67 research outputs found
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
A Search for Variability in Exoplanet Analogues and Low-Gravity Brown Dwarfs
We report the results of a -band survey for photometric variability in a
sample of young, low-gravity objects using the New Technology Telescope (NTT)
and the United Kingdom InfraRed Telescope (UKIRT). Surface gravity is a key
parameter in the atmospheric properties of brown dwarfs and this is the first
large survey that aims to test the gravity dependence of variability
properties. We do a full analysis of the spectral signatures of youth and
assess the group membership probability of each target using membership tools
from the literature. This results in a 30 object sample of young low-gravity
brown dwarfs. Since we are lacking in objects with spectral types later than
L9, we focus our statistical analysis on the L0-L8.5 objects. We find that the
variability occurrence rate of L0-L8.5 low-gravity brown dwarfs in this survey
is . We reanalyse the results of Radigan 2014 and find that
the field dwarfs with spectral types L0-L8.5 have a variability occurrence rate
of . We determine a probability of that the samples are
drawn from different distributions. This is the first quantitative indication
that the low-gravity objects are more likely to be variable than the field
dwarf population. Furthermore, we present follow-up and
observations of the young, planetary-mass variable object PSO 318.5-22 over
three consecutive nights. We find no evidence of phase shifts between the
and bands and find higher amplitudes. We use the lightcurves
to measure a rotational period of hr for PSO 318.5-22.Comment: accepted for publication in MNRA
Weather on the Nearest Brown Dwarfs: Resolved Simultaneous Multi-Wavelength Variability Monitoring of WISE J104915.57-531906.1AB
We present two epochs of MPG/ESO 2.2m GROND simultaneous 6-band ()
photometric monitoring of the closest known L/T transition brown dwarf binary
WISE J104915.57-531906.1AB. We report here the first resolved variability
monitoring of both the T0.5 and L7.5 components. We obtained 4 hours of focused
observations on the night of UT 2013-04-22, as well as 4 hours of defocused
(unresolved) observations on the night of UT 2013-04-16. We note a number of
robust trends in our light curves. The and light curves appear to be
anticorrelated with and for the T0.5 component and in the unresolved
lightcurve. In the defocused dataset, appears correlated with and
and anticorrelated with and , while in the focused dataset we measure
no variability for at the level of our photometric precision, likely due to
evolving weather phenomena. In our focused T0.5 component lightcurve, the
band lightcurve displays a significant phase offset relative to both and
. We argue that the measured phase offsets are correlated with atmospheric
pressure probed at each band, as estimated from 1D atmospheric models. We also
report low-amplitude variability in and intrinsic to the L7.5
component.Comment: 14 pages, 5 figures, accepted to ApJ Letter
Triple Reassortant H3N2 Influenza A Viruses, Canada, 2005
Since January 2005, H3N2 influenza viruses have been isolated from pigs and turkeys throughout Canada and from a swine farmer and pigs on the same farm in Ontario. These are human/classical swine/avian reassortants similar to viruses that emerged in US pigs in 1998 but with a distinct human-lineage neuraminidase gene
The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates Under Conservative Assumptions
We present the results of the largest (m) direct
imaging survey for exoplanets to date, the Large Binocular Telescope
Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98
stars with spectral types from B to M. Cool planets emit a larger share of
their flux in compared to shorter wavelengths, affording LEECH an
advantage in detecting low-mass, old, and cold-start giant planets. We
emphasize proximity over youth in our target selection, probing physical
separations smaller than other direct imaging surveys. For FGK stars, LEECH
outperforms many previous studies, placing tighter constraints on the hot-start
planet occurrence frequency interior to au. For less luminous,
cold-start planets, LEECH provides the best constraints on giant-planet
frequency interior to au around FGK stars. Direct imaging survey
results depend sensitively on both the choice of evolutionary model (e.g., hot-
or cold-start) and assumptions (explicit or implicit) about the shape of the
underlying planet distribution, in particular its radial extent. Artificially
low limits on the planet occurrence frequency can be derived when the shape of
the planet distribution is assumed to extend to very large separations, well
beyond typical protoplanetary dust-disk radii ( au), and when
hot-start models are used exclusively. We place a conservative upper limit on
the planet occurrence frequency using cold-start models and planetary
population distributions that do not extend beyond typical protoplanetary
dust-disk radii. We find that of FGK systems can host a 7 to 10
planet from 5 to 50 au. This limit leaves open the
possibility that planets in this range are common.Comment: 31 pages, 13 figures, accepted to A
A Near-infrared Variability Survey of Young Planetary-mass Objects
We present a photometric variability survey of young planetary-mass objects
using the New Technology Telescope in the Js and Ks bands. Surface gravity
plays an important role in the atmospheric structure of brown dwarfs, as young
low gravity L dwarfs have a higher variability rate than field L dwarfs. In
this study, we extend variability studies to young T-type planetary-mass
objects and investigate the effects of surface gravity on the variability of L
and T dwarfs across a large sample. We conduct continuous monitoring for 18
objects with spectral types from L5 to T8 and detect four new variables and two
variable candidates. Combining with previous variability surveys of field and
young L and T objects, we find that young objects tend to be more variable than
field objects within peak-to-peak variability amplitude ranges of 0.5-10 per
cent and period ranges of 1.5-20 hr. For the first time, we constrain the
variability rate of young T dwarfs to be 56 per cent compared to 25 per cent
for field T dwarfs. Both field and young samples have higher variability rates
at the L/T transition than outside the L/T transition. The differences in the
variability rates between field and young samples are about 1 sigma and
therefore larger sample sizes are needed to confirm and refine the results.
Besides the L/T transition, young L dwarfs with strong variability tend to
assemble in a narrow spectral type range of L6-L7.5. This work supports the
critical role of surface gravity on the atmospheric structure from L to T
spectral types.Comment: Accepted for publication in MNRAS, 21 pages of main text including 6
tables and 17 figure
Variability in a young, L/T transition planetary-mass object
As part of our ongoing NTT SoFI survey for variability in young free-floating planets and low-mass brown dwarfs, we detect significant variability in the young, free-floating planetary-mass object PSO J318.5-22, likely due to rotational modulation of inhomogeneous cloud cover. A member of the 23 ± 3 Myr β Pic moving group, PSO J318.5-22 has Teff = K and a mass estimate of 8.3 ± 0.5 MJup for a 23 ± 3 Myr age. PSO J318.5-22 is intermediate in mass between 51 Eri b and β Pic b, the two known exoplanet companions in the β Pic moving group. With variability amplitudes from 7% to 10% in JS at two separate epochs over 3-5 hr observations, we constrain the rotational period of this object to >5 hr. In KS, we marginally detect a variability trend of up to 3% over a 3 hr observation. This is the first detection of weather on an extrasolar planetary-mass object. Among L dwarfs surveyed at high photometric precision (<3%), this is the highest amplitude variability detection. Given the low surface gravity of this object, the high amplitude preliminarily suggests that such objects may be more variable than their high-mass counterparts, although observations of a larger sample are necessary to confirm this. Measuring similar variability for directly imaged planetary companions is possible with instruments such as SPHERE and GPI and will provide important constraints on formation. Measuring variability at multiple wavelengths can help constrain cloud structure.Peer reviewe
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