9,629 research outputs found
Mass-ratio distribution of extremely low-mass white dwarf binaries
Knowing the masses of the components of binary systems is very useful to
constrain the possible scenarios that could lead to their existence. While it
is sometimes possible to determine the mass of the primary star, for
single-lined spectroscopic binaries it is not trivial to have good estimates of
the mass of the secondary. If a large enough sample of such binaries is
available, it is possible, however, to use statistical methods to determine the
mass ratio distribution, and thus, the secondary mass distribution. Recently,
Andrews et al. (2014) studied the mass distribution of companions to extremely
low-mass white dwarfs, using a sample of binaries from the ELM WD Survey. I
reanalyse the same sample, using two different methods: in the first one, I
assume some functional form for the mass distribution, while in the second, I
apply an inversion method. I show that the resulting companion-mass
distribution can be as well approximated by either a uniform distribution or a
Gaussian distribution. The mass ratio distribution derived from the inversion
method, without assuming any a priori functional form, shows some additional
fine-grain structure, although, given the small sample, it is difficult to
claim that this structure is statistically significant. I conclude that it is
not possible yet to fully constrain the distribution of the mass of the
companions to extremely low-mass white dwarfs, although it appears that the
probability to have a neutron star in one of the systems is indeed very small.Comment: A&A Letters, in pres
Measurements of the top-antitop production cross section at the Tevatron Run II CDF experiment using b-tagging
We present measurements of the top-antitop production cross section in
b-tagged lepton + jets events from proton-antiproton collisions at 1.96 TeV
using the CDF detector at Fermilab. B-jets are tagged with either a secondary
vertex algorithm, or a soft lepton tagger that identifies muons from B hadron
semileptonic decays. With Tevatron Run II data, we estimate the top-antitop
signal fraction in two different ways: by estimating the various background
contributions, and by fitting directly the leading jet transverse energy
spectrum for the signal and background contributions. A subset of the sample
with two secondary vertex tagged jets yields a production cross section
consistent with the inclusive measurements. Results are consistent with a
Standard Model top-antitop signal and current measurements of the top quark
mass.Comment: 3 pages, 4 figures, DPF 2004 proceedin
Parallax and masses of alpha Centauri revisited
Context. Despite the thorough work of van Leeuwen (2007), the parallax of
alpha Centauri is still far from being carved in stone. Any derivation of the
individual masses is therefore uncertain, if not questionable. And yet, that
does not prevent this system from being used for calibration purpose in several
studies. Aims. Obtaining more accurate model-free parallax and individual
masses of this system. Methods. With HARPS, the radial velocities are not only
precise but also accurate. Ten years of HARPS data are enough to derive the
complement of the visual orbit for a full 3D orbit of alpha Cen. Results. We
locate alpha Cen (743 mas) right where Hipparcos (ESA 1997) had put it, i.e.
slightly further away than derived by Soderhjelm (1999). The components are
thus a bit more massive than previously thought (1.13 and 0.97 Msun for A and B
respectively). These values are now in excellent agreement with the latest
asteroseismologic results.Comment: 4 pages, 3 figures, accepted in Astronomy & Astrophysic
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