Radial Velocity Surveys Matthias Steinmetz (AIP)
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
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 40000 RVs for stars in the MW Several 1000 RVs for stars in M31 3
Historical Parallels George Michael Seabroke George Mitchell Seabroke MS Carl Hermann Vogel Director of the AOP 4
Radial velocity surveys Geneva-Copenhagen ~20000 stars (Hipparcos) SDSS/SEGUE spectra for 250000 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
SEGUE vs. RAVE: Different wavelength range (3800-9100 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
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
SEGUE imaging b First data release July, 2007 Same formats, interfaces as SDSS l SEGUE imaging SDSS imaging 8
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
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
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
Spectroscopy 3800Å 9100Å, 3Å good leverage for parameter estimates Radial velocities to 7 km/s @ 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
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
Start of observations 11 th April 2003 Duration (planned) 2003-2010 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
1 st Data Release Coverage : ~4,670 sq.deg 25,274 radial velocities 24,748 targets 2003/04/11 to 2004/04/02 240 fields 5.7 diameter 1 hour exposures 15
www.rave-survey.org RAVE : a Million Star Project 16
RAVE data access 17
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6dF plate and robot : 20
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
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
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 23 14 SI 5 14 CaI 2 CaII 3 3 TiI 18 CrI 7 MnI 7 FeI 60 19 FeII 3 CoI 3 NiI 4 tracers Gibson (2003) 23
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
Project Status (August 14 th ) 143,500 spectra 131,500 stars 25
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
Internal errors: 27
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
Comparison to Standards 3 external - Elodie (high resolution) sources: - 2.3m (long slit, medium resolution) - Geneva-Copenhagen (CORAVEL) Williams, Freeman, Bienayme, Zwitter, Siebert 29
Velocity difference vs SNR : No apparent bias Dispersion gets larger with low SNR 30
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 km/s @ 100pc ~20 km/s @ 1kpc (S. Roeser & A. Siebert) 31
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
RAVE DR2, radial velocities 33
RAVE DR2, stellar parameters 34
MK classification at the optical red end 35
Properties of Diffuse Interstellar Bands : Fiorucci & Munari 36
Properties of Diffuse Interstellar Bands : Fiorucci & Munari Eq. Width correlates with the extinction 37
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
The Mass of the Milky-Way Smith, Ruchti, et al 39
The Mass of the Milky-Way For an adiabatically contracted NFW dark halo: M MW = 1.45 10 12 + 1.08 0.52 M v vir 125 km/s 40