Double stars in TGAS some validation results Institute for Space - PowerPoint PPT Presentation

Double stars in TGAS some validation results Institute for Space Studies of Catalonia and Institute of Cosmos Sciences - University of Barcelona Claus Fabricius The science of Gaia and future challenges. Lund, 30 August 2017 1

HTPM → TMPM → TGAS • The Hundred Thousand Proper Motions - Combining Hipparcos (~ 1 mas) and Gaia (~ 1 mas) • Very good proper motions • Little more than half a year of Gaia observations • “ How would you like a TMPM ? ” - (Lindegren, July 2014) • Problem for HTPM - Cannot calibrate Gaia with 100 000 stars, 6–12 months of data The science of Gaia and future challenges, Lund, 30 Aug 2017 2

TGAS • T ycho – G aia A strometric S olution • Concept develloped at Lund - Michalik, Lindegren, Hobbs 2015, A&A, 574, A115 • NB: TGAS does not contain (close) binaries - Often the primary - Rarely the secondary - Sometimes neither component - Sometimes the other is in DR1 The science of Gaia and future challenges, Lund, 30 Aug 2017 3

TGAS 24 yr • TGAS: Combining HIPPARCOS/Tycho with Gaia • Bootstrapping Gaia calibrations • Using HIP/Tycho-2 positions • Positions, parallaxes, proper motions for 2M+ stars • Only well behaved sources • Parallaxes to 0.3 mas • Proper motions for HIP stars to 70 μ as/yr The science of Gaia and future challenges, Lund, 30 Aug 2017 4

Hipparcos focal plane 0.9º 1.2″ The science of Gaia and future challenges, Lund, 30 Aug 2017 ESA-1200, Vol 2, Fig 2.10 5

Hipparcos DMSA • 12 000 double and multiple systems - Mostly successfully resolved - Some ambiguous or poor solutions 76566 C&D 114923 Fabricius & Makarov 2000 • DMSA positions ( + ) on stacked Tycho counts - Resolving problematic cases using Hipparcos Transit Data • HTD concept develloped at Lund by Lindegren The science of Gaia and future challenges, Lund, 30 Aug 2017 6

Hipparcos DMSA • 12 000 double and multiple systems - Mostly successfully resolved - Some ambiguous or poor solutions 76566 C&D 114923 Fabricius & Makarov 2000 • DMSA positions ( + ) on stacked Tycho counts - Resolving problematic cases using Hipparcos Transit Data • HTD concept develloped at Lund by Lindegren The science of Gaia and future challenges, Lund, 30 Aug 2017 7

Orbiting doubles suffer in Hipparcos HIP @ 1706 • Problem: - Short mission duration compared to orbital period • Example: FK5 @ 1706 - Castor HIP @ 1991 • HIP – Gaia combination - new possibilities - HIP transit data for 38000 stars The science of Gaia and future challenges, Lund, 30 Aug 2017 8

Orbiting doubles suffer in Hipparcos HIP @ 1706 • Problem: - Short mission duration compared to orbital period • Example: FK5 @ 1706 - Castor Rømer 1706 HIP @ 1991 • HIP – Gaia combination - new possibilities - HIP transit data for 38000 stars The science of Gaia and future challenges, Lund, 30 Aug 2017 9

Gaia observing strategy • Gaia strategy - Only small “windows” are read from the CCDs 2.1″ 0.7″ The science of Gaia and future challenges, Lund, 30 Aug 2017 10

Gaia observing strategy • Gaia strategy - Only small “windows” are read from the CCDs - The fainter component of a binary gets a truncated window “winner” 2.1″ 0.7″ “loser” The science of Gaia and future challenges, Lund, 30 Aug 2017 11

Gaia observing strategy • Gaia DR1 & TGAS: - All sources treated as single - Bright sources observed with full pixel resolution • G < 13 mag • Applies to all TGAS The science of Gaia and future challenges, Lund, 30 Aug 2017 Integration time set by brighter source 12

DR1 angular resolution • Few resolved pairs in DR1 - Window conflicts set in around 2 – 3 arcsec Dense field The science of Gaia and future challenges, Lund, 30 Aug 2017 13

DR1 angular resolution • Few resolved pairs in DR1 - Window conflicts set in around 2 – 3 arcsec Sparse field The science of Gaia and future challenges, Lund, 30 Aug 2017 14

Fraction of HIP-DMSA in TGAS The science of Gaia and future challenges, Lund, 30 Aug 2017 15

HIP-DMSA, ρ < 2 ″ The science of Gaia and future challenges, Lund, 30 Aug 2017 16

TGAS, ρ < 2 ″ Zone of Trouble • ZoT: secondary disturbs primary too much The science of Gaia and future challenges, Lund, 30 Aug 2017 17

TGAS offset from Hipparcos • Hipparcos double propagated to Gaia epoch - TGAS will normally fall in between the two components B TGAS ρ A The science of Gaia and future challenges, Lund, 30 Aug 2017 18

TGAS offset from Hipparcos • Hipparcos double propagated to Gaia epoch - TGAS will normally fall in between the two components B TGAS ρ Δ x A phot centr A The science of Gaia and future challenges, Lund, 30 Aug 2017 19

TGAS pos offset from A → B B A The science of Gaia and future challenges, Lund, 30 Aug 2017 20

TGAS pos offset from A → phot cent phot cent A The science of Gaia and future challenges, Lund, 30 Aug 2017 21

TGAS magnitude offset from A The science of Gaia and future challenges, Lund, 30 Aug 2017 22

Close Hipparcos doubles • Separation < 0.25 arcsec - Small Δ H dominate • already in DMSA - Astrometry: Photo centre - G photometry: biased • Separation 0.3 – 0.5 arcsec - Large Δ H dominate • contrary to DMSA • Small Δ H give poor images - Astrometry: Photocentre → comp A - G photometry: biased The science of Gaia and future challenges, Lund, 30 Aug 2017 23

Proper motion bias in TGAS μ true phot cen 1991 2015 • Bias for close Hipparcos doubles - Much larger than formal uncertainty • Tycho-2: no resolved pairs closer than 0.8 ″ - No TGAS proper motion bias expected The science of Gaia and future challenges, Lund, 30 Aug 2017 24

Proper motion bias in TGAS μ true Δμ phot cen 1991 2015 • Bias for close Hipparcos doubles - Much larger than formal uncertainty • Tycho-2: no resolved pairs closer than 0.8 ″ - No TGAS proper motion bias expected The science of Gaia and future challenges, Lund, 30 Aug 2017 25

TGAS – HIP/Tycho HR diagram 838 pairs o: primaries -2 ρ: 0.3 – 2.5″ : secondaries ϖ/σ ϖ > 7 0 2 M Hp 4 6 8 10 0 0.5 1.5 2 B T – V T Makarov, Fabricius, Frouard 2017 The science of Gaia and future challenges, Lund, 30 Aug 2017 26

Near future: Gaia DR2 • Sources are still treated as single • No TGAS2 • Close binaries - Positional bias remains - No proper motion bias The science of Gaia and future challenges, Lund, 30 Aug 2017 27

Unresolved binaries • May go undetected if the companion is - Too close - Too faint • Gaia has several ways it can detect close companions - Scan direction dependence of • Image shape • Astrometric residuals • Photometric residuals - Image reconstruction The science of Gaia and future challenges, Lund, 30 Aug 2017 28

Thank you! Tack så mycket! The science of Gaia and future challenges, Lund, 30 Aug 2017 29