New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project
New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project
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DOI：
10.3847/1538-4357/ac013c
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发表时间：
2021-06
期刊：
影响因子：
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通讯作者：
A. Meisner;A. Schneider;A. Burgasser;F. Marocco;M. Line;J. Faherty;J. Kirkpatrick;D. Caselden
中科院分区：
文献类型：
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作者：
A. Meisner;A. Schneider;A. Burgasser;F. Marocco;M. Line;J. Faherty;J. Kirkpatrick;D. Caselden
Schneider等人。介绍了WISEA J041451.67−585456.7和WISEA J181006.18−101000.5的发现，这似乎是极端T型亚矮星的第一个例子(ESDT；金属丰度≤−1Dex，T ef≲1400K)。在这里，我们介绍了三个T型亚矮星候选的新发现和后续行动，着眼于扩大此类天体的样本，这些天体具有非常低的金属丰度和极高的运动学，这些特性表明它们是银晕的成员。Keck/NIRES对WISEA J155349.96+693355.2的近红外光谱分析证实，这是一颗中-T亚矮星。WISEA J155349.96+615是后院世界：行星9公民科学项目发现的一个快速移动的天体。在所有光谱确认的L和T亚矮星中，W2=22.3MAG的WISEA J155349.96+693355.2具有最大的W2折合自行，这表明它可能是运动学上的极端。然而，我们对WISEA J155349.96+693355.2近红外光谱的模拟表明，它的金属丰度仅略低于太阳。在分析J155349.96+693355.2光谱的过程中，我们提出了一种新的低温、低金属丰度模式大气光谱网格。我们还介绍了两个新的ESDT候选天体CWISE J073844.52−664334.6和CWISE J221706.28−145437.6的发现，它们的大运动和颜色与两个已知的ESDT天体相似。找到更多的esdT例子是绘制出这一新发现群体的光谱序列和观测特性的关键一步。
Schneider et al. presented the discovery of WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5, which appear to be the first examples of extreme T-type subdwarfs (esdTs; metallicity ≤−1 dex, T eff ≲ 1400 K). Here, we present new discoveries and follow-up of three T-type subdwarf candidates, with an eye toward expanding the sample of such objects with very low metallicity and extraordinarily high kinematics, properties that suggest membership in the Galactic halo. Keck/NIRES near-infrared spectroscopy of WISEA J155349.96+693355.2, a fast-moving object discovered by the Backyard Worlds: Planet 9 citizen science project, confirms that it is a mid-T subdwarf. With H W2 = 22.3 mag, WISEA J155349.96+693355.2 has the largest W2 reduced proper motion among all spectroscopically confirmed L and T subdwarfs, suggesting that it may be kinematically extreme. Nevertheless, our modeling of the WISEA J155349.96+693355.2 near-infrared spectrum indicates that its metallicity is only mildly subsolar. In analyzing the J155349.96+693355.2 spectrum, we present a new grid of low-temperature, low-metallicity model atmosphere spectra. We also present the discoveries of two new esdT candidates, CWISE J073844.52−664334.6 and CWISE J221706.28−145437.6, based on their large motions and colors similar to those of the two known esdT objects. Finding more esdT examples is a critical step toward mapping out the spectral sequence and observational properties of this newly identified population.