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Register a new userSCExAO/CHARIS Direct Imaging Discovery of a 20 au Separation, Low-Mass Ratio Brown Dwarf Companion to an Accelerating Sun-like Star
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We present the direct imaging discovery of a substellar companion to the nearby Sun-like star, HD 33632 Aa, at a projected separation of $sim$ 20 au, obtained with SCExAO/CHARIS integral field spectroscopy complemented by Keck/NIRC2 thermal infrared imaging. The companion, HD 33632 Ab, induces a 10.5$sigma$ astrometric acceleration on the star as detected with the $Gaia$ and $Hipparcos$ satellites. SCExAO/CHARIS $JHK$ (1.1--2.4 $mu$m) spectra and Keck/NIRC2 $L_{rm p}$ (3.78 $mu$m) photometry are best matched by a field L/T transition object: an older, higher gravity, and less dusty counterpart to HR 8799 cde. Combining our astrometry with $Gaia/Hipparcos$ data and archival Lick Observatory radial-velocities, we measure a dynamical mass of 46.4 $pm$ 8 $M_{rm J}$ and an eccentricity of $e$ $<$0.46 at 95% confidence. HD 33632 Abs mass and mass ratio (4.0% $pm$ 0.7%) are comparable to the low-mass brown dwarf GJ 758 B and intermediate between the more massive brown dwarf HD 19467 B and the (near-)planet mass companions to HR 2562 and GJ 504. Using $Gaia$ to select for direct imaging observations with the newest extreme adaptive optics systems can reveal substellar or even planet-mass companions on solar system-like scales at an increased frequency compared to blind surveys.
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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 $mu$m 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 $L_{rm p}$ photometry from Keck/NIRC2, the SCExAO data favors a spectral type, effective temperature, and luminosity of M4-M5.5, 3000-3200 $K$, and $log_{10}(L/L_{rm odot}) = -2.28^{+0.04}_{-0.04}$, 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 $0.280^{+0.18}_{-0.059}$ $M_{odot}$. 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.
The $sim500$, Myr A2IV star HR 1645 has one of the most significant low-amplitude accelerations of nearby early-type stars measured from a comparison of the {it Hipparcos} and {it Gaia} astrometric catalogues. This signal is consistent with either a stellar companion with a moderate mass ratio ($qsim0.5$) on a short period ($P<1$,yr), or a substellar companion at a separation wide enough to be resolved with ground-based high contrast imaging instruments; long-period equal mass ratio stellar companions that are also consistent with the measured acceleration are excluded with previous imaging observations. The small but significant amplitude of the acceleration made HR 1645 a promising candidate for targeted searches for brown dwarf and planetary-mass companions around nearby, young stars. In this paper we explore the origin of the astrometric acceleration by modelling the signal induced by a wide-orbit M8 companion discovered with the Gemini Planet Imager, as well as the effects of an inner short-period spectroscopic companion discovered a century ago but not since followed-up. We present the first constraints on the orbit of the inner companion, and demonstrate that it is a plausible cause of the astrometric acceleration. This result demonstrates the importance of vetting of targets with measured astrometric acceleration for short-period stellar companions prior to conducting targeted direct imaging surveys for wide-orbit substellar companions.
We present high signal-to-noise ratio, precise $YJH$ photometry and $Y$ band (gpiwave~$mu$m) spectroscopy of HD 1160 B, a young substellar companion discovered from the Gemini NICI Planet Finding Campaign, using the Subaru Coronagraphic Extreme Adaptive Optics instrument and the Gemini Planet Imager. HD 1160 B has typical mid-M dwarf-like infrared colors and a spectral type of M5.5$^{+1.0}_{-0.5}$, where the blue edge of our $Y$ band spectrum rules out earlier spectral types. Atmospheric modeling suggests HD 1160 B having an effective temperature of 3000--3100 $K$, a surface gravity of log $g$ = 4--4.5, a radius of~bestfitradius~$R_{rm J}$, and a luminosity of log $L$/$L_{odot} = -2.76 pm 0.05$. Neither the primarys Hertzspring-Russell diagram position nor atmospheric modeling of HD 1160 B show evidence for a sub-solar metallicity. The interpretation of the HD 1160 B depends on which stellar system components are used to estimate an age. Considering HD 1160 A, B and C jointly, we derive an age of 80--125 Myr, implying that HD 1160 B straddles the hydrogen-burning limit (70--90 $M_{rm J}$). If we consider HD 1160 A alone, younger ages (20--125 Myr) and a brown dwarf-like mass (35--90 $M_{rm J}$) are possible. Interferometric measurements of the primary, a precise GAIA parallax, and moderate resolution spectroscopy can better constrain the systems age and how HD 1160 B fits within the context of (sub)stellar evolution.
We present the discovery of a planetary-mass companion to CFHTWIR-Oph 98, a low-mass brown dwarf member of the young Ophiuchus star-forming region, with a wide 200-au separation (1.46 arcsec). The companion was identified using Hubble Space Telescope images, and confirmed to share common proper motion with the primary using archival and new ground-based observations. Based on the very low probability of the components being unrelated Ophiuchus members, we conclude that Oph 98 AB forms a binary system. From our multi-band photometry, we constrain the primary to be an M9-L1 dwarf, and the faint companion to have an L2-L6 spectral type. For a median age of 3 Myr for Ophiuchus, fits of evolutionary models to measured luminosities yield masses of $15.4pm0.8$ M$_mathrm{Jup}$ for Oph 98 A and $7.8pm0.8$ M$_mathrm{Jup}$ for Oph 98 B, with respective effective temperatures of $2320pm40$ K and $1800pm40$ K. For possible system ages of 1-7 Myr, masses could range from 9.6-18.4 M$_mathrm{Jup}$ for the primary, and from 4.1-11.6 M$_mathrm{Jup}$ for the secondary. The low component masses and very large separation make this binary the lowest binding energy system imaged to date, indicating that the outcome of low-mass star formation can result in such extreme, weakly-bound systems. With such a young age, Oph 98 AB extends the growing population of young free-floating planetary-mass objects, offering a new benchmark to refine formation theories at the lowest masses.
We present VLT/NACO SDI images of the very nearby star SCR 1845-6357 (hereafter SCR 1845). SCR 1845 is a recently discovered (Hambly et al. 2004) M8.5 star just 3.85 pc from the sun (Henry et al. 2006). Using the capabilities of the unique SDI device, we discovered a substellar companion to SCR 1845 at a separation of 4.5 AU (1.170+-0.003 on the sky) and fainter by 3.57+-0.057 mag in the 1.575 um SDI filter. This substellar companion has an H magnitude of 13.16+0.31-0.26 (absolute H magnitude of 15.30+0.31-0.26), making it likely the brightest mid-T dwarf known. The unique Simultaneous Differential Imager (SDI) consists of 3 narrowband filters placed around the 1.6 um methane absorption feature characteristic of T-dwarfs (Teff < 1200 K). The flux of the substellar companion drops by a factor of 2.7+-0.1 between the SDI F1(1.575 um) filter and the SDI F3(1.625 um) filter, consistent with strong methane absorption in a substellar companion. We estimate a spectral type of T5.5+-1 for the companion based on the strength of this methane break. The chances that this object is a background T dwarf are vanishing small -- and there is no isolated background T-dwarf in this part of the sky according to 2MASS. Thus, it is a bound companion, hereafter SCR 1845-6357B. For an age range of 100 Myr - 10 Gyr and spectral type range of T4.5-T6.5, we find a mass range of 9 - 65 MJup for SCR 1845B from the Baraffe et al. 2003 COND models. SCR 1845AB is the 24th closest stellar system to the Sun (at 3.85 pc); the only brown dwarf system closer to the Sun is Eps Indi Ba-Bb (at 3.626 pc). In addition, this is the first T-dwarf companion discovered around a low mass star.
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