Cited by 310Astrophysics and Star Formation StudiesStellar, planetary, and galactic studiesAstronomy and Astrophysical Research

Post–T Tauri Stars in the Nearest OB Association

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Mamajek, Eric E., Meyer, Michael R., Liebert, James·2002·The Astronomical Journal

Abstract

We present results of a spectroscopic survey of X-ray– and proper-motion–selected samples of late-type stars in the Lower Centaurus–Crux (LCC) and Upper Centaurus–Lupus (UCL) subgroups of the nearest OB association: Scorpius-Centaurus. The primary goals of the survey are to determine the star formation history of the OB subgroups and to assess the frequency of accreting stars in a sample dominated by "post–T Tauri" pre–main-sequence (PMS) stars. We investigate two samples: (1) proper-motion candidates from the ACT Catalog and Tycho Reference Catalog (TRC) with X-ray counterparts in the ROSAT All-Sky Survey (RASS) Bright Source Catalog and (2) G- and K-type stars in the Hipparcos catalog found to be candidate members by de Zeeuw et al. We obtained optical spectra of 130 candidates with the Siding Spring 2.3 m dual-beam spectrograph. PMS stars were identified by (1) strong Li λ6707 absorption, (2) subgiant surface gravities, (3) proper motions consistent with Sco-Cen membership, and (4) H-R diagram positions consistent with being PMS. We find 93% of the RASS-ACT/TRC stars to be probable PMS members, compared with 73% of the Hipparcos candidates. We demonstrate that measuring the gravity-sensitive band ratio of Sr II λ4077 to Fe I λ4071 is a valuable means of discriminating PMS and zero-age main-sequence (ZAMS) stars. Using secular parallaxes and Hipparcos , Tycho-2, and Two Micron All Sky Survey photometry, we construct an H-R diagram. Depending on the choice of published evolutionary tracks, we find the mean ages of the PMS populations to range between 17 and 23 Myr for LCC and 15 and 22 Myr for UCL. Taking into account observational errors, it appears that 95% of the low-mass star formation in each subgroup must have occurred in less than 8 Myr (LCC) and 12 Myr (UCL). Using the Bertelli et al. tracks, we find main-sequence turnoff ages for Hipparcos B-type members to be 16 ± 1 Myr for LCC and 17 ± 1 Myr for UCL. Contrary to previous findings, it appears that LCC is coeval with, or slightly older than, UCL. The secular parallaxes of the Sco-Cen PMS stars yield distances of 85–215 pc, with 12 of the LCC members lying within 100 pc of the Sun. Only one out of 110 (0.9 %; 1 σ) PMS solar-type stars in the sample with ages of 13 ± 1 (s.e.) ± 6 (1 σ) Myr and masses of 1.3 ± 0.2 (1 σ) M ⊙ shows both enhanced Hα emission and a K -band excess indicative of accretion from a truncated circumstellar disk: the nearby ( d ≃ 86 pc) classical T Tauri star PDS 66.

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  1. [9]9. Blaauw, A. 1946, Ph.D. thesis, Groningen Univ.
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Authors
Mamajek, E. E., Meyer, M. R., & Liebert, J.
Affiliations
University of Arizona (US)
Venue
The Astronomical Journal
Published
2002-09
Volume
124
Issue
3
Pages
1670-1694
ISSN
  • 0004-6256 (ISSN-L)
  • 1538-3881
OpenAlex
W2016878712
Cited by
310
References
74
Citations by year
2026: 5 · 2025: 12 · 2024: 10 · 2023: 9 · 2022: 5 · 2021: 13 · 2020: 20 · 2019: 11 · 2018: 15 · 2017: 10 · 2016: 15 · 2015: 12 · 2014: 17 · 2013: 17 · 2012: 11
FWCI
8.02
Type
journal article
Language
en
Open access
Locations
  • The Astronomical Journal (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • National Science Foundation
  • National Aeronautics and Space Administration
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysics and Star Formation Studies
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
  • Physical Sciences › Physics and Astronomy › Instrumentation › Astronomy and Astrophysical Research
Keywords
post-T Tauri stars, pre-main-sequence stars, Scorpius-Centaurus OB association, star formation history, accretion, lithium absorption, stellar ages, X-ray sources, low-mass star formation

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