We present the optical spectra of 338 nearby M dwarfs, and compute their spectral types, effective temperatures ($T_{\mathrm{eff}}$), and radii. Our spectra have been obtained using several optical spectrometers with spectral resolutions that range from 1200 to 10000. As many as 97% of the observed M-type dwarfs have a spectral type of M3-M6, with a typical error of 0.4 sub-type, among which the spectral types M4-M5 are the most common. We infer the $T_{\mathrm{eff}}$ of our sample by fitting our spectra with theoretical spectra from the PHOENIX model. Our inferred $T_{\mathrm{eff}}$ is calibrated with the optical spectra of M dwarfs whose $T_{\mathrm{eff}}$ have been well determined with the calibrations that are supported by previous interferometric observations. Our fitting procedures utilize the VO absorption band (7320-7570 {\AA}) and the optical region (5000-8000 {\AA}), yielding typical errors of 128 K (VO band) and 85 K (optical region). We also determine the radii of our sample from their spectral energy distributions (SEDs). We find most of our sample stars have radii of $<$ 0.6 $R_\odot$, with the average error being 3%. Our catalog enables efficient sample selection for exoplanet surveys around nearby M-type dwarfs.

中文翻译：

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使用光学中分辨率光谱表征 M 矮星，用于探索小型系外行星

我们展示了附近 338 个 M 矮星的光谱，并计算了它们的光谱类型、有效温度 ($T_{\mathrm{eff}}$) 和半径。我们的光谱是使用几个光谱分辨率从 1200 到 10000 的光谱仪获得的。 多达 97% 的观测到的 M 型矮星具有 M3-M6 的光谱类型，典型误差为 0.4 亚型，其中以M4-M5光谱型最为常见。我们通过将光谱与来自 PHOENIX 模型的理论光谱拟合来推断我们样本的 $T_{\mathrm{eff}}$。我们推断的 $T_{\mathrm{eff}}$ 是用 M 矮星的光谱校准的，其 $T_{\mathrm{eff}}$ 已经通过先前干涉观测支持的校准得到了很好的确定。我们的拟合程序利用 VO 吸收带 (7320-7570 {\AA}) 和光学区域 (5000-8000 {\AA})，产生 128 K（VO 带）和 85 K（光学区域）的典型误差。我们还根据样品的光谱能量分布 (SED) 确定样品的半径。我们发现我们的大多数样本恒星的半径为 $<$ 0.6 $R_\odot$，平均误差为 3%。我们的目录可以为附近 M 型矮星周围的系外行星调查提供有效的样本选择。