INFRARED SURVEY FOR THE CHARACTERIZATION OF STELLAR POPULATION OF: SPIRAL ARMS AND OF A BAR AT THE GALACTIC CENTER

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1 INFRARED SURVEY FOR THE CHARACTERIZATION OF STELLAR POPULATION OF: SPIRAL ARMS AND OF A BAR AT THE GALACTIC CENTER Eduardo B. de Amôres 1 and Jacques R. D. Lépine 1 1 Instituto de Astronomia Geofísica e de Ciências Atmosféricas USP - Brasil The Infrared Survey consists of observations using the infrared camera (CAMIV) in the telescope of 60 cm of LNA, whose main objective is to better characterize the population of the spiral arms and of a structure existent in the galactic center that we believed to be due to the existence of a bar; they would be located in l ~ + 23º and l ~ -14º. The observations were taken in several filters (J, H and K bands) that are particularly important in the directions re tangential to the spiral arms. In this way, we compared a direction that crosses an arm to the nearest direction that does not pass through by the arm, and both have the same contribution of foreground counting. In the last missions taken until the present, we observed the region in the tangential direction to the arm of Scuttum, with observations of l = 30.04º until l = 31.04º, to each longitude interval of 0.1º, for galactic latitude of 0.0, ± 0.125º, ± 0.25º, ± 0.50º. For the regions that we believed to be the extremities of the bar, we observed longitudes in the range 14.50º l º and 22.5º l 23.5º for each interval of 0.25º, for galactic latitude of 0.0 º and ± 0.25º. The observations in the filters J and H were made with time of integration of 60s, in the K band, the observations were made using the C1 filter with integration time of approximately 210 s (12x15s).

2 Main objectives: Observation of tangential directions to spiral arms and the limits of the bar Better characterization of the population of the bar and the spiral arms Elaboration of an Infrared Survey of tangential directions to the spiral arms (J, H and K Bands) Observational setup: Infrared camera using a type HAWAII (Rockwell Sci.) of 1024 x 1024 pixels with 18.5 µm/pixel, with sensitive level in the range µm. Observations in J, H and K Bands, with typical integration time of 60 s (J and H Band) and 210 s in K band (13 mag) To each direction the dithering of five positions were perfomed. The images presented on the poster are images of a field (4 arcmin) and represent the subtraction of two images of the same field with dithering of 20s.

3 Covered area observed by the infrared survey until now: Limits of the bar: - longitude (l) ~ 22.5º to 23.5º ( l = 0.125º) for galactic latitudes (b) ranging from -0.25º to º ( b = 0.125º) - l ~ -13.5º to 14.5º for galatic latitudes ranging from 0.375º to º. Spiral arms: - Scuttum: l ~ 30.04º to 31.04º ( l = 0.1º) for latitudes ranging from -0.50º to º ( b = 0.125º) - Centaurus: l ~ -48.5º to 49.50º ( l = 0.1º), galactic latitudes (-0.125º to º). - Carina: l ~ -72.5º to 73.5º, galactic latitudes (-0.125º to º) - 3 kpc arm: l ~ -23.0º to 22.0, galactic latitudes (-0.125º to º)

4 Observation of the bar (Determining the bar limits ) From analysis of GALACTIC MAP PLANE DIRBE/COBE map in 3.5 µm, geometrical arguments and latitudinal profiles for emission in 100 µm (IRAS- DIRBE/COBE), we can determine the main bar parameters. DIRBE/COBE map in 3.5 µm Scuttum Arm bulge Bar parameters: l(-) ~ -14º (d = 5.94 kpc) l(+) ~ +23º (d = kpc) Inclination angle = 50.75º radius = 2.95 kpc Bar limits

5 9 Positive limit for the bar (l ~ 23.0º) J Band G G G H Band G G G

6 Positive (longitude) limit for the bar (l ~ 23.0º) in the K Band G G G

7 Negative (longitude) limit for the bar (l ~ -14º) K band G Hband G G G

8 Observations of the Scuttum arm The tangential direction to the Scuttum arm was determined from analysis of longitudinal profile of intensity in 100 µm obtained by IRAS and DIRBE-COBE experiment. We have chosen three directions D1 (direction with the greater peak in 100 µm intensity) D2 and D3 directions with the lower intensity before and after the tangential direction, respectively (right figure). In this way, we can compare the direction which crosses a spiral arm and the nearest direction which do not cross the arm. l=31.04 Intensity in 100 µm l l=30.14 Scuttum R0 R d D1 D2 CG Tangential direction to the Scuttum arm D3 l=30.54

9 9 Regions in the tangential direction to the Scuttum arm G G J Band G H Band G G G

10 K Band (Scuttum arm) G G

11 Perspectives: To extend the regions of Infrared Survey covering galactic latitudes ( b < 2.0º). Observed others tangential directions to the spiral arms At the moment, the data reduction, is on its way, we intend to elaborate color-color and color-magnitude diagrams of observed regions. This work was supported by Conselho Nacional para o Desenvolvimento Científico e Tecnológico, CNPq and Núcleo de Excelência em Galáxias PRONEx.