The fundamental parameters of the Ap star 78 Virginis Could 78 Vir be a rapidly oscillating Ap star
The fundamental parameters of the Ap star 78 Virginis Could 78 Vir be a rapidly oscillating Ap star
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Ap 星 78 Virginis 的基本参数 78 Vir 可能是一颗快速振荡的 Ap 星
DOI：
10.1051/0004-6361/201526163
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发表时间：
2015
影响因子：
6.5
通讯作者：
N. Vargas
中科院分区：
文献类型：
--
作者：
K. Perraut;M. Cunha;I. Brandao;J. Loridat;D. Mourard;A. Meilland;N. Nardetto;H. Mcalister;T. Brummelaar;J. Sturmann;L. Sturmann;N. Turner;C. Farrington;N. Vargas
上下文。由于Ap恒星的强磁场和相关的斑点表面，确定Ap恒星的有效温度是一项艰巨的任务。然而，这是朝着约束其复杂大气模型和测试所提出的脉动激励机制迈出的重要一步。目标。利用长基线可见光干涉测量所提供的独特角分辨率，我们的目标是得到一些Ap目标的精确角直径，从而确定它们的无偏有效温度（Teff）和它们在赫罗图中的精确位置，估计它们的质量和年龄，并测试非绝热脉动模型。四颗Ap星的干涉测量结果已经在早期的作品中发表。这里我们报告了第五颗恒星的结果，这颗恒星的温度要高得多。方法。我们利用安装在CHARA长基线光学阵列组合焦点上的VEGA可见光谱仪对78 Vir进行了观测。我们从干涉测量中得到了这颗Ap星的暗斑直径。根据文献中可用的光度和光谱数据，我们估计了这颗恒星的热通量，并将其与视差和角直径结合起来，确定了这颗恒星的光度和有效温度。然后，我们使用导出的基本参数进行非绝热脉动分析。结果。我们确定了残肢暗化角直径为0.346±0.006 mas，并推导出线性半径R = 2.11±0.04 R′。在热通量为2.73±0.20 10−7 erg/ cm2 /s的条件下，得到的光度为L/L = 27±2a，有效温度为Teff = 9100±190 K。非绝热脉动模型使我们能够预测78 Vir在1.2至1.9 mHz频率范围内可以激发高泛音脉动，前提是磁场能够抑制极地区域的包络对流。结论。可见长基线干涉测量法是获得Ap星精确基本参数的一种独特方法。Ap星78vir被发现是一个有希望的roAp星候选者，它将使我们能够将最近对roAp星的激发机制的测试扩展到不稳定带的蓝色边缘。因此，这颗恒星的星震数据将引起人们的强烈兴趣。
Context. Determining the effective temperature of Ap stars, including the roAp stellar pulsators, is a difficult task owing to their strong magnetic field and their related spotted surfaces. It is, however, an important step towards constraining models of their complex atmosphere and testing proposed pulsation excitation mechanisms. Aims. Using the unique angular resolution provided by long-baseline visible interferometry, we aim at deriving accurate angular diameters of a number of Ap targets, so as to determine their unbiased effective temperature (Teff) and their accurate position in the Hertzsprung-Russell diagram, to estimate their mass and age, and to test non-adiabatic pulsation models. Interferometric results on four Ap stars have been published in earlier works. Here we report the results on a fifth, significantly hotter star. Methods. We observed 78 Vir with the visible spectrograph VEGA installed at the combined focus of the CHARA long-baseline optical array. We derived the limb-darkened diameter of this Ap star from our interferometric measurements. Based on photometric and spectroscopic data available in the literature, we estimated the star’s bolometric flux and used it, in combination with its parallax and angular diameter, to determine the star’s luminosity and effective temperature. We then used the derived fundamental parameters to perform a non-adiabatic pulsation analysis. Results. We determined a limb-darkened angular diameter of 0.346 ± 0.006 mas and deduced a linear radius of R = 2.11 ± 0.04 R� . Considering a bolometric flux of 2.73 ± 0.20 10 −7 erg/cm 2 /s we obtained a luminosity of L/L� = 27 ± 2a nd an effective temperature of Teff = 9100 ± 190 K. The non-adiabatic pulsation modeling allows us to predict that high overtone pulsations could be excited in 78 Vir at frequencies ranging from 1.2 to 1.9 mHz, provided that the magnetic field is capable of suppressing envelope convection in the polar regions. Conclusions. Visible long-baseline interferometry is a unique means of deriving accurate fundamental parameters of Ap stars. The Ap star 78 Vir is found to be a promising roAp-star candidate and one that would allow us to extend recent tests on the roAp stars’ excitation mechanism towards the blue edge of the instability strip. Asteroseismic data of this star would, therefore, be of strong interest.