High proper motion white dwarf candidates gscii annual meeting
1 / 19


  • Uploaded on

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?.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' HIGH PROPER MOTION WHITE DWARF CANDIDATES GSCII Annual Meeting' - lynn

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
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


Limit Magnitude

Area Covered


Number of Objects




Photographic Plates

R = 19


2 Halo WD

Spectra conf.


Photographic Plates

R = 19


1 Halo WD

Spectra conf.

De Jong


R = 23


3 High Proper Motion Objects No spectra



I = 20.5


0 Halo WD

Super Cosmos

Photographic Plates

R = 19


Few candidates

Spectra next year

State of the Art in the Halo WD search

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

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

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