We walked around Sinchon midnight,

we discovered a white color river,

like Milky Way…

What is this ?

This is Makgeolli’s river ( 막걸리강 )

We can understand it fully because it is on the table.

( We are “not IN” the Makgeolli. )My dream has

come true!

Wajima-san

Makgeolli is Korean traditional drink.Taste is very soft, sweet like a sparkling wine.But BE CAREFUL to drink too much.

Real Milky Way

We have not been understood our Galaxy (Milky Way) yet !

Because we are “IN”. It is hard to observe and understand.

The Milky Way as seen from Death Valley, CA, USA (wikipedia)

2008(Spitzer Space Telescope press release)

2005(Spitzer Space Telescope press release)

Artist image of Milky Way (based on scientific results)

Annual parallax measurements by VLBI (1999-2009)- Astrometry with the highest accuracy -

○ : H2O maser source● : CH3OH maser source■ : SiO maser source＋ : Pulsar□ : X-ray binary

Solar neighborhood

face on view

It is hard to detect annual parallax !!But there are so many interesting sources.

Next frontier of VLBI astrometry is

INNER GALAXY

Astrometry for Maser sources in Inner Galaxy

by VLBI Observation and Survey

AMIGOS project

Kazuya Hachisuka (Shanghai Astronomical Observatory, China)

(“AMIGOS” means friends/friendly in Spanish.)

Inner Galaxy

• Complex– Barred bulge (its nature is still mystery)– Spiral arms (5 kpc Galactic ring = many stars and gases) –

• Problem – Ambiguity kinematic distance (near and far distance)– Proper motion

• Large database of stars in bulge by optical observation, but the accuracy is not enough and the area are limited (e.g. Clarkson+ 2008)

• VLBI astrometry: peculiar motion is systemic or random?

bulge and spiral arms in galaxies

• Relationship between spiral arms and central mass of galaxy (Seigar+ 2008)– Pitch angle and mass– Bulge velocity dispersion and pit

ch angle

• We can study the relationship in detail for the Milky Way.

Red: Milky Way

Overview AMIGOS project• Aim: Pilot VLBI astrometric study of inner Galaxy

– Dynamics of inner Galaxy• Kinematical connection between bulge and arm

– Rough distance (structure) estimation • distinguish between near and far distance

• Method: phase referencing VLBI– Measuring absolute proper motion

• We give up to detect annual parallax (later we will do if it is possible)• Absolute proper motion = Galactic rotation + peculiar motion• Absolute proper motion is easy to detect (several mas/year)

• Expected results– Distinguish between near and far distance – Large database of absolute proper motion of inner Galaxy

• Database– Collect astrometric data for many objects from new VLBI observation

and archive data.

Target sources and area

• CH3OH, H2O and SiO maser source

• Distant source (> 3 kpc from the sun) – Sutum arm,

Perseus arm, bulge– It is hard to detect annu

al parallax. • Bright source• with reference source

Scutum arm

Perseus arm

6.7 GHz CH3OH maser sources(Pestalozzi+ 2005)

• EAVN, LBA, APT

Plot both near and far distance

> 1 Jy > 100 Jy

H2O maser sources(Batchelor+ 1980, Caswell+ 1983,1989, Valdettaro+ 2001, Sunada+ 200

7)

• EAVN, LBA, APT• Problem: highly time variation, lack of reference

> 1 Jy > 100 Jy

SiO maser sources(Deguchi+ 2004, 2007, Nakashima+ 2003ab, Fujii+ 2006)

• KVN, KVN + Kagoshima, KVN + VERA• Problems: Weak, time variation, lack of reference

> 5 Jy> 1 Jy

Primary target sources(total ~100 sources)

SiO > 5 JyCH3OH > 100 JyH2O > 100Jy

60°

30°

0°Dec. = -30°

VLBI kinematic distance (VLBI-KD)- rough distance estimation -

• Galactic objects rotate around the G.C. (red arrow)

• Measure proper motion– measure Galactic rotation for

target source relative to the Sun (Green arrow)

• near distance: smaller – same direction

• far distance: larger– opposite direction

Expected proper motions with peculiar motion of ±30 km/s

(Blue: near, Red: far)

• l > 20º : it is difficult to distinguish between near and far kinematic distance.

• l < 20º : It’s easy even if there is the large peculiar motion (30 km/s).

Galactic longitude

Vlsr = 20 km/s

Vlsr = 60 km/s

Vlsr = 100 km/s

Pro

per

mot

ion

(mas

/yea

r)

Expected result of VLBI-KD

• We can get the results by measuring absolute proper motion for Galactic objects in inner Galaxy.

• Near distance -> we perform annual parallax obs.

GCGC

Near >> FarReal structure? - Maybe NO.We have to survey deeper.

Plan

Source selection

VLA observations if necessary(to determination of accurate position)

VLBI observation

Past survey data(single dish)

Survey Maser and reference source

Data analysis

Flux monitor (single dish) for highly variable source

(e.g. SiO maser)

Archive data

Collecting data

Database

a) Only few epochs within few month or few year.

b) Snapshot observation (not large obs. time)

Reference sources

• Open circle: 6.7 GHz methanol maser source• Large circle: reference source with radius of 2 degrees

(detected at K band) (Petrov et al. 2007).

• We must search more reference sources, especially Q band.

Let’s perform phase referencing VLBI!

• If there is a reference source nearby your target source, please add the session of phase referencing VLBI into your observation. We will refer your paper.

• Merit of phase referencing VLBI– The absolute position will be determined with high accuracy.

• Easy to compare other observations (e.g. sub-mm, IR)

– If your target source is too weak, you can calibrate the data using the reference source.

• Demerit– Observing time for your target source is lost.

Otherwise you must request longer observing time.

LOS AMIGOS!

Spiral arms

BulgeH2O

CH3OH

SiO

CVN

JVNKVN

LBA

If you are interested in AMIGOS project,please contact me.