvia Torres-Peimbert steep one at small z values, a somewhat less steep component dominating at z between 2 and 7 kpc and W. F., Gawiser, E., & van Dokkum, P. 2005, ASP- finally a very shallow distribution predominantly at large values of z. The inner steep slope is not very Cox, A. N. 2000, Allen’s Astrophysical Quantities, 4th.
prominently seen in the z-distribution of M stars.
2006: Instituto de Astronomía, UNAM - XI IAU Regional Latin American Meeting of Astronomy The reason for this is that the actual volume of the Gawiser, E., van Dokkum, P., Herrera, D., Maza, J., Ca- innermost bins are small, so we are dealing with stander, F. J., & Infante, L. 2006, ApJS, 162, 1 small number statistics here. Moreover the closest Groenewegen, M. A. T., Girardi, L, Hatziminaoglou, E., Benoist, C., Olsen, L. F., da Costa, L., et al. 2002, stars are bright enough to be partly saturated, so they will be underrepresented. Curiously the K star Hatziminaoglou, E., Groenewegen, M. A. T., da Costa, sample (which consists of intrinsically much brighter L., Arnouds, S., Benoist, C., Madejski, R., et al. 2002, objects and should thus be more affected by the up- per cutoff) has a more prominent inner “spike”.
Phleps, S., Meisenheimer, K., Fuchs, B., & Wolf, C. 2000, In order to get a more quantitative measure, we fitted various equations to the distribution (Figure1). The most crude approximation is to use linear 4 in the case of a 2 component fit, the part where the third equations, each representing one exponential falloff.
component has significant influence is left out.

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