429 research outputs found
Recent Results from Infrared Observations of White Dwarfs, their Companions, and the Dust that Surrounds Them
Although "traditionally" observed at short wavelengths, white dwarfs have displayed many surprising features when probed in the infrared. We present an overview of recent results from ground- and space-based near- to mid-infrared observations of white dwarfs. These include the discovery of many new candidate binary stars containing low mass stellar or sub-stellar companions from a sample of objects previously thought to be single white dwarfs, and Spitzer Space Telescope observations that suggest that dust is common in the environs of white dwarfs in cataclysmic variables
A New Narrow-Line Seyfert 1 galaxy : RXJ1236.9+2656
We report identification of a narrow-line Seyfert 1 galaxy RXJ1236.9+2656.
X-ray emission from the NLS1 galaxy undergoes long-term variability with
0.1--2.0 keV flux changing by a factor of 2 within about 3 yr. The ROSAT PSPC
spectrum of RXJ1236.9+2656 is well represented by a power-law of Gamma = 3.7
absorbed by matter in our own Galaxy (N_H = 1.33X10^20 cm**-2). Intrinsic soft
X-ray luminosity of the NLS1 galaxy is estimated to be 1.5X10^43 erg/s in the
energy band of 0.1-2.0 keV. The optical spectrum of RXJ1236.9+2656 is typical
of NLS1 galaxies and shows narrow Balmer emission lines (1100 km/s < FWHM <
1700 km/s) of Hbeta, Halpha, and forbidden lines of [O III] and [N II]. Fe II
multiplets, usually present in optical spectra of NLS1 galaxies, are also
detected in RXJ1236.9+2656.Comment: 4 pages, A&A style Latex, To apear in A&A as a research not
Observations of V592 Cas -— an Outflow at Optical Wavelengths
We present new red optical spectra of V592 Cas aimed at exploring the properties of the outflow of this system in a spectral region where the underlying white dwarf and the accretion disk do not contribute significantly to the observed absorption components of the Hα and He I line profiles. We use the Hα emission line to study the wind, which appears as pronounced blueshifted P Cygni absorption troughs whose low velocity end contaminates the blue side of the emission line profile. The wind appears to be episodic in nature, with multiple events reaching velocities of 5000 km s^–1 in Hα. Similar (but weaker) wind signatures appear in the He I 5876 Å line but are absent in He I 6678 Å. Our data suggest that during wind episodes the wind is phase dependent and is visible for half of the orbit of the system. Considering that V592 Cas is viewed almost face-on, the symmetry axis of the outflow cannot be orthogonal to the disk and/or the outflow must have some other inherent asymmetry in outflow geometry. A possible origin of the wind is in a disk hotspot, either at the initial impact point of the accretion stream on the disk edge or as a result of disk overflow (similar to SW Sextantis stars). Simultaneous optical photometry during one night of our spectroscopic observations indicate that there is no clear relationship between the optical brightness variations and the strength of the outflow in this system
Technical management techniques for identification and control of industrial safety and pollution hazards
Constructive recommendations are suggested for pollution problems from offshore energy resources industries on outer continental shelf. Technical management techniques for pollution identification and control offer possible applications to space engineering and management
What’s Cool About Hot Stars? Cataclysmic Variables in the Mid-Infrared
We review recent results from mid-infrared observations of cataclysmic variables with the Spitzer Space Telescope. In general, these observations have revealed mid-infrared excesses, above the level expected from the stellar and accretion components, in numerous systems. This excess can be modeled as originating from circumstellar and/or circumbinary dust. We present an overview of spectral energy distributions spanning the ultraviolet to the mid-infrared, as well as mid-infrared light curves, of disk-accreting and magnetic cataclysmic variables. Physically realistic models constructed to reproduce these data indicate that the mid-infrared luminosity of many cataclysmic variables is dominated by emission from warm (T < 2000 K) dust. The presence and characteristics of dust in cataclysmic variables has potentially important implications for the secular evolution scenario for interacting binary stars
Constraints on the Lifetimes of Disks Resulting from Tidally Destroyed Rocky Planetary Bodies
Spitzer IRAC observations of 15 metal-polluted white dwarfs reveal infrared
excesses in the spectral energy distributions of HE 0110-5630, GD 61, and HE
1349-2305. All three of these stars have helium-dominated atmospheres, and
their infrared emissions are consistent with warm dust produced by the tidal
destruction of (minor) planetary bodies. This study brings the number of
metal-polluted, helium and hydrogen atmosphere white dwarfs surveyed with IRAC
to 53 and 38 respectively. It also nearly doubles the number of metal-polluted
helium-rich white dwarfs found to have closely orbiting dust by Spitzer. From
the increased statistics for both atmospheric types with circumstellar dust, we
derive a typical disk lifetime of log[t_{disk} (yr)] = 5.6+-1.1 (ranging from
3*10^4 - 5*10^6 yr). This assumes a relatively constant rate of accretion over
the timescale where dust persists, which is uncertain. We find that the
fraction of highly metal-polluted helium-rich white dwarfs that have an
infrared excess detected by Spitzer is only 23 per cent, compared to 48 per
cent for metal-polluted hydrogen-rich white dwarfs, and we conclude from this
difference that the typical lifetime of dusty disks is somewhat shorter than
the diffusion time scales of helium-rich white dwarf. We also find evidence for
higher time-averaged accretion rates onto helium-rich stars compared to the
instantaneous accretion rates onto hydrogen-rich stars; this is an indication
that our picture of evolved star-planetary system interactions is incomplete.
We discuss some speculative scenarios that can explain the observations.Comment: 20 pages, 9 figures, accepted to be published in Ap
"Dark Matter" in Accretion Disks
Using Spitzer Space Telescope photometric observations of the eclipsing,
interacting binary WZ Sge, we have discovered that the accretion disk is far
more complex than previously believed. Our 4.5 and 8 micron time series
observations reveal that the well known gaseous accretion disk is surrounded by
an asymmetric disk of dusty material with a radius approximately 15 times
larger than the gaseous disk. This dust ring contains only a small amount of
mass and is completely invisible at optical and near-IR wavelengths, hence
consisting of "dark matter". We have produced a model dust ring using 1 micron
spherical particles with a density of 3 g/cm and with a temperature profile
ranging from 700-1500K. Our discovery about the accretion disk structure and
the presence of a larger, outer dust ring have great relevance for accretion
disks in general, including those in other interacting binary systems, pre-main
sequence stars, and active galaxies.Comment: 34 pages, 8 figures (3 in color). Accepted to Ap
A Closer Look at the Soft X-ray Transient X1608-52: Long-term Optical/X-ray Observations
We report long-term simultaneous optical and (RXTE) X-ray observations of the
soft X-ray transient and low mass X-ray binary X1608-52 spanning from 1999 to
2001. In addition to the usual X-ray outburst and quiescent states, X1608-52
also exhibits an extended low intensity state during which the optical
counterpart, QX Nor, is found to be about two magnitudes brighter than during
quiescence. We detect optical photometric variability on a possible period of
0.5370 days with a semi-amplitude of ~0.27 mag in the I band. The modulation
could be orbital but is also consistent with a scenario invoking a superhump
with decreasing period. Observations of QX Nor during quiescence indicate an F
to G type main sequence secondary while theoretical considerations argue for an
evolved mass donor. Only an evolved mass donor would satisfy the condition for
the occurrence of superhumps.Comment: 26 pages, 10 figures, ApJ, in pres
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