Download stars - KIAS

Precise spectroscopy and
asteroseismology of Algol-type and
roAp stars
Mkrtichian D.
ARCSEC, Sejong Univ., Korea/ Odessa Nat. Univ., Ukraine
In collaboration with:
A. Hatzes, H. Lehmann & A.Gamarova (TLS, Germany)
E. Rodriguez
(IAA, Spain)
E. Olson
(Univ. of Illinois, USA)
S.-L. Kim
(KAO, Korea)
C. Kim
(Chonbuk Uni., Korea)
A. Kusakin
(GAISH, Russia/Kazakhstan)
A. Kanaan
(Brasil)
Solar and stellar seismology:
what is practical difference
in the observations?
We can not yet optically resolve
the discs of distant main sequence stars!
• For the case of the Sun it is possible to measure the
intensity or Doppler shifts signals from selected parts of
solar disc (~”) i.e. measure the spatial information about
NRP (Spatial filters - Hill (1978), Christensen-Dalsgaard
& Gough (1982)
• For slowly rotating stars information is disk-averaged.
The range of detectable modes
in Sun :
l,m<1000
in stars:
l,m<4
The basic problem of observational asteroseismology that should be solved
is:
NRP mode – detection and
identification problem
All existing mode-identification methods for stars are based on
information about the contributions from different parts of optically
unresolved stellar disk extracted somehow from the disk-integrated light,
line-profile, or radial velocity variations.
The power of each of method for NRP mode identification is determined
by how precisely it can select these spatial contributions in practice.
“Star as a Sun”
observations are possible?
In my talk (on Algols and roAp stars) I will show
that:
• using pecularities inherent to different types of
pulsating stars it is possible to gain 2-D (l,m)
and 3-D spatial information about NRPs
• using NRPs it is possible to gain new
information about of physics, evolution, rotation
and atmospheric structure of these stars
Pulsations in Algols:
new methods of studies
Definition of a new group of oEA (oscillating EA) stars:
"The A-F spectral type
mass-accreting
Main Seguence pulsating stars
in a semi-detached Algol-type
systems» (Mkrtichian et al. 2002)
Remarkable peculiarity of oEA stars is co-existence of pulsation
and accretion!
Structure of gas flow and envelope in Algol-type binary
2D hydrodynamic simulations
Secondary
Primary (oEA)
K 3 IV
Gas stream
F1V
Gas stream-star
impact zone
Orbital Separation Unites
Circumstellar envelope
List of oEA stars
(results of 3 years of cooperation)
________________________________________________________________________________________
System
Sp
P (orb)
P (puls)
(days)
(min)
Reference
_________________________________________________________________________________________
Y Cam
A7+K1 IV
3.3055
95.7, 78.8
Kim et al. (2002a)
AB Cas
A3+K0IV
1.3669
83.93
Rodriguez et al. (1998)
RZ Cas
A3V+KOIV
1.1953
22.43, 25.44
Mkrtichian et al. (2002)
R CMA
F1V +G2-K2IV
3.864
68.5
Mkrtichian & Gamarova (2000)
AS Eri
A3V+K0III
2.6642
24.39, 23.01, 23.34
Mkrtichian et al. (2003, in press)
TW Dra A6+K0IV
3.922
80
Kusakin et al. (2001)
RX Hya A8+K5
2.2816
74.26
Kim et al. (2002b)
AB Per
7.1602
282.02
Kim et al. (2002c)
A5+G9IV
Instability strip for oEA stars:
Being in the past ZAMS stars that
have started their evolution in a
detached binary system, and later
have undergone fast evolution during
a rapid mass-transfer phase when
the former massive and rapidly
evolving component overfills it’s
Roche lobe and mass-transfer has
started.
SMT
RMT
MS
Dotted line: An example of evol. of
1.8 M(sun) mass-accreting component in
binary system
During the Rapid Mass Transfer/
Accretion phase evolutions the
gainers move to the domain of
higher mass and luminosity stars
and sit in the H-R diagram closer to
the ZAMS.
oEA stars are not the normal MS Delta Scuti
stars:
Basic differences of oEA stars
with respect to the Delta Scuti-type stars and
Delta Scuti stars in detached binaries:
• Previous
of rapid
• They are
thermal
• They are
evolutionary life: they are remnants
mass-transfer phase in close binaries.
still accreting the mass and are in
inbalance.
evolving along (!!) the MS
In this sense they are attractive for asteroseismic
studies.
Eclipse NRP mode-identification
spatial structure of NRPs:
l,m quantum numbers
l=6, m=0
modes
l,m =6,3
modes
l,m =6,6
modes
Eclipses provides the unique possibility for mode –
identification using the transit effects on NRP amplitudes
and phases.
l=4, m=0
oEA star
The geometry of the eclipse is
accurately known from the
solution of photometric light curve
and RVs.
The secondary star acts as geometric
periodic spatial filter (PSF) with a timely
variable shape that produces specific
pulsation amplitude and phase changes of
NRP depending on the mode’s l,m,n
quantum numbers and the geometry of
eclipse in binary system .
Main adjustable parameters in
modelling are mode quantum
numbers, l,m, and the surface
pulsation amplitude of the mode
The Modeling of eclipse effects:
•
Fig.1. Theoretical modeling for system RZ Cas. The extracted pure pulsational light curve was
simulated for prograde NRP mode l=3, m=-3. Above the graph the different phases of eclipse are shown.
Mode identification in the oEA star AB Cas:
modelling
Considered pulsation characteristics:
•
Gain factor is the ratio of the observed pulsation amplitudes during the eclipse of
pulsating component to the amplitude outside the eclipse:
t max  t 0
Ppul s
tmax - the time moment of observed maximum;
t0
- predicted by the pulsation ephemeris time
of maximum;
Ppuls - the observed pulsation period.
•
Pulsational phase shift :
 
g l ,m 
( Aecli pse ) l ,m
Aout
l=1, m=+1 mode
Mode identification in the oEA star AB Cas:
observations
Important Result from NRP modelling and
observations:
• Amplitude and phase variability during eclipse
phases are the sensitive indicators of the
spatial structure (l,m) of modes and helps to
discriminate the NRP modes.
• Amplitudes of some modes (l,m,n) are
photometrically invisible or have small
amplitudes in out-of eclipse orbital phases.
During Min I they may increase their apparent
pulsation amplitudes (the gain factor).
• The ascending branches of Min I are affected by
effects of gas-stream and envelope attenuation on
NRPs. By these reasons the descending branches of
Min I are the more optimal for comparison with
the results of NRP modelling.
What new tools does asteroseismology
bring to the studies of binaries?
Spin Rotation of components and asynchronicity problem:
Theory predicts synchronization of components in binary
systems, but there are many asynchronized Algols
2-D hydrodynamic simulations,
Nazarenko &Mkrtichian (in prep)
Mass-loss
Mass accretion
Mass-loss
Asynchronism in Algols is due to angular momentum transfer during
high accretion transfer-rate episodes?
and/or it is apparent and caused by accretion stream that spin
up of the surface layers (differential rotation)?
Hypothesis I.
Asynchronous Algols are young Algols (t<106 years) that
recently finished RMT phase and just settled on the slow
mass-transfer phase
.
They are not yet synchronized .
Problems:
• We can not estimate from observations ages of
Algols (as it is possible for normal stars using
evolutionary tracks)
Hypothesis II:
The asynchronism that is determined on <v sin i> is
overestimated and is due equator-on visibility of all Algols
and strong accretion driven differential rotation of very
surface layers or is effect of the rapidly-rotating optically
thick quasi-stationary accretion disk or equatorial bulge
Problems:
• We could not measure spectroscopically differential rotation or
internal rotation of prime component, the spectral lines are the
superposition of atmospheric and envelope absorption and
emission lines
Hypothesis III.
Asynchronism is due to rapid mass-transfer
episodes during SMT phase and high rates of
angular momentum transfer.
Problems:
• We have not good photometric or spectroscopic methods to
prove the existence of rapid mass-transfer episodes
• Analysis of the orbital period O-C variations
is not good tool for study of angular momentum transfer .
For check the theories of asynchronicity and
evolution
we need new methods in:
• Accurate mass accretion rate determinations and
observational detection of high-mass
transfer/accretion episodes forced by the
magnetic activity of secondary companion.
• Accurate determination of rotation periods of
components
• Detection and measurement of accretion driven
differential rotation of surface layers
• Ages of Algols on a slow mass-transfer phase
New asteroseismic tools for studies of Algols
(Mkrtichian et al., 2002)
• Rotational NRP mode splitting is an accurate tool for
asynchronicity measurements (see AS Eri)
• Difference in NRP mode splitting of low and high-degree
modes gives the information about the accretion driven
strong differential rotation of surface layers
(to be detected)
• Accretion driven pulsation period changes may be used for
determination of mean accretion rate (to be detected).
• The high-rate accretion episodes result in a puls. period
jumps and/or rapid modal pattern changes ?
(is probably detected)
Pulsation period changes with increasing the
mass of star:
•
•
•
•
P=Q M-0.5 R 1.5
R ~M α α≈ 0.55 for ZAMS stars M>M(sun)
P~QM 1.5α- 0.5
dP/dt 1/P=dQ/Q + 0.325 dM/dt 1/M
for idealized case the pulsation period should increase
with a increasing the mass of star (what is expected
for MS stars)
But response of mass-accreting star is non-linear
and for given (M,R) depends on mass-accretion rate
(Ulrich &Burger 1976, Kippenhahn &Meyer-Hofmeister (1977)
Expected accretion driven pulsation period
changes (based on evol. binary models of De Greve 1993)
M-R relations for gainers in evolutionary models
of 3.0M+1.8M and 3.0 M+ 2.7M Algol
primaries, evol. models of De Greve, (1993).
Accretion driven mass (upper panel) changes in a 3 M
+2.7 M evolutionary model of De Greve (1993) and
calculated pulsation period changes of the fundamental
radial mode (bottom panel) (Mkrtichian, 2003 submitted)
The accretion-driven pulsation period changes dP/dt expected in
gainers will be (Mkrtichian et al. 2002):
•
•
•
•
Negative (10-5 -10-7) at end of Fast Mass Transfer phase
Negative (10-7 –9)
at beginning of Slow MT phase
Close to zero
at middle of Slow MT phase
Positive
at late stages of Slow MT phase
Theoretical dM/dt - dP(puls) / dt
relations could be found for slow
mass-transfer phase for gainers using
the evol. models. Accretion rate
estimations could be found from
pulsation period (O-C) variability
dP(puls)/dt vs dM/dt for slow masstransfer phase for 2.7M gainer
Episodes of high-mass tranfer rates
due to magnetic activity of secondary
late-type star could be dectected as
pulsation period jumps or changes of
modal pattern in the pulsations.
Asteroseismic Rotation Period and Asynchronicity
determination in AS Eri
Discovered as a rapid pulsator (P=24 min) in 1999 yr (Gamarova Mkrtichian & Kusakin, 2000)
2000 yr multisite Euro-Asian (Spain -Kazakhstan-Korea) campaign (PI, Mkrtichian)
Pulsation light curves (extracted)
P(orb) = 2.664152 days
AS Eri pulsation spectrum
v sin i  35 km/s ; i= 82.98
R=1. 57 R 
F(asyn)  1.175 (spectroscopic)
F(asyn) =1. 185 (asteroseismic)
P(rot)  2.27 d (spectroscopic)
P(rot) = 2.2477 d (asteroseismic)
f1 = 59.0311±0.0001 c/d
(l, m, n) = (2 or 1, -2 or -1, 5)
Mode identification:
f2 = 62.5633
c/d
(l, m, n) = (2, -2, 6)
l=2,m=0 and m=-2
f3 = 61.6732
c/d
(l, m, n) = (2, 0, 6)
f2-f3=0.8898  2F(asyn)P(orb)= 2P(rot) = -mP(rot)
mode splitting
Accuracy of seismic estimations of rotation,
asynchronism and accretion:
• The seismic estimations of rotation periods and asynchronism of
primary oEA star are as accurate as the measured pulsation periods.
For a several month long duration observations the accuracy is of order
values of 10 –5 .
• This means that we have a very precise tool for the study of
of rotation periods in the primary components of Algols and hence
asynchronicity and a precise estimation of mass-accretion rates.
1997-2001 yr studies of key object RZ Cas system (A3V+K0IV)
Discovery of pulsations - Ohshima et al. 1998, 2001
P=22.4 min, semi-amplitude 0.01mag
Multi-site campaigns:
• 1997/1998 (ph.) Japan (PI, Ohshima)
• 1999 (ph.)
USA, Spain, Ukraine, Georgia,
Kazakhstan, Korea (PI, E. Rodriguez)
• 2000 (ph.)
Spain, Ukraine, Uzbekistan, Kazakhstan,
Korea (PI, D. Mkrtichian)
• 2001 (spe.+ ph.) USA, Spain, Germany, Ukraine,
Kazakhstan, Korea (PI, D. Mkrtichian)
The 2-D hydrodynamic simulations of mass-transfer
in RZ Cas eclipsing binary
(Nazarenko & Mkrtichian, in prep.)
Mass transfer rate
~ 10 –8 M  /yr
 = 1.1
K0 IV
A3 V
 = 0.9
Orbital separation units
Hydrodinamic code,
based on
Large Particles
Method
(Belotserkovsky &
Davidov (1982)
RZ Cas: pulsation story
• 1997/1998 – monoperiodic oscillations 64.19 c/d, semi-amplitude ~0.01 mag
• 1998/1999 –
same as for 1997/1998
• 1999-Oct. 24, 2000
same as for 1997/1998/1999
First, exciting results of 2001 multisite photometric
campaign :
a) the amplitude of pulsations decreases in order values(!) ( from 0.01 to
0.001 mag !!)
b) the pulsation spectrum become multiperiodic(!) with at least 3 excited
periods including the older one
c) the amplitudes of all modes become variable (!) .
RZ Cas NRP modal spectrum and its variability
1997-2000
2001
Low amplitude multi-periodic oscillations
Monoperiodic
Oscillations
Δm=8-9 mmag
No signal above 0.6 mmag
2001 photometric campaign:
The DFT amplitude spectrum of combined
Mt. Laguna and Sierra Nevada Obs.
photometry: The low amplitude (<0.0015
mag) peaks between f= 30 - 64.2 c/d (48 -22
min) are well visible.
1999 Sierra-Nevada Obs. Photometry
(Rodriguez et al, in prep.)
The reasons of a such drastic changes in RZ Cas ?
Facts:
• Delta Scuti stars do not show such a abrupt amplitude
and modal pattern changes
• Main difference between oEA and DSCT stars
is a mass-accretion process
• The KOIV rapidly-rotating component of RZ Cas was
found to be a flare star (two 0.6 mag flares registered
in 1996 and 2001).
Magnetic activity?
L1 point
K0 IV
A3 V
I
Are there active regions on
the surface of cool star?
Orbital separation units
Rapid pulsator
and accretor
The reasons of a such drastic changes in RZ Cas ?
The rapid mass-accretion hypothesis:
• Did the characteristics of the pulsations in the primary result
from a rapid mass-transfer/accretion episode in 2000/2001,
possibly resulting from magnetic activity on the secondary,
rapidly rotating K0 IV companion?
• ...... Other reasons?
Independent observational check of the increase of the masstransfer rate in Nov. 2000/2001:
•
It should be a strong, transient circumstellar envelope around the
primary in 2001 (spectral and photometric manifestations?)!
•
It should be jump or change (increase) in the orbital
period (O-C diagram)!
Yes!!!
O-C diagram of RZ Cas show period jump
on +1 sec since Nov.-Dec. 2000,
K. Tikkanen (private com. , March 2003)
http://www.student.oulu.fi/~ktikkane/AST/RZCAS.html
Nov./ Dec. 2000
O-C (min)
Orbital cycles
RZ Cas: (Seismic) Life Story in 2000/2001:
November-December 2000:
1. The abrupt mass-transfer episode occur due to the magnetic activity
secondary K0 IV star.
2. The prime component have accreted at least 50% of transferred mass
(and change its internal resonance properties?)
3. Due to angular momentum transfer and loss during the episode the
orbital period of binary system become longer on 1 sec!!!!
December 2000-September 2001:
1. The internal resonance properties of A3 V component were changed?
2. The mode selection mechanism started to search for new combinations
of pulsation modes close to the resonance?!
3. The dominant mono-periodic oscillation was shifted on multi-periodic
and the amplitude of dominant mode drops to 0.001 mag
2001 year spectrocopic timeseries observations of RZ Cas
(Lehmann & Mkrtichian (A&A, submitted)
N=970 spectra (R=40,000, S/N~200 ) in 12 nights
in October at the 2.0m tel. of TLS Tautenburg.
The complete orbital period was covered 3 times,
time sampling ~200 sec. Accuracy of of RVs 110
m/s for primary, 1.5 km/sec for secondary:
New accurate RV orbit and masses of
components were obtained :
m1sin3 i=1.85 +/- 0.02 M
m2sin3 i=0.656 +/- 0.006 M
m1 / m2 =2.814 +/- 0.009
Anomalous rotation effect (SchlezingerRossiter-McLaughlin effect) in primary
component
The anomalous Schlesinger-Rossiter effect can be explained
by different limb-darkening at phases (0.9 - 1.0) and
(1.0-1.1) of Min I that is due to attenuation effect of a
asymmetric circumstellar envelope.
Cross- section of gas-density
distribution (in 2D hydrodynamic
simulations) through primaries
environment at orbital phase 0.75.
The integrated total number of
particles seen from phase 0.25 is
about 10-20 times lower than the
number seen from phase 0.75.
During Sept./Oct. 2001 orbital modulation of pulsational
RV amplitudes of both modes was detected
Phase diagram for the amplitudes of f1=64.19c/d (solid line)
and f2=56.6 c/d modes.
The pulsation amplitudes of both modes are maximal at orbital
phase ~ 1.1, and goes to minimum at phases 0.6-0.9
-
 = 1.1
K0 IV
A3 V
 = 0.9
Orbital separation units
Gas stream and assymetric envelope as
a spatial filter for NRP in RZ Cas
• Large amplitude of puls. RV orbital modulation
reflect the sectoral l=|m| nature of NRPs having
the maximal amplitudes in equatorial zone.
• Shape a amplitude modulation gives a
information about density variations of gasenvelope.
• It is max. at phases 0.9 and min. at 0.1
both in agreement with 2-D hydrodynamic
simulations.
Conclusions on Algols
• The Min I eclipse effects on NRP amplitudes and phases
helps us find unique and accurate solutions for (l,m) mode
identification. This makes oEA stars very attractive objects for
asteroseismic studies of their internal structure.
• Multisite and space-based studies of NRP modal spectra
should provide precise measurement of the rotation periods of
stars, accretion driven differential rotation, and asynchronism
at essentially higher accuracy levels then was done so far.
• Long-term study of pulsation period changes in oEA stars give
us understanding of Algols ages and the possibility of accurate
asteroseismic determination of mass-accretion rates.
• oEA stars are the unique laboratories of stellar
physics and asteroseismology.
Precise spectroscopy of roAp
stars.
Some well known facts about roAp stars:
•
•
•
•
Strong chemical anomalies (up to +4.0 dex), spotty
distributions of elements (see maps in Hatzes, 1990)
Strong (~kilogauss) dipole magnetic fields
Excited high-overtone low amplitude (<5 mmag), low degree
dipole(?) p-modes (5-15 min), pulsation axis
coincides with magnetic axis (Kurtz, 1990)
Oblique pulsator model
(Kurtz & Shibahashi, 1986)
Periodic spatial filter (PSF) concept for NRP mode
detection (2-D concept)
(Mkrtichian 1994, Solar Physics, 152, p.275)
Si abundance spots
Cr pseudo-mask
“roAp star as a Sun”
observations:
Si pseudo-mask
Modelling of sensitivity functions of PSFs
associated with the surface abundance spots
(Mkrtichian, Hatzes & Panchuk 2000)
Outside spot
Inside spot
NRP Sensitivity function for Cr spots
with different overabundances
Intensity of Cr lines
Oblique pulsator model (HR 3831) with a
polar abundance spots
• RV amplitude and phase modulation for
NRPs depends from geometry , coordinates
and overabundances in spots
• NRP (l,m=3-10) mode detection using
spectral lines of overabundant elements 10100 times more sensitive than photometric
detection
• The PSF technique is capable of the
detection of l =3-10 NRP modes in roAp.
Project “Asteroseismology with spatial resolution”
Start: 1997
PIs: A. Hatzes (Mc Donald Obs.) & Mkrtichian (Odessa Univ.).
First results of project:
Used telescopes: 2.7m and 2.1m McDonald Obs.(USA), 6.0m tel. SAO(Russia)
Stars observed with iodine absorption cell : γEqu, HR 1217…..
Detected of RV pulsations in roAp stars: 33 Lib, HD134214, HD 122970, 10Aql
Results on HR1217 and 33 Lib should be given now in details:
HR1217- “broad-band” RV data:
Dec. 1997-Febr. 1998 (2.7m tel. Mc Donald Obs., USA)
First results on HR1217:
• Detection of two new excited equidistant modes, total number of
detected modes N=9
“Enigmatic”
mode
New modes
HR 1217 echelle-diagram
of p-mode spectrum
“Enigmatic” mode
Echelle-diagram of l=1-4 p-mode
spectrum of the model L
from Gautschy et al. (1998)
Rotational amplitude and phase modulation
Conclusions on HR1217:
•
•
•
•
9 frequencies in the p-mode spectrum: 8 are equidistant
f7 frequency is probably relate to l=4 mode
Amplitude modulation of f2 and f4 mode is in agreement with
oblique pulsator model.
Phase modulation is in disagreement with simple oblique
pulsator model
roAp star 33Lib: Detection of atmospheric
standing waves and acoustic node
Method of vertical atmospheric sounding: RV Doppler shift
measurements of lines formed at different depths
Transformation scale EW-log τ
We use line-by-line analysis of Doppler shifts
Nd III line RVs
The histogram of pulsation phases
Two oppositely pulsating layers:
Week Nd II lines: log tau < -4.0
Strong NdIII lines: log tau >> -4.5
Schematic of acoustic cross-section
Reflecting layer in upper atmosphere?
Formation of Nd III lines
Formation of week lines
Lower atmosphere
33 Lib: Acoustic cross-section of lower atmosphere
Standing + running wave components?
Conclusions: on 33 Lib
•
•
•
This is a first application of acoustic cross-section
methods (2-D +3 rd Dimension). The time coverage is
short (2 hours), accuracy of phases is not high
We found the oppositely pulsating layers in lower and
upper atmosphere and acoustic node above log tau> -4.5.
NdIII lines are formed at superficial layers that
support the prediction from diffusion theory