11,924 research outputs found
Photometric redshift estimation based on data mining with PhotoRApToR
Photometric redshifts (photo-z) are crucial to the scientific exploitation of
modern panchromatic digital surveys. In this paper we present PhotoRApToR
(Photometric Research Application To Redshift): a Java/C++ based desktop
application capable to solve non-linear regression and multi-variate
classification problems, in particular specialized for photo-z estimation. It
embeds a machine learning algorithm, namely a multilayer neural network trained
by the Quasi Newton learning rule, and special tools dedicated to pre- and
postprocessing data. PhotoRApToR has been successfully tested on several
scientific cases. The application is available for free download from the DAME
Program web site.Comment: To appear on Experimental Astronomy, Springer, 20 pages, 15 figure
Tuning target selection algorithms to improve galaxy redshift estimates
We showcase machine learning (ML) inspired target selection algorithms to
determine which of all potential targets should be selected first for
spectroscopic follow up. Efficient target selection can improve the ML redshift
uncertainties as calculated on an independent sample, while requiring less
targets to be observed. We compare the ML targeting algorithms with the Sloan
Digital Sky Survey (SDSS) target order, and with a random targeting algorithm.
The ML inspired algorithms are constructed iteratively by estimating which of
the remaining target galaxies will be most difficult for the machine learning
methods to accurately estimate redshifts using the previously observed data.
This is performed by predicting the expected redshift error and redshift offset
(or bias) of all of the remaining target galaxies. We find that the predicted
values of bias and error are accurate to better than 10-30% of the true values,
even with only limited training sample sizes. We construct a hypothetical
follow-up survey and find that some of the ML targeting algorithms are able to
obtain the same redshift predictive power with 2-3 times less observing time,
as compared to that of the SDSS, or random, target selection algorithms. The
reduction in the required follow up resources could allow for a change to the
follow-up strategy, for example by obtaining deeper spectroscopy, which could
improve ML redshift estimates for deeper test data.Comment: 16 pages, 9 figures, updated to match MNRAS accepted version. Minor
text changes, results unchange
Deep Learning Applied to the Asteroseismic Modeling of Stars with Coherent Oscillation Modes
We develop a novel method based on machine learning principles to achieve
optimal initiation of CPU-intensive computations for forward asteroseismic
modeling in a multi-D parameter space. A deep neural network is trained on a
precomputed asteroseismology grid containing about 62 million coherent
oscillation-mode frequencies derived from stellar evolution models. These
models are representative of the core-hydrogen burning stage of
intermediate-mass and high-mass stars. The evolution models constitute a 6D
parameter space and their predicted low-degree pressure- and gravity-mode
oscillations are scanned, using a genetic algorithm. A software pipeline is
created to find the best fitting stellar parameters for a given set of observed
oscillation frequencies. The proposed method finds the optimal regions in the
6D parameters space in less than a minute, hence providing the optimal starting
point for further and more detailed forward asteroseismic modeling in a
high-dimensional context. We test and apply the method to seven pulsating stars
that were previously modeled asteroseismically by classical grid-based forward
modeling based on a statistic and obtain good agreement with past
results. Our deep learning methodology opens up the application of
asteroseismic modeling in +6D parameter space for thousands of stars pulsating
in coherent modes with long lifetimes observed by the space telescope
and to be discovered with the TESS and PLATO space missions, while applications
so far were done star-by-star for only a handful of cases. Our method is open
source and can be used by anyone freely.Comment: Accepted for publication in PASP Speciale Volume on Machine Learnin
Using machine learning to classify the diffuse interstellar bands
Using over a million and a half extragalactic spectra we study the
correlations of the Diffuse Interstellar Bands (DIBs) in the Milky Way. We
measure the correlation between DIB strength and dust extinction for 142 DIBs
using 24 stacked spectra in the reddening range E(B-V) < 0.2, many more lines
than ever studied before. Most of the DIBs do not correlate with dust
extinction. However, we find 10 weak and barely studied DIBs with correlations
that are higher than 0.7 with dust extinction and confirm the high correlation
of additional 5 strong DIBs. Furthermore, we find a pair of DIBs, 5925.9A and
5927.5A which exhibits significant negative correlation with dust extinction,
indicating that their carrier may be depleted on dust. We use Machine Learning
algorithms to divide the DIBs to spectroscopic families based on 250 stacked
spectra. By removing the dust dependency we study how DIBs follow their local
environment. We thus obtain 6 groups of weak DIBs, 4 of which are tightly
associated with C2 or CN absorption lines.Comment: minor changes, MNRAS accepte
A Census of Large-Scale ( 10 pc), Velocity-Coherent, Dense Filaments in the Northern Galactic Plane: Automated Identification Using Minimum Spanning Tree
Large-scale gaseous filaments with length up to the order of 100 pc are on
the upper end of the filamentary hierarchy of the Galactic interstellar medium.
Their association with respect to the Galactic structure and their role in
Galactic star formation are of great interest from both observational and
theoretical point of view. Previous "by-eye" searches, combined together, have
started to uncover the Galactic distribution of large filaments, yet inherent
bias and small sample size limit conclusive statistical results to be drawn.
Here, we present (1) a new, automated method to identify large-scale
velocity-coherent dense filaments, and (2) the first statistics and the
Galactic distribution of these filaments. We use a customized minimum spanning
tree algorithm to identify filaments by connecting voxels in the
position-position-velocity space, using the Bolocam Galactic Plane Survey
spectroscopic catalog. In the range of , we
have identified 54 large-scale filaments and derived mass (), length (10-276 pc), linear mass density (54-8625 ), aspect ratio, linearity, velocity gradient, temperature,
fragmentation, Galactic location and orientation angle. The filaments
concentrate along major spiral arms. They are widely distributed across the
Galactic disk, with 50% located within 20 pc from the Galactic mid-plane
and 27% run in the center of spiral arms (aka "bones"). An order of 1% of the
molecular ISM is confined in large filaments. Massive star formation is more
favorable in large filaments compared to elsewhere. This is the first
comprehensive catalog of large filaments useful for a quantitative comparison
with spiral structures and numerical simulations.Comment: Accepted to ApJS. 20 pages (in aastex6 compact format), 6 figures, 1
table. See http://www.eso.org/~kwang/MSTpaper for (1) a preprint with full
resolution Fig 6, (2) filaments catalog (Table 1) in ASCII format, and (3) a
DS9 region file for the coordinates of the filament
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