128 research outputs found
An Introduction to High Contrast Differential Imaging of Exoplanets and Disks
This tutorial is an introduction to High-Contrast Imaging, a technique that
enables astronomers to isolate light from faint planets and/or circumstellar
disks that would otherwise be lost amidst the light of their host stars.
Although technically challenging, high-contrast imaging allows for direct
characterization of the properties of detected circumstellar sources. The
intent of the article is to provide newcomers to the field a general overview
of the terminology, observational considerations, data reduction strategies,
and analysis techniques high-contrast imagers employ to identify, vet, and
characterize planet and disk candidates.Comment: Accepted for publication in the Proceedings of the Astronomical
Society of the Pacific (PASP
Complex Spiral Structure in the HD 100546 Transitional Disk as Revealed by GPI and MagAO
We present optical and near-infrared high-contrast images of the transitional disk HD 100546 taken with the Magellan Adaptive Optics system (MagAO) and the Gemini Planet Imager (GPI). GPI data include both polarized intensity and total intensity imagery, and MagAO data are taken in Simultaneous Differential Imaging mode at Hα. The new GPI H-band total intensity data represent a significant enhancement in sensitivity and field rotation compared to previous data sets and enable a detailed exploration of substructure in the disk. The data are processed with a variety of differential imaging techniques (polarized, angular, reference, and simultaneous differential imaging) in an attempt to identify the disk structures that are most consistent across wavelengths, processing techniques, and algorithmic parameters. The inner disk cavity at 15 au is clearly resolved in multiple data sets, as are a variety of spiral features. While the cavity and spiral structures are identified at levels significantly distinct from the neighboring regions of the disk under several algorithms and with a range of algorithmic parameters, emission at the location of HD 100546 "c" varies from point-like under aggressive algorithmic parameters to a smooth continuous structure with conservative parameters, and is consistent with disk emission. Features identified in the HD 100546 disk bear qualitative similarity to computational models of a moderately inclined two-armed spiral disk, where projection effects and wrapping of the spiral arms around the star result in a number of truncated spiral features in forward-modeled images
New Extinction and Mass Estimates from Optical Photometry of the Very Low Mass Brown Dwarf Companion CT Chamaeleontis B with the Magellan AO System
We used the Magellan adaptive optics (MagAO) system and its VisAO CCD camera
to image the young low mass brown dwarf companion CT Chamaeleontis B for the
first time at visible wavelengths. We detect it at r', i', z', and Ys. With our
new photometry and Teff~2500 K derived from the shape its K-band spectrum, we
find that CT Cha B has Av = 3.4+/-1.1 mag, and a mass of 14-24 Mj according to
the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r'
detection indicates that the companion has significant Halpha emission and a
mass accretion rate ~6*10^-10 Msun/yr, similar to some substellar companions.
Proper motion analysis shows that another point source within 2" of CT Cha A is
not physical. This paper demonstrates how visible wavelength AO photometry (r',
i', z', Ys) allows for a better estimate of extinction, luminosity, and mass
accretion rate of young substellar companions.Comment: Accepted for publication in ApJ; 6 figure
New Extinction and Mass Estimates of the Low-mass Companion 1RXS 1609 B with the Magellan AO System: Evidence of an Inclined Dust Disk
We used the Magellan adaptive optics system to image the 11 Myr substellar
companion 1RXS 1609 B at the bluest wavelengths to date (z' and Ys). Comparison
with synthetic spectra yields a higher temperature than previous studies of
and significant dust extinction of
mag. Mass estimates based on the DUSTY tracks gives
0.012-0.015 Msun, making the companion likely a low-mass brown dwarf surrounded
by a dusty disk. Our study suggests that 1RXS 1609 B is one of the 25% of Upper
Scorpius low-mass members harboring disks, and it may have formed like a star
and not a planet out at 320 AU.Comment: 5 pages, 4 figures; accepted to ApJ
Correlating Changes in Spot Filling Factors with Stellar Rotation: The Case of LkCa 4
We present a multi-epoch spectroscopic study of LkCa 4, a heavily spotted
non-accreting T Tauri star. Using SpeX at NASA's Infrared Telescope Facility
(IRTF), 12 spectra were collected over five consecutive nights, spanning
1.5 stellar rotations. Using the IRTF SpeX Spectral Library, we
constructed empirical composite models of spotted stars by combining a warmer
(photosphere) standard star spectrum with a cooler (spot) standard weighted by
the spot filling factor, . The best-fit models spanned two
photospheric component temperatures, = 4100 K (K7V) and 4400 K
(K5V), and one spot component temperature, = 3060 K (M5V) with an
of 0.3. We find values of to vary between 0.77 and 0.94 with
an average uncertainty of 0.04. The variability of is periodic
and correlates with its 3.374 day rotational period. Using a mean value for
to represent the total spot coverage, we calculated spot
corrected values for and . Placing these values alongside
evolutionary models developed for heavily spotted young stars, we infer mass
and age ranges of 0.45-0.6 and 0.50-1.25 Myr, respectively. These
inferred values represent a twofold increase in the mass and a twofold decrease
in the age as compared to standard evolutionary models. Such a result
highlights the need for constraining the contributions of cool and warm regions
of young stellar atmospheres when estimating and to infer
masses and ages as well as the necessity for models to account for the effects
of these regions on the early evolution of low-mass stars.Comment: 21 pages, 9 Figures; Accepted for publication in Ap
An Enigmatic Pointlike Feature within the HD 169142 Transitional Disk
We report the detection of a faint pointlike feature possibly related to
ongoing planet-formation in the disk of the transition disk star HD 169142. The
pointlike feature has a mag(L)6.4, at a separation of 0.11"
and PA0. Given its lack of an H or K counterpart despite
its relative brightness, this candidate cannot be explained by purely
photospheric emission and must be a disk feature heated by an as yet unknown
source. Its extremely red colors make it highly unlikely to be a background
object, but future multi-wavelength followup is necessary for confirmation and
characterization of this feature.Comment: Accepted to ApJ Letters, see also Reggiani et al. 201
New Spatially Resolved Observations of the T Cha Transition Disk and Constraints on the Previously Claimed Substellar Companion
We present multi-epoch non-redundant masking observations of the T Cha
transition disk, taken at the VLT and Magellan in H, Ks, and L' bands. T Cha is
one of a small number of transition disks that host companion candidates
discovered by high-resolution imaging techniques, with a putative companion at
a position angle of 78 degrees, separation of 62 mas, and contrast at L' of 5.1
mag. We find comparable binary parameters in our re-reduction of the initial
detection images, and similar parameters in the 2011 L', 2013 NaCo L', and 2013
NaCo Ks data sets. We find a close-in companion signal in the 2012 NaCo L'
dataset that cannot be explained by orbital motion, and a non-detection in the
2013 MagAO/Clio2 L' data. However, Monte-carlo simulations show that the best
fits to the 2012 NaCo and 2013 MagAO/Clio2 followup data may be consistent with
noise. There is also a significant probability of false non-detections in both
of these data sets. We discuss physical scenarios that could cause the best
fits, and argue that previous companion and scattering explanations are
inconsistent with the results of the much larger dataset presented here.Comment: 25 pages, 22 figures, accepted for publication in Ap
- …