Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt.........2n&link_type=abstract
Thesis (PhD). COLUMBIA UNIVERSITY, Source DAI-B 65/04, p. 1909, Oct 2004, 119 pages.
Astronomy and Astrophysics
Astronomy
Scientific paper
The theory describing the formation and evolution of cataclysmic variables (CVs) is currently hampered by strong biases in the observational sample. These biases include: selection effects that skew the sample toward brighter, higher mass-transfer rate objects, the uncertainty in the frequency and type of CVs within the sample, and the difficulty in obtaining pure samples from either disk (late-type) or bulge (early-type) populations. These problems make it nearly impossible to discern the effect of environment on the formation and evolution of CVs. This thesis presents the results from a series of studies sampling a range of stellar environments in which CVs are found. We employed new observing techniques that begin to address some of the worst selection biases with the aim of strengthening the observational constraints on models of CV formation and evolution. We have measured the first orbital period for a dwarf nova in a globular cluster (M5 V101). Globular clusters are known to produce and lose many hard binaries through dynamical encounters in their cores, and as such, may be important contributors to the CV population of their host galaxy. We have produced the most accurate nova rate and spatial distribution for an external (late- type) galaxy (M81). We have conducted the first systematic, long-term nova survey of local group dwarf elliptical galaxies (M32, NGC205, NGC147, NGC185). Additionally, we have searched for novae in an environment which has implications for galaxy formation, namely the region between galaxies in a cluster (Fornax). Our results confirm that CVs with orbital periods similar to Galactic CVs can be produced in globular clusters. We also provide some evidence that M5 V101 is being ejected from its host cluster. We show that our comprehensive, densely time-sampled nova survey of M81 produced a significantly larger and much more accurate global nova rate and spatial distribution than previous techniques. Our nova spatial distribution for M81 implies a bulge-to- disk nova ratio of >9, in stark contrast to theoretical predictions. We show that local group dwarf ellipticals have a higher nova rate than predicted from assuming a constant nova rate per unit light for galaxies of all luminosities. We have demonstrated that novae exist between the galaxies of the Fornax cluster, and proven the feasibility of using them as probes of cluster tidal debris. We also show that the distribution of novae in the Fornax cluster is consistent with ˜25% of the total cluster light being unassociated with any galaxy. Our overarching conclusion is that the biases listed above will be reduced by dense temporal and comprehensive spatial coverage. As astronomical resources begin to shift toward large scale synoptic imaging surveys, we can look forward to a much more complete sample of close binaries, which may be used to inform a much-improved theory of their formation and evolution.
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