RUSSIAN

SPACE ASTROMETRIC MISSION

THE PROJECT OF RUSSIAN SPACE INTERFEROMETER OSIRIS

About the Project

History

Scientific tasks

Orbit

Optical layout

Positioning

OSIRIS

LIDA

Current status

Publications

Contacts

 

 

SCIENTIFIC TASKS

Goals of the "Astrometry" Project:

Parallax measurement for selected Galactic objects

Direct estimates of distances in space are based on the triangular measurements. Up to date, only distances to the nearest stars have been measured precisely. So, the device that is able to measure coordinates of celestial objects with 1000 times higher accuracy than the one of modern equipment will make it possible to reliably measure distances to any object in our Galaxy.

 

The measurements with space interferometer will allow to lower errors on the order. In the table the main scientific program for the OSIRIS instrument for specification of a scale of distances in the Universe is given. There are the type of objects, their magnitudes and number of stars required .

Astronomical objects without known direct distances:

Objects

mV

The required number of stars

Variable stars

 

 

- Cepheides

< 11

> 54

- RR Lyr

< 13

> 27

- Red giants

< 10

> 27

Open clusters

< 12

> 270

Globular clusters

< 15

> 270

Planetary nebulae

< 15

> 27

Nearest spiral arms

< 12

> 20

Galactic centre

< 15

> 10

Magellanic clouds

< 13

> 20

 

For studying of physics and evolution of stars and other astrophysical problems in the framework of the project the following observations are planned.

Objects

mV

The required number of stars

  a) Stars on the HR diagram

< 15

> 432

  b) Novae-like stars

< 15

> 9

  c) Binary stars

10-18

>1000

 d) Planetary systems

< 10

> 50

The measurements with space interferometer will allow to lower errors on the order. In the table the main scientific program for the OSIRIS instrument for specification of a scale of distances in the Universe is given. There are the type of objects, their magnitudes and number of stars required .

 

The modern inertial reference system is based on the extragalactic sources (quasars), which relative positions were measured using Very Long Baseline Interferometry. The International Coordinate Reference System (ICRS) in radio waveband relies on the conventional coordinates of 608 extragalactic radio sources (quasars), which have been under observation since 1979. Its basic framework consists of 212 compact radio sources. The System's accuracy is maintained at 0.2 mas level, for its zero point the barycentre of the Solar System is chosen.

The current optic-waveband version of ICRS is HRC - Hipparcos Reference Catalogue. Its last edition contains about 100 000 stars.

The next step in astrometry will be the attainment of microsecond accuracy. This is necessitated by the new requirements, arisen from the practical determination of coordinates at the present millisecond accuracy level.