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Beryllium depletion in the solar atmosphere
CHINESE ASTRONOMY AND ASTROPHYSICS PERGAMON
Chinese Astronomy and Astrophysics 27 (2003) 1-3
B e r y l l i u m D e p l e t i o n in t h e Solar Atmosphere t * X I O N G D a - r u n 1,2
D E N G Li-cai 2
1purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 2National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 A b s t r a c t Using a non-local convection theory for chemically inhomogeneous stars, the beryllium depletion of the Sun is calculated. The results show that Be is slightly depleted(~5%) in the evolutionary model for the Sun. K e y words: Sun: abundances - - stars: abundances - - convection
Both Li and Be are destroyed at a modest temperature (2.5 and 3.5 x 106 K respectively for Li and Be) in stellar interior. Therefore, they are an ideal tracer of the extent of convective mixing in the stellar envelopes during their evolution. For exploring the structure of the solar convective overshooting zone we calculated the Li depletion of the solar model, and present a model of the solar non-local convective envelope, which contains both the depth of convective zone determined by helioseismic techniques and the observed Li abundance [1]. The Li abundance gives an upper limit of the extent of convective overshooting. As of now we still do not completely understand the mechanism of Li depletion. Various such mechanisms have been proposed, such as mass loss [2'3], microscopic diffusion[ 4'5] , wavedriven mixing[~'7], convective overshooting mixing[1'11'12] and so on. However, there is no single mechanism that can interpret all the observed characters of the Li and Be abundances of solar-type stars. It seems to be the case that several mechanisms of Li and Be depletion are at work in solar-type stars. The depletion mechanism is probably very different for low temperature stars (Te < 6000K) and for F stars in the Li gap (6300< Te <6850K). For low temperature stars, we think Li depletion results from overshooting mixing, whereas for F-type stars, their convective zones are too shallow to allow MS Li depletion. In order to examine the overshooting mixing mechanism of Li depletion, we calculated the Be depletion for a set of solar models using the same Code as in our last paper [1]. It will t Supported by National Natural Science Foundation Received 2002-11-08 * A translation of Acta Astron. Sin. Vol. 44, No. 1, pp. 1-4, 2003 0275-1062/03/S-see front m a t t e r © 2003 Elsevier Science B. V. All rights reserved. PII: S0275-1062(03)00002-X
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XIONG Da-run et al. / Chinese Astronomy and Astrophysics 27 (2003) 1-3
be a support for our theory of overshooting mixing, if the theoretical Be depletion matches the observed depletion. Otherwise, it will mean that there are other depletion mechanisms or factors, which have not been taken into account in our theory. The theoretical calculations are divided into the following three steps: 1) A series of solar evolutionary models is calculated using the Padova stellar evolutionary code [13]. 2) Along the evolutionary tracks mentioned above a set of solar envelope models is calculated using our non-local convection code. 3) The Be depletion of the evolutionary envelope model is calculated using the same non-local convection code as in our last paper [1]. All the evolutionary envelope models have the same grid division of mass. The surface boundary is set at optical depth r = 10 -2, and the bottom boundary is deep enough, at temperature around 5 x 106 K, for the theoretical calculation of Be depletion. The numerical results show that Be is only depleted by about 5% during the evolution of the Sun on the main sequence. There is still a large uncertainty in the abundance determination of Be. The Be abundance is sensitive to the stellar parameters (the effective temperature, gravity, rotation velocity) and to the atmosphere models used. The blending effect resulted from Mn I (3131.07/~), MnII (3131.15/~) and CH (3131.058/~) lines has also a marked influence on the Be abundance determination. The solar Be abundance A(Be) [A(Be)=logN(Be/H)+12] varies from 0.80 to 1.37 in the existing papers [14]. The differences among them can be as large as 0.57dex, or a factor of 3.7. The value derived by Boesgaard et al.[15] is 1.15dex, while the meteoritic abundance is 1.42. If the meteoritic abundance represents the initial solar Be abundance, then the Sun has had a slight Be depletion. Some people think that this difference is due to the incompleteness of the sources of opacity in the ultraviolet. Balachandran and Bell derived an empirical enhancement of a factor of 1.6 in the UV opacity [16]. If this enhancement is true, then the oxygen abundance derived from the OH lines in the IR and UV will agree and the Be abundance for the Sun will also be consistent with the meteoritic value. In other words, they suggested that Be is undepleted in the Sun. Apart from accurate determination of the solar Be abundance, it is also important, when evaluating the overshooting mixing mechanism of Li and Be depletion, to clarify the law of Be depletion during pre-main and main sequences. Unfortunately there is relatively little information on the Be abundance for solar-type stars. Hyades is the only cluster with extensive observations of Be abundance for F and G dwarfs [15]. It will be especially useful to determine more extensively and accurately the Be abundances of late dwarfs in open clusters with different ages.
XIONG Da-run et al. / Chinese Astronomy and Astrophysics 27 (2003) 1-3
References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Xiong D.R., Deng, L., Chinese Astron. Astrophys., 2001, 25, 412 Schramm D.N., Steigman G., Dearborn D.S.P., ApJ, 1990, 359, L55 Swenson F.J., Faulkner J., ApJ, 1992, 395, 654 Michaud G., ApJ, 1986, 302, 650 Richer J., Michaud G., ApJ, 1993, 416, 312 Garcia L6pez R.J., Spruit H.C., ApJ, 1991, 377,268 Montalban J., Schatzman E., A&A, 1996, 305, 513 Charbonneau P., Michaud G., ApJ, 1988, 334, 746 Zahn J.P., A&A, 1992, 265, 115 Chaboyer B., Demarque P., Pinsonneault M.H., ApJ, 1995, 441,865 Straus J.M., Blake J.B., Schramm D.N., ApJ, 1976, 204,481 Xiong D.R., Acta Astron. Sinica, 1991, 32, 333 Bressan A., Fagotto F., Bertelli G., A&AS, 1993, 100,647 King J.R., Deliyannis C.P., Moesgaard A.M., ApJ, 1997, 478, 778 Boesgaard A.M., King J.R., ApJ, 2002, 565, 587 Balachandran S., Bell R.A., Nature, 1998, 392, 791
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Chinese Astronomy and Astrophysics 27 (2003) 1-3
B e r y l l i u m D e p l e t i o n in t h e Solar Atmosphere t * X I O N G D a - r u n 1,2
D E N G Li-cai 2
1purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 2National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 A b s t r a c t Using a non-local convection theory for chemically inhomogeneous stars, the beryllium depletion of the Sun is calculated. The results show that Be is slightly depleted(~5%) in the evolutionary model for the Sun. K e y words: Sun: abundances - - stars: abundances - - convection
Both Li and Be are destroyed at a modest temperature (2.5 and 3.5 x 106 K respectively for Li and Be) in stellar interior. Therefore, they are an ideal tracer of the extent of convective mixing in the stellar envelopes during their evolution. For exploring the structure of the solar convective overshooting zone we calculated the Li depletion of the solar model, and present a model of the solar non-local convective envelope, which contains both the depth of convective zone determined by helioseismic techniques and the observed Li abundance [1]. The Li abundance gives an upper limit of the extent of convective overshooting. As of now we still do not completely understand the mechanism of Li depletion. Various such mechanisms have been proposed, such as mass loss [2'3], microscopic diffusion[ 4'5] , wavedriven mixing[~'7], convective overshooting mixing[1'11'12] and so on. However, there is no single mechanism that can interpret all the observed characters of the Li and Be abundances of solar-type stars. It seems to be the case that several mechanisms of Li and Be depletion are at work in solar-type stars. The depletion mechanism is probably very different for low temperature stars (Te < 6000K) and for F stars in the Li gap (6300< Te <6850K). For low temperature stars, we think Li depletion results from overshooting mixing, whereas for F-type stars, their convective zones are too shallow to allow MS Li depletion. In order to examine the overshooting mixing mechanism of Li depletion, we calculated the Be depletion for a set of solar models using the same Code as in our last paper [1]. It will t Supported by National Natural Science Foundation Received 2002-11-08 * A translation of Acta Astron. Sin. Vol. 44, No. 1, pp. 1-4, 2003 0275-1062/03/S-see front m a t t e r © 2003 Elsevier Science B. V. All rights reserved. PII: S0275-1062(03)00002-X
2
XIONG Da-run et al. / Chinese Astronomy and Astrophysics 27 (2003) 1-3
be a support for our theory of overshooting mixing, if the theoretical Be depletion matches the observed depletion. Otherwise, it will mean that there are other depletion mechanisms or factors, which have not been taken into account in our theory. The theoretical calculations are divided into the following three steps: 1) A series of solar evolutionary models is calculated using the Padova stellar evolutionary code [13]. 2) Along the evolutionary tracks mentioned above a set of solar envelope models is calculated using our non-local convection code. 3) The Be depletion of the evolutionary envelope model is calculated using the same non-local convection code as in our last paper [1]. All the evolutionary envelope models have the same grid division of mass. The surface boundary is set at optical depth r = 10 -2, and the bottom boundary is deep enough, at temperature around 5 x 106 K, for the theoretical calculation of Be depletion. The numerical results show that Be is only depleted by about 5% during the evolution of the Sun on the main sequence. There is still a large uncertainty in the abundance determination of Be. The Be abundance is sensitive to the stellar parameters (the effective temperature, gravity, rotation velocity) and to the atmosphere models used. The blending effect resulted from Mn I (3131.07/~), MnII (3131.15/~) and CH (3131.058/~) lines has also a marked influence on the Be abundance determination. The solar Be abundance A(Be) [A(Be)=logN(Be/H)+12] varies from 0.80 to 1.37 in the existing papers [14]. The differences among them can be as large as 0.57dex, or a factor of 3.7. The value derived by Boesgaard et al.[15] is 1.15dex, while the meteoritic abundance is 1.42. If the meteoritic abundance represents the initial solar Be abundance, then the Sun has had a slight Be depletion. Some people think that this difference is due to the incompleteness of the sources of opacity in the ultraviolet. Balachandran and Bell derived an empirical enhancement of a factor of 1.6 in the UV opacity [16]. If this enhancement is true, then the oxygen abundance derived from the OH lines in the IR and UV will agree and the Be abundance for the Sun will also be consistent with the meteoritic value. In other words, they suggested that Be is undepleted in the Sun. Apart from accurate determination of the solar Be abundance, it is also important, when evaluating the overshooting mixing mechanism of Li and Be depletion, to clarify the law of Be depletion during pre-main and main sequences. Unfortunately there is relatively little information on the Be abundance for solar-type stars. Hyades is the only cluster with extensive observations of Be abundance for F and G dwarfs [15]. It will be especially useful to determine more extensively and accurately the Be abundances of late dwarfs in open clusters with different ages.
XIONG Da-run et al. / Chinese Astronomy and Astrophysics 27 (2003) 1-3
References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Xiong D.R., Deng, L., Chinese Astron. Astrophys., 2001, 25, 412 Schramm D.N., Steigman G., Dearborn D.S.P., ApJ, 1990, 359, L55 Swenson F.J., Faulkner J., ApJ, 1992, 395, 654 Michaud G., ApJ, 1986, 302, 650 Richer J., Michaud G., ApJ, 1993, 416, 312 Garcia L6pez R.J., Spruit H.C., ApJ, 1991, 377,268 Montalban J., Schatzman E., A&A, 1996, 305, 513 Charbonneau P., Michaud G., ApJ, 1988, 334, 746 Zahn J.P., A&A, 1992, 265, 115 Chaboyer B., Demarque P., Pinsonneault M.H., ApJ, 1995, 441,865 Straus J.M., Blake J.B., Schramm D.N., ApJ, 1976, 204,481 Xiong D.R., Acta Astron. Sinica, 1991, 32, 333 Bressan A., Fagotto F., Bertelli G., A&AS, 1993, 100,647 King J.R., Deliyannis C.P., Moesgaard A.M., ApJ, 1997, 478, 778 Boesgaard A.M., King J.R., ApJ, 2002, 565, 587 Balachandran S., Bell R.A., Nature, 1998, 392, 791
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