Abstract
Abstract We report the direct imaging discovery of a low-mass companion to the nearby accelerating A star, HIP 109427, with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument coupled with the Microwave Kinetic Inductance Detector Exoplanet Camera (MEC) and CHARIS integral field spectrograph. CHARIS data reduced with reference star point spread function (PSF) subtraction yield 1.1–2.4 μm spectra. MEC reveals the companion in Y and J band at a comparable signal-to-noise ratio using stochastic speckle discrimination, with no PSF subtraction techniques. Combined with complementary follow-up L p photometry from Keck/NIRC2, the SCExAO data favors a spectral type, effective temperature, and luminosity of M4–M5.5, 3000–3200 K, and log 10 ( L / L ⊙ ) = − 2.28 − 0.04 + 0.04 , respectively. Relative astrometry of HIP 109427 B from SCExAO/CHARIS and Keck/NIRC2, and complementary Gaia–Hipparcos absolute astrometry of the primary favor a semimajor axis of 6.55+3.0 −0.48 au, an eccentricity of 0.54 − 0.15 + 0.28 , an inclination of 66.7 − 14 + 8.5 degrees, and a dynamical mass of 0.280 − 0.059 + 0.18 M ⊙. This work shows the potential for extreme AO systems to utilize speckle statistics in addition to widely used postprocessing methods to directly image faint companions to nearby stars near the telescope diffraction limit.
Highlights
Most of the ∼10–20 directly imaged planets discovered so far orbit their host stars at 10–150 au separations, typically ρ ∼ 0 4–2′′ on the sky (e.g., Marois et al 2008b; Lagrange et al 2009; Kuzuhara et al 2013; Rameau et al 2013; Currie et al 2014; Macintosh et al 2015; Chauvin et al 2017)
Angular Differential Imaging (ADI; Marois et al 2006) exploits parallactic angle (PA) rotation to distinguish speckles, which will rotate with the telescope field of view, from companions, which are at a fixed location on sky
With Subaru Coronagraphic Extreme Adaptive Optics (SCExAO)/Microwave Kinetic Inductance Detector Exoplanet Camera (MEC) photometry, SCExAO/CHARIS spectroscopy, and Keck/NIRC2 photometry, we have identified a low-mass stellar companion at a near-Jupiter-like separation around the nearby A1V star HIP 109427
Summary
Most of the ∼10–20 directly imaged planets discovered so far orbit their host stars at 10–150 au separations, typically ρ ∼ 0 4–2′′ on the sky (e.g., Marois et al 2008b; Lagrange et al 2009; Kuzuhara et al 2013; Rameau et al 2013; Currie et al 2014; Macintosh et al 2015; Chauvin et al 2017). Angular Differential Imaging (ADI; Marois et al 2006) exploits parallactic angle (PA) rotation to distinguish speckles, which will rotate with the telescope field of view, from companions, which are at a fixed location on sky The magnitude of this rotation, scales proportionally with angular separation for a given unit time, resulting in less rotation at smaller inner working angles (IWAs). This companion has a best-fit dynamical mass of ∼0.25 Me consistent with a spectral type of M4–M5.5 from spectral analysis This discovery serves as an important proof of concept for the use of time-domain information in addition to standard PSF subtraction methods exploiting spectral and spatial information to remove quasistatic speckles in high-contrast images
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