54 research outputs found
FacetClumps: A Facet-based Molecular Clump Detection Algorithm
A comprehensive understanding of molecular clumps is essential for
investigating star formation. We present an algorithm for molecular clump
detection, called FacetClumps. This algorithm uses a morphological approach to
extract signal regions from the original data. The Gaussian Facet model is
employed to fit the signal regions, which enhances the resistance to noise and
the stability of the algorithm in diverse overlapping areas. The introduction
of the extremum determination theorem of multivariate functions offers
theoretical guidance for automatically locating clump centers. To guarantee
that each clump is continuous, the signal regions are segmented into local
regions based on gradient, and then the local regions are clustered into the
clump centers based on connectivity and minimum distance to identify the
regional information of each clump. Experiments conducted with both simulated
and synthetic data demonstrate that FacetClumps exhibits great recall and
precision rates, small location error and flux loss, a high consistency between
the region of detected clump and that of simulated clump, and is generally
stable in various environments. Notably, the recall rate of FacetClumps in the
synthetic data, which comprises () emission line of the
MWISP within , and 5 km s 35 km s and simulated
clumps, reaches 90.2\%. Additionally, FacetClumps demonstrates satisfactory
performance when applied to observational data.Comment: 27pages,28figure
Searching for Variable Stars in the Open Cluster NGC 2355 and Its Surrounding Region
We have investigated the variable stars in the field surrounding NGC 2355
based on the time-series photometric observation data. More than 3000 CCD
frames were obtained in the V band spread over 13 nights with the Nanshan
One-meter Wide-field Telescope. We have detected 88 variable stars, containing
72 new variable stars and 16 known variable stars. By analyzing these light
curves, we classified the variable stars as follows: 26 eclipsing binaries, 52
pulsating stars, 4 rotating variables, and 6 unclear type variable stars for
which their periods are much longer than the time baseline chosen. Employing
Gaia DR2 parallax, kinematics, and photometry, the cluster membership of these
variable stars were also analyzed for NGC 2355. In addition to the 11 variable
members reported by Cantat-Gaudin et al. (2018), we identify 4 more variable
member candidates located at the outer region of NGC 2355 and showed
homogeneity in space positions and kinematic properties with the cluster
members. The main physical parameters of NGC 2355 estimated from the two-color
and color-magnitude diagrams are log(age/yr) = 8.9, E(B - V) = 0.24 mag, and
[Fe/H] = - 0.07 dex.Comment: 15 pages, 11 figures. 6 tables,Accepted for publication in A
Implications for the Explosion Mechanism of Type Ia Supernovae from their Late-time Spectra
Late-time spectra of Type Ia supernovae (SNe Ia) are important in clarifying
the physics of their explosions, as they provide key clues to the inner
structure of the exploding white dwarfs. We examined late-time optical spectra
of 36 SNe Ia, including five from our own project (SNe 2019np, 2019ein,
2021hpr, 2021wuf, and 2022hrs), with phase coverage of to
days after maximum light. At this late phase, the outer ejecta have become
transparent and the features of inner iron-group elements emerge in the
spectra. Based on multicomponent Gaussian fits and reasonable choices for the
pseudocontinuum around Ni and Fe emission features, we get reliable estimates
of the Ni to Fe ratio, which is sensitive to the explosion models of SNe Ia.
Our results show that the majority (about 67%) of our SNe Ia are more
consistent with the sub-Chandrasekhar-mass (i.e., double-detonation) model,
although they could be affected by evolutionary or ionisation effects.
Moreover, we find that the Si II 6355 velocity measured around the
time of maximum light tends to increase with the Ni to Fe ratio for the
subsample with either redshifted or blueshifted nebular velocities, suggesting
that progenitor metallicity might play an important role in accounting for the
observed velocity diversity of SNe Ia.Comment: 20 pages, 10 figures, accepted for publication in MNRA
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