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 The Milky Way Cepheid Leavitt law based on Gaia DR2 parallaxes of companion stars and host open cluster populations

2020 ◽  
Vol 643 ◽  
pp. A115 ◽  
Author(s):  
Louise Breuval ◽  
Pierre Kervella ◽  
Richard I. Anderson ◽  
Adam G. Riess ◽  
Frédéric Arenou ◽  
...  
Keyword(s):  
Milky Way ◽  
Open Cluster ◽  
Hubble Constant ◽  
Zero Point ◽  
Spatially Resolved ◽  
Trigonometric Parallax ◽  
Novel Approach ◽  
Classical Cepheids ◽  
Average Cluster ◽  
Gaia Dr2

Aims. Classical Cepheids provide the foundation for the empirical extragalactic distance ladder. Milky Way Cepheids are the only stars in this class accessible to trigonometric parallax measurements. However, the parallaxes of Cepheids from the second Gaia data release (GDR2) are affected by systematics because of the absence of chromaticity correction, and occasionally by saturation. Methods. As a proxy for the parallaxes of 36 Galactic Cepheids, we adopt either the GDR2 parallaxes of their spatially resolved companions or the GDR2 parallax of their host open cluster. This novel approach allows us to bypass the systematics on the GDR2 Cepheids parallaxes that is induced by saturation and variability. We adopt a GDR2 parallax zero-point (ZP) of −0.046 mas with an uncertainty of 0.015 mas that covers most of the recent estimates. Results. We present new Galactic calibrations of the Leavitt law in the V, J, H, KS, and Wesenheit WH bands. We compare our results with previous calibrations based on non-Gaia measurements and compute a revised value for the Hubble constant anchored to Milky Way Cepheids. Conclusions. From an initial Hubble constant of 76.18 ± 2.37 km s−1 Mpc−1 based on parallax measurements without Gaia, we derive a revised value by adopting companion and average cluster parallaxes in place of direct Cepheid parallaxes, and we find H0 = 72.8 ± 1.9 (statistical + systematics) ±1.9 (ZP) km s−1 Mpc−1 when all Cepheids are considered and H0 = 73.0 ± 1.9 (statistical + systematics) ±1.9 (ZP) km s−1 Mpc−1 for fundamental mode pulsators only.

scholarly journals A new look at Sco OB1 association with Gaia DR2

2020 ◽  
Vol 495 (1) ◽  
pp. 1349-1359 ◽  
Author(s):  
L Yalyalieva ◽  
G Carraro ◽  
R Vazquez ◽  
L Rizzo ◽  
E Glushkova ◽  
...  
Keyword(s):  
Open Cluster ◽  
Three Dimensional ◽  
Star Formation History ◽  
Optical Data ◽  
Dimensional Structure ◽  
Fundamental Parameters ◽  
Time Estimates ◽  
Young Open Cluster ◽  
Pms Stars ◽  
Gaia Dr2

ABSTRACT We present and discuss photometric optical data in the area of the OB association Sco OB1 covering about 1 deg2. UBVI photometry is employed in tandem with Gaia DR2 data to investigate the three-dimensional structure and the star formation history of the region. By combining parallaxes and proper motions, we identify seven physical groups located between the young open cluster NGC 6231 and the bright nebula IC 4628. The most prominent group coincides with the sparse open cluster Trumpler 24. We confirm the presence of the intermediate-age star cluster VdB-Hagen 202, which is unexpected in this environment, and provide for the first time estimates of its fundamental parameters. After assessing individual groups membership, we derive mean proper motion components, distances, and ages. The seven groups belong to two different families. To the younger family (family I) belong several pre-main-sequence (PMS) stars as well. These are evenly spread across the field, and also in front of VdB-Hagen 202. VdB-Hagen 202, and two smaller, slightly detached, groups of similar properties form family II, which do not belong to the association, but are caught in the act of passing through it. As for the younger population, this forms an arc-like structure from the bright nebula IC 4628 down to NGC 6231, as previously found. Moreover, the PMS stars density seems to increase from NGC 6231 northward to Trumpler 24.

scholarly journals New insights into the use of Ultra Long Period Cepheids as cosmological standard candles

2020 ◽  
Vol 501 (1) ◽  
pp. 866-874
Author(s):  
Ilaria Musella ◽  
Marcella Marconi ◽  
Roberto Molinaro ◽  
Giuliana Fiorentino ◽  
Vincenzo Ripepi ◽  
...  
Keyword(s):  
Time Series Data ◽  
Model Fitting ◽  
Hubble Constant ◽  
Variable Stars ◽  
Series Data ◽  
Long Period ◽  
Pulsating Variable Stars ◽  
Classical Cepheids ◽  
One Step ◽  
Homogeneous Data

ABSTRACT Ultra Long Period Cepheids (ULPs) are pulsating variable stars with a period longer than 80 d and have been hypothesized to be the extension of the Classical Cepheids (CCs) at higher masses and luminosities. If confirmed as standard candles, their intrinsic luminosities, ∼1 to ∼3 mag brighter than typical CCs, would allow to reach the Hubble flow and, in turn, to determine the Hubble constant, H0, in one step, avoiding the uncertainties associated with the calibration of primary and secondary indicators. To investigate the accuracy of ULPs as cosmological standard candles, we first collect all the ULPs known in the literature. The resulting sample includes 63 objects with a very large metallicity spread with 12 + log ([O/H]) ranging from 7.2 to 9.2 dex. The analysis of their properties in the VI period–Wesenheit plane and in the colour–magnitude diagram (CMD) supports the hypothesis that the ULPs are the extension of CCs at longer periods, higher masses and luminosities, even if, additional accurate and homogeneous data and a devoted theoretical scenario are needed to get firm conclusions. Finally, the three M31 ULPs, 8-0326, 8-1498, and H42, are investigated in more detail. For 8-1498 and H42, we cannot confirm their nature as ULPs, due to the inconsistency between their position in the CMD and the measured periods. For 8-0326, the light curve model fitting technique applied to the available time-series data allows us to constrain its intrinsic stellar parameters, distance, and reddening.

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 Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2

2019 ◽  
Vol 623 ◽  
pp. A117 ◽  
Author(s):  
Pierre Kervella ◽  
Alexandre Gallenne ◽  
Nancy Remage Evans ◽  
Laszlo Szabados ◽  
Frédéric Arenou ◽  
...  
Keyword(s):  
High Probability ◽  
Selection Algorithm ◽  
Rr Lyrae Stars ◽  
Long Period ◽  
Spatially Resolved ◽  
Rr Lyrae ◽  
Classical Cepheids ◽  
Lyrae Stars ◽  
Gaia Dr2 ◽  
Reference Samples

Context. The multiplicity of classical Cepheids (CCs) and RR Lyrae stars (RRLs) is still imperfectly known, particularly for RRLs. Aims. In order to complement the close-in short orbital period systems presented in Paper I, our aim is to detect the wide, spatially resolved companions of the targets of our reference samples of Galactic CCs and RRLs. Methods. Angularly resolved common proper motion pairs were detected using a simple progressive selection algorithm to separate the most probable candidate companions from the unrelated field stars. Results. We found 27 resolved, high probability gravitationally bound systems with CCs out of 456 examined stars, and one unbound star embedded in the circumstellar dusty nebula of the long-period Cepheid RS Pup. We found seven spatially resolved, probably bound systems with RRL primaries out of 789 investigated stars, and 22 additional candidate pairs. We report in particular new companions of three bright RRLs: OV And (companion of F4V spectral type), RR Leo (M0V), and SS Oct (K2V). In addition, we discovered resolved companions of 14 stars that were likely misclassified as RRLs. Conclusions. The detection of resolved non-variable companions around CCs and RRLs facilitates the validation of their Gaia DR2 parallaxes. The possibility to conduct a detailed analysis of the resolved coeval companions of CCs and old population RRLs will also be valuable to progress on our understanding of their evolutionary path.

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.

Trumpler 27 - A heavily reddened young open cluster with blue and red supergiants

1977 ◽  
Vol 215 ◽  
pp. 106 ◽  
Author(s):  
A. F. J. Moffat ◽  
M. P. Fitzgerald ◽  
P. D. Jackson
Keyword(s):  
Open Cluster ◽  
Young Open Cluster ◽  
Red Supergiants

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 NGC 3105: a young open cluster with low metallicity

2018 ◽  
Vol 616 ◽  
pp. A124 ◽  
Author(s):  
J. Alonso-Santiago ◽  
A. Marco ◽  
I. Negueruela ◽  
H. M. Tabernero ◽  
N. Castro ◽  
...  
Keyword(s):  
Open Cluster ◽  
High Mass ◽  
Complete Analysis ◽  
Evolutionary Models ◽  
Chemical Abundances ◽  
Evolved Stars ◽  
Young Open Cluster ◽  
Red Supergiants ◽  
Low Metallicity ◽  
First Time

Context. NGC 3105 is a young open cluster hosting blue, yellow, and red supergiants. This rare combination makes it an excellent laboratory for constraining evolutionary models of high-mass stars. It has been poorly studied, and the fundamental parameters such as its age or distance are not well defined. Aims. We intend to characterise in an accurate way the cluster and its evolved stars, for which we derive for the first time atmospheric parameters and chemical abundances. Methods. We performed a complete analysis combining UBVR photometry with spectroscopy. We obtained spectra with classification purposes for 14 blue stars and high-resolution spectroscopy for an in-depth analysis of the six other evolved stars. Results. We identify 126 B-type likely members within a radius of 2.7 ± 0.6 arcmin, which implies an initial mass, Mcl ≈ 4100 M⊙. We find a distance of 7.2 ± 0.7 kpc for NGC 3105, placing it at RGC = 10.0 ± 1.2 kpc. Isochrone fitting supports an age of 28 ± 6 Ma, implying masses around 9.5 M⊙ for the supergiants. A high fraction of Be stars (≈25%) is found at the top of the main sequence down to spectral type b3. From the spectral analysis we estimate for the cluster an average νrad = +46.9 ± 0.9 km s−1 and a low metallicity, [Fe/H] = −0.29 ± 0.22. We also have determined, for the first time, chemical abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved stars. The chemical composition of the cluster is consistent with that of the Galactic thin disc. An overabundance of Ba is found, supporting the enhanced s-process. Conclusions. NGC 3105 has a low metallicity for its Galactocentric distance, comparable to typical LMC stars. It is a valuable spiral tracer in a very distant region of the Carina–Sagittarius spiral arm, a poorly known part of the Galaxy. As one of the few Galactic clusters containing blue, yellow, and red supergiants, it is massive enough to serve as a test bed for theoretical evolutionary models close to the boundary between intermediate- and high-mass stars.

scholarly journals A massive open cluster hiding in full sight

2021 ◽  
Author(s):  
I Negueruela ◽  
A-N Chené ◽  
H M Tabernero ◽  
R Dorda ◽  
J Borissova ◽  
...  
Keyword(s):  
Milky Way ◽  
Open Cluster ◽  
Parameter Determination ◽  
Classical Cepheid ◽  
Evolved Stars ◽  
Young Open Cluster ◽  
Type Giant ◽  
Massive Clusters ◽  
G 13 ◽  
Gaia Dr2

Abstract Obscuration and confusion conspire to limit our knowledge of the inner Milky Way. Even at moderate distances, the identification of stellar systems becomes compounded by the extremely high density of background sources. Here we provide a very revealing example of these complications by unveiling a large, massive, young cluster in the Sagittarius arm that has escaped detection until now despite containing more than 30 stars brighter than G = 13. By combining Gaia DR2 astrometry, Gaia and 2MASS photometry and optical spectroscopy, we find that the new cluster, which we name Valparaiso 1, located at ∼2.3 kpc, is about 75 Ma old and includes a large complement of evolved stars, among which we highlight the 4 d classical Cepheid CM Sct and an M-type giant that probably represents the first detection of an AGB star in a Galactic young open cluster. Although strong differential reddening renders accurate parameter determination unfeasible with the current dataset, direct comparison to clusters of similar age suggests that Valparaiso 1 was born as one of the most massive clusters in the Solar Neighbourhood, with an initial mass close to 104 M⊙.

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