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Gaia's first data release in September 2016 provided positions, parallaxes, and proper motions for millions of stars, as well as spectroscopic parameters and redshifts for quasars. The upcoming releases will include astrometric solutions for all sources, photometric data, and radial velocities. Ground-based surveys such as RAVE, LAMOST, Gaia-ESO, and Galah are valuable for obtaining accurate radial velocities and spectroscopic parameters. Next steps include studying stellar parameters such as Fe abundance in Galah and RAVE.
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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. GaiaTomaž Zwitter
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: λcoverage byBP 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.
... it is: (a bug in astro-py discovered)
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
