HIGH PROPER MOTION WHITE DWARF CANDIDATES GSCII Annual Meeting

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HIGH PROPER MOTION WHITE DWARF CANDIDATES
 GSCII Annual Meeting

• October 19-20 2000
•   CBBS, Stevensville (MD)
• by Daniela Carollo
• Osservatorio Astronomico di Torino
• M.G. Lattanzi, B. McLean, R.L.Smart, A. Spagna

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Why look for WD in the Milky Way?

• Dark Matter problem halo WD could explain the
  recent results of microlensing events
• Galactic evolution the oldest (than coolest) WD
  give an estimation of the limit age of the
  galactic disk
• Stellar evolution comprehension new experimental
  points are needed to add to the theoretical
  cooling sequences

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Dark Matter Problem

• Spiral Galaxy Rotation Curves show a flat disk
  rotation curve which is a strong evidence of a
  massive Halo of Dark Matter surrounding the
  Galaxy
• Several types of dark matter are candidate
  remnants from early epochs of galactic star
  formation (white dwarf, neutron stars), remnants
  from the early epochs Universe (subatomic
  particles, primordial black-holes)
• MACHO project observations suggest that 10-20
  of the dark halo is composed from compact objects
  having masses of 0.5M?

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Cool White Dwarfs

• MACHO favorite candidates are very old, cool
  white dwarf (the evolutionary end state of all
  stars having masses m lt 8 M?) which have mean
  masses of 0.5 M? (m/L gt 104M? /L? )
• Recently new models predict unusual colors and
  magnitudes for the oldest (coolest) WD.
• Hydrogen atmosphere WD with ages gt 10 Gyr have
  suppressed red and near infrared fluxes, and they
  look blue (Hansen, 1998)

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State of the Art in the Halo WD search
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Expected number of halo WDsUsing GSCII Data
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The observative parameters GSC2 data can provide

• All sky observations (gt1 billion objects, mostly
  faint)
• J (blue) magnitude, F (red) magnitude, N
  magnitude
• Colors J-F, F-N
• Proper motions
• Object classification
• The selection of WD candidate can be performed by
  means
• of all these parameters.
• In any case, spectroscopic follow-up is required
  in order to
• confirm the nature of these candidates.

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Spectra can provide

• Effective temperature
• Metallicity
• Radial Velocity

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Object selection criteriaHalo WDs are difficult
to identify, due to their faint magnitude (Mv gt
15, and the small number of these objects. An
efficient methods is to select

• High proper motion stars (m gt 0.5 /yr)
• Faint target Rgt18
• Color cooling track inversion point fall in V-I
  1.2, 1.5 (late K) which correspond to J F
  1.5 1.8 (indicatively), then we search high
  proper motion objects with J-F lt 1.8
• Plates with epoch difference DT 1,10 yr
• High galactic latitude field low crowding

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Some Advantages

• Residual astrometric systematic errors are not a
  problem because in any case these are much
  smaller than the high PM of WD
• For the same reason, relative proper motions
  which sufficient for this search (cor. to
  absolute reference frame 0.01 as/yr)

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Operative Selection

• Matching algorithm (three POSSII plate)
• Proper motion algorithm
• Color-Magnitude Diagram
• Color-Color Diagram
• Vector Point Diagram
• Total PM error vs magnitude
• Reduced PM Diagram (H J 5log(m) 5)
• A short list of high proper motion candidates,
  which can include other peculiar objects (eg. M
  dwarf.)
• Visual inspection and cross correlation with
  other catalogues (2MASS, Luyten, etc)

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Future Observing Proposal

• In order to take spectra, recently we submit an
  observative proposal (PATT collaboration) for the
  4.2m William Herschel Telescope (Roque de Los
  Muchachos Observatory, La Palma, Spain).
• Involved Institutes STScI, Institute of
  Astronomy of Cambridge and Torino Astronomical
  Observatory
• The observing semester will be February-July
• The TAG meeting for the final decision will be in
  November 24

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Plate selected in the GSCII archive

• We select 25 fields in the GSCII archive (some of
  them are processed)
• They have RA fall in the range 8, 20
• Area covered 1000 square degree

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Summer Candidates Spectra

• Ask to Brian

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LHS Stars

• We insert also in the PATT proposal a list of 14
  LHS stars without spectroscopy. These objects are
  selected from the RPM diagram from Luytens
  catalogue and have properties consistant with
  cool white dwarfs, we expect to rediscover
  many of these stars in the rest of our survey