New pre-main-sequence stars in the Upper Scorpius subgroup of Sco–Cen

Abstract

We present 237 new spectroscopically confirmed pre-main-sequence K and M-type stars in the young Upper Scorpius subgroup of the Sco-Cen association, the nearest region of recent massive star formation. Using the Wide-Field Spectrograph at the Australian National University 2.3 m telescope at Siding Spring, we observed 397 kinematically and photometrically selected candidate members of Upper Scorpius, and identified new members by the presence of Lithium absorption. The HR-diagram of the new members shows a spread of ages, ranging from ∼3-20 Myr, which broadly agrees with the current age estimates of ∼5-10 Myr. We find a significant range of Li 6708 equivalent widths among the members, and a minor dependence of HR-diagram position on the measured equivalent width of the Li 6708Å line, with members that appear younger having more Lithium. This could indicate the presence of either populations of different age, or a spread of ages in Upper Scorpius. We also use Wide-Field Infrared Survey Explorer data to infer circumstellar disk presence in 25 of the members on the basis of infrared excesses, including two candidate transition disks. We find that 11.2±3.4% of the M0-M2 spectral type (0.4-0.8 M ) Upper Sco stars display an excess that indicates the presence of a gaseous disk.

M Dwarf Rotation from the K2 Young Clusters to the Field. I. A Mass–Rotation Correlation at 10 Myr

“…The Gaussian mean and σ for all stars (blue) are given in the top left. The 0.32mag spread of the Gaussian reflects the quadrature sum of our errors and the 0.2mag errors from Rizzuto et al (2015), suggesting an uncertainty of ∼0.25mag for our derived A V s. Black and red histograms show the hotter and cooler distributions, respectively, demonstrating that the most deviant outliers are indeed hot stars. simplicity, and A V =0 is set as a lower bound.…”

“…Stars redder than V K 3.7 -= (∼0.8 M  ) agree well, but bluer stars do not. Center: comparison between our A V s and those from Rizzuto et al (2015). The values correlate with one another, with a spread of 0.1-0.3mag around the one-toone line.…”

“…The values correlate with one another, with a spread of 0.1-0.3mag around the one-toone line. Right: histogram of the difference between our A V s and those from Rizzuto et al (2015). The Gaussian mean and σ for all stars (blue) are given in the top left.…”

“…We also compare in the center panel our A V s to those from Rizzuto et al (2015), who matched extinguished spectral templates to optical spectra of Upper Sco members. It is evident that the values correlate with one another, but there exists a spread of a few tenths of a mag around the one-to-one line.…”

The Greater Taurus–Auriga Ecosystem. I. There is a Distributed Older Population

“…We compared each observed spectrum to a sequence of field dwarfs (Pickles 1998;Bochanski et al 2007) that we artificially reddened using an R V =3.1 reddening law (Savage & Mathis 1979), selecting the best-fit model. We describe this process in more detail in Rizzuto et al (2015) and Kraus et al (2015), where it was applied to members of the Upper Scorpius OB association. References.…”