7,520 research outputs found
Mid-infrared size survey of Young Stellar Objects: Description of Keck segment-tilting experiment and basic results
The mid-infrared properties of pre-planetary disks are sensitive to the
temperature and flaring profiles of disks for the regions where planet
formation is expected to occur. In order to constrain theories of planet
formation, we have carried out a mid-infrared (wavelength 10.7 microns) size
survey of young stellar objects using the segmented Keck telescope in a novel
configuration. We introduced a customized pattern of tilts to individual mirror
segments to allow efficient sparse-aperture interferometry, allowing full
aperture synthesis imaging with higher calibration precision than traditional
imaging. In contrast to previous surveys on smaller telescopes and with poorer
calibration precision, we find most objects in our sample are partially
resolved. Here we present the main observational results of our survey of 5
embedded massive protostars, 25 Herbig Ae/Be stars, 3 T Tauri stars, 1 FU Ori
system, and 5 emission-line objects of uncertain classification. The observed
mid-infrared sizes do not obey the size-luminosity relation found at
near-infrared wavelengths and a companion paper will provide further modelling
analysis of this sample. In addition, we report imaging results for a few of
the most resolved objects, including complex emission around embedded massive
protostars, the photoevaporating circumbinary disk around MWC 361A, and the
subarcsecond binaries T Tau, FU Ori and MWC 1080.Comment: Accepted by Astrophysical Journal. 38 pages. 9 figure
Milli-arcsecond images of the Herbig Ae star HD 163296
The very close environments of young stars are the hosts of fundamental
physical processes, such as planet formation, star-disk interactions, mass
accretion, and ejection. The complex morphological structure of these
environments has been confirmed by the now quite rich data sets obtained for a
few objects by near-infrared long-baseline interferometry. We gathered numerous
interferometric measurements for the young star HD163296 with various
interferometers (VLTI, IOTA, KeckI and CHARA), allowing for the first time an
image independent of any a priori model to be reconstructed. Using the
Multi-aperture image Reconstruction Algorithm (MiRA), we reconstruct images of
HD 163296 in the H and K bands. We compare these images with reconstructed
images obtained from simulated data using a physical model of the environment
of HD 163296. We obtain model-independent and -band images of the
surroundings of HD 163296. The images present several significant features that
we can relate to an inclined asymmetric flared disk around HD 163296 with the
strongest intensity at about 4-5 mas. Because of the incomplete spatial
frequency coverage, we cannot state whether each of them individually is
peculiar in any way. For the first time, milli-arcsecond images of the
environment of a young star are produced. These images confirm that the
morphology of the close environment of young stars is more complex than the
simple models used in the literature so far.Comment: 11 pages, 10 figures, accepted A&A pape
KOI-1003: A new spotted, eclipsing RS CVn binary in the Kepler field
Using the high-precision photometry from the Kepler space telescope,
thousands of stars with stellar and planetary companions have been observed.
The characterization of stars with companions is not always straightforward and
can be contaminated by systematic and stellar influences on the light curves.
Here, through a detailed analysis of starspots and eclipses, we identify
KOI-1003 as a new, active RS CVn star---the first identified with data from
Kepler. The Kepler light curve of this close binary system exhibits the
system's primary transit, secondary eclipse, and starspot evolution of two
persistent active longitudes. The near equality of the system's orbital and
rotation periods indicates the orbit and primary star's rotation are nearly
synchronized ( days; days). By assuming the secondary star is on the main sequence, we suggest
the system consists of a subgiant primary and
a main-sequence companion. Our work gives a
distance of pc and an age of Gyr,
parameters which are discrepant with previous studies that included the star as
a member of the open cluster NGC 6791.Comment: 21 pages, 19 figures, accepted to Ap
Imaging starspot evolution on Kepler target KIC 5110407 using light curve inversion
The Kepler target KIC 5110407, a K-type star, shows strong quasi-periodic
light curve fluctuations likely arising from the formation and decay of spots
on the stellar surface rotating with a period of 3.4693 days. Using an
established light-curve inversion algorithm, we study the evolution of the
surface features based on Kepler space telescope light curves over a period of
two years (with a gap of .25 years). At virtually all epochs, we detect at
least one large spot group on the surface causing a 1-10% flux modulation in
the Kepler passband. By identifying and tracking spot groups over a range of
inferred latitudes, we measured the surface differential rotation to be much
smaller than that found for the Sun. We also searched for a correlation between
the seventeen stellar flares that occurred during our observations and the
orientation of the dominant surface spot at the time of each flare. No
statistically-significant correlation was found except perhaps for the very
brightest flares, suggesting most flares are associated with regions devoid of
spots or spots too small to be clearly discerned using our reconstruction
technique. While we may see hints of long-term changes in the spot
characteristics and flare statistics within our current dataset, a longer
baseline of observation will be needed to detect the existence of a magnetic
cycle in KIC 5110407.Comment: 32 pages, 15 figures, accepted to Ap
Born Again Protoplanetary Disk Around Mira B
The Mira AB system is a nearby (~107 pc) example of a wind accreting binary
star system. In this class of system, the wind from a mass-losing red giant
star (Mira A) is accreted onto a companion (Mira B), as indicated by an
accretion shock signature in spectra at ultraviolet and X-ray wavelengths.
Using novel imaging techniques, we report the detection of emission at
mid-infrared wavelengths between 9.7 and 18.3 m from the vicinity of Mira
B but with a peak at a radial position about 10 AU closer to the primary Mira
A. We interpret the mid-infrared emission as the edge of an optically-thick
accretion disk heated by Mira A. The discovery of this new class of accretion
disk fed by M-giant mass loss implies a potential population of young planetary
systems in white-dwarf binaries which has been little explored, despite being
relatively common in the solar neighborhood.Comment: Accepted for Ap
Fundamental properties and atmospheric structure of the red supergiant VY CMa based on VLTI/AMBER spectro-interferometry
We investigate the atmospheric structure and fundamental properties of the
red supergiant VY CMa. We obtained near-infrared spectro-interferometric
observations of VY CMa with spectral resolutions of 35 and 1500 using the AMBER
instrument at the VLTI. The visibility data indicate the presence of molecular
layers of water vapor and CO in the extended atmosphere with an asymmetric
morphology. The uniform disk diameter in the water band around 2.0 mu is
increased by \sim20% compared to the near-continuum bandpass at 2.20-2.25 mu
and in the CO band at 2.3-2.5 mu it is increased by up to \sim50%. The closure
phases indicate relatively small deviations from point symmetry close to the
photospheric layer, and stronger deviations in the extended H2O and CO layers.
Making use of the high spatial and spectral resolution, a near-continuum
bandpass can be isolated from contamination by molecular and dusty layers, and
the Rosseland-mean photospheric angular diameter is estimated to 11.3 +/- 0.3
mas based on a PHOENIX atmosphere model. Together with recent high-precision
estimates of the distance and spectro-photometry, this estimate corresponds to
a radius of 1420 +/- 120 Rsun and an effective temperature of 3490 +/- 90 K. VY
CMa exhibits asymmetric, possibly clumpy, atmospheric layers of H2O and CO,
which are not co-spatial, within a larger elongated dusty envelope. Our revised
fundamental parameters put VY CMa close to the Hayashi limit of recent
evolutionary tracks of initial mass 25 Msun with rotation or 32 Msun without
rotation, shortly before evolving blueward in the HR-diagram.Comment: 5 pages, 5 figures, accepted for publication in Astronomy and
Astrophysics (A&A) as a Lette
Interim And Long-Term Low-GWP Refrigerant Solutions For Air Conditioning
This paper will update on the feasibility status from the global test research efforts for ‘interim’ near drop-in refrigerants with low global warming potential (LGWP) with focus on R410A replacement for Unitary A/C & H/P. R32 and the HFO blends offer near drop-in solutions with a reasonable balance of trade-offs among GWP, efficiency, A2L flammability, and cost after  the building codes are available for commercialization. With the advent of further GWP phase down driven by the December 2015 Climate Change Agreement in Paris coupled with the imminent U.S. EPA SNAP de-listing and the U.S. DOE mandating new higher efficiency standards taking effect in 2020+, there is even more pressure for finding ‘long-term’ refrigerant solutions to meet the 15-20% GWP cap for 2030+ that can sustain efficiency, reduce charge requirement and are affordable. Theoretical and test results from various compressor and system tests with R32 and the HFO blends will be presented as ‘interim’ 2020+ solutions. Long-term 2030+ solutions and their tradeoffs are conceptualized and discussed for typical A/C residential and commercial applications from both GWP and LCCP standpoint including implications on HVAC system architecture.
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