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14:30 - 14:50 | Jos de Bruijne (ESA): The Potential of Gaia (Invited)
Gaia is on track for a first data release in late summer 2016. This presentation outlines the status of the mission and presents an overview of the data products to be released with a particular emphasis on open clusters.
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14:50 - 15:00 | Maroussia Roelens (University of Geneva): Short Timescale Variables in Stellar Clusters: From Gaia to Ground-Based Telescopes
Combined studies of variable stars and stellar clusters open great horizons, and they allow us to improve our understanding of stellar cluster formation and stellar evolution. In that prospect, the Gaia mission will provide astrometric, photometric and spectro-photometric data for about one billion stars of the Milky Way. This will represent a major census of stellar clusters, and it will drastically increase the number of known variable stars. The Gaia peculiar scanning law particularly offers the opportunity to investigate the rather unexplored domain of short timescale variability (from tens of seconds to a dozen of hours), bringing invaluable clues to the fields of stellar physics and stellar aggregates. We assess the Gaia capabilities in terms of short timescale variability detection, using extensive light curve simulations for various variable types. We show that Gaia can detect periodic and transient variability phenomena with amplitude variations larger than a few millimagnitudes. Additionally, we plan to perform subsequent follow-up of variables stars detected in clusters by Gaia to better characterize them. Hence, we develop a pipeline for the analysis of high cadence photometry from ground-based telescopes such as the 1.2 m Euler telescope (La Silla, Chile) and the 1.2 m Mercator telescope (La Palma, Canary Islands).
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15:00 - 15:10 | Ann Marie Cody (NASA Ames Research Center): Cool Young Stars in the Time Domain: The View with K2
In operation since 2014, the K2 mission is now acquiring high cadence, high precision, long time baseline on thousands of stars in the ecliptic plane. Unlike its predecessor the Kepler mission, K2 is observing a number of young to intermediate age star clusters. This provides the chance to not only look for relatively young planets, but to also study starspot evolution, accretion, and inner circumstellar disk dynamics on several month timescales. I will provide an overview of our K2 cluster photometry pipeline and highlight the variable processes evident in the first few campaigns, focusing on the pre-main-sequence stars observed in Upper Scorpius and rho Ophiuchus during Campaign 2.
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15:10 - 15:20 | Lorenzo Spina (Universidade de São Paulo): The Gaia-ESO Survey: Exploring the Galactic Metallicity Gradient Using Star Forming Regions and Young Open Clusters
Star Forming Regions and Young Open Clusters are the latest products of the Milky Way, therefore the study of their metal content can provide strong observational constraints on the Galactic chemical evolution. In addition, these young associations of stars have not had time to disperse through the Galactic disk, thus they are key objects in order to trace the present chemical pattern of the Galactic disk. The Gaia-ESO Survey is providing a large data set of precise and homogeneous chemical abundances of stellar clusters located at different Galactic radii. In my presentation I will provide a summary of the current status of the abundance determinations for the Star Forming Regions and Young Open Clusters observed by the Survey, that shades new light on the current metallicity gradient of the interstellar medium within the thin disk.
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15:20 - 15:30 | Poster pop-ups
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15:30 - 16:00 | Coffee break/poster session
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16:00 - 16:20 | Sean Matt (University of Exeter): Stellar Angular Momentum Over Time (Invited)
While on the main sequence, the structure and energy budget of cool stars change relatively little. By contrast, their angular momentum content varies by orders of magnitude, and observational studies of clusters are revealing a strong and clear mass-dependence to this spin-evolution. At the same time, we are still working to understand the complex relationships between rotation, convection, magnetic activity, and mass loss. I will discuss an emerging self-consistent picture that links all of these processes together and to the overall evolution of Sun-like and low-mass stars. This progress is due to large and diverse new datasets (especially from clusters), advances in physical models for the loss of angular momentum, and the incorporation of these models into long-term stellar evolution calculations.
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16:20 - 16:30 | Stephanie Douglas (Columbia University): Testing the Rotation-Activity Relation with the Hyades and Praesepe
As the nearest open cluster to the Sun, the Hyades is an important benchmark for calibrating stellar properties such as rotation and magnetic activity. Its proximity, however, means that cluster members are scattered across a wide area of the sky; previous studies of rotation in the Hyades relied on wide-area surveys designed to discover transiting exoplanets. I will present rotation periods measured using K2 data of the Hyades, including the first rotation periods of less than 1 day for cluster members and for fully convective Hyads. Discrepancies between Hyades data and gyrochronology models imply that we still do not fully understand how magnetic fields affect stellar spin-down. I will discuss how we can use the Hyades and the co-eval Praesepe cluster to test theories of stellar magnetic fields.
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16:30 - 16:40 | Luisa Rebull (IPAC/Caltech): Rotation Periods in the Pleiades with K2
The rotation rates of Pleiades members have been studied for years, and, because of its age of ~125 Myr, is one of the clusters anchoring many of the models for rotation evolution. With the K2 data, we can probe the rotation rate of more members, to smaller amplitudes, and with a far better cadence, than has even been probed before. What the K2 data allow that no previous dataset has allowed is to measure not only rotation periods but also to measure the shape of the light curve and to often detect evidence of multiple periods due to differential rotation, spot evolution or binarity. The general relationship between P and V-K (as a proxy for mass) follows the overall trends found in other Pleiades studies. There is a slowly rotating sequence for 1 < V-K < 3.5 (spectral types F, G and K); most of these stars show evidence for differential rotation and/or spot evolution. Most of the stars with V-K > 5 (spectral type > M3.5) are rapidly rotating; in general, these stars show little evidence for differential rotation or spot evolution. There is a "transition region" (3.5 < V-K < 5; spectral types M0 to M3) in which there seems to be a disorganized relationship between P and V-K; in many of these cases, one can see slow changes in the light curve shape over the K2 campaign.
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16:40 - 16:50 | Jason Curtis (Pennsylvania State University): Ruprecht 147 and the Quest to Date Middle-Aged Stars
Ages of stars are difficult to infer because stars change very little during the majority of their lifetimes. However, stars are observed to spin down over time due to magnetic braking, which weakens the magnetic dynamo as well. This spin down has led to a new age dating method called gyrochronology, which has been successfully calibrated for Sun-like stars up to 2.5 Gyr, but is still undetermined at older ages and lower masses. The decay of magnetic activity has also been utilized to empirically calibrate an age relationship at ages less than 600 Myr with nearby young star clusters (e.g., Hyades), and pinned down at 4 Gyr with M67, but the relationship is basically unconstrained at intermediate ages and sub-Solar masses. Advances in observational facilities have brought distant clusters into view, while the discovery of Ruprecht 147 has provided a new benchmark that is the oldest nearby cluster (3 Gyr, 300 pc, Curtis et al. 2013), and which provides a bridge across this historic age gap. I will present new, high quality chromospheric activity data for NGC 752 at 1.5 Gyr and Ruprecht 147 at 3 Gyr. The stars of Ruprecht 147 will demonstrate the typical activity level and variability experienced by the Sun at a time when multicellular life first evolved on Earth. I will also re-evaluate the M67 data by considering contamination by the interstellar medium, with implications for the frequency of Maunder Minima. Finally, I will discuss a new opportunity to investigate stellar spin down and variability in GKM dwarfs with the K2 Survey of Ruprecht 147, and will present preliminary results of our transit and rotation programs, along with chromospheric and coronal activity diagnostics for the cluster's Solar analogs.
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16:50 - 17:00 | Lison Malo (Canada-France-Hawaii Telescope): The Pre-Gaia Search for Young Objects in the Solar Neighborhood
Using the BANYAN I and BANYAN II tools, we identified more than 500 candidate members in nearby young kinematic groups. As part of the follow-up programs, we measured radial velocity and confirmed signs of youth (Halpha, X-ray emission, low surface gravity, lithium) for more than 150 red objects using optical and near-infrared spectroscopy. An accurate determination of the age of those objects requires a comparison of their fundamental properties to those of evolutionary models, which take into account the impact of their fully convective interior. As young low-mass objects display strong magnetic activity, the inclusion of magnetic fields in evolutionary models is a key step towards the accurate determination of their fundamental properties. We present the isochronal age determination using the Dartmouth magnetic evolutionary models and ESPaDOnS (soon SPIRou) instrument, and show that including magnetic fields generally increases the isochronal age, which better agree with the lithium depletion boundary method.
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17:00 - 17:10 | Loredana Prisinzano (INAF-Osservatorio Astronomico di Palermo): The Gaia-ESO Survey: Addressing Extinction and Reddening Towards NGC 6530
Accurate knowledge of the amount of interstellar extinction and its properties is crucial to determine fundamental stellar parameters, such as luminosities, masses and ages. This can be challenging in case of young clusters surrounded by or embedded in the original molecular gas. NGC 6530 is a rich young star forming region located towards a concentration of the native molecular gas. As a consequence, it is affected by a significant and variable reddening, as it has been reported in the literature, even with several hints of an anomalous reddening law. Several and also different literature results have been found about the reddening properties in this region. The Gaia-ESO survey data of NGC 6530 gives us a unique opportunity to address this issue. By using Gaia-ESO fundamental parameters and literature optical photometry, we derive the reddening law across the NGC 6530 field. We find that both extinction and reddening show a spatial pattern that is consistent with the density map of the Lagoon Nebula, allowing us to trace its tridimensional structure. Our results are crucial for deriving other stellar properties and then understanding the star formation history of this cluster.
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17:10 - 17:30 | Day 1 wrap up
A quick review of topics discussed during first day of splinter.
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14:30 - 14:50 | Cameron Bell (ETH Zürich): Clusters as Benchmarks for Measuring Fundamental Stellar Properties (Invited)
Star clusters have long represented benchmarks with respect to the determination of fundamental stellar parameters, in large part due to the underlying assumption that members within such ensembles share several common properties; namely they are coeval, have the same chemical composition and are located at roughly the same distance. By studying a given cluster we can infer the mass dependence of astrophysical phenomena at a given epoch and by studying several clusters spanning a range of ages we can track how such phenomena evolve with time, as well as investigate second-order effects such as the local environment. In this review I will focus on young star clusters (those with ages less than or approximately equal to that of the Pleiades) and discuss several methods employed to estimate fundamental stellar parameters. Specifically, I will focus on the use of stellar evolutionary models to determine the ages and masses of stars and discuss the limitations of such models, the use of eclipsing binaries in helping to constrain evolutionary models, and the use of large-scale spectroscopic surveys (e.g., Gaia-ESO and APOGEE) in calculating atmospheric parameters such as effective temperature, surface gravity and chemical composition. Finally, I will attempt to bring together recent studies to highlight the potential for sub-grouping and age spreads within a given cluster, thereby demonstrating that our traditional view of young star clusters is perhaps too simplistic.
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14:50 - 15:00 | Adam Kraus (University of Texas, Austin): The Mass-Radius Relation of Young Stars
Evolutionary models of pre-main sequence stars remain largely uncalibrated, especially for masses below that of the Sun, and dynamical masses and radii pose valuable tests of these theoretical models. Stellar mass dependent features of star formation (such as disk evolution, planet formation, and even the IMF) are fundamentally tied to these models, which implies a systematic uncertainty that can only be improved with precise measurements of calibrator stars. I will describe the discovery and characterization of 15 eclipsing binary systems in the Upper Scorpius star-forming region from K2 Campaign 2 data, spanning from B stars to the substellar boundary. We have obtained complementary RV curves, spectral classifications, and high-resolution imaging for these targets; the combination of these data yield high-precision masses and radii for the binary components, and hence a dense sampling of the (nominally coeval) mass-radius relation of 10 Myr old stars. We already reported initial results from this program for the young M4.5 eclipsing binary UScoCTIO 5 (Kraus et al. 2015), demonstrating that theoretically predicted masses are discrepant by ~50% for this pair of low-mass stars. Precise radii allow us to isolate the source of the discrepancy: models of young stars do not predict luminosities that are too low, as is commonly thought, but rather temperatures that are too warm.
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15:00 - 15:10 | Garrett Somers (Ohio State University): Open Cluster Lithium as a Strong Test of Core-Envelope Re-Coupling Timescales
Rotational mixing is a prime candidate for explaining the gradual depletion of light elements from the photospheres of cool stars during the main sequence. However, previous mixing calculations have relied primarily on incomplete treatments of angular momentum (AM) transport in stellar interiors, which do not predict the rotational evolution of open clusters. In order to produce new mixing calculations, we modify our rotating stellar evolution code to include an additional source of AM transport, a necessary ingredient for explaining the open cluster rotation pattern. With this machinery, we show for the first time that the main sequence evolution of surface rotation in open clusters and the evolving abundance of lithium in cool stars can be simultaneously predicted. Our mixing-derived core-envelope coupling strengths agree well with previous work, confirming the reliability of our mixing calculations. Using Li abundances, we argue that the timescale for core-envelope re-coupling during the main sequence is a strong function of mass, thus placing an important constraint on models seeking to identify the mechanism responsible for core-envelope coupling. We discuss implications of this finding for stellar physics, including the viability of gravity waves and magnetic fields as agents of AM transport.
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15:10 - 15:20 | Jieun Choi (Harvard University): Toward the Absolute Age of M92
Globular clusters provide a fundamental link between stars and galaxies. For example, it has been suggested that ultra faint dwarf galaxies formed all of their stars prior to the epoch of reionization, but this conclusion hinges entirely on the striking similarity of their stellar populations to the ancient, metal-poor globular cluster M92. The accurate measurement of absolute ages of ancient globular clusters therefore has direct implications for the formation histories of the smallest galaxies in the Universe. However, a reliable determination of the absolute ages of globular clusters has proven to be a challenge due to uncertainties in stellar physics and complications in how the models are compared to observations. I will present preliminary results from a comprehensive study to measure the absolute age of M92 using high-quality HST archival imaging data. We pair our new MESA Isochrones and Stellar Tracks (MIST) models with a full CMD fitting framework to jointly fit multi-color CMDs, taking into account the uncertainties in abundances, distance, and stellar physics. The goal of this project is two-fold. First, we aim to provide the most secure absolute age of M92 to date with robustly estimated uncertainties. Second, we explore and quantify the degeneracies between uncertain physical quantities and model variables, such as the distance, mixing-length-alpha parameter, and helium abundance, with the ultimate goal of better constraining these unknowns with data from ongoing and future instruments and surveys such as K2, Gaia, TESS, JWST, and WFIRST.
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15:20 - 15:30 | Poster pop-ups
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15:30 - 16:00 | Coffee break/poster session
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16:00 - 16:20 | Richard Parker (Liverpool John Moores University): The Diagnostic Potential of Spatial and Kinematic Tracers (Invited)
The advent of facilities such as ALMA, Gaia, and ground-based surveys such as GES and IN-SYNC will soon result in a deluge of information on the spatial and kinematic distributions of stars in both young and old star clusters. These distributions can be used to determine the dynamical history of a star cluster and hence they place strong constraints on the initial conditions of star formation in a given cluster. I will review the diagnostics available to attack this problem, starting from the spatial information and progressing to the kinematic information. I will conclude by highlighting some outstanding issues that we must address in the immediate future.
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16:20 - 16:30 | Nicola Da Rio (University of Florida): The IN-SYNC Orion Survey
I will present the results of the SDSS IN-SYNC Orion survey, a high resolution infrared spectroscopy of the young stellar population in the Orion A cloud. We obtained accurate stellar parameters and radial velocities for ~3000 objects in the region, down to the H-burning limit, from the dense Orion Nebula Cluster - the prototypical nearby region of active massive star formation - to the low-density environments of the L1641 region. From a number of independent indicators, we confirm a substantial age spread throughout the region, which on the other hand shares a common mean age. Based on kinematic arguments, we suggest that the older population of young sources in south of the ONC is not separate population. Using kinematics, stellar parameters, and surface gravity constraints, we identify few hundreds of new candidate young members, most of which are diskless sources in poorly studied areas of the cloud. We find evidence for kinematic subclustering along the star forming filament, where the stellar component remains kinematically associated to the gas; in the ONC we find that the stellar population is supervirial and currently expanding. These results are in agreement with structural analyses of the spatial distribution of sources in the ONC, which I will also outline.
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16:30 - 16:40 | Rob Jeffries (Keele University): Structure and Dynamics of Young Star Clusters With the Gaia-ESO Survey
The physical mechanisms driving the formation of star clusters and their early dynamical evolution are not yet fully understood. Recent theoretical and numerical studies show that unbiased analysis of the structural and kinematical properties of young (1-10 Myr) star clusters are required to constrain different models. The Gaia-ESO Survey is measuring precise radial velocities (~0.2-0.3 km/s), stellar parameters (e.g., effective temperatures and gravities) and other age indicators (e.g., Li abundance) for unbiased samples of the stellar population of several young star clusters. I will present some of the first results from the survey, which show that we are able to resolve the internal kinematics of the clusters and put in evidence how dynamical properties of nearby young star clusters are more complex than previously thought.
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16:40 - 16:50 | Mark Pecaut (Rockhurst University): Substructure in the Scorpius-Centaurus OB Association
OB associations are remnants of star formation on a large scale, producing everything from O- and B-type stars, down to the lowest mass brown dwarfs. OB associations represent the typical mode of star formation in the Galaxy. But is this process monolithic? We present the results of a survey for new, solar mass (0.7 - 1.3 Msun) members of Sco-Cen, the nearest OB Association to the Sun (~100-200 pc, 10-20 Myr; de Zeeuw et al. 1999, Mamajek et al. 2002, Pecaut et al. 2012). We identify ~150 new members and place the known B/A/F/G/K/M-type members on the Hertzsprung-Russell diagram. From these data, we construct an age map of Sco-Cen, occupying approximately 2,000 square degrees on the sky. These results indicate there is substantial substructure in Sco-Cen, and present the possibility that star formation on the largest scales can be considered a collection of many individual, small-scale star formation events along a giant molecular cloud.
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16:50 - 17:00 | Ruth Angus (University of Oxford): Exploring Gyrochronology with LSST
The Large Synoptic Survey Telescope (LSST) will provide sparse but precise ground-based photometry for billions of field and cluster cool dwarfs. We explore LSST's potential for large-scale rotation period measurement with an emphasis on applications to gyrochronology, the method of inferring stellar ages from rotation periods. With its ten year baseline, LSST light curves will be sensitive to long rotation periods which are characteristic of old and low-mass stars. New asteroseismic data from the Kepler spacecraft have revealed that magnetic braking may cease at around Solar Rossby number, implying that gyrochronology is not applicable to old stars. By measuring rotation periods of old, slowly rotating, low-mass stars we can decisively test the age-rotation relations at all ages. Of particular interest are the open clusters with precisely measured isochronal ages. These clusters will allow us to recalibrate the age-rotation relations in the old, low-mass regime, provided we can measure the photometric rotation periods of their members. Using representative distributions of stellar ages and spectral types from TRILEGAL outputs, we simulate thousands of light curves using a gyrochronology relation, a simple star-spot model and approximate LSST cadence. By running a rotation period recovery pipeline, we predict the number of accurately measured cool dwarf rotation periods expected from LSST as a function of spectral type, magnitude and rotation period.
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17:00 - 17:10 | Søren Meibom (Harvard-Smithsonian Center for Astrophysics): The TESS Open Cluster Survey
NASA's Transiting Exoplanet Survey Satellite (TESS) will launch in 2017. TESS is an all-sky survey over 2 years, covering the Northern and the Southern hemispheres with 2-minute cadence highly precise photometric observations. The TESS Open Cluster Survey (TOCS) is a project to ensure TESS observations of thousands of cool stars in dozens of galactic open clusters with ages from the PMS to billion of years. TOCS will provide a unique opportunity for studies of stellar variability and activity in clusters (e.g., stellar rotation, differential rotation, flares, pulsations and asteroseismology) and will lay the foundation for a statistical study of the frequency and nature of cluster planets. A TOCS working group is being formed to help construct lists of cluster stars to be included in the TESS target list and to lead open cluster research using TESS data. Researchers with a desire and ability to contribute to TOCS can apply to join the TOCS working group. TOCS promises to supply the astrophysical community with data for cool stars in clusters that will lead to exciting advances and new avenues for cool star research. In my talk I will give an overview of TOCS and the primary science goals, lay out the structure of the TOCS working group, and give details on the collaborative effort, and the criteria used, to select clusters and cluster stars for the TESS target list.
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17:10 - 17:30 | Wrap up and next steps
This will be an opportunity for the entire audience to hear what was discussed in the different break-out groups and summarize what has been learned.