153 research outputs found
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
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
On the first δ Sct–roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars
Abstract Strong magnetic fields in chemically peculiar A-type (Ap) stars typically suppress low-overtone pressure modes (p modes) but allow high-overtone p modes to be driven. KIC 11296437 is the first star to show both. We obtained and analysed a Subaru spectrum, from which we show that KIC 11296437 has abundances similar to other magnetic Ap stars, and we estimate a mean magnetic field modulus of 2.8 ± 0.5 kG. The same spectrum rules out a double-lined spectroscopic binary, and we use other techniques to rule out binarity over a wide parameter space, so the two pulsation types originate in one δ Sct–roAp hybrid pulsator. We construct stellar models depleted in helium and demonstrate that helium settling is second to magnetic damping in suppressing low-overtone p modes in Ap stars. We compute the magnetic damping effect for selected p and g modes, and find that modes with frequencies similar to the fundamental mode are driven for polar field strengths ≲ 4 kG, while other low-overtone p modes are driven for polar field strengths up to ∼1.5 kG. We find that the high-order g modes commonly observed in γ Dor stars are heavily damped by polar fields stronger than 1–4 kG, with the damping being stronger for higher radial orders. We therefore explain the observation that no magnetic Ap stars have been observed as γ Dor stars. We use our helium-depleted models to calculate the δ Sct instability strip for metallic-lined A (Am) stars, and find that driving from a Rosseland mean opacity bump at ∼5 × 104 K caused by the discontinuous H-ionization edge in bound-free opacity explains the observation of δ Sct pulsations in Am stars
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
Six new rapidly oscillating Ap stars in the Kepler long-cadence data using super-Nyquist asteroseismology
We perform a search for rapidly oscillating Ap stars in the Kepler long-cadence data, where true oscillations above the Nyquist limit of 283.21 µHz can be reliably distinguished from aliases as a con- sequence of the barycentric time corrections applied to the Kepler data. We find evidence for rapid oscillations in six stars: KIC 6631188, KIC 7018170, KIC 10685175, KIC 11031749, KIC 11296437 and KIC 11409673, and identify each star as chemically peculiar through either pre-existing classifica- tions or spectroscopic measurements. For each star, we identify the principal pulsation mode, and are able to observe several additional pulsation modes in KIC 7018170. We find that KIC 7018170 and KIC 11409673 both oscillate above their theoretical acoustic cutoff frequency, whilst KIC 11031749 oscillates at the cutoff frequency within uncertainty. All but KIC 11031749 exhibit strong amplitude modulation consistent with the oblique pulsator model, confirming their mode geometry and periods of rotation
Recommended from our members
Autonomous Ocean Measurements in the California Current Ecosystem
Event-scale phenomena, of limited temporal duration or restricted spatial extent, often play a disproportionately large role in ecological processes occurring in the ocean water column. Nutrient and gas fluxes, upwelling and downwelling, transport of biogeochemically important elements, predator-prey interactions, and other processes may be markedly influenced by such events, which are inadequately resolved from infrequent ship surveys. The advent of autonomous instrumentation, including underwater gliders, profiling floats, surface drifters, enhanced moorings, coastal high-frequency radars, and satellite remote sensing, now provides the capability to resolve such phenomena and assess their role in structuring pelagic ecosystems. These methods are especially valuable when integrated together, and with shipboard calibration measurements and experimental programs
First Observations of the Brown Dwarf HD 19467 B with JWST
We observed HD 19467 B with JWST's NIRCam in six filters spanning 2.5-4.6
with the Long Wavelength Bar coronagraph. The brown dwarf HD 19467 B
was initially identified through a long-period trend in the radial velocity of
G3V star HD 19467. HD 19467 B was subsequently detected via coronagraphic
imaging and spectroscopy, and characterized as a late-T type brown dwarf with
approximate temperature K. We observed HD 19467 B as a part of the
NIRCam GTO science program, demonstrating the first use of the NIRCam Long
Wavelength Bar coronagraphic mask. The object was detected in all 6 filters
(contrast levels of to ) at a separation of
1.6 arcsec using Angular Differential Imaging (ADI) and Synthetic Reference
Differential Imaging (SynRDI). Due to a guidestar failure during acquisition of
a pre-selected reference star, no reference star data was available for
post-processing. However, RDI was successfully applied using synthetic Point
Spread Functions (PSFs) developed from contemporaneous maps of the telescope's
optical configuration. Additional radial velocity data (from Keck/HIRES) are
used to constrain the orbit of HD 19467 B. Photometric data from TESS are used
to constrain the properties of the host star, particularly its age. NIRCam
photometry, spectra and photometry from literature, and improved stellar
parameters are used in conjunction with recent spectral and evolutionary
substellar models to derive physical properties for HD 19467 B. Using an age of
9.40.9 Gyr inferred from spectroscopy, Gaia astrometry, and TESS
asteroseismology, we obtain a model-derived mass of 62, which is
consistent within 2- with the dynamically derived mass of
81.Comment: 21 pages, 19 figures. Accepted to AAS Journal
- …