scholarly journals The Distance to the Center of the Galaxy

1987 ◽  
Vol 115 ◽  
pp. 554-555 ◽  
Author(s):  
M. J. Reid ◽  
M. H. Schneps ◽  
J. M. Moran ◽  
C. R. Gwinn ◽  
R. Genzel ◽  
...  
Keyword(s):  
Proper Motion ◽  
Radial Component ◽  
Proper Motions ◽  
Star Forming ◽  
The Galaxy

The distance to a star forming region can be determined by measuring the proper motions within H2O maser clusters. If the motions of the maser spots are random, the distance can be determined by applying the technique known as statistical parallax. Alternatively, if organized motions are evident in the proper motions, one can model the source to estimate its the distance. Both methods rely on a comparison of the radial component of the motion (in km/s) and the proper motion on the plane of the sky (in milli-arcseconds/year).

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 Correction to Absolute Proper Motion Using the IAS-Galaxy Model

1990 ◽  
Vol 141 ◽  
pp. 427-429
Author(s):  
Kavan U. Ratnatunga
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Theoretical Models ◽  
Galactic Structure ◽  
Coordinate Frame ◽  
Proper Motions ◽  
Software Interface ◽  
The Galaxy ◽  
Galaxy Model ◽  
Star Catalogs

The IAS-Galaxy model (Ratnatunga, Bahcall and Casertano 1989) is a software interface between theoretical models of the Galaxy and observed kinematic distributions. It has been developed for analysis of many kinematic catalogs to study global galactic structure. In addition, the IASG model can be used to estimate corrections needed to derive absolute parallax and absolute proper motion by evaluating, on a star-by-star basis, the expected mean motion of the reference stars.A theoretical Galaxy model is defined on an inertial coordinate frame. Proper motions are measured in a reference frame defined by a fundamental catalog. The observed distribution of proper motions in star catalogs can be directly compared with the expected distributions evaluated using IASG to check the accuracy of the adopted reference frame in realizing the inertial coordinate frame in the sky.

scholarly journals Micro-arcsecond astrometry with the VLBA

2007 ◽  
Vol 3 (S248) ◽  
pp. 141-147 ◽  
Author(s):  
M. J. Reid
Keyword(s):  
Galactic Center ◽  
Galactic Plane ◽  
Proper Motions ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Trigonometric Parallaxes ◽  
Sgr A ◽  
Definition Of ◽  
Almost All

AbstractThe VLBA is now achieving parallaxes and proper motions with accuracies approaching the micro-arcsecond domain. The apparent proper motion of Sgr A*, which reflects the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0/R0 and offers a dynamical definition of the Galactic plane with Sgr A*at its origin. The intrinsic motion of Sgr A*is very small and comparable to that expected for a supermassive black hole. Trigonometric parallaxes and proper motions for a number of massive star forming regions (MSFRs) have now been measured. For almost all cases, kinematic distances exceed the true distances, suggesting that the Galactic parameters, R0 and Θ0, are inaccurate. Solutions for the Solar Motion are in general agreement with those obtained from Hipparcos data, except that MSFRs appear to be rotating slower than the Galaxy. Finally, the VLBA has been used to measure extragalactic proper motions and to map masers in distant AGN accretion disks, which will yield direct estimates of H0.

scholarly journals Report on the Herstmonceux I.N.T. Parallax Programme

1974 ◽  
Vol 61 ◽  
pp. 167-167
Author(s):  
B. F. Jones
Keyword(s):  
Proper Motion ◽  
Reduction Technique ◽  
Royal Greenwich Observatory ◽  
Proper Motions ◽  
Isaac Newton ◽  
The Galaxy ◽  
Visual Magnitude ◽  
Isaac Newton Telescope

In 1971 a pilot parallax programme was initiated on the 98-in. Isaac Newton Telescope at the Royal Greenwich Observatory. Nineteen stars between visual magnitude 15 and 19 and of high proper motion were put on the programme. The plates were taken at prime focus through the Wynne corrector. Observations are now complete for two of these stars. Because of time allocations and the desire to observe at maximum parallax factor, observations are made at large hour angles. All stars in each field are being measured on the GALAXY measuring engine and parallaxes and proper motions will be computed for all stars. The fields are being reduced using an overlap reduction technique.

scholarly journals Proper motions of water masers: W 51 North, Main, and South

2002 ◽  
Vol 206 ◽  
pp. 88-91 ◽  
Author(s):  
Hiroshi Imai ◽  
Tetsuo Sasao ◽  
Osamu Kameya ◽  
Teruhiko Watanabe ◽  
Toshihiro Omodaka ◽  
...  
Keyword(s):  
Proper Motion ◽  
Massive Star ◽  
Model Fitting ◽  
Proper Motions ◽  
Star Forming ◽  
Motion Measurements ◽  
Water Masers ◽  
Reference Feature

We describe the proper motion measurements of water masers in the massive-star forming region W 51A and the analysis of the 3-D kinematics in three maser clusters of W 51A. We found a systematic expanding motion in one of the clusters named W 51 North, while no systematic motion was detected in other two clusters named W 51 Main and South. The 3-D motions of the clusters relative to the position reference feature in W 51 North indicate a separating motion between the W 51 North and the W 51 Main/South clusters. We estimated the distance to W 51 North as to be 6.7±2.1 kpc on basis of the statistical parallax and the model fitting methods.

scholarly journals Astrometry with Schmidt Telescopes for Probing the Galaxy

1995 ◽  
Vol 148 ◽  
pp. 234-240 ◽  
Author(s):  
C. Andrew Murray
Keyword(s):  
Proper Motion ◽  
Proper Motions ◽  
The South ◽  
Large Numbers ◽  
The Galaxy ◽  
Zero Points

AbstractThe use of proper motions and parallaxes for large numbers of stars, obtainable from a combination of Schmidt telescopes and automatic plate scanners, is discussed. The importance of deriving the zero points of both absolute proper motion, and of parallactic motion, is emphasised. Calibrations of proper motion and of parallaxes should be based on dispersions of proper motion. These methods are illustrated by results from a study in the South Galactic Cap.

scholarly journals A New Absolute Proper Motion Determination of Leo I Using HST/WFPC2 Images and Gaia EDR3

2021 ◽  
Vol 163 (1) ◽  
pp. 1
Author(s):  
Dana I. Casetti-Dinescu ◽  
Caitlin K. Hansen ◽  
Terrence M. Girard ◽  
Vera Kozhurina-Platais ◽  
Imants Platais ◽  
...  
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Proper Motions ◽  
Large Area ◽  
Field Of Study ◽  
Data Set ◽  
Polar Structure ◽  
The Galaxy ◽  
The Absolute

Abstract We measure the absolute proper motion of Leo I using a WFPC2/HST data set that spans up to 10 yr to date the longest time baseline utilized for this satellite. The measurement relies on ∼2300 Leo I stars located near the center of light of the galaxy; the correction to absolute proper motion is based on 174 Gaia EDR3 stars and 10 galaxies. Having generated highly precise, relative proper motions for all Gaia EDR3 stars in our WFPC2 field of study, our correction to the absolute EDR3 system does not rely on these Gaia stars being Leo I members. This new determination also benefits from a recently improved astrometric calibration of WFPC2. The resulting proper-motion value, (μ α , μ δ ) = (−0.007 ± 0.035, − 0.119 ± 0.026) mas yr−1 is in agreement with recent, large-area, Gaia EDR3-based determinations. We discuss all the recent measurements of Leo I’s proper motion and adopt a combined, multistudy average of ( μ α 3 meas , μ δ 3 meas ) = ( − 0.036 ± 0.016 , − 0.130 ± 0.010 ) mas yr−1. This value of absolute proper motion for Leo I indicates its orbital pole is well aligned with that of the vast polar structure, defined by the majority of the brightest dwarf spheroidal satellites of the Milky Way.

scholarly journals The substructure of the Perseus star-forming region: a survey with Gaia DR2

2021 ◽  
Vol 503 (3) ◽  
pp. 3232-3242
Author(s):  
Tatiana Pavlidou ◽  
Aleks Scholz ◽  
Paula S Teixeira
Keyword(s):  
Proper Motion ◽  
Motion Parallax ◽  
Young Stars ◽  
Galactic Latitude ◽  
Proper Motions ◽  
Kinematic Data ◽  
Star Forming ◽  
Moving Groups ◽  
Cold Dust ◽  
Gaia Dr2

ABSTRACT We use photometric and kinematic data from Gaia DR2 to explore the structure of the star-forming region associated with the molecular cloud of Perseus. Apart from the two well-known clusters, IC 348 and NGC 1333, we present five new clustered groups of young stars, which contain between 30 and 300 members, named Autochthe, Alcaeus, Heleus, Electryon, and Mestor. We demonstrate that these are co-moving groups of young stars, based on how the candidate members are distributed in position, proper motion, parallax, and colour–magnitude space. By comparing their colour–magnitude diagrams to isochrones, we show that they have ages between 1 and 5 Myr. Using 2MASS and WISE colours, we find that the fraction of stars with discs in each group ranges from 10 to ∼50 per cent. The youngest of the new groups is also associated with a reservoir of cold dust, according to the Planck map at 353 GHz. We compare the ages and proper motions of the five new groups to those of IC 348 and NGC 1333. Autochthe is clearly linked with NGC 1333 and may have formed in the same star formation event. The seven groups separate roughly into two sets that share proper motion, parallax, and age: Heleus, Electryon, and Mestor as the older set, and NGC 1333 and Autochthe as the younger set. Alcaeus is kinematically related to the younger set, but at a more advanced age, while the properties of IC 348 overlap with both sets. All older groups in this star-forming region are located at higher galactic latitude.

scholarly journals New member candidates of Upper Scorpius from Gaia DR1

2018 ◽  
Vol 618 ◽  
pp. A12 ◽  
Author(s):  
S. Wilkinson ◽  
B. Merín ◽  
P. Riviere-Marichalar
Keyword(s):  
Proper Motion ◽  
Clustering Algorithm ◽  
Proper Motions ◽  
Established Method ◽  
Kinematic Data ◽  
Star Forming ◽  
Density Based Clustering ◽  
Member Selection ◽  
Bona Fide ◽  
And Performance

Context. Selecting a cluster in proper motion space is an established method for identifying members of a star-forming region. The first data release from Gaia (DR1) provides an extremely large and precise stellar catalogue, which when combined with the Tycho-2 catalogue gives the 2.5 million parallaxes and proper motions contained within the Tycho-Gaia Astrometric Solution (TGAS). Aims. We aim to identify new member candidates of the nearby Upper Scorpius subgroup of the Scorpius-Centaurus Complex within the TGAS catalogue. In doing so, we also aim to validate the use of a density-based clustering algorithm (DBSCAN) on spatial and kinematic data as a robust member selection method. Methods. We constructed a method for member selection using a density-based clustering algorithm (DBSCAN) applied over proper motion and distance. We then applied this method to Upper Scorpius and evaluated the results and performance of the method. Results. We identified 167 member candidates of Upper Scorpius, of which 78 are new, distributed within a 10° radius from its core. These member candidates have a mean distance of 145.6 ± 7.5 pc and a mean proper motion of (−11.4, −23.5) ± (0.7, 0.4) mas yr−1. These values are consistent with measured distances and proper motions of previously identified bona fide members of the Upper Scorpius association.

scholarly journals Maser astrometry with VERA and Galactic structure

2012 ◽  
Vol 8 (S287) ◽  
pp. 386-390 ◽  
Author(s):  
Mareki Honma ◽  
Takumi Nagayama ◽  
Tomoya Hirota ◽  
Naoko Matsumoto ◽  
Nobuyuki Sakai ◽  
...  
Keyword(s):  
Rotation Curve ◽  
Galactic Structure ◽  
Proper Motions ◽  
Late Type ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Maser Sources

AbstractSince 2007 VERA (VLBI Exploration of Radio Astrometry) has been producing astrometric results (distances and/or proper motions) for Galactic maser sources. Nearly 30 parallaxes have been obtained for star-forming regions and late-type stars. By using VERA's astrometric results for star-forming regions, combined with those obtained with VLBA and EVN, fundamental Galactic parameters and Galactic structure may be derived. Our results show that R0 = 8.4 ± 0.4 kpc and Ω⊙ ≡ Ω0 + V⊙/R0=30.7±0.8 km s−1 kpc−1, and also show that the rotation curve of the Galaxy is nearly flat. The determinations of Galactic parameters and structures demonstrate that the maser astrometry can not only contribute significantly to research of individual maser sources, but also to studies of the structure of the Galaxy.

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