J/ApJS/228/24 GALAH semi-automated classification scheme (Traven+, 2017)
The GALAH survey: classification and diagnostics with t-SNE reduction of spectral information. Traven G., Matijevic G., Zwitter T., Zerjal M., Kos J., Asplund M., Bland-Hawthorn J., Casey A.R., De Silva G., Freeman K., Lin J., Martell S.L., Schlesinger K.J., Sharma S., Simpson J.D., Zucker D.B., Anguiano B., Da Costa G., Duong L., Horner J., Hyde E.A., Kafle P.R., Munari U., Nataf D., Navin C.A., Reid W., Ting Y.-S. <Astrophys. J. Suppl. Ser., 228, 24-24 (2017)> =2017ApJS..228...24T (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Milky Way ; Stars, bright Keywords: binaries: general; catalogs; methods: data analysis; stars: activity; stars: peculiar; surveys Abstract: Galah is an ongoing high-resolution spectroscopic survey with the goal of disentangling the formation history of the Milky Way using the fossil remnants of disrupted star formation sites that are now dispersed around the Galaxy. It is targeting a randomly selected magnitude-limited (V≤14) sample of stars, with the goal of observing one million objects. To date, 300000 spectra have been obtained. Not all of them are correctly processed by parameter estimation pipelines, and we need to know about them. We present a semi-automated classification scheme that identifies different types of peculiar spectral morphologies in an effort to discover and flag potentially problematic spectra and thus help to preserve the integrity of the survey results. To this end, we employ the recently developed dimensionality reduction technique t-SNE (t-distributed stochastic neighbor embedding), which enables us to represent the complex spectral morphology in a two-dimensional projection map while still preserving the properties of the local neighborhoods of spectra. We find that the majority (178483) of the 209533 Galah spectra considered in this study represents normal single stars, whereas 31050 peculiar and problematic spectra with very diverse spectral features pertaining to 28579 stars are distributed into 10 classification categories: hot stars, cool metal-poor giants, molecular absorption bands, binary stars, Hα/Hβ emission, Hα/Hβ emission superimposed on absorption, Hα/Hβ P-Cygni, Hα/Hβ inverted P-Cygni, lithium absorption, and problematic. Classified spectra with supplementary information are presented in the catalog, indicating candidates for follow-up observations and population studies of the short-lived phases of stellar evolution. Description: The GALactic Archaeology with HERMES (GALAH) survey was the main driver for the construction of Hermes (High Efficiency and Resolution Multi-Element Spectrograph), a fiber-fed multi-object spectrograph on the 3.9m Anglo-Australian Telescope. Its spectral resolving power (R) is about 28000, and there is also an R=45000 mode using a slit mask. Hermes has four simultaneous non-contiguous spectral arms centered at 4800, 5761, 6610, and 7740Å, covering about 1000Å in total, including Hα and Hβ lines. About 300000 spectra have been taken to date, including various calibration exposures. However, we concentrate on ∼210000 spectra recorded before 2016 January 30. We devise a custom classification procedure which is based on two independently developed methods, the novel dimensionality reduction technique t-SNE (t-distributed stochastic neighbor embedding; van der Maaten & Hinton 2008, Journal of Machine Learning Research 9, 2579) and the renowned clustering algorithm DBSCAN (Ester+ 1996, Proc. 2nd Int. Conf. on KDD, 226 ed. E. Simoudis, J. Han, and U. Fayyad). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 163 73 *Classification categories based on the general projection map table3.dat 163 39 *Classification categories based on the specific projection map produced in the search for young/active stars table4.dat 435 12210 Catalog containing results of our classification refs.dat 217 464 References listed in column "ADS" of table 4; column converted in table by CDS
Note on table1.dat: This table lists six distinct categories that were defined using the classification procedure. This classification is not strictly limited to peculiar objects that have spectra without a counterpart in the library of synthetic spectra, although they remain the principal motivation for this work. It is instead a search for any coherent group in the projection map, from which a category of interest can be selected. See section 4 for further explanations. Note on table3.dat: We also present additional classification results based on a more specific projection map, in contrast to the general map presented in Section 4. These results follow the same procedure, but with different t-SNE input parameters and input spectral ranges. See section 5 for further explanations.
See also: B/wds : The Washington Visual Double Star Catalog (Mason+ 2001-2014) B/sb9 : 9th Catalogue of Spectroscopic Binary Orbits (Pourbaix+ 2004-2014) I/337 : Gaia DR1 (Gaia Collaboration, 2016) V/146 : LAMOST DR1 catalogs (Luo+, 2015) II/328 : AllWISE Data Release (Cutri+ 2013) II/312 : GALEX-DR5 (GR5) sources from AIS and MIS (Bianchi+ 2011) J/MNRAS/465/3203 : GALAH observational overview (Martell+, 2017) J/A+A/581/A52 : Gaia-ESO Survey: Hα emission stars (Traven+, 2015) J/ApJ/808/16 : The Cannon: new approach to determine abundances (Ness+, 2015) J/AcA/63/21 : VI light curves of Galactic LPVs (Soszynski+, 2013) J/AJ/140/184 : RAVE double-lined spectroscopic binaries (Matijevic+, 2010) http://galah-survey.org/ : GALAH home page Byte-by-byte Description of file: table.dat
Bytes Format Units Label Explanations
1- 48 A48 --- Cat Classification category (1) 50- 53 I4 --- o_Cat [18/4130] Number of sources in Cat 55-103 A49 --- MType SIMBAD main source type (2) 105-107 I3 --- o_MType [0/371] Number of sources in MType 109-157 A49 --- OType SIMBAD other source type (2) 159-163 I5 --- o_OType [0/1486] Number of sources in OType
Note (1): Catalog excludes the results for spectra from the Problematic category, since these mainly stand out for data reduction reasons and will be recoverable in the upgraded versions of the reduction pipeline. Note (2): SIMBAD defines a main type for each astronomical object in its database, and usually several other types generally inferred from its identifiers. For these columns the less interesting type "Star" is excluded.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 5 I5 --- Seq [0/12209] Internal catalog index number (1) 7- 13 I7 --- GALAH [0/9520722] GALAH unique identifier 15- 27 F13.7 d MJD Modified Julian Date of observation 29- 44 F16.12 deg RAdeg Right Ascension in decimal degrees (J2000) 46- 63 F18.14 deg DEdeg Declination in decimal degrees (J2000) 65- 86 A22 --- GClass General classification category (see table 1) 88-135 A48 --- SClass Specific classification category (see table 3) 137-164 A28 --- Simbad SIMBAD identifier for 3289 sources 166-173 F8.6 arcsec Sep [0/1]? Angular distance from Galah target to SIMBAD source 175-223 A49 --- MType Main SIMBAD type 225-382 A158 --- OType Other SIMBAD type 384 I1 --- nRad [0/1] Number of VizieR tables for radio range 386-387 I2 --- nIR [0/31] Number of VizieR tables for IR range 391-392 I2 --- nOpt [0/61] Number of VizieR tables for optical range 396 I1 --- nUV [0/2] Number of VizieR tables for UV range 401 I1 --- nEUV  Number of VizieR tables for EUV range 406-407 I2 --- nXRay [0/19] Number of VizieR tables for X-ray range 411 I1 --- nGam  Number of VizieR tables for Gamma-ray range 416-435 A20 --- OClass OGLE variable star type/class
Note (1): Catalog excludes the results for spectra from the Problematic category, since these mainly stand out for data reduction reasons and will be recoverable in the upgraded versions of the reduction pipeline.
Byte-by-byte Description of file: refs.dat
Bytes Format Units Label Explanations
1- 5 I5 --- Seq [144/12188] Internal catalog index number 7- 25 A19 --- BibCode ADS bibcode 27-217 A191 --- Title Title of the reference
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-Apr-2017
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