Spectroscopic rotation velocities of L dwarfs from VLT/UVES and their comparison with periods from photometric monitoring
Spectroscopic rotation velocities of L dwarfs from VLT/UVES and their comparison with periods from photometric monitoring
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VLT/UVES 观测到的 L 型矮星的光谱旋转速度及其与光度监测周期的比较
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发表时间：
2004
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通讯作者：
C. Bailer
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作者：
C. Bailer
超冷矮星(UCD)的变率和自转为这些极低质量恒星和棕矮星的大气和演化提供了重要信息。作为正在进行的研究计划的一部分，给出了16个现场UCD(M9V-L7.5V)通过互相关高分辨率VLT/UVES光谱学得到的投影旋转速度v Sini。这使已经测量到的L矮星的数量翻了一番。所有目标都被发现在10到40公里之间有v西尼，S−1证实了L矮星是快速旋转星。径向速度的测量精度也达到了1-2公里S−1。根据旋转轴的随机分布、i和理论预测的半径，在各个对象的旋转周期上设置单侧的置信度区间。这些数据与从光度监测项目中获得的已公布的周期数据进行了比较。由此，Gelino等人发表了L0.5矮星2M0746+2000的31h周期。(2002)可被排除为轮换期。Bailer-Jones&Mundt(2001)得到的L1.5矮星2M1145+2317的自转周期为11.2±0.8h，这与目前的vSini结果相一致，这可能是真实的自转周期。旋转轴的倾斜度被约束为I=62◦-90◦，期望值为76◦。或者，数据设定了0.1R�半径的下限，这在超过0.5Gyr的棕矮星模型预测的半径范围内。同样，2M1334+1940的2.7h±0.1h的周期也被确认为可能的自转周期，倾角为I=27◦-44◦(�I�=34◦)。在监测程序没有检测到变化或周期的情况下，可能的原因是低对比度调制地表特征。然而，在三种情况下，没有检测到周期变化，即使从v Sini推断的可能的自转周期范围在监测敏感的时间尺度内。这强化了Bailer-Jones&Mundt(2001)的“掩蔽假说”，即光球特征在比自转周期更短的时间尺度上的演化掩盖了光曲线的规则调制。正如前面所讨论的，这种特征的一个可能的候选者是不均匀的尘埃云。
The variability and rotation of ultra cool dwarfs (UCDs) provide important information on the atmospheres and evolution of these very low mass stars and brown dwarfs. As part of an ongoing program to investigate this, the projected rotation velocities, v sini, derived from high resolution VLT/UVES spectroscopy via cross correlation are presented for 16 field UCDs (M9V-L7.5V). This doubles the number of L dwarfs for which v sini has been measured. All targets are found to have v sini between 10 and 40 km s −1 confirming that L dwarfs are rapid rotators. Radial velocities have also been measured to a precision of 1-2 km s −1 . From the random distribution of the rotation axes, i, and theoretically predicted radii, one-sided confidence intervals are placed on the rotation periods of individual objects. These are compared with published period data obtained from photometric monitoring programs. From this, the period of 31 h for the L0.5 dwarf 2M0746+2000 published by Gelino et al. (2002) may be ruled out as the rotation period. The period of 11.2 ± 0.8 h for the L1.5 dwarf 2M1145+2317 obtained by Bailer-Jones & Mundt (2001) is consistent with the present v sini results so is plausibly the true rotation period. The inclination of the rotation axis is constrained to be i = 62 ◦ -90 ◦ with an expectation value of 76 ◦ . Alternatively the data set a lower limit on the radius of 0.1R� , which is within the range of radii predicted by models for brown dwarfs older than 0.5 Gyr. Similarly, the period of 2.7 ± 0.1 h detected by the same authors for 2M1334+1940 is also confirmed as the likely rotation period; the inclination is i = 27 ◦ -44 ◦ (� i� = 34 ◦ ). Where no variability or period was detected by the monitoring programs the likely reason is low contrast modulating surface features. However, in three cases variability but no period was detected, even though the likely rotation period range inferred from v sini lies within the timescale to which the monitoring was sensitive. This reinforces the "masking hypothesis" of Bailer-Jones & Mundt (2001), the idea that the evolution of photospheric features on timescales shorter than the rotation period obscure the regular modulation of the light curve. As has been previously discussed, a likely candidate for such features is inhomogeneous dust clouds.