56 research outputs found
Discovery of new stellar groups in the Orion complex
We test the ability of two unsupervised machine learning algorithms,
\textit{EnLink} and Shared Nearest Neighbour (SNN), to identify stellar
groupings in the Orion star-forming complex as an application to the
5-dimensional astrometric data from \textit{Gaia} DR2. The algorithms represent
two distinct approaches to limiting user bias when selecting parameter values
and evaluating the relative weights among astrometric parameters.
\textit{EnLink} adopts a locally adaptive distance metric and eliminates the
need of parameter tuning through automation. The original SNN relies only on
human input for parameter tuning so we modified SNN to run in two stages. We
first ran the original SNN 7,000 times, each with a randomly generated sample
according to within-source co-variance matrices provided in \textit{Gaia} DR2
and random parameter values within reasonable ranges. During the second stage,
we modified SNN to identify the most repeating stellar groups from 25,798 we
obtained in the first stage. We reveal 21 spatially- and kinematically-coherent
groups in the Orion complex, 12 of which previously unknown. The groups show a
wide distribution of distances extending as far as about 150 pc in front of the
star-forming Orion molecular clouds, to about 50 pc beyond them where we find,
unexpectedly, several groups. Our results expose to view the wealth of
sub-structure in the OB association, within and beyond the classical Blaauw
Orion OBI sub-groups. A full characterization of the new groups is of the
essence as it offers the potential to unveil how star formation proceeds
globally in large complexes such as Orion. The data and code that generated the
groups in this work as well as the final table can be found at \protect\url{
https://github.com/BoquanErwinChen/GaiaDR2_Orion_Dissection}.Comment: 9 pages, 4 figures. Accepted by A&A. Comments welcom
Enzyme-linked immunosorbent assay of changes in serum levels of growth hormone (cGH) in common carps (Cyprinus carpio)
The aim of the present study was to purify the common native carp growth hormone (ncGH), produce monoclonal antibodies (mAbs) to common native carp growth hormone (ncGH), and further enhance the sensitivity of enzyme-linked immunosorbent assays (ELISA) for ncGH. Additionally, we investigated changes in serum ncGH levels in carps raised in different environmental conditions. The recombinant grass carp (Ctenopharyngodon idella) growth hormone was purified and used as antigen to immunize the rabbit. The natural ncGH was isolated from the pituitaries of common carp. SDS-PAGE and Western blot utilizing the polyclonal anti-rgcGH antibody confirmed the purification of ncGH from pituitaries. Purified ncGH was then used as an immunogen in the B lymphocyte hybridoma technique. A total of 14 hybridoma cell lines (FMU-cGH 1-14) were established that were able to stably secrete mAbs against ncGH. Among them, eight clones (FMU-cGH1-6, 12 and 13) were successfully used for Western blot while nine clones (FMU-cGH 1-7, 9 and 10) were used in fluorescent staining and immunohistochemistry. Epitope mapping by competitive ELISA demonstrated that these mAbs recognized five different epitopes. A sensitive sandwich ELISA for detection of ncGH was developed using FMU-cGH12 as the coating mAb and FMU-cGH6 as the enzyme labeled mAb. This detection system was found to be highly stable and sensitive, with detection levels of 70 pg/mL. Additionally, we found that serum ncGH levels in restricted food group and in the net cage group increased 6.9-and 5.8-fold, respectively, when compared to controls, demonstrating differences in the GH stress response in common carp under different living conditions.The aim of the present study was to purify the common native carp growth hormone (ncGH), produce monoclonal antibodies (mAbs) to common native carp growth hormone (ncGH), and further enhance the sensitivity of enzyme-linked immunosorbent assays (ELISA) for ncGH. Additionally, we investigated changes in serum ncGH levels in carps raised in different environmental conditions. The recombinant grass carp (Ctenopharyngodon idella) growth hormone was purified and used as antigen to immunize the rabbit. The natural ncGH was isolated from the pituitaries of common carp. SDS-PAGE and Western blot utilizing the polyclonal anti-rgcGH antibody confirmed the purification of ncGH from pituitaries. Purified ncGH was then used as an immunogen in the B lymphocyte hybridoma technique. A total of 14 hybridoma cell lines (FMU-cGH 1-14) were established that were able to stably secrete mAbs against ncGH. Among them, eight clones (FMU-cGH1-6, 12 and 13) were successfully used for Western blot while nine clones (FMU-cGH 1-7, 9 and 10) were used in fluorescent staining and immunohistochemistry. Epitope mapping by competitive ELISA demonstrated that these mAbs recognized five different epitopes. A sensitive sandwich ELISA for detection of ncGH was developed using FMU-cGH12 as the coating mAb and FMU-cGH6 as the enzyme labeled mAb. This detection system was found to be highly stable and sensitive, with detection levels of 70 pg/mL. Additionally, we found that serum ncGH levels in restricted food group and in the net cage group increased 6.9-and 5.8-fold, respectively, when compared to controls, demonstrating differences in the GH stress response in common carp under different living conditions
The K2-HERMES Survey: Age and Metallicity of the Thick Disc
Asteroseismology is a promising tool to study Galactic structure and
evolution because it can probe the ages of stars. Earlier attempts comparing
seismic data from the {\it Kepler} satellite with predictions from Galaxy
models found that the models predicted more low-mass stars compared to the
observed distribution of masses. It was unclear if the mismatch was due to
inaccuracies in the Galactic models, or the unknown aspects of the selection
function of the stars. Using new data from the K2 mission, which has a
well-defined selection function, we find that an old metal-poor thick disc, as
used in previous Galactic models, is incompatible with the asteroseismic
information. We show that spectroscopic measurements of [Fe/H] and
[/Fe] elemental abundances from the GALAH survey indicate a mean
metallicity of for the thick disc. Here is the
effective solar-scaled metallicity, which is a function of [Fe/H] and
[/Fe]. With the revised disc metallicities, for the first time, the
theoretically predicted distribution of seismic masses show excellent agreement
with the observed distribution of masses. This provides an indirect
verification of the asteroseismic mass scaling relation is good to within five
percent. Using an importance-sampling framework that takes the selection
function into account, we fit a population synthesis model of the Galaxy to the
observed seismic and spectroscopic data. Assuming the asteroseismic scaling
relations are correct, we estimate the mean age of the thick disc to be about
10 Gyr, in agreement with the traditional idea of an old -enhanced
thick disc.Comment: 21 pages, submitted to MNRA
The GALAH survey: chemodynamics of the solar neighbourhood
We present the chemodynamic structure of the solar neighbourhood using 55 652 stars within a 500 pc volume around the Sun observed by GALAH and with astrometric parameters from Gaia DR2. We measure the velocity dispersion for all three components (vertical, radial, and tangential) and find that it varies smoothly with [Fe/H] and [α/Fe] for each component. The vertical component is especially clean, with σvz increasing from a low of 10 km s−1 at solar [α/Fe] and [Fe/H] to a high of more than 50 km s−1 for more metal-poor and [α/Fe] enhanced populations. We find no evidence of a large decrease in the velocity dispersion of the highest [α/Fe] populations as claimed in surveys prior to Gaia DR2. The eccentricity distribution for local stars varies most strongly as a function of [α/Fe], where stars with [α/Fe] 0.1 dex), we find that the majority have e < 0.2 and are likely observed in the solar neighbourhood through churning/migration rather than blurring effects, as the epicyclic motion for these stars is not large enough to reach the radii at which they were likely born based on their metallicity.This research was supported
by the Australian Research Council Centre of Excellence for All
Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project
number CE170100013.
In addition to ASTRO3D, MRH received support from ARC DP
grant no. DP160103747. TZ acknowledges financial support of the
Slovenian Research Agency (research core funding no. P1-0188).
JBH is supported by an Australian Laureate Fellowship from the
ARC. SLM acknowledges support from the Australian Research
Council through grant no. DP180101791
The GALAH survey: chemodynamics of the solar neighbourhood
We present the chemodynamic structure of the solar neighbourhood using 55 652 stars within a 500 pc volume around the Sun observed by GALAH and with astrometric parameters from Gaia DR2. We measure the velocity dispersion for all three components (vertical, radial, and tangential) and find that it varies smoothly with [Fe/H] and [α/Fe] for each component. The vertical component is especially clean, with σ _{v_z} increasing from a low of 10 km s-1 at solar [α/Fe] and [Fe/H] to a high of more than 50 km s-1 for more metal-poor and [α/Fe] enhanced populations. We find no evidence of a large decrease in the velocity dispersion of the highest [α/Fe] populations as claimed in surveys prior to Gaia DR2. The eccentricity distribution for local stars varies most strongly as a function of [α/Fe], where stars with [α/Fe] 0.1 dex), we find that the majority have e < 0.2 and are likely observed in the solar neighbourhood through churning/migration rather than blurring effects, as the epicyclic motion for these stars is not large enough to reach the radii at which they were likely born based on their metallicity.This research was supported
by the Australian Research Council Centre of Excellence for All
Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project
number CE170100013.
In addition to ASTRO3D, MRH received support from ARC DP
grant no. DP160103747. TZ acknowledges financial support of the
Slovenian Research Agency (research core funding no. P1-0188).
JBH is supported by an Australian Laureate Fellowship from the
ARC. SLM acknowledges support from the Australian Research
Council through grant no. DP180101791
The GALAH Survey: Chemical Clocks
Previous studies have found that the elemental abundances of a star correlate
directly with its age and metallicity. Using this knowledge, we derive ages for
a sample of 250,000 stars taken from GALAH DR3 using only their overall
metallicity and chemical abundances. Stellar ages are estimated via the machine
learning algorithm , using main sequence turnoff stars with precise
ages as our input training set. We find that the stellar ages for the bulk of
the GALAH DR3 sample are accurate to 1-2 Gyr using this method. With these
ages, we replicate many recent results on the age-kinematic trends of the
nearby disk, including the age-velocity dispersion relationship of the solar
neighborhood and the larger global velocity dispersion relations of the disk
found using and GALAH. The fact that chemical abundances alone can be
used to determine a reliable age for a star have profound implications for the
future study of the Galaxy as well as upcoming spectroscopic surveys. These
results show that the chemical abundance variation at a given birth radius is
quite small, and imply that strong chemical tagging of stars directly to birth
clusters may prove difficult with our current elemental abundance precision.
Our results highlight the need of spectroscopic surveys to deliver precision
abundances for as many nucleosynthetic production sites as possible in order to
estimate reliable ages for stars directly from their chemical abundances.
Applying the methods outlined in this paper opens a new door into studies of
the kinematic structure and evolution of the disk, as ages may potentially be
estimated for a large fraction of stars in existing spectroscopic surveys. This
would yield a sample of millions of stars with reliable age determinations, and
allow precise constraints to be put on various kinematic processes in the disk,
such as the efficiency and timescales of radial migration.Comment: 13 pages, 15 figures, submitted to MNRA
The GALAH survey and Gaia DR2: Linking ridges, arches, and vertical waves in the kinematics of the Milky Way
Gaia DR2 has revealed new small-scale and large-scale patterns in the phase-space distribution of stars in the Milky Way. In cylindrical Galactic coordinates (R,φ ,z), ridge-like structures can be seen in the (R,V_φ) plane and asymmetric arch-like structures in the (V_R,V_φ) plane. We show that the ridges are also clearly present when the third dimension of the (R,V_φ) plane is represented by , , , , and . The maps suggest that stars along the ridges lie preferentially close to the Galactic mid-plane (|z| and suggests a coupling between planar and vertical directions. We demonstrate, using N-body simulations that such coupling can be generated both in isolated discs and in discs perturbed by an orbiting satellite like the Sagittarius dwarf galaxy.JBH is supported by an ARC Australian Laureate Fellowship
(FL140100278) and the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO-3D) through project number
CE170100013. SS is funded by a Dean’s University Fellowship
and through JBH’s Laureate Fellowship, which also supports TTG
and GDS. MJH is supported by an ASTRO-3D Fellowship. JK
is supported by a Discovery Project grant from the Australian
Research Council (DP150104667) awarded to JBH.
SB acknowledges funds from the Alexander von Humboldt
Foundation in the framework of the Sofja Kovalevskaja Award
endowed by the Federal Ministry of Education and Research.
HST-HF2-51425.001 awarded by the Space Telescope Science
Institute
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