标题： M型小行星的光谱调查 显示英文标题

标题： Spectroscopic survey of M--type asteroids

摘要： M型小行星，根据Tholen分类法（Tholen，1984）定义，是中等反照率天体，被认为具有金属成分，并且是分化的铁-镍陨石和顽火辉石球粒陨石的祖先。 我们对最初被分类为Tholen M型的小行星群体中的30颗小行星进行了可见光和近红外波长范围（0.4-2.5微米）的光谱调查，旨在研究它们的表面组成。 数据是在2004-2007年期间在TNG、NTT和IRTF望远镜上多次观测运行中获得的。 我们计算了每颗观测小行星在多个波长范围内的光谱斜率，并寻找诊断性光谱特征。 我们确认这些物体表现出广泛的光谱行为，因为它们的光谱延伸到近红外区，包括识别出弱吸收带，主要是0.9微米带，可能归因于单斜辉石，以及0.43微米带，可能与绿泥石和富含镁的蛇纹石或辉石矿物如易变辉石或斜方辉石有关。 与之前发表的数据比较表明，属于M类的某些小行星的表面可能有显著变化。 我们尝试通过在RELAB数据库中寻找陨石光谱类似物，并通过选定陨石/矿物的地理混合模型来限制样本中小行星的表面组成。 我们确认铁陨石、帕拉赛特陨石和顽火辉石球粒陨石是我们的样本中大多数物体的最佳匹配，正如对M型小行星所建议的那样。 在若干小行星上存在细微的吸收特征证实，并非所有由Tholen M类定义的物体都具有纯金属成分。 显示英文摘要

摘要： M-type asteroids, as defined in the Tholen taxonomy (Tholen, 1984), are medium albedo bodies supposed to have a metallic composition and to be the progenitors both of differentiated iron-nickel meteorites and enstatite chondrites. We carried out a spectroscopic survey in the visible and near infrared wavelength range (0.4-2.5 micron) of 30 asteroids chosen from the population of asteroids initially classified as Tholen M -types, aiming to investigate their surface composition. The data were obtained during several observing runs during the years 2004-2007 at the TNG, NTT, and IRTF telescopes. We computed the spectral slopes in several wavelength ranges for each observed asteroid, and we searched for diagnostic spectral features. We confirm a large variety of spectral behaviors for these objects as their spectra are extended into the near-infrared, including the identification of weak absorption bands, mainly of the 0.9 micron band tentatively attributed to orthopyroxene, and of the 0.43 micron band that may be associated to chlorites and Mg-rich serpentines or pyroxene minerals such us pigeonite or augite. A comparison with previously published data indicates that the surfaces of several asteroids belonging to the M-class may vary significantly. We attempt to constrain the asteroid surface compositions of our sample by looking for meteorite spectral analogues in the RELAB database and by modelling with geographical mixtures of selected meteorites/minerals. We confirm that iron meteorites, pallasites, and enstatite chondrites are the best matches to most objects in our sample, as suggested for M-type asteroids. The presence of subtle absorption features on several asteroids confirms that not all objects defined by the Tholen M-class have a pure metallic composition.