A REVISED AGE FOR UPPER SCORPIUS AND THE STAR FORMATION HISTORY AMONG THE F-TYPE MEMBERS OF THE SCORPIUS–CENTAURUS OB ASSOCIATION

By M. Pecaut, Eric Mamajek, Eric Bubar. 2011

362 citations recorded by the source corpus.

We present an analysis of the ages and star formation history of the F-type stars in the Upper Scorpius (US), Upper Centaurus–Lupus (UCL), and Lower Centaurus–Crux (LCC) subgroups of Scorpius–Centaurus (Sco-Cen), the nearest OB association. Our parent sample is the kinematically selected Hipparcos sample of de Zeeuw et al., restricted to the 138 F-type members. We have obtained classification-resolution optical spectra and have also determined the spectroscopic accretion disk fraction. With Hipparcos and 2MASS photometry, we estimate the reddening and extinction for each star and place the candidate members on a theoretical H-R diagram. For each subgroup we construct empirical isochrones and compare to published evolutionary tracks. We find that (1) our empirical isochrones are consistent with the previously published age-rank of the Sco-Cen subgroups; (2) subgroups LCC and UCL appear to reach the main-sequence turn-on at spectral types ∼F4 and ∼F2, respectively. An analysis of the A-type stars shows US reaching the main sequence at about spectral type ∼A3. (3) The median ages for the pre-main-sequence members of UCL and LCC are 16 Myr and 17 Myr, respectively, in agreement with previous studies, however we find that (4) Upper Sco is much older than previously thought. The luminosities of the F-type stars in US are typically a factor of ∼2.5 less luminous than predicted for a 5 Myr old population for four sets of evolutionary tracks. We re-examine the evolutionary state and isochronal ages for the B-, A-, and G-type Upper Sco members, as well as the evolved M supergiant Antares, and estimate a revised mean age for Upper Sco of 11 ± 1 ± 2 Myr (statistical, systematic). Using radial velocities and Hipparcos parallaxes we calculate a lower limit on the kinematic expansion age for Upper Sco of >10.5 Myr (99% confidence). However, the data are statistically consistent with no expansion. We reevaluate the inferred masses for the known substellar companions in Upper Sco using the revised age and find that the inferred masses are typically ∼20%–70% higher than the original estimates which had assumed a much younger age; specifically, we estimate the mass of 1RXS J1609-2105b to be 14+2−3 MJup, suggesting that it is a brown dwarf rather than a planet. Finally, we find the fraction of F-type stars exhibiting Hα emission and/or a K-band excess consistent with accretion to be 0/17 (<19%; 95% CL) in US at ∼11 Myr, while UCL has 1/41 (2+5−1%; 68% CL) accretors and LCC has 1/50 (2+4−1%; 68% CL) accretors at ∼16 Myr and ∼17 Myr, respectively.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/042238a022aae7357fa7ef8a22708f5ec3c14c25

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In Astronomy and Astrophysics

1. Michael C. Liu
2. A. Kraus
3. K. Luhman
4. Eric Mamajek
5. B. Bowler
6. L. Hillenbrand
7. Michael J. Ireland
8. T. Dupuy

In Instrumentation

1. Michael C. Liu
2. K. Luhman
3. A. Kraus
4. Eric Mamajek
5. K. Allers
6. B. Bowler
7. T. Dupuy
8. A. Mann

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): “To estimate nuclear ages, we collect membership lists for the most massive stars from de Zeeuw et al. (1999), Mamajek et al. (2002), Rizzuto et al. (2011) and Pecaut et al. (2012).”
• Binary Population and Spectral Synthesis Version 2.1: Construction, Observational Verification, and New Results (2017, result): “For Upper Sco, the strongest constraint is given by the existence of Antares, and this fixes our mo- dels to an approximate age of 10 Myr, very similar to the 11 Myr found by Pecaut et al. (2012).”
• Protoplanetary disk lifetimes vs stellar mass and possible implications for giant planet populations (2015, background): “For example, the age of Upper Sco was recently reestimated to 11 Myr Pecaut et al. (2012) from an original 5 Myr (Preibisch & Zinnecker 1999), resulting in a noisier distribution of disk fraction as a function of age in their study.”
• Imaging Extrasolar Giant Planets (2016, background): “…star-forming regions and young moving groups in particular have been systematically adjusted to older ages over the past few years, which has propagated to the ages and masses of planets in those 10 associations (Pecaut et al. 2012; Binks & Jeffries 2014; Kraus et al. 2014b; Bell et al. 2015).”
• Pre-main-sequence isochrones - II. Revising star and planet formation time-scales (2013, background): “The Spitzer analysis of Carpenter et al. (2006) shows that Upper Sco has a disc fraction (in the same spectral type range as adopted above) of 19 ± 4 per cent, in good agreement with the disc fractions of both λ Ori and NGC 2362 (see Fig.”
• DISCOVERY OF A PROBABLE 4–5 JUPITER-MASS EXOPLANET TO HD 95086 BY DIRECT IMAGING (2013, neutral): “About the age of the association, Mamajek et al. (2002) followed by Pecaut et al. (2012) derived 17 ± 2 Myr (based on isochrone fitting) while Song et al. (2012) derived ≃ 10 Myr (by comparison with Lithium equivalent width of members of other nearby associations).”
• BANYAN. VII. A NEW POPULATION OF YOUNG SUBSTELLAR CANDIDATE MEMBERS OF NEARBY MOVING GROUPS FROM THE BASS SURVEY (2015, background): “It is also possible that the current age estimate of THA is wrong– e.g., βPMG, Upper Scorpius, AB Doradus and the Pleiades have recently been found to be slightly older than previously thought (Luhman et al. 2005; Pecaut et al. 2012; Malo et al. 2014b; Binks & Jeffries 2014; Mamajek & Bell 2014).”
• A STELLAR CENSUS OF THE TUCANA–HOROLOGIUM MOVING GROUP (2014, result): “This trend is consistent with the results of Pecaut et al. (2012), who use several other age diagnostics to determine that the Upper Scorpius subgroup of the Sco-Cen OB association might be a factor of ∼2 older (τ ∼ 11 Myr) than its traditionally accepted isochronal age for low-mass members (τ ∼ 5…”
• Long-baseline interferometric multiplicity survey of the Sco-Cen OB association (2013, methodology): “This was done using Siess isochrones (Siess et al. 2000) of age 6 Myr for US members and 16 Myr for members of UCL and LCC .”
• INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS (2013, methodology): “Spectral Classification The optical spectra were visually classified by directly comparing them with spectral standards using a custom spectral software tool, sptool3, described in Pecaut et al. (2012).”
• ACCRETION RATES FOR T TAURI STARS USING NEARLY SIMULTANEOUS ULTRAVIOLET AND OPTICAL SPECTRA (2013, background): “…old Taurus Molecular Cloud (Kenyon & Hartmann 1995), the 2–3 Myr old Chamaeleon I star forming region (Gauvin & Strom 1992), the ∼9 Myr η Chamaeleon region (Lawson et al. 2004), the 10 Myr TW Hydra Association (Webb et al. 1999), and the 16 Myr Lower Centaurus Crux subgroup (Pecaut et al. 2012).”
• SOAR TESS Survey. I. Sculpting of TESS Planetary Systems by Stellar Companions (2019, methodology): “We prepare our sample by removing stars with Teff in the TIC inconsistent with an FGK-type star (i.e., Teff>7200 and <3900 K) using the relations of Pecaut et al. (2012).”
• THE DISK POPULATION OF THE UPPER SCORPIUS ASSOCIATION (2012, background): “The combination of these data and the latest age estimate for Upper Sco (τ ∼ 11 Myr, Pecaut et al. 2012) indicate that a significant fraction of primordial disks around low-mass stars survive for at least ∼ 10 Myr.”
• ZODIACAL EXOPLANETS IN TIME (ZEIT). III. A SHORT-PERIOD PLANET ORBITING A PRE-MAIN-SEQUENCE STAR IN THE UPPER SCORPIUS OB ASSOCIATION (2016, methodology): “Our survey, Zodiacal Exoplanets in Time, includes Upper Scorpius (≃11 Myr, Pecaut et al. 2012; Rizzuto et al. 2016), Taurus (Kenyon et al. 2008, 0-5 Myr, ), Pleiades (≃125 Myr, Dahm 2015), and Praesepe and Hyades (650-800 Myr, Brandt & Huang 2015).”
• MESA ISOCHRONES AND STELLAR TRACKS (MIST). I. SOLAR-SCALED MODELS (2016, methodology): “In particular, the age of Upper Sco is quoted to be either ∼ 5 or ∼ 11 Myr depending on the analysis method and the spectral types of stars used to estimate the age (de Geus et al. 1989; Preibisch et al. 2002; Lodieu et al. 2008; Slesnick et al. 2008; Pecaut et al. 2012; Herczeg & Hillenbrand 2015).”
• THE MASS DEPENDENCE BETWEEN PROTOPLANETARY DISKS AND THEIR STELLAR HOSTS (2013, background): “There is no evidence for the latter; indeed, if anything, young clusters tend to exhibit preferentially older ages among their early-type members (e.g., see Pecaut et al. 2012).”