skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Young Stars with SALT

Abstract

We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77 systems. All of these dwarfs are low-proper-motion southern hemisphere objects and were identified in a nearby star survey with a demonstrated sensitivity to young stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph on the South African Large Telescope, we have determined radial velocities, H-alpha, lithium 6708 Å, and potassium 7699 Å equivalent widths linked to age and activity, and spectral types for all of our targets. Combined with astrometric information from literature sources, we identify 44 young stars. Eighteen are previously known members of moving groups within 100 pc of the Sun. Twelve are new members, including one member of the TW Hydra moving group, one member of the 32 Orionis moving group, 9 members of Tucana-Horologium, one member of Argus, and two new members of AB Doradus. We also find 14 young star systems that are not members of any known groups. The remaining 33 star systems do not appear to be young. This appears to be evidence of a new population of nearby young stars not related to the known nearby young moving groups.

Authors:
 [1]; ; ;  [2];  [3]
  1. Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)
  2. Department of Astrophysics, The American Museum of Natural History, New York, NY 10024 (United States)
  3. RECONS Institute, Chambersburg, PA (United States)
Publication Date:
OSTI Identifier:
22663620
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 840; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DWARF STARS; LITHIUM; MASS; POTASSIUM; PROPER MOTION; RADIAL VELOCITY; RESOLUTION; SENSITIVITY; SOUTHERN HEMISPHERE; SPECTROSCOPY; TELESCOPES

Citation Formats

Riedel, Adric R., Alam, Munazza K., Rice, Emily L., Cruz, Kelle L., and Henry, Todd J., E-mail: arr@caltech.edu. Young Stars with SALT. United States: N. p., 2017. Web. doi:10.3847/1538-4357/840/2/87.
Riedel, Adric R., Alam, Munazza K., Rice, Emily L., Cruz, Kelle L., & Henry, Todd J., E-mail: arr@caltech.edu. Young Stars with SALT. United States. doi:10.3847/1538-4357/840/2/87.
Riedel, Adric R., Alam, Munazza K., Rice, Emily L., Cruz, Kelle L., and Henry, Todd J., E-mail: arr@caltech.edu. Wed . "Young Stars with SALT". United States. doi:10.3847/1538-4357/840/2/87.
@article{osti_22663620,
title = {Young Stars with SALT},
author = {Riedel, Adric R. and Alam, Munazza K. and Rice, Emily L. and Cruz, Kelle L. and Henry, Todd J., E-mail: arr@caltech.edu},
abstractNote = {We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77 systems. All of these dwarfs are low-proper-motion southern hemisphere objects and were identified in a nearby star survey with a demonstrated sensitivity to young stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph on the South African Large Telescope, we have determined radial velocities, H-alpha, lithium 6708 Å, and potassium 7699 Å equivalent widths linked to age and activity, and spectral types for all of our targets. Combined with astrometric information from literature sources, we identify 44 young stars. Eighteen are previously known members of moving groups within 100 pc of the Sun. Twelve are new members, including one member of the TW Hydra moving group, one member of the 32 Orionis moving group, 9 members of Tucana-Horologium, one member of Argus, and two new members of AB Doradus. We also find 14 young star systems that are not members of any known groups. The remaining 33 star systems do not appear to be young. This appears to be evidence of a new population of nearby young stars not related to the known nearby young moving groups.},
doi = {10.3847/1538-4357/840/2/87},
journal = {Astrophysical Journal},
number = 2,
volume = 840,
place = {United States},
year = {Wed May 10 00:00:00 EDT 2017},
month = {Wed May 10 00:00:00 EDT 2017}
}
  • Theoretical work suggests that a young star's angular momentum content and rotation rate may be strongly influenced by magnetic interactions with its circumstellar disk. A generic prediction of these 'disk-locking' theories is that a disk-locked star will be forced to co-rotate with the Keplerian angular velocity of the inner edge of the disk; that is, the disk's inner-truncation radius should equal its co-rotation radius. These theories have also been interpreted to suggest a gross correlation between young stars' rotation periods and the structural properties of their circumstellar disks, such that slowly rotating stars possess close-in disks that enforce the star'smore » slow rotation, whereas rapidly rotating stars possess anemic or evacuated inner disks that are unable to brake the stars and instead the stars spin up as they contract. To test these expectations, we model the spectral energy distributions (SEDs) of 33 young stars in IC 348 with known rotation periods and infrared excesses indicating the presence of circumstellar disks. For each star, we match the observed SED, typically sampling 0.6-8.0 {mu}m, to a grid of 200,000 pre-computed star+disk radiative transfer models, from which we infer the disk's inner-truncation radius. We then compare this truncation radius to the disk's co-rotation radius, calculated from the star's measured rotation period. We do not find obvious differences in the disk truncation radii of slow rotators versus rapid rotators. This holds true both at the level of whether close-in disk material is present at all, and in analyzing the precise location of the inner disk edge relative to the co-rotation radius among the subset of stars with close-in disk material. One interpretation is that disk locking is unimportant for the IC 348 stars in our sample. Alternatively, if disk locking does operate, then it must operate on both the slow and rapid rotators, potentially producing both spin-up and spin-down torques, and the transition from the disk-locked state to the disk-released state must occur more rapidly than the stellar contraction timescale.« less
  • Four color and IR observations were obtained for a large sample of G-type and K-type stars in the Bright Star Catalogue. Data are first presented for 110 evolved stars. Photometry of evolved young disk population stars have then been calibrated for luminosity, reddening, and metallicity on the basis of results for members of the Hyades and Sirius superclusters. New DDO results are given for 120 stars. 115 references.
  • The distributions in the HR diagram with theoretical time-constant loci for stars in several young clusters and superclusters are compared to demonstrate that blue stragglers in these aggregates are most frequently simply single massive (mode B) stars formed in bursts of star formation that occur at discrete intervals in time following the formation of the bulk of the low-mass (mode A) stars in the aggregate. The characteristics of the close binary systems in these aggregates are examined to show that, in several cases, mass transfer by Roche lobe overflow has or will occur and that, in some instances, the systemmore » would have appeared as a blue straggler prior to the mass-transfer event, and, in other instances, mass transfer will lead to the identification of the system as a blue straggler. Thus, it is concluded that the blue straggler phenomenon has at least two distinct physical origins: it may originate from delayed formation (starbursts) or from delayed evolution in some close binaries (mass transfer from an evolved primary). 185 references.« less