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Abstract:

12 pags., 10 figs., 2 tabs.We analyze JWST NIRSpec+MIRI/MRS observations of the infrared (IR) gas-phase molecular bands of the most enshrouded source (D1) within the interacting system and luminous IR galaxy II Zw 096. We report the detection of rovibrational lines of HO ν = 1-0 (~4;5.3-7.2 μm) and CO ν = 1-0 (~4;4.45-4.95 μm) in D1. The CO band shows the R- and P-branches in emission and the spectrum of the HO band shows the P-branch in emission and the R-branch in absorption. The HO R-branch in absorption unveils an IR-bright embedded compact source in D1 and the CO broad component features a highly turbulent environment. From both bands, we also identified extended intense star-forming (SF) activity associated with circumnuclear photodissociation regions (PDRs), consistent with the strong emission of the ionised 7.7 μm polycyclic aromatic hydrocarbon band in this source. By including the 4.5-7.0 μm continuum information derived from the HO and CO analysis, we modelled the IR emission of D1 with a dusty torus and SF component. The torus is very compact (diameter of ~4;3 pc at 5 μm) and characterised by warm dust (~4;370 K), giving an IR surface brightness of ~4;3.6 × 10 L pc. This result suggests the presence of a dust-obscured active galactic nucleus (AGN) in D1, which has an exceptionally high covering factor that prevents the direct detection of AGN emission. Our results open a new way to investigate the physical conditions of inner dusty tori via modelling the observed IR molecular bands.I.G.B. and D.R. acknowledge support from STFC through grants ST/S000488/1 and ST/W000903/1. E.G.-A. acknowledges grants PID2019-105552RB-C4 and PID2022-137779OB-C41 funded by the Spanish MCIN/AEI/10.13039/501100011033. M.P.S. acknowledges support from grant RYC2021-033094-I funded by MCIN/AEI/10.13039/501100011033 and the EU NextGenerationEU/PRTR

Abstract:

Although instruments for measuring the radial velocities (RVs) of stars now routinely reach sub-meter per second accuracy, the detection of low-mass planets is still very challenging. The rotational modulation and evolution of spots and/or faculae can induce variations in the RVs at the level of a few m/s in Sun-like stars. To overcome this, a multi-dimensional Gaussian Process framework has been developed to model the stellar activity signal using spectroscopic activity indicators together with the RVs. A recently published computationally efficient implementation of this framework, S+LEAF 2, enables the rapid analysis of large samples of targets with sizeable data sets. In this work, we apply this framework to HARPS observations of 268 well-observed targets with precisely determined stellar parameters. Our long-term goal is to quantify the effectiveness of this framework to model and mitigate activity signals for stars of different spectral types and activity levels. In this first paper in the series, we initially focus on the activity indicators (S-index and Bisector Inverse Slope), and use them to a) measure rotation periods for 49 slow rotators in our sample, b) explore the impact of these results on the spin-down of middle-aged late F, G & K stars, and c) explore indirectly how the spot to facular ratio varies across our sample. Our results should provide valuable clues for planning future RV planet surveys such as the Terra Hunting Experiment or the PLATO ground-based follow-up observations program, and help fine-tune current stellar structure and evolution models.