9,596 research outputs found
Followup Observations of SDSS and CRTS Candidate Cataclysmic Variables
We present photometry of 11 and spectroscopy of 35 potential cataclysmic
variables from the Sloan Digital Sky Survey, the Catalina Real-Time Transient
Survey and vsnet-alerts. The photometry results include quasi-periodic
oscillations during the decline of V1363 Cyg, nightly accretion changes in the
likely Polar (AM Herculis binary) SDSS J1344+20, eclipses in SDSS J2141+05 with
an orbital period of 76+/-2 min, and possible eclipses in SDSS J2158+09 at an
orbital period near 100 min. Time-resolved spectra reveal short orbital periods
near 80 min for SDSS J0206+20, 85 min for SDSS J1502+33, and near 100 min for
CSS J0015+26, RXS J0150+37, SDSS J1132+62, SDSS J2154+15 and SDSS J2158+09. The
prominent HeII line and velocity amplitude of SDSS J2154+15 are consistent with
a Polar nature for this object, while the lack of this line and a low velocity
amplitude argue against this classification for RXS J0150+37. Single spectra of
10 objects were obtained near outburst and the rest near quiescence, confirming
the dwarf novae nature of these objects.Comment: 34 pages, 14 figures, in press at A
THEORETICAL ASSESSMENT OF A STIRLING ENGINE 'AMAZON' BY USING PROSA AND MATHCAD
This study describes how to build a prototype Stirling engine named Amazon, focusing on how to apply it to generate electric power in remote areas, with an expected power of 8 kW. Such engine was assessed theoretically by using two different computer software, i.e. PROSA and 'a model to simulate Stirling engines by the theory of Schmidt', which was formulated in Mathcad. The results from Mathcad software were on average 6.8% higher than the results from PROSA software. Such fact occurs since Mathcad does not consider the losses in a real system. Hence, the PROSA is generally more accurate in its results. Modeling performed in Mathcad presents higher values for partial loads and similar values for the project operating point
The Nature of the Secondary Star in the Black Hole X-Ray Transient V616 Mon (=A0620-00)
We have used NIRSPEC on Keck II to obtain -band spectroscopy of the low
mass X-ray binary V616 Mon (= A062000). V616 Mon is the proto-typical soft
x-ray transient containing a black hole primary. As such it is important to
constrain the masses of the binary components. The modeling of the infrared
observations of ellipsoidal variations in this system lead to a derived mass of
11.0 M_{\sun} for the black hole. The validity of this derivation has been
called into question due to the possiblity that the secondary star's spectral
energy distribution is contaminated by accretion disk emission (acting to
dilute the variations). Our new -band spectrum of V616 Mon reveals a
late-type K dwarf secondary star, but one that has very weak CO
absorption features. Comparison of V616 Mon with SS Cyg leads us to estimate
that the accretion disk supplies only a small amount of -band flux, and the
ellipsoidal variations are not seriously contaminated. If true, the derived
orbital inclination of V616 Mon is not greatly altered, and the mass of the
black hole remains large. A preliminary stellar atmosphere model for the
-band spectrum of V616 Mon reveals that the carbon abundance is
approximately 50% of the solar value. We conclude that the secondary star in
V616 Mon has either suffered serious contamination from the accretion of
supernova ejecta that created the black hole primary, or it is the stripped
remains of a formerly more massive secondary star, one in which the CNO cycle
had been active.Comment: 20 pages, 5 figure
Response of the equatorial ionosphere to the geomagnetic DP 2 current system
The response of equatorial ionosphere to the magnetospheric origin DP 2 current system fluctuations is examined using ground‐based multiinstrument observations. The interaction between the solar wind and magnetosphere generates a convection electric field that can penetrate to the ionosphere and cause the DP 2 current system. The quasiperiodic DP 2 current system, which fluctuates coherently with fluctuations of the interplanetary magnetic field (IMF) Bz, penetrates nearly instantaneously to the dayside equatorial region at all longitudes and modulates the electrodynamics that governs the equatorial density distributions. In this paper, using magnetometers at high and equatorial latitudes, we demonstrate that the quasiperiodic DP 2 current system penetrates to the equator and causes the dayside equatorial electrojet (EEJ) and the independently measured ionospheric drift velocity to fluctuate coherently with the high‐latitude DP 2 current as well as with the IMF Bz component. At the same time, radar observations show that the ionospheric density layers move up and down, causing the density to fluctuate up and down coherently with the EEJ and IMF Bz.Key PointsThe solar wind‐magnetosphere interaction generates DP 2 current fluctuationThe DP 2 current fluctuations penetrate to the equator and cause the equatorial electrodynamics to fluctuateIt also causes the equatorial density to fluctuate which might affect the communication and navigation systemsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134255/1/grl54722.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134255/2/grl54722_am.pd
Variability of Kepler Solar-Like Stars Harboring Small Exoplanets
We examine Kepler light-curve variability on habitable zone transit timescales for a large uniform sample of spectroscopically studied Kepler exoplanet host stars. The stars, taken from Everett et al., are solar-like in their properties and each harbors at least one exoplanet (or candidate) of radius ≤2.5 R_e. The variability timescale examined is typical for habitable zone planets orbiting solar-like stars and we note that the discovery of the smallest exoplanets (≤1.2 R_e with corresponding transit depths of less than ~0.18 mmag occur for the brightest and photometrically quietest stars. Thus, these detections are quite rare in Kepler observations. Some brighter and more evolved stars (subgiants), the latter of which often show large radial velocity jitter, are found to be among the photometrically quietest solar-like stars in our sample and the most likely small planet transit hunting grounds. The Sun is discussed as a solar-like star proxy to provide insight into the nature and cause of photometric variability. It is shown that Kepler's broad, visible light observations are insensitive to variability caused by chromospheric activity that may be present in the observed stars
BENCHMARKING OF TWO SYSTEMS FOR TRANSMISSION OF MOTION FOR A DOUBLE ACTION STIRLING ENGINE
In a four-piston Stirling engine, Siemens configuration, the displacement of the pistons is governed by the motion transmission element, which converts the reciprocating motion of pistons into rotary motion. This study aimed to evaluate the influence of the geometry of the transmission element in the mechanical efficiency of a Stirling engine. Analyses were performed using a mathematical computer simulation that uses the geometric and operating data of the engine to calculate the mechanical power and efficiency through a first order thermodynamic mathematical model, also known as the Schmidtmodel. First, an analysis was performed to evaluate the mechanical efficiency of the transmission element with a sinusoidal curve surface. Later, it was implemented in the transmission mechanism a segment based straight plans surface, and then the same analysis was performed with this new transmission element. The results showed that using the transmission element with segment based straight plans the engine showed a significant increase in efficiency. Moreover, one can observe an increase in the vibration of the system, making it necessary to develop an appropriate system for balancing
HST Fine Guidance Sensor Astrometric Parallaxes for Three Dwarf Novae: SS Aurigae, SS Cygni, and U Geminorum
We report astrometric parallaxes for three well known dwarf novae obtained
using the Fine Guidance Sensors on the Hubble Space Telescope. We found a
parallax for SS Aurigae of Pi = 5.00 +/- 0.64 mas, for SS Cygni we found Pi =
6.02 +/- 0.46 mas, and for U Geminorum we obtained Pi = 10.37 +/- 0.50 mas.
These represent the first true trigonometric parallaxes of any dwarf novae. We
briefly compare these results with previous distance estimates. This program
demonstrates that with a very modest amount of HST observing time, the Fine
Guidance Sensors can deliver parallaxes of unrivaled precision.Comment: 15 pages, 2 Table
Observations of the SW Sextantis star DW Ursae Majoris with the Far Ultraviolet Spectroscopic Explorer
We present an analysis of the first far-ultraviolet observations of the SW
Sextantis-type cataclysmic variable DW Ursae Majoris, obtained in November 2001
with the Far Ultraviolet Spectroscopic Explorer. The time-averaged spectrum of
DW UMa shows a rich assortment of emission lines (plus some contamination from
interstellar absorption lines including molecular hydrogen). Accretion disk
model spectra do not provide an adequate fit to the far-ultraviolet spectrum of
DW UMa. We constructed a light curve by summing far-ultraviolet spectra
extracted in 60-sec bins; this shows a modulation on the orbital period, with a
maximum near photometric phase 0.93 and a minimum half an orbit later. No other
periodic variability was found in the light curve data. We also extracted
spectra in bins spanning 0.1 in orbital phase; these show substantial variation
in the profile shapes and velocity shifts of the emission lines during an
orbital cycle of DW UMa. Finally, we discuss possible physical models that can
qualitatively account for the observed far-ultraviolet behavior of DW UMa, in
the context of recent observational evidence for the presence of a
self-occulting disk in DW UMa and the possibility that the SW Sex stars may be
the intermediate polars with the highest mass transfer rates and/or weakest
magnetic fields.Comment: accepted by the Astronomical Journal; 36 pages, including 12 figures
and 4 table
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