243 research outputs found
Does TV Col Have the longest Recorded Positive Superhumps?
Re-examination of extensive photometric data of TV Col reveals evidence for a
permanent positive superhump. Its period (6.4 h) is 16 percent longer than the
orbital period and obeys the well known relation between superhump period
excess and binary period. At 5.5-h, TV Col has an orbital period longer than
any known superhumping cataclysmic variable and, therefore, a mass ratio which
might be outside the range at which superhumps can occur according to the
current theory. We suggest several solutions for this problem.Comment: 5 pages, 2 eps. figures, Latex, proceedings of `Evolution of Binary
and Multiple Star Systems', a Meeting in Celebration of Peter Eggleton's 60th
Birthday, Bormio, Italy, ASP Conference Series, eds. Ph. Podsiadlowski et
al., ASP, San Francisc
The IR counterpart of the black-hole candidate 4U 1630-47
We present K band photometry of the region including the radio error box of
the soft X-ray transient 4U 1630-47 during its 1998 outburst. We detect a
variable source at K=16.1 mag located inside the radio error circle which we
identify as the counterpart to the X-ray source. We discuss the properties of
the source, and conclude that it is most likely a black-hole X-ray binary
similar to 4U 1543-47, GRO J1655-40 or SAX J1819.3-2525, containing a
relatively early-type secondary.Comment: 7 pages, 3 figures, A&A, in pres
Dwarf Novae with Newly Determined Parallaxes: Model Analyses of VY Aquari, RU Pegasi, and T Leonis
Using newly determined parallaxes for dwarf novae, we have derived outburst
accretion rates for VY Aqr, RU Peg and T Leo and for T Leo during quiescence.
The two short-period dwarf novae, VY Aqr and T Leo, show good agreement with
optically thick steady-state accretion disks in outburst, whereas RU Peg shows
a significant departure from a steady-state disk. We have determined that the
white dwarf in T Leo has T K, a value consistent with
long term compressional heating when gravitational wave emission drives mass
transfer. The white dwarf in T Leo has a temperature in the same narrow range
as other WZ Sge-like dwarf novae.Comment: The paper will apear in the October, 2004 issue of PAS
The Dwarf Novae of Shortest Period
We present observations of the dwarf novae GW Lib, V844 Her, and DI UMa.
Radial velocities of H-alph yield orbital periods of 0.05332 +- 0.00002 d (=
76.78 m) for GW Lib and and 0.054643 +- 0.000007 d (= 78.69 m) for V844 Her.
Recently, the orbital period of DI UMa was found to be only 0.054564 +-
0.000002 d (= 78.57 m) by Fried et al. (1999), so these are the three shortest
orbital periods among dwarf novae with normal-abundance secondaries.
GW Lib has attracted attention as a cataclysmic binary showing apparent ZZ
Ceti-type pulsations of the white dwarf primary. Its spectrum shows sharp
Balmer emission flanked by strong, broad Balmer absorption, indicating a
dominant contribution by white-dwarf light. Analysis of the Balmer absorption
profiles is complicated by the unknown residual accretion luminosity and lack
of coverage of the high Balmer lines. Our best-fit model atmospheres are
marginally hotter than the ZZ Ceti instability strip, in rough agreement with
recent ultraviolet results from HST. The spectrum and outburst behavior of GW
Lib make it a near twin of WZ Sge, and we estimate it to have a quiescent V
absolute magnitude 12. Comparison with archival data reveals proper motion of
65 +- 12 mas/yr.
The mean spectrum of V844 Her is typical of SU UMa dwarf novae. We detected
superhumps in the 1997 May superoutburst with superhump period = 0.05597 +-
0.00005 d. The spectrum of DI UMa appears normal for a dwarf nova near minimum
light.
These three dwarf novae have nearly identical short periods but completely
dissimilar outburst characteristics. We discuss possible implications.Comment: Accepted for publication in Publications of the Astronomical Society
of the Pacific; 16 pages, 6 figure
The new X-ray transient SAX J1711.6-3808: decoupling between its 3-20 keV luminosity and its state transitions
We present a study of the correlated spectral and timing behavior of the new
X-ray transient SAX J1711.6-3808 during its 2001 outburst using data obtained
with the RXTE. We also investigate the correlations between those source
properties and the 3-20 keV X-ray luminosity. The behavior of the source during
the observations can be divided into two distinct state types. During the hard
state, the energy spectra are relatively hard and can be described by only a
power-law component, and the characteristic frequencies (i.e., the frequency of
the 1-7 Hz QPOs observed for the first time in this source) in the power
spectra are low. However, during the ``soft'' state, the spectra are
considerably softer (in addition to the power-law component, a soft component
is necessary to fit the spectra) and the frequencies are the highest observed.
Remarkably, this distinction into two separate states cannot be extrapolated to
also include the 3-20 keV X-ray luminosity. Except for one observation, this
luminosity steadily decreased but the hard state was observed both at the
highest and lowest observed luminosities. In contrast, the soft state occurred
only at intermediate luminosities. This clearly demonstrates that the state
behavior of SAX J1711.6-3808 is decoupled from its X-ray luminosity and that if
the X-ray luminosity traces the accretion rate in SAX J1711.6-3808, then the
state transitions are not good accretion rate indicators, or vice versa. The
data of SAX J1711.6-3808 does not allow us to conclusively determine its exact
nature. The source resembles both neutron star and black hole systems when they
have low luminosities. We discuss our results with respect to the correlated
timing and spectral behavior observed in other LMXBs and the implications of
our results on the modeling of the outburst light curves of X-ray transients.Comment: Accepted for publication in ApJ Main Journal, 13 September 200
Photometric Variability in the Faint Sky Variability Survey
The Faint Sky Variability Survey (FSVS) is aimed at finding photometric
and/or astrometric variable objects between 16th and 24th mag on time-scales
between tens of minutes and years with photometric precisions ranging from 3
millimag to 0.2 mag. An area of 23 deg, located at mid and high Galactic
latitudes, was covered using the Wide Field Camera (WFC) on the 2.5-m Isaac
Newton Telescope (INT) on La Palma. Here we present some preliminary results on
the variability of sources in the FSVS.Comment: 4 pages, 3 figures, to appear in 14th European Workshop on White
Dwarfs, ASP Conference Series, eds. D. Koester, S. Moehle
The spectroscopic evolution of the recurrent nova T Pyxidis during its 2011 outburst. II.The optically thin phase and the structure of the ejecta in recurrent novae
We continue our study of the physical properties of the recurrent nova T Pyx,
focussing on the structure of the ejecta in the nebular stage of expansion
during the 2011 outburst. The nova was observed contemporaneously with the
Nordic Optical Telescope (NOT), at high resolution spectroscopic resolution (R
~ 65000) on 2011 Oct. 11 and 2012 Apr. 8 (without absolute flux calibration),
and with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble
Space Telescope, at high resolution (R ~ 30000) on 2011 Oct. 10 and 2012 Mar.
28 (absolute fluxes). We use standard plasma diagnostics (e.g. [O III] and [N
II] line ratios and the H line fluxes) to constrain electron densities
and temperatures. Using Monte Carlo modeling of the ejecta, we derive the
structure and filling factor from comparisons to the optical and ultraviolet
line profiles. The ejecta can be modeled using an axisymmetric conical --
bipolar -- geometry with a low inclination of the axis to the line of sight,
i=15+/-5 degrees, compatible with published results from high angular
resolution optical spectro-interferometry. The structure is similar to that
observed in the other short orbital period recurrent novae during their nebular
stages. We show that the electron density scales as as expected from a
ballistically ejected constant mass shell; there is no need to invoke a
continuing mass outflow following the eruption. The derived mass for the ejecta
with filling factor f ~ 3%, M_ej ~ 2E-6$M_sun is similar to that obtained for
other recurrent nova ejecta but inconsistent with the previously reported
extended optically thick epoch of the explosion. We suggest that the system
underwent a common envelope phase following the explosion that produced the
recombination event. Implications for the dynamics of the recurrent novae are
discussed. (truncated)Comment: accepted for publication in A&A (10 Nov. 2012), 10 pgs, 16 fig
Water-ice driven activity on Main-Belt Comet P/2010 A2 (LINEAR) ?
The dust ejecta of Main-Belt Comet P/2010 A2 (LINEAR) have been observed with
several telescopes at the at the Observatorio del Roque de los Muchachos on La
Palma, Spain. Application of an inverse dust tail Monte Carlo method to the
images of the dust ejecta from the object indicates that a sustained, likely
water-ice driven, activity over some eight months is the mechanism responsible
for the formation of the observed tail. The total amount of dust released is
estimated to be 5E7 kg, which represents about 0.3% of the nucleus mass. While
the event could have been triggered by a collision, this cannot be decided from
the currently available data.Comment: Accepted for ApJ Letter
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