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Register a new userRuprecht 147 DANCe I. Members, empirical isochrone, luminosity and mass distributions
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Context. Ruprecht 147 is the oldest (2.5 Gyr) open cluster in the solar vicinity (< 300 pc), making it an important target for stellar evolution studies and exoplanet searches. Aims. Derive a census of members and the luminosity, mass, and spatial distributions of the cluster. Methods. We use an astro-photometric data set including all available information from the literature together with our own observations. We process the data with an updated version of an existent membership selection methodology. Results. We identify 259 high-probability candidate members, including 58 previously unreported. All these candidates cover the luminosity interval between G > 6 mag to i< 21 mag. The cluster luminosity and mass distributions are derived with an unprecedented level of details allowing us to recognize, among other features, the Wielen dip. The mass distribution in the low-mass regime drops sharply at 0.4 $M_{odot}$ even though our data are sensitive to stellar masses down to 0.1 $M_{odot}$, suggesting that most very-low-mass members left the cluster as the result of its dynamical evolution. In addition, the cluster is highly elongated (ellipticity $sim$ 0.5) towards the galactic plane, and mass segregated. Conclusions. Our combined Gaia+DANCe data set allows us to obtain an extended list of cluster candidate members, and to derive luminosity, mass and projected spatial distributions in the oldest open cluster of the solar vicinity.
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Context. The study of star formation is extremely challenging due to the lack of complete and clean samples of young, nearby clusters, and star forming regions. The recent Gaia DR2 catalogue complemented with the deep, ground based COSMIC DANCe catalogue offers a new database of unprecedented accuracy to revisit the membership of clusters and star forming regions. The 30 Myr open cluster IC 4665 is one of the few well-known clusters of this age and it is an excellent target where to test evolutionary models and study planetary formation. Aims. We aim to provide a comprehensive membership analysis of IC 4665 and to study the following properties: empirical isochrones, distance, magnitude distribution, present-day system mass function, and spatial distribution. Methods. We use the Gaia DR2 catalogue together with the DANCe catalogue to look for members using a probabilistic model of the distribution of the observable quantities in both the cluster and background populations. Results. We obtain a final list of 819 candidate members which cover a 12.4 magnitude range (7 < J < 19.4). We find that 50% are new candidates, and we estimate a conservative contamination rate of 20%. This unique sample of members allows us to obtain a present-day system mass function in the range of 0.02-6 Msun, which reveals a number of details not seen in previous studies. In addition, they favour a spherically symmetric spatial distribution for this young open cluster. Conclusions. Our membership analysis represents a significant increase in the quantity and quality (low-contamination) with respect to previous studies. As such, it offers an excellent opportunity to revisit other fundamental parameters such as the age.
The DANCe survey provides photometric and astrometric (position and proper motion) measurements for approximately 2 millions unique sources in a region encompassing $approx$80deg$^{2}$ centered around the Pleiades cluster. We aim at deriving a complete census of the Pleiades, and measure the mass and luminosity function of the cluster. Using the probabilistic selection method described in Sarro+2014, we identify high probability members in the DANCe ($ige$14mag) and Tycho-2 ($Vlesssim$12mag) catalogues, and study the properties of the cluster over the corresponding luminosity range. We find a total of 2109 high probability members, of which 812 are new, making it the most extensive and complete census of the cluster to date. The luminosity and mass functions of the cluster are computed from the most massive members down to $approx$0.025M$_{odot}$. The size, sensitivity and quality of the sample result in the most precise luminosity and mass functions observed to date for a cluster. Our census supersedes previous studies of the Pleiades cluster populations, both in terms of sensitivity and accuracy.
Eclipsing binaries in star clusters offer more stringent tests of stellar evolution theory than field binaries because models must not only match the binary properties, but also the radiative properties of all other cluster members at a single chemical composition and a single age. Here we report new spectroscopic observations of the G type, detached eclipsing binary EPIC 219394517 in the open cluster Ruprecht 147 ([Fe/H] = +0.10), which was observed in late 2015 by the K2 mission. A joint analysis of our radial-velocity measurements and the K2 light curve shows the 6.5 day orbit to be very nearly circular. We derive highly precise masses of 1.0782 +/- 0.0019 Msun and 1.0661 (+0.0027/-0.0021) Msun, radii of 1.055 +/- 0.011 Rsun and 1.042 +/- 0.012 Rsun, and effective temperatures of 5930 +/- 100 K and 5880 +/- 100 K for the primary and secondary, respectively. The distance we infer, 283 (+18/-16) pc, corresponds to a parallax in good agreement with the Gaia/DR2 value for the star. Current stellar evolution models from the MIST and PARSEC series match the above physical properties very well at ages of 2.48 and 2.65 Gyr. Isochrones for these same ages and the measured composition, along with our reddening estimate for EPIC 219394517, also show generally good agreement with the optical and near-infrared color-magnitude diagrams of the cluster, which can be constructed with no free parameters as the distances of all member stars are known from Gaia.
The goal of this paper is to increase the membership list of the Chamaeleon star forming region and the $epsilon$ Cha moving group, in particular for low-mass stars and substellar objects. We extended the search region significantly beyond the dark clouds. Our sample has been selected based on proper motions and colours obtained from Gaia and 2MASS. We present and discuss the optical spectroscopic follow-up of 18 low-mass stellar objects in Cha I and $epsilon$ Cha. We characterize the properties of objects by deriving their physical parameters, both from spectroscopy and photometry. We add three more low-mass members to the list of Cha I, and increase the census of known $epsilon$ Cha members by more than 40%, confirming spectroscopically 13 new members and relying on X-ray emission as youth indicator for 2 more. In most cases the best-fitting spectral template is from objects in the TW Hya association, indicating that $epsilon$ Cha has a similar age. The first estimate of the slope of the initial mass function in $epsilon$ Cha down to the sub-stellar regime is consistent with that of other young clusters. We estimate our IMF to be complete down to $approx 0.03$M$_{odot}$. The IMF can be represented by two power laws: for M $<$ 0.5 M$_{odot}$ $alpha = 0.42 pm 0.11$ and for M $>$ 0.5 M$_{odot}$ $alpha = 1.44 pm 0.12$. We find similarities between $epsilon$ Cha and the southernmost part of Lower Centaurus Crux (LCC A0), both lying at similar distances and sharing the same proper motions. This suggests that $epsilon$ Cha and LCC A0 may have been born during the same star formation event
Gyrochronology allows the derivation of ages for cool main sequence stars based on their observed rotation periods and masses, or a suitable proxy thereof. It is increasingly well-explored for FGK stars, but requires further measurements for older ages and K-M-type stars. We study the nearby, 3 Gyr-old open cluster Ruprecht 147 to compare it with the previously-studied, but far more distant, NGC 6819 cluster, and especially to measure cooler stars than was previously possible there. We constructed an inclusive list of 102 cluster members from prior work, including Gaia DR2, and for which light curves were also obtained during Campaign 7 of the Kepler/K2 space mission. [...] Periodic signals are found for 32 stars, 21 of which are considered to be both highly reliable and to represent single, or effectively single, Ru147 stars. These stars cover the spectral types from late-F to mid-M stars, and they have periods ranging from 6d-32d, allowing for a comparison of Ruprecht 147 to both of the other open clusters and to models of rotational spindown. The derived rotation periods connect reasonably to, overlap with, and extend to lower masses the known rotation period distribution of the 2.5 Gyr-old cluster NGC 6819. The data confirm that cool stars lie on a single surface in rotation period-mass-age space, and they simultaneously challenge its commonly assumed shape. The shape at the low mass region of the color-period diagram at the age of Ru147 favors a recently-proposed model, which requires a third mass-dependent timescale in addition to the two timescales required by a former model, suggesting that a third physical process is required to model rotating stars effectively.
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