Post-T Tauri Stars in the Nearest OB Association

By Eric Mamajek, M. Meyer, J. Liebert. 2002

233 citations recorded by the source corpus.

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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/30fce1ce0f1048bc39ba98a01037605839457dc0

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In Astronomy and Astrophysics

1. Eric Mamajek
2. K. Luhman
3. N. Evans II
4. L. Hillenbrand
5. M. Pecaut
6. P. Myers
7. B. Bowler
8. C. Bell

Citations in the corpus

• The star formation history and accretion-disc fraction among the K-type members of the Scorpius–Centaurus OB association (2016, methodology): “In addition, we reanalyzed the low resolution spectra from the Mamajek et al. (2002) study.”
• NEW DEBRIS DISKS AROUND YOUNG, LOW-MASS STARS DISCOVERED WITH THE SPITZER SPACE TELESCOPE (2009, unknown): “We obtain photo-electric optical UBVRcIc photometry from the literature, with B and V magnitudes primarily from the Tycho catalog, transformed to the Johnson photometric system using the corrected relations in Mamajek et al. (2006, 2002).”
• The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs (2005, background): “Finally, the BM03 ‘‘Upper Sco’’ sample includes sources in the Sco-Cen UCL+LLC subgroups as well; since the latter are expected to be significantly older than the Upper Sco region alone (Mamajek et al. 2002), they are unsuitable for inclusion in our age analysis here.”
• Young Stars Near the Sun (2004, methodology): “The age of LCC is thought to be 10–15 Myr (de Geus et al. 1989), but use of different methods results in a somewhat older age (15–25 Myr; Mamajek et al. 2002).”
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics (2008, methodology): “…pc and presumed to have no reddening, (10) Gray et al. (2006), (11) Henry et al. (1996), (12) Soderblom et al. (1998), (13) Wichmann et al. (1997), (14) Mamajek et al. (2002), (15) Nordström et al. (2004), (16) Prosser (1992), (17) Crawford & Barnes (1974), (18) Messina (2001), (19) Mermilliod…”
• A REVISED AGE FOR UPPER SCORPIUS AND THE STAR FORMATION HISTORY AMONG THE F-TYPE MEMBERS OF THE SCORPIUS–CENTAURUS OB ASSOCIATION (2011, methodology): “For UCL and LCC our age spreads are larger than that found in Mamajek et al. (2002), who found that 68% of the star formation had occurred within 4–6 Myr for UCL and LCC. 5.2.”
• A CHARA ARRAY SURVEY OF CIRCUMSTELLAR DISKS AROUND NEARBY Be-TYPE STARS (2013, methodology): “The magnitude difference of A,B was determined in the Tycho system by Fabricius & Makarov (2000), and we converted this to a Johnson △V = 1.46 ± 0.02 mag using the formulae from Mamajek et al. (2002).”
• THE PALOMAR/KECK ADAPTIVE OPTICS SURVEY OF YOUNG SOLAR ANALOGS: EVIDENCE FOR A UNIVERSAL COMPANION MASS FUNCTION (2008, methodology): “For stars belonging to the Upper Scorpius association we adopted 145 ± 40 pc (de Zeeuw et al. 1999; Mamajek et al. 2002).”
• An Empirical Criterion to Classify T Tauri Stars and Substellar Analogs Using Low-Resolution Optical Spectroscopy (2003, unknown): “They were selected from Natta & Testi (2001), Natta et al. (2002), Testi et al. (2002), Comerón et al. (1998), and Jayawardhana et al. (2002b, 2003b).”
• On the age of the β Pictoris moving group (2014, methodology): “The mean LCC and UCL ages estimated by Mamajek et al. (2002) and Pecaut et al. (2012) are consistent with the Li depletion pattern observed by Song et al. (2012) if indeed BPMG is ∼ 23 Myr and TWA is ∼ 8 − 10 Myr (Weinberger et al. 2013; Ducourant et al. 2014).”
• The primordial binary population. I. A near-infrared adaptive optics search for close visual companions to A star members of Scorpius OB2 (2004, unknown): “:3) for US, UCL, and LCC, respectively.”
• INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS (2013, methodology): “V with the conversions of Mamajek et al. (2002, 2006), resorting to the conversions in Høg et al. (2000) when BT − VT > 2.0.”
• A Moving Cluster Distance to the Exoplanet 2M1207b in the TW Hydrae Association (2005, background): “There have been suggestions that some TWA stars may actually be background members of the ∼16-Myr-old Lower Centaurus-Crux (LCC) OB subgroup at d ≃ 110 pc (e.g. Mamajek & Feigelson 2001; Mamajek et al. 2002).”