Scientific requirements

Friday 10 August 2012, by cneiner

SpecificationMinimal requirementGoalComment
Wavelength range117-320+390-870 nm90-1000 nmThis 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 resolution25000100000 and 2000100000 is needed to resolve lineprofiles in stellar spectra. 2000 is needed for faint targets
UV S/N100200enough for most diagnostics
Optical resolution3500080000needed to resolve line profiles and Stokes signatures in stellar spectra
Optical S/N100300needed to detect weak magnetic fields
PolarizationV in linesQUV in lines and continuumcircular 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 polarization3%1%On the ground, we manage < 1%
Accuracy in radial velocity1 km/s0.3 km/sRequired for e.g. Doppler Imaging
Target magnitudeV=3-10V=2-15
Targeted stars50100
Time per targeted star4 weeks6 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 stars40008000
Time per survey star20 min30 min
Mission duration4 years12 yearsThe mission duration derives from this mean rotation period and the
number of targets.