scholarly journals With and without spectroscopy: Gaia DR2 proper motions of seven ultra-faint dwarf galaxies

2018 ◽  
Vol 620 ◽  
pp. A155 ◽  
Author(s):  
D. Massari ◽  
A. Helmi
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Dwarf Galaxies ◽  
Stellar System ◽  
Initial Guess ◽  
Proper Motions ◽  
Spectroscopic Information ◽  
The Mean ◽  
Astrometric Data ◽  
Full Covariance Matrix

Aims. We present mean absolute proper motion measurements for seven ultra-faint dwarf galaxies orbiting the Milky Way, namely Boötes III, Carina II, Grus II, Reticulum II, Sagittarius II, Segue 2, and Tucana IV. For four of these dwarfs our proper motion estimate is the first ever provided. Methods. The adopted astrometric data come from the second data release of the Gaia mission. We determine the mean proper motion for each galaxy starting from an initial guess of likely members, based either on radial velocity measurements or using stars on the horizontal branch identified in the Gaia (GBP – GRP, G) colour-magnitude diagram in the field of view towards the UFD. We then refine their membership iteratively using both astrometry and photometry. We take into account the full covariance matrix among the astrometric parameters when deriving the mean proper motions for these systems. Results. Our procedure provides mean proper motions with typical uncertainties of ∼0.1 mas yr−1, even for galaxies without prior spectroscopic information. In the case of Segue 2 we find that using radial velocity members only leads to biased results, presumably because of the small number of stars with measured radial velocities. Conclusions. Our procedure allows the number of member stars per galaxy to be maximized regardless of the existence of prior spectroscopic information, and can therefore be applied to any faint or distant stellar system within reach of Gaia.

scholarly journals A Comprehensive Astrometric Data Base: An Instrument for Combining Earth-Bound Observations With Hipparcos Data

1990 ◽  
Vol 141 ◽  
pp. 483-488
Author(s):  
Roland Wielen
Keyword(s):  
Data Base ◽  
Proper Motion ◽  
Data Bank ◽  
Space Missions ◽  
Proper Motions ◽  
Astrometric Data

The astrometric data bank ARIGFH will contain all relevant astrometric data on stellar positions and proper motions of stars from ground-based observations and space missions. For each star in the ARIGFH, the best available position and proper motion shall be derived. We rediscuss the accuracy of proper motions and positions of fundamental stars, resulting from a combination of data in the FK5 with the expected results from a revised HIPPARCOS mission. The FK5 data could be significantly improved even by rather degraded positions from a revised HIPPARCOS mission.

scholarly journals Kinematics of Galactic Globular Clusters from Schmidt-Plate Astrometry

1995 ◽  
Vol 164 ◽  
pp. 405-405 ◽  
Author(s):  
R.-D. Scholz ◽  
S. Hirte ◽  
M.J. Irwin ◽  
M. Odenkirchen
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Globular Clusters ◽  
Proper Motions ◽  
Large Numbers ◽  
Solar Motion ◽  
The Galaxy ◽  
Ursa Minor ◽  
Galactic Globular Clusters

From measurements of Tautenburg Schmidt plates with the APM facility in Cambridge we obtained absolute proper motions of the Galactic globular clusters M 3 and M 92 directly with respect to large numbers of background galaxies (Scholz et al. 1993, 1994). We have extended our work to the dSphs in Draco and Ursa Minor (Scholz & Irwin 1994) and to other Galactic globular clusters using Tautenburg, Palomar and UK Schmidt plates. Combining our absolute proper motion of a cluster with its known radial velocity and distance (using common parameters of the solar motion) we derive the cluster orbit in the Galaxy (cf. Odenkirchen & Brosche 1992).

scholarly journals The VMC survey

2020 ◽  
Vol 641 ◽  
pp. A134
Author(s):  
Thomas Schmidt ◽  
Maria-Rosa L. Cioni ◽  
Florian Niederhofer ◽  
Kenji Bekki ◽  
Cameron P. M. Bell ◽  
...  
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Dynamical Evolution ◽  
Large Magellanic Cloud ◽  
Small Population ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Proper Motions ◽  
Flow Motion

Context. The Magellanic Clouds are a nearby pair of interacting dwarf galaxies and satellites of the Milky Way. Studying their kinematic properties is essential to understanding their origin and dynamical evolution. They have prominent tidal features and the kinematics of these features can give hints about the formation of tidal dwarfs, galaxy merging and the stripping of gas. In addition they are an example of dwarf galaxies that are in the process of merging with a massive galaxy. Aims. The goal of this study is to investigate the kinematics of the Magellanic Bridge, a tidal feature connecting the Magellanic Clouds, using stellar proper motions to understand their most recent interaction. Methods. We calculated proper motions based on multi-epoch Ks-band aperture photometry, which were obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA), spanning a time of 1−3 yr, and we compared them with Gaia Data Release 2 (DR2) proper motions. We tested two methods for removing Milky Way foreground stars using Gaia DR2 parallaxes in combination with VISTA photometry or using distances based on Bayesian inference. Results. We obtained proper motions for a total of 576 411 unique sources over an area of 23 deg2 covering the Magellanic Bridge including mainly Milky Way foreground stars, background galaxies, and a small population of possible Magellanic Bridge stars (< 15 000), which mostly consist of giant stars with 11.0 <  Ks <  19.5 mag. The first proper motion measurement of the Magellanic Bridge centre is 1.80 ± 0.25 mas yr−1 in right ascension and −0.72 ± 0.13 mas yr−1 in declination. The proper motion measurements of stars along the Magellanic Bridge from the VISTA survey of the Magellanic Cloud system (VMC) and Gaia DR2 data confirm a flow motion from the Small to the Large Magellanic Cloud. This flow can now be measured all across the entire length of the Magellanic Bridge. Conclusions. Our measurements indicate that the Magellanic Bridge is stretching. By converting the proper motions to tangential velocities, we obtain ∼110 km s−1 in the plane of the sky. Therefore it would take a star roughly 177 Myr to cross the Magellanic Bridge.

scholarly journals Globular clusters in the era of precision astrometry

2019 ◽  
Vol 14 (S351) ◽  
pp. 412-415
Author(s):  
Paolo Bianchini
Keyword(s):  
Formation Mechanism ◽  
Proper Motion ◽  
Measurement Errors ◽  
Globular Clusters ◽  
Tangential Component ◽  
Proper Motions ◽  
The Mean ◽  
Motion Measurements ◽  
Precision Astrometry

Abstracthe study of the kinematics of globular clusters (GCs) offers the possibility of unveiling their long term evolution and uncovering their yet unknown formation mechanism. Gaia DR2 has strongly revitalized this field and enabled the exploration of the 6D phase-space properties of Milky Way GCs, thanks to precision astrometry. However, to fully leverage on the power of precision astrometry, a thorough investigations of the data is required. In this contribution, we show that the study of the mean radial proper motion profiles of GCs offers an ideal benchmark to assess the presence of systematics in crowded fields. Our work demonstrates that systematics in Gaia DR2 for the closest 14 GCs are below the random measurement errors, reaching a precision of ∼0.015 mas yr−1 for mean proper motion measurements. Finally, through the analysis of the tangential component of proper motions, we report the detection of internal rotation in a sample of ∼50 GCs, and outline the implications of the presence of angular momentum for the formation mechanism of proto-GC. This result gives the first taste of the unparalleled power of Gaia DR2 for GCs science, in preparation for the subsequent data releases.

scholarly journals On two possible groups of flare stars in Pleiades

1990 ◽  
Vol 137 ◽  
pp. 77-80
Author(s):  
A.L. Mirzoyan ◽  
M.A. Mnatsakanian
Keyword(s):  
Proper Motion ◽  
Star Cluster ◽  
Proper Motions ◽  
Mean Frequency ◽  
Cluster Region ◽  
Flare Stars ◽  
The Mean

The correlation between the magnitude of the proper motion and the mean frequency of flares for flare stars in the Pleiades cluster region is discussed. The magority of them are physical members of this star cluster. It is shown that there exist probably two groups of flare stars which differ each other by their parameters, in particular by the magnitude of proper motions. A possible explanation of this phenomenon is suggested.

Complex study of the open cluster NGC 2281

2017 ◽  
Vol 12 (S330) ◽  
pp. 273-274
Author(s):  
Jaroslav Velčovský ◽  
Jan Janík
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Open Cluster ◽  
Open Clusters ◽  
Ccd Photometry ◽  
Complex Study ◽  
Colour Excess ◽  
Dynamical Parameters ◽  
Astrometric Data ◽  
Selection Of

AbstractWe present the complex study of the open cluster NGC 2281 where both traditional and newly developed methods for study of open clusters have been used. Morphological and dynamical parameters of the cluster were obtained from the accepted astrometric data. The new method “Superposition of Gaussian surfaces” along with proper motion of stars was used to determine membership probabilities which were helpful in selection of stars for further analysis. Metallicity and radial velocity of the cluster were obtained from spectroscopic measurements. Age, colour excess, and distance of the cluster were determined using absolute CCD photometry combined with previous results. The results were compared with those of previous studies.

scholarly journals Relativistic and perspective effects in proper motions and radial velocities of stars

1986 ◽  
Vol 114 ◽  
pp. 193-198
Author(s):  
P. Stumpff
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Additional Term ◽  
Radial Velocities ◽  
Proper Motions ◽  
Speed Of Light ◽  
Inertial Motion ◽  
Finite Speed ◽  
Numerical Example ◽  
Doppler Shifts

The heliocentric motion of stars is investigated by taking into account all effects due to the geometry and due to the finite speed of light. It is shown that the proper motions as given in star catalogues contain the main light retardation term; an additional term of this type modifies Schlesinger's (1917) term but is less significant than a 3rd order perspective term neglected in conventional astrometry. Kapteyn's star serves as a numerical example. The ambiguous relativistic relation between Doppler shifts and radial velocities is discussed and demonstrated in a diagram. The ambiguity is solved with rigorous equations which allow to compute the inertial motion of a star from its proper motion, classical radial velocity, and distance. -

scholarly journals Review of Observational Data on RR Lyrae Stars

1971 ◽  
Vol 2 ◽  
pp. 781-787
Author(s):  
G. van Herk
Keyword(s):  
Radial Velocity ◽  
Observational Data ◽  
Proper Motion ◽  
Point Of View ◽  
Proper Motions ◽  
Physical Point ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Complete Set ◽  
Lyrae Stars

The data on which my work on the secular parallaxes of RR Lyrae stars is based (Bull. Astron. Inst. Neth.18) were in many respects so incomplete that I have tried to interest astronomers to get a more complete set of data. The number of stars for which I had a proper motion was only 168, and for which a radial velocity was known, was 180, with an overlap of only 138 stars. The accuracy of the proper motions was certainly unsatisfactory for 43% of the total. The greatest trouble in dealing with such insufficient numbers arises when one wants to subdivide the material into groups which are homogeneous from a physical point of view. Many subdivisions, in making up my paper, were not tried at all, simply because the material was inadequate.In recent years plenty of work has been done by various investigators, of which I will at this point only mention the work on proper motions done at the Leander McCormick Observatory, and the great number of radial velocities determined by Dr. Clube and his associates. I do not, however, believe we are yet in a position to consider the whole subject as finished. Discussions about space motions, as given by Professor Oort in the book Stellar Structures, Volume V, will, at this time, be hardly improved upon. I still feel we should increase the number of stars substantially in order to get a better statistical discussion possible. This means we have to go to fainter stars. Plenty of these stars will be found on the plates which have served to make the Charts of the Carte du Ciel, which means we have at least one old position available for proper motions. At Leiden we are now engaged in the determination or redetermination of the proper motions of 430 RR Lyrae stars.

scholarly journals Open clusters: a program to analyse the color–magnitude diagram with the help of stellar kinematic data

2009 ◽  
Vol 5 (S266) ◽  
pp. 385-385
Author(s):  
Wilton S. Dias ◽  
Thiago Costa Caetano
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Open Clusters ◽  
Uncertain Parameters ◽  
Kinematic Data ◽  
Magnitude Diagram ◽  
The Mean ◽  
Stellar Kinematic

AbstractWe constructed a program that allows one to use simultaneously and interactively photometric and astrometric stellar data (proper motion) to analyse color–color and color–magnitude diagrams. With this program, we are able to determine, based on photometric membership, the distance and age as well as the mean proper motion and radial velocity of several open clusters which had very uncertain parameters in previous analyses.

scholarly journals Astrometric Distances of Globular Clusters

1988 ◽  
Vol 126 ◽  
pp. 523-524
Author(s):  
Kyle Cudworth ◽  
Ruth C. Peterson
Keyword(s):  
Radial Velocity ◽  
High Precision ◽  
Proper Motion ◽  
Globular Clusters ◽  
Small Distance ◽  
Radial Velocities ◽  
Proper Motions ◽  
Velocity Dispersions

With high-precision radial velocities and proper motions, one can equate the proper motion and radial velocity dispersions to obtain astrometric distances independent of any standard candles. We discuss the method and the small distance it yields to M 22.

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