The vertical structure of the Galactic Halo Carla Cacciari, Angela Bragaglia - INAF OA Bologna Tom Kinman - NOAO Alberto Buzzoni - INAF TNG Alessandro Spagna - INAF OA Torino

What is a good halo tracer?  1960 ’ s : RR Lyraes (Kinman  Co.) • ~1975 : concerns on HB structure high prop.mot. subdwarfs (Carney  Co.) K giants (Freeman  Co.)  1990 ’ s : surveys for metal-poor stars (PSB, KSK) HB stars (Kinamn  Co., Morrison  Co.)  2000 ’ s : about everything suitable, but mostly giants, subgiants, MS-TO (Beers  Co., Gilmore  Co.)

Selection criteria: rotation, orbit eccentricity? NO (bias on kinematics) metallicity? Better, BUT … a) high-res spectroscopy of Halo stars restricted to nearby stars b) possible contamination from MW Thick Disk (up to 30  for [Fe/H]  -1.6 (Beers et al. 2002)  not easy to distinguish Halo from Disk in solar neighb.  BHB and RR Lyr ’ s are relatively unanbiguous Halo indicators, they are bright and can be observed at large distances  Thick disk  Halo Total space motion (km/s) Fulbright 2002, AJ, 123, 404 Problem: how to define local Halo stars ?

Halo rotation from nearby stars (Z  2 kpc) : Nr.Stars Type  RV  reference 162 RRLyr -210  12 Layden et al. 1996, AJ, 112, RRLyr -219  10 Martin  Morrison 1998, AJ, 116, 1724 Note that other estimates based on RRLyr, subdwarfs, K giants (e.g. Chiba  Yoshi 1998, Carney et al. 1996, 1999, Chiba  Beers 2000) may have varying amounts of disk included RV (hel) = -219  10 km/s Older data gave rotation slightly prograde

Halo rotation from distant stars (observed at Z  5 kpc): Nr.Stars Type  RV  reference 21 metal-poor sd -271  16 Majewski 1992, ApJS, 78, 87 Majewski et al. 1996, ApJ, 459, L73 Other estimates, based on metal-poor dwarf and subdwarf stars with Zmax  4-5 kpc calculated from orbital parameters, give: prograde (Carney 1999) zero (Chiba  Beers 2000) rotation retrograde (Gilmore et al. 2002) Is the high halo in retrograde rotation ?

Our sample of RRLyr and BHB within 10  from NGP 73 RRLyr, 87 BHB V  12.0 – 16.5 i.e., d(Sun) = 2-15 kpc Z  2 – 12 kpc above Gal. plane RVs already available for 35 BHB and 18 RRLyr Present preliminary results based on less than 50  of total sample

Data needed to get space velocities UVW Identification as halo objects  BHB (Case, Beers) : uBV  RRLyr (GCVS, var. BHB, ROTSE) : light curves Absolute magnitudes (i.e. distances)  BHB : Mv vs (B-V) from Preston et al. (1991)  RRLyr : luminosity vs [Fe/H]; Fourier analysis (E(B-V) from Schlegel et al. 1998) Proper motions  GSC2 (Spagna et al., unpubl.) ; and others Radial velocities and [Fe/H]  low-res spectra at KPNO-4m and TNG-LRS

FHB Kinman, Suntzeff, Kraft 1994 Preston, Schectman, Beers 1991 BHB identification Mv

RRLyr Absolute magnitude Mv with two compatible scales: a.From [Fe/H] Mv=0.23 [Fe/H] (Cacciari 2002, mean of several recent determinations) •From Fourier components Mv= LogP – A A (Kovacs constant by Kinman from Fourier analysis of RRLyr – Mv=0.61, Benedict et al. 2002) Mean Mv for the 18 RRLyr completely studied: 0.584

Proper motions: GSC2 proper motions, unpublished, derived as described in Spagna et al (1996, A  A, 311, 758), adjusted to give zero pm for galaxies Formal rms errors  3 mas/yr Systematic errors (from pm of 42 QSO at NGP)  25 km/s at 5 kpc STARS

LRS – TNG : observations of BHB  RR Lyr: 2001 to 2003 Feb. 2001

Results: Halo space velocities U V W Adding BHB and RRLyr we obtain (Johnson  Soderblom 1987): U = - 10  26 (  =146 km/s) - 32 stars V = -283  18 (  =120 km/s) - 43 stars W = -31  15 (  = 86 km/s) - 32 stars Compare with sample of 84 local RRLyr (Martin  Morrison 1998): U= -1  26 (  = 193 km/s) V= -210  10 (  = 91 km/s) W= -5  10 (  = 96 km/s) RETROGRADE ?

Directions mapped: Ra,Dec l,b Halo rot. (V) Note NGP 12:50,  ,  km/s SGP 00:50, ,  km/s Kinman, prel. result - 10:50, ,  33 retrogr. Gilmore et al. - 04:00, ,  45 retrogr Gilmore, Wyse, Norris 2002: retrograde halo stream detected as peak in RV distrib. Kinman: Halo stars isolated from a sample of BMP stars (Preston et al. 1994), with available RVs and USNO pm.

CONCLUSIONS  Likely halo stars show distinct retrograde rotation at Z  5 kpc in the direction of the NGP (this agrees with Majewski et al. and Gilmore et al. results)  Streaming motions may be present, and to disentangle from average motion better statistic needed (TNG obs. being taken)  Systematic effects in proper motions (and for non-HB stars in absolute magnitudes too) can be critical  Most precise proper motions: GSC2 … but Yale/Lick/USNO can be used (no systematic errors) Needed: other directions to check results (e.g. Anticenter)