The MONS-project has the purpose to measure oscillations of stars, in order to investigate their inner structure and dynamics. In this way we can significantly strengthen the foundations for astrophysics in general which is constituted by stellar astrophysics. The project is based in the Astronomy-group at the Institute of Physics and Astronomy (IFA), University of Aarhus, and the Theoretical Astrophysics Center (TAC), of the Danish National Research Foundation.

MONS is the scientific project on the Danish Rømer satellite, which is currently under development as an element of the Danish Small Satellite Programme. The satellite is scheduled for launch in 2003, and the mission is expected to last for 2 years.

Contents:

• Scientific aims
• A little history
• MONS is for everyone
• The group behind MONS
• Some relevant links

Scientific aims

The amplitudes of the oscillations are extremely small : relative variations in the stellar luminosity are in the parts per million range, and variations in the surface temperature only around 1 thousandth of a degree. Observations from the Earth's surface are virtually impossible because of the interference from the Earth's atmosphere. However, they are relatively easy to perform from a satellite, even with quite modest instrumentation. MONS wil use a compact telescope with a diameter of 40 cm.

Investigations of this type have already been undertaken for one particular star : our own Sun. The group behind the MONS project has contributed substantially to these helioseismic studies of the Sun; experience from this, and from the wide-ranging observations of stars done by this group, create a firm foundation for the MONS project.

The main telescope of MONS will concentrate on observing around 20 stars with oscillations corresponding to those of the Sun, observing each star for 1 - 2 months. These stars will be chosen in such a way as to be representative for an appropriate selection of masses and ages ; one possible candidate is a star which closely corresponds to the future state of the Sun, in about 3 billion years. Observations of a large number of other stars will be undertaken with the star trackers, which are used to control and point the satellite. Even though the precision is lower than it is for the main telescope, these observations will nevertheless be far better than Earth-based observations, for a large number of variable stars of many different types.

Further information about the purposes of the project can be found in a press release of April 14, 2000.

A little history

• Mid-term review, October 2000. The complexity of the combined mission and the marginal mass constraints led to the decision to continue the studies with a mission that only includes the MONS project.

• Kick-off meeting, Copenhagen, May 11 - 12, 2000. Start of system-definition phase.
• Approval by the relevant parties of commencing investigations of a combined mission, Spring 2000. In addition to MONS, this included the Ballerina project to study cosmic gamma-ray bursts. This mission was named Rømer. Official announcement of the project April 14, 2000.
• Detailed proposal for MONS sent to the Small Satellite Committee of the Science Research Councils, March 31, 1999.
• The Small Satellite Committee of the Research Councils selects four project proposals for detailed investigation, August 1998.
• A call for project proposals for the next small satellite, Spring 1998.
• Decision for starting the Danish Small Satellite Programme, 1997.