1,474 research outputs found
Search for free-floating planetary-mass objects in the Pleiades
(Abridged) We aim at identifying the least massive population of the solar
metallicity, young (120 Myr), nearby (133.5 pc) Pleiades star cluster with the
ultimate goal of understanding the physical properties of intermediate-age,
free-floating, low-mass brown dwarfs and giant planetary-mass objects, and
deriving the cluster substellar mass function across the deuterium-burning mass
limit at ~0.012 Msol. We performed a deep photometric and astrometric J- and
H-band survey covering an area of ~0.8 deg^2. The images with completeness and
limiting magnitudes of J,H ~ 20.2 and ~ 21.5 mag were acquired ~9 yr apart
(proper motion precision of +/-6 mas/yr). J- and H-band data were complemented
with Z, K, and mid-infrared magnitudes up to 4.6 micron coming from UKIDSS,
WISE, and follow-up observations of our own. Pleiades member candidates were
selected to have proper motions compatible with that of the cluster, and colors
following the known Pleiades sequence in the interval J = 15.5-8.8 mag, and
Z_UKIDSS - J > 2.3 mag or Z nondetections for J > 18.8 mag. We found a neat
sequence of astrometric and photometric Pleiades substellar member candidates
in the intervals J = 15.5-21.2 mag and ~0.072-0.008 Msol. The faintest objects
show very red near- and mid-infrared colors exceeding those of field
high-gravity dwarfs by >0.5 mag. The Pleiades photometric sequence does not
show any color turn-over because of the presence of photospheric methane
absorption down to J = 20.3 mag, which is about 1 mag fainter than predicted by
the color-computed models. Pleiades brown dwarfs have a proper motion
dispersion of 6.4-7.5 mas/yr and are dynamically relaxed at the age of the
cluster. The Pleiades mass function extends down to the deuterium burning-mass
threshold, with a slope fairly similar to that of other young star clusters and
stellar associations.Comment: Accepted for publication in A&A. 16 page
A Search for Very Low-mass Stars and Brown Dwarfs in the Young sigma Orionis Cluster
We present a CCD-based photometric survey covering 870 sq. arcmin in a young
stellar cluster around the young multiple star sigma Orionis. Our survey
limiting R, I, and Z magnitudes are 23.2, 21.8, and 21.0, respectively. From
our colour-magnitude diagrams, we have selected 49 faint objects, which
smoothly extrapolate the photometric sequence defined by more massive known
members. Adopting the currently accepted age interval of 2-10 Myr for the Orion
1b association and considering recent evolutionary models, our objects may span
a mass range from 0.1 down to 0.02 Msun, well within the substellar regime.
Follow-up low-resolution optical spectroscopy (635-920 nm) for eight of our
candidates (I=16-19.5) shows that they have spectral types M6-M8.5 which are
consistent with the expectations for true members. Compared with their Pleiades
counterparts of similar types, Halpha emission is generally stronger, while NaI
and KI absorption lines appear weaker, as expected for lower surface gravities
and younger ages. Additionally, TiO bands and in particular VO bands appear
clearly enhanced in our candidate with the latest spectral type, SOri 45 (M8.5,
I=19.5), compared to objects of similar types in older clusters and the field.
We have estimated the mass of this candidate at only 0.020-0.040 Msun, hence it
is one of the least massive brown dwarfs yet discovered. We also discuss in
this paper the potential role of deuterium as a tracer of both substellar
nature and age in very young clusters.Comment: Accepted for publication in ApJ Main Journal. 32 pages of text and
tables + 9 pages of figures. Figures 3a and 3b (gif format) provided
separatel
Confirming the least massive members of the Pleiades star cluster
We present optical photometry (i- and Z-band) and low-resolution spectroscopy
(640-1015 nm) of very faint candidate members (J = 20.2-21.2 mag) of the
Pleiades star cluster (120 Myr). The main goal is to address their cluster
membership via photometric, astrometric, and spectroscopic studies, and to
determine the properties of the least massive population of the cluster through
the comparison of the data with younger and older spectral counterparts and
state-of-the art model atmospheres. We confirm three bona-fide Pleiades members
that have extremely red optical and infrared colors, effective temperatures of
~1150 K and ~1350 K, and masses in the interval 11-20 Mjup, and one additional
likely member that shares the same motion as the cluster but does not appear to
be as red as the other members with similar brightness. This latter object
requires further near-infrared spectroscopy to fully address its membership in
the Pleiades. The optical spectra of two bona-fide members were classified as
L6-L7 and show features of KI, a tentative detection of CsI, hydrides and water
vapor with an intensity similar to high-gravity dwarfs of related
classification despite their young age. The properties of the Pleiades L6-L7
members clearly indicate that very red colors of L dwarfs are not a direct
evidence of ages younger than ~100 Myr. We also report on the determination of
the bolometric corrections for the coolest Pleiades members. These data can be
used to interpret the observations of the atmospheres of exoplanets orbiting
stars.Comment: Accepted for publication in MNRAS (17 pages
AB Doradus C: Age, Spectral Type, Orbit, and Comparison to Evolutionary Models
We expand upon the results of Close et al. 2005 regarding the young, low-mass
object AB Dor C and its role as a calibration point for theoretical tracks. We
present an improved spectral reduction and a new orbital solution with two
additional epochs. Our improved analysis confirms our spectral type of M8 (+/-
1) and mass of 0.090+/-0.003 solar masses for AB Dor C. Comparing the results
for AB Dor C with other young, low-mass objects with dynamical masses we find a
general trend where current evolutionary models tend to over-predict the
temperature (or under-predict the mass) for low mass stars and brown dwarfs.
Given our precision, there is a ~99% chance that the mass of AB Dor C is
underestimated by the DUSTY tracks in the HR diagram.Comment: 7 pages, 10 figures, proceedings for the workshop "Ultralow-mass star
formation and evolution", to be published in Astronomische Nachrichten -
Astronomical Note
A Hubble Space Telescope ACS Search for Brown Dwarf Binaries in the Pleiades Open Cluster
We present the results of a high-resolution imaging survey for brown dwarf
binaries in the Pleiades open cluster. The observations were carried out with
the Advance Camera for Surveys onboard the Hubble Space Telescope. Our sample
consists of 15 bona-fide brown dwarfs. We confirm 2 binaries and detect their
orbital motion, but we did not resolve any new binary candidates in the
separation range between 5.4AU and 1700AU and masses in the range
0.035--0.065~Msun. Together with the results of our previous study (Martin et
al., 2003), we can derive a visual binary frequency of 13.3\%
for separations greater than 7~AU masses between 0.055--0.065~M_{\sun} and
mass ratios between 0.45--0.91.0. The other observed properties of
Pleiades brown dwarf binaries (distributions of separation and mass ratio)
appear to be similar to their older counterparts in the field.Comment: 29 pages, 7 figures, 6 tables, accepted for publication in Ap
Monitoring spatial sustainable development: Semi-automated analysis of satellite and aerial images for energy transition and sustainability indicators
Solar panels are installed by a large and growing number of households due to
the convenience of having cheap and renewable energy to power house appliances.
In contrast to other energy sources solar installations are distributed very
decentralized and spread over hundred-thousands of locations. On a global level
more than 25% of solar photovoltaic (PV) installations were decentralized. The
effect of the quick energy transition from a carbon based economy to a green
economy is though still very difficult to quantify. As a matter of fact the
quick adoption of solar panels by households is difficult to track, with local
registries that miss a large number of the newly built solar panels. This makes
the task of assessing the impact of renewable energies an impossible task.
Although models of the output of a region exist, they are often black box
estimations. This project's aim is twofold: First automate the process to
extract the location of solar panels from aerial or satellite images and
second, produce a map of solar panels along with statistics on the number of
solar panels. Further, this project takes place in a wider framework which
investigates how official statistics can benefit from new digital data sources.
At project completion, a method for detecting solar panels from aerial images
via machine learning will be developed and the methodology initially developed
for BE, DE and NL will be standardized for application to other EU countries.
In practice, machine learning techniques are used to identify solar panels in
satellite and aerial images for the province of Limburg (NL), Flanders (BE) and
North Rhine-Westphalia (DE).Comment: This document provides the reader with an overview of the various
datasets which will be used throughout the project. The collection of
satellite and aerial images as well as auxiliary information such as the
location of buildings and roofs which is required to train, test and validate
the machine learning algorithm that is being develope
Effective Use of Dilated Convolutions for Segmenting Small Object Instances in Remote Sensing Imagery
Thanks to recent advances in CNNs, solid improvements have been made in
semantic segmentation of high resolution remote sensing imagery. However, most
of the previous works have not fully taken into account the specific
difficulties that exist in remote sensing tasks. One of such difficulties is
that objects are small and crowded in remote sensing imagery. To tackle with
this challenging task we have proposed a novel architecture called local
feature extraction (LFE) module attached on top of dilated front-end module.
The LFE module is based on our findings that aggressively increasing dilation
factors fails to aggregate local features due to sparsity of the kernel, and
detrimental to small objects. The proposed LFE module solves this problem by
aggregating local features with decreasing dilation factor. We tested our
network on three remote sensing datasets and acquired remarkably good results
for all datasets especially for small objects
Spectral classification of Pleiades brown dwarf candidates
We report on the results of the spectroscopy of 10 objects previously
classified as brown dwarf candidates via RIJHK colors by Eisenbeiss et al.
(2009), who performed deep imaging observations on a 0.4 sq.deg. field at the
edge of the Pleiades. We describe and judge on classification techniques in the
region of M-type stars. To classify and characterise the objects, visual and
near infrared spectra have been obtained with VLT FORS and ISAAC. The spectral
classification was performed using the shape of the spectra as well as spectral
indices that are sensitive to the spectral type and luminosity class of Mtype
stars and late M-type brown dwarfs. Furthermore a spectrophotometric distance
was calculated and compared the distance of the Pleiades to investigate the
membership probability. As a second argument we analyzed the proper motion. The
brown dwarf candidates were found not to be brown dwarfs, but late-K to
mid-M-type dwarf stars. Based on the obtained distance and tabulated proper
motions we conclude that all objects are background dwarf stars.Comment: 10 pages, 5 figure
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