105 research outputs found
Long-term polarization observations of Mira variable stars suggest asymmetric structures
Mira and semi-regular variable stars have been studied for centuries but
continue to be enigmatic. One unsolved mystery is the presence of polarization
from these stars. In particular, we present 40 years of polarization
measurements for the prototype o Ceti and V CVn and find very different
phenomena for each star. The polarization fraction and position angle for Mira
is found to be small and highly variable. On the other hand, the polarization
fraction for V CVn is large and variable, from 2 - 7 %, and its position angle
is approximately constant, suggesting a long-term asymmetric structure. We
suggest a number of potential scenarios to explain these observations.Comment: 2 pages, 1 figure, poster presented at IAU Symposium 301, Precision
Asteroseismology, August 2013, Wroclaw, Polan
The Relationship Between Displaying Political Yard Signs and Voting Turnout in Omaha, Nebraska: An Exploratory Study
In recent studies of voting behavior, few variables have been ignored. These studies have produced a mass socio-psychological data through which the political scientists, sociologists, and various others have attempted to discover what has influenced voting behavior. Studies have ranged from the macro-influence of national alternatives to micro studies of psychological reasons for preference and turnout. Many of the studies have utilized what is termed the behavioral approach
Evidence of a Mira-like tail and bow shock about the semi-regular variable V CVn from four decades of polarization measurements
Polarization is a powerful tool for understanding stellar atmospheres and
circumstellar environments. Mira and semi-regular variable stars have been
observed for decades and some are known to be polarimetrically variable,
however, the semi-regular variable V Canes Venatici displays an unusually
large, unexplained amount of polarization. We present ten years of optical
polarization observations obtained with the HPOL instrument, supplemented by
published observations spanning a total interval of about forty years for V
CVn. We find that V CVn shows large polarization variations ranging from 1 -
6%. We also find that for the past forty years the position angle measured for
V CVn has been virtually constant suggesting a long-term, stable, asymmetric
structure about the star. We suggest that this asymmetry is caused by the
presence of a stellar wind bow shock and tail, consistent with the star's large
space velocity.Comment: 8 pages, 5 figures, 1 table. Accepted for publication in A&
A Study of H Line Profile Variations in Lyr
We examine over 160 archival H spectra from the Ritter Observatory
for the interacting binary ~Lyr obtained between 1996 and 2000. The
emission is characteristically double-peaked, but asymmetric, and with an
absorption feature that is persistently blueshifted. Using a set of simplifying
assumptions, phase varying emission line profiles are calculated for H
formed entirely in a Keplerian disk, and separately for the line formed
entirely from an off-center bipolar flow. However, a dynamic spectrum of the
data indicate the blueshifted feature is not always present, and the data are
even suggestive of a drift of the feature in velocity shift. We explore whether
a circumbinary envelope, hot spot on the accretion disk, or accretion stream
could explain the observations. While none are satisfactory, an accretion
stream explanation is somewhat promising.Comment: accepted to Astronomical Journa
Variability in Protoplanetary Nebulae: X. Multi-year Periods as an Indicator of Potential Binaries
New observations are presented of four evolved objects that display long,
multi-year variations in their light curves. These are interpreted as good
evidence of their binary nature, with the modulation caused by the barycenter
motion of the evolved star resulting in a periodic obscuration by a
circumbinary disk. Although protoplanetary nebulae (PPNe) commonly possess
bipolar nebulae, which are thought to be shaped by a binary companion, there
are very few PPNe in which a binary companion has been found. Three of the
objects in this study appear to be PPNe, IRAS 07253-2001, 08005-2356, and
17542-0603, with long periods of 5.2, 6.9, and 8.2 yrs, respectively. The
binary nature of IRAS 08005-2356 has recently been confirmed by a radial
velocity study. Two samples, one of PPNe and the other of post-AGB star
candidates, are investigated for further evidence on how common is a
long-period light curve variation. Both samples suggest such light variations
are not common. The fourth object, IRAS 20056+1834 (QY Sge), is an obscured RV
Tau variable of the RVb subclass, with a long period of 3.9 yrs and pulsation
periods of 102.9 and 51.5 days. The period of this object is seen to vary by
2%. Evidence is presented for a recent mass ejection in IRAS 17542-0603.Comment: 22 pages, 6 figures, 1 machine-readable tabl
A Study of Hα Line Profile Variations in β Lyr
We examine over 160 archival Hα spectra from the Ritter Observatory for the interacting binary β Lyr obtained between 1996 and 2000. The emission is characteristically double-peaked, but asymmetric, and with an absorption feature that is persistently blueshifted. Using a set of simplifying assumptions, phase varying emission line profiles are calculated for Hα formed entirely in a Keplerian disk, and separately for the line formed entirely from an off-center bipolar flow. However, a dynamic spectrum of the data indicates that the blueshifted feature is not always present, and the data are even suggestive of a drift of the feature in velocity shift. We explore whether a circumbinary envelope, hot spot on the accretion disk, or accretion stream could explain the observations. While none are satisfactory, an accretion stream explanation is somewhat promising
The Remote Observatories of the Southeastern Association for Research in Astronomy (SARA)
We describe the remote facilities operated by the Southeastern Association for Research in Astronomy (SARA) , a consortium of colleges and universities in the US partnered with Lowell Observatory, the Chilean National Telescope Allocation Committee, and the Instituto de AstrofÃsica de Canarias. SARA observatories comprise a 0.96 m telescope at Kitt Peak, Arizona; one of 0.6 m aperture on Cerro Tololo, Chile; and the 1 m Jacobus Kapteyn Telescope at the Roque de los Muchachos, La Palma, Spain. All are operated using standard VNC or Radmin protocols communicating with on-site PCs. Remote operation offers considerable flexibility in scheduling, allowing long-term observational cadences difficult to achieve with classical observing at remote facilities, as well as obvious travel savings. Multiple observers at different locations can share a telescope for training, educational use, or collaborative research programs. Each telescope has a CCD system for optical imaging, using thermoelectric cooling to avoid the need for frequent local service, and a second CCD for offset guiding. The Arizona and Chile telescopes also have fiber-fed echelle spectrographs. Switching between imaging and spectroscopy is very rapid, so a night can easily accommodate mixed observing modes. We present some sample observational programs. For the benefit of other groups organizing similar consortia, we describe the operating structure and principles of SARA, as well as some lessons learned from almost 20 years of remote operations
A Multi-Year Photopolarimetric Study of the Semi-Regular Variable V CVn and Identification of Analogue Sources
The semi-regular variable star V Canum Venaticorum (V CVn) is well-known for
its unusual linear polarization position angle (PA). Decades of observing V CVn
reveal a nearly constant PA spanning hundreds of pulsation cycles. This
phenomenon has persisted through variability that has ranged by 2 magnitudes in
optical brightness and through variability in the polarization amplitude over
0.3% and 6.9%. Additionally, the polarization fraction of V CVn varies
inversely with brightness.
This paper presents polarization measurements obtained over three pulsation
cycles. We find that the polarization maximum does not always occur precisely
at the same time as the brightness minimum. Instead, we observe a small lead or
lag in relation to the brightness minimum, spanning a period of a few days up
to three weeks. Furthermore, the PA sometimes exhibits a non-negligible
rotation, especially at lower polarization levels.
To elucidate the unusual optical behavior of V CVn, we present a list of
literature sources that also exhibit polarization variability with a roughly
fixed PA. We find this correlation occurs in stars with high tangential space
velocities, i.e., "runaway" stars, suggesting that the long-term constant PA is
related to how the circumstellar gas is shaped by the star's high-speed motion
through the interstellar medium.Comment: 9 pages + appendices, 7 figures, accepted for publication in A&
Peering into the tilted heart of Cyg X-1 with high-precision optical polarimetry
We present the high-precision optical polarimetric observations of black hole
X-ray binary Cyg X-1, spanning several cycles of its 5.6 day orbital period.
Week-long observations on two telescopes located in opposite hemispheres
allowed us to track the evolution of the polarization within one orbital cycle
with the highest temporal resolution to date. Using the field stars, we
determine the interstellar polarization in the source direction and
subsequently its intrinsic polarization. The optical polarization angle is
aligned with that in the X-rays as recently obtained with the Imaging X-ray
Polarimetry Explorer. Furthermore, it is consistent, within the uncertainties,
with the position angle of the radio ejections. We show that the intrinsic PD
is variable with the orbital period with the amplitude of 0.2% and
discuss various sites of its production. Assuming the polarization arises from
a single Thomson scattering of the primary star radiation by the matter that
follows the black hole in its orbital motion, we constrain the inclination of
the binary orbit and its eccentricity . The asymmetric
shape of the orbital profiles of Stokes parameters implies also the asymmetry
of the scattering matter distribution about the orbital plane, which may arise
from the tilted accretion disk. We compare our data to the polarimetric
observations made over 1975-1987 and find good, within , agreement
between the intrinsic polarization angles. On the other hand, the PD decreased
by 0.4% over half a century, suggesting the presence of secular changes in the
geometry of accreting matter.Comment: 12 pages, 18 figure
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