SCExAO/MEC and CHARIS Discovery of a Low Mass, 6 AU-Separation Companion to HIP 109427 using Stochastic Speckle Discrimination and High-Contrast Spectroscopy

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 MKID Exoplanet Camera (MEC) and CHARIS integral field spectrograph. CHARIS data reduced with reference star 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 +0.28 −0.15 , an inclination of 66.7 +8.5 −14 degrees, and a dynamical mass of 0.280 +0.18 −0.059 M . This work shows the potential for extreme AO systems to utilize speckle statistics in addition to widely-used post-processing methods to directly image faint companions to nearby stars near the telescope diffraction limit.

SCExAO/CHARIS Direct Imaging of A Low-Mass Companion At A Saturn-Like Separation from an Accelerating Young A7 Star

“…The inclusion of data from these indirect methods, however, yields a mass precision of ∼10%. Finally, this result with other companions discovered from our Hipparcos-Gaia direct imaging survey reinforce the value of using astrometry to screen for promising direct imaging targets(Currie et al 2020;Steiger et al 2021). The revised version of HGCA uses Gaia-eDR3 astrometry, which is about a factor of 3 more precision than that in the DR2 release(Brandt et al 2021, submitted), making the catalogue more sensitive to the presence of jovian companions.…”

“…Direct imaging surveys targeting these accelerating stars may have significantly higher yields than blind surveys and allow substantially improved characterization capabilities (e.g. Calissendorff & Janson 2018;Fontanive et al 2019;Currie et al 2020;Bowler et al 2021;Steiger et al 2021).…”

New binaries from the SHINE survey

“…The X-ray non-detection is compatible with the moderately old age and low luminosity of the companion There is no IR excess from Spitzer and Herschel observations (Su et al 2006;Thureau et al 2014). Steiger et al (2021) published a preliminary orbit for the system. We combined our astrometric measure with theirs and the PMA measures by Kervella et al (2019) to improve this orbit determination.…”

“…The newly imaged companion was not detected in previous AO observations by De Rosa et al (2014) and Stone et al (2018). After submission of the first version of our paper, Steiger et al (2021) published an independent discovery of this companion. Most of the spectral types determinations for the primary in the literature are either A1 or A2.…”

The Mysterious Lives Of Speckles. I. Residual atmospheric speckle lifetimes in ground-based coronagraphs

“…The temporal decorrelation of speckle noise is one of the main benefits of PSF-subtraction post-processing (Marois et al 2006(Marois et al , 2008, even though algorithms have typically focused on exploiting spatial correlations. Recently, studies have begun to consider the time-domain in post-processing explicitly (Samland et al 2021), and several algorithms show promise in exploiting short exposure focal-plane data (Walter et al 2019;Steiger et al 2021) and WFS telemetry (Rodack et al 2021, submitted) (Frazin & Rodack 2021, submitted) to estimate speckle intensity. Knowledge of the intensity PSD allows for such algorithms to be analyzed efficiently.…”