scholarly journals An HST/STIS View of Protoplanetary Disks in Upper Scorpius: Observations of Three Young M-Stars

2021 ◽  
Author(s):  
Sam Walker ◽  
Maxwell Andrew Millar-Blanchaer ◽  
Bin Ren ◽  
Paul Kalas ◽  
John Carpenter
Keyword(s):  
Reduction Method ◽  
Hubble Space Telescope ◽  
Classical Method ◽  
Scattered Light ◽  
Protoplanetary Disks ◽  
The Third ◽  
Reduction Techniques ◽  
M Stars ◽  
Differential Imaging ◽  
Small Dust

Abstract We present observations of three protoplanetary disks in visible scattered light around M-type stars in the Upper Scorpius OB association using the STIS instrument on the Hubble Space Telescope. The disks around stars 2MASS J16090075–1908526, 2MASS J16142029–1906481 and 2MASS J16123916–1859284 have all been previously detected with ALMA, and 2MASS J16123916–1859284 has never previously been imaged at scattered light wavelengths. We process our images using Reference Differential Imaging, comparing and contrasting three reduction techniques – classical subtraction, Karhunen-Loéve Image Projection and Non-Negative Matrix Factorisation, selecting the classical method as the most reliable of the three for our observations. Of the three disks, 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 disk, illustrating the utility of visible-wavelength observations in probing the distribution of small dust grains at large angular separations.

scholarly journals Dust-driven viscous ring-instability in protoplanetary disks

2018 ◽  
Vol 609 ◽  
pp. A50 ◽  
Author(s):  
C. P. Dullemond ◽  
A. B. T. Penzlin
Keyword(s):  
Surface Density ◽  
Scattered Light ◽  
Protoplanetary Disks ◽  
Continuum Emission ◽  
Rotational Instability ◽  
Local Pressure ◽  
Ionization Degree ◽  
Local Maxima ◽  
Gas Ionization ◽  
Small Dust

Protoplanetary disks often appear as multiple concentric rings in dust continuum emission maps and scattered light images. These features are often associated with possible young planets in these disks. Many non-planetary explanations have also been suggested, including snow lines, dead zones and secular gravitational instabilities in the dust. In this paper we suggest another potential origin. The presence of copious amounts of dust tends to strongly reduce the conductivity of the gas, thereby inhibiting the magneto-rotational instability, and thus reducing the turbulence in the disk. From viscous disk theory it is known that a disk tends to increase its surface density in regions where the viscosity (i.e. turbulence) is low. Local maxima in the gas pressure tend to attract dust through radial drift, increasing the dust content even more. We have investigated mathematically if this could potentially lead to a feedback loop in which a perturbation in the dust surface density could perturb the gas surface density, leading to increased dust drift and thus amplification of the dust perturbation and, as a consequence, the gas perturbation. We find that this is indeed possible, even for moderately small dust grain sizes, which drift less efficiently, but which are more likely to affect the gas ionization degree. We speculate that this instability could be triggered by the small dust population initially, and when the local pressure maxima are strong enough, the larger dust grains get trapped and lead to the familiar ring-like shapes. We also discuss the many uncertainties and limitations of this model.

Aberrations

2019 ◽  
pp. 215-248
Author(s):  
B. D. Guenther
Keyword(s):  
Hubble Space Telescope ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Optical Path Difference ◽  
Path Difference ◽  
Optical Path ◽  
Wavefront Aberration ◽  
Third Order ◽  
The Third ◽  
Field Curvature

Using simple ray tracinig technliques presented in Chapter 6, we demonstrate that a general ray is not focused to the position predicted by paraxial theory. The aberration displayed is spherical aberration. Two methods of measuring aberration: the use of optical path difference to characterize wavefront aberration. The transverse ray coefficients to generate a ray intercept plot. Experimental examples of all the third order aberrations are given. In addition to spherical aberration, they include coma, astigmatism, field curvature, and distortion Only two types of aberration correction are discussed, removal of spherical aberration in the Hubble Space telescope and chromatic aberration. A detailed example of chromatic aberration is given.

scholarly journals Surveying the Solar Neighborhood for Brown Dwarf Companions with the ECLIPSE Discovery Mission

2003 ◽  
Vol 211 ◽  
pp. 523-524
Author(s):  
Karl Stapelfeldt
Keyword(s):  
Luminosity Function ◽  
Hubble Space Telescope ◽  
Scattered Light ◽  
Solar Neighborhood ◽  
Brown Dwarf ◽  
Space Telescope ◽  
Effective Temperatures

The proposed Eclipse Discovery mission is an optical space telescope designed to provide a thousandfold reduction in scattered light near bright stars in comparison to any Hubble Space Telescope instrument. A survey of 500 single stars within 15 pc can detect companions with absolute z magnitude of 22 at separations > 10 AU in most of the targets. Spectrophotometry of CH4 and H2O bands between 0.8-1.0 μm can be used to derive the effective temperatures of the objects. The ECLIPSE brown dwarf survey would directly measure the luminosity function of brown dwarf companions down to ~20 Jupiter masses, providing a crucial comparison with field objects.

scholarly journals Photometric Characteristics of Data from the Hubble Space Telescope Goddard-High Resolution Spectrograph

1988 ◽  
Vol 132 ◽  
pp. 35-38
Author(s):  
Dennis C. Ebbets ◽  
Sara R. Heap ◽  
Don J. Lindler
Keyword(s):  
Exposure Time ◽  
Hubble Space Telescope ◽  
Signal To Noise Ratio ◽  
Scattered Light ◽  
Signal To Noise ◽  
Space Telescope ◽  
Additional Noise ◽  
Reduction Strategies ◽  
Noise Ratio

The G-HRS is one of four axial scientific instruments which will fly aboard the Hubble Space Telescope (ref 1,2). It will produce spectroscopic observations in the 1050 A ≤ λ ≤ 3300 A region with greater spectral, spatial and temporal resolution than has been possible with previous space-based instruments. Five first order diffraction gratings and one Echelle provide three modes of spectroscopic operation with resolving powers of R = λ/ΔΔ = 2000, 20000 and 90000. Two magnetically focused, pulse-counting digicon detectors, which differ only in the nature of their photocathodes, produce data whose photometric quality is usually determined by statistical noise in the signal (ref 3). Under ideal circumstances the signal to noise ratio increases as the square root of the exposure time. For some observations detector dark count, instrumental scattered light or granularity in the pixel to pixel sensitivity will cause additional noise. The signal to noise ratio of the net spectrum will then depend on several parameters, and will increase more slowly with exposure time. We have analyzed data from the ground based calibration programs, and have developed a theoretical model of the HRS performance (ref 4). Our results allow observing and data reduction strategies to be optimized when factors other than photon statistics influence the photometric quality of the data.

scholarly journals Hubble Space Telescope Imaging of the Disks and Jets of Taurus Young Stellar Objects

1997 ◽  
Vol 182 ◽  
pp. 355-364 ◽  
Author(s):  
Karl Stapelfeldt ◽  
Christopher J. Burrows ◽  
John E. Krist ◽  
Keyword(s):  
High Spatial Resolution ◽  
Hubble Space Telescope ◽  
Scattered Light ◽  
Young Stellar Objects ◽  
Opening Angle ◽  
Stellar Objects ◽  
Space Telescope ◽  
Spread Function ◽  
Large Opening ◽  
T Tau

We report on Hubble Space Telescope imaging of eleven young stellar objects in the nearby Taurus molecular clouds. The high spatial resolution and stable point spread function of HST reveal important new details of the circumstellar nebulosity of these objects. Three sources (HH 30, FS Tau B, and DG Tau B) are resolved as compact bipolar nebulae without a directly visible star. In all three cases, jet widths near the sources are found to be 50 AU or less. Flattened disk structures are seen in absorption in HH 30 and FS Tau B, and in reflection about GM Aur. Extended envelope structures traced by scattered light are present in HL Tau, T Tau, DG Tau, and FS Tau. The jet in DG Tau exhibits a large opening angle and is already resolved into a bow-like structure less than 3″ from the star.

Linearization and Model Reduction of Contact Dynamics Simulation

2011 ◽  
Author(s):  
Jianxun Liang ◽  
Ou Ma ◽  
Caishan Liu
Keyword(s):  
Model Reduction ◽  
Multibody Systems ◽  
Reduction Method ◽  
Contact Dynamics ◽  
Dynamics Simulation ◽  
Dynamics Model ◽  
Time Step ◽  
Reduction Techniques ◽  
Proposed Model ◽  
Simulation Time

Finite element methods are widely used for simulations of contact dynamics of flexible multibody systems. Such a simulation is computationally very inefficient because the system’s dimension is usually very large and the simulation time step has to be very small in order to ensure numerical stability. A potential solution to the problem is to apply a model reduction method in the simulation. Although many model reduction techniques have been developed, most of them cannot be readily applied due to the high nonlinearity of the involved contact dynamics model. This paper presents a solution to the problem. The approach is based on a modified Lyapunov balanced truncation method. A numerical example is presented to demonstrate that, by applying the proposed model reduction method, the simulation process can be significantly speeded up while the resulting error caused by the model reduction is still within an acceptable level.

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