5,211 research outputs found
The OmegaWhite Survey for Short-Period Variable Stars IV: Discovery of the warm DQ white dwarf OW J175358.85-310728.9
We present the discovery and follow-up observations of the second known
variable warm DQ white dwarf OW J175358.85-310728.9 (OW J1753-3107). OW
J1753-3107 is the brightest of any of the currently known warm or hot DQ and
was discovered in the OmegaWhite Survey as exhibiting optical variations on a
period of 35.5452 (2) mins, with no evidence for other periods in its light
curves. This period has remained constant over the last two years and a
single-period sinusoidal model provides a good fit for all follow-up light
curves. The spectrum consists of a very blue continuum with strong absorption
lines of neutral and ionised carbon, a broad He I 4471 A line, and possibly
weaker hydrogen lines. The C I lines are Zeeman split, and indicate the
presence of a strong magnetic field. Using spectral Paschen-Back model
descriptions, we determine that OW J1753-3107 exhibits the following physical
parameters: T_eff = 15430 K, log(g) = 9.0, log(N(C)/N(He)) = -1.2, and the mean
magnetic field strength is B_z =2.1 MG. This relatively low temperature and
carbon abundance (compared to the expected properties of hot DQs) is similar to
that seen in the other warm DQ SDSS J1036+6522. Although OW J1753-3107 appears
to be a twin of SDSS J1036+6522, it exhibits a modulation on a period slightly
longer than the dominant period in SDSS J1036+6522 and has a higher carbon
abundance. The source of variations is uncertain, but they are believed to
originate from the rotation of the magnetic white dwarf.Comment: 11 pages, 8 figures, 7 tables. Accepted for publication by MNRA
Generalized q-Oscillators and their Hopf Structures
We study the relationships among the various forms of the oscillator
algebra and consider the conditions under which it supports a Hopf structure.
We also present a generalization of this algebra together with its
corresponding Hopf structure. Its multimode extensions are also considered.Comment: 14 page
Development of a unified tensor calculus for the exceptional Lie algebras
The uniformity of the decomposition law, for a family F of Lie algebras which
includes the exceptional Lie algebras, of the tensor powers ad^n of their
adjoint representations ad is now well-known. This paper uses it to embark on
the development of a unified tensor calculus for the exceptional Lie algebras.
It deals explicitly with all the tensors that arise at the n=2 stage, obtaining
a large body of systematic information about their properties and identities
satisfied by them. Some results at the n=3 level are obtained, including a
simple derivation of the the dimension and Casimir eigenvalue data for all the
constituents of ad^3. This is vital input data for treating the set of all
tensors that enter the picture at the n=3 level, following a path already known
to be viable for a_1. The special way in which the Lie algebra d_4 conforms to
its place in the family F alongside the exceptional Lie algebras is described.Comment: 27 pages, LaTeX 2
Some remarks on the Gauss decomposition for quantum group GL_q(n)
In this letter some properties of the Gauss decomposition of quantum group
with application to q-bosonization are considered.Comment: 11 page
High Resolution X-ray Spectra of the Brightest OB Stars in the Cygnus OB2 Association
The Cygnus OB2 Association contains some of the most luminous OB stars in our
Galaxy, the brightest of which are also among the most luminous in X-rays. We
have obtained a Chandra High Energy Transmission Grating Spectrometer (HETGS)
observation centered on Cyg OB2 No. 8a, the most luminous X-ray source in the
Association. Although our analysis will focus on the X-ray properties of Cyg
OB2 No. 8a, we also present limited analyses of three other OB stars (Cyg OB2
Nos. 5, 9, and 12). Applying standard diagnostic techniques as used in previous
studies of early-type stars, we find that the X-ray properties of Cyg OB2 No.
8a are very similar to those of other OB stars that have been observed using
high-resolution X-ray spectroscopy. From analyses of the He-like ion "fir"
emission lines, we derive radial distances of the He-like line emission sources
and find these fir-inferred radii are consistent with their corresponding X-ray
continuum optical depth unity radii. Contrary to other O-star results, the
emission lines of Cyg OB2 No. 8a show a large range in line centroid shifts
(roughly -800 to +250 km/s). We discuss the implications of our results in
light of the fact that Cyg OB2 No. 8a is a member of a rather tight stellar
cluster, and shocks could arise at interfaces with the winds of these other
stars.Comment: 36 pages (including 4 tables and 12 figures). LaTeX. Submitted to Ap
The -boson-fermion realizations of quantum suprealgebra
We show that our construction of realizations for Lie algebras and quantum
algebras can be generalized to quantum superalgebras, too. We study an example
of quantum superalgebra and give the boson-fermion realization
with respect to one pair od q-deformed boson operator and 2 pairs of fermions.Comment: 8 page
Unitarizable Representations of the Deformed Para-Bose Superalgebra Uq[osp(1/2)] at Roots of 1
The unitarizable irreps of the deformed para-Bose superalgebra , which
is isomorphic to , are classified at being root of 1. New
finite-dimensional irreps of are found. Explicit expressions
for the matrix elements are written down.Comment: 19 pages, PlainTe
q-Supersymmetric Generalization of von Neumann's Theorem
Assuming that there exist operators which form an irreducible representation
of the q-superoscillator algebra, it is proved that any two such
representations are equivalent, related by a uniquely determined superunitary
transformation. This provides with a q-supersymmetric generalization of the
well-known uniqueness theorem of von Neumann for any finite number of degrees
of freedom.Comment: 10 pages, Latex, HU-TFT-93-2
On boson algebras as Hopf algebras
Certain types of generalized undeformed and deformed boson algebras which
admit a Hopf algebra structure are introduced, together with their Fock-type
representations and their corresponding -matrices. It is also shown that a
class of generalized Heisenberg algebras including those algebras including
those underlying physical models such as that of Calogero-Sutherland, is
isomorphic with one of the types of boson algebra proposed, and can be
formulated as a Hopf algebra.Comment: LaTex, 18 page
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