162 research outputs found
Protoplanetary disks around young stellar and substellar objects in the Orionis cluster
Understanding the evolution and dissipation of protoplanetary disks are
crucial in star and planet formation studies. We report the protoplanetary disk
population in the nearby young Orionis cluster (d408 pc;
age1.8 Myr) and analyse the disk properties such as dependence on stellar
mass and disk evolution. We utilise the comprehensive census of 170
spectroscopic members of the region refined using astrometry from Gaia DR3 for
a wide mass range of 19-0.004 M. Using the near infrared (2MASS)
and mid infrared (WISE) photometry we classify the sources based on the
spectral index into class I, class II, flat spectrum and class III young
stellar objects. The frequency of sources hosting a disk with stellar mass 2
M in this region is 417% which is consistent with the disk
fraction estimated in previous studies. We see that there is no significant
dependence of disk fraction on stellar mass among T Tauri stars (2
M), but we propose rapid disk depletion around higher mass stars (2
M). Furthermore we find the lowest mass of a disk bearing object to be
20 M and the pronounced disk fraction among the brown
dwarf population hints at the formation scenario that brown dwarfs form similar
to low-mass stars.Comment: Accepted for publication in The Journal of Astrophysics and
Astronomy. 17 pages, 6 figures, 2 table
High-Cadence, High-Contrast Imaging for Exoplanet Mapping: Observations of the HR 8799 Planets with VLT/SPHERE Satellite Spot-Corrected Relative Photometry
Time-resolved photometry is an important new probe of the physics of
condensate clouds in extrasolar planets and brown dwarfs. Extreme adaptive
optics systems can directly image planets, but precise brightness measurements
are challenging. We present VLT/SPHERE high-contrast, time-resolved broad
H-band near-infrared photometry for four exoplanets in the HR 8799 system,
sampling changes from night to night over five nights with relatively short
integrations. The photospheres of these four planets are often modeled by
patchy clouds and may show large-amplitude rotational brightness modulations.
Our observations provide high-quality images of the system. We present a
detailed performance analysis of different data analysis approaches to
accurately measure the relative brightnesses of the four exoplanets. We explore
the information in satellite spots and demonstrate their use as a proxy for
image quality. While the brightness variations of the satellite spots are
strongly correlated, we also identify a second-order anti-correlation pattern
between the different spots. Our study finds that PCA-based KLIP reduction with
satellite spot-modulated artificial planet-injection based photometry (SMAP)
leads to a significant (~3x) gain in photometric accuracy over standard
aperture-based photometry and reaches 0.1 mag per point accuracy for our
dataset, the signal-to-noise of which is limited by small field rotation.
Relative planet-to-planet photometry can be compared be- tween nights, enabling
observations spanning multiple nights to probe variability. Recent high-quality
relative H-band photometry of the b-c planet pair agree to about 1%.Comment: Astrophysical Journal, in pres
Observing Strategies for the NICI Campaign to Directly Image Extrasolar Planets
We discuss observing strategy for the Near Infrared Coronagraphic Imager
(NICI) on the 8-m Gemini South telescope. NICI combines a number of techniques
to attenuate starlight and suppress superspeckles: 1) coronagraphic imaging, 2)
dual channel imaging for Spectral Differential Imaging (SDI) and 3) operation
in a fixed Cassegrain rotator mode for Angular Differential Imaging (ADI). NICI
will be used both in service mode and for a dedicated 50 night planet search
campaign. While all of these techniques have been used individually in large
planet-finding surveys, this is the first time ADI and SDI will be used with a
coronagraph in a large survey. Thus, novel observing strategies are necessary
to conduct a viable planet search campaign.Comment: 12 pages, 10 figures, submitted to Proceedings of the SPI
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