123 research outputs found
Detection of an inner gaseous component in a Herbig Be star accretion disk: Near- and mid-infrared spectro-interferometry and radiative transfer modeling of MWC 147
We study the geometry and the physical conditions in the inner (AU-scale)
circumstellar region around the young Herbig Be star MWC 147 using
long-baseline spectro-interferometry in the near-infrared (NIR K-band,
VLTI/AMBER observations and PTI archive data) as well as the mid-infrared (MIR
N-band, VLTI/MIDIobservations). The emission from MWC 147 is clearly resolved
and has a characteristic physical size of approx. 1.3 AU and 9 AU at 2.2 micron
and 11 micron respectively (Gaussian diameter). The spectrally dispersed AMBER
and MIDI interferograms both show a strong increase in the characteristic size
towards longer wavelengths, much steeper than predicted by analytic disk models
assuming power-law radial temperature distributions. We model the
interferometric data and the spectral energy distribution of MWC 147 with 2-D,
frequency-dependent radiation transfer simulations. This analysis shows that
models of spherical envelopes or passive irradiated Keplerian disks (with
vertical or curved puffed-up inner rim) can easily fit the SED, but predict
much lower visibilities than observed; the angular size predicted by such
models is 2 to 4 times larger than the size derived from the interferometric
data, so these models can clearly be ruled out. Models of a Keplerian disk with
optically thick gas emission from an active gaseous disk (inside the dust
sublimation zone), however, yield a good fit of the SED and simultaneously
reproduce the absolute level and the spectral dependence of the NIR and MIR
visibilities. We conclude that the NIR continuum emission from MWC 147 is
dominated by accretion luminosity emerging from an optically thick inner
gaseous disk, while the MIR emission also contains contributions from the
outer, irradiated dust disk.Comment: 44 pages, 15 figures, accepted for publication in The Astrophysical
Journal. The quality of the figures was slightly reduced in order to comply
with the astro-ph file-size restrictions. You can find a high-quality version
of the paper at http://www.mpifr-bonn.mpg.de/staff/skraus/papers/mwc147.pd
Far-Ultraviolet Dust Albedo Measurements in the Upper Scorpius Cloud Using the SPINR Sounding Rocket Experiment
The Spectrograph for Photometric Imaging with Numeric Reconstruction (SPINR)
sounding rocket experiment was launched on 2000 August 4 to record
far-ultraviolet (912-1450 A) spectral and spatial information for the giant
reflection nebula in the Upper Scorpius region. The data were divided into
three arbitrary bandpasses (912-1029 A, 1030-1200 A, and 1235-1450 A) for which
stellar and nebular flux levels were derived. These flux measurements were used
to constrain a radiative transfer model and to determine the dust albedo for
the Upper Scorpius region. The resulting albedos were 0.28+/-0.07 for the
912-1029 A bandpass, 0.33+/-0.07 for the 1030-1200 A bandpass, and 0.77+/-0.13
for the 1235-1450 A bandpass
Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption line measurements
for the high- and intermediate velocity clouds (HVCs and IVCs). New values are
derived for N(HI) in the direction of observed probes, in order to arrive at
reliable abundances and abundance limits (the HI data are described in Paper
II). Distances to stellar probes are revisited and calculated consistently, in
order to derive distance brackets or limits for many of the clouds, taking care
to properly interpret non-detections. The main conclusions are the following.
1) Absolute abundances have been measured using lines of SII, NI and OI, with
the following resulting values: ~0.1 solar for one HVC (complex C), ~0.3 solar
for the Magellanic Stream, ~0.5 solar for a southern IVC, and ~ solar for two
northern IVCs (the IV Arch and LLIV Arch). Finally, approximate values in the
range 0.5-2 solar are found for three more IVCs. 2) Depletion patterns in IVCs
are like those in warm disk or halo gas. 3) Most distance limits are based on
strong UV lines of CII, SiII and MgII, a few on CaII. Distance limits for major
HVCs are >5 kpc, while distance brackets for several IVCs are in the range
0.5-2 kpc. 4) Mass limits for major IVCs are 0.5-8x10^5 M_sun, but for major
HVCs they are >10^6 M_sun. 5) The CaII/HI ratio varies by up to a factor 2-5
within a single cloud, somewhat more between clouds. 6) The NaIHI ratio varies
by a factor >10 within a cloud, and even more between clouds. Thus, CaII can be
useful for determining both lower and upper distance limits, but NaI only
yields upper limits.Comment: To appear in the "Astrophysical Journal Supplement"; 82 pages;
figures 6, 9 and 10 are in color; degraded figures (astro-ph restriction) -
ask for good version
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