Science Results Enabled by SDSS Astrometric Observations

Transcription

1 Science Results Enabled by SDSS Astrometric Observations Željko Ivezić 1, Mario Jurić 2, Nick Bond 2, Jeff Munn 3, Robert Lupton 2, et al. 1 University of Washington 2 Princeton University 3 USNO Flagstaff Astrometry in the Age of the Next Generation of Large Telescopes Flagstaff, Oct 17-20,

2 SDSS Astrometric Data Quality 1. Pipeline astrom developed by USNO (Pier et al. 2003) 2. Dynamic range: 14 < V < 22.5, exposure 54 sec, 5 bands (ugriz) over 5 minutes 3. Absolute accuracy: < 50 mas 4. Relative band-to-band accuracy: 30 mas for sources not limited by photon statistics, and 100 mas at the survey limit 5. SDSS DR3: 141 million unique objects 2

3 3

4 4

5 Science Results Based on SDSS Astrometric Data 1. Solar System Objects: move during 5 minutes 2. Stellar Proper Motions: SDSS-POSS: 50 yrs baseline, g < 20, proper motion errors 3 mas/yr SDSS-SDSS: 5 yrs baseline, g < 22, proper motion errors 6 mas/yr 3. Stellar Parallaxes: 100 deg 2, out to 10 pc, advantage of faint flux limit 4. Optical identifications for sources detected at other wavelengths (FIRST, Chandra, 2MASS) 5

6 SDSS Asteroid Observations Moving objects in Solar System can be efficiently detected out to 20 AU even in a single scan: 5 minutes between the exposures in the r and g bands 6

7 Asteroids move during 5 minutes and thus appear to have peculiar colors. The images map the i-r-g filters to RGB. The data is taken in the order riuzg, i.e. GR B 7

8 SDSS Asteroid Observations Moving objects must be efficiently found to prevent the contamination of quasar candidates (and other objects with nonstellar colors) Detected as moving objects with a baseline of only 5 minutes The sample completeness is 90%, with a contamination of 3%, to a magnitudes fainter completeness limit than available before The velocity errors 2-10%, sufficient for recovery within a few weeks Accurate ( 0.02 mag) 5-band photometry SDSS Moving Object Catalog is public at Detected 204,305 moving objects, 67,637 are identified with known objects in Bowell s catalog, 43,329 are unique 8

9 Asteroid Counts 9

10 Main SDSS Asteroid Results The size distribution for main-belt asteroids: measured to a significantly smaller size limit (< 1 km) than possible before, discovery of a change of slope at D 5 km, a smaller number of asteroids compared to previous work by a factor of 2 (N(D>1km) 0.75 million) Strong correlation between colors and position/dynamics: Confirmation of color gradient: rocky S-type in the inner belt vs. carbonaceous C type asteroids in the outer belt; dynamical families have distinctive colors; Colors are correlated with the family age: space weathering 10

11 COMPARISON OF ASTEROID SIZE DISTR IBUTION: OBSERVATIONS AND MODELS Farinella et al. 92 (1) CUMULATIVE NUMBER > D <---- Farinella et al. 92 (2) Farinella et al. 92 (3) Farinella et al. 92 (4) Galileo team Davis et al. 94 Durda et al 98. Model SAM99 Model SDSS 2001 SMALL SIZE BUMP <----- LARGE SIZE BUMP D (km) The asteroid size distribution (Davis 2002, in Asteroids III). SDSS results: 1) Extended the observed range to 300m 2) Detected the second break at 5 km 11

12 The semi-major axis v. (proper) inclination for known asteroids from Bowell s catalog that were observed by SDSS 12

13 The semi-major axis v. (proper) inclination for known asteroids color-coded using measured SDSS colors 13

14 The osculating inclination vs. semi-major axis diagram. 14

15 What is the meaning of different color shades? Chemistry, of course, for the gross differences (red vs. blue), but what about different shades of red? 15

16 0.65 Eunomia Rafita Maria 0.5 Brangane Gefion Massalia Koronis Colour Karin Agnia Merxia Eos Solar System 0.3 Iannini Age (Years) 16

17 What is the meaning of different color shades? Chemistry, of course, for the gross differences (red vs. blue) Within a given chemical class, colors also depend on age: SDSS colors can be used to date asteroids 17

18 18

19 Prospects for Proper Motion Studies SDSS-POSS proper motions limited by the POSS astrometric accuracy (0.15 arcsec) resulting in proper motion accuracy of 3 mas/yr; usable to g 20 (recalibrated POSS astrometry by Munn et al.) SDSS-SDSS proper motions with 5 years baseline accurate to 6 mas/yr (using only 2 epochs); usable to g 22 SDSS-LSST proper motions will be limited by the SDSS astrometric accuracy ( 30 mas): with 15 years baseline accurate to 2 mas/yr This is >100 times more sensitive than Luyten s catalog (a standard resource for proper motion studies)! SDSS (and especially LSST) may revolutionize proper motion based studies of the Galactic structure (2 mas/yr corresponds to 10 km/s at 1 kpc)! 19

20

21 Tangential Velocity Distributions for M dwarfs (D<1 kpc) Top row: l=0, b 45, v l and v b for D=300 pc Middle row: l=90, b 45, v l for D=300 pc and D=800 pc Bottom row: l=180, D=300 pc, v l for b 45 and b -45 Note strong non-gaussianity: asymmetric drift The main advantage of SDSS- POSS sample: probes larger distances than possible before, accurate distance estimates, large number of sources: enormous amount of detailed information! 21

22 Thick Disk vs. Halo Velocity Distributions Top: v b, bottom: v l Turn-off stars selected in r vs. g r color diagram: black Further separated by u g color (metallicity proxy) into halo (blue) and thick disk (red) stars Note the strong lag Note strong non-gaussianity: asymmetric drift The main advantage of SDSS- POSS sample: probes larger distances than possible before, accurate distance estimates, large number of sources: enormous amount of detailed information! 22

23 Conclusions It s good to have accurate astrometry for a lot of faint sources across a large chunk of the sky. 23

24 Conclusions It s good to have accurate astrometry for a lot of faint sources across a large chunk of the sky. Especially when accurate multi-band photometry is also available. 24

25 Conclusions It s good to have accurate astrometry for a lot of faint sources across a large chunk of the sky. Especially when accurate multi-band photometry is also available. And radial velocities, and variability information, and... 25