Gaia Tomaž Zwitter Gaia: > 1.1 billion objects (V ≤ 20.9), positions accurate to between 5 and 400 μas, spatial resolution ~ 100 mas, blue and red SED at 50 - 200+ epochs over 5-9 years, RVs for objects brighter than V~15.5, spectroscopic parameters for the one brighter than V~12.5.

Gaia - first data release The first data release (September 2016): (Brown et al. 2016) positions, parallaxes (error ~0.3 mas) and proper motions (error ~1 mas/yr) for 2 million Hipparcos/Tycho-2 stars; positions (error ~10 mas) and G magnitudes (error < 0.03 mag) for 1.1 billion objects (V ≤ 20.9); (V = 1.02 G − 0.24 for V-I ~ 0.7) G-band light curves and characterization for ~3000 Cepheids and RR Lyrae stars around the south ecliptic pole. QSOs: (Lindegren et al. 2016, Mignard et al. 2016) 135,000 observed (from the list of Andrei et al. 2014); positions compared to VLBI reference frame; formal standard error for 2191 quasars (with 17.6 < V < 20.7) compared to ICRF2: 0.76 mas for 50% and 3.35 mas for 90% sources; alignement with the ICRF2 to better than 0.1 mas at epoch 2015.0, non-rotation to within 0.03 mas/yr; there are now 11,444 objects with VLBI positions, i.e. 3.5-times more than in ICRF2 (Petrov & Kovalev 2016).

Sky chart of 1,142,679,969 sources Brown et al. 2016

3 problems: damped throughput (ice), basic angle variation, stray-light. They are now solved or under control.

Focal plane: 3 main instruments Prusti et al. 2016

Positional accuracy errors after 5 yr mission Jester et al. 2005 Proft et al. 2016 Brown et al. 2016

Gaia: photometric accuracy 3 bands: white (G: 330-1050 nm), blue (BP: 330-680 nm), red (RP: 640-1050 nm), ~ 72 transits in 5 yrs (min 50, max 200+). errors for a single transit

Gaia QSOs: λ coverage by BP and RP spectra Proft et al. 2016, number of photons per 5 transits

Redshifts of QSOs with V ~ 20.2 after 5 yrs of mission Proft et al. 2016

Gaia QSOs: variability detection by sums of five transits z = 2.03 r' = 17.5 (Proft et al. 2016)

Offsets in Gaia vs. VLBI positions Kovalev et al. (2017) determined VLBI-jet direction for 2957 AGNs observed by Gaia. Position offsets along the jet require strong, extended parsec- scale optical jets. Small (<1 mas) offsets in direction opposite to the jet can be due to extended VLBI jet structure or a “core-shift” effect due to synchrothon opacity.

Gaia timeline Launch: 19 December 2013, The 1st data release: 14 September 2016: TGAS parallaxes & proper motions for Tycho stars, VLBI coordinate system match. The 2nd data release: April 2018: Five-parameter astrometric solutions for all sources with acceptable formal standard errors (>109 anticipated), and positions (α, δ) for sources for which parallaxes and proper motions cannot be derived. G and integrated GBP and GRP photometric fluxes and magnitudes for all sources. Median radial velocities for sources brighter than GRVS= 12 mag (V=12.8 for G0 V star, V=13.2 for K1 III star). For stars brighter than G = 17 mag estimates of the effective temperature and, where possible, line-of-sight extinction will be provided, based on the above photometric data. Photometric data for a sample of variable stars. Epoch astrometry for a pre-selected list of >10,000 asteroids. Mission duration: 2019, 2021, 2023? Final release with everything: 3 yrs later.

Gaia timeline In perspective (7 months from now): Parallax & proper motion accuracy of 70 μas implies 10% error at 1.3 kpc and 3% error at 400 pc. BP/RP: only integrated magnitudes, perhaps to be so at least to 2020 or 2022+. Parameters: Teff+reddening from BP/RP, logg from G & parallax. RVS: for V < 12, maybe V < 13, only average reported and for non-variable RVs, accuracy ~1-2 km/s. So ground based surveys valuable for: RVs, spectroscopic params, abundances. Why we need accurate RVs? Long period SB1s, vertically resolved atmospheres, cluster micro-dynamics, LSR.

On-going ground-based optical stellar spectroscopic surveys Goals: individual element abundances, radial velocities. Surveys: RAVE (www.rave-survey.org), LAMOST (www.lamost.org), Gaia-ESO (www.gaia-eso.eu), Galah (www.galah-survey.org), Apogee, FunnelWeb.

The 3 ground-based surveys

... it was:

... it is: (a bug in astro-py discovered)

shift applied: RVRAVE = RVGalah – 0.17 ± 0.03 km/s.

shift applied: RVHR21 = RVHR15N + 0.70 ± 0.05 km/s.

RV shifts between surveys RAVE = Galah – 0.17 ± 0.03 km/s HR15N = HR10 = Galah + 0.16 ± 0.06 km/s UVESU = Galah + 0.69 ± 0.05 km/s UVESL = HR21 = Galah + 0.86 ± 0.03 km/s Note how small are the errors. Next: stellar parameters

Fe abundance of Galah and RAVE

+ median, within □ 68% of objects.