686 research outputs found
Properties of the close binary and circumbinary torus of the Red Rectangle
New diffraction-limited speckle images of the Red Rectangle in the wavelength
range 2.1--3.3 microns with angular resolutions of 44--68 mas and previous
speckle images at 0.7--2.2 microns revealed well-resolved bright bipolar
outflow lobes and long X-shaped spikes originating deep inside the outflow
cavities. This set of high-resolution images stimulated us to reanalyze all
infrared observations of the Red Rectangle using our two-dimensional radiative
transfer code. The new detailed modeling, together with estimates of the
interstellar extinction in the direction of the Red Rectangle enabled us to
more accurately determine one of the key parameters, the distance D=710 pc with
model uncertainties of 70 pc, which is twice as far as the commonly used
estimate of 330 pc. The central binary is surrounded by a compact, massive
(M=1.2 Msun), very dense dusty torus with hydrogen densities reaching
n_H=2.5x10^12 cm^-3 (dust-to-gas mass ratio rho_d/rho~0.01). The bright
component of the spectroscopic binary HD 44179 is a post-AGB star with mass
M*=0.57 Msun, luminosity L*=6000 Lsun, and effective temperature T*=7750 K.
Based on the orbital elements of the binary, we identify its invisible
component with a helium white dwarf with Mwd~0.35 Msun, Lwd~100 Lsun, and
Twd~6x10^4 K. The hot white dwarf ionizes the low-density bipolar outflow
cavities inside the dense torus, producing a small HII region observed at radio
wavelengths. We propose an evolutionary scenario for the formation of the Red
Rectangle nebula, in which the binary initially had 2.3 and 1.9 Msun components
at a separation of 130 Rsun. The nebula was formed in the ejection of a common
envelope after Roche lobe overflow by the present post-AGB star.Comment: 20 pages, 10 figures, accepted by Astronomy and Astrophysics, also
available at
http://www.mpifr-bonn.mpg.de/div/ir-interferometry/publications.htm
Direct Detection of the Brown Dwarf GJ 802B with Adaptive Optics Masking Interferometry
We have used the Palomar 200" Adaptive Optics (AO) system to directly detect
the astrometric brown dwarf GJ 802B reported by Pravdo et al. 2005. This
observation is achieved with a novel combination of aperture masking
interferometry and AO. The dynamical masses are 0.1750.021 M and
0.0640.032 M for the primary and secondary respectively. The
inferred absolute H band magnitude of GJ 802B is M=12.8 resulting in a
model-dependent T of 1850 50K and mass range of
0.057--0.074 M.Comment: 4 Pages, 5 figures, emulateapj format, submitted to ApJ
Effect of spectacular reflection on outâofâplane ultrasonographic images reconstructed from threeâdimensional data sets.
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135445/1/jum2000196391.pd
Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A with sparse aperture masking and spectroastrometry
Contemporary theory holds that massive stars gather mass during their initial
phases via accreting disk-like structures. However, conclusive evidence for
disks has remained elusive for the most massive young objects. This is mainly
due to significant observational challenges. Incisive studies, even targeting
individual objects, are therefore relevant to the progression of the field. NGC
3603 IRS 9A* is a young massive stellar object still surrounded by an envelope
of molecular gas. Previous mid-infrared observations with long-baseline
interferometry provided evidence for a disk of 50 mas diameter at its core.
This work aims at a comprehensive study of the physics and morphology of IRS 9A
at near-infrared wavelengths. New sparse aperture masking interferometry data
taken with NACO/VLT at Ks and Lp filters were obtained and analysed together
with archival CRIRES spectra of the H2 and BrG lines. The calibrated
visibilities recorded at Ks and Lp bands suggest the presence of a partially
resolved compact object of 30 mas at the core of IRS 9A, together with the
presence of over-resolved flux. The spectroastrometric signal of the H2 line
shows that this spectral feature proceeds from the large scale extended
emission (300 mas) of IRS 9A, while the BrG line appears to be formed at the
core of the object (20 mas). This scenario is consistent with the brightness
distribution of the source for near- and mid-infrared wavelengths at various
spatial scales. However, our model suffers from remaining inconsistencies
between SED modelling and the interferometric data. Moreover, the BrG
spectroastrometric signal indicates that the core of IRS 9A exhibits some form
of complexity such as asymmetries in the disk. Future high-resolution
observations are required to confirm the disk/envelope model and to flesh out
the details of the physical form of the inner regions of IRS 9A.Comment: Accepted to be published in Astronomy & Astrophysics, 13 pages, 14
figure
Diffraction-limited polarimetric imaging of protoplanetary disks and mass-loss shells with VAMPIRES
Both the birth and death of a stellar system are areas of key scientific importance. Whether it's understanding the process of planetary formation in a star's early years, or uncovering the cause of the enormous mass-loss that takes place during a star's dying moments, a key to scientific understanding lies in the inner few AU of the circumstellar environment. Corresponding to scales of 10s of milli-arcseconds, these observations pose a huge technical challenge due to the high angular-resolutions and contrasts required. A major stumbling block is the problem of the Earth's own atmospheric turbulence. The other difficulty is that precise calibration is required to combat the extremely high contrast ratios and high resolutions faced. By taking advantage of the fact that starlight scattered by dust in the circumstellar region is polarized, differential polarimetry can help achieve this calibration. Spectral features can also be utilized
The Angular Diameter and Fundamental Parameters of Sirius A
The Sydney University Stellar Interferometer (SUSI) has been used to make a
new determination of the angular diameter of Sirius A. The observations were
made at an effective wavelength of 694.1 nm and the new value for the
limb-darkened angular diameter is 6.048 +/- 0.040mas (+/-0.66%). This new
result is compared with previous measurements and is found to be in excellent
agreement with a conventionally calibrated measurement made with the European
Southern Observatory's Very Large Telescope Interferometer (VLTI) at 2.176
microns (but not with a second globally calibrated VLTI measurement). A
weighted mean of the SUSI and first VLTI results gives the limb-darkened
angular diameter of Sirius A as 6.041 +/- 0.017mas (+/-0.28%). Combination with
the Hipparcos parallax gives the radius equal to 1.713 +/- 0.009R_sun. The
bolometric flux has been determined from published photometry and
spectrophotometry and, combined with the angular diameter, yields the emergent
flux at the stellar surface equal to (5.32+/- 0.14)x10^8 Wm^-2 and the
effective temperature equal to 9845 +/- 64 K. The luminosity is 24.7 +/- 0.7
L_sun.Comment: Accepted for publication in PAS
A complex relationship between immunity and metabolism in Drosophila diet-induced insulin resistance
Modeling Forbidden Line Emission Profiles from Colliding Wind Binaries
This paper presents calculations for forbidden emission line profile shapes
arising from colliding wind binaries. The main application is for systems
involving a Wolf-Rayet (WR) star and an OB star companion. The WR wind is
assumed to dominate the forbidden line emission. The colliding wind interaction
is treated as an archimedean spiral with an inner boundary. Under the
assumptions of the model, the major findings are as follows. (a) The
redistribution of the WR wind as a result of the wind collision is not flux
conservative but typically produces an excess of line emission; however, this
excess is modest at around the 10% level. (b) Deviations from a flat-top
profile shape for a spherical wind are greatest for viewing inclinations that
are more nearly face-on to the orbital plane. At intermediate viewing
inclinations, profiles display only mild deviations from a flat-top shape. (c)
The profile shape can be used to constrain the colliding wind bow shock opening
angle. (d) Structure in the line profile tends to be suppressed in binaries of
shorter periods. (e) Obtaining data for multiple forbidden lines is important
since different lines probe different characteristic radial scales. Our models
are discussed in relation to ISO data for WR 147 and gamma Vel (WR11). The
lines for WR 147 are probably not accurate enough to draw firm conclusions. For
gamma Vel, individual line morphologies are broadly reproducible but not
simultaneously so for the claimed wind and orbital parameters. Overall, the
effort demonstrates how lines that are sensitive to the large-scale wind can
help to deduce binary system properties and provide new tests of numerical
simulations.Comment: to appear in MNRA
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