16 research outputs found
Nearby Young, Active, Late-type Dwarfs in Gaia's First Data Release
The Galex Nearby Young Star Survey (GALNYSS) has yielded a sample of
2000 UV-selected objects that are candidate nearby (150 pc), young (age 10--100 Myr), late-type stars.
Here, we evaluate the distances and ages of the subsample of (19) GALNYSS stars
with Gaia Data Release 1 (DR1) parallax distances pc. The overall
youth of these 19 mid-K to early-M stars is readily apparent from their
positions relative to the loci of main sequence stars and giants in Gaia-based
color-magnitude and color-color diagrams constructed for all Galex- and
WISE-detected stars with parallax measurements included in DR1. The isochronal
ages of all 19 stars lie in the range 10--100 Myr. Comparison with
Li-based age estimates indicates a handful of these stars may be young
main-sequence binaries rather than pre-main sequence stars. Nine of the 19
objects have not previously been considered as nearby, young stars, and all but
one of these are found at declinations north of 30. The Gaia DR1
results presented here indicate that the GALNYSS sample includes several
hundred nearby, young stars, a substantial fraction of which have not been
previously recognized as having ages 100 Myr.Comment: 30 pages, 4 tables, 7 figures; to appear in The Astrophysical
Journal; 1st replacement to correct typos/omissions in Table 3 and
acknowledgments; 2nd replacement to incorporate corrections to ApJ proof
A Dusty M5 Binary in the beta Pictoris Moving Group
We report the identification of a new wide separation binary (LDS 5606) in
the ~20 Myr-old beta Pic moving group. This M5+M5 pair has a projected
separation of 26'', or ~1700 AU at a distance of 65 pc. Both stars host warm
circumstellar disks and many strong hydrogen and helium emission lines.
Spectroscopic observations reveal signatures of youth for both stars and
on-going mass accretion in the primary. The properties of LDS 5606 make it an
older analog to the ~8 Myr TWA 30 system, which is also composed of a pair of
widely separated mid-M dwarfs, each hosting their own warm circumstellar disks.
LDS 5606 joins a rather exclusive club of only 3 other known stellar systems
where both members of a binary, far from any molecular cloud, are orbited by
detected circumstellar disks.Comment: 8 pages, 6 figures; Accepted for publication in A&
Resolved Debris Discs Around A Stars in the Herschel DEBRIS Survey
The majority of debris discs discovered so far have only been detected
through infrared excess emission above stellar photospheres. While disc
properties can be inferred from unresolved photometry alone under various
assumptions for the physical properties of dust grains, there is a degeneracy
between disc radius and dust temperature that depends on the grain size
distribution and optical properties. By resolving the disc we can measure the
actual location of the dust. The launch of Herschel, with an angular resolution
superior to previous far-infrared telescopes, allows us to spatially resolve
more discs and locate the dust directly. Here we present the nine resolved
discs around A stars between 20 and 40 pc observed by the DEBRIS survey. We use
these data to investigate the disc radii by fitting narrow ring models to
images at 70, 100 and 160 {\mu}m and by fitting blackbodies to full spectral
energy distributions. We do this with the aim of finding an improved way of
estimating disc radii for unresolved systems. The ratio between the resolved
and blackbody radii varies between 1 and 2.5. This ratio is inversely
correlated with luminosity and any remaining discrepancies are most likely
explained by differences to the minimum size of grain in the size distribution
or differences in composition. We find that three of the systems are well fit
by a narrow ring, two systems are borderline cases and the other four likely
require wider or multiple rings to fully explain the observations, reflecting
the diversity of planetary systems.Comment: 19 pages, 13 figures, 6 tables. Accepted for publication in MNRA
Warm ice giant GJ 3470b - II. Revised planetary and stellar parameters from optical to near-infrared transit photometry
It is important to explore the diversity of characteristics of low-mass, low-density planets to understand the nature and evolution of this class of planets. We present a homogeneous analysis of 12 new and 9 previously published broad-band photometric observations of the Uranus-sized extrasolar planet GJ 3470b, which belongs to the growing sample of sub-Jovian bodies orbiting M dwarfs. The consistency of our analysis explains some of the discrepancies between previously published results and provides updated constraints on the planetary parameters. Our data are also consistent with previous transit observations of this system. The physical properties of the transiting system can only be constrained as well as the host star is characterized, so we provide new spectroscopic measurements of GJ 3470 from 0.33 to 2.42 μm to aid our analysis. We find R* = 0.48 ± 0.04 R⊙, M* = 0.51 ± 0.06 M⊙, and T_(eff) = 3652 ± 50K for GJ 3470, along with a rotation period of 20.70 ± 0.15 d and an R-band amplitude of 0.01 mag, which is small enough that current transit measurements should not be strongly affected by stellar variability. However, to report definitively whether stellar activity has a significant effect on the light curves, this requires future multiwavelength, multi-epoch studies of GJ 3470. We also present the most precise orbital ephemeris for this system: To = 2455983.70472 ± 0.00021BJD_(TDB), P = 3.336 6487^(+0.0000043)_(−0.0000033)
 d, and we see no evidence for transit timing variations greater than 1 min. Our reported planet to star radius ratio is 0.076 42 ± 0.000 37. The physical parameters of this planet are R_p = 3.88 ± 0.32 R⊕ and M_p = 13.73 ± 1.61 M⊕. Because of our revised stellar parameters, the planetary radius we present is smaller than previously reported values. We also perform a second analysis of the transmission spectrum of the entire ensemble of transit observations to date, supporting the existence of an H_2-dominated atmosphere exhibiting a strong Rayleigh scattering slope