Scientific requirements

Friday 10 August 2012, by cneiner

SpecificationMinimal requirementGoalComment
Wavelength range 117-320+390-870 nm 90-1000 nm This UV range contains many diagnostic transitions for hot stars and galaxies. The optical domain covers most of the important lines for both hot and cool stars, from CaII H&K to the Ca triplet, and including the Balmer and Paschen jumps. Polarimetry in the UV would allow direct measurement of polarization in the wind.
UV resolution 25000 100000 and 2000 100000 is needed to resolve lineprofiles in stellar spectra. 2000 is needed for faint targets
UV S/N 100 200 enough for most diagnostics
Optical resolution 35000 80000 needed to resolve line profiles and Stokes signatures in stellar spectra
Optical S/N 100 300 needed to detect weak magnetic fields
Polarization V in lines QUV in lines and continuum circular polarization (V) is needed to measure magnetic fields, full polarization (VQU) is needed to study disks and full magnetospheres. Continuum polarization is very
useful to study dusty environments.
Instrumental polarization 3% 1% On the ground, we manage < 1%
Accuracy in radial velocity 1 km/s 0.3 km/s Required for e.g. Doppler Imaging
Target magnitude V=3-10 V=2-15
Targeted stars 50 100
Time per targeted star 4 weeks 6 weeks (4+1+1) Some hot stars rotate very fast (of the order of 1 day), other targets have
rotation periods of several weeks. We considered that on average the rotation
period is 2 weeks.
Survey stars 4000 8000
Time per survey star 20 min 30 min
Mission duration 4 years 12 years The mission duration derives from this mean rotation period and the
number of targets.