2,498 research outputs found
The relation between and for solar-like oscillations
Establishing relations between global stellar parameters and asteroseismic
quantities can help improve our understanding of stellar astrophysics and
facilitate the interpretation of observations. We present an observed relation
between the large frequency separation, , and the frequency of
maximum power, . We find that is proportional to
, allowing prediction of to about 15 per cent
given . Our result is further supported by established scaling
relations for and and by extended stellar model
calculations, which confirm that can be estimated using this
relation for basically any star showing solar-like oscillations in the
investigated range (0.5<M/Msol<4.0).Comment: 5 pages, 8 figures, Letter accepted by MNRA
Amplitude variability in satellite photometry of the non-radially pulsating O9.5V star zeta Oph
We report a time-series analysis of satellite photometry of the non-radially
pulsating Oe star zeta Oph, principally using data from SMEI obtained
2003--2008, but augmented with MOST and WIRE results. Amplitudes of the
strongest photometric signals, at 5.18, 2.96, and 2.67/d, each vary
independently over the 6-year monitoring period (from ca. 30 to <2 mmag at
5.18/d), on timescales of hundreds of days. Signals at 7.19/d and 5.18/d have
persisted (or recurred) for around two decades. Supplementary spectroscopic
observations show an H-alpha emission episode in 2006; this coincided with
small increases in amplitudes of the three strongest photometric signals.Comment: MNRAS, in pres
Temporal heterogeneity in microregional erythrocyte flux in experimental solid tumours.
Using a multichannel laser Doppler system equipped with custom-developed microprobes, we have evaluated real-time fluctuations in microregional blood flow in two experimental murine tumour systems. The results show that in both the sarcoma F and the carcinoma NT over 50% of the microregions evaluated show a fluctuation in red blood cell flux by at least a factor of 2 over a 60 min time period. Approximately 20% of the regions monitored demonstrated a change in flow by a factor of 5 or more. Within the 1 h monitoring period, approximately 20% of the changes were reversed (SaF, 21%; CaNT, 19%). The duration of change for these regions ranged from 6 to 45 min. Similar temporal fluctuations in flow were seen in anaesthetised and unanaesthetised animals, indicating that artifacts due to probe movement were minimal. These findings clearly demonstrate that fluctuations in microregional erythrocyte flux are a common feature of the experimental tumours studied
K2P A photometry pipeline for the K2 mission
With the loss of a second reaction wheel, resulting in the inability to point
continuously and stably at the same field of view, the NASA Kepler satellite
recently entered a new mode of observation known as the K2 mission. The data
from this redesigned mission present a specific challenge; the targets
systematically drift in position on a ~6 hour time scale, inducing a
significant instrumental signal in the photometric time series --- this greatly
impacts the ability to detect planetary signals and perform asteroseismic
analysis. Here we detail our version of a reduction pipeline for K2 target
pixel data, which automatically: defines masks for all targets in a given
frame; extracts the target's flux- and position time series; corrects the time
series based on the apparent movement on the CCD (either in 1D or 2D) combined
with the correction of instrumental and/or planetary signals via the KASOC
filter (Handberg & Lund 2014), thus rendering the time series ready for
asteroseismic analysis; computes power spectra for all targets, and identifies
potential contaminations between targets. From a test of our pipeline on a
sample of targets from the K2 campaign 0, the recovery of data for multiple
targets increases the amount of potential light curves by a factor .
Our pipeline could be applied to the upcoming TESS (Ricker et al. 2014) and
PLATO 2.0 (Rauer et al. 2013) missions.Comment: 14 pages, 20 figures, Accepted for publication in The Astrophysical
Journal (Apj
NGC 6819: testing the asteroseismic mass scale, mass loss, and evidence for products of non-standard evolution
We present an extensive peakbagging effort on Kepler data of 50 red
giant stars in the open star cluster NGC 6819. By employing sophisticated
pre-processing of the time series and Markov Chain Monte Carlo techniques we
extracted individual frequencies, heights and linewidths for hundreds of
oscillation modes.
We show that the "average" asteroseismic parameter , derived
from these, can be used to distinguish the stellar evolutionary state between
the red giant branch (RGB) stars and red clump (RC) stars.
Masses and radii are estimated using asteroseismic scaling relations, both
empirically corrected to obtain self-consistency as well as agreement with
independent measures of distance, and using updated theoretical corrections.
Remarkable agreement is found, allowing the evolutionary state of the giants to
be determined exclusively from the empirical correction to the scaling
relations. We find a mean mass of the RGB stars and RC stars in NGC 6819 to be
and ,
respectively. The difference is
almost insensitive to systematics, suggesting very little RGB mass loss, if
any.
Stars that are outliers relative to the ensemble reveal overmassive members
that likely evolved via mass-transfer in a blue straggler phase. We suggest
that KIC 4937011, a low-mass Li-rich giant, is a cluster member in the RC phase
that experienced very high mass-loss during its evolution. Such over- and
undermassive stars need to be considered when studying field giants, since the
true age of such stars cannot be known and there is currently no way to
distinguish them from normal stars.Comment: 21 pages, 11 figure
Asteroseismic surface gravity for evolved stars
Context: Asteroseismic surface gravity values can be of importance in
determining spectroscopic stellar parameters. The independent log(g) value from
asteroseismology can be used as a fixed value in the spectroscopic analysis to
reduce uncertainties due to the fact that log(g) and effective temperature can
not be determined independently from spectra. Since 2012, a combined analysis
of seismically and spectroscopically derived stellar properties is ongoing for
a large survey with SDSS/APOGEE and Kepler. Therefore, knowledge of any
potential biases and uncertainties in asteroseismic log(g) values is now
becoming important. Aims: The seismic parameter needed to derive log(g) is the
frequency of maximum oscillation power (nu_max). Here, we investigate the
influence of nu_max derived with different methods on the derived log(g)
values. The large frequency separation between modes of the same degree and
consecutive radial orders (Dnu) is often used as an additional constraint for
the determination of log(g). Additionally, we checked the influence of small
corrections applied to Dnu on the derived values of log(g). Methods We use
methods extensively described in the literature to determine nu_max and Dnu
together with seismic scaling relations and grid-based modeling to derive
log(g). Results: We find that different approaches to derive oscillation
parameters give results for log(g) with small, but different, biases for
red-clump and red-giant-branch stars. These biases are well within the quoted
uncertainties of ~0.01 dex (cgs). Corrections suggested in the literature to
the Dnu scaling relation have no significant effect on log(g). However somewhat
unexpectedly, method specific solar reference values induce biases of the order
of the uncertainties, which is not the case when canonical solar reference
values are used.Comment: 8 pages, 5 figures, accepted for publication by A&
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