| 1. |
- Quanz, S. P., et al.
(author)
-
Large Interferometer For Exoplanets (LIFE) I. Improved exoplanet detection yield estimates for a large mid-infrared space-interferometer mission
- 2022
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 664
-
Journal article (peer-reviewed)abstract
- Context. One of the long-term goals of exoplanet science is the atmospheric characterization of dozens of small exoplanets in order to understand their diversity and search for habitable worlds and potential biosignatures. Achieving this goal requires a space mission of sufficient scale that can spatially separate the signals from exoplanets and their host stars and thus directly scrutinize the exoplanets and their atmospheres.Aims. We seek to quantify the exoplanet detection performance of a space-based mid-infrared (MIR) nulling interferometer that measures the thermal emission of exoplanets. We study the impact of various parameters and compare the performance with that of large single-aperture mission concepts that detect exoplanets in reflected light.Methods. We have developed an instrument simulator that considers all major astrophysical noise sources and coupled it with Monte Carlo simulations of a synthetic exoplanet population around main-sequence stars within 20 pc of the Sun. This allows us to quantify the number (and types) of exoplanets that our mission concept could detect. Considering single visits only, we discuss two different scenarios for distributing 2.5 yr of an initial search phase among the stellar targets. Different apertures sizes and wavelength ranges are investigated.Results. An interferometer consisting of four 2 m apertures working in the 4–18.5 μ.m wavelength range with a total instrument throughput of 5% could detect up to ≈550 exoplanets with radii between 0.5 and 6 R⊕ with an integrated S/N ≥ 7. At least ≈160 of the detected exoplanets have radii ≤1.5 R⊕. Depending on the observing scenario, ≈25–45 rocky exoplanets (objects with radii between 0.5 and 1.5 R⊕) orbiting within the empirical habitable zone (eHZ) of their host stars are among the detections. With four 3.5 m apertures, the total number of detections can increase to up to ≈770, including ≈60–80 rocky eHZ planets. With four times 1 m apertures, the maximum detection yield is ≈315 exoplanets, including ≤20 rocky eHZ planets. The vast majority of small, temperate exoplanets are detected around M dwarfs. The impact of changing the wavelength range to 3–20 μm or 6–17 μm on the detection yield is negligible.Conclusions. A large space-based MIR nulling interferometer will be able to directly detect hundreds of small, nearby exoplanets, tens of which would be habitable world candidates. This shows that such a mission can compete with large single-aperture reflected light missions. Further increasing the number of habitable world candidates, in particular around solar-type stars, appears possible via the implementation of a multi-visit strategy during the search phase. The high median S/N of most of the detected planets will allow for first estimates of their radii and effective temperatures and will help prioritize the targets for a second mission phase to obtain high-S/N thermal emission spectra, leveraging the superior diagnostic power of the MIR regime compared to shorter wavelengths.
|
|
| 2. |
- Godoy, N., et al.
(author)
-
ISPY - NaCo Imaging Survey for Planets around Young stars : CenteR: The impact of centering and frame selection
- 2022
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 663
-
Journal article (peer-reviewed)abstract
- Context. Direct imaging has made significant progress over the past decade, in part thanks to a new generation of instruments and excellent adaptive optic systems, but also thanks to advanced post-processing techniques. The combination of these two factors allowed the detection of several giant planets with separations as close as 0.2 arcsec with contrasts typically reaching 9-10 magnitudes at nearinfrared wavelengths. Observing strategies and data rates vary depending on the instrument and the wavelength, with L- and M-band observations yielding tens of thousands of images to be combined.Aims. We present a new approach, tailored for VLT/NaCo observations performed with the Annular Groove Phase Mask (AGPM) coronagraph, but that can be applied to other instruments using similar coronagraphs. Our pipeline aims to improve the post-processing of the observations on two fronts: identifying the location of the star behind the AGPM to better align the science frames and performing frame selection.Methods. Our method relies on finding the position of the AGPM in the sky frame observations, and correlating it with the circular aperture of the coronagraphic mask. This relationship allows us to retrieve the location of the AGPM in the science frames. We are then able to model the torus shape visible in the sky-subtracted science frames, as a combination of negative and positive 2D Gaussian functions. The model provides additional information that is useful to design our frame selection criteria. Results. We tested our pipeline on three targets (β Pictoris, R CrA, and HD 34282), two of which have companions at intermediate and close separations, and the third hosts a bright circumstellar disk. We find that the centering of the science frames has a significant impact on the signal-to-noise ratio (S/N) of the companions. Our results suggest that the best reduction is achieved when performing the principal component analysis centered on the location of the AGPM and derotating the frames centered at the location of the star before collapsing the final datacube. We improved the S/N of companions around β Pictoris and R CrA by 24 +/- 3% and 117 +/- 11% respectively, compared to other state-of-the-art reductions. We find that the companion position for all the centering strategies are consistent within 3 σ. Finally, we find that even for NaCo observations with tens of thousands of frames, frame selection yields just marginal improvement for point sources, but may improve the final images for objects with extended emission such as disks.Conclusions. We propose a novel approach to identify the location of the star behind a coronagraph even when it cannot easily be determined by other methods. We led a thorough study on the importance of frame selection, concluding that the improvements are marginal in most cases, but may yield better contrast in some specific cases. Our approach can be applied to the wealth of archival NaCo data and, assuming that the field of view includes the edges of the coronagraphic mask, its implementation can be adapted to other instruments with coronagraphs similar to the AGPM used on NaCo (e.g., Keck/NIRC2, LBT/LMIRCam).
|
|
| 3. |
- Squicciarini, V., et al.
(author)
-
A scaled-up planetary system around a supernova progenitor
- 2022
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 664
-
Journal article (peer-reviewed)abstract
- Context. Virtually all known exoplanets reside around stars with M < 2.3 M⊙ either due to the rapid evaporation of the protostellar disks or to selection effects impeding detections around more massive stellar hosts.Aims. To clarify if this dearth of planets is real or a selection effect, we launched the planet-hunting B-star Exoplanet Abundance STudy (BEAST) survey targeting B stars (M > 2.4 M⊙) in the young (5-20 Myr) Scorpius-Centaurus association by means of the high-contrast spectro-imager SPHERE at the Very Large Telescope.Methods. In this paper we present the analysis of high-contrast images of the massive (M - 9 M⊙) star μ2 Sco obtained within BEAST. We carefully examined the properties of this star, combining data from Gaia and from the literature, and used state-of-the-art algorithms for the reduction and analysis of our observations.Results. Based on kinematic information, we found that μ2 Sco is a member of a small group which we label Eastern Lower Scorpius within the Scorpius-Centaurus association. We were thus able to constrain its distance, refining in turn the precision on stellar parameters. Around this star we identify a robustly detected substellar companion (14.4 ± 0.8 MJ)at a projected separation of 290 ± 10 au, and a probable second similar object (18.5 ± 1.5 MJ) at 21 ± 1 au. The planet-to-star mass ratios of these objects are similar to that of Jupiter to the Sun, and the flux they receive from the star is similar to those of Jupiter and Mercury, respectively.Conclusions. The robust and the probable companions of μ2 Sco are naturally added to the giant 10.9 MJ planet recently discovered by BEAST around the binary b Cen system. While these objects are slightly more massive than the deuterium burning limit, their properties are similar to those of giant planets around less massive stars and they are better reproduced by assuming that they formed under a planet-like, rather than a star-like scenario. Irrespective of the (needed) confirmation of the inner companion, μ2 Sco is the first star that would end its life as a supernova that hosts such a system. The tentative high frequency of BEAST discoveries is unexpected, and it shows that systems with giant planets or small-mass brown dwarfs can form around B stars. When putting this finding in the context of core accretion and gravitational instability formation scenarios, we conclude that the current modeling of both mechanisms is not able to produce this kind of companion. The completion of BEAST will pave the way for the first time to an extension of these models to intermediate and massive stars.
|
|
