| Description |
We have recently obtained PACS/Photometer monitoring observations of 100 protostars in the ORION A molecular ridge as part of the program OT1_nbillot_1. We have built about 20 reliable light curves at 70 micron spanning a period of 2 months. We find that a dozen protostars exhibit measurable variability, with flux amplitude of up to 20%, on weekly to monthly timescales. In some cases, the 160 micron light curve also shows variability with amplitude in excess of 10%. For a couple of sources, the 70 and 160 micron light curves appear to be in phase.
The observed timescales are orders of magnitude shorter than the dynamical timescales of far-IR emitting material around protostars, which suggests that the mechanism responsible for the far-IR variability might originate from the inner region of the protostars. We have identified a couple of scenarios that could explain the observed far-IR variability, specifically the accretion luminosity variations originating from the inner disk that could lead to the heating of the entire envelope, and thus cause the far-IR variability. The other scenario involves a variable scale height of the disk inner edge that would cast a shadow on the outer disk and inner wall of the envelop cavity.
Several of the far-IR variable protostars have already been observed with the PACS/Spectrometer as part of the HOPS program (KPOT_tmegeath_2). Some of the HOPS targets show rich spectra with multiple water and CO lines diagnostic of the activity of infalling envelopes, disks, envelope-disk accretion, and outflows.
We propose a small (14.5 hours) exploratory program with the PACS/Spectrometer to monitor the physical and chemical conditions that prevail in the outer disk and envelope of a couple of far-IR variable protostars over a 2-months period. |
