ADDITIONAL SCIENCE POTENTIAL FOR COROT
1;2 1 1 1 1 1 1
W. W. Weiss , C. Aerts , S. Aigrain , G. Alecian ,E.Antonello , A. Baglin , M. Bazot ,
1 1 1 1 1 1
A. Collier-Cameron , St. Charpinet ,A.Gamarova , G. Handler , A. Hatzes , A.-M. Hub ert ,
1 1 1 1 1 1 1
H. Lammer , T. Lebzelter , C. Maceroni , M. Marconi , D. de Martino , E. Janot-Pacheco ,I.Pagano ,
1 1 1 1 1 1 1 1
E. Paunzen , F.J.G. Pinheiro ,E.Poretti ,I.Ribas , V. Rip epi ,F.Roques , R. Silvotti , J. Surdej ,
1 1 1
G. Vauclair ,S.Vauclair , and K. Zwintz
1
COROT Additional Program Working Group
2
Department of Astronomy, University Vienna, Tuerkenschanzstrasse 17, A-1180 Wien, Austria
Abstract { archival data. Successful prop osals will have to address
science outside the primary goals and will get access
Space exp eriments which are aiming towards astero-
to sp eci c archival data for proprietary use, but ex-
seismology and the detection of exoplanets, like corot or
clusively in the context of the science addressed in the
most, eddington and kepler, are designed to deliver
prop osal.
high precision photometric data. Obviously, the they can
{ short runs ( 5to20days) devoted to sp eci c target
b e used also for other purp oses than the primary science
elds.
goals and in addition many other targets can or will be
{ long runs (up to 130 days). Ab out 100 windows of the
automatically observed simultaneously with the primary
exoplanet elds will b e available for additional science.
targets. As a consequence, fascinating p ossibilities for ad-
{ windows. During short runs of the core program, it
ditional (parallel, secondary) science pro jects emerge. For
will also b e p ossible to apply for sp eci c windows in
corot a dedicated working group was thus established
the exoplanet elds.
with the goal to contribute any useful information which
Asteroseismological programs using the exoplanetary CCDs
may optimize the scienti c output of the mission.
are considered to b e part of the AP, as are exoplanetary
programs using the seismology CCDs.
Key words: COROT { Stars: variable, pulsating { Aster-
In order to prepare the AO mentioned ab ove and to
oseismology { Exoplanets
help de ning the corot science, an Additional Program
Working Group (APWG) was established.
All resp onse to the AOwillbeevaluated bythecorot
Scienti c Committee, whichwillbeincharge for the selec-
tion, taking into account the quality of the prop osed sci-
1. Introduction
ence. A successful prop oser will obtain status of a Guest
COROT (COnvection, ROtation and planetary Transits)
Investigator and will have exclusive data rights for the
is based on ultra high precision, wide eld, relativestellar
science describ ed in his prop osal. The corot Scienti c
photometry for very long continuous observing runs in the
Committee, however, will have the rights to use the same
same eld of view.
data for any other science.
It has two main scienti c programs working simultane-
One year after the rst release of data to the Co-
ously on adjacent regions of the sky: asteroseismology
and/or Guest-Investigators the data will b e available for
& extrasolar planet search.
the public.
The corot instrument is a white-light wide- eld pho-
tometer with an entrance pupil of 27 cm and a set of 4
3. The additional science
frame-transfer CCDs as detectors. Two CCDs are devoted
to asteroseismology (defo cussed, un ltered light), resp ec-
In the context of the Additional Program various asp ects
tively to exoplanet search (fo cussed, color information).
of variabilitywere discussed. In the following subsections
corot will b e launched in mid of 2006 on a low-earth p o-
we describ e with some arbitrarily chosen examples the
lar inertial orbit, allowing it to monitor continuously stel-
corot additional science p otential. For some of the pre-
lar elds near the pole of the orbit for ab out 5 months.
sented target groups no members are yet known within
The mission lifetime will b e nominally 3 years.
the visibility region of corot, but dedicated surveys may
change this situation.
Many of the ideas outlined in the following, are elab o-
2. The Additional Program (AP) concept
rated in more detail by memb ers of the corot Additional
Program Working Group in the p oster section of these The Additional Program (AP) section of corot will be
pro ceedings and the reader is encouraged to browse the available to the community after an AnnouncementofOp-
table of content for authors name and/or topic. Further p ortunity(AO) and has the goal to maximize the scienti c
information can b e found at return of the mission. This will b e achieved by using
Pro c. 2nd Eddington workshop \Stel lar Structure and Habitable Planet Finding",Palermo, 9{11 April 2003 (ESA SP-538,
July 2003, F. Favata, S. Aigrain eds.)
a) b)
http://www.astrsp-mrs.fr/pro jets/corot/
selecting the link "meetings" and further the contributions
to the various corot Science Weeks. All science addressed
in the following will b ene t from or b e made p ossible by
the high photometric quality of the data obtained during
power
long and uninterrupted observing sequences provided by
normalised flux
corot.
ariability not caused by pulsation
3.1. V time (days) frequency (micro Hz)
3.1.1. Kuiper belt objects, Exo-comets transits
Figure1. a): Total solar irradiance light curve from PMO6
The discovery of hundreds of transneptunian ob jects has
data, covering the period 1996-2001. b): Power spectrum of the
light curve, with a multiple powerlaw t with threecomponents
con rmed the hyp othesis of a residual protoplanetary disk
(active regions, meso-granulation and granulation) overlaid.
beyond Neptune. The knowledge of the structure of this
residual disk is a key element to reconstruct the history
of the Solar System, but the large distance (up to 100 AU
(Ro dono et al. 1995, Lanza et al. 1998), and to measure ro-
and even b eyond) excludes the direct detection of ob jects
tation and stellar di erential rotation. This information is
smaller than some tens of kilometers. Moreover, the ob-
fundamental to test the available hydromagnetic dynamo
jects already detected show a steep size distribution with
mo dels.
the consequence that most of the disk mass is in the small,
Variability on time scales of hours to days is thought
hitherto undetectable ob jects.
to be due to distributed networks of smaller structures,
Ro ques & Moncuquet (2000) demonstrated that seren-
rather than a few active regions or sp ots. This is the range
dipitous stellar o ccultations could be a powerful to ol to
of time scales that is most critical for planetary transit de-
detect these small ob jects orbiting b eyond Neptune if they
tection, as it corresp onds to the duration of a typical tran-
are dense enough in the sky plane. A dedicated program
sit. The identi cation and characterisation of the surface
with corot will allow the detection of very small ob jects
structures involved is underway for the Sun using soho
and will constrain their size distribution.
data (Fligge et al. 2000). corot data will allowthistobe
A by-pro duct of the exoplanet search program could
done for the entire range of stars observed, yielding the
b e the detection of exo-comets. In the Pictoris system,
relative coverage, contrast, rotation of the various typ es
comet-like ob jects falling onto the star have b een detected
of structures. These will b e included in irradiance mo dels
by their signature in the stellar sp ectrum. Such ob jects
currently applicable to the Sun only (Unruh et al 1999,
could also b e discovered by the comet tail transit in front
Krivova et al. 2003).
of the star.
corot data and the improved knowledge of intrinsic
stellar variabilitywe will gain from it will b e used to test
3.1.2. Pre-main-sequence stars
and re ne ltering to ols designed to minimise the e ect
of stellar activity on transit detections ahead of missions
The photometric study of TTauri stars, a subgroup of
suchaseddington and kepler (Carpano et al. 2003).
PMS stars, provides valuable information on p erio dic phe-
Finally, the monitoring of a few dMe are stars in the
nomena, such as the rotational mo dulation due to hot/cold
seismology channel could help in shedding some lighton
sp ots on the stellar surface, or non-p erio dic, like accretion
the mechanisms of coronal heating by investigating the
events and ares. The characterisation of such photomet-
statistics of white-light stellar micro/nano- ares and re-
ric variabilities will help to determine the conditions which
lated precursor phenomena and assessing the power law
may cause pulsation in solar-typ e PMS stars.
distribution of very low energy events.
3.1.3. Stellar activity and flares
3.1.4. Stellar rotation
The activitylevel and the characteristic time scales of the
It is now observationally well established that stars with luminosity variations of magnetic active late-typ e stars
masses similar to or b elow that of the Sun initiate their will b e monitored by corot b etter than ever b efore what
lives at the main sequence as relatively fast rotators, with will improve signi cantly our knowledge of stellar intrinsic
asso ciated strong high-energy chromospheric and coronal variability on all time scales (Fig. 1). Studying the bright-
emissions resulting from magnetic pro cesses. In addition, ness variations on time scales of days to weeks will al-
observations suggest that young stars exhibit high rates of low us to detect small solar-like sp ots, derive the lifetimes
powerful are events and have dense stellar winds. Then, of surface features, hence to estimate the turbulent mag-
the magnetic activity of the stars decreases with time as netic di usivityintheupperlayers of the convection zones
Figure2.Plotoftherotation period vs. stel lar age for a sample
of solar-type stars. The solid line corresponds to a power law
Figure 3. The di erencebetween two synthetic light curves (V)
t and indicates a spindown of solar-type stars with increasing
obtained by changing the linear limb darkening coecient from
age.
0.57 to 0.67. The corresponding system is a model of V805 Aql,
according to Popper (1981), i.e. a detached binary with rela-
d
tively short period and MS components (P = 2 :41, e ective
they evolve across the main sequence and the rotation
temperatures T = 8164 K, T = 7178 K). The other parame-
p s
slows down from the loss of angular momentum via stel-
o
ters are: mass ratio q = m =m =0:81, inclination i =86 ,
s p
lar winds. Besides providing imp ortant tests to stellar dy-
fractional radii r =0:18, r =0:15, and fractional luminosity
p s
namo mo dels, the enhanced XUV (0.1 to 100 nm) radia-
L =L =0:362. The synthetic light curves werecomputedwith
s p
tion and particle environments could have a ma jor impact
the 1995 version of the Wilson and Devinney code.
on the atmospheres and on the eventual development of
life in p ossible orbiting planets around young, active stars.
As an example, the results obtained from solar proxies in
wards the magnetic p oles. Hence CVs represent close{by
the narrow G0 to G5 sp ectral typ e range (Guinan & Ribas
test ob jects of accretion pro cesses in di erentphysical en-
2002) indicate that the solar XUV ux 2.5 Gyr and 3.5
vironments.
Gyr ago was ab out 3 and 6 times higher than to day, re-
The dwarf-nova CW Mon is observable in the exoplanet
sp ectively, and that the high-energy ux of the zero-age
eld of corot contemp oraneously with the primary seis-
main sequence Sun was stronger byuptoahundred-fold.
mology target HD 45067. These observations would allow
The extension of this study to other sp ectral typ es of rel-
to precisely measure the amplitude of the orbital variabil-
evance to exoplanetary research (G-K-M stars) hinges on
ityinlow state and to provide a constraint on the hot sp ot
the establishment of calibrated rotation p erio d-age rela-
comp onent. Photometry in high state will give information
tionships (see Fig. 2). corot data will p ermit the de -
on the evolution of an outburst (Flickering, Quasi Perio dic
nition of such relationships (from rotational mo dulation)
Oscillations, Dwarf Novae Oscillations and their relation)
and provide detailed information on are statistics for an
with unprecedented details. The results will p ose a unique
extended sample of late-typ e stars.
challenge to theory of accretion pro cesses in galactic bi-
naries.
3.1.5. Binaries
3.1.7. Outbursts in Mira variables
corot photometry has the p otential of distinguishing b e-
tween various mo dels of limb darkening of detached bi-
Short brightness outbursts have b een observed on top of
naries as is illustrated in Fig. 3 for synthetic lightcurves
the periodic light change of several Mira variables (e.g.
with di erentlimb darkening co ecients.
de Laverny et al. 1998). One explanation is the interac-
tion b etween the stellar pulsation and hyp othetical giant
planets orbiting in the outskirts of a Mira atmosphere,
3.1.6. Cataclysmic variables
developing an accretion disk during the stellar expansion
phase. In the cycle of contraction the accretion disk ro- The cataclysmic variables (CVs) are binary systems con-
tating around the planet and the orbital motion leads to sisting of an accreting white dwarf (WD) and a late typ e
a collapse of accreted matter causing outbursts observed secondary star lling its Ro che lob e. The p erio dic light
hitherto only at light minimum (Struck et al. 2002), prob- variations are related to the binary system, while non-
ably due to the low amplitude which contrasts to the noise p erio dic variations are due to mass accretion changes or
suciently only at minimum. But outbursts are exp ected instabilities in the accretion disc or accretion ow. De-
to happ en also at other phases of their light curve, de- p ending on the strength of the magnetic eld, matter ac-
p ending on the di erent orbits of large planets. corot cretes onto the WD via a disk or directly channelled to-
observean X-ray/radio loud quasar simultaneously with
corot, XMM and a ground-based radio telescop e.
3.2. Variability caused by pulsation
One of the crucial by-pro ducts of the corot exoplanet
searches will be the discovery of new p erio dically vari-
able stars, starting from an unbiased sample. The most
interesting of these new variables will then be used to
perform asteroseismology. Figure 4 illustrates nicely the
existence of pulsating variables nearly everywhere in the
HR-diagram. The observation strategy adopted by the
planet hunters is ideally suited for asteroseismology of
many classes of pulsators, i.e. the variables with p erio ds
longer than an hour such as Cep, Scuti, slowly pul-
sating B and Dor stars. Besides eddington and ke-
pler, corot is a very suitable mission to study the grav-
ity mo des in the latter two groups of stars, as they have
beat periods of several months and some even of years.
Asteroseismology of gravity-mo de oscillators is therefore
a unique by-pro duct of the search for exoplanets (Aerts
2001).
3.2.1. Pre-main-sequence stars
PMS stars with masses 1.5 M , called Herbig Ae/Be
stars, cross the instability region during their evolution
to the main sequence. Although the crossing times are
Figure4. Prominent groups of variable stars in the HR-
diagram, based on Hipparcos data. The EC14026 group is now
BE
BE
etter known as sdB stars (seeSect. 3.2.13). b 2.5 F
2.0 3.0M
sun observations have the p otential to follow such p erio dic
RE
obs
tinuously in the exo eld for a suciently phenomena con 1.5 2.5M sun sun
V 588 Mon
ver full light cycles. large sample of Miras o V 589 Mon 2.0M HR 5999 sun log L/L 1.0 HD 104237 HD 35929 V 351 Ori NGC 6823 BL50
3.1.8. QSOs NGC 6823 HP 57 1.5M HD 142666 sun 0.5 V 346 Ori NGC 6383 4
IC 348 H254
knowledge of photometric variations of QSOs over Our IP Per
4.2 4.1 4.0 3.9 3.8 3.7
short time scales (i.e. less than a day) is not only ham- log T
eff
p ered by a lack of data but also by the fact that high fre-
quency variations have so small amplitudes that they are
Figure 5. HR diagram including the 13 known PMS pulsators
often lost in the observational noise. corot observations
and the PMS evolutionary tracks for 1.5, 2.0, 2.5 and 3.0 M
in the exoplanet search elds ought to provide time series
(D'Antona & Mazzitel li, 1994)
of several well sampled (t 15 min, S/N ' 40 100)
QSO photometric lightcurves which will lead to the iden-
very short (e.g. only 80 000 years for a 4 M star), several
ti cation of sp ecial or fundamental time scales for QSO
Herbig Ae/Be stars are lo cated in the classical instability
variability or at least a measure of the variabilitypower
strip. PMS stars di er from MS stars of same mass and
at short p erio ds. This pseudo-imaging has the p otential
temp erature mostly in their inner structure, whereas their
to provide information on the QSO inner core structure
envelop es are quite similar to those of their more evolved
on scales (typically, less than one lightday) much smaller
counterparts, the classical Scuti stars (Marconi & Palla,
than those currently accessible with mo dern VLBI tech-
1998).
niques (typically, of the order of several tens of parsec). In-
Recentinvestigations (Montalban et al. 2003) indicate formation on time evolution and stability of the accretion
a strong dep endence of the PMS evolutionary tracks on disk should also become accessible. It would be ideal to
the treatment of convection. In addition to the known tallic star which is di erent to that of stars exp eriencing
driven pulsation, solar typ e oscillation could be also ex- accretion of planets, but with an initial solar like metal-
cited due to the presence of a strong convectiveenvelop e licity. For example, the di erences of the squared sound
in lowmassPMS.From the seismological analysis of these sp eed for b oth stars can b e as high as 6.5 % (Fig. 6). The
oscillations, one can constrain stellar evolutionary mo dels rst results concerning the diagnostic p otential of oscilla-
for those stars, in a similar manner as is presently done tion frequencies in these stars are encouraging.
for PMS stars with Scuti typ e pulsation (Pinheiro et al.
2003, and references therein).
3.2.3. Eclipsing binaries
3.2.2. Central stars of planetary systems
Various typ es of pulsating stars are known to b e comp o-
nents of eclipsing binaries e.g. Cep, RR Lyr or Cepheids
Central stars of planetary systems are claimed to b e over-
(Szatmary K., 1990). Other very interesting ob jects are
abundant in metals (e.g. Santos et al. 2001) with presently
detached or semi-detached systems, like AI Her, MM Cas,
two explanations. First, the protostellar gas is metal-rich
AB and RZ Cas, and more (Lamp ens & Bon 2000, Mkr-
and so is the star. The high density of heavy elements,
tichian et al. 2002). The virtue of such binaries is the p os-
compared to stars without planets, increase the probabil-
ity of planetisimal formation, and thus of planet forma-
tion. The second explanation assumes that the system is
formed from gas with solar metallicity, but planets accrete
onto the stars, enhancing thus the metallicity of the latter.
Figure7. Pulsation amplitude modulation during primary
eclipse
sibility to determine precisely their mass, radius and e ec-
tive temp erature and the p otential of mo de identi cation
during the primary eclipse, using the transiting compan-
ion as a spatial lter (see Fig. 7). Furthermore, a precise
estimate for the accretion rate and mass transfer could b e
obtained.
Figure6. Relative density, pressure, temperature and square
sound speed di erences for two 1.1 M stel lar models. One
3.2.4. Cepheids
Fe
is homogeneous with an initial =0:18, the other has an
H
Fe
initial = 0:00 and an accreted mass of 0:5M of so-
Jup The opacity-driven main sequence pulsators for which as-
H
lar like material assuming microscopic di usion. The 's are
teroseismology has very recently implied considerable progress
T T
hom
(accr +dif f )
. de nedinanalogy to, e.g., T which is for
in understanding of stellar structure are the Cephei stars
T
hom
(Aerts et al. 2003). These ob jects can be used to tackle
many op en problems in astrophysics, such as angular mo-
These two scenarios can b e tested by comparing oscil- mentum transp ort, convectivecoreoversho oting and even
lation frequencies of stellar mo dels with the same external the chemical evolution of galaxies. Due to the sparse eigen-
parameters but with di erent histories: with and without mo de sp ectra of Cephei stars it is imp ortant to detect as
accretion and/or di usion. Preliminary investigations in- many pulsational signals in their light curves as p ossible,
dicate an internal structure of a homogeneous sup erme- a task for which corot is p erfectly suited.
3.2.5. Be{stars b ecause it would add very strong additional constraints
on the Cepheid mo deling. These mo des have not yet b een
Be stars are main-sequence or slightly evolved, usually
detected, since the ground based observations are proba-
rapidly rotating stars, surrounded by an equatorially con-
bly a ected by spurious variations related to the instru-
centrated envelop e (disk) fed by discrete mass-loss events
mentation and observing conditions. corot will b e able
caused byyet unkown mechanisms. In the H-R diagram,
to detect also very small variations due to, e.g., p ossible
early Be stars are lo cated at the lower b order of the insta-
nonradial mo des, which have been probably detected in
bilitydomainofthe Cephei stars, while mid and late Be
rst overtone mo de Cepheids from line pro le variations
stars are mixed with SPB stars. Short p erio ds have b een
(Kovtyukh et al. 2003). Several known Cepheids and yel-
commonly detected in lightcurves and sp ectral line pro le
low sup ergiant stars fall in the sky areas of interest for
variations are generally attributed to nonradial pulsation.
corot.
Acombination of high rotation and b eating of pulsation
mo des having closely spaced frequencies are considered as
3.2.7. HgMn stars
a p ossible explanation for discontinuous mass loss events;
stellar activity of magnetic origin could b e also involved.
HgMn stars are known to b e not variable, at least at the
COROT will o er the opp ortunity to detect new pulsation
current level of detection. However, according to recent
p erio ds, esp ecially b eating p erio ds, and to b etter under-
calculations, pulsation could exist in these stars due to
stand how the disk is b eeing generated.
iron accumulation in the outer envelop e (Fig. 8) where this
element is the main contributor to the Rosseland opacity.
HgMn stars are among the b est lab oratories to study dif-
fusion pro cesses and corot o ers an exceptional opp or-
tunitytocheck some of the theoretical mo dels concerning
particle transp ort in stars.
3.2.8. High{Amplitude Scuti stars
In the Scuti domain, there is a rough sub division be-
tween radial, mostly monop erio dic high{amplitude ob jects
(HADS) and mostly nonradial, multip erio dic low-ampli-
tude ob jects. However, Walraven et al. (1992) found the
Figure8.Radiation accel leration and gravitational settling re-
sults in strati cation of elements (iron, in the given case, from
Alecian & LeBlanc 2000)
3.2.6. Cepheids
Strange pulsation mo des were predicted for Cepheids and
other sup ergiant stars near the instability strip (Buchler
et al. 2001). The mo des are high order radial overtones
and have a very small amplitude. They could app ear in
di erent ways: a) as single mo de pulsations with peri-
ods typically 1/4 to 1/5 that of the fundamental mo de
(this would o ccur outside the instability strip, on b oth
sides); b) as double mo de pulsations with incommensu-
rate frequencies (most likely near the edges of the insta-
Figure 9. Observed( lled dots) frequency ratios among HADS
stars. Numbers indicate stars in the MACHO catalogue. Verti-
bility strip); c) as phase lo cked pulsation similar to that
cal lines indicate the theoretical ratio between fundamental (F)
of bump cepheids (with resonance 4:1 or 5:1). The detec-
and overtone (1O, rst; 2O, second) radial modes.
tion of this typ e of pulsation would be very imp ortant
HADS star AI Vel to b e multip erio dic (fundamental and
0.0
rst three radial overtones) and they also susp ect a non-
guez (1996) analyzed
radial mo de. Later, Garrido & Ro dr 0.5 some time{series of HADS stars and detected indications
1.0
for other radial and nonradial mo des in SX Phe and DY
eg. Arentoft et al. (2001) found evidence for amplitude P 1.5
V
variation and nonradial mo des for V1162 Ori. Therefore,
M
phenomenology of HADS stars b ecomes similar to
the 2.0
low{amplitude Scuti stars. The case of V974 Oph (Poretti
2.5
2003) corrob orates this trend, as this star shows a domi-
tmodewithavery large amplitude and a number of
nan 3.0 nonradial mo des. 3.5 -0.03 0.00 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24
(b -) y
vide an immediate identi cation of the high{
HADS pro 0
amplitude mo des with the radial ones, providing thus the
Figure10. M versus (b y ) diagram for the non-variable
V 0
density of the star as an imp ortant physical parameter.
(open circles) and pulsating ( l led circles) Bootis stars from
As shown in Fig. 9, the frequency ratios among HADS
Paunzen et al. (2002). The borders of the classical instability
stars have di erentvalues (suggesting a nonradial nature)
strip (dotted lines) aretakenfrom Breger (1995). The observed
and are quite di erent from the canonical F/O1=0.77 and
borders for the Bootis stars areindicatedas lled lines.
F/O2=0.62 values for radial mo des. The results obtained
by large{scale pro jects (see Poretti 2001) demonstrate that
HADS variables are commonly found and hence are promis-
3.2.10. Rapidly oscillating Ap stars
ing targets for the additional program using the Exoplanet
Rapidly oscillating Ap (roAp) stars are chemically p ecu-
CCDs of corot.
liar hydrogen core burning stars of ab out two solar masses
with a global magnetic eld and which pulsate with few
3.2.9. Bootis stars
minutes up to ab out 25 minutes in radial and nonradial p{
mo des. roAp stars havecontributed much to the advances
of asteroseismology and have b een sub ject of manyinter-
In general, chemical p eculiarity inhibits Scuti typ e pul-
national conferences during the last 15 years. A fascinat-
sation but for the group of Bo otis stars it is just the op-
ing asp ect of roAp star asteroseismology is the p otential
p osite. That small group comprises late B- to early F-typ e,
to derive information on the global stellar magnetic eld
Population I stars which are metal weak (particularly the
geometry what was shown, e.g., for 10 Aql (Bigot & Weiss,
iron group elements), but with the clear exception of C,
2000), a roAp corot target candidate.
N, O and S (Paunzen et al. 2003). Only a maximum of
About3%ofA0toA5{typ e stars are chemically p ecu-
ab out 2% of all ob jects in the relevant sp ectral domain
liar, and even less of the co oler A{typ e stars (Vogt et al.
are b elieved to b e Bo otis typ e stars. This is a small frac-
1998). Within this group of co ol CP2 stars (in the more
tion, but with thousands of stars observed by corot and
precise terminology of Preston, 1974), the fraction of roAp
up to 100 000 and more stars by eddington and kepler,
stars is high. Hence, we estimate that ab out 1% of the
we can exp ect a substantial improvement of the statistics
co ol A to earlyF{typ e stars may b e rapidly oscillating,
for Bo otis stars.
which op ens another rich source for asteroseimology in the
corot exoplanetary eld. Unfortunately, due to the short
pulsation p erio d which is comparable to the standard in-
Di usion in interaction with accretion probably is the
tegration time for windows in the exo eld, candidate roAp
main source of the Bo otis phenomenon (e.g. Kamp &
stars havetobeidenti ed in advance and selected for one
Paunzen 2002). Turcotte et al. (2000) found little direct
of the few tens windows in the exo eld which allow for a
pulsational excitation from Fe-p eak elements (see Sec. 3.2.7),
32 sec integration time.
but e ects due to settling of helium along with the en-
hancementofhydrogen are imp ortant. Paunzen et al. (2002)
analyzed the pulsational characteristics of the group of
3.2.11. Am { stars
Bo otis stars (Fig. 10) and found that a) at least 70% of
all Bo otis typ es stars inside the classical instabilitystrip Some Am stars have b een observed to oscillate with fre-
pulsate; b) only a maximum of two stars may pulsate in quencies ranging from 0.1 mHz to 0.21 mHz and with os-
the fundamental mo de but there is a high p ercentage with cillation constants, Q, ranging from 0.028 to 0.034, which
Q< 0.020 d (high overtone mo des); and c) the instability are typical for Scuti stars cohabitating the same param-
strip of the Bo otis stars at the ZAMS is 25 mmag more eter space in the HR-diagram (Kurtz, 1989; Martinez et
blue in (b y ) than that of the Scuti stars. al., 1999; Zhiping, 2000; Joshi et al., 2002). But according 0
to standard theory microscopic di usion of helium should ual mo de? How do the characteristics of the oscillations
inhibit oscillations induced by the mechanism what is change up to the giant branch?
corrob orated by the slow rotation of Am stars (less than With many mo des having p erio ds of several hours to
1
50 km s ) whereas the Scuti stars rotate faster. The dif- days and low amplitudes it is very dicult to answer these
ferent behavior is interpreted in terms of rotational in- questions with ground-based observations. The relative
duced mixing. high photometric amplitude (100{400 mag) of some of
these mo des and the long p erio ds make G/K Giants ideal
Turcotte et al. (2000) found that low radial mo des
targets for the exoplanet eld of corot.
of pulsation can become stable for evolved stars. A new
mo del of the internal structure of Am stars, where dif-
fusion o ccurs in a partially mixed zone, will b e develop ed
3.2.13. Subluminous dwarf B-type stars
and shall b e constrained with asteroseismic measurements
Pulsating sub dwarf B (sdB) stars (sometimes also called
from corot.
EC 14026 { stars, see Fig. 4) have b een discovered in 1996
and identi ed as extended horizontal branch stars which
3.2.12. K { Giants
are He-core burning with an extremely thin H-richenve-
lop e. Their life time is ab out 100 Myr, they remain hot
Precise radial velo city studies have established that K gi-
ant stars are a new class of pulsating stars with p erio ds
of 2{10 days (Hatzes & Co chran 1994). Figure 11 shows
suchvariations for Arcturus with at least 4 di erentperi-
100 12-19 Jun 1992 0
-100
48786 48788 48790 48792
100 P = 2.1 d 8-14 Mar 1996 0
-100
Radial Velocity (m/s) 50152 50154 50156 50158
100 P=6.5 d 26 Apr-2 May 1996 0
-100
50200 50202 50204 50206
JD-2400000
Figure11.RVmeasurements for the K Giant star Arcturus ob-
tained at McDonald Observatory.
Figure 12. Pulsating subdwarf B stars with p-modes (short pe-
riod, redcircles) and g-modes (long period, blue triangles), de-
ods which later were extended to 10 pulsation mo des with
tected in a sample of 205 sdB stars.
p erio ds of 2{10 days equally spaced in frequency (Mer-
line 1997). Photometry of UMa (Buzasi et al. 2000) also
showed that many mo des can exist in K giants.
(22 000 to 40 000 K, Fig. 12) during all the evolution and
The rst rm discovery of solar-like oscillations in a
presumably reach the white dwarf (WD) track without
giant star were rep orted by Frandsen et al. (2002) for
exp eriencing the AGB phase. sdB's should form WD's
the G7iii star Hya. At least nine acoustic mo des were
with lower than average masses ( 0.5 solar masses) and
detected in accurate radial-velo city measurements. These
it seems that ab out 1% of the WD's are formed in this
mo des have periods in the range of 2{6 hours and am-
way. Because of their role in the UV excess seen in gi-
plitudes b elow 2 m/s. The p otential of space photometry
ant elliptical galaxies and the p ossibility to use this excess
is illustrated with data obtained for a K4 iii star with
as an age indicator there is a rising cosmological interest
the Fine Guidance Sensor of the Hubble Space Telescop e
in these stars. However, their structure and evolution are
(Zwintz et al. 2000, VGS 18 in their Fig. 4).
still p o orly understo o d: the formation pro cess, physics of
the He burning convective core, and there are controver- There are several basic questions regarding G/K gi-
sies concerning their evolutionary paths. Currently ab out ant oscillations that remain unanswered: What is the full
30 multip erio dic, radial and nonradial p-mo de pulsators oscillation sp ectrum? What is the lifetime of an individ-
are known. With the discovery in 2001 of another typ e of
sdB's which are pulsating with longer p erio ds in g-mo des,
the signi cance of this part of the HR{diagram for aster-
oseismology increased considerably.
3.2.14. White Dwarfs
Ab out 97% of the stars in our galaxy end their evolu-
tion as white dwarfs. WD's do keep the memory of all the
physical pro cesses which o ccurred during the prior evolu-
tion, explaining the interest in their internal structure and
the co oling sequence, which is another promising age in-
dicator. However, its current use for the determination of
the age of the galactic disk or stellar clusters has to wait
until the internal structure of the white dwarfs is b etter
Figure13. Attempt to determine the instability strip of Dor
understo o d.
stars (ful l vertical lines). The cool border of the Scuti insta-
There are presently two main uncertainties in the age
bility strip determinedfrom observations is marked by a dashed
line. Circles: candidate Dor stars; asterisks: de nitely pulsat-
determined from mo dels of co oling white dwarfs: one comes
ing Dor stars; dots: multiperiodical ly pulsating stars which
from the description of the C/O core crystallisation phase
probably are Dor stars, but have to becon rmed as members
and the other from the determination of the hydrogen
of this group. The two asterisks left of the proposed Dor insta-
mass fraction in the DA white dwarfs. This latter quantity
bility strip indicate two binaries (HD 209295 and HD 221866)
could b e, in principle, deduced from the asteroseismolog-
with colors possibly in uenced by the companion which might
ical analysis of their multimo de nonradial g -mo de oscilla-
be even the pulsating component.
tions. A number of low amplitude oscillation mo des can b e
exp ected to b e detectable by corot adding signi cantly
to the p otential of asteroseismology.
4. And eddington?
While it is well established that most variable white
dwarfs exhibit long term amplitude variations, nothing
Thanks to the larger ap erture of the 4 parallel telescop es,
is known ab out the relevant time scales. Such amplitude
which also will provide color information for eachof the
variations may be due to the natural lifetime of the os-
targets, eddington will push the magnitude limits well
cillation mo des linked to the excitation mechanisms, or
beyond those of corot.Astheeddington instrumenta-
to nonlinear mo de interactions, or to pulsation-convection
tion is the same for asteroseismology and exoplanet search
interaction.
the de nition of an additional program is di erenttothat
for corot.However, all what has b een discussed as addi-
3.2.15. Borders of instability strips
tional science p otential for corot is also relevant for the
science goals of eddington (Favata et al. 2000).
The hot and co ol b order of the instability strip are deter-
mined for classical pulsators by several imp ortantastro-
More (some tens) fainter QSO's will come into reach
physical parameters, like Y, Z, excitation and convection.
of the instrument, but also long-integration imaging, p os-
These b orders are not yet well de ned for classical pul-
sible for the rst time with eddington, in combination
sators, like Scuti and Bo otis stars (Fig. 10), and even
with a very stable p oint spread function will allowtoin-
more so for rapidly oscillating Ap stars, for which, in ad-
vestigate the surface brightness of the very outer parts of
dition, a global magnetic eld is imp ortant. The situation
galaxies with unprecedented accuracy.About once every
is even worse for the Dor stars (Fig. 13, from Handler &
30 days of op eration complete fully-sampled light curves
Shobbro ok 2002).
of sup ernovae will b e obtained, starting from the pre-nova
The exoplanet CCDs will provide a large sample of
phase, which also would b e a novum in astrophysics! The
such pulsating stars covering the entire temp erature and
low brightness limit of eddington will allow to detect the
luminosity range and thus allow to improve signi cantly
brighter slowly moving Kuip er b elt ob jects and also aster-
the theoretical background for mo delling pulsation. The
oids. All of these go o dies { and some more { are describ ed
exp ected improvement in the detection of small amplitude
in the Assessment Study Rep ort (Favata et al. 2000) and
variations will also improve considerably on the separation
in these pro ceedings.
of otherwise similar stars which are pulsating, resp ectively
non{variable. This will allow to determine the various in-
Acknowledgements
The following authors wanttoacknowledge receipt of funding:
stability areas in the HR{diagram and provide further in-
AH (DLR 50OW 0204); TL (APART-grant); EP, WW, KZ
formation on yet p o orly understo o d or mo delled physical
(BM:BWK, FWF P14984)
pro cesses, likeconvection and excitation.
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