Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.gao.spb.ru/english/as/j2014/presentations/malkin.pdf Äàòà èçìåíåíèÿ: Sat Dec 27 22:55:34 2014 Äàòà èíäåêñèðîâàíèÿ: Sun Apr 10 01:09:58 2016 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: m 43

The ICRF-3:
Status, plans, and progress on the next generation International Celestial Reference Frame

Zinovy Malkin1, Christopher Jacobs2, and ICRF-3 Working Group
(1) Pulkovo Observatory and St. Petersburg State University, St. Petersburg, Russia (2) Jet Propulsion Laboratory/NASA, Pasadena, CA, USA
Journees 2014 "SystÕmes de rÈfÈrence spatio-temporels", St. Petersburg, Russia, 22-24 Sep 2014

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Overview

· ICRF-2: what we got and what we still have to work on · Plans for improving the ICRF · Connecting radio and optical frames

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Overview of 2

nd

International Celestial Reference Frame

Brief description of how the current ICRF-2 was realized: · S/X data (2.3/ 8.4 GHz or 13/ 3.6 cm) for 3414 sources

· 6.5 Million group delay observations 1979 to 2009
· No-Net-Rotation relative to ICRF-1 · Estimate TRF and EOPs internally from VLBI data Constrain to VTRF2008 (VLBI part of ITRF-08: BÆckmann et al, JGeod, 84, 2010) as ITRF2008 was not yet released. 4 constraints: Positions: No-Net-Translation, No-Net-Rotation Velocities: No-Net-Translation, No-Net-Rotation · Produced from a single monolithic fit. Verified with solutions from various groups using independent software packages.
Details in ICRF-2 Technical Note: Ma et al, IERS, 2009. http://adsabs.harvard.edu/abs/2009ITN....35....1M

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S/X-band (2/8 GHz) ICRF-2

ICRF-2
Ma et al, IERS, 2009

· 3414 Sources in ICRF2. Huge improvement over ICRF1's 608 sources · ~2200 are single session VCS sources (VLBA Calibrator Survey). · ICRF-2 is sparse south of about -40 deg.

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Systematic errors
ICRF2 - ICRF, smoothed differences, as

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Systematic errors
Differences between recent VLBI catalogues and ICRF2, as
usn2012a - ICRF2

gsf2012a - ICRF2

..

Sokolova, Malkin (2014)

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Systematic errors
Rotation of GSFC astrometric catalogues w.r.t. ICRF2

Malkin (2014)

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Observations by declination zones
Number of observations, thousand
Epoch ICRF1 ICRF2 Current 90... 60 9 (0.5%) 23 (0.3%) 60 (0.6%) 60... 30 13 (0.7%) 136 (2.0%) 279 (2.9%) 30...0 296 (16.6%) 1163 (16.8%) 1653 (17.1%) 0...+30 617 (34.7%) 1949 (28.2%) 2673 (27.6%) +30...+60 632 (35.5%) 2668 (38.6%) 3569 (36.9%) +60 ...+90 213 (11.9%) 965 (14.0%) 1446 (14.9%)

(uniform distribution is shown in red)

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Non-uniform uncertainties

Arc sources (highlighted) do not follow the general law!
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ICRF2 Summary: What we got and what we still need
Achieved
Increasing total # of sources from 608 (717 with two extensions) to 3414. Increasing # of the defining sources from 212 to 295. More uniform distribution of the defining sources. Improving the source position uncertainty (from 250 as to 40 as for noise floor). Elimination of large systematic error at the level of ~0.2 mas.

To do
Increase # of ICRF multi-session sources. Increase # of core (defining) sources. Improve the source position uncertainty and accuracy. Provide more uniform distribution of both all and core sources.




Provide more uniform distribution of the source position errors (VCS sources, southern sources, arc sources).
Mitigate the large-scale systematic errors (slides 5, 6) to a level of below 5-10 µas. Enhance CRF at higher frequencies. 10


S/X-band Plan for Southern Improvements
· Plans from Titov et al, IAG, 2013 · 2013-15: Observe 100-200 strong sources (> 400 mJy) using the small, fast stations of the southern CRF Network at S/X-bands. · Goal > 100 scans per source, 50 µas precision. · 7 astrometric sessions observed since January 2014 as a part of AuScope observing program.
ICRF-2
Ma et al, IERS, 2009

· Weaker sources observed with large telescopes: Parkes, DSS45, Hobart26, HartRAO 100-200 sources over 2 years.
· Goal 20 scans/source, 100-150 µas precision.
Southern Hemisphere CRF stations Credit: Titov el al, IAG, 2013

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S/X Survey sources (VCS)
·

VCS precision is typically 1,000 µas or 5 times worse than the rest of ICRF-2

VCS
Beasley et al, ApJS, 2002

· · ·

Deficiency: Uneven precision of ICRF-2 VCS's 2200 sources (2/3 of the ICRF-2) Plan: Re-observe VCS sources with VLBA VLBA approved 8 x 24-hour sessions to re-observe VCS sources. PI: David Gordon. 5 sessions completed and processed, 3 more scheduled, waiting in VLBA queue

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VCS-II

Note ~3X improvement in precision and much more uniform distribution of the position uncertainties over declination.

Gordon, 2014

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Source Structure vs. Wavelength

S-band 2.3 GHz 13.6cm

X-band 8.6 GHz 3.6cm

K-band 24 GHz 1.2cm
Ka-band 32 GHz 0.9cm

Q-band 43 GHz 0.7cm

The sources become better ----->
Image credit: P. Charlot et al, AJ, 139, 5, 2010

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X/Ka-band (8/32 GHz) CRF

X/Ka: s

a

Jacobs et al, 2014

· Deficiency: Weak in the south. S. cap 134 sources (dec< -45); 27 ICRF2 Defining · Full sky coverage (644 sources): NASA baselines CA to Madrid & Australia + recently added ESA MalargÝe, Argentina to Tidbinbilla, Australia, PI: Jacobs · 2 Gbps operational data acquisition. · Ka-band phase cal installed at Goldstone. · Median RA precision now 85 µas matching ICRF2 for the 525 common sources.

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Plan to improve X/Ka: baselines to Argentina
8400 km

9900 km 10,600 km 8500 km

9810 km

Maps credit: Google maps

ESA's Argentina 35-meter antenna adds 3 baselines to DSN's 2 baselines · Full sky coverage by accessing south polar cap · near perpendicular mid-latitude baselines: CA to Aust./Argentina

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K-band (24 GHz) CRF: 275 sources

Lacking in South

K-band
Lanyi et al, AJ, 2010; Charlot et al, 2010

· Deficiency: lacking in the south Plan: New K-band full sky coverage collaboration (Bertarini+, Journees, 2013) First southern K-band fringes: Hobart-HartRAO (23 Aug 2013) First 24h southern session: 21 Dec 2013, in correlation (de Witt+, IVS-2014)
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Gaia/VLBI frame tie & Accuracy test
Gaia:
· 500,000 quasars V< 20 mag 20,000 quasars V< 18 mag · radio loud 30-300+ mJy and optically bright: V<18 mag ~2000 quasars (Mignard, 2013) · S/X frame tie Strategy: Bring 100+ new optically bright quasars into the radio frame (Bourda, et al., 2008-2012). · X/Ka frame tie: Measured X/Ka precision and simulated Gaia optical precision yields frame tie alignment of ~ 10 µas per 3-D rotation angle Limited by X/Ka precision, but improving as more data arrives. · Several groups: Titov et al. , Andrei et al., Taris et al. working on optical measurements of the current and prospective ICRF sources (identification, redshifts, photometry).

· Quasar positions precision 70 µas @ V=18 25 µas @ V=16
may get worse due to stray light, especially for fainter objects
Figure credit: http://www.esa.int/esaSC/120377_index_1_m.html#subhead7

XKa: ~175 optically bright counterparts: V< 18 mag (optical V magnitudes: Veron-Cetty & Veron, 2010) 18


Optical vs. Radio positions
Positions differences from: · Astrophysics of emission centroids - radio: synchrotron from jet

- optical: synchrotron from jet? non-thermal ionization from corona? "big blue bump" from accretion disk?
- optical centroid biased by host galaxy? · Instrumental errors both radio & optical · Analysis errors
Credit: Wehrle et al, µas Science, Socorro, 2009

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9mm vs. 3.6cm: Core shift & structure

R~0.1-1 µas

1mas

Positions differences from `core shift' · wavelength dependent shift in radio centroid. · 3.6cm to 9mm core shift: 100 µas in phase delay centroid? <<100 µas in group delay centroid? (Porcas,

Credit: A. Marscher, Proc. Sci., Italy, 2006. Overlay image: Krichbaum, et al, IRAM, 1999. Montage: Wehrle et al, ASTRO-2010, no. 310.

) · shorter wavelength closer to Black hole and Optical: 9mm X/Ka better
AA, 505, 1, 2009

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LQAC-3
Third release of the Large Quasars Astrometric Catalogue Objectives:

-

Compilation of all the recorded quasars (~374000) Strategy insisting on astrometric quality Cross-identifications between ICRF and optical catalogues Extended photometry & redshift Morphology indexes Calculation of absolute magnitudes MI & MB Basis for regular up-dates (=> GAIA) Final ASCII file with V.O. tools in parallel Comparisons / statistics / coherence

Souchay et al., in prep. end 2014

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Summary of ICRF-3 tasks: · Improving VLBA Cal Survey's 2000+ positions More uniform precision for all sources · Improving southern observations More uniform spatial coverage · Improving number, accuracy, and southern coverage of high frequency frames 24, 32, 43? GHz (K, X/Ka, Q?) Improved frequency coverage · ICRF-3 completed by Aug 2018 in time for comparisons & alignment with Gaia optical frame · Competitive accuracy with Gaia ~ 70 µas (1-sigma RA, Dec) · Improving set of optical-radio frame tie sources for Gaia
Sponsorship of U.S. Government and our respective agencies acknowledged. Research done in part under contract with NASA. Copyright 2014. All Rights reserved.

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IAU Working Group on ICRF3
Charter for IAU Division A Working Group on the Third Realization of the International Celestial Reference Frame
The purpose of the IAU Division A Working Group on the Third Realization of the International Celestial Reference Frame (ICRF) is to produce a detailed implementation and execution plan for formulation of the third realization of the ICRF and to begin the process of executing that plan. The implementation plan along with execution progress will be reported to IAU Division A at the XXIX General Assembly of the IAU in 2015.

Targeted completion of the third realization of the ICRF will be the XXX General Assembly of the IAU in 2018.
Derived from VLBI observations of extragalactic radio sources, the third realization of the ICRF will apply state-of-the-art astronomical and geophysical models and analysis strategies, and utilize the entire relevant astrometric and geodetic data set. The Working Group will examine and discuss new processes and procedures for formulating the frame along with the potential incorporation of new global VLBI arrays, and new observing frequencies offering the potential for an improvement over ICRF2. The Working Group will provide oversight and guidance for improving the relevant data sets.

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IAU Working Group on ICRF3

Felicitas Arias, France David Boboltz, USA Johannes BÆhm, Austria Sergei Bolotin, USA GÈraldine Bourda, France Patrick Charlot, France Aletha de Witt, South Africa Alan Fey, USA Ralph Gaume, USA David Gordon, USA

Robert Heinkelmann, Germany Christopher Jacobs, USA (chair) SÈbastien Lambert, France Chopo Ma, USA Zinovy Malkin, Russia Axel Nothnagel, Germany Manuela Seitz, Germany Elena Skurikhina, Russia Jean Souchay, France Oleg Titov, Australia

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