Searching for Gas Giant Planets on Solar System Scales: VLT NACO/APP Observations of the Debris Disk Host Stars HD172555 and HD115892

TL;DR

This study used VLT NACO/APP to search for planetary companions around debris disk stars HD115892 and HD172555, setting new detection limits but finding no planets, demonstrating the instrument's high contrast capabilities in thermal infrared imaging.

Contribution

First application of VLT NACO/APP in thermal infrared to set stringent mass detection limits for planets around debris disk stars.

Findings

No planetary companions detected around the target stars.

Achieved unprecedented contrast performance at small inner working angles.

Set new upper mass limits for potential undetected planets.

Abstract

Using the APP coronagraph of VLT/NACO we searched for planetary mass companions around HD115892 and HD172555 in the thermal infrared at 4 micron. Both objects harbor unusually luminous debris disks for their age and it has been suggested that small dust grains were produced recently in transient events (e.g., a collision) in these systems. Such a collision of planetesimals or protoplanets could have been dynamically triggered by yet unseen companions. We did not detect any companions in our images but derived the following detection limits: For both objects we would have detected companions with apparent magnitudes between ~13.2-14.1 mag at angular separations between 0.4- 1.0" at the 5-sigma level. For HD115892 we were sensitive to companions with 12.1 mag even at 0.3". Using theoretical models these magnitudes are converted into mass limits. For HD115892 we would have detected objects with 10-15 M_Jup at angular separations between 0.4-1.0" (7-18 AU). At 0.3" (~5.5 AU) the detection limit was ~25 M_Jup. For HD172555 we reached detection limits between 2-3 M_Jup at separations between 0.5-1.0" (15-29 AU). At 0.4" (~11 AU) the detection limit was ~4 M_Jup. Despite the non-detections our data demonstrate the unprecedented contrast performance of NACO/APP in the thermal infrared at very small inner working angles and we show that our observations are mostly background limited at separation >0.5".