- ID:
- ivo://CDS.VizieR/J/BaltA/19/197
- Title:
- King 7 Vilnius photometry
- Short Name:
- J/BaltA/19/197
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of CCD photometry in the seven-color Vilnius system for 1549 stars down to V=16mag in a 1.5 square degree field around the cluster King 7, at the Perseus and Camelopardalis border. Using photometric parameters, two-dimensional spectral types, interstellar extinctions and distances for most of the stars are determined.
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- ID:
- ivo://CDS.VizieR/II/44
- Title:
- K-Line photometry of stars in Population I clusters
- Short Name:
- II/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric photometry of the K-line of calcium has been performed for the A stars of five open clusters (Hyades, Pleiades, IC 2391, IC 2602, and NGC 6475) and one association (Orion). All observations were carried out simultaneously with the field stars measurements in Paper II (II/43), with the 16-inch (40cm) and 36-inch (91cm) telescopes of the Cerro Tololo Inter-American Observatory, between May 1969 and January 1970.
- ID:
- ivo://CDS.VizieR/J/ApJS/246/15
- Title:
- K2 periodic variables in M35 & NGC2158
- Short Name:
- J/ApJS/246/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 1143 periodic variables, compiled from our image-subtracted photometric analysis of the K2 Campaign-0 super stamp. This super stamp is centered on the open clusters M35 and NGC2158. Approximately 46% of our periodic variables were previously unreported. Of the catalog variables, we find that 331 are members of M35 and 56 are members of NGC 2158 (P_m_>0.5). Our catalog contains two new transiting exoplanet candidates, both of which orbit field stars. The smaller planet candidate has a radius of 0.35+/-0.04R_J_ and orbits a K dwarf (Kp=15.4mag) with a transit depth of 2.9mmag. The larger planet candidate has a radius of 0.72+/-0.02R_J_ and orbits a late G-type star (Kp=15.7mag) with a transit depth of 2.2mmag. The larger planet candidate may be an unresolved binary or a false alarm. Our catalog includes 44 eclipsing binaries (EBs), including ten new detections. Of the EBs, one is an M35 member and five are NGC 2158 members. Our catalog contains a total of 1097 nontransiting variable stars, including a field {delta} Cepheid exhibiting double mode pulsations, 561 rotational variables, and 251 pulsating variables (primarily {gamma} Doradus and {delta} Scuti types). The periods of our catalog sources range between 43 minutes to 24 days. The known ages of our reported cluster variables will facilitate investigations of a variety of stellar evolutionary processes.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/47
- Title:
- K2 rotation periods for 65 Hyades members
- Short Name:
- J/ApJ/822/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As the closest open cluster to the Sun, the Hyades is an important benchmark for many stellar properties, but its members are also scattered widely over the sky. Previous studies of stellar rotation in the Hyades relied on targeted observations of single stars or data from shallower all-sky variability surveys. The re-purposed Kepler mission, K2, is the first opportunity to measure rotation periods (P_rot_) for many Hyads simultaneously while also being sensitive to fully convective M dwarf members. We analyze K2 data for 65 Hyads and present P_rot_ values for 48. Thirty-seven of these are new measurements, including the first Prot measurements for fully convective Hyads. For 9 of the 11 stars with P_rot_ in the literature and this work, the measurements are consistent; we attribute the two discrepant cases to spot evolution. Nearly all stars with masses <~0.3M_{sun}_ are rapidly rotating, indicating a change in rotation properties at the boundary to full convection. When confirmed and candidate binaries are removed from the mass-period plane, only three rapid rotators with masses >~0.3M_{sun}_ remain. This is in contrast to previous results showing that the single-valued mass-period sequence for ~600Myr old stars ends at ~0.65M_{sun}_ when binaries are included. We also find that models of rotational evolution predict faster rotation than is actually observed at ~600Myr for stars <~0.9M_{sun}. The dearth of single rapid rotators more massive than ~0.3M_{sun}_ indicates that magnetic braking is more efficient than previously thought, and that age-rotation studies must account for multiplicity.
- ID:
- ivo://CDS.VizieR/J/ApJ/879/100
- Title:
- K2 rotation periods for Hyades & Praesepe members
- Short Name:
- J/ApJ/879/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze K2 light curves for 132 low-mass (1M_{sun}_>~M*>~0.1M_{sun}_) members of the 600-800Myr old Hyades cluster and measure rotation periods (P_rot_) for 116 of these stars. These include 93 stars with no prior P_rot_ measurements; the total number of Hyads with a known P_rot_ is now 232. We then combine literature binary data with Gaia DR2 photometry and astrometry to select single-star sequences in the Hyades and its roughly coeval Praesepe open cluster and derive a new reddening value of A_V_=0.035+/-0.011 for Praesepe. Comparing the effective temperature-P_rot_ distributions for the Hyades and Praesepe, we find that solar-type Hyads rotate, on average, 0.4d slower than their Praesepe counterparts. This P_rot_ difference indicates that the Hyades is slightly older than Praesepe: we apply a new gyrochronology model tuned with Praesepe and the Sun and find an age difference between the two clusters of 57Myr. However, this P_rot_ difference decreases and eventually disappears for lower-mass stars. This provides further evidence for stalling in the rotational evolution of these stars and highlights the need for more detailed analysis of angular momentum evolution for stars of different masses and ages.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/1026
- Title:
- Lagoon Nebula M8 T tauri accretion rates
- Short Name:
- J/MNRAS/453/1026
- Date:
- 03 Nov 2021
- Publisher:
- CDS
- Description:
- We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using ugri H{alpha} photometry from the VST Photometric H{alpha} survey+. Our sample consists of stars displaying H{alpha} excess, the intensity of which is used to derive accretion rates. For a subset of 87 stars, the intensity of the u-band excess is also used to estimate accretion rates. We find the mean variation in accretion rates measured using H{alpha} and u-band intensities to be ~0.17dex, agreeing with previous estimates (0.04-0.4dex) but for a much larger sample. The spatial distribution of CTTS align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. Strong accretors are concentrated spatially, while weak accretors are more distributed. Our results do not support the sequential star-forming processes suggested in the literature.
- ID:
- ivo://CDS.VizieR/J/ApJ/747/51
- Title:
- Lagoon Nebula stars. I. Rotation periods
- Short Name:
- J/ApJ/747/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a long-term, wide-field, high-cadence photometric monitoring survey of ~50000 stars in the Lagoon Nebula H II region. This first paper presents rotation periods for 290 low-mass stars in NGC 6530, the young cluster illuminating the nebula, and for which we assemble a catalog of infrared and spectroscopic disk indicators, estimated masses and ages, and X-ray luminosities. The distribution of rotation periods we measure is broadly uniform for 0.5days<P<10days; the short-period cutoff corresponds to breakup. We observe no obvious bimodality in the period distribution, but we do find that stars with disk signatures rotate more slowly on average. The stars' X-ray luminosities are roughly flat with rotation period, at the saturation level (log L_X_/L_bol_{approx} -3.3). However, we find a significant positive correlation between L_X_/L_bol_ and corotation radius, suggesting that the observed X-ray luminosities are regulated by centrifugal stripping of the stellar coronae. The period-mass relationship in NGC 6530 is broadly similar to that of the Orion Nebula Cluster (ONC), but the slope of the relationship among the slowest rotators differs from that in the ONC and other young clusters. We show that the slope of the period-mass relationship for the slowest rotators can be used as a proxy for the age of a young cluster, and we argue that NGC 6530 may be slightly younger than the ONC, making it a particularly important touchstone for models of angular momentum evolution in young, low-mass stars.
- ID:
- ivo://CDS.VizieR/J/other/RAA/15.1197
- Title:
- LAMOST DR2 star clusters candidate members
- Short Name:
- J/other/RAA/15.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we provide 2189 photometrically- and kinematically-selected candidate members of 24 star clusters from the LAMOST DR2 catalog. We perform two-step membership identification: selection along the stellar track in the color-magnitude diagram, i.e., photometric identification, and selection from the distribution of radial velocities, i.e. the kinematic identification. We find that the radial velocities from the LAMOST data are very helpful in the membership identification. The mean probability of membership is 40% for the sample selected with radial velocity. With these 24 star clusters, we investigate the performance of the radial velocity and metallicity estimated with the LAMOST pipeline. We find that the systematic offsets in radial velocity and metallicity are 0.85+/-1.26km/s and -0.08+/-0.04dex, with dispersions of 5.47^+1.16^_-0.71_km/s and 0.13^+0.04^_-0.02_dex, respectively. Finally, we propose that the photometrically-selected candidate members of the clusters covered by the LAMOST footprint should be assigned higher priority so that more candidate stars can be observed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/328/45
- Title:
- Late-type stars members of young groups
- Short Name:
- J/MNRAS/328/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first paper of a series aimed at studying the properties of late-type members of young stellar kinematic groups. We concentrate our study on classical young moving groups such as the Local Association (Pleiades moving group, 2-150Myr), IC 2391 supercluster (35Myr), Ursa Major group (Sirius supercluster, 300Myr), and Hyades supercluster (600Myr), as well as on recently identified groups such as the Castor moving group (200Myr). In this paper we compile a preliminary list of single late-type possible members of some of these young stellar kinematic groups. Stars are selected from previously established members of stellar kinematic groups based on photometric and kinematic properties as well as from candidates based on other criteria such as their level of chromospheric activity, rotation rate and lithium abundance. Precise measurements of proper motions and parallaxes taken from the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, and published radial velocity measurements are used to calculate the Galactic space motions (U, V, W) and to apply Eggen's kinematic criteria in order to determine the membership of the selected stars to the different groups.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A84
- Title:
- Li abundance and mixing in giant stars
- Short Name:
- J/A+A/651/A84
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We aim to constrain the mixing processes in low-mass stars by investigating the behaviour of the Li surface abundance after the main sequence. We take advantage of the data from the sixth internal data release of Gaia-ESO, idr6, and from the Gaia Early Data Release 3, EDR3. We selected a sample of main-sequence, sub-giant, and giant stars in which the Li abundance is measured by the Gaia-ESO survey. These stars belong to 57 open clusters with ages from 130Myr to about 7Gyr and to Milky Way fields, covering a range in [Fe/H] between -1.0 and +0.5dex, with few stars between -1.0 and -2.5dex. We studied the behaviour of the Li abundances as a function of stellar parameters. We inferred the masses of giant stars in clusters from the main-sequence turn-off masses, and for field stars through comparison with stellar evolution models using a maximum likelihood technique. We compared the observed Li behaviour in field giant stars and in giant stars belonging to individual clusters with the predictions of a set of classical models and of models with mixing induced by rotation and thermohaline instability. The comparison with stellar evolution models confirms that classical models cannot reproduce the observed lithium abundances in the metallicity and mass regimes covered by the data. The models that include the effects of both rotation-induced mixing and thermohaline instability account for the Li abundance trends observed in our sample in all metallicity and mass ranges. The differences between the results of the classical models and of the rotation models largely differ (up to~2 dex), making lithium the best element with which to constrain stellar mixing processes in low-mass stars. We discuss the nature of a sample of Li-rich stars. We demonstrate that the evolution of the surface abundance of Li in giant stars is a powerful tool for constraining theoretical stellar evolution models, allowing us to distinguish the effect of different mixing processes. For stars with well-determined masses, we find a better agreement of observed surface abundances and models with rotation-induced and thermohaline mixing. Rotation effects dominate during the main sequence and the first phases of the post-main-sequence evolution, and the thermohaline induced mixing after the bump in the luminosity function.
