Measuring the variability of directly imaged exoplanets using vector Apodizing Phase Plates combined with ground-based differential spectrophotometry

Monthly Notices of the Royal Astronomical Society, vol. 520, pp. 4235–4257

Abstract

ABSTRACT Clouds and other features in exoplanet and brown dwarf atmospheres cause variations in brightness as they rotate in and out of view. Ground-based instruments reach the high contrasts and small inner working angles needed to monitor these faint companions, but their small fields of view lack simultaneous photometric references to correct for non-astrophysical variations. We present a novel approach for making ground-based light curves of directly imaged companions using high-cadence differential spectrophotometric monitoring, where the simultaneous reference is provided by a double-grating 360○ vector Apodizing Phase Plate (dgvAPP360) coronagraph. The dgvAPP360 enables high-contrast companion detections without blocking the host star, allowing it to be used as a simultaneous reference. To further reduce systematic noise, we emulate exoplanet transmission spectroscopy, where the light is spectrally dispersed and then recombined into white-light flux. We do this by combining the dgvAPP360 with the infrared Arizona Lenslets for Exoplanet Spectroscopy integral field spectrograph on the Large Binocular Telescope Interferometer. To demonstrate, we observed the red companion HD 1160 B (separation ∼780 mas) for one night, and detect $8.8{{\ \rm per\ cent}}$ semi-amplitude sinusoidal variability with an ∼3.24 h period in its detrended white-light curve. We achieve the greatest precision in ground-based high-contrast imaging light curves of sub-arcsecond companions to date, reaching $3.7{{\ \rm per\ cent}}$ precision per 18-min bin. Individual wavelength channels spanning 3.59–3.99 μm further show tentative evidence of increasing variability with wavelength. We find no evidence yet of a systematic noise floor; hence, additional observations can further improve the precision. This is therefore a promising avenue for future work aiming to map storms or find transiting exomoons around giant exoplanets.

Authors 14

1. Ben J. Sutlieff corresponding Aachen Leiden Observatory

   Leiden University · Leiden Observatory · University of Amsterdam

   Affiliation as printed

   Anton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam , the Netherlands

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden , the Netherlands

2. Jayne Birkby

   University of Oxford · University of Amsterdam

   Affiliation as printed

   Anton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam , the Netherlands

   Astrophysics, University of Oxford , Denys Wilkinson Building, Keble Road, Oxford OX1 3RH , UK

3. Jordan M. Stone

   Naval Research Laboratory Remote Sensing Division

   Affiliation as printed

   Naval Research Laboratory, Remote Sensing Division , 4555 Overlook Avenue SW, Washington, DC 20375 , USA

4. David S. Doelman Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden , the Netherlands

5. Matthew A. Kenworthy Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden , the Netherlands

6. Vatsal Panwar

   University of Warwick · University of Amsterdam

   Affiliation as printed

   Anton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam , the Netherlands

   Department of Physics, University of Warwick , Coventry, West Midlands CV4 7AL , UK

7. Alexander J. Bohn Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden , the Netherlands

8. Steve Ertel

   University of Arizona

   Affiliation as printed

   Large Binocular Telescope Observatory, University of Arizona , 933 North Cherry Avenue, Tucson, AZ 85721 , USA

   Steward Observatory and Department of Astronomy, University of Arizona , 933 North Cherry Avenue, Tucson, AZ 85721 , USA

9. Frans Snik Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden , the Netherlands

10. Charles E. Woodward

    University of Minnesota

    Affiliation as printed

    Minnesota Institute for Astrophysics, University of Minnesota , 116 Church Street SE, Minneapolis, MN 55455 , USA

11. Andrew J. I. Skemer

    University of California, Santa Cruz

    Affiliation as printed

    Department of Astronomy and Astrophysics, University of California , Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 , USA

12. Jarron Leisenring

    University of Arizona

    Affiliation as printed

    Steward Observatory and Department of Astronomy, University of Arizona , 933 North Cherry Avenue, Tucson, AZ 85721 , USA

13. K. G. Strassmeier

    Leibniz Institute for Astrophysics Potsdam

    Affiliation as printed

    Leibniz Institute for Astrophysics Potsdam (AIP) , An der Sternwarte 16, D-14482 Potsdam , Germany

14. David Charbonneau

    Center for Astrophysics Harvard & Smithsonian

    Affiliation as printed

    Center for Astrophysics | Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138 , USA