We mainly aim to search for the lithium depletion boundary (LDB) among the sub-stellar population of the open star cluster Coma Berenices. We carried out a search for brown dwarf (BD) candidates using colour-magnitude diagrams combining optical and infrared photometry from the latest public releases of the following large-scale surveys: UKIRT/UKIDSS, Pan-STARRS, SDSS, and AllWISE. We checked astrometric consistency with cluster membership using $Gaia$ DR2. A couple dozen new candidate BDs located inside the tidal radius of Coma Ber are reported, but none of these are significantly fainter and cooler than previously known members. A search for Li in three new and five previously known BD candidate cluster members was performed via spectroscopic observations using the OSIRIS instrument at the 10.4-m GTC. No LiI resonance doublet at 6707.8 A was detected in any of eight Coma Ber targets in the magnitude range J=15--19 and G=20--23 observed with the GTC. Spectral types and radial velocities were derived from the GTC spectra. These values confirm the cluster membership of four L2--L2.5 dwarfs, two of which are new in the literature. The large Li depletion factors found among the four bona fide BD members in Coma Ber implies that the LDB must be located at spectral type later than L2.5 in this cluster. Using the latest evolutionary models for BDs, a lower limit of 550 Myr on the cluster age is set. This constraint has been combined with other dating methods to obtain an updated age estimate of 780$\pm$230 Myr for the Coma Ber open cluster. Identification of significantly cooler sub-stellar cluster members in Coma Ber awaits the advent of the Euclid wide survey, which should reach a depth of about J=23; this superb sensitivity will make it possible to determine the precise location of the sub-stellar LDB in this cluster and to carry out a complete census of its sub-stellar population.
Coma Berenices (Coma Ber), an open cluster about the same age as Praesepe and the Hyades (700-800 Myr) is, despite being only 85 pc away, less well studied than its famous cousins. This is due principally to its sparseness and low proper motion, which together made Coma Ber's membership challenging to establish pre-Gaia. We have curated a new list of its members based on Gaia DR2 astrometry, derived its metallicity and interstellar reddening using LAMOST data, and inferred the cluster's age by fitting PARSEC isochrones to its color$-$magnitude diagram. We then measured rotation periods for Com…
We present a study of metallicities in a sample of main sequence stars with spectral types M, K, G and F ($T_{\rm eff}$ $\sim$ 3200 -- 6500K and log $g$ $\sim$ 4.3 -- 5.0 dex) belonging to the solar neighborhood young open cluster Coma Berenices. Metallicities were determined using the high-resolution (R=$λ$/$Δ$ $λ$ $\sim$ 22,500) NIR spectra ($λ$1.51 -- $λ$1.69 $μ$m) of the SDSS-IV APOGEE survey. Membership to the cluster was confirmed using previous studies in the literature along with APOGEE radial velocities and Gaia DR2. An LTE analysis using plane-parallel MARCS model atmospheres and the…
We present atmospheric parameters and abundances for chemical elements from carbon to barium in metal-poor stars in Segue 1 (seven stars), Coma Berenices (three stars), and Triangulum II (one star) ultra-faint dwarf galaxies (UFDs). The effective temperatures rely on new photometric observations in the visible and infra-red bands, obtained with the 2.5 m telescope of the SAI MSU Caucasian observatory. Abundances of up to fourteen chemical elements were derived under the non-local thermodynamic equilibrium (NLTE) line formation, and LTE abundances were obtained for up to five more elements. For…
Searching for short-period variable stars in the direction of Coma Berenices and Upgren 1 open clusters: Melotte 111 AV 1224 a new eclipsing binary star
本文报道了在后发座Berenices和Upgren 1疏散星团方向进行的CCD测光观测结果，目的是寻找新的短周期变星。总共检查了35颗恒星的变异性。经过这次搜索，在SIMBAD数据库中被命名为Melotte 111 AV 1224的恒星被发现是一颗新的食双星。后续的斯特伦格伦测光和光谱观测使我们能够推导出恒星的光谱类型，距离，红化和有效温度。对双星的光变曲线进行了初步分析，并导出了轨道系统的参数。从导出的物理参数，我们得出结论，Melotte 111 AV 1224是最有可能的W UMA食双星，是不是后发座疏散星团的成员。另一方面，在后发座疏散星团中，我们没有发现先前被编目为变星的NSV 5612和NSV 5615的亮度变化的证据。
We present wind models of ten young Solar-type stars in the Hercules-Lyra association and the Coma Berenices cluster aged around 0.26 Gyr and 0.58 Gyr respectively. Combined with five previously modelled stars in the Hyades cluster, aged 0.63 Gyr, we obtain a large atlas of fifteen observationally based wind models. We find varied geometries, multi-armed structures in the equatorial plane, and a greater spread in quantities such as the angular momentum loss. In our models we infer variation of a factor of ~6 in wind angular momentum loss $\dot J$ and a factor of ~2 in wind mass loss $\dot M$ b…
Crowning the Queen: Membership, Age, Rotation, and Activity for the Open Cluster Coma Berenices
Columbia University（哥伦比亚大学）；Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多天体物理实验室，波尔多大学，法国国家科学研究中心）；Rutgers, the State University of New Jersey（新泽西州立罗格斯大学）
后发座FK是一颗快速旋转的磁活性恒星，其光变曲线受到其表面冷斑的调制。它是第一颗发现“翻转”现象的恒星。从那时起，在许多其他恒星中，也报道了黑子活动的变化。因此，对FK Com中的斑点活动的演变进行更彻底的研究是有意义的。在这项研究中，我们用两种不同的时间序列分析方法分析了15年的测光观测，特别强调从数据中检测触发器类型的事件。我们应用连续周期搜索和载波拟合方法对1995- 2010年的长期标准Johnson-Ruminins V观测值进行了分析。这些观测是用两台自动测光望远镜进行的，凤凰-10和Amadeus T7位于亚利桑那州。我们在15个分析数据段中的6个中识别出复杂的相位行为。我们确定了五个触发事件和两个相位跳变的情况，其中相移为Δ << 0.4. In addition we see two mergers of spot regions and two cases where the apparent phase shifts are caused by spot regions drifting with respect to each other. Furthermore we detect variations in the rotation period corresponding to a differential rotation coefficien…
We analyze the 3D morphology and kinematics of 13 open clusters (OCs) located within 500 pc of the Sun, using Gaia EDR3 and kinematic data from literature. Members of OCs are identified using the unsupervised machine learning method StarGO, using 5D parameters (X, Y, Z, $μ_α\cosδ, μ_δ$). The OC sample covers an age range of 25Myr--2.65Gyr. We correct the asymmetric distance distribution due to the parallax error using Bayesian inversion. The uncertainty in the corrected distance for a cluster at 500~pc is 3.0--6.3~pc, depending on the intrinsic spatial distribution of its members. We determine…
Gyrochronology is one of the methods currently used to estimate the age of stellar open clusters. Hundreds of new clusters, associations, and moving groups unveiled by Gaia and complemented by accurate rotation period measurements provided by recent space missions such as Kepler and TESS are allowing us to significantly improve the reliability of this method. We use gyrochronology, that is, the calibrated age-mass-rotation relation valid for low-mass stars, to measure the age of the recently discovered moving group Group X. We extracted the light curves of all candidate members from the TESS f…
