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HIGH PROPER MOTION WHITE DWARF CANDIDATES GSCII Annual Meeting

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. Why look for WD in the Milky Way?.

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HIGH PROPER MOTION WHITE DWARF CANDIDATES GSCII Annual Meeting

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  1. 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

  2. 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

  3. 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

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

  5. Material Limit Magnitude Area Covered (deg2) Number of Objects Found Survey Ibata Photographic Plates R = 19 790 2 Halo WD Spectra conf. Monet Photographic Plates R = 19 1378 1 Halo WD Spectra conf. De Jong CCD R = 23 2.5 3 High Proper Motion Objects No spectra EROS CCD I = 20.5 250 0 Halo WD Super Cosmos Photographic Plates R = 19 5000 Few candidates Spectra next year State of the Art in the Halo WD search

  6. Expected number of halo WDsUsing GSCII Data

  7. The observative parametersGSC2 data can provide • All sky observations (>1 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.

  8. Spectra can provide: • Effective temperature • Metallicity • Radial Velocity

  9. Object selection criteriaHalo WDs are difficult to identify, due to their faint magnitude (Mv > 15, and the small number of these objects. Anefficient methods is to select: • High proper motion stars (m > 0.5 “ /yr) • Faint target: R>18 • 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 < 1.8 • Plates with epoch difference DT = [1,10] yr • High galactic latitude field: low crowding

  10. 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)

  11. 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)

  12. 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

  13. 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

  14. Summer Candidates Spectra • Ask to Brian

  15. 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 Luyten’s catalogue and have properties consistant with cool white dwarfs, we expect to “ rediscover” many of these stars in the rest of our survey

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