Abstract
ABSTRACT We present observations of three protoplanetary discs in visible scattered light around M-type stars in the Upper Scorpius OB association using the Space Telescope Imaging Spectrograph (STIS) instrument on the Hubble Space Telescope (HST). The discs around stars 2MASS J16090075–1908526, 2MASS J16142029–1906481, and 2MASS J16123916–1859284 have all been previously detected with the Atacama Large Millimeter/submillimeter Array (ALMA), and 2MASS J16123916–1859284 has never previously been imaged at scattered light wavelengths. We process our images using reference star differential imaging, comparing and contrasting three reduction techniques – classical subtraction, Karhunen–Loève Image Projection, and non-negative matrix factorization, selecting the classical method as the most reliable of the three for our observations. Of the three discs, two are tentatively detected (2MASS J16142029–1906481 and 2MASS J16123916–1859284), with the third going undetected. Our two detections are shown to be consistent when varying the reference star or reduction method used, and both detections exhibit structure out to projected distances of ≳200 au. Structures at these distances from the host star have never been previously detected at any wavelength for either disc, illustrating the utility of visible-wavelength observations in probing the distribution of small dust grains at large angular separations.
Highlights
Protoplanetary disks provide a window into the development of all types of planetary systems (Andrews 2020)
Accretion onto the star can occur for both the dust and gas within the disk, whereas most dust grains are too heavy to be directly removed via photoevaporation, smaller ( 100μm) dust grains remain coupled to the gas in the disk and can be evacuated along with it (e.g. Takeuchi & Lin 2002)
Our work aims to address a gap in the knowledge of disks around M-stars by imaging disks around three targets in scattered light, one for the first time, with a view to using these images to study the evolution of small dust grains around late-type stars
Summary
Protoplanetary disks provide a window into the development of all types of planetary systems (Andrews 2020). Observations at millimetre and sub-millimetre wavelengths can be used to detect continuum emission from larger mm-scale dust grains in the disk, as well as spectral line emissions from tracer molecules in the gas These data can be used to directly probe the temperature of the gas In this paper we present new scattered light observations of three M-type stars in the Upper Scorpius OB association This association (hereafter known as Upper Sco) is a star-forming region at a distance of ∼145 pc (Preibisch & Mamajek 2008) that plays host to M-type stars with ages of 5-11 Myr (Preibisch et al 2002; Pecaut et al 2012), up to 22% of which have circumstellar disks (Luhman & Esplin 2020), providing a unique opportunity for the study of protoplanetary disks. The results of the analysis of these final science images are presented in Section 4, followed by a brief conclusion
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