| Abstract : | In the last five years, detailed images of dust structures in young protoplanetary disks have contributed significantly to planet formation research. In this work, we have used a new observing technique called star-hopping with Reference Difference Imaging (RDI) commissioned on the VLT instrument SPHERE. With star-hopping, we can quickly move the telescope between two nearby stars (1 - 2 degrees apart), a science target and a reference star, subtracting the reference PSF from the science. Thus we can detect faint companions and planets near the science star. Unlike the classical technique, Angular Differential Imaging (ADI), such reference frames will not subtract the flux from a dust disk or a possible planet around the science star. In ADI, the science images themselves are used for PSF subtraction. However, this creates significant self-subtraction artefacts in images of extended structures, especially when they are aligned with the plane of the sky (face-on). In star-hopping RDI, the reference images are obtained within minutes of the science images. Thus the subtraction quality is superior to reference images captured an hour later or on a different night as in classical RDI. Star-hopping outperforms traditional ADI and RDI (with references obtained hours or days later) significantly (2 mag improvement at 0.1'' separation). We have completed the star-hopping disk reductions for the first time for 12 disks in the nearby star-forming region (in Taurus, Lupus and Ophiuchus). Also, for the first time, the inner 30 AU disk features are clearly imaged for these disks. We have also estimated the systematic and random errors (<10%) associated with these reductions using another star HR8799 as a reference which does not host any protoplanetary disk. |
