86 research outputs found
Age spreads and the temperature dependence of age estimates in Upper Sco
Past estimates for the age of the Upper Sco Association are typically 11-13
Myr for intermediate-mass stars and 4-5 Myr for low-mass stars. In this study,
we simulate populations of young stars to investigate whether this apparent
dependence of estimated age on spectral type may be explained by the star
formation history of the association. Solar and intermediate mass stars begin
their pre-main sequence evolution on the Hayashi track, with fully convective
interiors and cool photospheres. Intermediate mass stars quickly heat up and
transition onto the radiative Henyey track. As a consequence, for clusters in
which star formation occurs on a similar timescale as the transition from a
convective to a radiative interior, discrepancies in ages will arise when ages
are calculated as a function of temperature instead of mass. Simple simulations
of a cluster with constant star formation over several Myr may explain about
half of the difference in inferred ages versus photospheric temperature;
speculative constructions that consist of a constant star formation followed by
a large supernova-driven burst could fully explain the differences, including
those between F and G stars where evolutionary tracks may be more accurate. The
age spreads of low-mass stars predicted from these prescriptions for star
formation are consistent with the observed luminosity spread of Upper Sco. The
conclusion that a lengthy star formation history will yield a temperature
dependence in ages is expected from the basic physics of pre-main sequence
evolution and is qualitatively robust to the large uncertainties in pre-main
sequence evolutionary models.Comment: 13 pages, accepted by Ap
SPYGLASS. IV. New Stellar Survey of Recent Star Formation within 1 kpc
Young stellar populations provide a powerful record that traces millions of
years of star formation history in the solar neighborhood. Using a revised form
of the SPYGLASS young star identification methodology, we produce an expanded
census of nearby young stars (Age Myr). We then use the HDBSCAN
clustering algorithm to produce a new SPYGLASS Catalog of Young Associations
(SCYA), which reveals 116 young associations within 1 kpc. More than 25\% of
these groups are largely new discoveries, as 20 are substantively different
from any previous definition, and 10 have no equivalent in the literature. The
new associations reveal a yet undiscovered demographic of small associations
with little connection to larger structures. Some of the groups we identify are
especially unique for their high transverse velocities, which can differ from
the solar velocity by 30-50 km s, and for their positions, which can
reach up to 300 pc above the galactic plane. These features may suggest a
unique origin, matching existing evidence of infalling gas parcels interacting
with the disk ISM. Our clustering also suggests links between often-separated
populations, hinting to direct structural connections between Orion Complex and
Perseus OB2, and between the subregions of Vela. The 30 Myr old
Cepheus-Hercules association is another emerging large-scale structure, with a
size and population comparable to Sco-Cen. Cep-Her and other similarly-aged
structures are also found clustered along extended structures perpendicular to
known spiral arm structure, suggesting that arm-aligned star formation patterns
have only recently become dominant in the solar neighborhood.Comment: Accepted to ApJ. 34 Pages, 14 Figures, 4 Tables in AASTEX63 format.
Online-only catalog files and interactive figures are available in the
ancillary dat
WISE circumstellar discs in the young Sco-Cen association
We present an analysis of the WISE photometric data for 829 stars in the Sco-Cen OB2 association, using thelatest high-mass membership probabilities. We detect infrared excesses associated with 135 BAF-type stars, 99 ofwhich are secure Sco-Cen members. There is a clear increase in excess fraction with membership probability, which can be fitted linearly.We infer that 41 ± 5 per cent of Sco-Cen OB2 BAF stars have excesses, while the field star excess fraction is consistent with zero. This is the first time that the probability of non-membership has been used in the calculation of excess fractions for young stars. We do not observe any significant change in excess fraction between the three subgroups.Within our sample, we have observed that B-type association members have a significantly smaller excess fraction than Aand F-type association members
The Mass-Radius Relation Of Young Stars. I. Usco 5, An M4.5 Eclipsing Binary In Upper Scorpius Observed By K2
We present the discovery that UScoCTIO 5, a known spectroscopic binary in the Upper Scorpius star-forming region (P = 34 days, M-tot sin(i) = 0.64M(circle dot)), is an eclipsing system with both primary and secondary eclipses apparent in K2 light curves obtained during Campaign 2. We have simultaneously fit the eclipse profiles from the K2 light curves and the existing RV data to demonstrate that UScoCTIO 5 consists of a pair of nearly identical M4.5 stars with M-A = 0.329 +/- 0.002 M-circle dot, R-A = 0.834 +/- 0.006 R-circle dot, M-B = 0.317 +/- 0.002 M-circle dot, and R-B = 0.810 +/- 0.006 R-circle dot. The radii are broadly consistent with pre-main-sequence ages predicted by stellar evolutionary models, but none agree to within the uncertainties. All models predict systematically incorrect masses at the 25%-50% level for the HR diagram position of these mid-M dwarfs, suggesting significant modifications to mass-dependent outcomes of star and planet formation. The form of the discrepancy for most model sets is not that they predict luminosities that are too low, but rather that they predict temperatures that are too high, suggesting that the models do not fully encompass the physics of energy transport (via convection and/or missing opacities) and/or a miscalibration of the SpT-T-eff scale. The simplest modification to the models (changing T-eff to match observations) would yield an older age for this system, in line with the recently proposed older age of Upper Scorpius (tau similar to 11 Myr).NASA Science Mission directorateW. M. Keck FoundationAstronom
The First Scattered Light Image of the Debris Disk around the Sco-Cen target HD 129590
We present the first scattered light image of the debris disk around HD
129590, a ~1.3 M G1V member of the Scorpius Centaurus association with
age ~10-16 Myr. The debris disk is imaged with the high contrast imaging
instrument SPHERE at the Very Large Telescope, and is revealed by both the
IRDIS and IFS subsytems, operating in the H and YJ bands respectively. The disk
has a high infrared luminosity of
~510, and has been resolved
in other studies using ALMA. We detect a nearly edge on ring, with evidence of
an inner clearing. We fit the debris disk using a model characterized by a
single bright ring, with radius ~60-70 AU, in broad agreement with previous
analysis of the target SED. The disk is vertically thin, and has an inclination
angle of ~75. Along with other previously imaged edge-on disks in the
Sco-Cen association such as HD 110058, HD 115600, and HD 111520, this disk
image will allow of the structure and morphology of very young debris disks,
shortly after the epoch of planet formation has ceased.Comment: 8 pages, 4 figures. Accepted for publication in ApJ
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