276 research outputs found
Estimating Stellar Parameters from LAMOST Low-resolution Spectra
The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has
acquired tens of millions of low-resolution spectra of stars. This paper
investigated the parameter estimation problem for these spectra. To this end,
we proposed a deep learning model StarGRU network (StarGRUNet). This network
was further applied to estimate the stellar atmospheric physical parameters and
13 elemental abundances from LAMOST low-resolution spectra. On the spectra with
signal-to-noise ratios greater than or equal to , the estimation precisions
are K and dex on and respectively,
dex to dex on [C/H], [Mg/H], [Al/H], [Si/H], [Ca/H], [Ni/H] and
[Fe/H], and dex to dex on [O/H], [S/H], [K/H], [Ti/H] and [Mn/H],
and dex and dex on [N/H] and [Cr/H] respectively. The model shows
advantages over available models and high consistency with high-resolution
surveys. We released the estimated catalog computed from about 8.21 million
low-resolution spectra in LAMOST DR8, code, trained model, and experimental
data for astronomical science exploration and data processing algorithm
research respectively.Comment: 15 pages, 12 figures, 3 tables, MNRA
Linearly Supporting Feature Extraction For Automated Estimation Of Stellar Atmospheric Parameters
We describe a scheme to extract linearly supporting (LSU) features from
stellar spectra to automatically estimate the atmospheric parameters ,
log, and [Fe/H]. "Linearly supporting" means that the atmospheric
parameters can be accurately estimated from the extracted features through a
linear model. The successive steps of the process are as follow: first,
decompose the spectrum using a wavelet packet (WP) and represent it by the
derived decomposition coefficients; second, detect representative spectral
features from the decomposition coefficients using the proposed method Least
Absolute Shrinkage and Selection Operator (LARS); third, estimate the
atmospheric parameters , log, and [Fe/H] from the detected
features using a linear regression method. One prominent characteristic of this
scheme is its ability to evaluate quantitatively the contribution of each
detected feature to the atmospheric parameter estimate and also to trace back
the physical significance of that feature. This work also shows that the
usefulness of a component depends on both wavelength and frequency. The
proposed scheme has been evaluated on both real spectra from the Sloan Digital
Sky Survey (SDSS)/SEGUE and synthetic spectra calculated from Kurucz's NEWODF
models. On real spectra, we extracted 23 features to estimate , 62
features for log, and 68 features for [Fe/H]. Test consistencies between
our estimates and those provided by the Spectroscopic Sarameter Pipeline of
SDSS show that the mean absolute errors (MAEs) are 0.0062 dex for log
(83 K for ), 0.2345 dex for log, and 0.1564 dex for [Fe/H]. For
the synthetic spectra, the MAE test accuracies are 0.0022 dex for log
(32 K for ), 0.0337 dex for log, and 0.0268 dex for [Fe/H].Comment: 21 pages, 7 figures, 8 tables, The Astrophysical Journal Supplement
Series (accepted for publication
The magnetic, electronic, and light-induced topological properties in two-dimensional hexagonal FeX2 (X = Cl, Br, I) monolayers
Topological materials are fertile ground for investigating topological phases
of matter and topological phase transitions. In particular, the quest for novel
topological phases in 2D materials is attracting fast growing attention. Here,
using Floquet-Bloch theory, we propose to realize chiral topological phases in
2D hexagonal FeX2 (X=Cl, Br, I) monolayers under irradiation of circularly
polarized light. Such 2D FeX2 monolayers are predicted to be dynamical stable,
and exhibit both ferromagnetic and semiconducting properties. To capture the
full topological physics of the magnetic semiconductor under periodic driving,
we adopt ab initio Wannier-based tight-binding methods for the Floquet-Bloch
bands, with the light-induced band gap closings and openings being obtained as
the light field strength increases. The calculations of slab with open
boundaries show the existence of chiral edge states. Interestingly, the
topological transitions with branches of chiral edge states changing from zero
to one and from one to two by tuning the light amplitude are obtained, showing
that the topological floquet phase of high Chern number can be induced in the
present Floquet-Bloch systems
- …