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 (CH 3 OH, H 2 O, 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 CH 3 OH(6.7GHz), H 2 O(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) H 2 O masers in T Lep (Nakagawa et al. 2011)

5. Current scientific targets in VERA High-mass star forming regions (H 2 O, CH 3 OH) low-mass young stellar objects (YSOs), (H 2 O) Evolved stars (H 2 O, 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: H 2 O and CH 3 OH 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 VERA VLBA SKA (expectation) Dishes 4 × 20 m10 × 25 m5 000 x 15 m (1° FoV, 100 m 2 @1GHz) Effective A e 630 m 2 @22 GHz2950 m 2 @22 GHz500 000 m 2 @10 GHz Baseline SEFD (antenna pair) 1760 Jy500 Jy940 Jy, 17 Jy (station) Baseline SEFD (with large tel.) 250 Jy with GBT130 Jy with GBT2.4 Jy with core (0.34 Jy) Baseline length2 300 km8 600 km~3 000 km (+α) N baselines645 (within VLBA)50 (core – stations) 600 (within stations) Maser astrometry~20 μas for ~10 Jy~20 μas for ~1 Jy~10 μas for ~20 mJy Continuum astrometry ~20 μas for ~70 mJy (Δν=256 MHz) ~20 μas for ~5 mJy (Δν=512 MHz) ~10 μas for ~25 μJy (Δν=8 GHz)

9. Astrometric specification @ 10μas updated 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: θ VLBA ~ 1/3 θ SKA ~ θ SKA +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 S 8GHz > 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 deg 2 @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 (N field < 100) – NIR/MIR sources (MSX, AKARI) – molecular cloud cores (NANTEN, ASTE/AzTEC, GASKAP) Blind astrometry with wild-field correlation Toward unknown sources (N field > 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~1/10 3 [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 – CH 3 OH: 6669, 12179 – H 2 O: 22235, NH 3 : 23694, 23723, 23870 (high-band) thermal lines …… – CH 3 OH: 834,..., NH 2 CHO: 1539, CH 3 OCHO: 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 – CH 3 OH, NH 2 CHO, CH 3 OCHO – Recombination lines in HII regions and planetary nebulae

14. Wide band astrometry with SKA Non-thermal continuum sources – 25 μJy/(10μas) 2 ⇒ T b ~3×10 9 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/mas 2 ⇒ T b ~3×10 5 K c.f. R * ~0.1 AU ⇒ 1 mas @ 100 pc O-type stars (10 μas level astrometry) – 25 μJy/(10 mas) 2 ⇒ T b ~3×10 3 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, ~10 8 stars – SIM: σ~4 μas all over the sky, >>10 4 stars – JASMIN (2020~): σ~10 μas for K W <11 mag, ~10 5 stars towards 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!