The Galah survey: classification and diagnostics with t-SNE reduction of spectral information

Traven, G. and Matijevic, G. and Zwitter, T. and Zerjal, M. and Kos, J. and Asplund, M. and Bland-Hawthorn, J. and Casey, A. R. and de Silva, G. and Freeman, K. and Lin, J. and Martell, S. L. and Schlesinger, K. J. and Sharma, S. and Simpson, J. D. and Zucker, D. B. and Anguiano, B. and Da Costa, G. and Duong, L. and Horner, J. and Hyde, E. A. and Kafle, P. R. and Munari, U. and Nataf, D. and Navin, C. A. and Reid, W. and Ting, Y.-S. (2017) The Galah survey: classification and diagnostics with t-SNE reduction of spectral information. Astrophysical Journal, Supplement Series, 228 (2). pp. 1-19. ISSN 0067-0049

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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 which 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, 300,000 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 which 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's results. To this end we employ a recently developed dimensionality reduction technique t-SNE (t-distributed Stochastic Neighbour Embedding), which enables us to represent the complex spectral morphology in a two-dimensional projection map while still preserving the properties of the local neighbourhoods of spectra. We find that the majority (178,483) of the 209,533 Galah spectra considered in this study represents normal single stars, whereas 31,050 peculiar and problematic spectra with very diverse spectral features pertaining to 28,579 stars are distributed into 10 classification categories: Hot stars, Cool metal-poor giants, Molecular absorption bands, Binary stars, Ha\Hβ emission, Ha/Hβ emission superimposed on absorption, Ha/Hβ P-Cygni, Ha/Hβ inverted P-Cygni, Lithium absorption, and Problematic. Classified spectra with supplementary information are presented in the catalogue, indicating candidates for follow-up observations and population studies of the short-lived phases of stellar evolution.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to published version allowed due to publisher copyright policy. First place winner of the USQ Publication Excellence Award for Journal Articles published Jan-March 2017. Published version made accessible, in accordance with the copyright policy of the publisher.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 25 May 2017 02:44
Last Modified: 15 Feb 2019 05:14
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020104 Galactic Astronomy
Identification Number or DOI: 10.3847/1538-4365/228/2/24

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