BAL QSOs La Palma International Time

ITP projects / time awarded

ITP BAL QSO sample

Physical conditions in BALs

• High S:N, high-resolution WHT spectra -> column densities -> ionisation parameter U -> constraints on distance from QSO nucleus

• Many good spectra obtained - Flori will report separately on this

• Same spectra can be used for search for line-locking -> evidence of radiative acceleration

Why does depth of absorbers vary with time?

• ~20% BALS show depth variations with time (but sample studied is small)

• (1) Motion of cloud across line of sight. If so, timescale + diameter of source -> transverse velocity of wind

• (2) Change in ionisation parameter at outflow, due to change in luminosity

Absorber changes - experiment

• Spectroscopy and imaging of large number of BALs (ideally > once)

• Compare with SDSS, ~ 20% will have varied• Compare light curve with spectroscopic variation,

tests if variation due to change in ionising continuum. If not, variation gives rough estimate of transverse velocity, to compare with radial velocity.

Absorber changes - status

• WHT, INT and NOT data from La Palma international-time project for 94 BAL QSOs, with resolution >~ SDSS.

• WHT data reduced by Flori.• INT data (for larger number of objects) just

reduced by Jo.• Mercator imaging for some of above objects (one

epoch)• Same data can be used to search for changes in

velocity of absorbers

Q13/001SDSS vs INT

Q13/001SDSS vs INT

Absorber changes: conclusion

• Spectroscopic resolution and S:N, and number of QSOs observed, are sufficient to characterise changes of depth, and also to search for changes of velocity.