IPs
AE Aqr
FO Aqr
XY Ari
V405 Aur
HT Cam
MU Cam
DW Cnc
BG CMi
V709 Cas
V1025 Cen
TV Col
TX Col
UU Col
V2306 Cyg
YY Dra
PQ Gem
DQ Her
EX Hya
NY Lup
V2400 Oph
GK Per
AO Psc
WX Pyx
V1223 Sgr
V1062 Tau
EI UMa
IGR 00234
IGR 15094
IGR 17303
Swift J0732
RX J0704
RX J1803
RX J2133
XSS 00564
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The Accretion Modes of IPs
The simplest picture of IPs is that they have a partial (and
fully Keplerian) accretion disk, truncated by the magnetic
field of the white dwarf. There is strong evidence of
accretion disks (or at least disk-like structures) in many IPs
(Hellier 1991). The X-ray orbital modulations seen in many
IPs are also often (if not always) caused by azimuthal structure
of the disk (Hellier et al. 1993; Parker, Norton & Mukai 2005).
The well known exception is V2400
Oph, which is a diskless accretor. That is, the primary's magnetic
field is too strong to permit the formation of an accretion disk.
X-ray modulations at one of two possible sidebands (\omega-\Omega
or 2\omega-\Omega) are expected in diskless IPs (Wynn & King 1992),
but not seen in most IPs (Hellier 1992).
There are three important numbers: the minimum distance between the
ballistic trajectory from the L1 point and the white dwarf,
rmin; the magnetospheric radius, rmag; and the
circularization radius, rcir, where the specific angular
momentum of the material in a Keplerian disk would equal that of the
co-rotating material at the L1 point. A disk will definitely
form if rmin > rmag, while a disk will definitely
disappear if rmag > rcir. The case of
rmin < rmag < rcir is
tricky, since a disk should not be able to form but once formed,
it can remain undisrupted. Since rmag is determined
in part by the accretion rate, an episode of high accretion rate
can establish a disk in this regime. Depending on the mass ratio
of the binary, Pspin/Porb~0.1 corresponds to
this regime.
This means that systems such as EX Hya
are hard to understand in the standard, Keplerian, accretion disk picture.
A series of papers based on the diamagnetic blob picture, however, explain
such systems (Wynn & King 1995; Norton, Wynn & Somerscales 2004;
Norton et al. 2008). So far, there are 2 other confirmed IPs in this
regime; other candidates have been proposed, but not been confirmed (yet).
Then there is disk overflow accretion (Hellier 1993). For the overflow stream
to directly accrete, something like this condition:
rmin < rmag < rcir
must be met.
Since this makes it a key parameter, we provide
a table of confirmed
IPs sorted by Pspin/Porb.
We also show this graphically on the IP Home page.
References
Please send your comments, suggestions etc. to
Koji.Mukai@nasa.gov
and/or
Koji.Mukai@umbc.edu
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