scholarly journals Providing Contexts for Classification of Transients in a Wide-Area Sky Survey: An Application of Noise-Induced Cluster Ensemble

2021 ◽  
Author(s):  
Tossapon Boongoen ◽  
Natthakan Iam-On ◽  
James Mullaney
Keyword(s):  
Wide Area ◽  
Cluster Ensemble ◽  
Sky Survey

scholarly journals A method for classification of red, blue, and green galaxies using fuzzy set theory

2020 ◽  
Vol 499 (1) ◽  
pp. L31-L35
Author(s):  
Biswajit Pandey
Keyword(s):  
Fuzzy Sets ◽  
Set Theory ◽  
Fuzzy Set ◽  
Fuzzy Set Theory ◽  
Sloan Digital Sky Survey ◽  
Sky Survey ◽  
Blue Galaxies ◽  
Boundary Sets ◽  
Red Galaxies

ABSTRACT Red and blue galaxies are traditionally classified using some specific cuts in colour or other galaxy properties, which are supported by empirical arguments. The vagueness associated with such cuts are likely to introduce a significant contamination in these samples. Fuzzy sets are vague boundary sets that can efficiently capture the classification uncertainty in the absence of any precise boundary. We propose a method for classification of galaxies according to their colours using fuzzy set theory. We use data from the Sloan Digital Sky Survey (SDSS) to construct a fuzzy set for red galaxies with its members having different degrees of ‘redness’. We show that the fuzzy sets for the blue and green galaxies can be obtained from it using different fuzzy operations. We also explore the possibility of using fuzzy relation to study the relationship between different galaxy properties and discuss its strengths and limitations.

scholarly journals The optical identification of radio sources

1959 ◽  
Vol 9 ◽  
pp. 507-513
Author(s):  
D. W. Dewhirst
Keyword(s):  
Radio Sources ◽  
Astronomy Observatory ◽  
National Geographic Society ◽  
Optical Identification ◽  
National Geographic ◽  
Extensive Search ◽  
Sky Survey ◽  
A Minor ◽  
Minor Character

Previous attempts to identify any large proportion of the discrete sources discovered at meter wavelengths have met with small success. In the investigation briefly reported here an extensive search has been made on the original plates of the 48-inch Palomar—National Geographic Society Sky Survey, using the available published radio data, but more especially the as yet unpublished results of a survey between +50 and −10 degrees declination that has been made with the interferometer of the Mullard Radio Astronomy Observatory, Cambridge. This radio survey (3C) has been carried out at 159.5 Mc/s using the aerial array of the 2C survey [1] in modified form. An account of the observation and reduction of this recent survey is given by other speakers in the Symposium. The area of sky covered by the 3C survey, and the criteria for the selection and classification of the sources, are likely to undergo small extensions and modifications before the final catalog is ready for publication, but these modifications will be of a minor character and will not alter the general conclusions of the present paper.

scholarly journals Real-Time Classification of Transient Events in Synoptic Sky Surveys

2011 ◽  
Vol 7 (S285) ◽  
pp. 355-357 ◽  
Author(s):  
Ashish A. Mahabal ◽  
C. Donalek ◽  
S. G. Djorgovski ◽  
A. J. Drake ◽  
M. J. Graham ◽  
...  
Keyword(s):  
Real Time ◽  
Automated Classification ◽  
Next Generation ◽  
Classification Techniques ◽  
Sky Surveys ◽  
Sky Survey ◽  
Transient Events ◽  
Real Time Classification

AbstractAn automated rapid classification of the transient events detected in modern synoptic sky surveys is essential for their scientific utility and effective follow-up when resources are scarce. This problem will grow by orders of magnitude with the next generation of surveys. We are exploring a variety of novel automated classification techniques, mostly Bayesian, to respond to those challenges, using the ongoing CRTS sky survey as a testbed. We describe briefly some of the methods used.

scholarly journals Spectral Classification of Optical Counterparts toROSATAll-Sky Survey X-Ray Sources

2007 ◽  
Vol 133 (6) ◽  
pp. 2495-2501 ◽  
Author(s):  
Diana Dragomir ◽  
Philippe Roy ◽  
Robert E. Rutledge
Keyword(s):  
Spectral Classification ◽  
X Ray ◽  
Sky Survey

scholarly journals Detecting neutral hydrogen at z ≳ 3 in large spectroscopic surveys of quasars

2020 ◽  
Vol 498 (2) ◽  
pp. 1951-1962
Author(s):  
Michele Fumagalli ◽  
Sotiria Fotopoulou ◽  
Laura Thomson
Keyword(s):  
Random Forest ◽  
Neutral Hydrogen ◽  
Sloan Digital Sky Survey ◽  
Broad Absorption Line ◽  
Quasar Spectra ◽  
Sky Survey ◽  
William Herschel ◽  
High Column

ABSTRACT We present a pipeline based on a random forest classifier for the identification of high column density clouds of neutral hydrogen (i.e. the Lyman limit systems, LLSs) in absorption within large spectroscopic surveys of z ≳ 3 quasars. We test the performance of this method on mock quasar spectra that reproduce the expected data quality of the Dark Energy Spectroscopic Instrument and the WHT (William Herschel Telescope) Enhanced Area Velocity Explorer surveys, finding ${\gtrsim}90{{\ \rm per\ cent}}$ completeness and purity for $N_{\rm H\,\rm{\small I}} \gtrsim 10^{17.2}~\rm cm^{-2}$ LLSs against quasars of g < 23 mag at z ≈ 3.5–3.7. After training and applying our method on 10 000 quasar spectra at z ≈ 3.5–4.0 from the Sloan Digital Sky Survey (Data Release 16), we identify ≈6600 LLSs with $N_{\rm H\,\rm{\small I}} \gtrsim 10^{17.5}~\rm cm^{-2}$ between z ≈ 3.1 and 4.0 with a completeness and purity of ${\gtrsim}90{{\ \rm per\ cent}}$ for the classification of LLSs. Using this sample, we measure a number of LLSs per unit redshift of ℓ(z) = 2.32 ± 0.08 at z = [3.3, 3.6]. We also present results on the performance of random forest for the measurement of the LLS redshifts and H i column densities, and for the identification of broad absorption line quasars.

scholarly journals A homogeneous sample of 34 000 M7−M9.5 dwarfs brighter than J = 17.5 with accurate spectral types

2019 ◽  
Vol 623 ◽  
pp. A127 ◽  
Author(s):  
S. Ahmed ◽  
S. J. Warren
Keyword(s):  
Luminosity Function ◽  
Galactic Plane ◽  
Effective Area ◽  
Sloan Digital Sky Survey ◽  
M Dwarfs ◽  
Homogeneous Sample ◽  
Type Method ◽  
Sky Survey ◽  
Better Than

The space density of late M dwarfs, subtypes M7–M9.5, is not well determined. We applied the photo-type method to iz photometry from the Sloan Digital Sky Survey and YJHK photometry from the UKIRT Infrared Deep Sky Survey, over an effective area of 3070 deg2, to produce a new, bright J(Vega) <  17.5, homogeneous sample of 33 665 M7–M9.5 dwarfs. The typical S/N of each source summed over the six bands is > 100. Classifications are provided to the nearest half spectral subtype. Through a comparison with the classifications in the BOSS Ultracool Dwarfs (BUD) spectroscopic sample, the typing is shown to be accurately calibrated to the BUD classifications and the precision is better than 0.5 subtypes rms; i.e. the photo-type classifications are as precise as good spectroscopic classifications. Sources with large χ2 >  20 include several catalogued late-type subdwarfs. The new sample of late M dwarfs is highly complete, but there is a bias in the classification of rare peculiar blue or red objects. For example, L subdwarfs are misclassified towards earlier types by approximately two spectral subtypes. We estimate that this bias affects only ∼1% of the sources. Therefore the sample is well suited to measure the luminosity function and investigate the softening towards the Galactic plane of the exponential variation of density with height.

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