基于疏散星团的银河系结构研究
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摘要
银河系除了场星外,还有非常多成团的恒星系统。研究这些星团对我们了解银河系形成、结构和演化有重要意义。不同的星团在很多性质上有差异,如光度、结构的紧密性、金属丰度等。结构紧密、光度较大的星团被划分为“球状星团”;而结构相对较疏松、光度稍小的星团则被划分为“疏散星团”。
有关恒星形成的观测研究指出,恒星在分子云中形成,并且所形成的恒星大部分是成团的(Lada[1])。因为星团内的恒星具有共同的起源,有关星团的观测结果则成为经典恒星形成理论的最好检验。除此之外,疏散星团由于其宽的年龄谱(贯穿整个银盘的形成历史)和质量谱(从几百上千到几万个太阳质量),长期以来一直被当作是研究银盘形成和演化的有效探针。例如,一方面人们利用年轻的疏散星团来确定银河系的旋臂结构(Humphreys [2]),讨论银河系的旋转曲线(Schmidt [3],Merrifield [4]),研究恒星的形成机制及星团的动力学演化(Boutloukos [5], Fukushige [6], Gerhard [7]),并进一步用来对恒星的初始质量谱及形成星团的分子云质量函数提供限制(Larson [8], Elmegreen [9]);另一方面,由于老年的疏散星团的年龄可以较好地测定,它们成为研究早期银盘形成的最好工具之一(Phelps [10], Janes [11], Friel [12])。不仅如此,老年星团中最亮的成员星一般是有强发射线的红巨星,可以较好地利用其谱线观测得到星团成员星的化学成分和视向速度(Behr [13])。因此,疏散星团是研究银河系结构演化、动力学及化学的有力工具,已有一系列文章对此作了良好的综述(石火明[14],赵君亮[15],俎中良[16])。
本文研究的样本来自WEBDA1 2007年的疏散星团数据库。此数据库由维也纳大学的天体物理研究所管理更新。这个疏散星团的数据库共有970个疏散星团,其中911个有年龄,920个有距离,911个有色余。我们的研究目的是利用疏散星团统计分析得到银盘的性质,如银盘标高、银盘标长及太阳银面距等。
对星团年龄分布的研究指出,银河系在过去3.4Gyr可能出现了一个恒星形成较为剧烈的时期;星团年龄分布的双指数结构意味着年轻星团较年老星团更易瓦解,该结论在对星团银道面的投影分布和银河系巨分子云分布的讨论中得到进一步确认;利用星团样本,我们还得到了太阳位于银道面以北约20pc的位置;并且随着年龄的增加,星团垂直银道面的标高分布变大;最后,利用太阳内圈和外圈星团的资料,我们发现相对于太阳,外银盘具有比内银盘更大的垂直银道面的标高,这可用维里定理加以合理解释。
虽然WBBDA星团表提供了大量的疏散星团资料,但是该样本仍是不完备的。利用蒙特卡罗数值模拟,以太阳附近疏散星团的观测为基准,我们对样本的不完备性进行了分析。在考虑位置固定和位置随机的情况下,我们分别得到了银盘的标长为和。
In addiction to the field stars, there are many star clusters in the Milky Way. They play an important role in understanding the formation, structure and evolution of the Galaxy. However, their observational properties differ in many aspects, such as luminosities, compactness, and metallicities. Star clusters with compact structures and high luminosities are named as“globular clusters”; while the others with lose structures and low luminosities are named as“open clusters”.
Observations have pointed out that stars form in molecular clouds and most of them are clustered. Since the stars in a cluster have the same origins, their observations present a good laboratory to test the theory of star formation; Secondly, because of the wide distributions of open clusters in age (overlap the whole history of the Galactic disk) and mass (from hundreds to more than 10 thousand solar masses), they have been taken effectively to probe the formation and evolution of the Galactic disk. For example, on one hand young open clusters are adopted to determine the structures of spiral arms of the Galaxy, to study the rotation curve of the Galaxy, to investigate the star formation mechanisms and the dynamic evolution of star clusters, and to constrain the stellar initial mass function and the mass function of clouds where clusters were born. On the other hand, because ages of old open clusters are relatively easy to obtain, they have become one of the best tools to investigate the early epoch of the Galactic disk formation. Furthermore, the brightest member stars in an old open cluster are red giants always with strong emission lines, so that they can be observed spectroscopily to get their chemical composition and radial velocities. As a result, open clusters are effective tools to investigate the structure and evolution, dynamics and chemical evolution of the Galaxy. There have been several good papers as the overview of open clusters.
The WEBDA open cluster catalogue (version 2007), developed and maintained by Ernst Paunzen working in the Institute of Astronomy of the University of Vienna, is adopted in the present study. The total number of open clusters in the catalogue is 970, within which 911 clusters have age determinations, 920 clusters have distances, and 911 clusters have color excesses. The goal of the present thesis is to study statistically the structure of the Galactic disk by open clusters, such as the scale height and length of the disk, and the position of the Sun above the Galactic plane as well.
It implies that an active star forming period might occur 3.4Gyr ago when the age distribution of open clusters is taken into account. Most of old open clusters were destroyed in the inner solar circle due to the interactions with giant molecular clouds. The Sun locates about 20pc north to the Galactic plane. The scale height perpendicular to the Galactic plane for open clusters increases with their ages.
Although WEBDA catalogue provides a large amount of information on open clusters, it is still not completed yet. We analyzed the incompleteness of our sample with Monte Carlo simulations, based on the observation results of open clusters near the Sun. Under the consideration of fixed and random positions of open clusters, we derive the scale length of the Galactic disk to be and , respectively.
有关恒星形成的观测研究指出,恒星在分子云中形成,并且所形成的恒星大部分是成团的(Lada[1])。因为星团内的恒星具有共同的起源,有关星团的观测结果则成为经典恒星形成理论的最好检验。除此之外,疏散星团由于其宽的年龄谱(贯穿整个银盘的形成历史)和质量谱(从几百上千到几万个太阳质量),长期以来一直被当作是研究银盘形成和演化的有效探针。例如,一方面人们利用年轻的疏散星团来确定银河系的旋臂结构(Humphreys [2]),讨论银河系的旋转曲线(Schmidt [3],Merrifield [4]),研究恒星的形成机制及星团的动力学演化(Boutloukos [5], Fukushige [6], Gerhard [7]),并进一步用来对恒星的初始质量谱及形成星团的分子云质量函数提供限制(Larson [8], Elmegreen [9]);另一方面,由于老年的疏散星团的年龄可以较好地测定,它们成为研究早期银盘形成的最好工具之一(Phelps [10], Janes [11], Friel [12])。不仅如此,老年星团中最亮的成员星一般是有强发射线的红巨星,可以较好地利用其谱线观测得到星团成员星的化学成分和视向速度(Behr [13])。因此,疏散星团是研究银河系结构演化、动力学及化学的有力工具,已有一系列文章对此作了良好的综述(石火明[14],赵君亮[15],俎中良[16])。
本文研究的样本来自WEBDA1 2007年的疏散星团数据库。此数据库由维也纳大学的天体物理研究所管理更新。这个疏散星团的数据库共有970个疏散星团,其中911个有年龄,920个有距离,911个有色余。我们的研究目的是利用疏散星团统计分析得到银盘的性质,如银盘标高、银盘标长及太阳银面距等。
对星团年龄分布的研究指出,银河系在过去3.4Gyr可能出现了一个恒星形成较为剧烈的时期;星团年龄分布的双指数结构意味着年轻星团较年老星团更易瓦解,该结论在对星团银道面的投影分布和银河系巨分子云分布的讨论中得到进一步确认;利用星团样本,我们还得到了太阳位于银道面以北约20pc的位置;并且随着年龄的增加,星团垂直银道面的标高分布变大;最后,利用太阳内圈和外圈星团的资料,我们发现相对于太阳,外银盘具有比内银盘更大的垂直银道面的标高,这可用维里定理加以合理解释。
虽然WBBDA星团表提供了大量的疏散星团资料,但是该样本仍是不完备的。利用蒙特卡罗数值模拟,以太阳附近疏散星团的观测为基准,我们对样本的不完备性进行了分析。在考虑位置固定和位置随机的情况下,我们分别得到了银盘的标长为和。
In addiction to the field stars, there are many star clusters in the Milky Way. They play an important role in understanding the formation, structure and evolution of the Galaxy. However, their observational properties differ in many aspects, such as luminosities, compactness, and metallicities. Star clusters with compact structures and high luminosities are named as“globular clusters”; while the others with lose structures and low luminosities are named as“open clusters”.
Observations have pointed out that stars form in molecular clouds and most of them are clustered. Since the stars in a cluster have the same origins, their observations present a good laboratory to test the theory of star formation; Secondly, because of the wide distributions of open clusters in age (overlap the whole history of the Galactic disk) and mass (from hundreds to more than 10 thousand solar masses), they have been taken effectively to probe the formation and evolution of the Galactic disk. For example, on one hand young open clusters are adopted to determine the structures of spiral arms of the Galaxy, to study the rotation curve of the Galaxy, to investigate the star formation mechanisms and the dynamic evolution of star clusters, and to constrain the stellar initial mass function and the mass function of clouds where clusters were born. On the other hand, because ages of old open clusters are relatively easy to obtain, they have become one of the best tools to investigate the early epoch of the Galactic disk formation. Furthermore, the brightest member stars in an old open cluster are red giants always with strong emission lines, so that they can be observed spectroscopily to get their chemical composition and radial velocities. As a result, open clusters are effective tools to investigate the structure and evolution, dynamics and chemical evolution of the Galaxy. There have been several good papers as the overview of open clusters.
The WEBDA open cluster catalogue (version 2007), developed and maintained by Ernst Paunzen working in the Institute of Astronomy of the University of Vienna, is adopted in the present study. The total number of open clusters in the catalogue is 970, within which 911 clusters have age determinations, 920 clusters have distances, and 911 clusters have color excesses. The goal of the present thesis is to study statistically the structure of the Galactic disk by open clusters, such as the scale height and length of the disk, and the position of the Sun above the Galactic plane as well.
It implies that an active star forming period might occur 3.4Gyr ago when the age distribution of open clusters is taken into account. Most of old open clusters were destroyed in the inner solar circle due to the interactions with giant molecular clouds. The Sun locates about 20pc north to the Galactic plane. The scale height perpendicular to the Galactic plane for open clusters increases with their ages.
Although WEBDA catalogue provides a large amount of information on open clusters, it is still not completed yet. We analyzed the incompleteness of our sample with Monte Carlo simulations, based on the observation results of open clusters near the Sun. Under the consideration of fixed and random positions of open clusters, we derive the scale length of the Galactic disk to be and , respectively.
引文
[1] Lada C.J., Lada E.A. [ARA&A]. 2003, 41: 57
[2] Humphreys R. M. [IAUS].1979,84: 93
[3] Schmidt, M. In: Blaauw A. & Schmidt M. eds. [Galactic Structure]. Chicago, University of Chicago Press, 1965
[4] Merrifield, Michael R. [AJ]. 1992,103:1552
[5] Boutloukos, S.G. & Lamers H.J.G.L.M. [MNRAS]. 2003, 338: 717
[6] Fukushige T. & Heggie D.C. [MNRAS]. 2000, 318: 753
[7] Gerhard O. [ASPC].2000, 211: 12
[8] Larson R.B. [MNRAS]. 1998, 301: 569
[9] Elmegreen B.G. [ApJ]. 2006, 648: 572
[10] Phelps R.L., Janes K.A. & Montgomery K.A. [AJ]. 1994, 107: 1079
[11] Janes K.A., Phelps R.L. [AJ]. 1994, 108: 1773
[12] Friel E.D. [ARA&A]. 1995, 33: 381
[13] Behr, B.B. [ApJS]. 2003, 149: 67
[14] 石火明,赵君亮. [天文学进展]. 1992, 10: 22
[15] 赵君亮. [天文学进展].2007,25: 13
[16] 俎中良,赵君亮. [天文学进展] 2003, 21: 152
[17] Mermilliod, J.C. In: Star Clusters, J.E.Hesser, ed. [IAU Symposium]. Dordrecht: Reidel Publishing Co., 1980. 85: 129
[18] Dias, W.S., Alessi, B.S., Moitinho, A., & Lepine, J.R.D. [EAS]. 2003, 10: 195
[19] Spitzer, Lyman, Jr. [ApJ]. 1958, 127: 17
[20] Shapley, H. [ApJ]. 1919, 49: 249
[21] Shapley, H. [ApJ]. 1919, 49: 311
[22] Shapley, H. [ApJ]. 1919, 50: 107
[23] 图 2-4 来自 http://www.spacetelescope.org/images/html/heic0615a.html
[24] Westerlund, B. [AJ]. 1961, 66: 57
[25]Koposov, S.E., Glushkova, E.V. [IAUJD]. 2006, 13: 43
[26] J. [ApJ]. 2001, 563: 151
[27] Messier C., Niles P.H. [QB]. 1981, 6: 6413
[28] Trumpler R. [Lick Obs. Bull.]. 1930, 14: 154
[29] Binney J. & Merrifield M. [Galactic Astronomy]. Princeton, New Jersey: Princeton University Press, 1998. 377-392
[30] Piatti,A.E., Claria, J.J., & Abadi, M.G. [AJ]. 1995, 110: 2813
[31] Edvardsson B., Andersen J., Gustafsson B., et al. [A&A]. 1993, 275: 101
[32] Chen, L., Hou, J. L., Zhao, J. L., de Grijs, R.,submitted to [Proceeding of IAU Symposium No.248: “A Giant Step:from Milli- to Micro-arcsecond Astrometry”]
[33] Chen, L., Hou, J.L., & Wang, J.J. [AJ]. 2003, 125: 1397
[34] Salpeter E.E. [ApJ]. 1955, 121: 161
[35] Scalo J.M. [FCPh]. 1986, 11: 1
[36] Scalo J. [ASSL]. 2005, 327: 23
[37] Kroupa P. [MNRAS]. 2001, 322: 231
[38] Taff, L. G. [AJ]. 1974, 79: 1280
[39] Clausdius, M. & Grosbel, P.J. [A&A]. 1980, 87: 339
[40] Tarrab, I. [A&A]. 1982, 109: 285
[41]Chabrier G. [ASSL]. 2005, 327: 41
[42] Chabrier, G. [ApJ]. 2003b, 585: 133
[43] Jose, J., Pandey, A. K., Ojha, D. K. et al. [MNRAS]. 2008, 384: 1675
[44] van den Bergh, S. [ZA]. 1958, 46: 176
[45] Zhao, G., Chen, Y.Q, Shi, J.R., Liang, Y.C., Hou, J.L., Chen, L., Zhang, H.W., Li, A.G. [ChJAA] 2006,6: 265
[46] Arp H.C., et al. [ApJ]. 1959, 130: 80
[47] Gimenez A. & Garcia-Pelayo J. [A&AS]. 1980, 41: 9
[48] del Rio G. & Huestamendia G. [A&AS]. 1988, 73: 425
[49] Cuffey J. [AnHar]. 1937, 105: 403
[50] Turner D.G., et al. [AJ]. 1994, 107: 1796
[51] Westerlund B. [A&AS]. 70, 1987: 311
[52] Giorgi E.E., et al. [RmxAA]. 2001, 37: 1
[53] Bernabei S. & Polcaro V.F. [A&A]. 2001, 371: 123
[54] Turner D.G. [A&AS]. 1993, 97: 755
[55] Pedreros M.H. [RMxAA]. 2000, 36: 13
[56] , G. [Catalogue of open clusters data]. Fifth edition. Strasbourg (VII/92): CDS, 1987
[57] Schneider P. [Extragalactic Astronomy and Cosmology]. Berlin, Heidelberg: Springer, 2006. 46-51
[58] Sparke Linda S. & Gallagher John S. [Galaxies in the Universe]. Cambridge: Cambridge University Press, 2000. 51-94
[59] Eggen O.J., Lynden-Bell D., Sandage A. [ApJ]. 1962, 136: 746
[60] 陈力,侯金良,王家骥,常瑞香.[中国科学院上海天文台年刊]. 2004,25: 74
[61] Bonatto, C., Kerber, L.O. & Santiago, B.X. [A&A]. 2006, 446: 121
[62] Kharchenko, N.V., Piskunov, A.E., , S., Schilbach, E., & Scholz, R-D. [A&A]. 2005, 440: 403
[63] King, I. [AJ]. 1966, 71: 64
[64] Girardi, L., Bertelli, G., Bressan, A. et al. [A&A]. 2002, 391: 195
[65] Bica, E. & Bonatto, C.J. [A&A]. 2005, 443: 465
[2] Humphreys R. M. [IAUS].1979,84: 93
[3] Schmidt, M. In: Blaauw A. & Schmidt M. eds. [Galactic Structure]. Chicago, University of Chicago Press, 1965
[4] Merrifield, Michael R. [AJ]. 1992,103:1552
[5] Boutloukos, S.G. & Lamers H.J.G.L.M. [MNRAS]. 2003, 338: 717
[6] Fukushige T. & Heggie D.C. [MNRAS]. 2000, 318: 753
[7] Gerhard O. [ASPC].2000, 211: 12
[8] Larson R.B. [MNRAS]. 1998, 301: 569
[9] Elmegreen B.G. [ApJ]. 2006, 648: 572
[10] Phelps R.L., Janes K.A. & Montgomery K.A. [AJ]. 1994, 107: 1079
[11] Janes K.A., Phelps R.L. [AJ]. 1994, 108: 1773
[12] Friel E.D. [ARA&A]. 1995, 33: 381
[13] Behr, B.B. [ApJS]. 2003, 149: 67
[14] 石火明,赵君亮. [天文学进展]. 1992, 10: 22
[15] 赵君亮. [天文学进展].2007,25: 13
[16] 俎中良,赵君亮. [天文学进展] 2003, 21: 152
[17] Mermilliod, J.C. In: Star Clusters, J.E.Hesser, ed. [IAU Symposium]. Dordrecht: Reidel Publishing Co., 1980. 85: 129
[18] Dias, W.S., Alessi, B.S., Moitinho, A., & Lepine, J.R.D. [EAS]. 2003, 10: 195
[19] Spitzer, Lyman, Jr. [ApJ]. 1958, 127: 17
[20] Shapley, H. [ApJ]. 1919, 49: 249
[21] Shapley, H. [ApJ]. 1919, 49: 311
[22] Shapley, H. [ApJ]. 1919, 50: 107
[23] 图 2-4 来自 http://www.spacetelescope.org/images/html/heic0615a.html
[24] Westerlund, B. [AJ]. 1961, 66: 57
[25]Koposov, S.E., Glushkova, E.V. [IAUJD]. 2006, 13: 43
[26] J. [ApJ]. 2001, 563: 151
[27] Messier C., Niles P.H. [QB]. 1981, 6: 6413
[28] Trumpler R. [Lick Obs. Bull.]. 1930, 14: 154
[29] Binney J. & Merrifield M. [Galactic Astronomy]. Princeton, New Jersey: Princeton University Press, 1998. 377-392
[30] Piatti,A.E., Claria, J.J., & Abadi, M.G. [AJ]. 1995, 110: 2813
[31] Edvardsson B., Andersen J., Gustafsson B., et al. [A&A]. 1993, 275: 101
[32] Chen, L., Hou, J. L., Zhao, J. L., de Grijs, R.,submitted to [Proceeding of IAU Symposium No.248: “A Giant Step:from Milli- to Micro-arcsecond Astrometry”]
[33] Chen, L., Hou, J.L., & Wang, J.J. [AJ]. 2003, 125: 1397
[34] Salpeter E.E. [ApJ]. 1955, 121: 161
[35] Scalo J.M. [FCPh]. 1986, 11: 1
[36] Scalo J. [ASSL]. 2005, 327: 23
[37] Kroupa P. [MNRAS]. 2001, 322: 231
[38] Taff, L. G. [AJ]. 1974, 79: 1280
[39] Clausdius, M. & Grosbel, P.J. [A&A]. 1980, 87: 339
[40] Tarrab, I. [A&A]. 1982, 109: 285
[41]Chabrier G. [ASSL]. 2005, 327: 41
[42] Chabrier, G. [ApJ]. 2003b, 585: 133
[43] Jose, J., Pandey, A. K., Ojha, D. K. et al. [MNRAS]. 2008, 384: 1675
[44] van den Bergh, S. [ZA]. 1958, 46: 176
[45] Zhao, G., Chen, Y.Q, Shi, J.R., Liang, Y.C., Hou, J.L., Chen, L., Zhang, H.W., Li, A.G. [ChJAA] 2006,6: 265
[46] Arp H.C., et al. [ApJ]. 1959, 130: 80
[47] Gimenez A. & Garcia-Pelayo J. [A&AS]. 1980, 41: 9
[48] del Rio G. & Huestamendia G. [A&AS]. 1988, 73: 425
[49] Cuffey J. [AnHar]. 1937, 105: 403
[50] Turner D.G., et al. [AJ]. 1994, 107: 1796
[51] Westerlund B. [A&AS]. 70, 1987: 311
[52] Giorgi E.E., et al. [RmxAA]. 2001, 37: 1
[53] Bernabei S. & Polcaro V.F. [A&A]. 2001, 371: 123
[54] Turner D.G. [A&AS]. 1993, 97: 755
[55] Pedreros M.H. [RMxAA]. 2000, 36: 13
[56] , G. [Catalogue of open clusters data]. Fifth edition. Strasbourg (VII/92): CDS, 1987
[57] Schneider P. [Extragalactic Astronomy and Cosmology]. Berlin, Heidelberg: Springer, 2006. 46-51
[58] Sparke Linda S. & Gallagher John S. [Galaxies in the Universe]. Cambridge: Cambridge University Press, 2000. 51-94
[59] Eggen O.J., Lynden-Bell D., Sandage A. [ApJ]. 1962, 136: 746
[60] 陈力,侯金良,王家骥,常瑞香.[中国科学院上海天文台年刊]. 2004,25: 74
[61] Bonatto, C., Kerber, L.O. & Santiago, B.X. [A&A]. 2006, 446: 121
[62] Kharchenko, N.V., Piskunov, A.E., , S., Schilbach, E., & Scholz, R-D. [A&A]. 2005, 440: 403
[63] King, I. [AJ]. 1966, 71: 64
[64] Girardi, L., Bertelli, G., Bressan, A. et al. [A&A]. 2002, 391: 195
[65] Bica, E. & Bonatto, C.J. [A&A]. 2005, 443: 465
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