scholarly journals Independent Distance Determinations to Milky Way Cepheids in Open Clusters: A progress report on four stars

1995 ◽  
Vol 155 ◽  
pp. 361-362
Author(s):  
Wolfgang P. Giere ◽  
Jaymie M. Matthews ◽  
Jean-Claude Mermilliod ◽  
Douglas Welch
Keyword(s):  
Surface Brightness ◽  
Milky Way ◽  
Zero Point ◽  
Progress Report ◽  
Open Clusters ◽  
Open Clusters And Associations ◽  
Preliminary Results

AbstractWe have undertaken a programme to calibrate the Cepheid PL relation zero-point by obtaining distances of Cepheids in open clusters and associations via the visual surface brightness technique. Results are now available for four stars (SZ Tau, CF Cas, CV Mon and DL Cas) and others are currently under analysis. Preliminary results suggest the ‘ZAMS-fitting’ distances to the host clusters are systematically smaller than those we derive from Cepheid surface brightnesses.

Independent distance determinations to Milky Way Cepheids in open clusters and associations. 1: The binary Cepheid DL CAS in NGC 129

1994 ◽  
Vol 107 ◽  
pp. 2093 ◽  
Author(s):  
Wolfgang P. Gieren ◽  
Douglas L. Welch ◽  
Jean-Claude Mermilliod ◽  
Jaymie M. Matthews ◽  
Gisela Hertling
Keyword(s):  
Milky Way ◽  
Open Clusters ◽  
Open Clusters And Associations

Independent Distance Determinations to Milky Way Cepheids in Open Clusters and Associations. III. CV MON in Anon Van Den Bergh

1996 ◽  
Vol 111 ◽  
pp. 2059 ◽  
Author(s):  
Wolfgang P. Gieren ◽  
Jean-Claude Mermilliod ◽  
Jaymie M. Mathews ◽  
Douglas L. Welch
Keyword(s):  
Milky Way ◽  
Open Clusters ◽  
Open Clusters And Associations

scholarly journals Orbits versus Star Formation Histories: A Progress Report

1999 ◽  
Vol 192 ◽  
pp. 447-450 ◽  
Author(s):  
Eva K. Grebel ◽  
Tsafrir Kolatt ◽  
Wolfgang Brandner
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Statistical Approach ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Progress Report ◽  
Polar Plane ◽  
Preliminary Results ◽  
Star Formation Histories

Milky Way dwarf companions and satellites of distant spirals seem to show a preference for polar orbits. We suggest that five out of six M31 dwarf spheroidal companions as well as two dwarf irregulars may also be located near a polar plane.We briefly discuss preliminary results from a statistical approach to study correlations between star formation histories and orbits of Local Group dwarf galaxies, such as a possible correlation between star formation episodes and galaxy separations.

Variation of the amount of hydrogen along the galactic ridge

1967 ◽  
Vol 31 ◽  
pp. 171-172
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Surface Brightness ◽  
Milky Way ◽  
Neutral Hydrogen ◽  
Line Of Sight ◽  
Optical Surface ◽  
Hydrogen Density ◽  
Continuous Radiation ◽  
Galactic Longitude

The integralNHof neutral-hydrogen density along the line of sight is determined from the Kootwijk and Sydney surveys. The run ofNHwith galactic longitude agrees well with that of thermal continuous radiation and that of the optical surface brightness of the Milky Way.

Systematic effects in observed parallaxes

1978 ◽  
Vol 48 ◽  
pp. 31-35
Author(s):  
R. B. Hanson
Keyword(s):  
Error Estimates ◽  
Zero Point ◽  
Absolute Zero ◽  
Apparent Magnitude ◽  
Coherent System ◽  
Preliminary Results ◽  
General Catalogue ◽  
Systematic Effects ◽  
New Evidence ◽  
Right Ascension

Several outstanding problems affecting the existing parallaxes should be resolved to form a coherent system for the new General Catalogue proposed by van Altena, as well as to improve luminosity calibrations and other parallax applications. Lutz has reviewed several of these problems, such as: (A) systematic differences between observatories, (B) external error estimates, (C) the absolute zero point, and (D) systematic observational effects (in right ascension, declination, apparent magnitude, etc.). Here we explore the use of cluster and spectroscopic parallaxes, and the distributions of observed parallaxes, to bring new evidence to bear on these classic problems. Several preliminary results have been obtained.

scholarly journals Reanalysis of nearby open clusters using Gaia DR1/TGAS and HSOY

2018 ◽  
Vol 615 ◽  
pp. A12 ◽  
Author(s):  
Steffi X. Yen ◽  
Sabine Reffert ◽  
Elena Schilbach ◽  
Siegfried Röser ◽  
Nina V. Kharchenko ◽  
...  
Keyword(s):  
Milky Way ◽  
Open Cluster ◽  
Star Clusters ◽  
Open Clusters ◽  
Parameter Estimates ◽  
Cluster Membership ◽  
Fitting Procedure ◽  
Cluster Data ◽  
The Galaxy ◽  
Automatic Tool

Context. Open clusters have long been used to gain insights into the structure, composition, and evolution of the Galaxy. With the large amount of stellar data available for many clusters in the Gaia era, new techniques must be developed for analyzing open clusters, as visual inspection of cluster color-magnitude diagrams is no longer feasible. An automatic tool will be required to analyze large samples of open clusters. Aims. We seek to develop an automatic isochrone-fitting procedure to consistently determine cluster membership and the fundamental cluster parameters. Methods. Our cluster characterization pipeline first determined cluster membership with precise astrometry, primarily from TGAS and HSOY. With initial cluster members established, isochrones were fitted, using a χ2 minimization, to the cluster photometry in order to determine cluster mean distances, ages, and reddening. Cluster membership was also refined based on the stellar photometry. We used multiband photometry, which includes ASCC-2.5 BV, 2MASS JHKs, and Gaia G band. Results. We present parameter estimates for all 24 clusters closer than 333 pc as determined by the Catalogue of Open Cluster Data and the Milky Way Star Clusters catalog. We find that our parameters are consistent to those in the Milky Way Star Clusters catalog. Conclusions. We demonstrate that it is feasible to develop an automated pipeline that determines cluster parameters and membership reliably. After additional modifications, our pipeline will be able to use Gaia DR2 as input, leading to better cluster memberships and more accurate cluster parameters for a much larger number of clusters.

scholarly journals Extended Main-sequence Turnoff as a Common Feature of Milky Way Open Clusters

2018 ◽  
Vol 869 (2) ◽  
pp. 139 ◽  
Author(s):  
G. Cordoni ◽  
A. P. Milone ◽  
A. F. Marino ◽  
M. Di Criscienzo ◽  
F. D’Antona ◽  
...  
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Open Clusters

scholarly journals A Gaia DR2 view of the open cluster population in the Milky Way

2018 ◽  
Vol 618 ◽  
pp. A93 ◽  
Author(s):  
T. Cantat-Gaudin ◽  
C. Jordi ◽  
A. Vallenari ◽  
A. Bragaglia ◽  
L. Balaguer-Núñez ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Milky Way ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Open Cluster ◽  
Open Clusters ◽  
Number Of Clusters ◽  
History Of ◽  
Gaia Dr2

Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.

scholarly journals Dwarf Galaxies in Nearby Groups

1999 ◽  
Vol 171 ◽  
pp. 154-156
Author(s):  
T. Bremnes ◽  
B. Binggeli ◽  
P. Prugniel
Keyword(s):  
Surface Brightness ◽  
Dwarf Galaxies ◽  
Photometric Data ◽  
Preliminary Results ◽  
Central Surface ◽  
Total Magnitude ◽  
Evolutionary Connection

AbstractWe present preliminary results from two observing campaigns where global photometric data for most dwarf galaxies in the M81 and M101 groups as well as some field dwarfs were obtained. The galaxies in the denser M81 group are more often of dwarf elliptical type and are redder and fainter than those of the M101 group and surrounding field, which are mostly of the dwarf irregular types. But both types follow the same total magnitude - central surface brightness relation, so there might be an evolutionary connection between the two classes.

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.

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