scholarly journals Strongly magnetic Ap stars in the Gaia DR2 Hertzsprung-Russell diagram

2019 ◽  
Vol 628 ◽  
pp. A81 ◽  
Author(s):  
R.-D. Scholz ◽  
S. Drew Chojnowski ◽  
S. Hubrig
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
Quality Criterion ◽  
Quality Criteria ◽  
Quality Parameters ◽  
Unit Weight ◽  
Close Binaries ◽  
Cluster Membership ◽  
Ap Stars ◽  
Gaia Dr2

Context. Knowing the distribution of strongly magnetic Ap stars in the Hertzsprung-Russell diagram (HRD) allows us to study the evolution of their magnetic fields across the main sequence (MS). With a newly extended Ap star sample from APOGEE and available Gaia DR2 data, we can now critically review the results of previous studies based on HIPPARCOS data. Aims. To investigate our targets in the Gaia DR2 HRD, we need to define astrometric and photometric quality criteria to remove unreliable data from the HRD. Methods. We used the Gaia DR2 renormalised unit weight error RUWE as our main quality criterion. We considered known (close) binaries in our sample compared to their (partly affected) astrometry and used the Gaia DR2 data to find common parallax and proper motion (CPPM) wide companions and open cluster members. We studied G, BP, and RP variability amplitudes and their significance as a function of magnitude. In colour-magnitude diagrams (CMDs) with absolute G magnitude (determined from inverted parallax) versus BP − RP colour and HRDs, where BP − RP is replaced by effective temperature, we studied the appearance of outliers with respect to their astrometric quality, binarity, and variability. Results. We present a catalogue of 83 previously known and 154 new strongly magnetic Ap stars with Gaia DR2 data, including astrometric quality parameters, binary flags, information on cluster membership, variability amplitudes, and data from HIPPARCOS. Our astrometrically cleaned subsamples include 47 and 46 old and new Ap stars with parallaxes > 2 mas. Most of the known 26 binaries among all 237 stars and 14 out of 15 CMD/HRD outliers were excluded by astrometric criteria. The remaining 11 known binaries and a few highly variable objects mainly appear in the bright and red CMD/HRD parts. A CMD based on HIPPARCOS photometry and Gaia DR2 parallaxes shows a much more narrow distribution in the absolute V magnitudes of 75 common Ap stars over the full B − V colour range than the corresponding CMD based on HIPPARCOS parallaxes.

scholarly journals Tidal Circularization Among the Close Binaries in M67

1992 ◽  
Vol 151 ◽  
pp. 471-472
Author(s):  
David W. Latham ◽  
Robert D. Mathieu ◽  
Alejandra A. E. Milone ◽  
Robert J. Davis
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
Radial Velocities ◽  
Spectroscopic Binaries ◽  
Close Binaries ◽  
To Come ◽  
Mirror Telescope

In 1971 Roger Griffin and Jim Gunn began monitoring the radial velocities of most of the members brighter than the main-sequence turnoff in the old open cluster M67, primarily using the 200-inch Hale Telescope. In 1982 the torch was passed to Dave Latham and Bob Mathieu, who began monitoring many of the same stars with the 1.5-meter Tillinghast Reflector and the Multiple-Mirror Telescope on Mt. Hopkins. We have successively combined these two sets of data, plus some additional CORAVEL velocities kindly provided by Michel Mayor, to obtain 20 years of time coverage (e.g. Mathieu et al. 1986). Among the stars brighter than magnitude V = 12.7 we have already published orbits for 22 spectroscopic binaries (Mathieu et al. 1990). At Mt. Hopkins an extension of this survey to many of the cluster members down to magnitude V = 15.5 has already yielded thirteen additional orbital solutions, with the promise of many more to come.

scholarly journals The extended main-sequence turn-off of the Milky Way open cluster Collinder 347

2019 ◽  
Vol 490 (2) ◽  
pp. 2414-2420 ◽  
Author(s):  
Andrés E Piatti ◽  
Charles Bonatto
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Open Cluster ◽  
Age Difference ◽  
Proper Motions ◽  
Gaussian Distributions ◽  
Young Object ◽  
Magnitude Diagram ◽  
Chemical Content ◽  
Gaia Dr2

ABSTRACT We made use of the Gaia DR2 archive to comprehensively study the Milky Way open cluster Collinder 347, known until now as a very young object of solar metal content. However, the G versus GBP − GRP colour–magnitude diagram (CMD) of bonafide probable cluster members, selected on the basis of individual stellar proper motions, their spatial distribution, and placement in the CMD, reveals the existence of a Hyades-like age open cluster (log(t /yr) = 8.8) of moderately metal-poor chemical content ([Fe/H]  = −0.4 dex), with a present-day mass of 3.3 × 103 M⊙. The cluster exhibits an extended main-sequence turn-off (eMSTO) of nearly 500 Myr, while that computed assuming Gaussian distributions from photometric errors, stellar binarity, rotation, and metallicity spread yields an eMSTO of ∼340 Myr. Such an age difference points to the existence within the cluster of stellar populations with different ages.

scholarly journals Stellar population of Sco OB2 revealed by Gaia DR2 data

2019 ◽  
Vol 623 ◽  
pp. A112 ◽  
Author(s):  
F. Damiani ◽  
L. Prisinzano ◽  
I. Pillitteri ◽  
G. Micela ◽  
S. Sciortino
Keyword(s):  
Stellar Population ◽  
Main Sequence ◽  
Open Cluster ◽  
Proper Motions ◽  
Lower Mass ◽  
Global Pattern ◽  
Field Star ◽  
Photometric Measurements ◽  
Stellar Masses ◽  
Gaia Dr2

Context. The Sco OB2 association is the nearest OB association, extending over approximately 2000 square degrees on the sky. Only its brightest and most massive members are already known (from HIPPARCOS) across its entire size, while studies of its lower mass population refer only to small portions of its extent. Aims. In this work we exploit the capabilities of Gaia DR2 measurements to search for Sco OB2 members across its entire size and down to the lowest stellar masses. Methods. We used both Gaia astrometric (proper motions and parallaxes) and photometric measurements (integrated photometry and colors) to select association members, using minimal assumptions derived mostly from the HIPPARCOS studies. Gaia resolves small details in both the kinematics of individual Sco OB2 subgroups and their distribution with distance from the Sun. We developed methods to explore the 3D kinematics of a stellar population covering large sky areas. Results. We find nearly 11 000 pre-main-sequence (PMS) members of Sco OB2 (with less than 3% field-star contamination), plus ∼3600 main-sequence (MS) candidate members with a larger (10–30%) field-star contamination. A higher confidence subsample of ∼9200 PMS (and ∼1340 MS) members is also selected (<1% contamination for the PMS), however this group is affected by larger (∼15%) incompleteness. We separately classify stars in compact and diffuse populations. Most members belong to one of several kinematically distinct diffuse populations, whose ensemble clearly outlines the shape of the entire association. Upper Sco is the densest region of Sco OB2. It is characterized by a complex spatial and kinematical structure and has no global pattern of motion. Other dense subclusters are found in Lower Centaurus-Crux and in Upper Centaurus-Lupus; the richest example of the latter, which has been recently identified, is coincident with the group near V1062 Sco. Most of the clustered stars appear to be younger than the diffuse PMS population, suggesting star formation in small groups that rapidly disperse and are diluted, reaching space densities lower than field stars while keeping memory of their original kinematics. We also find that the open cluster IC 2602 has a similar dynamics to Sco OB2, and its PMS members are currently evaporating and forming a diffuse (size ∼10°) halo around its double-peaked core.

scholarly journals White dwarf-open cluster associations based on Gaia DR2

2020 ◽  
Vol 645 ◽  
pp. A13
Author(s):  
M. Prišegen ◽  
M. Piecka ◽  
N. Faltová ◽  
M. Kajan ◽  
E. Paunzen
Keyword(s):  
Open Cluster ◽  
Open Clusters ◽  
Photometric Data ◽  
Mass Relation ◽  
Physical Processes ◽  
Satellite Mission ◽  
Cluster Membership ◽  
Fundamental Parameters ◽  
Data Release ◽  
Gaia Dr2

Context. Fundamental parameters and physical processes leading to the formation of white dwarfs (WDs) may be constrained and refined by discovering WDs in open clusters (OCs). Cluster membership can be utilized to establish the precise distances, luminosities, ages, and progenitor masses of such WDs. Aims. We compile a list of probable WDs that are OC members in order to facilitate WD studies that are impractical or difficult to conduct for Galactic field WDs. Methods. We use recent catalogs of WDs and OCs that are based on the second data release of the Gaia satellite mission (GDR2) to identify WDs that are OC members. This crossmatch is facilitated by the astrometric and photometric data contained in GDR2 and the derived catalogs. Assuming that most of the WD members are of the DA type, we estimate the WD masses, cooling ages, and progenitor masses. Results. We have detected several new likely WD members and reassessed the membership of the literature WDs that had been previously associated with the studied OCs. Several of the recovered WDs fall into the recently reported discontinuity in the initial-final mass relation (IFMR) around Mi ∼ 2.0 M⊙, which allows for tighter constrains on the IFMR in this regime.

scholarly journals ML-MOC: Machine Learning (kNN and GMM) based Membership determination for Open Clusters

2021 ◽  
Vol 502 (2) ◽  
pp. 2582-2599
Author(s):  
Manan Agarwal ◽  
Khushboo K Rao ◽  
Kaushar Vaidya ◽  
Souradeep Bhattacharya
Keyword(s):  
Machine Learning ◽  
Open Cluster ◽  
A Priori ◽  
Gaussian Mixture ◽  
Open Clusters ◽  
Proper Motions ◽  
Cluster Membership ◽  
Priori Information ◽  
Gaia Dr2 ◽  
Good Agreement

ABSTRACT The existing open-cluster membership determination algorithms are either prior dependent on some known parameters of clusters or are not automatable to large samples of clusters. In this paper, we present ml-moc, a new machine-learning-based approach to identify likely members of open clusters using the Gaia DR2 data and no a priori information about cluster parameters. We use the k-nearest neighbour (kNN) algorithm and the Gaussian mixture model (GMM) on high-precision proper motions and parallax measurements from the Gaia DR2 data to determine the membership probabilities of individual sources down to G ∼ 20 mag. To validate the developed method, we apply it to 15 open clusters: M67, NGC 2099, NGC 2141, NGC 2243, NGC 2539, NGC 6253, NGC 6405, NGC 6791, NGC 7044, NGC 7142, NGC 752, Blanco 1, Berkeley 18, IC 4651, and Hyades. These clusters differ in terms of their ages, distances, metallicities, and extinctions and cover a wide parameter space in proper motions and parallaxes with respect to the field population. The extracted members produce clean colour–magnitude diagrams and our astrometric parameters of the clusters are in good agreement with the values derived in previous work. The estimated degree of contamination in the extracted members ranges between 2 ${{\ \rm per\ cent}}$ and 12 ${{\ \rm per\ cent}}$. The results show that ml-moc is a reliable approach to segregate open-cluster members from field stars.

scholarly journals Cluster membership for the long-period Cepheid calibrator SV Vul

2020 ◽  
Vol 494 (2) ◽  
pp. 3028-3036 ◽  
Author(s):  
I Negueruela ◽  
R Dorda ◽  
A Marco
Keyword(s):  
Open Cluster ◽  
Hubble Constant ◽  
Cluster Membership ◽  
Long Period ◽  
Classical Cepheids ◽  
Good Accordance ◽  
Young Open Cluster ◽  
Red Supergiants ◽  
Stellar Properties ◽  
Gaia Dr2

ABSTRACT Classical Cepheids represent the first step of the distance scale ladder. Claims of tension between the locally calculated Hubble constant and the values deduced from Planck’s results have sparked new interest in these distance calibrators. Cluster membership provides an independent distance measurement, as well as astrophysical context for studies of their stellar properties. Here, we report the discovery of a young open cluster in the vicinity of SV Vul, one of the most luminous Cepheids known in the Milky Way. Gaia DR2 data show that SV Vul is a clear astrometric and photometric member of the new cluster, which we name Alicante 13. Although dispersed, Alicante 13 is moderately well populated, and contains three other luminous stars, one early-A bright giant and two low-luminosity red supergiants. The cluster is about 30 Ma old at a nominal distance of 2.5 kpc. With this age, SV Vul should have a mass around $10$ M⊙, in good accordance with its luminosity, close to the highest luminosity for Cepheids allowed by recent stellar models.

scholarly journals On the Distance to the Open Cluster Lyngå 6

1985 ◽  
Vol 82 ◽  
pp. 203-204
Author(s):  
E. R. Anderson ◽  
B. F. Madore ◽  
M. H. Pedreros
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
Distance Modulus ◽  
Cluster Membership ◽  
Computerized Method ◽  
Open Time ◽  
Galactic Cluster

The determination of the membership of the Cepheid TW Normae to the galactic cluster Lyngå. 6 is important because TW Nor would then be the intrinsically brightest Cepheid associated with a cluster.A series of nine photographic exposures (three each in U,B and V) were obtained during open time at the Anglo-Australian Telescope. The plates were measured with an iris photometer and the data calibrated using the photoelectric standards of van den Bergh and Harris (1976). The data for 300 stars were then analysed using a new computerized method of main sequence fitting and cluster membership determination developed by Pedreros (1984). We found 41 member stars with a mean reddening E(B-V)=1.33±0.10 and a distance modulus of 11.1±0.4 magnitudes.

scholarly journals SPECTROSCOPIC INVESTIGATIONS OF GALACTIC OPEN CLUSTER COLLINDER 394 – NEW RESULTS

2021 ◽  
Vol 34 ◽  
pp. 65-69
Author(s):  
I.A. Usenko ◽  
A.Yu. Kniazev ◽  
A.S. Miroshnichenko ◽  
S. Danford ◽  
V.V. Kovtyukh ◽  
...  
Keyword(s):  
Inverse Problem ◽  
Main Sequence ◽  
Open Cluster ◽  
Eclipsing Binaries ◽  
Spectroscopic Investigations ◽  
Gaia Dr2

Confident main-sequence (MS) members of the Collinder 394 open cluster are perfect objects to check the correctness of their distances, obtained from the GAIA GR2 (2018) catalogue. The differences in the distances to the open cluster Collinder 394, determined by photometry and from the GAIA parallaxes have raised doubts about the correctness of the latter. Therefore we used spectroscopically determined T eff and loggvalues for these stars from Usenko et al. (2019) and tried to solve the inverse problem: determine radii of these stars using the derived distances and calibrations “T eff - radius” for MS stars and compare with similar ones. For this purpose we used the calibrations from Torres et al. (2010), based on the nearest MS eclipsing binaries and compilations for MS stars from Mamajek (2018). As a result, we obtained relationships that connect T eff , logg, radii, masses, and distances for the confident Collinder 394 MS stars. We have confirmed the correctness of the GAIA DR2 (2018) distances for these stars and determined their radii and masses. The latter estimates turned out to be close to those of the evolutionary masses calculated by the PARSEC model

On The Radii of Ap Stars

1976 ◽  
Vol 32 ◽  
pp. 49-55 ◽  
Author(s):  
F.A. Catalano ◽  
G. Strazzulla
Keyword(s):  
Observational Data ◽  
Line Width ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Ap Stars

SummaryFrom the analysis of the observational data of about 100 Ap stars, the radii have been computed under the assumption that Ap are main sequence stars. Radii range from 1.4 to 4.9 solar units. These values are all compatible with the Deutsch's period versus line-width relation.

THE QUALITY OF PUBLIC HOSPITALS IN CAN THO CITY, 2016

2018 ◽  
Vol 8 (6) ◽  
pp. 76-81
Author(s):  
Chu Cao Minh ◽  
Thang Vo Van ◽  
Dat Nguyen Tan ◽  
Hung Vo Thanh
Keyword(s):  
Hospital Medicine ◽  
Secondary Data ◽  
Quality Criterion ◽  
Quality Criteria ◽  
Public Hospitals ◽  
Ministry Of Health ◽  
Cross Sectional ◽  
Significant Difference ◽  
Can Tho City

Background: The criteria set of assessing hospital quality in Vietnam in 2016 was revied from the criteria set in 2013 by the Ministry of Health in order to help hospitals to self-assess towards improvinge quality of hospitals in the international integration context. The study aimed to assess the quality of public hospitals in Can Tho City according to the revised criteria set of the Ministry of Health in 2016 and compare the quality among three hospital ranks (including grade I, grade II, and grade III) via to 5 groups of quality criteria. Methods: A cross-sectional study, using secondary data analysis was applied to assess the service quality of 7 general public hospitals in Can Tho City. Results: The average total score of 7 hospitals is 245 and the average for the criteria of 7 hospitals is 2.99, which is just satisfactory. In the criterion of quality, criterion D and E had the lowest scores compared to the other three groups. There was no statistically significant difference (p = 0.076) among the mean scores for the three hospital categories. Conclusion: The quality of public hospitals in Can Tho city in 2016 only reached moderately good level (2.99). Interventions should be developed to improve the quality of hospitals, with particular emphasis on improving the quality of criteria groups D and E. Key words: Quality, hospital, medicine, health, public, Can Tho

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