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 resolvethe 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<1000in 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 determinedby 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!
F1VK 3 IV
Orbital Separation Unites
Primary (oEA)Secondary
Gas stream Circumstellar envelopeGas stream-star impact zone
2D hydrodynamic simulations
Structure of gas flow and envelope in Algol-type binary
List of oEA stars
________________________________________________________________________________________
System Sp P (orb) P (puls) Reference
(days) (min) _________________________________________________________________________________________
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 A5+G9IV 7.1602 282.02 Kim et al. (2002c)
(results of 3 years of cooperation)
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.
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.
-
RMT
SMT
MS
Dotted line: An example of evol. of 1.8 M(sun) mass-accreting component in binary system
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 evolutionary life: they are remnants of rapid mass-transfer phase in close binaries.
• They are still accreting the mass and are in thermal inbalance.• They are evolving along (!!) the MS
In this sense they are attractive for asteroseismic studies.
Eclipse NRP mode-identificationspatial structure of NRPs:
l,m quantum numbers
l=6, m=0 modes
l,m =6,3 l,m =6,6 modes modes
Eclipses provides the unique possibility for mode –identification using the transit effects on NRP amplitudes and phases.
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
l=4, m=0 oEA star
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: • Pulsational phase shift :
tmax - the time moment of observed maximum;t0 - predicted by the pulsation ephemeris time of maximum;Ppuls - the observed pulsation period.
out
mleclipseml A
Ag ,
,)(
pulsPtt 0max
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
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)?
Mass-loss
Mass-loss
2-D hydrodynamic simulations,Nazarenko &Mkrtichian (in prep)
Mass accretion
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-linearand 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 3.0+1.8 and 3.0 + 2.7 Algol primaries, evol. models of De Greve, (1993).
Accretion driven mass (upper panel) changes in a 3 evolutionary model of De Greve (1993) and calculated pulsation period changes of the fundamental radial mode (bottom panel) (Mkrtichian, 2003 submitted)
• 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
dP(puls)/dt vs dM/dt for slow mass-transfer phase for 2.7 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.
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
The accretion-driven pulsation period changes dP/dt expected in gainers will be (Mkrtichian et al. 2002):
Asteroseismic Rotation Period and Asynchronicity determination in AS Eri
2000 yr multisite Euro-Asian (Spain -Kazakhstan-Korea) campaign (PI, Mkrtichian)
Discovered as a rapid pulsator (P=24 min) in 1999 yr (Gamarova Mkrtichian & Kusakin, 2000)
Pulsation light curves (extracted)
AS Eri pulsation spectrum
f1 = 59.0311±0.0001 c/d (l, m, n) = (2 or 1, -2 or -1, 5)
f2 = 62.5633 c/d (l, m, n) = (2, -2, 6)
f3 = 61.6732 c/d (l, m, n) = (2, 0, 6)
f2-f3=0.8898 2F(asyn)P(orb)= 2P(rot) = -mP(rot)
P(orb) = 2.664152 days
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)
Mode identification:l=2,m=0 and m=-2 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)
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)
Discovery of pulsations - Ohshima et al. 1998, 2001
P=22.4 min, semi-amplitude 0.01mag
The 2-D hydrodynamic simulations of mass-transfer in RZ Cas eclipsing binary
(Nazarenko & Mkrtichian, in prep.)
K0 IV A3 V
= 0.9
= 1.1
Orbital separation units
Mass transfer rate ~ 10 –8 /yr
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
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.
1997-2000 2001
MonoperiodicOscillationsΔm=8-9 mmag
No signal above 0.6 mmag
1999 Sierra-Nevada Obs. Photometry(Rodriguez et al, in prep.)
Low amplitude multi-periodic oscillations
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?
K0 IV A3 V
Orbital separation units
L1 point
I
Are there active regions onthe surface of cool star?
Rapid pulsatorand 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 mass-transfer 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 time-series 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 (Schlezinger-Rossiter-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
K0 IV A3 V
= 0.9
= 1.1
Orbital separation units
-
Gas stream and assymetric envelope asa 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 gas-envelope.
• 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)
“roAp star as a Sun” observations:
Si abundance spots
Si pseudo-mask
Cr pseudo-mask
Modelling of sensitivity functions of PSFsassociated with the surface abundance spots
(Mkrtichian, Hatzes & Panchuk 2000)
NRP Sensitivity function for Cr spotswith different overabundances
Intensity of Cr lines
Inside spot
Outside spot
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 10-100 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
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:
PIs: A. Hatzes (Mc Donald Obs.) & Mkrtichian (Odessa Univ.).
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
New modes
“Enigmatic” mode
HR 1217 echelle-diagram of p-mode spectrum
“Enigmatic” mode
Echelle-diagram of l=1-4 p-modespectrum 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?
Lower atmosphere
Formation of Nd III lines
Formation of week lines
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
