1,253 research outputs found
A Chandra Observation of a TW Hydrae Association Brown Dwarf
We present Chandra observations of the young brown dwarf 2MASSW
J1207334-393254, which is a probable member of the TW Hya association. Although
this substellar object has strong H alpha emission, it has no detected X Ray
flux in a fifty kilosecond ACIS-S observation. We place a conservative upper
limit of 1.2 x 10^{26} erg/sec on its X-ray luminosity. We compare our M8
target to the similar mass object TWA 5B, which has weaker H alpha emission but
strong X-ray emission. We argue our results are consistent with the notion that
2MASSW J1207334-393254 is interacting with a disk.Comment: ApJ Letter, in pres
Structure of matter in strong magnetic fields
We give a detailed presentation of Hartree-Fock calculations of atoms and molecular chains in 10^12 G magnetic fields, as are supposed to exist on the surface of neutron stars. These calculations are the first self-consistent ones treating exchange properly for atoms heavier than helium in high fields. We find that the isolated atom is energetically favored over molecular chains for Z>2 at fields greater than 1Ă—10^12G and for Z>4 at fields greater than 5Ă—10^12 G. These results indicate that matter on the surface of neutron stars is bound very weakly, if at all
Maximally symmetric stabilizer MUBs in even prime-power dimensions
One way to construct a maximal set of mutually unbiased bases (MUBs) in a
prime-power dimensional Hilbert space is by means of finite phase-space
methods. MUBs obtained in this way are covariant with respect to some subgroup
of the group of all affine symplectic phase-space transformations. However,
this construction is not canonical: as a consequence, many different choices of
covariance sugroups are possible. In particular, when the Hilbert space is
dimensional, it is known that covariance with respect to the full group
of affine symplectic phase-space transformations can never be achieved. Here we
show that in this case there exist two essentially different choices of maximal
subgroups admitting covariant MUBs. For both of them, we explicitly construct a
family of covariant MUBs. We thus prove that, contrary to the odd
dimensional case, maximally covariant MUBs are very far from being unique.Comment: 22 page
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