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

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

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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

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The science of Gaia and future challenges. Lund, 30 August 2017 1

Institute for Space Studies of Catalonia

and

Institute of Cosmos Sciences - University of Barcelona

Double stars in TGAS

some validation results Claus Fabricius

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The science of Gaia and future challenges, Lund, 30 Aug 2017 2

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
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The science of Gaia and future challenges, Lund, 30 Aug 2017 3

TGAS

  • Tycho – Gaia Astrometric Solution
  • 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
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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 μas/yr
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Hipparcos focal plane

0.9º 1.2″

ESA-1200, Vol 2, Fig 2.10

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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

  • DMSA positions (+) on stacked Tycho counts
  • Resolving problematic cases using Hipparcos Transit Data
  • HTD concept develloped at Lund by Lindegren

Fabricius & Makarov 2000

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The science of Gaia and future challenges, Lund, 30 Aug 2017 7

Hipparcos DMSA

  • 12 000 double and multiple systems
  • Mostly successfully resolved
  • Some ambiguous or poor solutions

76566 C&D 114923

  • DMSA positions (+) on stacked Tycho counts
  • Resolving problematic cases using Hipparcos Transit Data
  • HTD concept develloped at Lund by Lindegren

Fabricius & Makarov 2000

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The science of Gaia and future challenges, Lund, 30 Aug 2017 8

Orbiting doubles suffer in Hipparcos

HIP @ 1991 HIP @ 1706 FK5 @ 1706

  • HIP – Gaia combination
  • new possibilities
  • HIP transit data for 38000 stars
  • Problem:
  • Short mission duration

compared to orbital period

  • Example:
  • Castor
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The science of Gaia and future challenges, Lund, 30 Aug 2017 9

Orbiting doubles suffer in Hipparcos

HIP @ 1991 HIP @ 1706 FK5 @ 1706 Rømer 1706

  • HIP – Gaia combination
  • new possibilities
  • HIP transit data for 38000 stars
  • Problem:
  • Short mission duration

compared to orbital period

  • Example:
  • Castor
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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

2.1″ 0.7″

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The science of Gaia and future challenges, Lund, 30 Aug 2017 11

Gaia observing strategy

  • Gaia strategy
  • Only small “windows” are read from the CCDs
  • The fainter component of a binary gets a truncated window

2.1″ 0.7″ “winner” “loser”

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The science of Gaia and future challenges, Lund, 30 Aug 2017 12

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

Integration time set by brighter source

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DR1 angular resolution

  • Few resolved pairs in DR1
  • Window conflicts set in around 2 – 3 arcsec

Dense field

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DR1 angular resolution

  • Few resolved pairs in DR1
  • Window conflicts set in around 2 – 3 arcsec

Sparse field

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Fraction of HIP-DMSA in TGAS

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HIP-DMSA, ρ < 2″

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TGAS, ρ < 2″

Zone of Trouble

  • ZoT: secondary disturbs primary too much
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TGAS offset from Hipparcos

A B ρ

TGAS

  • Hipparcos double propagated to Gaia epoch
  • TGAS will normally fall in between the two components
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TGAS offset from Hipparcos

A

phot centr

B ρ ΔxA

TGAS

  • Hipparcos double propagated to Gaia epoch
  • TGAS will normally fall in between the two components
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TGAS pos offset from A → B

A B

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TGAS pos offset from A → phot cent

A

phot cent

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TGAS magnitude offset from A

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Close Hipparcos doubles

  • Separation < 0.25 arcsec
  • Small ΔH dominate
  • already in DMSA
  • Astrometry: Photo centre
  • G photometry: biased
  • Separation 0.3 – 0.5 arcsec
  • Large ΔH dominate
  • contrary to DMSA
  • Small ΔH give poor images
  • Astrometry: Photocentre → comp A
  • G photometry: biased
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Proper motion bias in TGAS

  • 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

1991 2015

phot cen

μtrue

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Proper motion bias in TGAS

  • 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

1991 2015

phot cen

μtrue Δμ

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TGAS – HIP/Tycho HR diagram

Makarov, Fabricius, Frouard 2017

MHp BT – VT

  • : primaries

: secondaries 838 pairs ρ: 0.3 – 2.5″ ϖ/σϖ > 7 2 4 6 8 2 0.5 1.5

  • 2

10

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Near future: Gaia DR2

  • Sources are still treated as single
  • No TGAS2
  • Close binaries
  • Positional bias remains
  • No proper motion bias
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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
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Thank you! Tack så mycket!