1,177 research outputs found
The design and construction of a Hohlraum spectral analyzer
Design and construction of Hohlraum spectral analyzer to aid in research of air pollutant
IR Monitoring of the Microquasar GRS 1915+105: Detection of Orbital and Superhump Signatures
We present the results of seven years of K-band monitoring of the low-mass
X-ray binary GRS 1915+105. Positive correlations between the infrared flux and
the X-ray flux and X-ray hardness are demonstrated. Analysis of the frequency
spectrum shows that the orbital period of the system is
days. The phase and amplitude of the orbital modulation suggests that the
modulation is due to the heating of the face of the secondary star. We also
report another periodic signature between 31.2 and 31.6 days, most likely due
to a superhump resonance. From the superhump period we then obtain a range on
the mass ratio of the system, .Comment: 16 pages, 6 figures; v2: minor change
On Echo Outbursts and ER UMa Supercycles in SU UMa-type Cataclysmic Variables
I present a variation on Osaki's tidal-thermal-instability model for SU UMa
behavior. I suggest that in systems with the lowest mass ratios, the
angular-momentum dissipation in an eccentric disk is unable to sustain the disk
on the hot side of the thermal instability. This decoupling of the tidal and
thermal instabilities in systems with q < 0.07 allows a better explanation of
the `echo' outbursts of EG Cnc and the short supercycles of RZ LMi and DI UMa.
The idea might also apply to the soft X-ray transients.Comment: To appear in PASP, April 2001 (6 pages, 4 figs
Evidence for Superhumps in the Radio Light Curve of Algol and a New Model for Magnetic Activity in Algol Systems
Extensive radio data of two Algol systems and two RS CVn binaries were
re-analyzed. We found evidence for a new periodicity that we interpret as a
superhump in Algol, in which it may have been expected according to its
semi-detached nature and low binary mass ratio. This is the first detection of
the superhump phenomenon in the radio and the first observation of superhumps
in Algol systems. According to our result, the accretion disk in Algol
precesses in spite of its non-Keplerian nature and therefore this phenomenon is
not restricted to the classical Keplerian disks in compact binaries.We propose
that in Algol systems with short orbital periods, the disk is magnetically
active as well as the secondary star. The magnetic field in the disk originates
from amplification of the seed field in the magnetized material transferred
from the secondary. The disk and stellar fields interact with each other, with
reconnection of the field lines causing flares and particle acceleration.
Relativistic particles are trapped in the field and directed toward the polar
regions of the secondary star because of the dipole structure of its magnetic
field. Our proposed model for the magnetic activity in Algol systems provides a
simple explanation to the observed properties of Algol in the radio
wavelengths, and to the presence of quiescent gyrosynchrotron emission near the
polar region of the secondary star, where electrons are difficult to be
confined if the field lines are open as in normal single magnetic stars. We
propose that the superhump variation in the radio is generated by enhanced
reconnection when the elongated side of the elliptic disk is the closest to the
cool star. This leads to flares and enhancement in particle acceleration and is
manifested as stronger gyrosynchrotron radiation.Comment: 8 pages, 5 figures, ApJ, accepted, uses apjfonts.sty and
emulateapj5.sty, full abstract in pape
Smoothed Particle Hydrodynamics Simulations of Apsidal and Nodal Superhumps
In recent years a handful of systems have been observed to show "negative"
(nodal) superhumps, with periods slightly shorter than the orbital period. It
has been suggested that these modes are a consequence of the slow retrograde
precession of the line of nodes in a disk tilted with respect to the orbital
plane. Our simulations confirm and refine this model: they suggest a roughly
axisymmetric, retrogradely-precessing, tilted disk that is driven at a period
slightly less than half the orbital period as the tidal field of the orbiting
secondary encounters in turn the two halves of the disk above and below the
midplane. Each of these passings leads to viscous dissipation on one face of an
optically-thick disk -- observers on opposite sides of the disk would each
observe one brightening per orbit, but 180 degrees out of phase with each
other.Comment: 11 pages. Accepted for publication in The ApJ Letter
Periodic Variability During the X-ray Decline of 4U 1636-53
We report the onset of a large amplitude, statistically significant
periodicity (~46 d) in the RXTE/ASM data of the prototype X-ray burster 4U
1636-53, the X-ray flux of which has been gradually declining over the last
four years. This behaviour is remarkably similar to that observed in the
neutron star LMXB KS 1731-260, which is a long-term transient. We also report
on an INTEGRAL/IBIS observation of 4U 1636-53 during its decline phase, and
find that the hard X-ray flux (20-100 keV) indicates an apparent
anti-correlation with soft X-rays (2-12 keV). We argue that 4U 1636-53 is
transiting from activity to quiescence, as occurred in KS 1731-260. We also
suggest that the variability during the X-ray decline is the result of an
accretion rate variability related to the X-ray irradiation of the disc.Comment: 6 pages. Accepted by MNRA
Using binary stars to bound the mass of the graviton
Interacting white dwarf binary star systems, including helium cataclysmic
variable (HeCV) systems, are expected to be strong sources of gravitational
radiation, and should be detectable by proposed space-based laser
interferometer gravitational wave observatories such as LISA. Several HeCV star
systems are presently known and can be studied optically, which will allow
electromagnetic and gravitational wave observations to be correlated.
Comparisons of the phases of a gravitational wave signal and the orbital light
curve from an interacting binary white dwarf star system can be used to bound
the mass of the graviton. Observations of typical HeCV systems by LISA could
potentially yield an upper bound on the inverse mass of the graviton as strong
as km (
eV), more than two orders of magnitude better than present solar system derived
bounds.Comment: 21 pages plus 4 figures; ReVTe
Spectroscopic evidence for the binary nature of AM CVn
We analysed archival spectroscopic data of AM CVn taken with the William
Herschel Telescope in 1996. In the literature two orbital periods for AM CVn
are proposed. A clear S-wave in the HeI 4471, 4387 and 4143 \AA lines is
revealed when the spectra are folded on the 1029 s period. No signature of this
S-wave is seen when folded on 1051 s. Doppler tomography of the line profiles
shows a clear signature of the hotspot. Using this we can constrain the value
of K_2 to lie between 210 and 280 km/s. Our work confirms the binary nature of
AM CVn beyond any doubt, establishes 1028.73 s as the true orbital period and
supports the interpretation of AM CVn as a permanent superhump system.Comment: Accepted by MNRA
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