分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yifan Zhou
Brendan P. Bowler
Kevin R. Wagner
Glenn Schneider
Dániel Apai
Adam L. Kraus
Laird M. Close
Gregory J. Herczeg
Min Fang
摘要： Recent discoveries of young exoplanets within their natal disks offer exciting opportunities to study ongoing planet formation. In particular, a planet's mass accretion rate can be constrained by observing the accretion-induced excess emission. So far, planetary accretion is only probed by the H$\alpha$ line, which is then converted to a total accretion luminosity using correlations derived for stars. However, the majority of the accretion luminosity is expected to emerge from hydrogen continuum emission, and is best measured in the ultraviolet (UV). In this paper, we present HST/WFC3/UVIS F336W (UV) and F656N (H$\alpha$) high-contrast imaging observations of PDS 70. Applying a suite of novel observational techniques, we detect the planet PDS 70 b with signal-to-noise ratios of 5.3 and 7.8 in the F336W and F656N bands, respectively. This is the first time that an exoplanet has been directly imaged in the UV. Our observed H$\alpha$ flux of PDS 70 b is higher by $3.5\sigma$ than the most recent published result. However, the light curve retrieved from our observations does not support greater than 30% variability in the planet's H$\alpha$ emission in six epochs over a five-month timescale. We estimate a mass accretion rate of $1.4\pm0.2\times10^{-8}M_{\mathrm{Jup}}/\mathrm{yr}$. H$\alpha$ accounts for 36% of the total accretion luminosity. Such a high proportion of energy released in line emission suggests efficient production of H$\alpha$ emission in planetary accretion, and motivates using the H$\alpha$ band for searches of accreting planets. These results demonstrate HST/WFC3/UVIS's excellent high-contrast imaging performance and highlight its potential for planet formation studies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jéa I. Adams Redai
Katherine B. Follette
Jason Wang
William Balmer
Laird M. Close
Beck Dacus
Jared R. Males
Katie M. Morzinski
Joseph Palmo
Laurent Pueyo
Elijah Spiro
Helena Treiber
Kimberly Ward-Duong
Alex Watson
摘要： High-contrast imaging has afforded astronomers the opportunity to study light directly emitted by adolescent (tens of Myr) and ``proto" ($<$10Myr) planets still undergoing formation. Direct detection of these planets is enabled by empirical Point Spread Function (PSF) modeling and removal algorithms. The computational intensity of such algorithms, and their multiplicity of tunable input parameters, has led to the prevalence of ad-hoc optimization approaches to high-contrast imaging results. In this work, we present a new, systematic approach to optimization vetted using data of the high-contrast stellar companion HD 142527 B from the Magellan Adaptive Optics (MagAO) Giant Accreting Protoplanet Survey (GAPlanetS). More specifically, we present a grid search technique designed to explore three influential parameters of the PSF-subtraction algorithm pyKLIP -- annuli, movement, and KL modes. We consider multiple metrics for post-processed image quality in order to optimally recover at H$\alpha$ (656nm) synthetic planets injected into contemporaneous continuum (643nm) images. These metrics include: peak (single-pixel) SNR, average (multi-pixel average) SNR, 5$\sigma$ contrast, and false-positive fraction. We apply continuum-optimized KLIP reduction parameters to six H$\alpha$ direct detections of the low-mass stellar companion HD142527 B, and recover the companion at a range of separations. Relative to a single-informed, non-optimized set of KLIP parameters applied to all datasets uniformly, our multi-metric grid search optimization led to improvements in companion SNR of up to 1.2$\sigma$, with an average improvement of 0.6$\sigma$. Since many direct imaging detections lie close to the canonical 5$\sigma$ threshold, even such modest improvements may result in higher yields in future imaging surveys.
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