3,244 research outputs found
Orbital Solutions and Absolute Elements of the Eclipsing Binary MY Cygni
Differential UBV photoelectric photometry for the eclipsing binary MY Cyg is presented. The Wilson-Devinney program is used to simultaneously solve the three light curves together with previously published radial velocities. A comparison is made with the previous solution found with the Russell-Merrill method. We examine the long-term apsidal motion of this well-detached, slightly eccentric system. We determine absolute dimensions, discuss metallicity/Am-star issues, and estimate the evolutionary status of the stars
Classifying the unknown: discovering novel gravitational-wave detector glitches using similarity learning
The observation of gravitational waves from compact binary coalescences by
LIGO and Virgo has begun a new era in astronomy. A critical challenge in making
detections is determining whether loud transient features in the data are
caused by gravitational waves or by instrumental or environmental sources. The
citizen-science project \emph{Gravity Spy} has been demonstrated as an
efficient infrastructure for classifying known types of noise transients
(glitches) through a combination of data analysis performed by both citizen
volunteers and machine learning. We present the next iteration of this project,
using similarity indices to empower citizen scientists to create large data
sets of unknown transients, which can then be used to facilitate supervised
machine-learning characterization. This new evolution aims to alleviate a
persistent challenge that plagues both citizen-science and instrumental
detector work: the ability to build large samples of relatively rare events.
Using two families of transient noise that appeared unexpectedly during LIGO's
second observing run (O2), we demonstrate the impact that the similarity
indices could have had on finding these new glitch types in the Gravity Spy
program
KIC 4247791: A SB4 system with two eclipsing binaries (2EBs)
KIC 4247791 is an eclipsing binary observed by the Kepler satellite mission.
We wish to determine the nature of its components and in particular the origin
of a shallow dip in its Kepler light curve that previous investigations have
been unable to explain in a unique way. We analyze newly obtained
high-resolution spectra of the star using synthetic spectra based on atmosphere
models, derive the radial velocities of the stellar components from
cross-correlation with a synthetic template, and calculate the orbital
solution. We use the JKTEBOP program to model the Kepler light curve of KIC
4247791. We find KIC 4247791 to be a SB4 star. The radial velocity variations
of its four components can be explained by two separate eclipsing binaries. In
contradiction to previous photometric findings, we show that the observed
composite spectrum as well as the derived masses of all four of its components
correspond to spectral type F. The observed small dip in the light curve is not
caused by a transit-like phenomenon but by the eclipses of the second binary
system. We find evidence that KIC 4247791 might belong to the very rare
hierarchical SB4 systems with two eclipsing binaries.Comment: 6 pages, 8 figures, 2 table
Delayed X-ray brightening accompanied by variable ionized absorption following a tidal disruption event
Supermassive black holes can experience super-Eddington peak mass fallback
rates following the tidal disruption of a star. The theoretical expectation is
that part of the infalling material is expelled by means of an accretion disk
wind, whose observational signature includes blueshifted absorption lines of
highly ionized species in X-ray spectra. To date, however, only one such
ultra-fast outflow (UFO) has been reported in the tidal disruption event (TDE)
ASASSN-14li. Here we report on the discovery of transient absorption-like
signatures in X-ray spectra of the TDE AT2020ksf/Gaia20cjk (at a redshift of
=0.092), following an X-ray brightening days after UV/optical
peak. We find that while no statistically significant absorption features are
present initially, they appear on a timescale of several days, and remain
detected up to 770 days after peak. Simple thermal continuum models, combined
with a power-law or neutral absorber, do not describe these features well.
Adding a partial covering, low velocity ionized absorber improves the fit at
early times, but fails at late times. A high velocity (v 42000 km
s, or -0.15c), ionized absorber (ultra-fast outflow) provides a good fit
to all data. The few day timescale of variability is consistent with
expectations for a clumpy wind. We discuss several scenarios that could explain
the X-ray delay, as well as the potential for larger scale wind feedback. The
serendipitous nature of the discovery could suggest a high incidence of UFOs in
TDEs, alleviating some of the tension with theoretical expectations.Comment: 14 pages + appendices, accepted for publication in Ap
Lack of Transit Timing Variations of OGLE-TR-111b: A re-analysis with six new epochs
We present six new transits of the exoplanet OGLE-TR-111b observed with the
Magellan Telescopes in Chile between April 2008 and March 2009. We combine
these new transits with five previously published transit epochs for this
planet between 2005 and 2006 to extend the analysis of transit timing
variations reported for this system. We derive a new planetary radius value of
1.019 +/- 0.026 R_J, which is intermediate to the previously reported radii of
1.067 +/- 0.054 R_J (Winn et al. 2007) and 0.922 +/- 0.057 R_J (Diaz et al.
2008). We also examine the transit timing variation and duration change claims
of Diaz et al. (2008). Our analysis of all eleven transit epochs does not
reveal any points with deviations larger than 2 sigma, and most points are well
within 1 sigma. Although the transit duration nominally decreases over the four
year span of the data, systematic errors in the photometry can account for this
result. Therefore, there is no compelling evidence for either a timing or a
duration variation in this system. Numerical integrations place an upper limit
of about 1 M_E on the mass of a potential second planet in a 2:1 mean-motion
resonance with OGLE-TR-111b.Comment: 28 pages, 7 tables, 6 figures. Accepted by Ap
Identification of long-duration noise transients in LIGO and Virgo
The LIGO and Virgo detectors are sensitive to a variety of noise sources,
such as instrumental artifacts and environmental disturbances. The Stochastic
Transient Analysis Multi-detector Pipeline (STAMP) has been developed to search
for long-duration (t1s) gravitational-wave (GW) signals. This pipeline
can also be used to identify environmental noise transients. Here we present an
algorithm to determine when long-duration noise sources couple into the
interferometers, as well as identify what these noise sources are. We analyze
the cross-power between a GW strain channel and an environmental sensor, using
pattern recognition tools to identify statistically significant structure in
cross-power time-frequency maps. We identify interferometer noise from
airplanes, helicopters, thunderstorms and other sources. Examples from LIGO's
sixth science run, S6, and Virgo's third scientific run, VSR3, are presented.Comment: 10 pages, 7 figures, Gravitational-wave Physics & Astronomy Worksho
Seismic topographic scattering in the context of GW detector site selection
In this paper, we present a calculation of seismic scattering from irregular
surface topography in the Born approximation. Based on US-wide topographic
data, we investigate topographic scattering at specific sites to demonstrate
its impact on Newtonian-noise estimation and subtraction for future
gravitational-wave detectors. We find that topographic scattering at a
comparatively flat site in Oregon would not pose any problems, whereas
scattering at a second site in Montana leads to significant broadening of wave
amplitudes in wavenumber space that would make Newtonian-noise subtraction very
challenging. Therefore, it is shown that topographic scattering should be
included as criterion in the site-selection process of future low-frequency
gravitational-wave detectors.Comment: 16 pages, 7 figure
Supplement: Going the Distance: Mapping Host Galaxies of LIGO and Virgo Sources in Three Dimensions Using Local Cosmography and Targeted Follow-up
This is a supplement to the Letter of Singer et al.
(https://arxiv.org/abs/1603.07333), in which we demonstrated a rapid algorithm
for obtaining joint 3D estimates of sky location and luminosity distance from
observations of binary neutron star mergers with Advanced LIGO and Virgo. We
argued that combining the reconstructed volumes with positions and redshifts of
possible host galaxies can provide large-aperture but small field of view
instruments with a manageable list of targets to search for optical or infrared
emission. In this Supplement, we document the new HEALPix-based file format for
3D localizations of gravitational-wave transients. We include Python sample
code to show the reader how to perform simple manipulations of the 3D sky maps
and extract ranked lists of likely host galaxies. Finally, we include
mathematical details of the rapid volume reconstruction algorithm.Comment: For associated data release, see
http://asd.gsfc.nasa.gov/Leo.Singer/going-the-distanc
A randomised trial of robotic and open prostatectomy in men with localised prostate cancer
Background: Prostate cancer is the most common male cancer in the Western world however there is ongoing debate about the optimal treatment strategy for localised disease. While surgery remains the most commonly received treatment for localised disease in Australia more recently a robotic approach has emerged as an alternative to open and laparoscopic surgery. However, high level data is not yet available to support this as a superior approach or to guide treatment decision making between the alternatives. This paper presents the design of a randomised trial of Robotic and Open Prostatectomy for men newly diagnosed with localised prostate cancer that seeks to answer this question.Methods/design: 200 men per treatment arm (400 men in total) are being recruited after diagnosis and before treatment through a major public hospital outpatient clinic and randomised to 1) Robotic Prostatectomy or 2) Open Prostatectomy. All robotic prostatectomies are being performed by one surgeon and all open prostatectomies are being performed by one other surgeon. Outcomes are being measured pre-operatively and at 6 weeks and 3, 6, 12 and 24 months post-surgery. Oncological outcomes are being related to positive surgical margins, biochemical recurrence +/- the need for further treatment. Non-oncological outcome measures include: pain, physical and mental functioning, fatigue, summary (preference-based utility scores) and domain-specific QoL (urinary incontinence, bowel function and erectile function), cancer specific distress, psychological distress, decision-related distress and time to return to usual activities. Cost modelling of each approach, as well as full economic appraisal, is also being undertaken.Discussion: The study will provide recommendations about the relative benefits of Robotic and Open Prostatectomy to support informed patient decision making about treatment for localised prostate cancer; and to assist in treatment services planning for this patient group.Trial registration: ACTRN12611000661976
Maintaining Structural Stability of Poly(lactic acid): Effects of Multifunctional Epoxy based Reactive Oligomers
In order to reduce the effects of hydrolytic degradation and to maintain sufficient viscosity during processing of biomass based poly(l-lactic acid) (PLLA), various epoxy functional reactive oligomers have been characterized and incorporated into the degraded fragments as chain extenders. The molecular weight of PLLA increased with the increase in functionality of the reactive oligomers. No further increase in molecular weight was observed for oligomers with functionality of greater than five. Under our experimental conditions, no gelation was found even when the highest functionality reactive oligomers were used. This is attributed to the preferential reaction of the carboxylic acid versus the negligible reactivity of the hydroxyl groups, present at the two ends of the degraded PLLA chains, with the epoxy groups. The study provides a clear understanding of the degradation and chain extension reaction of poly(lactic acid) (PLA) with epoxy functional reactive oligomers. It is also shown that a higher functionality and concentration of the reactive oligomers is needed, to bring about a sufficient increase in the molecular weight and hence the hydrolytic stability in circumstances when PLA chains suffer significant degradation during processing
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