scholarly journals Flares in open clusters with K2

2021 ◽  
Vol 645 ◽  
pp. A42
Author(s):  
Ekaterina Ilin ◽  
Sarah J. Schmidt ◽  
Katja Poppenhäger ◽  
James R. A. Davenport ◽  
Martti H. Kristiansen ◽  
...  
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
Sample Selection ◽  
Mass Range ◽  
Open Clusters ◽  
Light Curves ◽  
Rapid Decline ◽  
Sequence Evolution ◽  
Mass Relation ◽  
Rotation Periods

Context. Magnetic fields are a key component in the main sequence evolution of low mass stars. Flares, energetic eruptions on the surfaces of stars, are an unmistakable manifestation of magnetically driven emission. The occurrence rates and energy distributions of flares trace stellar characteristics such as mass and age. However, before flares can be used to constrain stellar properties, the flaring-age-mass relation requires proper calibration. Aims. This work sets out to quantify the flaring activity of independently age-dated main sequence stars for a broad range of spectral types using optical light curves obtained by the Kepler satellite. Methods. Drawing from the complete K2 archive, we searched 3435 ∼80 day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates. Results. We confirmed a total of 3844 flares on high probability open cluster members with ages from zero age main sequence (Pleiades) to 3.6 Gyr (M 67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-M dwarfs. We added the Hyades (690 Myr) to the sample as a comparison cluster to Praesepe (750 Myr), the 2.6 Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. We found that the flare energy distribution was similar in the entire parameter space, following a power law relation with exponent α ≈ 1.84−2.39. Conclusions. We confirm that flaring rates decline with age, and decline faster for higher mass stars. Our results are in good agreement with most previous statistical flare studies. We find evidence that a rapid decline in flaring activity occurred in M1–M2 dwarfs around the ages of the Hyades and Praesepe, when these stars spun down to rotation periods of about 10 d, while higher mass stars had already transitioned to lower flaring rates and lower mass stars still resided in the saturated activity regime. We conclude that some discrepancies between our results and flare studies that used rotation periods for their age estimates could be explained by sample selection bias toward more active stars, but others may point to the limitations of using rotation as an age indicator without additional constraints from stellar activity.

scholarly journals Observational problems in determining the ages of open clusters

2008 ◽  
Vol 4 (S258) ◽  
pp. 141-152
Author(s):  
Elizabeth J. Jeffery
Keyword(s):  
White Dwarf ◽  
Main Sequence ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Stellar Populations ◽  
Statistical Technique ◽  
Open Clusters ◽  
Sequence Evolution ◽  
Data Set ◽  
Wide Range

AbstractOpen clusters have long been objects of interest in astronomy. As a good approximation of essentially pure stellar populations, they have proved very useful for studies in a wide range of astrophysically interesting questions, including stellar evolution and atmospheres, the chemical and dynamical evolution of our Galaxy, and the structure of our Galaxy. Of fundamental importance to our understanding of open clusters is accurate determinations of cluster ages. Currently there are two main techniques for independently determining the ages of stellar populations: main sequence evolution theory (via cluster isochrones) and white dwarf cooling theory. We will provide an overview of these two methods, the current level of agreement between them, as well as a look to the current state of increasing precision in the determination of each. Particularly I will discuss the comprehensive data set collection that is being done by the WIYN Open Cluster Study, as well as a new Bayesian statistical technique that has been developed by our group and its applications in improving and determining white dwarf ages of open clusters. I will review the so-called bright white dwarf technique, a new way of measuring cluster ages with just the bright white dwarfs. I will discuss the first application of the Bayesian technique to the Hyades, also demonstrating the first successful application of the bright white dwarf technique. These results bring the white dwarf age of the Hyades into agreement with the main sequence turn off age for the first time.

scholarly journals Rotation periods for cool stars in the open cluster Ruprecht 147 (NGC 6774)

2020 ◽  
Vol 644 ◽  
pp. A16
Author(s):  
D. Gruner ◽  
S. A. Barnes
Keyword(s):  
Open Cluster ◽  
Rotation Period ◽  
Principal Component ◽  
Mass Region ◽  
Open Clusters ◽  
Light Curves ◽  
Rotating Stars ◽  
Rotation Periods ◽  
Periodicity Analysis ◽  
Cool Stars

Context. 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. Aims. We study the 2.7 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. Methods. 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. We placed them in the cluster color-magnitude diagram and checked the related information against appropriate isochrones. The light curves were then corrected for data systematics using Principal Component Analysis on all observed K2 C07 stars and subsequently subjected to periodicity analysis. Results. Periodic signals are found for 32 stars, 21 of which are considered to be both highly reliable and to represent single, or effectively single, Ru 147 stars. These stars cover the spectral types from late-F to mid-M stars, and they have periods ranging from 6 d – 33 d, allowing for a comparison of Ruprecht 147 to both 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. Conclusions. 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 Ru 147 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.

scholarly journals Central Stars of Planetary Nebulae in Galactic Open Clusters: Providing additional data for the White Dwarf Initial-to-Final-Mass Relation

2018 ◽  
Vol 14 (S343) ◽  
pp. 400-401
Author(s):  
Vasiliki Fragkou ◽  
Quentin A. Parker ◽  
Albert Zijlstra ◽  
Richard Shaw ◽  
Foteini Lykou
Keyword(s):  
White Dwarf ◽  
Additional Data ◽  
Open Cluster ◽  
Central Star ◽  
Open Clusters ◽  
Physical Parameters ◽  
Mass Relation ◽  
Carbon And Nitrogen ◽  
Final Mass ◽  
Central Stars

AbstractAccurate (< 10%) distances of Galactic star clusters allow a precise estimation of the physical parameters of any physically associated Planetary Nebula (PN) and also that of its central star (CSPN) and its progenitor. The progenitor’s mass can be related to the PN’s chemical characteristics and, furthermore, provides additional data for the widely used white dwarf (WD) initial-to-final mass relation (IFMR) that is crucial for tracing the development of both carbon and nitrogen in entire galaxies. To date, there is only one PN (PHR1315- 6555) confirmed to be physically associated with a Galactic open cluster (ESO 96 -SC04) that has a turn-off mass ∼2Mʘ. Our deep HST photometry was used for the search of the CSPN of this currently unique PN. In this work, we present our results.

scholarly journals Activity and rotation of the X-ray emitting Kepler stars

2019 ◽  
Vol 628 ◽  
pp. A41 ◽  
Author(s):  
D. Pizzocaro ◽  
B. Stelzer ◽  
E. Poretti ◽  
S. Raetz ◽  
G. Micela ◽  
...  
Keyword(s):  
White Light ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Light Curves ◽  
Late Type ◽  
Main Sequence Stars ◽  
Photometric Variability ◽  
X Ray ◽  
Rotation Periods ◽  
Flare Frequency

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation-activity studies found in the literature suffer from inhomogeneity in the measurement of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting, late-type main-sequence stars observed by XMM-Newton and Kepler. We measured rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopted the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 20 of which do not have period reported in the previous literature. In the X-ray activity-rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~10 d but it can be probed only marginally with this sample, which is biased towards fast rotators due to the X-ray selection. We observe seven bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~0.15 d−1, consistent with the optical flare frequency obtained from the much longer Kepler time-series.

scholarly journals Cepheid distances from the Baade–Wesselink method

2012 ◽  
Vol 8 (S289) ◽  
pp. 138-144 ◽  
Author(s):  
Wolfgang Gieren ◽  
Jesper Storm ◽  
Nicolas Nardetto ◽  
Alexandre Gallenne ◽  
Grzegorz Pietrzyński ◽  
...  
Keyword(s):  
Excellent Agreement ◽  
Surface Brightness ◽  
Recent Progress ◽  
Main Sequence ◽  
Near Infrared ◽  
Open Cluster ◽  
Open Clusters ◽  
Distance Scale ◽  
Systematic Uncertainties ◽  
Classical Cepheids

AbstractRecent progress on Baade–Wesselink (BW)-type techniques to determine the distances to classical Cepheids is reviewed. Particular emphasis is placed on the near-infrared surface-brightness (IRSB) version of the BW method. Its most recent calibration is described and shown to be capable of yielding individual Cepheid distances accurate to 6%, including systematic uncertainties. Cepheid distances from the IRSB method are compared to those determined from open cluster zero-age main-sequence fitting for Cepheids located in Galactic open clusters, yielding excellent agreement between the IRSB and cluster Cepheid distance scales. Results for the Cepheid period–luminosity (PL) relation in near-infrared and optical bands based on IRSB distances and the question of the universality of the Cepheid PL relation are discussed. Results from other implementations of the BW method are compared to the IRSB distance scale and possible reasons for discrepancies are identified.

scholarly journals A Rotational Period Study of a Large Sample of Pre-Main Sequence stars in NGC 2264

2004 ◽  
Vol 215 ◽  
pp. 125-126 ◽  
Author(s):  
M. Lamm ◽  
C.A.L. Bailer-Jones ◽  
R. Mundt ◽  
W. Herbst
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
Monitoring Program ◽  
Bimodal Distribution ◽  
Main Sequence Stars ◽  
Lower Mass ◽  
Rotation Periods ◽  
Photometric Monitoring ◽  
Pms Stars ◽  
Mass Dependent

We present the results of a photometric monitoring program of pre-main sequence (PMS) stars in the young (2-4 Myr) open cluster NGC 2264 (d=700 pc). We find that the rotation periods are mass dependent and show a bimodal distribution for higher mass stars with M ≳ 0.3 M⊙ and a unimodal distribution for lower mass stars with M ≲ 0.3 M⊙.

scholarly journals Fragile Binaries: Observational Leverage on Difficult Astrophysical Problems

2006 ◽  
Vol 2 (S240) ◽  
pp. 300-305
Author(s):  
T.D. Oswalt ◽  
K.B. Johnston ◽  
M. Rudkin ◽  
T. Vaccaro ◽  
D. Valls-Gabaud
Keyword(s):  
Binary Stars ◽  
White Dwarfs ◽  
Main Sequence ◽  
Age Determination ◽  
Open Clusters ◽  
Mass Relation ◽  
Space Motion ◽  
Sequence Components ◽  
Determination Methods ◽  
Cool White Dwarfs

AbstractLoosely bound,fragilebinary stars, whose separations may reach ∼ 0.1 pc, are like open clusters with two coeval components. They provide a largely overlooked avenue for the investigation of many astrophysical questions. For example, the orbital distribution of fragile binaries with two long-lived main-sequence components provides a sensitive test of the cumulative effects of the Galactic environment. In pairs where one component is evolved, the orbits have been amplified by post-main-sequence mass loss, potentially providing useful constraints on the initial-to-final mass relation for white dwarfs. The nearly featureless spectra of cool white dwarfs usually provide little information about intrinsic radial velocity, full space motion, population membership, metallicity, etc. However, distant main sequence companions provide benchmarks against which those properties can be determined. In addition, the cooling ages of white dwarf components provide useful limits on the ages of their main sequence companions, independent of other stellar age determination methods. This paper summarizes some of the ways fragile binaries provide useful leverage on these and other problems of interest.

Variable Star Identification in the BATC Field of M67

2005 ◽  
Vol 277-279 ◽  
pp. 869-875
Author(s):  
Hwihyun Kim ◽  
Yong Ik Byun
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Variable Star ◽  
Open Cluster ◽  
Open Clusters ◽  
Eclipsing Binaries ◽  
Photometric Variability ◽  
Phase Dispersion ◽  
Star Identification

We present the result of photometric variability investigation for stars in the field of M67. The old open cluster M67, one of the most studied open clusters, shows the sign of significant main-sequence binary population in its color-magnitude diagrams. Identification of eclipsing binaries and follow-up studies will enable us to study the nature of binary population in most direct manner. We used approximately 350 images from the BATC (Beijing-Arizona-Taipei-Connecticut) data archive to examine variability within one square degree field centered on M67. A total of 18 stars were classified to be real variables. Our new discoveries include seven eclipsing binary systems of which two are likely to be W UMa systems. All of these variables were found using the phase dispersion minimization (PDM) method developed by Shin and Byun[11].

scholarly journals A million binaries from Gaia eDR3: sample selection and validation of Gaia parallax uncertainties

2021 ◽  
Author(s):  
Kareem El-Badry ◽  
Hans-Walter Rix ◽  
Tyler M Heintz
Keyword(s):  
White Dwarf ◽  
Binary Stars ◽  
Main Sequence ◽  
Sample Selection ◽  
Mass Relation ◽  
The Sun ◽  
The Public ◽  
Spatially Resolved ◽  
The Masses

Abstract We construct from Gaia eDR3 an extensive catalog of spatially resolved binary stars within ≈ 1 kpc of the Sun, with projected separations ranging from a few au to 1 pc. We estimate the probability that each pair is a chance alignment empirically, using the Gaia catalog itself to calculate the rate of chance alignments as a function of observables. The catalog contains 1.3 (1.1) million binaries with &gt;90% (&gt;99%) probability of being bound, including 16,000 white dwarf – main sequence (WD+MS) binaries and 1,400 WD+WD binaries. We make the full catalog publicly available, as well as the queries and code to produce it. We then use this sample to calibrate the published Gaia DR3 parallax uncertainties, making use of the binary components’ near-identical parallaxes. We show that these uncertainties are generally reliable for faint stars (G ≳ 18), but are underestimated significantly for brighter stars. The underestimates are generally $\le 30\%$ for isolated sources with well-behaved astrometry, but are larger (up to ∼80%) for apparently well-behaved sources with a companion within ≲ 4 arcsec, and much larger for sources with poor astrometric fits. We provide an empirical fitting function to inflate published σϖ values for isolated sources. The public catalog offers wide ranging follow-up opportunities: from calibrating spectroscopic surveys, to precisely constraining ages of field stars, to the masses and the initial-final mass relation of white dwarfs, to dynamically probing the Galactic tidal field.

scholarly journals Extended main sequence turnoffs in open clusters as seen by Gaia – II. The enigma of NGC 2509

2019 ◽  
Vol 491 (2) ◽  
pp. 2129-2136 ◽  
Author(s):  
M de Juan Ovelar ◽  
S Gossage ◽  
S Kamann ◽  
N Bastian ◽  
C Usher ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Narrow Range ◽  
Open Cluster ◽  
Open Clusters ◽  
Stellar Rotation ◽  
Rotation Rates ◽  
Magnitude Diagram ◽  
Stellar Density

ABSTRACT We investigate the morphology of the colour–magnitude diagram (CMD) of the open cluster NGC 2509 in comparison with other Galactic open clusters of similar age using Gaia photometry. At ${\sim}900\,\rm {Myr}$ Galactic open clusters in our sample all show an extended main sequence turnoff (eMSTO) with the exception of NGC 2509, which presents an exceptionally narrow CMD. Our analysis of the Gaia data rules out differential extinction, stellar density, and binaries as a cause for the singular MSTO morphology in this cluster. We interpret this feature as a consequence of the stellar rotation distribution within the cluster and present the analysis with mesa Isochrones and Stellar Tracks (MIST) stellar evolution models that include the effect of stellar rotation on which we based our conclusion. In particular, these models point to an unusually narrow range of stellar rotation rates (Ω/Ωcrit, ZAMS = [0.4, 0.6]) within the cluster as the cause of this singular feature in the CMD of NGC 2509. Interestingly, models that do not include rotation are not as good at reproducing the morphology of the observed CMD in this cluster.

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