|Planets, Debris Disks, and the Lambda Bootis Stars
|We propose to explore the link between lambda Bootis stars, debris disks, and planetesimal formation and evolution. The lambda Boo stars are a rare type of peculiar A star (2%), which are Population 1 and metal poor. Planet bearing systems and debris disk stars appear unusually well represented in the lambda Boo class: for example, beta Pic, Vega, and HR 8799 are all lambda Boo candidates. A small sample of 14 lambda Boo stars observed by Spitzer suggests an occurrence of infrared excess approaching 100%. Only two lambda Boo stars are included in the DEBRIS-DUNES Herschel key program debris disk surveys. We will use PACS-Herschel to make sensitive, high-resolution maps of 27 new lambda Boo stars. Like DEBRIS-DUNES, we will reach the stellar photosphere for all targets, enabling a measurement of the true rate of excess infrared emission among lambda Boo stars compared to normal A stars. The depletion pattern of heavy elements in the atmospheres of lambda Boo stars suggests they may have accreted gas from which dust grains have condensed and been removed: this gas may be circumstellar gas that has formed planetesimals or dusty interstellar gas. While the circumstellar disk scenario predicts sizes of a few hundred AU, the cloud accretion scenario predicts 1000-2000 AU bow structures oriented in the direction of the relative motion of the cloud and star. With target distances of &amp;lt; 140 pc, these bow structures are expected to be resolved for all targets. These will be the first mid-infrared observations of lambda Boo stars outside of the low density Local Bubble: if interstellar medium interactions dominate the lambda Boo phenomenon then systematic variations in excess strength and morphology may occur with distance.
|IR excesses around nearby Lambda Boo stars are caused by debris discs rather than ISM bow waves . Draper Z. H. et al. . Monthly Notices of the Royal Astronomical Society, Volume 456, Issue 1, p.459-476 . 456 . 10.1093/mnras/stv2696 . 2016MNRAS.456..459D ,
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2012, OT1_hmaness_1, SPG v14.2.0. https://doi.org/10.5270/esa-ucnmwg7