PRIMA Astrometry Object and Reference Selection Doc. Nr. VLTPLAAOS157590003

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PRIMA Astrometry Object and Reference
SelectionDoc. Nr. VLT-PLA-AOS-15759-0003

• Astrometric Survey for Extra-Solar Planets with
  PRIMA

J.Setiawan R. Launhardt
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Chapter 1. Introduction
Scope of the document To provide a guideline for
observers who want to use PRIMA for
high-precision differential astrometric
measurements on how to select and characterize
their target and phase reference stars.
Observers should be able to select and
characterize their own science target and
reference star pairs so that they are both
suitable for the specific observing mode and
ensure the achievement of the anticipated
astrometric accuracy.
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Chapter 2. High-precision differential
astrometry with PRIMA
- Interferometry with the VLTI (especially
ATs) - PRIMA and its subsystems (what is PRIMA,
star separator,metrology,FSU,DDLs) -
High-precision differential astrometry with PRIMA
(general description how it works, what is the
difference to other astrometry programs) - The
need for phase reference stars (how to define
and select reference stars) - From the
observables to astrometric data (short
description about the data reduction and
analysis format, software, etc.)
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Chapter 3. Requirements on PRIMA astrometric
target and reference stars
Constrains set by the instrument, observing mode
and atmosphere
- Location (telescope site, declination
limitations, u-v coverage, baseline, others) -
Minimum brightness of target and reference
stars (K magnitude brighter than 12 for target,
15? for reference stars) - Color difference
between target and reference stars (OPD
calibration uncertainty (and astrometric
accuracy) as function of color difference) -
Angular separation between target and reference
stars (minimum separation due to star separator,
maximum separation) - Number and relative
location of reference stars (dependence of
astrometric accuracy on the number of reference
stars)
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Chapter 3. Requirements on PRIMA astrometric
target and reference stars
Astrometric stability of target and reference
stars

• - Parallax and proper motions of reference stars
• (preferred distant and bright reference stars,
  e.g. K giants)
• - Perspective acceleration
• (under study Sabine)
• - Unseen companion
• (radial velocity survey of reference star
  candidates is needed)
• - Chromospheric activity and stellar pulsations
• (photocentric displacement by the starspots,
  nonradial pulsations, etc.)
• Circumstellar disks, extended/resolved targets

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Chapter 4. Selection criteria for astrometric
target and reference stars

• This section contains practical selection
  criteria (numbers and diagrams) based on the
  requirements and effects described in the
  previous section.
• Top level selection criteria for astrometric
  targets (brightness, declination,
  magnitude and time scale of expected astrometric
  signal,...)
• - Top level selection criteria and availability
  of reference stars
• (diagrams, statistical probability to find one or
  more ref. stars, list of catalogs, etc.)
• - Target and goal-specific refined selection
  criteria
• anticipated astrometric accuracy vs. angular
  separation and number of available reference
  stars, astrometric noise as function activity
  levels, ...

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Chapter 5. Recommended selection strategy

• Setting the goal, accuracy, and strategy of the
  anticipated astrometric observations
• (e.g. Properties of target stars --gt which
  astrometric accuracy)
• - Defining the specific requirements and
  selection criteria
• (from top level criteria calculation )
• Pre-selecting reference stars from existing data
  bases (catalogs 2MASS, USNO, other
  publications )
• Defining strategy for preparatory observations
  (photometric and
  spectroscopic surveys )
• Final characterization and selection of target
  and reference stars pairs.