- ID:
- ivo://CDS.VizieR/J/ApJ/887/134
- Title:
- Classification of Fermi blazar cand. from the 4FGL
- Short Name:
- J/ApJ/887/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recently published fourth Fermi Large Area Telescope source catalog (4FGL) reports 5065 gamma-ray sources in terms of direct observational gamma-ray properties. Among the sources, the largest population is the active galactic nuclei (AGNs), which consists of 3137 blazars, 42 radio galaxies, and 28 other AGNs. The blazar sample comprises 694 flat-spectrum radio quasars (FSRQs), 1131 BL Lac-type objects (BL Lacs), and 1312 blazar candidates of an unknown type (BCUs). The classification of blazars is difficult using optical spectroscopy given the limited knowledge with respect to their intrinsic properties, and the limited availability of astronomical observations. To overcome these challenges, machine-learning algorithms are being investigated as alternative approaches. Using the 4FGL catalog, a sample of 3137 Fermi blazars with 23 parameters is systematically selected. Three established supervised machine-learning algorithms (random forests (RFs), support vector machines (SVMs), artificial neural networks (ANNs)) are employed to general predictive models to classify the BCUs. We analyze the results for all of the different combinations of parameters. Interestingly, a previously reported trend the use of more parameters leading to higher accuracy is not found. Considering the least number of parameters used, combinations of eight, 12 or 10 parameters in the SVM, ANN, or RF generated models achieve the highest accuracy (Accuracy ~91.8%, or ~92.9%). Using the combined classification results from the optimal combinations of parameters, 724 BL Lac type candidates and 332 FSRQ type candidates are predicted; however, 256 remain without a clear prediction.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/427/2917
- Title:
- Classification of Hipparcos variables
- Short Name:
- J/MNRAS/427/2917
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hipparcos catalogue (ESA 1997, Cat. I/239) and the AAVSO Variable Star Index (Watson et al., 2011, Cat. B/vsx) are employed to complement the training set of periodic variables of Dubath et al. (2011, Cat. J/MNRAS/414/2602) with irregular and non-periodic representatives, leading to 3881 sources in total which described 24 variability types. The attributes employed to characterize light-curve features are selected according to their relevance for classification. Classifier models are produced with random forests and a multi-stage methodology based on Bayesian networks, achieving overall misclassification rates under 12%. Both classifiers are applied to predict variability types for 6051 Hipparcos variables associated with uncertain or missing types in the literature.
- ID:
- ivo://CDS.VizieR/J/ApJS/112/557
- Title:
- Classification of IRAS Sources
- Short Name:
- J/ApJS/112/557
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- IRAS low-resolution spectra were extracted for 11,224 IRAS sources. These spectra were classified into astrophysical classes, based on the presence of emission and absorption features and on the shape of the continuum. Counterparts of these IRAS sources in existing optical and infrared catalogs are identified, and their optical spectral types are listed if they are known. The correlations between the photospheric/ optical and circumstellar/infrared classifications are discussed.
- ID:
- ivo://CDS.VizieR/J/ApJ/646/161
- Title:
- Classification of IR galaxies
- Short Name:
- J/ApJ/646/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mid-infrared diagnostics are presented for a large portion of the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample plus archival data from ISO and Spitzer. The SINGS data set includes low- and high-resolution spectral maps and broadband imaging in the infrared for over 160 nuclear and extranuclear regions within 75 nearby galaxies spanning a wide range of morphologies, metallicities, luminosities, and star formation rates. Our main result is that these mid-infrared diagnostics effectively constrain a targets dominant power source. The combination of a high-ionization line index and PAH strength serves as an efficient discriminant between AGNs and star-forming nuclei, confirming progress made with ISO spectroscopy on starbursting and ultraluminous infrared galaxies. The sensitivity of Spitzer allows us to probe fainter nuclear and star-forming regions within galaxy disks.
- ID:
- ivo://CDS.VizieR/J/MNRAS/451/3504
- Title:
- Classification of IRS sources in the SMC
- Short Name:
- J/MNRAS/451/3504
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Magellanic clouds are uniquely placed to study the stellar contribution to dust emission. Individual stars can be resolved in these systems even in the mid-infrared, and they are close enough to allow detection of infrared excess caused by dust. We have searched the Spitzer Space Telescope data archive for all Infrared Spectrograph (IRS) staring-mode observations of the Small Magellanic Cloud (SMC) and found that 209 Infrared Array Camera (IRAC) point sources within the footprint of the Surveying the Agents of Galaxy Evolution in the Small Magellanic Cloud (SAGE-SMC) Spitzer Legacy programme were targeted, within a total of 311 staring mode observations. We classify these point sources using a decision tree method of object classification, based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information. We find 58 asymptotic giant branch (AGB) stars, 51 young stellar objects (YSOs), 4 post-AGB objects, 22 Red Supergiants (RSGs), 27 stars (of which 23 are dusty OB stars), 24 planetary nebulae (PNe), 10 Wolf-Rayet (WR) stars, 3 HII regions, 3 R Coronae Borealis (R CrB) stars, 1 Blue Supergiant and 6 other objects, including 2 foreground AGB stars. We use these classifications to evaluate the success of photometric classification methods reported in the literature.
- ID:
- ivo://CDS.VizieR/J/MNRAS/474/1873
- Title:
- Classification of LAMOST DR4 galaxies
- Short Name:
- J/MNRAS/474/1873
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the classification and composite spectra of galaxies in the fourth data release (DR4) of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST). We select 40182 spectra of galaxies from LAMOST DR4, which have photometric information but no spectroscopic observations in the Sloan Digital Sky Survey (SDSS). These newly observed spectra are recalibrated and classified into six classes - passive, H{alpha}-weak, star-forming, composite, LINER and Seyfert - using the line intensity (H{beta}, [OIII] 5007, H{alpha} and [NII] 6585). We also study the correlation between spectral class and morphological type through three parameters: concentration index, (u-r) colour and D4000n index. We calculate composite spectra of high signal-to-noise ratio (S/N) for six spectral classes and, using these composites, we pick out some features that can differentiate the classes effectively, including H{beta}, Fe5015, H{gamma}A, HK and the Mg2 band. In addition, we compare our composite spectra with the SDSS ones and analyse their differences. A galaxy catalogue of 40182 newly observed spectra (36601 targets) and the composite spectra of the six classes are available online (http://sciwiki.lamost.org/downloads/wll).
- ID:
- ivo://CDS.VizieR/J/MNRAS/286/500
- Title:
- Classification of Late Type Stars
- Short Name:
- J/MNRAS/286/500
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Energy distributions for 33 galactic (super)giants situated mostly in the southern Milky Way in the range from 4800 to 7700 Angstroems with an effective resolution of 10 Angstroems are presented here. The observations and reductions are described in the paper. The errors of the absolute and relative flux calibration are 0.028 and 0.021 mag, respectively. The S/N ratio is at least 80 for each star. Cross references, MK classifications and spectral indices one may find in the paper. Further informations are available at M.O.Oestreicher (mio@astro.ruhr-uni-bochum.de). The data are given in three files: 1) stars.dat A list of the programme stars listing the HD/HDE numbers, MK types and positions related to J2000 2) absolute.dat A list of absolute fluxes for each star observed under photometric conditions (18 stars). The fluxes are given in magnitudes according to the system of Hayes & Latham (1975). A monochromatic magnitude of 0.00 corresponds to a flux of 3.5x10^-20^ erg.cm-2.s-1.Hz-1, (3.5x10^-23^ W/m2/Hz), i.e. the fluxes are related to FREQUENCY INTERVALS. 3) relative.dat A list of relative fluxes for each star observed in nights of low quality (15 stars). The fluxes are normalized to 1 at 5555 Angstr. and are related to WAVELENGTH INTERVALS.
- ID:
- ivo://CDS.VizieR/J/ApJS/147/1
- Title:
- Classification of nearby galaxies
- Short Name:
- J/ApJS/147/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A major problem in extragalactic astronomy is the inability to distinguish in a robust, physical, and model-independent way how galaxy populations are physically related to each other and to their formation histories. A similar, but distinct, and also long-standing question is whether the structural appearances of galaxies, as seen through their stellar light distributions, contain enough physical information to offer this classification. We argue through the use of 240 images of nearby galaxies that three model-independent parameters measured on a single galaxy image reveal its major ongoing and past formation modes and can be used as a robust classification system. These parameters quantitatively measure: the concentration (C), asymmetry (A), and clumpiness (S) of a galaxy's stellar light distribution. When combined into a three-dimensional "CAS" volume all major classes of galaxies in various phases of evolution are cleanly distinguished. We argue that these three parameters correlate with important modes of galaxy evolution: star formation and major merging activity. This is argued through the strong correlation of H{alpha} equivalent width and broadband colors with the clumpiness parameter S, the uniquely large asymmetries of 66 galaxies undergoing mergers, and the correlation of bulge to total light ratios, and stellar masses, with the concentration index. As an obvious goal is to use this system at high redshifts to trace evolution, we demonstrate that these parameters can be measured, within a reasonable and quantifiable uncertainty with available data out to z~3 using the Hubble Space Telescope GOODS ACS and Hubble Deep Field images.
- ID:
- ivo://CDS.VizieR/J/AJ/140/34
- Title:
- Classification of nova light curves
- Short Name:
- J/AJ/140/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 93 very-well-observed nova light curves. The light curves were constructed from 229,796 individual measured magnitudes, with the median coverage extending to 8.0mag below peak and 26% of the light curves following the eruption all the way to quiescence. Our time-binned light curves are presented in figures and as complete tabulations. We also calculate and tabulate many properties about the light curves, including peak magnitudes and dates, times to decline by 2, 3, 6, and 9mag from maximum, the time until the brightness returns to quiescence, the quiescent magnitude, power-law indices of the decline rates throughout the eruption, the break times in this decline, plus many more properties specific to each nova class. We present a classification system for nova light curves based on the shape and the time to decline by 3mag from the peak (t3). The designations are "S" for smooth light curves (38% of the novae), "P" for plateaus (21%), "D" for dust dips (18%), "C" for cusp-shaped secondary maxima (1%), "O" for quasi-sinusoidal oscillations superposed on an otherwise smooth decline (4%), "F" for flat-topped light curves (2%), and "J" for jitters or flares superposed on the decline (16%). Our classification consists of this single letter followed by the t3 value in parentheses; so, for example, V1500 Cyg is S(4), GK Per is O(13), DQ Her is D(100), and U Sco is P(3).
- ID:
- ivo://CDS.VizieR/J/A+A/475/217
- Title:
- Classification of planetary nebulae
- Short Name:
- J/A+A/475/217
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we present a re-analysis of the criteria used to characterize the Peimbert classes I, IIa, IIb, III and IV, through a statistical study of a large sample of planetary nebulae previously classified according to these groups. In the original classification, it is usual to find planetary nebulae that cannot be associated with a single type; these most likely have dubious classifications into two or three types. Statistical methods can greatly contribute in providing a better characterization of planetary nebulae groups. We use the Bayes Theorem to calculate the posterior probabilities for an object to be member of each of the types I, IIa, IIb, III and IV. This calculation is particularly important for planetary nebulae that are ambiguously classified in the traditional method. The posterior probabilities are defined from the probability density function of classificatory parameters of a well-defined sample, composed only by planetary nebulae unambiguously fitted into the Peimbert types. Because the probabilities depend on the available observational data, they are conditional probabilities, and, as new observational data are added to the sample, the classification of the nebula can be improved, to take into account this new information. This method differs from the original classificatory scheme, because it provides a quantitative result of the representativity of the object within its group. Also, through the use of marginal distributions it is possible to extend the Peimbert classification even to those objects for which only a few classificatory parameters are known.
