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Astrometry from VERA to SKA

Astrometry from VERA to SKA. Hiroshi Imai Graduate School of Science and Engineering, Kagoshima University SKA-JP Astrometry Sub-Working Group. Contents. Current VLBI astrometry VERA (CH 3 OH, H 2 O, SiO maser sources) VLBA/EVN/LBA (BeSSeL, Gould's Belt, Pulsar, …)

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Astrometry from VERA to SKA

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  1. Astrometry from VERA to SKA Hiroshi Imai Graduate School of Science and Engineering, Kagoshima University SKA-JP Astrometry Sub-Working Group

  2. Contents • Current VLBI astrometry • VERA (CH3OH, H2O, SiO maser sources) • VLBA/EVN/LBA (BeSSeL, Gould's Belt, Pulsar, …) • Possible astrometry with SKA • Wide-field astrometry • Multi-frequency astrometry • Deep space astrometry • Astrometry for transient objects • Challenging issues towards SKA • High resolution network construction and operation • Data calibration and processing • Target sources and their numbers after GAIA era

  3. VERA (VLBI Exploration of Radio Astrometry) • First VLBI array dedicated for radio astrometry • Dual-beam system used for phase compensation against atmospheric fluctuation within 0.3-2.2 deg separation • CH3OH(6.7GHz), H2O(22GHz), SiO(43GHz) maser sources • Operation for ~5,000 hours/year in the next decade • Total bandwidth: 512 MHz(1 Gbps) ⇒ 1GHz (4 Gbps)

  4. VERA astrometry • 1%-level accuracy within 500 pc • 10%-level within 5 kpc, up to 15 kpc • Papers in PASJ special issues (2008, 2011) • Astrometry towards ~500 maser sources within 10 years SiO masers in Orion Source I (Kim et al. 2008) H2O masers in T Lep (Nakagawa et al. 2011)

  5. Current scientific targets in VERA • High-mass star forming regions (H2O, CH3OH) • low-mass young stellar objects (YSOs), (H2O) • Evolved stars (H2O, SiO) • Maser sources at sites of star formation and stellar mass loss • Galactic plane for the Galactic dynamics • Nearby (~1 kpc) the Solar system for distance-scale calibration (e.g. Mira’s P-L relation) • AGN, Blazers for core-shifts with frequency • X-ray binary for SN kick

  6. VLBA/HSA/EVN/LBA • Multi-purpose VLBI arrays • VLBA Large Projects for astrometry • BeSSeL: H2O and CH3OH masers towards ~400 high-mass star forming regions • Gould's Belt astrometry: continuum sources towards ~200 YSOs • PSRPI: astrometry towards ~140 pulsars ~1000-1500 hours/year for astrometry? • LBA towards the southern hemisphere • Radio astrometry in any field (e.g. planet search) Spitzer Gould’s Belt Survey

  7. Possible astrometry with SKA • Astrometry for non-thermal and thermal sources • Wide-field astrometry • in-beam, multi-beam, multi-field delay tracking • Wide-band/multi-frequency astrometry • wide-band receiving, flexible spectroscopy • Deep space astrometry • high sensitivity • Astrometry for transient objects • snapshot, blind survey, flexible operation (ToO) • Earth rotation and geodesy • Maintenance of reference frames

  8. Empirical astrometric accuracies (VERA/VLBA) and expectations to SKA

  9. Astrometric specification @ 10μasupdated with SKA • Reference source candidates: 30 mJy⇒1 mJy @8 GHz • Super-synthesis: 2 hours ⇒ 10 min • Target maser flux for 10 min: 1 Jy ⇒ 20 mJy • Target continuum flux for 10 min: 5 mJy ⇒ 25 μJy • Geodetic VLBI: residual monitoring in semi-real-time ~20 tels., ~500 scans/day ⇒ ~50 sta., 50×10 scans/30 min • Angular resolution: θVLBA ~ 1/3 θSKA~ θSKA +α

  10. Wide-field astrometry with SKA Permitted phase coherence angle within atmospheric fluctuation for 10-μas level astrometry Δθ(target – reference) < 2 deg @22 GHz Δθ(target – reference) < 6 deg @6 GHz ~30,000 reference sources with S8GHz > 1 mJy Δθ(reference – reference) ~0.7 deg Multi-reference, in-beam astrometry is possible. Wide-field astrometry is still necessary and possible for estimation/ correction of zenith delay residuals. ASKAP focal plane phased array FoV=30 deg2 @1.5GHz

  11. Data correlation for SKA wide-field astrometry • Time-average smearing in data correlation • Targeted astrometry with multi-field correlation Toward known/selected sources (Nfield< 100) • NIR/MIR sources (MSX, AKARI) • molecular cloud cores (NANTEN, ASTE/AzTEC, GASKAP) • Blind astrometry with wild-field correlation Toward unknown sources (Nfield> 1 000) • Stellar OH masers in the Galactic halo (HIPPARCOS, GAIA) • γ-ray bursts from the objects that are not QSOs • Astrometric micro-lensing events towards the Galactic bulge and LMC/SMC (P~1/103 [stars] for 10 μas) (Onishi 1995)

  12. Multi-frequency astrometry with SKA • Spectral lines per observation: 1 or 2 lines ⇒ >2 lines • Multi-frequency astrometry at mid-band Masers [MHz] • OH: 1612, 1665, 1667, 1720, 4751, 4766, 6031, 6035, 13441 • CH3OH: 6669, 12179 • H2O: 22235, NH3: 23694, 23723, 23870 (high-band) thermal lines …… • CH3OH: 834, ... , NH2CHO: 1539, CH3OCHO: 1065 [MHz] • recombination lines

  13. Targets of SKA line astrometry • Astrometry towards maser sources • low/intermediate-mas young stellar objects (YSOs) • nearby regions (in TMC, Ophiucus, Serpens, up to ~5 kpc) • high-mass YSOs • Galactic plane, LMC, M33, M31, up to ~10 Mpc • Evolved stars (Mira variables, OH/IR stars) • Galactic halo, bulge, LMC, SMC, up to ~100 kpc • Thermal lines: mas-level astrometry • Mainly proper motion measurements • CH3OH, NH2CHO, CH3OCHO • Recombination lines in HII regions and planetary nebulae

  14. Wide band astrometry with SKA • Non-thermal continuum sources • 25 μJy/(10μas)2 ⇒ Tb~3×109 K c.f. R●~1 AU ⇒10 μas @100kpc • Nearby super massive black holes ⇒ Deep space astrometry • Micro quasars • Pulsars ⇒ Kemeya-san’s talk • Gyro-synchrotron radiation from YSOs, brown dwarfs and planets • Thermal continuum sources (@10GHz) • 25 μJy/mas2 ⇒ Tb~3×105 K c.f. R*~0.1 AU ⇒1 mas @ 100 pc O-type stars (10 μas level astrometry) • 25 μJy/(10 mas)2 ⇒ Tb~3×103 K c.f. R*~1 AU ⇒10 mas @ 100 pc red giants (100 μas level astrometry)

  15. Deep space astrometry with SKA • The Magellanic System • Proper motions, trigonometric parallaxes (SKA + α) • M31 (Andromeda Galaxy) • Proper motions (~100 km/s) ~50 μas/yr, dependent on cosmological model • SKA site dependent (low elevation) • Galaxies in the Local Group • Proper motions (~10 μas/yr) (SKA + α) • Virgo cluster • Cluster proper motions (~1 μas/yr) (SKA + α) • Quasars, sources at the cosmological scale • Stability of the celestial reference frame • Stability of metric (e.g. physical constants)

  16. Astrometry for transient objects with SKA • Contribution to quick source identification • Good advantage thanks to the wide field of view • Astrometry, spectroscopy, SED in 1-10 GHz • Depending on SKA operation modes • Target sources for radio transient objects • Radio super novae, γ-ray burst after grows • Stellar outbursts and flares (YSOs, evolved stars) • Photometric micro-lensing events • Extra-Terrestrial Intelligence (ETI) signals

  17. What can we learn/obtain from SKA astrometry? • 3D visualization of the movements of stars, interstellar gas clumps, and galaxies, including exotic objects. • History of the Universe probed by these movements in the whole sky. • Evolution of the time-space surrounding the Earth, the Solar System, and the Milky Way.

  18. Challenging issues towards SKA • Data calibration and processing • Wide angle astrometry • Near field astrometry dependent on reference sources • Monitoring instrumental and atmospheric excess path delays • Observation scheduling • geodetic-type operation?, multiple beam direction? • Multiple-field delay tracking • Maintenance of reference frames • Meet the “VLBI2010” specification for geodesy • Quick measurements of Earth orientation parameters and their real-time feedback to data correlation • Contribution to ICRF maintenance • Identification of reference sources nearby the Galactic plane

  19. Challenging issues towards SKA High resolution network construction and operation • SKA (<3000 km) alone • Higher sensitivity (by a factor of ~100) • ~1 mas @22GHz, ~3 mas @6.7 GHz, ~18 mas @1.6 GHz • Global array: ~10,000 km with VLBA, EVN, APT • Compatibility in system operation and signal recording • Dependent on Earth’s rotation, limited obs. efficiency • SKA + spacecraft: >20,000 km • More efficient (u,v)-plane recovery (<30,000 km) • Poor sensitivity with small spacecrafts (by a factor of ~10) • high costs (excluding operation cost) • Spacecraft: 200M USD for 10-m dish for 5 years • Ground radio telescope: 20M USD for 30-m dish for 20 years

  20. Challenging issues towards SKA • Target source number after GAIA era • GAIA: σ~24 μas for V<15 mag, ~108 stars • SIM: σ~4 μas all over the sky, >>104 stars • JASMIN (2020~): σ~10 μas for KW<11 mag, ~105 starstowards MW bulge • SKA: How many optical/IR invisible radio objects? GAIA SIM Nano-JASMIN FM

  21. From VERA to SKA • Domestic meeting on astrometry and the Galaxy • 1995 October 23—24 • 2000 December 4—5 • There still exist many remained explorations proposed in 1990’s, which should come true with SKA!

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