84 research outputs found
Finding binaries from phase modulation of pulsating stars with \textit{Kepler}: VI. Orbits for 10 new binaries with mischaracterised primaries
Measuring phase modulation in pulsating stars has proved to be a highly
successful way of finding binary systems. The class of pulsating main-sequence
A and F variables known as delta Scuti stars are particularly good targets for
this, and the \textit{Kepler} sample of these has been almost fully exploited.
However, some \textit{Kepler} Scuti stars have incorrect temperatures
in stellar properties catalogues, and were missed in previous analyses. We used
an automated pulsation classification algorithm to find 93 new Scuti
pulsators among tens of thousands of F-type stars, which we then searched for
phase modulation attributable to binarity. We discovered 10 new binary systems
and calculated their orbital parameters, which we compared with those of
binaries previously discovered in the same way. The results suggest that some
of the new companions may be white dwarfs.Comment: 8 pages, 6 figures that make liberal use of colou
The effect of tides on near-core rotation: analysis of 35 Kepler Doradus stars in eclipsing and spectroscopic binaries
We systematically searched for gravity- and Rossby-mode period spacing
patterns in Kepler eclipsing binaries with Doradus pulsators. These
stars provide an excellent opportunity to test the theory of tidal
synchronisation and angular momentum transport in F- and A-type stars. We
discovered 35 systems that show clear patterns, including the spectroscopic
binary KIC 10080943. Combined with 45 non-eclipsing binaries with Dor
components that have been found using pulsation timing, we measured their
near-core rotation rates and asymptotic period spacings. We find that many
stars are tidally locked if the orbital periods are shorter than 10 days, in
which the near-core rotation periods given by the traditional approximation of
rotation (TAR) are consistent with the orbital period. Compared to the single
stars, Dor stars in binaries tend to have slower near-core rotation
rates, likely a consequence of tidal spin-down. We also find three stars that
have extremely slow near-core rotation rates. To explain these, we hypothesise
that unstable tidally excited oscillations can transfer angular momentum from
the star to the orbit, and slow the star below synchronism, a process we refer
to as `inverse tides'.Comment: 13 pages, 10 figures, accepted by MNRA
TESS observations of the Pleiades cluster: a nursery for delta Scuti stars
We studied 89 A- and F-type members of the Pleiades open cluster, including
five escaped members. We measured projected rotational velocities (v sin i) for
49 stars and confirmed that stellar rotation causes a broadening of the main
sequence in the color-magnitude diagram. Using time-series photometry from
NASA's TESS Mission (plus one star observed by Kepler/K2), we detected delta
Scuti pulsations in 36 stars. The fraction of Pleiades stars in the middle of
the instability strip that pulsate is unusually high (over 80%), and their
range of effective temperatures agrees well with theoretical models. On the
other hand, the characteristics of the pulsation spectra are varied and do not
correlate with stellar temperature, calling into question the existence of a
useful nu_max relation for delta Scutis, at least for young stars. By including
delta Scuti stars observed in the Kepler field, we show that the instability
strip is shifted to the red with increasing distance by interstellar reddening.
Overall, this work demonstrates the power of combining observations with Gaia
and TESS for studying pulsating stars in open clusters.Comment: submitted to AAS journal
Forward modeling the orbits of companions to pulsating stars from their light travel time variations
Mutual gravitation between a pulsating star and an orbital companion leads to
a time-dependent variation in path length for starlight traveling to Earth.
These variations can be used for coherently pulsating stars, such as the
{\delta} Scuti variables, to constrain the masses and orbits of their
companions. Observing these variations for {\delta} Scuti stars has previously
relied on subdividing the light curve and measuring the average pulsation phase
in equally sized subdivisions, which leads to under-sampling near periapsis. We
introduce a new approach that simultaneously forward-models each sample in the
light curve and show that this method improves upon current sensitivity limits
- especially in the case of highly eccentric and short-period binaries. We find
that this approach is sensitive enough to observe Jupiter mass planets around
{\delta} Scuti stars under ideal conditions, and use gravity-mode pulsations in
the subdwarf B star KIC 7668647 to detect its companion without radial velocity
data. We further provide robust detection limits as a function of the SNR of
the pulsation mode and determine that the minimum detectable light travel time
amplitude for a typical Kepler {\delta} Scuti is around 2 s. This new method
significantly enhances the application of light travel time variations to
detecting short period binaries with pulsating components, and pulsating A-type
exoplanet host stars, especially as a tool for eliminating false positives.Comment: 14 pages, accepted for publication in A
A binary with a ~Scuti star and an oscillating red giant: orbit and asteroseismology of KIC9773821
We study the Scuti -- red giant binary KIC9773821, the first
double-pulsator binary of its kind. It was observed by \textit{Kepler} during
its four-year mission. Our aims are to ascertain whether the system is bound,
rather than a chance alignment, and to identify the evolutionary state of the
red giant via asteroseismology. An extension of these aims is to determine a
dynamical mass and an age prior for a Sct star, which may permit mode
identification via further asteroseismic modelling. We determine spectroscopic
parameters and radial velocities (RVs) for the red giant component using
HERMES@Mercator spectroscopy. Light arrival-time delays from the Sct
pulsations are used with the red-giant RVs to determine that the system is
bound and to infer its orbital parameters, including the binary mass ratio. We
use asteroseismology to model the individual frequencies of the red giant to
give a mass of M and an age of
Gyr. We find that it is a helium-burning secondary clump
star, confirm that it follows the standard scaling relation,
and confirm its observed period spacings match their theoretical counterparts
in the modelling code MESA. Our results also constrain the mass and age of the
Sct star. We leverage these constraints to construct Sct
models in a reduced parameter space and identify four of its five pulsation
modes.Comment: Accepted for publication in MNRA
Tackling loneliness evidence review
n 2018, some of us (Barreto, Matthews, Qualter, Victor) contributed to an ESRC Think Piece on Loneliness and recommended that there needed to be increased investment from UKRI for research examining loneliness. We highlighted key gaps in the evidence and suggested those areas for priority funding. Since then, there has been increased investment for research on loneliness from UKRI and some of those evidence gaps have or are being filled. However, some have not been addressed and there remain important gaps to fill. In the 2018 ESRC Think Piece, the following recommendations were made: (1) the monitoring of loneliness and its drivers and consequences across the population and among specific subgroups, (2) the capturing of changes in prevalence or groups most affected by transient loneliness, with a view to understanding when and how it becomes chronic, (3) comparisons of local estimates of loneliness with national estimates, and (4) greater measurement consistency for population level surveys. In the first section of our review, we discuss the extent to which those recommendations have been endorsed, with new funding and knowledge made available
The far side of the Galactic bar/bulge revealed through semi-regular variables
The Galactic bulge and bar are critical to our understanding of the Milky
Way. However, due to the lack of reliable stellar distances, the structure and
kinematics of the bulge/bar beyond the Galactic center have remained largely
unexplored. Here, we present a method to measure distances of luminous red
giants using a period-amplitude-luminosity relation anchored to the Large
Magellanic Cloud, with random uncertainties of 10-15% and systematic errors
below 1-2%. We apply this method to data from the Optical Gravitational Lensing
Experiment (OGLE) to measure distances to stars in the Galactic bulge
and beyond out to 20 kpc. Using this sample we measure a distance to the
Galactic center of = pc,
consistent with astrometric monitoring of stars orbiting Sgr A*. We cross-match
our distance catalog with Gaia DR3 and use the subset of overlapping
stars to provide the first constraints on the Milky Way's velocity field
() beyond the Galactic center. We show that the
quadrupole from the bar's near side is reflected with respect to the Galactic
center, indicating that the bar is both bi-symmetric and aligned with the inner
disk, and therefore dynamically settled along its full extent. We also find
that the vertical height map has no major structure in the region of the
Galactic bulge, which is inconsistent with a current episode of bar buckling.
Finally, we demonstrate with N-body simulations that distance uncertainty plays
a major factor in the alignment of the major and kinematic axes of the bar and
distribution of velocities, necessitating caution when interpreting results for
distant stars.Comment: Accepted to the Astronomical Journa
exoplanet : gradient-based probabilistic inference for exoplanet data & other astronomical time series
Funding: This research was partially conducted during the Exostar19 program at the Kavli Institute for Theoretical Physics at UC Santa Barbara, which was supported in part by the National Science Foundation under Grant No. NSF PHY-1748958."exoplanet" is a toolkit for probabilistic modeling of astronomical time series data, with a focus on observations of exoplanets, using PyMC3 (Salvatier et al., 2016). PyMC3 is a flexible and high-performance model-building language and inference engine that scales well to problems with a large number of parameters. "exoplanet" extends PyMC3's modeling language to support many of the custom functions and probability distributions required when fitting exoplanet datasets or other astronomical time series. While it has been used for other applications, such as the study of stellar variability, the primary purpose of "exoplanet" is the characterization of exoplanets or multiple star systems using time-series photometry, astrometry, and/or radial velocity. In particular, the typical use case would be to use one or more of these datasets to place constraints on the physical and orbital parameters of the system, such as planet mass or orbital period, while simultaneously taking into account the effects of stellar variability.Publisher PDFPeer reviewe
The pesticidal Cry6Aa toxin from Bacillus thuringiensis is structurally similar to HlyE-family alpha pore-forming toxins
Background The Cry6 family of proteins from Bacillus thuringiensis represents a group of powerful toxins with great potential for use in the control of coleopteran insects and of nematode parasites of importance to agriculture. These proteins are unrelated to other insecticidal toxins at the level of their primary sequences and the structure and function of these proteins has been poorly studied to date. This has inhibited our understanding of these toxins and their mode of action, along with our ability to manipulate the proteins to alter their activity to our advantage. To increase our understanding of their mode of action and to facilitate further development of these proteins we have determined the structure of Cry6Aa in protoxin and trypsin-activated forms and demonstrated a pore-forming mechanism of action. Results The two forms of the toxin were resolved to 2.7 Å and 2.0 Å respectively and showed very similar structures. Cry6Aa shows structural homology to a known class of pore-forming toxins including hemolysin E from Escherichia coli and two Bacillus cereus proteins: the hemolytic toxin HblB and the NheA component of the non-hemolytic toxin (pfam05791). Cry6Aa also shows atypical features compared to other members of this family, including internal repeat sequences and small loop regions within major alpha helices. Trypsin processing was found to result in the loss of some internal sequences while the C-terminal region remains disulfide-linked to the main core of the toxin. Based on the structural similarity of Cry6Aa to other toxins, the mechanism of action of the toxin was probed and its ability to form pores in vivo in Caenorhabditis elegans was demonstrated. A non-toxic mutant was also produced, consistent with the proposed pore-forming mode of action. Conclusions Cry6 proteins are members of the alpha helical pore-forming toxins – a structural class not previously recognized among the Cry toxins of B. thuringiensis and representing a new paradigm for nematocidal and insecticidal proteins. Elucidation of both the structure and the pore-forming mechanism of action of Cry6Aa now opens the way to more detailed analysis of toxin specificity and the development of new toxin variants with novel activities
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