HIP 38939B: A New Benchmark T Dwarf in the Galactic Plane Discovered with Pan-STARRS1
Niall R. Deacon, Michael C. Liu, Eugene A. Magnier, Brendan P. Bowler, Joshua Redstone, Bertrand Goldman, W. S. Burgett, K. C. Chambers, H. Flewelling, N. Kaise… 展开作者
Niall R. Deacon, Michael C. Liu, Eugene A. Magnier, Brendan P. Bowler, Joshua Redstone, Bertrand Goldman, W. S. Burgett, K. C. Chambers, H. Flewelling, N. Kaiser, J. S. Morgan, P. A. Price, W. E. Sweeney, J. L. Tonry, R. J. Wainscoat, C. Waters
备注：
ApJ, in press. Tiny changes incorporated into final version: added analysis of likelihood of companionship, clarified the fitting proceedure, and updated the benchmark analysis to highlight when the quoted evolutionary models use the atmospheric model they are being compared to as a boundary condition
We report the discovery of a wide brown dwarf companion to the mildly metal-poor ([Fe/H]=-0.24), low galactic latitude (b = 1.88 deg) K4V star HIP 38939. The companion was discovered by its common proper motion with the primary and its red optical (Pan-STARRS1) and blue infrared (2MASS) colors. It has a projected separation of 1630 AU and a near-infrared spectral type of T4.5. As such it is one of only three known companions to a main sequence star which have early/mid-T spectral types (the others being HN Peg B and eps Indi B). Using chromospheric activity we estimate an age for the primary of 900{+1900,-600} Myr. This value is also in agreement with the age derived from the star's weak ROSAT detection. Comparison with evolutionary models for this age range indicates that HIP 38939B falls in the mass range 38+/-20 Mjup with an effective temperature range of 1090+/-60 K. Fitting our spectrum with atmospheric models gives a best fitting temperature of 1100 K. We include our object in an analysis of the population of benchmark T dwarfs and find that while older atmospheric models appeared to over-predict the temperature of the coolest objects compared to evolutionary models, more recent atmospheric models provide better agreement.
The Pan-STARRS1 Proper-motion Survey for Young Brown Dwarfs in Nearby Star-forming Regions. I. Taurus Discoveries and a Reddening-free Classification Method for Ultracool Dwarfs
我们正在进行一项基于泛星1 3 $π$巡天的金牛座-御夫座分子云中年轻棕矮星的自行巡天。我们的搜索使用多波段测光和天体测量来选择候选者，并且比以前的搜索更宽（370度$^{2}$）和更深（$\approx$ 3 M $_{\rm Jup}$）。我们在这里介绍我们的搜索方法和光谱跟踪我们的高优先级候选人。由于消光使光谱分类复杂化，我们开发了一种新的方法，使用低分辨率（$R \approx 100$）近红外光谱来量化M中期至L晚期超冷矮星（金牛座的$\approx 100-3$ M $_{\rm Jup}$）的无红化光谱类型、消光和重力分类。我们已经发现了金牛座的25个低重力（VL-G）和前11个中等重力（INT-G）亚恒星（M6-L1）成员，这是迄今为止金牛座褐矮星数量增加最多的一次。我们还发现了一个新的昴星团成员和13个英仙座OB 2星协的新成员，包括一个候选的非常宽的分离（58 kAU）的二进制。我们对所有以前已知的金牛座褐矮星的光谱类型和灭绝进行了均匀的重新分类。总之，我们的发现使金牛座的亚恒星数量增加了$\approx 40\%$，并增加了三个L型成员（$\approx 5-10$ M $_{\rm Jup}$）。最值得注意的是，我们的发现揭示了金牛座中一个更古老（$>$ 1000万年）的低质量人口，与最近对高质量恒星成员的研究一致。质量函数似乎在年轻和年老的金牛座群体之间存…
