The Phoebus Home Page
Agenda and minutes of the teleconfs of 1998
Minutes of the teleconfs
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September 16, 1998
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Discussion with Roger Ulrich: Roger wanted to know if the group was
interested into a 'GOLF'-like instrument that would be put onaboard the
STEREO spacecrafts. The advantage of 2 instruments measuring oscillations
subject to independent solar noise is to increase the signal-to-noise ratio
by a factor 1.414 (square root of 2). The group clearly stressed
that such an improvement was not worth the effort of building 2 space instruments
given the fact there is no a hint of a g-mode signal. TA argued
that the factor of square root of 2 could be already gained by combining
GOLF and MDI which is what is already done by Roger and his co-workers...but
outside of the Phoebus group. TA argued that perhaps detection
of g modes (or p modes) at the limb could be easier (MDI data could be
available for checking that).
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Roger asked whether somebody from his team (Carl Henney) could participate
at the workshop: this was a hot potato! Some members of the group
felt that this could be feasible only if the group were to have access
to GOLF data. Unfortunately, this will not be the case! Even if it
were, it would imply that other GOLF team members would like to join as
well. Obviously a source of conflict with the GOLF PI. Talking
afterwards to BA, it is clear that the first year of data should
have already became public domain...somw pressures could be put on the
GOLF PI for achieving this goal!
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The time series dates were discussed. Due to the difficulties of
processing BiSON data quickly, it was agreed that the end date would be
December 31, 1997; the starting date being May 1, 1996. The responsible
for time series generation are the following: TT (MDI), TA
(LOI), WC (BiSON), WF (PMO6/SPM)
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September 2, 1998
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We discussed the subject of the next workshop. After the short note
published in Science, the group felt that we have to work on dismissing
or confirming the candidate found by GOLF at 220.65 microHz.
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The time series to be produced again for the workshop will start from May
1, 1996 and end on June 24, 1998
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June 17, 1998
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Some discussions took place over the participation of IRIS in the Phoebus
group. The overall feeling was that IRIS is too close form the GOLF
to be included.
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It was agreed that the Phoebus home page be partiallt opened
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May 20, 1998
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g-mode paper presentation: We discussed the materials put on the
Vega site. Most of it is appropriate for the purpose. ThierryA
will produce a collapsogramme in the g-mode range with a 0.1 probability
limit. The collapsogramme over a wide frequency band may be useless
because the splitting varies over the range. It is probably more
useful to produce it over a theoretical frequency where we believe that
only 1 peak might appear. We discuss the conversion factor between
velocity and intensity: a 1 mm/s velocity is equivalent to 0.1 ppm (Please
confirm this!)
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Preparations of posters: All of the figures needed from TA,
WC
and TT are ready. We still need urgently the material from
BA and WF. Please check the minutes of April 22 to
see what is left out. In addition we need the linewidth of BiSON
and SOI/MDI as measured by WC and TT; we will put a linewidth
plot in the poster.
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May 13, 1998
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g-mode paper presentation: We agreed that Wolfgang will present
the results of the Phoebus group. In parallel, we will also make
a poster so that anyone can look and think at what we have been doing.
The poster is still to be produced by ThierryA. We agreed to put
materials for the poster/presentation on the Vega site (namely under g_workshop/plots/poster_gmodes).
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Paper writing: Claus agreed on writing the g-mode contribution.
The Thierry's agreed on writing the p-mode contribution, the share of tasks
is TBD. The unofficial deadline is about 2 weeks after the end of
the Boston meeting.
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AOB: We also discuss some peaks that Phil found in the SOI/MDI spectra
(110.185 microHz, 122.185 microHz and 196.79 microHz).
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April 22, 1998
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Data preparation update: All the data are ready to be used!
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Paper submitted for SOHO6:
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g-mode poster: It was agreed that combining data with 2 very different
signal-to-noise ratio will not help to detect the g modes. Instead
combining data with similar signal-to-noise ratio is likely to be better
than not combining, e.g. using the different time series of a single intrument,
or using coeval data from 2 different instruments.
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List of actions for the posters:
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g-mode poster:
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10-sigma limit: BiSON; 1 figure + text if necessary. Use (cm/s)^2
not spectral density, Action on WC. MDI; 1 figure for
the degree of your choice + text if necessary. Use (cm/s)^2 not spectral
density, Action on TT. LOI; 1 figure for l=0
+ text if necessary. Use (ppm)^2 not spectral density) Action
on TA.
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Multivariate technique: VIRGO; 1 or 2 figures + text explaining
the technique. Also in (ppm)^2, Action on WF.
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Collapsogramme: MDI; Example of p-mode detection with the technique
for l=1, in (cm/s)^2, Action TA. Probably better suited in
the p-mode poster!
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Bo's technique: BA to ptovide 1 or 2 figures + necessary text describing
some of the techniques he used.
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p-mode poster:
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Echelle diagrammes: for collapsogramme of LOI, MDI both for l=1 and l=6,
Action
on TA. For BiSON data, Action on BC. For SPM data, Action
on TA.
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Frequency list (cut off at 2500 microHz): LOI, Action on TA. BiSON,
Action
on BC. MDI, Action on TT. SPM, Action on TA.
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Frequency differences: difference with respect to the LOI, Action on
TA.
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April 8, 1998
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Data preparation update: All the data but MDI are ready, this will
be done soon by ThierryT
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Paper submitted for SOHO6:
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p-mode poster: The high-frequency cut-off for displaying p-mode frequency
was set to 2500 microHz. We will display echelle diagramme of the
various instruments
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g-mode poster: A 10-sigma limit was set as a reasonable value for detecting
modes. It gives a 0.1 chance of finding a peak 10 larger than the
noise in a window of 70 microHz in a 1-year power spectra.
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p-mode fitting strategy: We agreed that for the p-mode poster a
lorentzian profile be used for fitting the data.
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March 19, 1998
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Data preparation update: BiSON data almost ready (they now can be
found at the Norwegian site). The MDI data are not yet ready.
It is likely that the first year can be easily done from the data available.
The second year will start from May 23, 1997 and end on March 1st, 1998
or so. If the MDI team does not find time to produce the data, one
of the Phoebus team member will do it (namely ThierryT).
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Discussion of p1: Nothing to report.
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Paper submission for SOHO6: We will submit 2 papers. One about
the g-mode amplitude upper limit. One about low-frequency low-order
p modes. Bo will produce the abstracts, and ThierryA will produce
the posters in the usual fancy way. More detailed responsibilities
are listed below
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Responsabilities: For the p-mode paper: ThierryA will fit the VIRGO
data, ThierryT the MDI data, Bill the BiSON data. The highest frequency
to be fitted or listed in a table is TBD. For the g-mode paper: a
discussion will take place at the next teleconf.
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March 11, 1998
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Data preparation update: Not discussed
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Discussion of p1: Wolfgang looked at the variation of 'p1' with
time using a Hilbert transform. The 'p1' seems not to be a long living
phenomena: the
files are on the Vega account in a zip file. Sasha used the 'p1'
frequency to see if it could compatible with the MDI inversion.
It seems not be compatible especially in the view of the good agreement
with theory of the frequencies measured for low-degree p modes down to
1 mHz for l=1! The 'p1' mode seems way too different from theoretical
frequencies. At the time of writing, the 'p1' peak being an n=1 p
mode is excluded.
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Responsabilities: Postponed until we have a full team.
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February 25, 1998
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Data preparation update:
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VIRGO/Non-LOI: SPM and PMO time series are now recomputed and should be
available on the Vega site.
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BiSON: Work progressing...
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SOI: Nothing reported (No Californian available...)
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Discussion of p1: Wolfgang rotated the phase of the PMO Fourier
spectra, and after multivariate analysis 'p1' disappeared from the resulting
spectrum. The phase rotation is close to Pi/2. After Douglas,
the amplitude of 'p1' should be about 1 m/s which is close to the 0.4 m/s
given 2 weeks ago. Given the differential effect of the multivariate
analysis, this would mean an amplitude of a bout a few % in intensity,
very unlikely!
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Responsabilities: Postponed until we have a full team.
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February 11, 1998
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Data preparation update:
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VIRGO/LOI: All 6 Fourier spectra for the new period have been computed.
At least 4 of them are on the Vega site
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VIRGO/Non-LOI: The Fourier spectra can in principle be recomputed from
the available Fourier spectra by inverting them. This is doable by
anybody having some knowledge of the fft properties. To be on the
safe side, we advised Claus and Wolfgang to redo the job from their end,
and put it on the Vega site.
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BiSON: Performance of each site has now been assessed. An optimal
combination of the site is now possible depending on the frequency band
to be used for searching g modes and low-frequency p modes.
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SOI: Nothing reported (No Californian available...)
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Discussion of p1: The group agreed that the peak was not due to
the noise. The signal-to-noise ratio is at least 15. with a chi square
with 2 d.o.f. statistics, this is very significant; given the number of
bins (44756) there 1 chance over 100 that this is due to noise. The
amplitude of the peak is about 0.5 ppm. When the time series are
cut into 3 (or 4?) independent time series, the peak is still there although
at a lower S/N ratio, probably due to shorter time series. Although
the multivariate analysis decrease the noise by a factor of 10, it does
not help to enhance low-frequency p modes; this is annoying...There are
lots of concern that the 'p1' peak may be of S/C origin. ThierryA
has looked at the spectra of the LOI guiding signals to verify that there
are no guiding periodicities induced by the S/C. Beating between
2 frequencies should not be excluded. Last, we discussed the equivalent
amplitude of 'p1' it it were to be detected in velocity. An article
in the Asilomar conference mentionned a 1 to 1 relationship between ppm
and m/s. From this, we concluded that the equivalent 'p1' amplitude
was 40 cm/s! This is way too large (to be compared to 2 cm/s of 2
weeks ago...). Douglas agreed to look into the conversion factor
for the next teleconf.
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Responsabilities: Postponed to the next meeting or the one after
next.
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January 28, 1998
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Data preparation update:
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VIRGO: Nothing done yet...
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BiSON: Started to look at the noise characteristics of each station, and
how to combine optimally the stations to achieve the best S/N ratio in
the low frequency range
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SOI: Started to work on a project aiming at killing the existence, once
for all, of the 160 minutes oscillation, using SOI, WSO and Crimea data.
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GOLF involvement: Phil and Claus has received a 1
and half page e-mail from Alan Gabriel. The GOLF team is still
trying to produce either a g-mode paper with proper detection or an upper
limit paper. The production of this paper seems to be related to
the need of the funding agency (e.g. CNES) of having evidence that some
work has been achieved regarding the g modes. The reluctance of Alan
Gabriel of joining the group seems to be related to the lost of the GOLF
identity as such. If g modes were to be discovered by the Phoebus
group, the credits will go to the group not to GOLF. Here is the
personnal opinion of the secretary: In the name of science, I am prepared
to trade fame for a g-mode discovery (another naive approach).
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2nd workshop time frame and location: The last week of October 98
was confirmed as a firm week for holding the workshop at ESTEC. Other
locations were suggested such as Birmingham (to which the BiSON team did
not subscribe...), or Stanford which invitation was greatly acknowledged.
The financial support provided by SSD/ESA, if the meeting is hold at ESTEC,
was a strong argument for holding the workshop in Noordwijk (the weather
is not necessarily better in Noordwijk than in Birmingham...).
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Multivariate analysis: Wolfgang and Claus have applied their
technique, as decribed in the aide memoire, to the SPM and PMO data.
They have found a peak at about 3-4 sigma above the noise at 287.3 microHz,
and possible splitting of 0.95 microHz. This could be a possible
detection of p1. The peaks seem to keep phase within 1 degree using
4 independent time series; they are present in all 4. There were
some discussion about the statistics of the noise and the significance
of the 3-4 sigma. The tentative estimate of the amplitude in velocity
is about 2 mm/s (after Douglas). Wolfgang and Claus agreed to put
ps files of the spectra on the Vega
account, together with fits file of the data.
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Future paper: The group agreed to prepare a poster for Boston
about the upper limit of g-mode amplitude at a possible 5-sigma level.
The group felt that this work would not be suitable for a referee journal.
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Tuning: Yvonne pointed out that the low frequency limits mentionned
in the minutes of the last teleconf should be labelled as limits below
which the data cannot be trusted anymore. These are fuzzy limits,
not hard limits. Here I rephrased it as: 'A lower frequency area,
around which we will not search for g modes, was set at about 60 microHz
for the SOHO instruments, and at about 200- 250 microHz for BiSON.'
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January 14, 1998
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Ground rules: There are no firm ground rules yet. The goal
is really to discover the g modes and not much thought has been given beyond.
We will exchange data as a mean for achieving the goal.
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Publication policy: If there is any scientific results to
be published coming from the exchange of the data in the group, it is clear
that the articles have to be co-authored by the member of the group.
Any other thoughts related to publication policy might have to come in
due time...
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How can other's people data be used?: The data can be used in anyway
we want (?) provided that the data are available (sic).
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Role of the various teams: Each responsible of the instrument
prepare the data according to the wishes of the group: Phil for SOI/MDI,
ThierryT for SPM and SOI/MDI vel, Wolfgang for PMO6, ThierryA for VIRGO/LOI
and SOI/MDI int (?), Bill for BiSON. The other member of the group
either analyze the data: Bo for VIRGO/SPM, Claus for VIRGO/PMO6; or give
theoretical support to the group: Yvonne, Douglas, George, Janine and Sasha.
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Ground rules: There are no firm ground rules yet. The goal
is really to discover the g modes and not much thought has been given beyond.
We will exchange data as a mean for achieving the goal.
-
Publication policy: If there is any scientific results to
be published coming from the exchange of the data in the group, it is clear
that the articles have to be co-authored by the member of the group.
Any other thoughts related to publication policy might have to come in
due time...
-
How can other's people data be used?: The data can be used in anyway
we want (?) provided that the data are available (sic).
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Role of the various teams: Each responsible of the instrument
prepare the data according to the wishes of the group: Phil for SOI/MDI,
ThierryT for SPM and SOI/MDI vel, Wolfgang for PMO6, ThierryA for VIRGO/LOI
and SOI/MDI int (?), Bill for BiSON. The other member of the group
either analyze the data: Bo for VIRGO/SPM, Claus for VIRGO/PMO6; or give
theoretical support to the group: Yvonne, Douglas, George, Janine and Sasha.
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GOLF involvement: ThierryA talked to Sylvaine Turck-Chieze.
In no way GOLF will take the leadership [of the group] on g-mode search:
this was a misunderstanding and does not reflect the position of GOLF.
Their position is to write an article in April that will either put some
upper limits on g-mode amplitudes or publicize the discovery of g modes.
The possible unambiguous identification of the g modes by the GOLF team
will be and is put to question: they have the SOI/MDI data while none of
us have the GOLF data. Phil will talk to Alan Gabriel to force him
somehow to join the group. Phil might utilize the use of the SOI/MDI
data as a fait accompli of SOI/MDI-GOLF collaboration, and force GOLF to
team with us (correctly stated?).
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Timing of the 2nd workshop: The preferred timing is the last week
of October 98 starting the 26th and ending on the 30th.
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Data preparation: The starting dates of the time series will May
23rd, 1996 at 00 : 00 UT (or TAI?) and ends on May 22nd, 1998 at 23 h 59
UT (or TAI). Sampling time is 60 sec; the BiSON team will resample
the data from 40 s to 60 s. The teams agreed to prepare the 1st year
of data soon (for the end of February?). The data will be either
time series or Fourier spectra (no power spectra!). A lower frequency
limit, below which we will not search for g modes, was set as 60 microHz
for the SOHO instruments, and as 250 microHz for BiSON.
Last updated by Thierry
Appourchaux on Tuesday, September 17, 1998 at 15:00