DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

Q
Q “Quality”; a measure of attenuation in an
oscillating system. It is conventionally defined
in terms of the energy in the oscillation:
Q= 2π E
E
where E is the energy stored in the oscillation,
andE is the energy dissipated over the period
of one cycle. If there is no other process at work,
thenQ can be expressed in terms of the real and
imaginary parts of the complex frequency:
Q= ωr
2ωi
where the amplitude of the oscillation is governed
by
A=A0e iωt =A0e i(ωr+iωi)t =A0e iωrt e −ωit .
Q may also be written in terms of (or measured
from) the width of the peak associated with the
oscillation in a power spectrum (that might be
obtained from data through a fourier transform):
Q= ω
ω
ω in this case is real and is the frequency of
the center of the peak, while ω is the width
between the half power points on each side of the
peak. Q may be a function of frequency. There
are many different geophysical oscillations for
whichQmaybedefined, suchasthefreeseismic
oscillations of the Earth, torsional oscillations of
the core, and gravity waves in the atmosphere.
QCD Quantum Chromo–Dynamics, the
quantum theory of the strong interactions.
Q factor Quality factor, Q.
QSO Acronym for QuasiStellarObject.
QSOs are high luminosity active galactic nuclei
which show optical appearance almost undistinguished
from stars, and a spectrum with strong
quanta meter
andbroademissionlinesinvariablyshiftedtothe
red. The optical emission line spectrum closely
resembles that of Seyfert-1 galaxies. Searches
for quasars have been carried out in several regions
of the electromagnetic spectrum, from the
infrared to the X-ray. The final identification
of a quasar is, however, made on the identification
of redshifted spectral emission lines. Many
QSOs are strong radio sources, but a large class
is radio-quiet. The terms QSO and radio-quiet
QSO are a synonym of radio-quiet high luminosity
active galactic nucleus. While in typical
Seyfert galaxies the luminosity of the nucleus
is comparable to the luminosity of the host
galaxy, in QSOs the nucleus can be hundreds
of times more luminous. It is customary to define
as QSOs all radio-quiet active galactic nuclii
(AGN) above the luminosity of 10 11 L⊙. This
subdivision is somewhat arbitrary, since at this
limit there is no break in continuity of the luminosity
distribution.
Other defining properties of QSOs are large
UV flux, broad emission lines, large redshift,
and time-variable continuum flux. Some of the
brightest radio sources are associated with QSOs
whose host galaxy is not clearly visible. The
most distant QSOs are now being observed at
redshift < ∼ 5. The 8th Edition of A Catalogue
of Quasars and Active Nuclei by M.- P. Vé-Cétty
and P. Véron lists more than 11,000 QSOs (both
radio-quiet and radio-loud) known as of early
1998. See Seyfert galaxies.
quadrupole formula In general relativity the
radiated power of a slowly varying source of
gravitational waves is given by the quadrupole
formula
P = G2
45c 5
3
µ,ν=1
d 3 Qµν
dt 3
2
where the quadrupole moment of a point mass
m at xµ is
2
Qµν = 3m xµxν − (1/3)δµν xρ .
quanta meter An instrument to measure
the number of photons (e.g., photosynthetically
available radiation), as opposed to energy.
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