Publications (8)4.9 Total impact
-
Article: Multisite campaign on the open cluster M67. III. Delta Scuti pulsations in the blue stragglers
[show abstract] [hide abstract]
ABSTRACT: 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 meter telescopes with a time baseline of 43 days. In two stars, EW Cnc and EX Cnc, we detect the highest number of frequencies (41 and 26) detected in delta Scuti stars belonging to a stellar cluster, and EW Cnc has the second highest number of frequencies detected in any delta 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 show 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 either from multi-colour photometry or spectroscopy. Comment: 15 pages, 14 figs, one appendix. Part three in a series of papers describing results from an extensive multi-site campaign on the open cluster M6704/2007; -
Article: Multisite campaign on the open cluster M67. II. Evidence for solar-like oscillations in red giant stars
[show abstract] [hide abstract]
ABSTRACT: 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. (1993) who targeted 11 turn-off stars in the open cluster M67 (NGC 2682), but the oscillation amplitudes were too small (<20micromag) to obtain unambiguous detections. Like Gilliland et al. (1993) we also aim at detecting solar-like oscillations in M67, but we target red giant stars with expected amplitudes in the range 50-500micromag and periods of 1 to 8 hours. 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 27micromag are obtained for single sites, while the combined data reach 19micromag, 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.03/2007; -
Article: Solar-like oscillations in open cluster stars
[show abstract] [hide abstract]
ABSTRACT: Asteroseismology of stellar clusters is potentially a powerful tool. The assumption of a common age, distance, and chemical composition provides constraints on each cluster member, which significantly improves the asteroseismic output. Driven by this great potential, we carried out multi-site observations aimed at detecting solar-like oscillations in the red giant stars in the open cluster M67 (NGC 2682) (Stello et al. 2006). Here we present the first analysis of our data, which show evidence of excess power in the Fourier spectra, shifting to lower frequencies for more luminous stars, consistent with expectations from oscillations. If the observed power excesses were due to stellar oscillations, this result would show great prospects for asteroseismology in stellar clusters. Comment: 2 pages, 2 figures. Accepted for publication in CoAst02/2007; -
Article: Multisite campaign on the open cluster M67 – I. Observations and photometric reductions
[show abstract] [hide abstract]
ABSTRACT: 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.Monthly Notices of the Royal Astronomical Society 12/2006; 373(3):1141 - 1150. · 4.90 Impact Factor -
Article: Multi-site campaign on the open cluster M67. I. Observations and photometric reductions
[show abstract] [hide abstract]
ABSTRACT: We report on an ambitious multi-site 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 optimisation of the signal-to-noise of the low amplitude (50-500 micromag) solar-like oscillations. This includes a new and efficient method for obtaining the linearity profile of the CCD response at ultra high 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 micromag. 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 delta Scuti stars.10/2006; -
Article: The light curve of the semiregular variable L2 Puppis: II. Evidence for solar-like excitation of the oscillations
[show abstract] [hide abstract]
ABSTRACT: We analyse visual observations of the pulsations of the red giant variable L2 Pup. The data cover 77 years between 1927 and 2005, thus providing an extensive empirical base for characterizing properties of the oscillations. The power spectrum of the light curve shows a single mode resolved into multiple peaks under a narrow envelope. We argue that this results from stochastic excitation, as seen in solar oscillations. The random fluctuations in phase also support this idea. A comparison with X Cam, a true Mira star with the same pulsation period, and W Cyg, a true semiregular star, illustrates the basic differences in phase behaviours. The Mira shows very stable phase, consistent with excitation by the kappa-mechanism, whereas W Cyg shows large phase fluctuations that imply stochastic excitation. We find L2 Pup to be intermediate, implying that both mechanisms play a role in its pulsation. Finally, we also checked the presence of low-dimensional chaos and could safely exclude it. Comment: 7 pages, 7 figures, MNRAS in press07/2005; -
Article: Whole Earth Telescope observations of the pulsating hot white dwarf PG 1707+427
[show abstract] [hide abstract]
ABSTRACT: We report on the analysis of multisite time-series photometry of the pulsating pre-white dwarf (GW Vir star) PG 1707+427, obtained by the Whole Earth Telescope collaboration. This is the last of the known GW Vir stars without surrounding nebulae to be resolved by multisite data. Successful resolution of the pulsation spectrum resulted from the combination of high signal-to-noise observations with a large telescope and wide coverage in longitude with smaller telescopes. We find a series of 8 pulsation frequencies (along with two nonlinear combination frequencies), and identify 7 of them as part of a sequence of $\ell=1$ modes, with a common period spacing of 23.0 s. This spacing implies that the mass of PG 1707+427 is $0.57~M_{\odot}$. Preliminary model fits suggest that the mass determined via asteroseismology is consistent with the mass determined from spectroscopy combined with evolutionary tracks.http://dx.doi.org/10.1051/0004-6361:20041475. -
Article: Applying Weights to Whole Earth Telescope Data: Results for Four Stars
-1:417-420.
Top co-authors
Top Journals
Institutions
-
2006–2007
-
University of Sydney
- School of Physics
Sydney, New South Wales, Australia
-
