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Department of Physics, University of Rijeka, Croatia · 2014. 4. 21. · white dwarf) as the most...
1
DETERMINATION OF DUST PARAMETERS AROUND SYMBIOTIC MIRAS Tomislav Jurkić, Dubravka Kotnik-Karuza Department of Physics, University of Rijeka, Croatia Observational data and methods of analysis ( ) 2 2 1 1 / i e y y y v v η ∝ − + Symbiotic Mira Other name Spectral class A v d (kpc) P (days) ο Cet HD 14386 MWC 35 Mira M2-7III Karovska et al. 1997, ApJ, 482, L175 Whitelock et al. 1988, IAUC 103, p. 47 0.01 0.12 331-333 Whitelock et al. 2000, MNRAS, 319, 728 Kholopov et al, 1985, GCVS, Nauka Perryman et al. 1997, Hipp.Cat. ESA SP-1200 KM Vel Hen 2-34 Mira M Acker et al. 1988, A&AS, 73, 325 Whitelock et al. 1988, IAUC 103, p. 47 3.2 9.0 370 Feast et al. 1983a, MNRAS, 203, 373 V835 Cen Hen 2-106 Mira M ≥ M5 Schulte-Ladbeck 1988, A&A, 189, 97 3.9 9.4 400 Feast et al. 1983a, MNRAS, 203, 373 V366 Car Hen 2-38 Mira M6 Muerset & Schmid 1999, A&AS, 137, 473 2.8 3.8 433 Feast et al. 1983a, MNRAS, 203, 373 RR Tel Hen 3-1811 Mira M6/M5 Allen 1980, MNRAS, 192, 521 Muerset & Schmid 1999, A&AS, 137, 473 0.3 2.5 387 Feast et al. 1983b, MNRAS, 202, 951 Penston et al. 1983, MNRAS, 202, 833 Kotnik-Karuza et al. 2006, A&A, 452, 503 R Aqr HD 222800 MWC 400 Mira M7, M8, M4 Kenyon, 1986 Muerset & Schmid 1999, A&AS, 137, 473 Whitelock et al. 2000, MNRAS, 319, 728 0.01 0.27 383-386 Whitelock et al. 2000, MNRAS, 319, 728 Kholopov et al, 1985, GCVS, Nauka Perryman et al. 1997, Hipp.Cat. ESA SP-1200 RX Pup HD 69190 Hen 3-138 Mira M5.5/M5 Allen 1980, MNRAS, 192, 521 Muerset & Schmid 1999, A&AS, 137, 473 2.0 3.0 580 Whitelock et al. 1983, MNRAS, 203, 363 Feast et al. 1977, MNRAS, 179, 499 Mikolajewska et al. 1999, MNRAS, 205, 190 Results (1) fitted by the model (2) fixed parameter defined by its spectral class and from Feast (1983a) (3) fixed parameter defined by its spectral class and from Feast (1983b) (4) fixed parameter defined by its spectral class and from Whitelock (2000) and Danchi (1994) (5) fixed parameter defined by its spectral class and from Mikolajewska (1999) ** Minimum obscuration 1980, 1986 and 1994; Obscuration events I and II T Mira Mira temperature T dust dust sublimation temperature a max maximum grain size τ v visual optical depth A K extinction at K mass-loss rate v e terminal wind velocity RR Tel Six other southern symbiotic Miras ISO SWS spectra + SAAO JHKL during minimum obsucration (phase difference: 0.49 - 188 days) 1997/05/15 Two-colour diagram of RR Tel with theoretical models M Results References Danchi W. C. et al. 1994, AJ, 107, 1469 Ivezic Z., Elitzur M. 1997, MNRAS 287, 799 Ivezic Z. et al. 1999, User Manual for DUSTY, University of Kentucky Internal Report, www.pa.uky.edu/ ~ moshe/dusty Jurkić T., Kotnik-Karuza D. 2007, Balt.Astr., 16, 76 Kotnik-Karuza D., Jurkić T., Friedjung M. 2007, Balt.Astr., 16, 98 Kotnik-Karuza D. et al. 2006, A&A, 452, 503 Mathis J.S., Rumpl W., Nordsieck K.H. 1977, ApJ, 217, 425 Mikolajewska J. 1999, in Optical and Infrared Spectroscopy of Circumstellar Matter, eds. E. W. Guenther, B. Stecklum, S. Klose, ASP Conf. Ser. 188, 291 Ossenkopf V., Henning, Th., Mathis J.S. 1992, A&A, 261, 567 Whitelock P. A. 2002, in Symbiotic stars probing stellar evolution, eds. R. L. M. Corradi, J. Mikolajewska, T. J. Mahoney, ASP Conf. Ser. 303, 41 0.0 0.5 1.0 1.5 2.0 1.0 1.5 2.0 2.5 3.0 1100 K; 0.15 µ m black body 0.3 0.6 0.8 1500 K 2000 K 2500 K JHKL from Whitelock et al, MNRAS 2000, 319, 728 1976-1980 1980-1984 1984-1988 1988-1992 1992-1996 1996-2000 ο C et J-K K-L 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 650 K; 0.15 µ m black body 0.6 1.1 1.7 2.2 2.8 1500 K 2000 K 2500 K JHKL from Whitelock et al, MNRAS 2000, 319, 728 1975-1977; obsc. event 1980-1985; minimum obsc. 1985-1992; minimum obsc. 1992-1998; minimum obsc. R Aqr J-K K-L 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 700 K; 1.70-2.00 µ m 900 K; 1.10 µ m black body RX Pup 1.0 0.7 0.5 0.2 0.9 1500 K 2000 K 2500 K 0.7 0.6 0.2 JHKL from Mikolajewska et al, MNRAS 1999, 305, 190 J-K K-L 1975-1980 Minimum obsc. 1980, 1986, 1994 Obsc. events I and II Obsc. event III (1994-1998) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 950 K 0.15 µ m 2.9 black body 2.2 1.6 1.1 0.2 1500 K 2000 K 2500 K JHKL from Feast et al, MNRAS, 1983, 203, 373 1973-1974; obsc. event 1978-1980; obsc. event 1980-1982; obsc. event 1982-1983; minimum obsc. V835 C en J-K K-L 2000 4000 6000 8000 10000 12000 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 -4.0 Years ο C et magnitudes J.D. - 2440000 1976 1980 1984 1988 1992 1996 2000 J H K L JHKL from Whitelock et al, MNRAS 2000, 319, 728 2000 4000 6000 8000 10000 12000 4 3 2 1 0 -1 -2 -3 I J H K L JHKL from Whitelock et al, MNRAS 2000, 319, 728 R Aqr magnitudes J.D. - 2440000 1972 1976 1980 1984 1988 1992 1996 2000 Years 2000 4000 6000 8000 10000 12000 8 7 6 5 4 3 2 1 0 III II I JHKL from Mikolajewska et al, MNRAS 1999, 305, 190 RX Pup magnitudes J.D. - 2440000 1972 1976 1980 1984 1988 1992 1996 2000 J H K L Years 2000 3000 4000 5000 10 9 8 7 6 5 4 3 2 JHKL from Feast et al, MNRAS, 1983, 203, 373 Years V835 C en magnitudes J.D. - 2440000 1974 1976 1978 1980 1982 J H K L 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 950 K; 1.8 µ m 1100 K; 4 µ m 700 K BB black body JHKL from Kotnik-Karuza et al, A&A, 2006, 452, 503 1500 K 2000 K 2500 K K-L J-K RR T e l Minimum obsc. Obsc. events I, II and III 2000 4000 6000 8000 10000 12000 9 8 7 6 5 4 3 2 JHKL from Kotnik-Karuza et al, A&A, 2006, 452, 503 J H K L RR T e l magnitudes J.D. - 2440000 1975 1980 1985 1990 1995 2000 III II I Years Abstract JHKL light curves corrected for Mira pulsations and two-colour diagrams with theoretical models and extinctions at K (A K ) of 4 chosen southern symbiotic Miras observations theoretical model observations theoretical model JHKL lightcurves of RR Tel corrected for Mira pulsations In search for possible common properties of circumstellar dust around symbi- otic Miras, we have modelled six other symbiotic Miras beside RR Tel using only the long-term JHKL observations. To fully remove possible degeneracy among the dust models, near- and mid-infrared spectra are needed. Four out of six sample stars have ISO infrared spectra taken in the same period of time as the near-IR ones, so we plan to reconstruct infrared SEDs using both long-term JHKL observations and ISO spectra. Models which use only JHKL observations but represent a good starting point for further numerical modeling of fully reconstructed SEDs are given below. We have also tested the difference between single shell model with the cen- tral heating source (Mira) and the model with two central sources (Mira and white dwarf) as the most extreme possibility. No significant differences were found. All objects except RX Pup and RR Tel show similar dust properties – rather small grain size of up to 0.15 microns and sublimation tempera- ture of around 1000 K, except in R Aqr where sublimation temperature is much lower. The latter agrees with interferometric studies of Danchi (1994). The only differences among symbiotic Miras come from different optical depth and mass loss rate, suggesting different amounts of dust present around Mira. Obscuration events in all Miras except in RX Pup and RR Tel show no change in sublimation tem- perature and grain size. These obscurations can be fully understood as a result of the change in dust optical depth. RX Pup is rather compli- cated object where both dust grain size and sublimation temperature change, while RR Tel shows grain growth and increase of sublimation temperature during the obscuration. Conclusion Single-shell dust model around cold Mira with realistic grain sizes, chemical composition and radiatively driven winds can successfully explain near-infrared spectra of symbiotic binaries with Mira component. Obscuration events can be explained by dust condensed around inner dust shell radius originating from the Mira component. Modeling of RR Tel in the near- and mid-infrared gives evidence that obscuration events show change not only in dust optical depth, but also increase maximum grain size from 1.8 µm to 4.0 µm, which also affects dust sublimation temperature. JHKL magnitudes of seven southern symbiotic stars, ο Cet, KM Vel, V835 Cen, V366 Car, RR Tel, R Aqr and RX Pup, as ob- served for at least 10 years at different epochs at SAAO, have been analyzed. The magnitudes have been corrected for inter- stellar reddening using visual extinctions A v given in Table 1. In order to show only the long-term variations, the light curves were corrected for Mira pulsations by an approximate procedure. RR Tel, R Aqr and RX Pup give evidence of marked obscuration events. We reconstructed spectral energy distribution (SED) for RR Tel at different time intervals when both JHKL magnitudes and ISO short wavelength spectra were available. Reconstructed SEDs cover the near- and mid-infrared spectral region in the periods with and without obscuration. Modeling of circumstellar properties of the dust shell around the cool Mira component was carried out by use of the numerical code DUSTY , assuming spherical geometry , with Mira in the centre of the spherical dust shell. We used black body input ra- diation from the Mira at a temperature between 2300 K and 2600 K depending on spectral class and in agreement with data from the literature. Contrary to other Miras of the sample, ο Cet stellar temperature was obtained by modeling because of its high spectral class variability. As the Mira component has strong stellar winds, envelope expansion is driven by radiation pres- sure on the dust grains. In the analytical approximation for radiatively driven winds the number density η is a function of the scaled radius y = r/r in , of the initial v i and final wind v e velocity, while r in is the inner dust shell radius (sublimation radius): In the applied MRN dust grain size distribution , ( a min < a < a max ), the minimum grain size of a = 0.005 µm and q = 3.5 are taken as fixed input parameters, while maximum grain size a max is a free parameter determined by modeling. Dust composition typical for Mira stars containing 100% warm silicates has been assumed. Outer dust shell radius is fixed to 20 r in , contrary to the inner dust shell radius r in which is obtained by fitting, together with the dust sublimation temperature T dust as a linked parameter. () q na a − ∝ 1997/11/19 Obscuration Parameters RR Tel T Mira (K) 2500 (4) T dust (K) 950 ± 100 Minimum a max (µm) 1.8 ± 0.4 Obscuration τ v 1.9 – 4.2 A K 0.23 – 0.52 M (10 -6 M Sun /yr) 4.6 – 9.7 v e (km/s) 17 – 21 T Mira (K) 2500 T dust (K) 1200 ± 100 Obscuration a max (µm) 4.0 ± 0.5 Events τ v 4.6 – 9.5 A K 0.56 – 1.16 M (10 -6 M Sun /yr) 9.7 – 17.3 v e (km/s) 12 – 16 RR Tel shows three distinct obscuration intervals. Single shell model with realistic physical dust properties can reproduce very well both long-term JHKL observations and ISO infrared spectra during periods with and without obscuration. According to our results, obscuration events can be explained by the change in dust optical depth, accompanied by an increase in dust grain size and sublimation temperature. Higher dust optical depth means larger amount of dust present around Mira and hence, a higher mass loss. Increase in dust grain size during the obscuration can be caused by grain growth as the mass loss and optical depth is increased. Sublimation temperature also rises as the larger grains can sustain higher temperatures. Symbiotic Miras Obscuration Parameters ο Cet KM Vel V835 Cen V366 Car R Aqr RX Pup** T Mira (K) 2600 (1) 2500 (2) 2500 (2) 2500 (2) 2300 (4) 2300 (5) T dust (K) 1100 ± 100 1150 ± 100 1000 ± 100 650 ± 20 700 ± 100 Minimum a max (µm) 0.15 ± 0.05 0.10 ± 0.05 0.15 ± 0.05 0.15 ± 0.02 1.70 ±0.20 τ v 0.4 – 3.4 8.3 – 12.6 1.3 – 5.4 0.55 – 8.80 3.2 – 5.3 A K 0.05 – 0.40 0.9 – 1.4 0.2 – 0.7 0.07 – 1.07 0.4 – 0.6 (10 -6 M Sun /yr) 2.7 – 3.3 9 – 14 5 – 10 0.7 – 10 9 – 14 v e (km/s) 14 – 16 11 – 12 17 – 21 8 – 10 14 – 16 T Mira (K) 2500 2500 2300 2300 T dust (K) 950 ± 50 1000 ± 100 650 ± 100 900 ± 50 Obscuration a max (µm) 0.15 ± 0.05 0.15 ± 0.05 0.15 ± 0.05 1.10 ± 0.05 event(s) τ v 11.9 – 20.3 15.3 10.9 – 21.4 5.6 – 7.5 A K 1.3 – 2.3 1.9 1.3 – 2.6 0.6 – 0.8 (10 -6 M Sun /yr) 10 – 15 11 12 – 23 10 – 13 v e (km/s) 9 – 11 11 6 – 7 17 – 19 T Mira (K) 2300 Obscuration T dust (K) 700 ±50 event a max (µm) 2.00 ± 0.20 1994 – τ v 2.5 – 5.1 1998 A K 0.3 – 0.6 (10 -6 M Sun /yr) 7 – 14 v e (km/s) 14 – 17 M M M M M We determined circumstellar dust properties and modeled inner dust re- gions around the cool Mira component in a sample of symbiotic Miras which showed obscuration events during the observed time intervals. The published JHKL magnitudes of o Ceti, RX Pup, KM Vel, V366 Car, V835 Cen, RR Tel, R Aqr have been collected. In order to follow the evolution of their colours in time, their light curves were corrected by removing the Mira pulsations. Using the simultaneously available JHKL magnitudes and ISO spectra for different time intervals we obtained SEDs for RR Tel which cover the near- and mid-infrared spectral region in the periods with and without obscuration. Assuming spherical temperature distribution of the dust in the close neigh- bourhood around the Mira component, the DUSTY code was used to solve the radiative transfer in order to determine the dust temperatureand its properties in each particular case. Dust temperature, grain size, density distribution and optical depth during intervals with and without obscuration have been obtained. Special attention was given to model circumstellar envelope around RR Tel.
Transcript of Department of Physics, University of Rijeka, Croatia · 2014. 4. 21. · white dwarf) as the most...
DETERMINATION OF DUST PARAMETERS AROUND SYMBIOTIC MIRAS
Tomislav Jurkić, Dubravka Kotnik-KaruzaDepartment of Physics, University of Rijeka, Croatia
Observational data and methods of analysis
( )22
11 /i e
yy y v v
η ∝− +
Symbiotic Mira
Other name Spectral class Av d (kpc)
P (days)
ο Cet HD 14386 MWC 35
Mira M2-7III Karovska et al. 1997, ApJ, 482, L175 Whitelock et al. 1988, IAUC 103, p. 47 0.01 0.12 331-333 Whitelock et al. 2000, MNRAS, 319, 728
Kholopov et al, 1985, GCVS, Nauka Perryman et al. 1997, Hipp.Cat. ESA SP-1200
KM Vel Hen 2-34 Mira M Acker et al. 1988, A&AS, 73, 325 Whitelock et al. 1988, IAUC 103, p. 47 3.2 9.0 370 Feast et al. 1983a, MNRAS, 203, 373
V835 Cen Hen 2-106 Mira M ≥ M5 Schulte-Ladbeck 1988, A&A, 189, 97 3.9 9.4 400 Feast et al. 1983a, MNRAS, 203, 373
V366 Car Hen 2-38 Mira M6 Muerset & Schmid 1999, A&AS, 137, 473 2.8 3.8 433 Feast et al. 1983a, MNRAS, 203, 373
RR Tel Hen 3-1811 Mira M6/M5 Allen 1980, MNRAS, 192, 521 Muerset & Schmid 1999, A&AS, 137, 473 0.3 2.5 387 Feast et al. 1983b, MNRAS, 202, 951
Penston et al. 1983, MNRAS, 202, 833 Kotnik-Karuza et al. 2006, A&A, 452, 503
R Aqr HD 222800 MWC 400
Mira M7, M8, M4
Kenyon, 1986 Muerset & Schmid 1999, A&AS, 137, 473 Whitelock et al. 2000, MNRAS, 319, 728
0.01 0.27 383-386 Whitelock et al. 2000, MNRAS, 319, 728 Kholopov et al, 1985, GCVS, Nauka Perryman et al. 1997, Hipp.Cat. ESA SP-1200
RX Pup HD 69190 Hen 3-138
Mira M5.5/M5
Allen 1980, MNRAS, 192, 521 Muerset & Schmid 1999, A&AS, 137, 473 2.0 3.0 580 Whitelock et al. 1983, MNRAS, 203, 363
Feast et al. 1977, MNRAS, 179, 499 Mikolajewska et al. 1999, MNRAS, 205, 190
Results
(1) fitted by the model (2) fixed parameter defined by its spectral class and from Feast (1983a) (3) fixed parameter defined by its spectral class and from Feast (1983b) (4) fixed parameter defined by its spectral class and from Whitelock (2000) and Danchi (1994) (5) fixed parameter defined by its spectral class and from Mikolajewska (1999)
** Minimum obscuration 1980, 1986 and 1994; Obscuration events I and II
TMira Mira temperatureTdust dust sublimation temperatureamax maximum grain sizeτv visual optical depthAK extinction at K mass-loss rateve terminal wind velocity
RR Tel
Six other southern symbiotic Miras
ISO SWS spectra + SAAO JHKL during minimum obsucration(phase difference: 0.49 - 188 days)
1997/05/15
Two-colour diagram of RR Tel with theoretical models
M
Results
ReferencesDanchi W. C. et al. 1994, AJ, 107, 1469Ivezic Z., Elitzur M. 1997, MNRAS 287, 799 Ivezic Z. et al. 1999, User Manual for DUSTY, University of Kentucky Internal Report, www.pa.uky.edu/ ~ moshe/dustyJurkić T., Kotnik-Karuza D. 2007, Balt.Astr., 16, 76Kotnik-Karuza D., Jurkić T., Friedjung M. 2007, Balt.Astr., 16, 98Kotnik-Karuza D. et al. 2006, A&A, 452, 503Mathis J.S., Rumpl W., Nordsieck K.H. 1977, ApJ, 217, 425 Mikolajewska J. 1999, in Optical and Infrared Spectroscopy of Circumstellar Matter, eds. E. W. Guenther, B. Stecklum, S. Klose, ASP Conf. Ser. 188, 291Ossenkopf V., Henning, Th., Mathis J.S. 1992, A&A, 261, 567Whitelock P. A. 2002, in Symbiotic stars probing stellar evolution, eds. R. L. M. Corradi, J. Mikolajewska, T. J. Mahoney, ASP Conf. Ser. 303, 41
0.0 0.5 1.0 1.5 2.01.0
1.5
2.0
2.5
3.0
1100
K; 0.15
µm
black
body
0.3
0.6
0.8
1500 K
2000 K
2500 K
JHKL from Whitelock et al, MNRAS 2000, 319, 728
1976-1980 1980-1984 1984-1988 1988-1992 1992-1996 1996-2000
ο Cet
J-K
K-L
0.0 0.5 1.0 1.5 2.0 2.5 3.01.0
1.5
2.0
2.5
3.0
3.5
4.0
650 K
; 0.15
µm
black
body
0.6
1.1
1.7
2.2
2.81500 K
2000 K
2500 K
JHKL from Whitelock et al, MNRAS 2000, 319, 728
1975-1977; obsc. event 1980-1985; minimum obsc. 1985-1992; minimum obsc. 1992-1998; minimum obsc.
R Aqr
J-K
K-L
0.0 0.5 1.0 1.5 2.0 2.5 3.01.0
1.5
2.0
2.5
3.0
3.5
4.0
700 K; 1.
70-2.0
0 µm
900 K
; 1.10
µm
black
body
RX Pup
1.00.7
0.5
0.2
0.9
1500 K
2000 K
2500 K
0.70.6
0.2
JHKL from Mikolajewska et al, MNRAS 1999, 305, 190
J-K
K-L
1975-1980 Minimum obsc. 1980, 1986, 1994 Obsc. events I and II Obsc. event III (1994-1998)
0.0 0.5 1.0 1.5 2.0 2.5 3.01.0
1.5
2.0
2.5
3.0
3.5
4.0
950 K
0.1
5 µm2.9
black
body
2.2
1.61.1
0.2
1500 K
2000 K
2500 K
JHKL from Feast et al, MNRAS, 1983, 203, 373
1973-1974; obsc. event 1978-1980; obsc. event 1980-1982; obsc. event 1982-1983; minimum obsc.
V835 Cen
J-K
K-L
2000 4000 6000 8000 10000 120000.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0Years
ο Cet
mag
nitu
des
J.D. - 2440000
1976 1980 1984 1988 1992 1996 2000
J
H
K
L
JHKL from Whitelock et al, MNRAS 2000, 319, 728
2000 4000 6000 8000 10000 120004
3
2
1
0
-1
-2
-3
I
J
H
K
L
JHKL from Whitelock et al, MNRAS 2000, 319, 728
R Aqr
mag
nitu
des
J.D. - 2440000
1972 1976 1980 1984 1988 1992 1996 2000Years
2000 4000 6000 8000 10000 120008
7
6
5
4
3
2
1
0
IIIIII
JHKL from Mikolajewska et al, MNRAS 1999, 305, 190
RX Pup
mag
nitu
des
J.D. - 2440000
1972 1976 1980 1984 1988 1992 1996 2000
J
H
K
L
Years
2000 3000 4000 5000
10
9
8
7
6
5
4
3
2
JHKL from Feast et al, MNRAS, 1983, 203, 373
Years
V835 Cen
mag
nitu
des
J.D. - 2440000
1974 1976 1978 1980 1982
JHK
L
0.0 0.5 1.0 1.5 2.0 2.5 3.01.0
1.5
2.0
2.5
3.0
3.5
4.0
950 K; 1
.8 µm
1100
K; 4 µm70
0 K
BB
black
body
JHKL from Kotnik-Karuza et al, A&A, 2006, 452, 503
1500 K
2000 K
2500 K
K-L
J-K
RR Tel Minimum obsc. Obsc. events I, II and III
2000 4000 6000 8000 10000 12000
9
8
7
6
5
4
3
2
JHKL from Kotnik-Karuza et al, A&A, 2006, 452, 503
J
H
K
LRR Tel
mag
nitu
des
J.D. - 2440000
1975 1980 1985 1990 1995 2000
IIIIII
Years
Abstract
JHKL light curves corrected for Mira pulsations and two-colour diagrams with theoretical models and extinctions at K (AK) of 4 chosen southern symbiotic Miras
observationstheoretical model
observationstheoretical model
JHKL lightcurves of RR Tel corrected for Mira pulsations
In search for possible common properties of circumstellar dust around symbi-otic Miras, we have modelled six other symbiotic Miras beside RR Tel using only the long-term JHKL observations. To fully remove possible degeneracy among the dust models, near- and mid-infrared spectra are needed. Four out of six sample stars have ISO infrared spectra taken in the same period of time as the near-IR ones, so we plan to reconstruct infrared SEDs using both long-term JHKL observations and ISO spectra.
Models which use only JHKL observations but represent a good starting point for further numerical modeling of fully reconstructed SEDs are given below. We have also tested the difference between single shell model with the cen-tral heating source (Mira) and the model with two central sources (Mira and white dwarf) as the most extreme possibility. No significant differences were found.
All objects except RX Pup and RR Tel show similar dust properties – rather small grain size of up to 0.15 microns and sublimation tempera-ture of around 1000 K, except in R Aqr where sublimation temperature is much lower. The latter agrees with interferometric studies of Danchi (1994). The only differences among symbiotic Miras come from different optical depth and mass loss rate, suggesting different amounts of dust present around Mira. Obscuration events in all Miras except in RX Pup and RR Tel show no change in sublimation tem-perature and grain size. These obscurations can be fully understood as a result of the change in dust optical depth. RX Pup is rather compli-cated object where both dust grain size and sublimation temperature change, while RR Tel shows grain growth and increase of sublimationtemperature during the obscuration.
ConclusionSingle-shell dust model around cold Mira with realistic grain sizes, chemical composition and radiatively driven winds can successfully explain near-infrared spectra of symbiotic binaries with Mira component. Obscuration events can be explained by dust condensed around inner dust shell radius originating from the Mira component. Modeling of RR Tel in the near- and mid-infrared gives evidence that obscuration events show change not only in dust optical depth, but also increase maximum grain size from 1.8 µm to 4.0 µm, which also affects dust sublimation temperature.
JHKL magnitudes of seven southern symbiotic stars, ο Cet, KM Vel, V835 Cen, V366 Car, RR Tel, R Aqr and RX Pup, as ob-served for at least 10 years at different epochs at SAAO, have been analyzed. The magnitudes have been corrected for inter-stellar reddening using visual extinctions Av given in Table 1. In order to show only the long-term variations, the light curves were corrected for Mira pulsations by an approximate procedure. RR Tel, R Aqr and RX Pup give evidence of marked obscuration events. We reconstructed spectral energy distribution (SED) for RR Tel at different time intervals when both JHKL magnitudes and ISO short wavelength spectra were available. Reconstructed SEDs cover the near- and mid-infrared spectral region in the periods with and without obscuration.
Modeling of circumstellar properties of the dust shell around the cool Mira component was carried out by use of the numerical code DUSTY, assuming spherical geometry, with Mira in the centre of the spherical dust shell. We used black body input ra-diation from the Mira at a temperature between 2300 K and 2600 K depending on spectral class and in agreement with data from the literature. Contrary to other Miras of the sample, ο Cet stellar temperature was obtained by modeling because of its high spectral class variability. As the Mira component has strong stellar winds, envelope expansion is driven by radiation pres-sure on the dust grains. In the analytical approximation for radiatively driven winds the number density η is a function of the scaled radius y = r/rin, of the initial vi and final wind ve velocity, while rin is the inner dust shell radius (sublimation radius):
In the applied MRN dust grain size distribution , ( amin < a < amax ), the minimum grain size of a = 0.005 µm and q = 3.5 are taken as fixed input parameters, while maximum grain size amax is a free parameter determined by modeling. Dust composition typical for Mira stars containing 100% warm silicates has been assumed. Outer dust shell radius is fixed to 20 rin, contrary to the inner dust shell radius rin which is obtained by fitting, together with the dust sublimation temperature Tdust as a linked parameter.
( ) qn a a−∝
1997/11/19
Obscuration Parameters RR Tel
TMira (K) 2500(4)
Tdust (K) 950 ± 100 Minimum amax (µm) 1.8 ± 0.4
Obscuration τv 1.9 – 4.2 AK 0.23 – 0.52 M (10-6 MSun/yr) 4.6 – 9.7 ve (km/s) 17 – 21 TMira (K) 2500 Tdust (K) 1200 ± 100 Obscuration amax (µm) 4.0 ± 0.5
Events τv 4.6 – 9.5 AK 0.56 – 1.16 M (10-6 MSun/yr) 9.7 – 17.3 ve (km/s) 12 – 16
RR Tel shows three distinct obscuration intervals. Single shell model with realistic physical dust properties can reproduce very well both long-term JHKL observations and ISO infrared spectra during periods with and without obscuration.
According to our results, obscuration events can be explained by the change in dust optical depth, accompanied by an increase in dust grain size and sublimation temperature. Higher dust optical depth means larger amount of dust present around Mira and hence, a higher mass loss.
Increase in dust grain size during the obscuration can be caused by grain growth as the mass loss and optical depth is increased. Sublimation temperature also rises as the larger grains can sustain higher temperatures.
Symbiotic Miras Obscuration Parameters ο Cet KM Vel V835 Cen V366 Car R Aqr RX Pup**
TMira (K) 2600 (1) 2500 (2) 2500 (2) 2500 (2) 2300 (4) 2300 (5)
Tdust (K) 1100 ± 100 1150 ± 100 1000 ± 100 650 ± 20 700 ± 100 Minimum amax (µm) 0.15 ± 0.05 0.10 ± 0.05 0.15 ± 0.05 0.15 ± 0.02 1.70 ±0.20
τv 0.4 – 3.4 8.3 – 12.6 1.3 – 5.4 0.55 – 8.80 3.2 – 5.3 AK 0.05 – 0.40 0.9 – 1.4 0.2 – 0.7 0.07 – 1.07 0.4 – 0.6 (10-6 MSun/yr) 2.7 – 3.3 9 – 14 5 – 10 0.7 – 10 9 – 14 ve (km/s) 14 – 16 11 – 12 17 – 21 8 – 10 14 – 16 TMira (K) 2500 2500 2300 2300 Tdust (K) 950 ± 50 1000 ± 100 650 ± 100 900 ± 50 Obscuration amax (µm) 0.15 ± 0.05 0.15 ± 0.05 0.15 ± 0.05 1.10 ± 0.05
event(s) τv 11.9 – 20.3 15.3 10.9 – 21.4 5.6 – 7.5 AK 1.3 – 2.3 1.9 1.3 – 2.6 0.6 – 0.8 (10-6 MSun/yr) 10 – 15 11 12 – 23 10 – 13 ve (km/s) 9 – 11 11 6 – 7 17 – 19
TMira (K) 2300 Obscuration Tdust (K) 700 ±50
event amax (µm) 2.00 ± 0.20 1994 – τv 2.5 – 5.1 1998 AK 0.3 – 0.6
(10-6 MSun/yr) 7 – 14 ve (km/s)
14 – 17
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We determined circumstellar dust properties and modeled inner dust re-gions around the cool Mira component in a sample of symbiotic Miras which showed obscuration events during the observed time intervals. The published JHKL magnitudes of o Ceti, RX Pup, KM Vel, V366 Car, V835 Cen, RR Tel, R Aqr have been collected. In order to follow the evolution of their colours in time, their light curves were corrected by removing the Mira pulsations. Using the simultaneously available JHKL magnitudes and ISO spectra for different time intervals we obtained SEDs for RR Tel which cover the near- and mid-infrared spectral region in the periods with and without obscuration. Assuming spherical temperature distribution of the dust in the close neigh-bourhood around the Mira component, the DUSTY code was used to solve the radiative transfer in order to determine the dust temperatureand its properties in each particular case. Dust temperature, grain size, density distribution and optical depth during intervals with and without obscuration have been obtained. Special attention was given to model circumstellar envelope around RR Tel.
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