Download Report for European Helioseismology and Asteroseismology Network

AsteroFLAG – From the Sun to the Stars: Outcomes of the ISSI
Workshops WJC February 2008
For HELAS 2007 Annual Report
At the first asteroFLAG workshop, hosted in January 2008 by the International Space
Science Institute (ISSI), it was agreed that asteroFLAG would undertake a series of hareand-hounds exercises to help in preparations for the asteroseismic component of the
upcoming NASA Kepler mission. The asteroseismic component, the Kepler
Asteroseismic Investigation (KAI), is being co-ordinated from Aarhus, and involves a
large international collaboration of scientists called the Kepler Asteroseismic Science
Consortium (KASC).
Shortly after the first ISSI workshop, WJC and his fellow “hares” completed
development of the asteroFLAG simulator. The simulator is designed to generate
artificial timeseries data that mimic observations made by Kepler. The first release of
artificial timeseries data was made on three artificial stars (named Pancho, Boris and
Katrina). This release comprised multiple datasets on each artificial star, to cover a range
of different apparent visual magnitudes, angles of inclination, and internal rates of
rotation. Several members of the group acted as “hounds”, and undertook to estimate the
large frequency spacings of the acoustic mode spectra of these stars, from analysis of the
timeseries data. The results of this first “Exercise #1” were reported at the HELAS NA3-2
Workshop, “low-degree and low-frequency modes” (La Palma, 2007 September); at the
First KASC Workshop (Orsay, Paris, 2007 October); and in print (Chaplin et al. 2008b).
We demonstrated that it was possible to extract robust estimates of the large frequency
spacings from many of the artificial timeseries. Estimation of the large frequency
spacings is important, in that those estimates may be used to obtain accurate estimates of
the radii of the stars, and therefore estimates of the radii of any exoplanets found around
those stars.
For the next phase of asteroFLAG, we have begun two new hare-and-hounds exercises.
In Exercise #2, results on the large spacings from Exercise #1 are being used to estimate
the radii of the stars. In Exercise #3, new artificial timeseries data have been released on
four new artificial stars (called Arthur, Hector, Myrtille and Gus). Only one timeseries
has been released for each star, meaning the objective – which is to estimate the large and
small frequency spacings of the acoustic mode spectra – this time represents a true, blind
test of the analysis. Preliminary results on Exercise #2 and Exercise #3 were discussed at
the second ISSI workshop, held 2008 Feb 18 – 22.
The objective is to use lessons learned from the exercises to help inform development of
data analysis tools for Kepler. AsteroFLAG is therefore now moving into a new mode,
where it will be involved in development and testing of analysis codes for use on the
Kepler data. For example, the group has offered to provide a “peak bagging” pipeline for
Kepler, which will implement multi-component model fitting of mode peaks in the
frequency power spectrum to yield estimates of the mode parameters. The group has
resident expertise in peak bagging, from involvement in analysis of “Sun-as-a-star”
helioseismology data, and asteroseismology data from the space-borne COROT and
WIRE instruments.
An important aim of the second ISSI workshop was to reach consensus on the philosophy
of the peak-bagging approach to Kepler, and to plan out development and testing to be
ready for launch.
At the second workshop the subject of how to select Sun-like asteroseismic targets for
Kepler was also discussed in some detail.
The group will be liaising closely with the Kepler Asteroseismic Science Operations
Centre (KASOC) over the coming months. The asteroFLAG P.I. will be visiting Aarhus
in March. Presentation of results on on-going exercises will be made at upcoming
meetings, include the Second KASC Workshop, in 2008 June.
AsteroFLAG Papers
J. Ballot, T. Appourchaux, T. Toutain, M. Guittet, ‘Fitting stellar p modes: errors,
correlations and biases’, 2008, Astronomy and Astrophysics, submitted
J. Ballot, T. Appourchaux, T. Toutain, ‘Effect of the stellar inclination angle upon
theoretical errors of l=1 p-mode parameters’, 2008, Astronomische Nachrichten, in press
W. J. Chaplin, T. Appourchaux, T. Arentoft, J. Ballot, F. Baudin, M. Bazot, T. R.
Bedding, J. Christensen-Dalsgaard, O. L. Creevey, V. Duez, Y. Elsworth, S. T. Fletcher,
R. A. García, D. O. Gough, A. Jiménez, S. J. Jiménez-Reyes, G. Houdek, H. Kjeldsen,
M. Lazrek, J. W. Leibacher, M. J. P. F. G. Monteiro, C. Neiner, R. New, C. Régulo,
D. Salabert, R. Samadi, T. Sekii, S. G. Sousa, T. Toutain, S. Turck-Chièze,
‘AsteroFLAG: From the Sun to the Stars’, 2008a, in: Helioseismology, Asteroseismology
and MHD Connections, proceedings of HELAS II, JPCS, IOP publishing, in press
W. J. Chaplin, T. Appourchaux, T. Arentoft, J. Ballot, J. Christensen-Dalsgaard,
O. L. Creevey, Y. Elsworth, S. T. Fletcher, R. A. García, G. Houdek, S. J. JiménezReyes, H. Kjeldsen, R. New, C. Régulo, D. Salabert, T. Sekii, S. G. Sousa, T. Toutain,
‘AsteroFLAG: first results from hare-and-hounds Exercise #1’, 2008b, Astronomische
Nachrichten, submitted
W. J. Chaplin, G. Houdek, T. Appourchaux, Y. Elsworth, R. New, T. Toutain, ‘On
challenges for asteroseismic analysis of Sun-like stars’, 2008c, Astronomy and
Astrophysics, submitted
R. A. García, J Ballot, ‘On the backwards difference filter’, 2008, Astronomy and
Astrophysics, 477, 611