论文标题
RR Lyre和II型Cepheid变量的近红外观察，金属富含金属凸起的球状簇NGC 6441
Near-infrared observations of RR Lyrae and Type II Cepheid variables in the metal-rich bulge globular cluster NGC 6441
论文作者
论文摘要
NGC 6441是一个凸起的球状簇，具有不寻常的水平分支形态，RR Lyrae（RRL）和II型头孢菌（T2C）变量的众多人数相对较高，这是出乎意料的。我们介绍了NGC 6441中的近红外（NIR，$ JHK_S $）的时间序列观测值，其中42 rrl，8 T2C和10个Eclips二进制候选变量。使用8-m Gemini South TeleScope上的Flamingos-2乐器获得了多上述观测。多带数据用于调查RRL和T2C变量的脉动性能，包括其光曲线，不稳定性带，周期 - 升高图以及周期 - 亮度和周期 - wesenheit关系（PLRS和PWRS）在$ jhk_s $ efters中。 RRL变量的NIR脉动特性非常适合NGC 6441（[Fe/H] $ = -0.44 \ pM0.07 $ 〜DEX）的理论模型。氦增强的RRL模型比群集中RRL的观察值更明亮的NIR尺寸和蓝色颜色。这表明NGC 6441中的这些RRL变量要么不像以前的想象那样显着增强氦，要么在NIR中的影响要小于脉动模型的预测。我们还使用RRL周期 - 亮度 - 金属性（PLZ）关系的理论校准同时估计平均变红，$ e（J-k_s）= 0.26 \ pm0.06 $ 〜mag和距离，$ d = 12.67 \ pm0.09 $ 〜kpc，to ngc 6 $ 〜kpc to t to ngc 644414444414441441均为我们的含义。基于红色团恒星和最新的Gaia数据的凸起红色地图。我们的距离和红色值在NGC 6441中的T2C的PLR与横跨多种金属性的银河球状簇中的RRL和T2C的PLR之间提供了很好的一致性。
NGC 6441 is a bulge globular cluster with an unusual horizontal branch morphology and a rich population of RR Lyrae (RRL) and Type II Cepheid (T2C) variables that is unexpected for its relatively high metallicity. We present near-infrared (NIR, $JHK_s$) time-series observations of 42 RRL, 8 T2Cs, and 10 eclipsing binary candidate variables in NGC 6441. The multi-epoch observations were obtained using the FLAMINGOS-2 instrument on the 8-m Gemini South telescope. Multi-band data are used to investigate pulsation properties of RRL and T2C variables including their light curves, instability strip, period--amplitude diagrams, and period--luminosity and period--wesenheit relations (PLRs and PWRs) in $JHK_s$ filters. NIR pulsation properties of RRL variables are well fitted with theoretical models that have canonical helium content and mean-metallicity of NGC 6441 ([Fe/H]$=-0.44\pm0.07$~dex). The helium-enhanced RRL models predict brighter NIR magnitudes and bluer colors than the observations of RRL in the cluster. This suggests that these RRL variables in NGC 6441 are either not significantly helium enhanced as previously thought or the impact of such enhancement is smaller in NIR than the predictions of the pulsation models. We also use theoretical calibrations of RRL period--luminosity--metallicity (PLZ) relations to simultaneously estimate the mean reddening, $E(J-K_s)=0.26\pm0.06$~mag, and the distance, $d=12.67\pm0.09$~kpc, to NGC 6441. Our mean reddening value and the distance are consistent with the independent estimates from the bulge reddening map based on red clump stars and the latest Gaia data, respectively. Our distance and reddening values provide a very good agreement between the PLRs of T2Cs in NGC 6441 and those for RRL and T2Cs in Galactic globular clusters that span a broad range of metallicity.
