Girven, J. (Jonathan) (2012) Stellar and planetary remnants in digital sky surveys. PhD thesis, University of Warwick.

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Abstract

Large scale digital sky surveys have produced an unprecedented volume of
uniform data covering both vast proportions of the sky and a wide range of wavelength,
from the ultraviolet to the near-infrared. The challenge facing astronomers
today is how to use this multitude of information to extract trends, outliers and
and rare objects. For example, a large sample of single white dwarf stars has the
potential to probe the Galaxy through the luminosity function.
The aim of this work was to study stellar and planetary remnants in these
surveys. In the last few decades, it has been shown that a handful of white dwarfs
have remnants of planetary systems around them, in the form of a dusty disc.
These are currently providing the best constraints on the composition of extra-solar
planetary systems. Finding significant numbers of dusty discs is only possible in
large scale digital sky surveys.
I ultilised the SDSS DR7 and colour-colour diagrams to and DA white dwarfs
from optical photometry. This nearly doubled the number of spectroscopically con-
armed DA white dwarfs in the SDSS compared with DR4 [Eisenstein et al., 2006],
and introduced nearly 10; 000 photometric-only DA white dwarf candidates. I further
cross-matched our white dwarf catalogue with UKIDSS LAS DR8 to carry out
the currently largest and deepest untargeted search for low-mass companions to,
and dust discs around, DA white dwarfs. Simultaneously, I analyzed Spitzer observations
of 15 white dwarfs with metal-polluted atmospheres, all but one having
helium-dominated atmospheres. Three of these stars were found to have an infrared
excess consistent with a dusty disc. I used the total sample to estimate a typical
disc lifetime of log[tdisc(yr)] = 5:6+1:1, which is compatible with the relatively large
range estimated from different theoretical models.
Subdwarf population synthesis models predicted a vast population of subdwarfs
with F to K-type companions, produced in the effcient RLOF formation
channel. I used a cross-match of ultraviolet, optical and infrared surveys to search
for this unseen population. I select a complementary sample to those found from
radial velocity surveys, offering direct tests of binary evolution pathways.
Finally, I present a method to use common proper motion white dwarf pairs
to constrain the initial-final mass relation, which is extremely uncertain at low
masses. In the example I show, one of the stars is a magnetic white dwarf with
B ' 6 MG, making this a rare and intriguing system from a magnetic white dwarf
formation point of view.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QB Astronomy
Library of Congress Subject Headings (LCSH):	Astronomy -- Observations, White dwarf stars, Astronomical photometry, Astronomical spectroscopy, Sloan Digital Sky Survey
Official Date:	June 2012
Dates:	Date Event June 2012 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Gänsicke, B. T. (Boris T.) ; Steeghs, D. (Danny), 1972-
Extent:	xiii, 229 leaves : illustrations, charts.
Language:	eng

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