Astrometry (positions, proper motions, Trigonometric parallaxes)

Pisa, 4 May 2009 Alessandro Spagna

A new kinematic survey (from GSC-II and SDSS-DR7)

to study the stellar populations of the Milky Way

Alessandro Spagna1, Beatrice Bucciarelli1, Mario Lattanzi1, Paola Re Fiorentin2, Richard Smart1

(1 - INAF-OATo, 2 – Univ. of Ljubljana)


Astrometry(positions, proper motions,Trigonometric parallaxes)

Photometry(stellar classification,Photometric distances)

Spectroscopy(Radial velocities,Chemical abundances)

Surveys of galactic stellar populations: basic ingredients


SDSS DR7

Imaging

•11,660 deg2 of imaging data (1/4 of the sky)

• 357 million objects

• Photometry ugriz, 14.0<g<22.2

Abazajian et al. 2009 ApJS, in press

Spectroscopy

• 300,000 galactic stars

• 3850 < < 9000 A , R = 2000

• Radial velocities, 10 km/s accuracy

Yanny et al. 2009 ApJ, 127, 4377


Guide Star Catalog II - Database

• All sky archive from the digitized Palomar and Anglo Australian Obs. Schmidt surveys

• 1 billion objects

• positions ICRF, classification (stellar/extended sources)

• BJ V 12 RF IN photographic photometry, B<22

• Multi-epoch positions, 1950< Epoch < 2000

Lasker, Lattanzi, McLean et al, AJ, 136, 735

GSC 2.3 counts: objects per deg2 down to RF=20.


Proper motions

• Multi-epoch positions from SDSS and GSC-II (mainly POSS-I and POSS-II) available in the GSC-II DB mirror in Torino.

• Database structure: HEALPix tesselation level 6, i.e. 49152 regions (0.839 deg2)

• Transformations from (X,Y) plate coordinates to standard coordinates (, ) computed for HEALPix level 7 (27’x27’)

• Relative proper motions

• Absolute p.m. computed with zero-point derived from extra-galactic sources (SDSS classification adopted)


Proper motions

• Proper motion formal errors: (µ) = 2-3 mas/yr

• Proper motions accuracy (test based on 235 QSOs towards the galactic anticenter):

Torino catalog

<µ cos> = 0.13 ± 0.20 mas/yr < µ > = 0.10 ± 0.18 mas/yr

(µ cos) = 3.0 mas/yr(µ) = 2.7 mas/yr

Munn’s catalog <µ cos> = 0.07 ± 0.29 mas/yr

< µ > = 1.07 ± 0.31 mas/yr(µ cos) = 4.5 mas/yr

(µ)= 4.8 mas/yr

, (arcsec) vs. t (yr)

SDSSPOSS-IIPOSS-I

p.m. solution from Spagna et al. (1996)


Stellar astrophysical parameters ( Teff, log(g), [Fe/H] )

Methods:

• SDSS pipeline (SSPP)

Lee et al 2008, AJ, 136, 2022

• Supervised feed forward neural network (ANN)

Re Fiorentin et al 2007, A&A, 467, 1374

Precision :

(Teff) = 130K (log g) = 0.21

[Fe/H] = 0.11

External comparisons by

Allende Prieto et al 2008, AJ, 136, 2070


Stellar astrophysical parameters

E(Teff)=0.083 E(log g)=0.31 E(Fe/H)=0.25


Photometric distances

Method:

1. Magnitude correction: extinction maps of Schlegel et al. (1998).

2. Photometric parallax: absolute magnitude from Eq. 1 of Ivezic et al (2008), calibrated for FGK (sub)dwarfs with [Fe/H]< -0.5.


SDSS - GSC-II catalog

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Object Number* ugriz (µ,µ) Teff, log g, [Fe/H] Vr d UVW

mag mas/yr K dex dex km/s kpc km/s

______________________________________________________________________________________________

41,551,644 sources X X

151,711 stars X X X X X X

30,700 FGK dwarfs** X X X X X X X X

______________________________________________________________

* Area: 9000 deg2

** Kinematic sample: 4500<Teff<7500 K, log g >3.5, [Fe/H]< -0.5, d < 3 kpc


Kinematics & Chemical properties: overview


From Re Fiorentin et al (2005)

Kinematics & Chemical properties: stellar streams



-1< [Fe/H] < -0.5

-1.0< [Fe/H] < -1.5



-2.0< [Fe/H] < -1.5

[Fe/H] < -2.0


CONCLUSIONS

• We have produced a new proper motion survey covering 9000 deg2 based on the multi-epoch positions derived SDSS – DR7 combined with the plate material from the GSC-II database.

• Accurate absolute proper motions (µ,µ) have been computed for 40 million sources down to magnitude g~22 (r~20). Proper motion errors attain 2-3 mas/yr.

• Stellar astrophysical parameters (Teff, log g, [Fe/H] ) have been (re)estimated for the SDSS spectroscopic sample by means of updated ANN methods.

• Full astrometric, photometric, and spectroscopic measurements are available for 150,000 stars.

• Photometric distances and 3D velocities (UVW) have been computed for FGK (sub)dwarfs with [Fe/H]< -0.5.

• A kinematic sample of 30,700 tracers within 3 kpc from the Sun has been extracted and will be used to (1) study the kinematic properties of the thick disk and inner halo and (2) search for members of known/new kinematic substructures produced by past merging events.

Astrometry (positions, proper motions, Trigonometric parallaxes)

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