10 research outputs found
Circumbinary Ring, Circumstellar disks and accretion in the binary system UY Aurigae
Recent exo-planetary surveys reveal that planets can orbit and survive around
binary stars. This suggests that some fraction of young binary systems which
possess massive circumbinary disks (CB) may be in the midst of planet
formation. However, there are very few CB disks detected. We revisit one of the
known CB disks, the UY Aurigae system, and probe 13CO 2-1, C18O 2-1, SO
5(6)-4(5) and 12CO 3-2 line emission and the thermal dust continuum. Our new
results confirm the existence of the CB disk. In addition, the circumstellar
(CS) disks are clearly resolved in dust continuum at 1.4 mm. The spectral
indices between the wavelengths of 0.85 mm and 6 cm are found to be
surprisingly low, being 1.6 for both CS disks. The deprojected separation of
the binary is 1.26" based on our 1.4 mm continuum data. This is 0.07" (10 AU)
larger than in earlier studies. Combining the fact of the variation of UY Aur B
in band, we propose that the CS disk of an undetected companion UY Aur Bb
obscures UY Aur Ba. A very complex kinematical pattern inside the CB disk is
observed due to a mixing of Keplerian rotation of the CB disk, the infall and
outflow gas. The streaming gas accreting from the CB ring toward the CS disks
and possible outflows are also identified and resolved. The SO emission is
found to be at the bases of the streaming shocks. Our results suggest that the
UY Aur system is undergoing an active accretion phase from the CB disk to the
CS disks. The UY Aur B might also be a binary system, making the UY Aur a
triple system.Comment: 14 pages, 11 figures; accepted for publication in Ap
Mapping CO Gas in the GG Tauri A Triple System with 50 AU Spatial Resolution
We aim to unveil the observational imprint of physical mechanisms that govern
planetary formation in the young, multiple system GG Tau A. We present ALMA
observations of CO and CO 3-2 and 0.9 mm continuum emission with
0.35" resolution. The CO 3-2 emission, found within the cavity of the
circumternary dust ring (at radius AU) where no CO emission is
detected, confirms the presence of CO gas near the circumstellar disk of GG Tau
Aa. The outer disk and the recently detected hot spot lying at the outer edge
of the dust ring are mapped both in CO and CO. The gas emission
in the outer disk can be radially decomposed as a series of slightly
overlapping Gaussian rings, suggesting the presence of unresolved gaps or dips.
The dip closest to the disk center lies at a radius very close to the hot spot
location at ~AU. The CO excitation conditions indicate that the
outer disk remains in the shadow of the ring. The hot spot probably results
from local heating processes. The two latter points reinforce the hypothesis
that the hot spot is created by an embedded proto-planet shepherding the outer
disk.Comment: 8 pages, 4 figures. Accepted by Ap
Near-ultraviolet Excess in Slowly Accreting T Tauri Stars: Limits Imposed by Chromospheric Emission
Young stars surrounded by disks with very low mass accretion rates are likely in the final stages of inner disk evolution and therefore particularly interesting to study. We present ultraviolet (UV) observations of the ~5-9 Myr old stars RECX-1 and RECX-11, obtained with the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph on the Hubble Space Telescope , as well as optical and near-infrared spectroscopic observations. The two stars have similar levels of near-UV emission, although spectroscopic evidence indicates that RECX-11 is accreting and RECX-1 is not. The line profiles of H_ and He I _10830 in RECX-11 show both broad and narrow redshifted absorption components that vary with time, revealing the complexity of the accretion flows. We show that accretion indicators commonly used to measure mass accretion rates, e.g., U -band excess luminosity or the Ca II triplet line luminosity, are unreliable for low accretors, at least in the middle K spectral range. Using RECX-1 as a template for the intrinsic level of photospheric and chromospheric emission, we determine an upper limit of 3 _ 10 –10 M _ yr –1 for RECX-11. At this low accretion rate, recent photoevaporation models predict that an inner hole should have developed in the disk. However, the spectral energy distribution of RECX-11 shows fluxes comparable to the median of Taurus in the near-infrared, indicating that substantial dust remains. Fluorescent H 2 emission lines formed in the innermost disk are observed in RECX-11, showing that gas is present in the inner disk, along with the dust.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90770/1/0004-637X_743_2_105.pd
Embracing the Dark Side: The Market for Dark Skies Tourism
Dark sky tourism is a rapidly growing but little understood Appalachian tourism segment. This presentation will focus on the market for dark skies destinations, the typical dark skies visitor, and emerging or potential markets for dark skies sites. It will also introduce strategies for developing these sites and for helping protect night-sky assets. Much of the market research will be culled from recent surveys of night sky stakeholders across the ARC region. These surveys were conducted as part of economic impact and market research related to the development of Calhoun County Park in Central West Virginia. The survey data provides demographic and economic information related to amateur astronomers and other night sky tourists. The research shows that while amateur astronomers are a niche market, they could prove to be a valuable source of revenue for many regional communities. While amateur astronomers remain the core market for these destination, recent research suggests demand for night sky travel among other groups. These destinations appear to have a number of important secondary markets, including programming related to the arts, humanities, faith communities, and environmental sciences. This presentation will intorduce these secondary markets and discuss their potential imact. Lastly, the presentation will introduce strategies to help communities develop and protect their dark sky resources. These include building local support, creating jurisdictional protections, and adopting low-impact ligating technologies