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Title: AN ENHANCED SPECTROSCOPIC CENSUS OF THE ORION NEBULA CLUSTER

We report new spectral types or spectral classification constraints for over 600 stars in the Orion Nebula Cluster (ONC) based on medium resolution (R ≈ 1500-2000) red optical spectra acquired using the Palomar 200'' and Kitt Peak 3.5 m telescopes. Spectral types were initially estimated for F, G, and early K stars from atomic line indices while for late K and M stars, which constitute the majority of our sample, indices involving TiO and VO bands were used. To ensure proper classification, particularly for reddened, veiled, or nebula-contaminated stars, all spectra were then visually examined for type verification or refinement. We provide an updated spectral type table that supersedes previous work, increasing the percentage of optically visible ONC stars with spectral type information from 68% to 90%. However, for many objects, repeated observations have failed to yield spectral types primarily due to the challenges of adequate sky subtraction against a bright and spatially variable nebular background. The scatter between our new and our previously determined spectral types is approximately two spectral sub-classes. We also compare our grating spectroscopy results with classification based on narrow-band TiO filter photometry, finding similar scatter. While the challenges of working in the ONC may explainmore » much of the spread, we highlight several stars showing significant and unexplained bona fide spectral variations in observations taken several years apart; these and similar cases could be due to a combination of accretion and extinction changes. Finally, nearly 20% of ONC stars exhibit obvious Ca II triplet emission indicative of strong accretion.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)
  2. Current affiliation: Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48823, USA. (United States)
  3. Current affiliation: Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian Qu, Beijing 100871 (China)
Publication Date:
OSTI Identifier:
22273348
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 146; Journal Issue: 4; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; ASTRONOMY; ASTROPHYSICS; CALCIUM IONS; CLASSIFICATION; COMPARATIVE EVALUATIONS; EMISSION SPECTRA; LIMITING VALUES; NEBULAE; PHOTOMETRY; RESOLUTION; STAR CLUSTERS; STARS; TELESCOPES; TITANIUM OXIDES; TRIPLETS; VANADIUM OXIDES