31 research outputs found
Eclipse Timing Modeling of Three Post-Common Envelope Binaries: Hybrid Solutions
We report 88 new observations of three post common envelope binaries at
primary eclipse spanning between December 2018 to February 2021. We combine
recent primary eclipse timing observations with previously published values to
search for substellar circumbinary components consistent with timing variations
from a linear ephemeris. We used a least-squares minimization fitting algorithm
weighted by a Hill orbit stability function, followed by Bayesian inference, to
determine best-fit orbital parameters and associated uncertainties. For
HS2231+2441, we find that the timing data are consistent with a constant period
and that there is no evidence to suggest orbiting components. For HS0705+6700,
we find both two and three-component solutions that are stable for at least 10
Myr but have very different parameters. For HW Vir, we find multi-component
solutions that fit the timing data but they are unstable on short timescale,
and therefore highly improbable. Conversely, both the least-squares and
Bayesian solutions provide a poor fit. In both systems, the best-fit stable
solutions significantly deviate from the ensemble timing data.
For both HS0705+6700 and HW Vir, substellar component solutions that fit all
observed eclipse timing data are dynamically unstable, whereas best-fit
solutions with stable orbits provide poor O-C fits. We speculate that the
observed timing variations for these systems, and very possibly other sdB
binaries, may result from a combination of substellar component perturbations
and an Applegate-Lanza mechanism.Comment: 17 pages, 12 figure
A search for thermal gyro-synchrotron emission from hot stellar coronae
We searched for thermal gyro-synchrotron radio emission from a sample of five
radio-loud stars whose X-ray coronae contain a hot ( K) thermal
component. We used the JVLA to measure Stokes I and V/I spectral energy
distributions (SEDs) over the frequency range 15--45 GHz, determining the
best-fitting model parameters using power-law and thermal gyro-synchrotron
emission models. The SEDs of the three chromospherically active binaries
(Algol, UX Arietis, HR 1099) were well-fit by a power-law gyro-synchrotron
model, with no evidence for a thermal component. However, the SEDs of the two
weak-lined T Tauri stars (V410 Tau, HD 283572) had a circularly polarized
enhancement above 30 GHz that was inconsistent with a pure power-law
distribution. These spectra were well-fit by summing the emission from an
extended coronal volume of power-law gyro-synchrotron emission and a smaller
region with thermal plasma and a much stronger magnetic field emitting thermal
gyro-synchrotron radiation. We used Bayesian inference to estimate the physical
plasma parameters of the emission regions (characteristic size, electron
density, temperature, power-law index, and magnetic field strength and
direction) using independently measured radio sizes, X-ray luminosities, and
magnetic field strengths as priors, where available. The derived parameters
were well-constrained but somewhat degenerate. The power-law and thermal
volumes in the pre-main-sequence stars are probably not co-spatial, and we
speculate they may arise from two distinct regions: a tangled-field
magnetosphere where reconnection occurs and a recently discovered axisymmetric
toroidal magnetic field, respectively.Comment: Submitted to MNRAS; 18 pages, 10 figure
Meter- to Millimeter Emission from Cool Stellar Systems : Latest Results, Synergies Across the Spectrum, and Outlook for the Next Decade
Splinter session summary, to appear in the proceedings of the 20th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (ed. S. J. Wolk)Radio observations of cool stellar systems provide unique information on their magnetic fields, high-energy processes, and chemistry. Buoyed by powerful new instruments (e.g. ALMA, JVLA, LOFAR), advances in related fields (e.g., the Gaia astrometric revolution), and above all a renewed interest in the relevant stellar astrophysics, stellar radio astronomy is experiencing a renaissance. In this splinter session, participants took stock of the present state of stellar radio astronomy to chart a course for the field's future
Climate Change Impacts on Iowa, 2010
Climate change is already affecting the way Iowans live and work. Without action to mitigate these effects, our future responses will become more complex and costly . The following policy recommendations are offered as initial steps to help safeguard our state’s economy, environment, and residents
Tele-branding in TVIII: the network as brand and the programme as brand
In the era of TVIII, characterized by deregulation, multimedia conglomeration, expansion and increased competition, branding has emerged as a central industrial practice. Focusing on the case of HBO, a particularly successful brand in TVIII, this article argues that branding can be understood not simply as a feature of television networks, but also as a characteristic of television programmes. It begins by examining how the network as brand is constructed and conveyed to the consumer through the use of logos, slogans and programmes. The role of programmes in the construction of brand identity is then complicated by examining the sale of programmes abroad, where programmes can be seen to contribute to the brand identity of more than one network. The article then goes on to examine programme merchandising, an increasingly central strategy in TVIII. Through an analysis of different merchandising strategies the article argues that programmes have come to act as brands in their own right, and demonstrates that the academic study of branding not only reveals the development of new industrial practices, but also offers a way of understanding the television programme and its consumption by viewers in a period when the texts of television are increasingly extended across a range of media platforms
Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event
We report the lens mass and distance measurements of the nearby microlensing
event TCP J05074264+2447555. We measure the microlens parallax vector
using Spitzer and ground-based light curves with constraints on
the direction of lens-source relative proper motion derived from Very Large
Telescope Interferometer (VLTI) GRAVITY observations. Combining this
determination with the angular Einstein radius
measured by VLTI GRAVITY observations, we find that the lens is a star with
mass at a distance . We find that the blended light basically all comes from the lens.
The lens-source proper motion is , so with currently available adaptive-optics (AO) instruments,
the lens and source can be resolved in 2021. This is the first microlensing
event whose lens mass is unambiguously measured by interferometry + satellite
parallax observations, which opens a new window for mass measurements of
isolated objects such as stellar-mass black holes.Comment: 3 Figures and 6 Tables Submitted to AAS Journa