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. 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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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

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


Dark matter problem

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


Cool white dwarfs

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)


State of the art in the halo wd search

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


Expected number of halo wds using gscii data

Expected number of halo WDsUsing GSCII Data


The observative parameters gsc2 data can provide

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.


Spectra can provide

Spectra can provide:

  • Effective temperature

  • Metallicity

  • Radial Velocity


High proper motion white dwarf candidates gscii annual meeting

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


Some advantages

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)


Operative selection

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)


Future observing proposal

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


Plate selected in the gscii archive

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


Summer candidates spectra

Summer Candidates Spectra

  • Ask to Brian


Lhs stars

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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