Radial Velocity Surveys. Matthias Steinmetz (AIP)

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1 Radial Velocity Surveys Matthias Steinmetz (AIP)

2 The Galactic case for RV surveys Information on how galaxies form is locked in n the phase-space (position,velocities) Information is locked in stars (abundances) The Milky-Way can be used to gain knowledge on galaxy formation TO DO SO WE NEED : Phase-space information (radial velocities to a few km/s) Chemical abundances (medium to high resolution spectroscopy) A large and representative sample of all of the major components 2

3 Some historical notes First measurement of a RV by Huggins (1868) and Vogel (1872) 1888: First photographic RV measurement by Vogel 1879: First RV survey (29 stars) by Seabroke 1912: First extragalactic RV by Slipher By 2000+: about 10 6 galaxy RVs Only RVs for stars in the MW Several 1000 RVs for stars in M31 3

4 Historical Parallels George Michael Seabroke George Mitchell Seabroke MS Carl Hermann Vogel Director of the AOP 4

5 Radial velocity surveys Geneva-Copenhagen ~20000 stars (Hipparcos) SDSS/SEGUE spectra for stars RAVE 10 6 stars all sky to I=12 by 2010; v r, Z Several targeted surveys (e.g. AAOmega, M31) GAIA (2012 -) 5

6 SEGUE vs. RAVE: Different wavelength range ( Å vs Ca triplet) Different resolution (R = 2000 vs 7500) Imaging (5-color) and spectroscopy northern vs southern hemisphere Different magnitude range Different types of stars (more distant etc.) Other Galactic components Separated stripes instead of (nearly) contiguous coverage 6

7 The Sloan Digital Sky Survey Black dotted Line: b = 0, δ= -20 Blue, yellow: Spectral plates, 20.3 > g > 14.5 Red: Sgr Black: SDSS SEGUE imaging plan (approximate) 7

8 SEGUE imaging b First data release July, 2007 Same formats, interfaces as SDSS l SEGUE imaging SDSS imaging 8

9 What is SEGUE good at? Area and Depth = Volume: census of substructure in the distant hal well-matched to RV accuracy map Galactic anticenter, outer disk Accurate, homogeneous photometry trace disks, halo, in l,b stellar overdensities find rare things: k-giants, low-metallicity stars,... Spectroscopy: kinematics and abundances substructure stellar population discrimination 9

10 Imaging 3500 sq. degrees b < 35 and South Galactic sky ~20 grid in Gal. longitude sample Galactic components, spatially coherent substructure photometric accuracy: 2% in gri, 3% in u,z stellar parameters distance star counts r g-r 10

11 Spectroscopy 240,000 stars 200 lines of sight, 14.5<g<20 Target in log(distance) to 100 kpc+ 12 categories, color, magnitude selection large volume of Galaxy, distant halo simple, robust selection at 8< b <20 SEGUE k-giant selection: a likely success 11

12 Spectroscopy 3800Å 9100Å, 3Å good leverage for parameter estimates Radial velocities to 7 g=18.2 Teff, log(g), [Fe/H] Δ Teff 150K, [Fe/H] 0.3 dex, log(g) 0.5 dex external checks against high-resolution data, globular and open clusters August, status: 90,000 spectra on 75 LOS 12

13 Radial Velocities g-r > 0.45 Repeat targets to monitor RV accuracy 7 km/s for g-r > 0.45, ~ MSTO of thick disk 11 km/s for g-r < 0.45, metal-poor MSTO, BHB stars Note population in 2-sigma tails is well-matched to Gaussian distribution 13

14 Start of observations 11 th April 2003 Duration (planned) Goals 1,000,000 spectra RVs to better than 3 km/s Stellar Parameters (log g, T eff, [M/H],V rot,[α/fe]) Abundances 14

15 1 st Data Release Coverage : ~4,670 sq.deg 25,274 radial velocities 24,748 targets 2003/04/11 to 2004/04/ fields 5.7 diameter 1 hour exposures 15

16 RAVE : a Million Star Project 16

17 RAVE data access 17

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20 6dF plate and robot : 20

21 RAVE spectroscopic configuration : Medium resolution (R~7,500) Uses 1700I VPH gratting 8400 < λ < 8800Å (8460 to 8746 effective) 2 plates 120 science fibers/ plate Picture by G. Seabroke 21

22 Survey Design Wavelength interval centered on the CaII triplet Input catalog I-band selected Sky coverage ~15,000 sq.deg. in the southern hemisphere 22

23 Survey Design Besides the CaII triplet: Calcium triplet region contains a wealth of chemical information (need for good resolution to measure some of those lines) Also gravity and metallicity K0 III A7 IV HI 5 CI 1 1 NI 11 MgI 11 7 SiI SI 5 14 CaI 2 CaII 3 3 TiI 18 CrI 7 MnI 7 FeI FeII 3 CoI 3 NiI 4 tracers Gibson (2003) 23

24 Input catalogue DR1-3: 2 observed sets of stars/field with 9< I(IC)< 12 renormalized to DENIS 9 < I < 11: Tycho 2 11 < I < 12: Supercosmos DR4+: up to 5 sets of stars/field with 9 < I DENIS < 12 fixed exposure time : 1 hour SNR is magnitude dependent 24

25 Project Status (August 14 th ) 143,500 spectra 131,500 stars 25

26 Internal errors: Mean : 2.3km/s Median : 1.9km/s Peak : 1.7km/s 80% : 2.7 km/s 50% : 2.0 km/s 20% : 1.5 km/s 26

27 Internal errors: 27

28 Stability of Radial Velocities Based on 840 reobserved targets: mean diff=-0.02 km/s rms=2.83 km/s Good stability of solution with time 28

29 Comparison to Standards 3 external - Elodie (high resolution) sources: - 2.3m (long slit, medium resolution) - Geneva-Copenhagen (CORAVEL) Williams, Freeman, Bienayme, Zwitter, Siebert 29

30 Velocity difference vs SNR : No apparent bias Dispersion gets larger with low SNR 30

31 Proper Motions Mean : 10 mas/yr Median : 4.1 mas/yr Peak : 3.5 mas/yr 13.5 mas/yr Median accuracy on velocities : ~ 2 100pc ~20 1kpc (S. Roeser & A. Siebert) 31

32 What's to come Stellar parameters Abundances More radial velocities More scientific results! 41x25,000 RV measurements for DR1 DR2 and further will have a larger number of RVs to estimate need for a new pipeline use GRID technology 32

33 RAVE DR2, radial velocities 33

34 RAVE DR2, stellar parameters 34

35 MK classification at the optical red end 35

36 Properties of Diffuse Interstellar Bands : Fiorucci & Munari 36

37 Properties of Diffuse Interstellar Bands : Fiorucci & Munari Eq. Width correlates with the extinction 37

38 The Mass of the Milky-Way Smith, Rutchi et al Poster JD13-36: Terrace 1 #94 Leonard & Tremaine (1990): near escape velocity: f = ε ( ε ) ε k ( 2 2 v ) e v 38

39 The Mass of the Milky-Way Smith, Ruchti, et al 39

40 The Mass of the Milky-Way For an adiabatically contracted NFW dark halo: M MW = M v vir 125 km/s 40