76 research outputs found
Nature Versus Nurture: Luminous Blue Variable Nebulae in and near Massive Stellar Clusters at the Galactic Center
Three Luminous Blue Variables (LBVs) are located in and near the Quintuplet
Cluster at the Galactic Center: the Pistol star, G0.120-0.048, and qF362. We
present imaging at 19, 25, 31, and 37 {\mu}m of the region containing these
three LBVs, obtained with SOFIA using FORCAST. We argue that the Pistol and
G0.120-0.048 are identical ``twins" that exhibit contrasting nebulae due to the
external influence of their different environments. Our images reveal the
asymmetric, compressed shell of hot dust surrounding the Pistol Star and
provide the first detection of the thermal emission from the symmetric, hot
dust envelope surrounding G0.120-0.048. Dust and gas composing the Pistol
nebula are primarily heated and ionized by the nearby Quintuplet Cluster stars.
The northern region of the Pistol nebula is decelerated due to the interaction
with the high-velocity (2000 km/s) winds from adjacent Wolf-Rayet Carbon (WC)
stars. With the DustEM code we determine that the Pistol nebula is composed of
a distribution of very small, transiently-heated grains (10-~35 {\AA}) and that
it exhibits a gradient of decreasing grain size from the south to the north due
to differential sputtering by the winds from the WC stars. Dust in the
G0.120-0.048 nebula is primarily heated by the central star; however, the
nebular gas is ionized externally by the Arches Cluster. Unlike the Pistol
nebula, the G0.120-0.048 nebula is freely expanding into the surrounding
medium. Given independent dust and gas mass estimates we find that the Pistol
and G0.120-0.048 nebulae exhibit similar gas-to-dust mass ratios of ~310 and
~290, respectively. Both nebulae share identical size scales (~ 0.7 pc) which
suggests that they have similar dynamical timescales of ~10^5 yrs, assuming a
shell expansion velocity of v_exp 60 km/s.Comment: 18 pages, 7 figures, accepted to Ap
An Infrared Study of the Circumstellar Material Associated with the Carbon Star R Sculptoris
The asymptotic giant branch (AGB) star R Sculptoris (R Scl) is one of the
most extensively studied stars on the AGB. R Scl is a carbon star with a
massive circumstellar shell () which
is thought to have been produced during a thermal pulse event years
ago. To study the thermal dust emission associated with its circumstellar
material, observations were taken with the Faint Object InfraRed CAMera for the
SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1 m. Maps of
the infrared emission at these wavelengths were used to study the morphology
and temperature structure of the spatially extended dust emission. Using the
radiative transfer code DUSTY and fitting the spatial profile of the emission,
we find that a geometrically thin dust shell cannot reproduce the observed
spatially resolved emission. Instead, a second dust component in addition to
the shell is needed to reproduce the observed emission. This component, which
lies interior to the dust shell, traces the circumstellar envelope of R Scl. It
is best fit by a density profile with where
and dust mass of
. The strong departure from an
law indicates that the mass-loss rate of R Scl has not been constant.
This result is consistent with a slow decline in the post-pulse mass-loss which
has been inferred from observations of the molecular gas.Comment: 10 pages, 10 figures, accepted to Ap
Old supernova dust factory revealed at the Galactic center
Dust formation in supernova ejecta is currently the leading candidate to
explain the large quantities of dust observed in the distant, early Universe.
However, it is unclear whether the ejecta-formed dust can survive the hot
interior of the supernova remnant (SNR). We present infrared observations of
~0.02 of warm (~100 K) dust seen near the center of the ~10,000
yr-old Sgr A East SNR at the Galactic center. Our findings signify the
detection of dust within an older SNR that is expanding into a relatively dense
surrounding medium ( ~ 100 ) and has survived the
passage of the reverse shock. The results suggest that supernovae may indeed be
the dominant dust production mechanism in the dense environment of early
Universe galaxies.Comment: 25 pages, 5 figures. Includes supplementary materials. Published
Online March 19 2015 on Science Expres
The Rotation Curves of Galaxies at Intermediate Redshift
We have undertaken a pilot project to measure the rotation velocities of
spiral galaxies in the redshift range 0.18 < z < 0.4 using high dispersion long
slit spectroscopy obtained with the Palomar 5m telescope. One field galaxy and
three cluster objects known to have strong emission lines were observed over
wavelength ranges covering the redshifted lines of [OII], CaII K, H beta, and
[OIII]. Two of the objects show extended line emission that allows the tracing
of the rotation curve in one or more lines. A line width similar to that
obtained with single dish telescopes for the 21-cm HI line observed in lower
redshift galaxies can be derived from the observed H beta, [OII], and [OIII]
emission by measuring a characteristic width from the velocity histogram. These
moderately distant galaxies have much stronger emission lines than typical
low-redshift spirals but they appear to be kinematically similar. Application
of the Tully-Fisher relation suggests that the two galaxies with rotation
curves are intrinsically brighter at R-band than nearby galaxies.Comment: Text is 15 pages (18 with figures). Full text and postscript figures
are also available at http://www.ucolick.org/~nicole/pubs/pubs.html#highz
LBT Reveals Large Dust Particles and a High Mass Loss Rate for K2-22 b
The disintegrating planet candidate K2-22 b shows periodic and stochastic
transits best explained by an escaping debris cloud. However, the mechanism
that creates the debris cloud is unknown. The grain size of the debris as well
as its sublimation rate can be helpful in understanding the environment that
disintegrates the planet. Here, we present simultaneous photometry with the g
band at 0.48 microns and KS band at 2.1 microns using the Large Binocular
Telescope. During an event with very low dust activity, we put a new upper
limit on the size of the planet of 0.71 earth radii or 4500 km. We also
detected a medium-depth transit which can be used to constrain the dust
particle sizes. We find that the median particle size must be larger than about
0.5 to 1.0 microns, depending on the composition of the debris. This leads to a
high mass loss rate of about 3e8 kg/s that is consistent with hydrodynamic
escape models. If they are produced by some alternate mechanism such as
explosive volcanism, it would require extraordinary geological activity.
Combining our upper limits on the planet size with the high mass loss rate, we
find a lifetime of the planet of less than 370 Myr. This drops to just 21 Myr
when adopting the 0.02 earth masses predicted from hydrodynamical models.Comment: AJ, accepted, 13 page
The large Atacama submillimeter telescope
Cornell and Caltech are undertaking a two year conceptual design study for a 25-m class sub-mm telescope. The nominal location for this facility will be the high Atacama Desert of Northern Chile. The baseline design is a segmented mirror telescope optimized for operation at wavelengths longer than 200 microns to take advantage of a low precipitable water vapor at the site. We discuss science drivers and their implications for telescope design and technical requirements, and planned technical study areas
- …