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 Absolute Proper Motions of the Dwarf Spheroidal Galaxies in Draco and Ursa Minor

1994 ◽  
Vol 161 ◽  
pp. 535-539 ◽  
Author(s):  
R.-D. Scholz ◽  
M.J. Irwin
Keyword(s):  
Proper Motion ◽  
Globular Clusters ◽  
Reduction Process ◽  
Systematic Errors ◽  
Base Line ◽  
Proper Motions ◽  
Dwarf Spheroidal Galaxies ◽  
Accuracy Level ◽  
Ursa Minor ◽  
The Mean

Palomar and Tautenburg Schmidt plates with a base line of about 35 years have been measured with the Automated Photographic Measuring (APM) system in Cambridge (UK) in order to obtain the proper motions of the Galactic dwarf spheroidal satellites (dSph) in Draco and Ursa Minor with respect to a well defined extragalactic reference frame. The investigations were encouraged by the accuracy level achieved for the mean absolute proper motions of galactic globular clusters (0.05 arcsec/century from 25 years base line Tautenburg plate pairs) which is comparable to the expected proper motion of the Draco and Ursa Minor dSph assuming tangential motions of about 100 km/s. Different methods for the removal of systematic errors in the absolute proper motion introduced by the measuring and reduction process are discussed. The more accurate relative proper motions of individual stars in both dSphs obtained by Stetson (1980) and by Cudworth, Olszewski & Schommer (1986) provide an external comparison and are also used to obtain the mean absolute proper motion of the dSphs.

scholarly journals The Luyten – Control Data Stellar Proper Motion Measuring Machine

1970 ◽  
Vol 7 ◽  
pp. 5-25
Author(s):  
James Newcomb
Keyword(s):  
Proper Motion ◽  
Time Scale ◽  
Proper Motions ◽  
Control Data ◽  
Stellar Proper Motions ◽  
Measurement Function ◽  
Measuring Machine ◽  
Motion Measurements

The discovery and measurement of stellar proper motions has always been associated with machines: for proper motion measurements involve four activities: observation, recording, comparison and measurement. Participation by the astronomer in these activities has step by step been replaced partically or wholly by machines. First the observation and recording functions changed from visual to photographic – with the fine guiding done by the astronomer; then the comparison by the blink microscope and the measurement by visually operated measuring machines. On a comparative time scale, the next step – automation of the comparison and measurement function – has been much money, time, and effort away from the previous steps, but as this presentation and other presentations at this conference will show, machines of varying degrees of automation and astronomer participation are now in operation.

scholarly journals On Inconsistencies Found in Long-Term Parallax Series

1974 ◽  
Vol 61 ◽  
pp. 317-317
Author(s):  
W. D. Heintz
Keyword(s):  
Proper Motion ◽  
Orbital Motion ◽  
Proper Motions ◽  
Great Caution

Two recent papers (Hershey; Gatewood and Eichhorn; Astron. J., 1973) pointed out that:(1) A proper motion irregularity interpreted as orbital motion was found duplicated in another field.(2) The discontinuity found at one telescope failed to be confirmed by others, and might be ascribed to mere instrumental errors.After the duplication was discovered two years ago, further measurements have revealed an identical pattern in at least seven parallax stars. Yet the cause of the effect, and the reason for its absence in other cases, have not been located. Colour effects and filter problems appear to be ruled out. Indications for discontinuities occurring at other epochs were found. Thus, the question cannot yet be safely answered whether the small variations (one or two micron) of proper motions reported in some cases are spurious; in any case, great caution should be exercised in interpreting one-micron effects unless confirmation from another instrument is obtained.

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 Proper motion measurements for stars up to 100 kpc with Subaru HSC and SDSS Stripe 82

2020 ◽  
Author(s):  
Tian Qiu ◽  
Wenting Wang ◽  
Masahiro Takada ◽  
Naoki Yasuda ◽  
Željko Ivezić ◽  
...  
Keyword(s):  
Proper Motion ◽  
Tangential Velocity ◽  
Space Structures ◽  
Galactic Centre ◽  
Proper Motions ◽  
Distance Range ◽  
Common Reference ◽  
Motion Display ◽  
Motion Measurements ◽  
Set Up

Abstract We present proper motion measurements for more than 0.55 million main-sequence stars, by comparing astrometric positions of matched stars between the multi-band imaging datasets from the Hyper Suprime-Cam (HSC) Survey and the SDSS Stripe 82. In doing this we use 3 million galaxies to recalibrate the astrometry and set up a common reference frame between the two catalogues. The exquisite depth and the nearly 12 years of time baseline between HSC and SDSS enable high-precision measurements of statistical proper motions for stars down to i ≃ 24. A validation of our method is demonstrated by the agreement with the Gaia proper motions, to the precision better than 0.1 mas yr−1. To retain the precision, we make a correction of the subtle effects due to the differential chromatic refraction in the SDSS images based on the comparison with the Gaia proper motions against colour of stars, which is validated using the SDSS spectroscopic quasars. Combining with the photometric distance estimates for individual stars based on the precise HSC photometry, we show a significant detection of the net proper motions for stars in each bin of distance out to 100 kpc. The two-component tangential velocities after subtracting the apparent motions due to our own motion display rich phase-space structures including a clear signature of the Sagittarius stream in the halo region of distance range [10,35] kpc. We also measure the tangential velocity dispersion in the distance range 5–20 kpc and find that the data are consistent with a constant isotropic dispersion of 80 ± 10 km/s. More distant stars appear to have random motions with respect to the Galactic centre on average.

scholarly journals Accurate mass estimates from the proper motions of dispersion-supported galaxies

2020 ◽  
Vol 493 (4) ◽  
pp. 5825-5837 ◽  
Author(s):  
Alexandres Lazar ◽  
James S Bullock
Keyword(s):  
Dark Matter ◽  
Proper Motion ◽  
Cold Dark Matter ◽  
Dwarf Galaxy ◽  
Tangential Velocity ◽  
Line Of Sight ◽  
Proper Motions ◽  
Characteristic Radius ◽  
Motion Measurements ◽  
Rule Out

ABSTRACT We derive a new mass estimator that relies on internal proper motion measurements of dispersion-supported stellar systems, one that is distinct and complementary to existing estimators for line-of-sight velocities. Starting with the spherical Jeans equation, we show that there exists a radius where the mass enclosed depends only on the projected tangential velocity dispersion, assuming that the anisotropy profile slowly varies. This is well-approximated at the radius where the log-slope of the stellar tracer profile is −2: r−2. The associated mass is $M(r_{-2}) = 2 G^{-1} \langle \sigma _{\mathcal {T}}^{2}\rangle ^{*} r_{-2}$ and the circular velocity is $V^{2}({r_{-2}}) = 2\langle \sigma _{\mathcal {T}}^{2}\rangle ^{*}$. For a Plummer profile r−2 ≃ 4Re/5. Importantly, r−2 is smaller than the characteristic radius for line-of-sight velocities derived by Wolf et al. Together, the two estimators can constrain the mass profiles of dispersion-supported galaxies. We illustrate its applicability using published proper motion measurements of dwarf galaxies Draco and Sculptor, and find that they are consistent with inhabiting cuspy NFW subhaloes of the kind predicted in CDM but we cannot rule out a core. We test our combined mass estimators against previously published, non-spherical cosmological dwarf galaxy simulations done in both cold dark matter (CDM; naturally cuspy profile) and self-interacting dark matter (SIDM; cored profile). For CDM, the estimates for the dynamic rotation curves are found to be accurate to $10\rm { per\, cent}$ while SIDM are accurate to $15\rm { per\, cent}$. Unfortunately, this level of accuracy is not good enough to measure slopes at the level required to distinguish between cusps and cores of the type predicted in viable SIDM models without stronger priors. However, we find that this provides good enough accuracy to distinguish between the normalization differences predicted at small radii (r ≃ r−2 < rcore) for interesting SIDM models. As the number of galaxies with internal proper motions increases, mass estimators of this kind will enable valuable constraints on SIDM and CDM models.

scholarly journals Absolute proper motions of water masers in NGC 281 measured with VERA

2007 ◽  
Vol 3 (S242) ◽  
pp. 170-171
Author(s):  
Mayumi Sato ◽  
Tomoya Hirota ◽  
Mareki Honma ◽  
Hideyuki Kobayashi ◽  
Keyword(s):  
Vertical Velocity ◽  
Proper Motion ◽  
Molecular Cloud ◽  
Direct Evidence ◽  
Galactic Plane ◽  
Proper Motions ◽  
Supernova Explosions ◽  
Motion Measurements ◽  
Water Masers

AbstractWe report on absolute proper-motion measurements of H2O maser features in the NGC 281 West molecular cloud, located ~320 pc above the Galactic plane and associated with an HI loop extending from the Galactic plane. We conducted six-epoch phase-referencing observations of the maser source with VERA (VLBI Exploration of Radio Astrometry) over six months since May 2006. The H2O maser features are found to be systematically moving toward the southwest and further away from the Galactic plane with a vertical velocity of ~20–30 km s−1 at its estimated distance of 2.2–3.5 kpc. Our new results provide the most direct evidence that the gas in the NGC 281 region was blown out from the Galactic plane, most likely in a superbubble driven by multiple or sequential supernova explosions in the Galactic plane.

scholarly journals Microarcsecond astrometry in the Local Group

2007 ◽  
Vol 3 (S248) ◽  
pp. 474-480
Author(s):  
A. Brunthaler ◽  
M. J. Reid ◽  
H. Falcke ◽  
C. Henkel ◽  
K. M. Menten
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Local Group ◽  
Statistical Error ◽  
Dark Matter Halo ◽  
Proper Motions ◽  
Angular Rotation ◽  
Vlbi Observations ◽  
Ic 10 ◽  
Motion Measurements

AbstractMeasuring the proper motions and geometric distances of galaxies within the Local Group is very important for our understanding of its history, present state and future. Currently, proper motion measurements using optical methods are limited only to the closest companions of the Milky Way. However, given that VLBI provides the best angular resolution in astronomy and phase-referencing techniques yield astrometric accuracies of ≈ 10 micro-arcseconds, measurements of proper motions and angular rotation rates of galaxies out to a distance of ~ 1 Mpc are feasible. This paper presents results of VLBI observations in regions of H2O maser activity of the Local Group galaxies M33 and IC 10. Two masing regions in M33 are on opposite sides of the galaxy. This allows a comparison of the angular rotation rate (as measured by the VLBI observations) with the known inclination and rotation speed of the Hi gas disk leading to a determination of a geometric distance of 730 ± 100 ± 135 kpc. The first error indicates the statistical error of the proper-motion measurements, while the second error is the systematic error of the rotation model. Within the errors, this distance is consistent with the most recent Cepheid distance to M33. Since all position measurements were made relative to an extragalactic background source, the proper motion of M33 has also been measured. This provides a three dimensional velocity vector of M33, showing that this galaxy is moving with a velocity of 190 ± 59 km s−1 relative to the Milky Way. For IC 10, we obtain a motion of 215 ± 42 km s−1 relative to the Milky Way. These measurements promise a new handle on dynamical models for the Local Group and the mass and dark matter halo of Andromeda and the Milky Way.

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 Determining Motions and Birthplaces of Pulsars through VLBI Astrometry

1998 ◽  
Vol 164 ◽  
pp. 391-392
Author(s):  
T. J. Galama ◽  
J. Van Paradijs ◽  
E. P. J. van den Heuvel ◽  
A. G. de Bruyn ◽  
R. M. Campbell ◽  
...  
Keyword(s):  
Flux Density ◽  
Proper Motion ◽  
Mass Range ◽  
Solar Neighborhood ◽  
Proper Motions ◽  
First Results ◽  
Motion Measurements

AbstractWe present first results of global VLBI astrometric pulsar parallax and proper motion measurements (phase-reference). The aim is to obtain information on pulsar motions and pulsar birthplaces. Proper motions could provide answers to questions like: How large are pulsar velocities at birth? How are these velocities produced and what is the final galactic pulsar distribution? Identification of birthplaces (with, e.g., an OB-association) provides information on the pulsar progenitor population (the fraction of pulsars born in binaries; the mass range of the progenitors etc.). We have a first epoch on three pulsars, selected on the basis of age (young < 3 Myr), flux density (relatively strong) and presence in the solar neighborhood (d < 3 kpc). Gating increases the SNR by typically a factor of 5.

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