Microarcsecond instability of the celestial reference frame

Sazhin, M. V.; Zharov, V. E.; Volynkin, A. V.; Калинина, Т. А.

doi:10.1046/j.1365-8711.1998.01908.x

Cited by 33 publications

(32 citation statements)

References 12 publications

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“…On the other hand, Klioner [83] points out that unpredictable microlensing noise can spoil the determination of positions and proper motions of the objects resulting from future astrometric missions on a submicroarcsecond level. The gravitational image motion (GIM) due to microlensing effects may be comparable to proper motion of quasars [8,9,[84][85][86].…”

Section: Preliminary Commentsmentioning

confidence: 99%

“…Unlike the previous sections, here we rule out strong microlensing events that are accompanied by a considerable brightness amplification. In some situations it will be difficult to separate GIM from real proper motions, and this is important for accuracy of the fundamental reference frame based on extragalactic sources [83,85,86]. The gravitational field of point masses (which is essentially inhomogeneous) induces a stochastic motion of the source image in the reference frame of the source.…”

Section: Statistical Effect Of Gravitational Dragging Of a Distantmentioning

confidence: 99%

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Analytical Methods in Gravitational Microlensing

Жданов

Alexandrov

Fedorova

et al. 2012

ISRN Astronomy and Astrophysics

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We discuss analytical results dealing with photometric and astrometric gravitational microlensing. The first two sections concern approximation methods that allow us to get solutions of the general lens equation near fold caustics and cusp points up to any prescribed accuracy. Two methods of finding approximate solutions near the fold are worked out. The results are applied to derive new corrections to total amplifications of critical source images. Analytic expressions are obtained in case of the Gaussian, power-law, and limb-darkening extended source models; here we present the first nonzero corrections to the well-known linear caustic approximation. Possibilities to distinguish different source models in observations are discussed on the basis of statistical simulations of microlensed light curves. In the next section, we discuss astrometric microlensing effects in various cases of extended sources and extended lenses, including a simple model of weak statistical microlensing by extended dark matter clumps. Random walks of a distant source image microlensed by stochastic masses are estimated. We note that the bulk motion of foreground stars induces a small apparent rotation of the extragalactic reference frame. Compact analytical relations describing the statistics of such motions are presented.

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Section: Preliminary Commentsmentioning

confidence: 99%

Section: Statistical Effect Of Gravitational Dragging Of a Distantmentioning

confidence: 99%

Analytical Methods in Gravitational Microlensing

Жданов

Alexandrov

Fedorova

et al. 2012

ISRN Astronomy and Astrophysics

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“…Such angular fluctuations may range up to hundreds of microarcseconds. Sazhin et al (1998) found a good example of a quasar with large positional uncertainties caused by the lensing effects of a nearby Hipparcos star; the distance of the star is very close, just 50 pcs. Figure 16 shows a contour plot of number of sources which have an astrometric or photometric variation caused by microlensing of the same order of magnitude as the mission target accuracy.…”

Section: Noise Caused By Microlensingmentioning

confidence: 99%

“…Microlensing noise is a fundamental limit to the accuracy to which we can know the positions of sources. For example, Sazhin et al (1998Sazhin et al ( , 2001 have pointed out that fluctuations of the angular positions of reference extragalactic radio and optical sources will be caused by the microlensing effects of stars in the Galaxy. Such angular fluctuations may range up to hundreds of microarcseconds.…”

Section: Noise Caused By Microlensingmentioning

confidence: 99%

Astrometric Microlensing with the GAIA Satellite

Belokurov

Evans

2002

EAS Publications Series

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GAIA is the "super-Hipparcos" survey satellite selected as a Cornerstone 6 mission by the European Space Agency. GAIA can measure microlensing by the brightening of source stars. For the broad G band photometer, the all-sky source-averaged photometric optical depth is ∼ 10 −7 . There are ∼ 1300 photometric microlensing events for which GAIA will measure at least one datapoint on the amplified lightcurve. GAIA can also measure microlensing by the small excursions of the light centroid that occur during events. The all-sky source-averaged astrometric microlensing optical depth is ∼ 2.5 × 10 −5 . Some ∼ 25000 sources will have a significant variation of the centroid shift, together with a closest approach, during the lifetime of the mission. This is not the actual number of events that can be extracted from the GAIA dataset, as the false detection rate has not been assessed.A covariance analysis is used to study the propagation of errors and the estimation of parameters from realistic sampling of the GAIA datastream of transits in the alongscan direction during microlensing events. The mass of the lens can be calculated to good accuracy if the lens is nearby so that angular Einstein radius θ E is large; if the Einstein radius projected onto the observer planer E is about an astronomical unit; if the duration of the astrometric event is long ( ∼ > 1 year) or if the source star is bright. Monte Carlo simulations are used to study the ∼ 2500 events for which the mass can be recovered with an error of < 50%. These high quality events are dominated by disk lenses within a few tens of parsecs and source stars within a few hundred parsecs. We show that the local mass function can be recovered from the high quality sample to good accuracy. GAIA is the first instrument with the capabilities of measuring the mass locally in very faint objects like black holes and very cool white and brown dwarfs.For only ∼ 5% of all astrometric events will GAIA record even one photometric datapoint. There is a need for a dedicated telescope that densely samples the Galactic Centre and spiral arms, as this can improve the accuracy of parameter estimation by a factor of ∼ 10. The total number of sources that have an astrometric microlensing variation exceeding the mission target accuracy is ∼ 10 5 . The positional measurement of one source in every twenty thousand is affected by microlensing noise at any instant. We show that microlensing is negligible as an unbiased random error source for GAIA.

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“…As a related work, the fluctuation of the angular positions of reference extragalactic radio and optical sources under the influence of the irregular gravitational field of visible Galactic stars is considered by Sazhin et al (1998). The fluctuation leads to a small rotation of the celestial reference frame.…”

Section: Introductionmentioning

confidence: 99%

Cosmic Error Caused by the Gravitational Microlensing Effect in High-Precision Astrometry

Yano

2012

ApJ

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We have investigated an expected deviation of the positions or the proper motions of stars as the cosmic error caused by the gravitational microlensing effect. In observing stars in the Galactic bulge region, we obtain an expected deviation of a star positions by the gravitational microlensing effect of about 7 μas. We have also estimated the expected deviation of the proper motions of stars in the Galactic bulge caused by the gravitational microlensing effect. The expected deviation of the proper motions is mainly caused by the lens object located at the nearest angular distance from the source star. Each deviation of the proper motion has a value of less than 0.02 μas yr −1 for 99% of the sources. We have investigated the correlation of the deviation of Galactic bulge stars caused by the gravitational microlensing effect. The value of the correlation angle of the positional deviation is estimated to be about 1 arcmin. In the same way, we have estimated the correlation angle of the deviation of the proper motions. The angle is estimated to be about 1 arcsec. The following difference distinguishes the deviation of the position and that of the proper motion. The positional deviation is affected not only by lenses near the source but also by the lenses far from the source. On the other hand, the deviation of the proper motion by microlensing is mainly only caused by the nearest lens from the source. This difference causes that of the correlation angle.

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Microarcsecond instability of the celestial reference frame

Cited by 33 publications

References 12 publications

Analytical Methods in Gravitational Microlensing

Analytical Methods in Gravitational Microlensing

Astrometric Microlensing with the GAIA Satellite

Cosmic Error Caused by the Gravitational Microlensing Effect in High-Precision Astrometry

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