495 research outputs found
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A Status Report On A Planet Search Around White Dwarf Stars
We have continued monitoring a pilot sample of 15 isolated, pulsating DA white dwarfs for center-of-mass motion caused by a planetary companion. Roughly 7 years into our survey, we have preliminary evidence for periodic variations in pulse arrival times for at least two white dwarfs in our sample. The variations in these systems are unlikely to be caused by secular evolution and are possibly the result of motion of the white dwarf around a center of mass. We have yet to claim confirmation of a planet. GD66 is a previously published candidate system, with a modulation in pulse arrival times that could be caused by a 2.0 M-J sin i planetary companion with an 8.3 year orbital period. Another candidate system, WD1354+0108, has a phase modulation consistent with a 0.7 M-J sin i planet at 2.3 AU (a 4.5 year orbit). We see similar behavior in two independent frequencies within this star, and while a sinusoid is currently a marginally better fit to the data than a straight line (as we might expect from cooling alone in a DAV), we are hesitant to over-interpret our results. Finally, we have a third system, WD0018+0031, that shows a change in pulse arrival times inconsistent with cooling alone; a 2.7 M-J planet at an orbit of about 5 AU could cause the observed trend. Observations of these candidate systems are ongoing in order to constrain any planetary companions that may be present.Astronom
Discovery of a Nova-Like Cataclysmic Variable in the Kepler Mission Field
We announce the identification of a new cataclysmic variable star in the
field of the Kepler Mission, KIC J192410.81+445934.9. This system was
identified during a search for compact pulsators in the Kepler field.
High-speed photometry reveals coherent large-amplitude variability with a
period of 2.94 h. Rapid, large-amplitude quasi-periodic variations are also
detected on time scales of ~1200 s and ~650 s. Time-resolved spectroscopy
covering one half photometric period shows shallow, broad Balmer and He I
absorption lines with bright emission cores as well as strong He II and Bowen
blend emission. Radial velocity variations are also observed in the Balmer and
He I emission lines that are consistent with the photometric period. We
therefore conclude that KIC J192410.81+445934.9 is a nova-like variable of the
UX UMa class in or near the period gap, and it may belong to the rapidly
growing subclass of SW Sex systems. Based on 2MASS photometry and companion
star models, we place a lower limit on the distance to the system of ~500 pc.
Due to limitations of our discovery data, additional observations including
spectroscopy and polarimetry are needed to confirm the nature of this object.
Such data will help to further understanding of the behavior of nova-like
variables in the critical period range of 3-4 h, where standard cataclysmic
variable evolutionary theory finds major problems. The presence of this system
in the Kepler mission field-of-view also presents a unique opportunity to
obtain a continuous photometric data stream of unparalleled length and
precision on a cataclysmic variable system.Comment: Accepted for publication in the Astronomical Journal. 8 pages, 7
figures, uses emulateapj
The diffusion of sustainability and Dingle Peninsula 2030
Instilling a collaborative approach can widen participation to a range of stakeholders, enabling the diffusion of sustainability and increasing local capacity to meet decarbonisation targets to mitigate against climate change. Dingle Peninsula 2030 has emerged as an international case study of a collaborative regional sustainability project, whereby a wide range of initiatives, beyond the initial remit of the project, have emerged in the area. This holistic scale of action is required for effective climate action. Using the Sustainable Development Goals (SDGs) as a framing, the interrelated nature of climate action has been shown through this study. In setting out to undergo energy projects a wide range of new initiatives emerged as community members became engaged in the process. Initiatives have emerged related to energy, transport, agriculture, education, tourism and employment, in what we have coined the ‘diffusion of sustainability’
The Mystery Deepens: Spitzer Observations of Cool White Dwarfs
We present 4.5m and 8m photometric observations of 18 cool white
dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate
that four white dwarfs with T_eff< 6000 K show slightly depressed mid-infrared
fluxes relative to white dwarf models. In addition, another white dwarf with a
peculiar optical and near-infrared spectral energy distribution (LHS 1126) is
found to display significant flux deficits in Spitzer observations. These
mid-infrared flux deficits are not predicted by the current white dwarf models
including collision induced absorption due to molecular hydrogen. We postulate
that either the collision induced absorption calculations are incomplete or
there are other unrecognized physical processes occuring in cool white dwarf
atmospheres. The spectral energy distribution of LHS 1126 surprisingly fits a
Rayleigh-Jeans spectrum in the infrared, mimicking a hot white dwarf with
effective temperature well in excess of 10 K. This implies that the source
of this flux deficit is probably not molecular absorption but some other
process.Comment: 17 pages, 4 figures, ApJ in press, 10 May 200
Understanding how institutions may support the development of transdisciplinary approaches to sustainability research
This article analyses the approaches of academics seeking to engage with private, public and community-based stakeholders through transdisciplinary research about pressing sustainability challenges and, in particular, climate change; it outlines aspects of the institutional factors which influence transdisciplinary research. A qualitative approach was employed in conducting 10 semi-structured interviews to analyse the challenges and motivations of academic researchers when working with a range of other stakeholders through transdisciplinary practice. Two key contributions are made through this work. First, this article adds to the existing literature on motivations and challenges for undertaking research with private, public and community stakeholders in a cross-disciplinary manner. Second, the current institutional circumstances influencing such research practices are outlined, alongside potential ways forward. The research presented here has been undertaken in light of the experiences of the two lead co-authors as early career researchers coming from the disciplines of sociology and energy engineering, engaging in transdisciplinary research within a local community context in relation to a regional energy transition project
Precision asteroseismology of the pulsating white dwarf GD 1212 using a two-wheel-controlled Kepler spacecraft
We present a preliminary analysis of the cool pulsating white dwarf GD 1212,
enabled by more than 11.5 days of space-based photometry obtained during an
engineering test of the two-reaction-wheel-controlled Kepler spacecraft. We
detect at least 19 independent pulsation modes, ranging from 828.2-1220.8 s,
and at least 17 nonlinear combination frequencies of those independent
pulsations. Our longest uninterrupted light curve, 9.0 days in length,
evidences coherent difference frequencies at periods inaccessible from the
ground, up to 14.5 hr, the longest-period signals ever detected in a pulsating
white dwarf. These results mark some of the first science to come from a
two-wheel-controlled Kepler spacecraft, proving the capability for
unprecedented discoveries afforded by extending Kepler observations to the
ecliptic.Comment: 8 pages, 4 figures, accepted for publication in The Astrophysical
Journa
A dense disk of dust around the born-again Sakurai's object
In 1996, Sakurai's object (V4334 Sgr) suddenly brightened in the centre of a
faint Planetary Nebula (PN). This very rare event was interpreted as the
reignition of a hot white dwarf that caused a rapid evolution back to the cool
giant phase. From 1998 on, a copious amount of dust has formed continuously,
screening out the star which has remained embedded in this expanding high
optical depth envelope. The new observations, reported here, are used to study
the morphology of the circumstellar dust in order to investigate the hypothesis
that Sakurai's Object is surrounded by a thick spherical envelope of dust. We
have obtained unprecedented, high-angular resolution spectro-interferometric
observations, taken with the mid-IR interferometer MIDI/VLTI, which resolve the
dust envelope of Sakurai's object. We report the discovery of a unexpectedly
compact (30 x 40 milliarcsec, 105 x 140 AU assuming a distance of 3.5 kpc),
highly inclined, dust disk. We used Monte Carlo radiative-transfer simulations
of a stratified disk to constrain its geometric and physical parameters,
although such a model is only a rough approximation of the rapidly evolving
dust structure. Even though the fits are not fully satisfactory, some useful
and robust constraints can be inferred. The disk inclination is estimated to be
75+/-3 degree with a large scale height of 47+/-7 AU. The dust mass of the disk
is estimated to be 6 10^{-5} solar mass. The major axis of the disk (132+/-3
degree) is aligned with an asymmetry seen in the old PN that was
re-investigated as part of this study. This implies that the mechanism
responsible for shaping the dust envelope surrounding Sakurai's object was
already at work when the old PN formed.Comment: A&A Letter, accepte
Seismic evidence for a rapidly rotating core in a lower-giant-branch star observed with Kepler
Rotation is expected to have an important influence on the structure and the
evolution of stars. However, the mechanisms of angular momentum transport in
stars remain theoretically uncertain and very complex to take into account in
stellar models. To achieve a better understanding of these processes, we
desperately need observational constraints on the internal rotation of stars,
which until very recently were restricted to the Sun. In this paper, we report
the detection of mixed modes - i.e. modes that behave both as g modes in the
core and as p modes in the envelope - in the spectrum of the early red giant
KIC7341231, which was observed during one year with the Kepler spacecraft. By
performing an analysis of the oscillation spectrum of the star, we show that
its non-radial modes are clearly split by stellar rotation and we are able to
determine precisely the rotational splittings of 18 modes. We then find a
stellar model that reproduces very well the observed atmospheric and seismic
properties of the star. We use this model to perform inversions of the internal
rotation profile of the star, which enables us to show that the core of the
star is rotating at least five times faster than the envelope. This will shed
new light on the processes of transport of angular momentum in stars. In
particular, this result can be used to place constraints on the angular
momentum coupling between the core and the envelope of early red giants, which
could help us discriminate between the theories that have been proposed over
the last decades.Comment: Accepted in ApJ, 39 pages, 16 figure
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