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Stello, D.,Bruntt, H.,Kjeldsen, H.,Bedding, T. R.,Arentoft, T.,Gilliland, R. L.,Nuspl, J.,Kim, S.-L.,Kang, Y. B.,Koo, J.-R.,Lee, J.-A.,Sterken, C.,Lee, C.-U.,Jensen, H. R.,Jacob, A. P.,Szabó,, R Blackwell Publishing Ltd 2007 Monthly notices of the Royal Astronomical Society Vol.377 No.2
<P>ABSTRACT</P><P>Measuring solar-like oscillations in an ensemble of stars in a cluster, holds promise for testing stellar structure and evolution more stringently than just fitting parameters to single field stars. The most-ambitious attempt to pursue these prospects was by Gilliland et al. who targeted 11 turn-off stars in the open cluster M67 (NGC 2682), but the oscillation amplitudes were too small (<20 μmag) to obtain unambiguous detections. Like Gilliland et al. we also aim at detecting solar-like oscillations in M67, but we target red giant stars with expected amplitudes in the range 50–500 μmag and periods of 1 to 8 h. We analyse our recently published photometry measurements, obtained during a six-week multisite campaign using nine telescopes around the world. The observations are compared with simulations and with estimated properties of the stellar oscillations. Noise levels in the Fourier spectra as low as 27 μmag are obtained for single sites, while the combined data reach 19 μmag, making this the best photometric time series of an ensemble of red giant stars. These data enable us to make the first test of the scaling relations (used to estimate frequency and amplitude) with an homogeneous ensemble of stars. The detected excess power is consistent with the expected signal from stellar oscillations, both in terms of its frequency range and amplitude. However, our results are limited by apparent high levels of non-white noise, which cannot be clearly separated from the stellar signal.</P>
Multisite campaign on the open cluster M67 – I. Observations and photometric reductions
Stello, D.,Arentoft, T.,Bedding, T. R.,Bouzid, M. Y.,Bruntt, H.,Csubry, Z.,Dall, T. H.,Dind, Z. E.,Frandsen, S.,Gilliland, R. L.,Jacob, A. P.,Jensen, H. R.,Kang, Y. B.,Kim, S.-L.,Kiss, L. L.,Kjeldsen, Blackwell Publishing Ltd 2006 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.373 No.3
<P>ABSTRACT</P><P>We report on an ambitious multisite campaign aimed at detecting stellar variability, particularly solar-like oscillations, in the red giant stars in the open cluster M67 (NGC 2682). During the six-week observing run, which comprised 164 telescope nights, we used nine 0.6-m to 2.1-m class telescopes located around the world to obtain uninterrupted time series photometry. We outline here the data acquisition and reduction, with emphasis on the optimization of the signal-to-noise ratio of the low-amplitude (50–500 μmag) solar-like oscillations. This includes a new and efficient method for obtaining the linearity profile of the CCD response at ultrahigh precision (∼10 parts per million). The noise in the final time series is 0.50 mmag per minute integration for the best site, while the noise in the Fourier spectrum of all sites combined is 20 μmag. In addition to the red giant stars, this data set proves to be very valuable for studying high-amplitude variable stars such as eclipsing binaries, W UMa systems and δ Scuti stars.</P>
Multisite campaign on the open cluster M67 – III. δ Scuti pulsations in the blue stragglers
Bruntt, H.,Stello, D.,Suá,rez, J. C.,Arentoft, T.,Bedding, T. R.,Bouzid, M. Y.,Csubry, Z.,Dall, T. H.,Dind, Z. E.,Frandsen, S.,Gilliland, R. L.,Jacob, A. P.,Jensen, H. R.,Kang, Y. B.,Kim, S.-L. Blackwell Publishing Ltd 2007 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.378 No.4
<P>ABSTRACT</P><P>We have made an asteroseismic analysis of the variable blue stragglers in the open cluster M67. The data set consists of photometric time-series from eight sites using nine 0.6–2.1 m telescopes with a time-baseline of 43 d. In two stars, EW Cnc and EX Cnc, we detect the highest number of frequencies (41 and 26) detected in δ Scuti stars belonging to a stellar cluster, and EW Cnc has the second highest number of frequencies detected in any δ Scuti star. We have computed a grid of pulsation models that take the effects of rotation into account. The distribution of observed and theoretical frequencies shows that in a wide frequency range a significant fraction of the radial and non-radial low-degree modes are excited to detectable amplitudes. Despite the large number of observed frequencies we cannot constrain the fundamental parameters of the stars. To make progress we need to identify the degrees of some of the modes from either multicolour photometry or spectroscopy.</P>
WFIRST ULTRA-PRECISE ASTROMETRY II: ASTEROSEISMOLOGY
Andrew Gould,Daniel Huber,Matthew Penny,Dennis Stello 한국천문학회 2015 Journal of The Korean Astronomical Society Vol.48 No.2
WFIRST microlensing observations will return high-precision parallaxes, σ(π) . 0.3 μas, for the roughly 1 million stars with H < 14 in its 2.8 deg2 field toward the Galactic bulge. Combined with its 40,000 epochs of high precision photometry (∼ 0.7 mmag at Hvega = 14 and ∼ 0.1 mmag at H = 8), this will yield a wealth of asteroseismic data of giant stars, primarily in the Galactic bulge but including a substantial fraction of disk stars at all Galactocentric radii interior to the Sun. For brighter stars, the astrometric data will yield an external check on the radii derived from the two asteroseismic parameters, the large-frequency separation hνnli and the frequency of maximum oscillation power νmax, while for the fainter ones, it will enable a mass measurement from the single measurable asteroseismic parameter νmax. Simulations based on Kepler data indicate that WFIRST will be capable of detecting oscillations in stars from slightly less luminous than the red clump to the tip of the red giant branch, yielding roughly 1 million detections.
Euclid ASTEROSEISMOLOGY AND KUIPER BELT OBJECTS
Andrew Gould,Daniel Huber,Dennis Stello 한국천문학회 2016 Journal of The Korean Astronomical Society Vol.49 No.1
Euclid, which is primarily a dark-energy/cosmology mission, may have a microlensing component, consisting of perhaps four dedicated one-month campaigns aimed at the Galactic bulge. We show that such a program would yield excellent auxilliary science, including asteroseismology detections for about 100\,000 giant stars, and detection of about 1000 Kuiper Belt Objects (KBOs), down to 2--2.5 mag below the observed break in the KBO luminosity function at $I\sim 26$. For the 400 KBOs below the break, {\it Euclid} will measure accurate orbits, with fractional period errors $\lesssim 2.5\%$.}