Fourth-order Coronagraph for High-contrast Imaging of Exoplanets with Off-axis Segmented Telescopes
Abstract
We propose a coronagraphic system with fourth-order null for off-axis segmented telescopes, which is sufficiently insensitive to the telescope pointing errors and finite angular diameter of the host star to enable high-contrast imaging of potentially habitable planets. The inner working angle of the coronagraphic system is close to 1λ/D, and there is no outer limit. The proposed coronagraphic system is made up of a new focal plane mask and an optimized Lyot stop with the second-order null. The new focal plane mask is an extension of the band-limited masks with a phase modulation. We construct a coronagraphic system with fourth-order null by placing two of the new coronagraph systems in succession to be orthogonal to each other. The proposed system is limited to narrow-band usage. The characteristics of the proposed coronagraph system are derived analytically, which includes (1) the leak of stellar lights due to the finite stellar diameter and pointing jitter of a telescope, and (2) the peak throughput. We achieve the performance simulations of this coronagraphic system based on these analytical expressions, considering a monochromatic light of 0.75 μm and an off-axis primary mirror with a diameter of 8.5 m. Thanks to the wide working area of the mask, the result shows that terrestrial planets orbiting K and G dwarfs can be detected under the condition that the telescope pointing jitter is less than 0.01λ/D ≈ 240 as. The proposed coronagraphic system is promising for the detection of potentially habitable planets with future space off-axis hexagonally segmented telescopes.
- Publication:
-
The Astronomical Journal
- Pub Date:
- May 2020
- DOI:
- 10.3847/1538-3881/ab811c
- arXiv:
- arXiv:2002.10762
- Bibcode:
- 2020AJ....159..213I
- Keywords:
-
- Exoplanet detection methods;
- Direct imaging;
- Exoplanet astronomy;
- Coronagraphic imaging;
- Astronomical techniques;
- Observational astronomy;
- Pointing accuracy;
- Pointing error;
- Astrobiology;
- Exoplanets;
- Habitable planets;
- Biosignatures;
- 489;
- 387;
- 486;
- 313;
- 1684;
- 1145;
- 1271;
- 1272;
- 74;
- 498;
- 695;
- 2018;
- Astrophysics - Instrumentation and Methods for Astrophysics;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- Accepted for Publication in The Astronomical Journal