159 research outputs found
Identification of temperature profile and heat transfer on a dielectric membrane for gas sensors by `COSMOS' program simulation
The application of commercial 3-D software `COSMOS' for the design and thermal analysis of the low power consumption test structures with dielectric membrane for gas microsensors is presented. Within this work, the simulation provides the estimation of the temperature profile on the active area and the whole membrane including the four bridges and the heating efficiency in the temperature range 20-500 °C. Unravelling of the heat loss mechanisms in terms of radiation, convection, conduction by air and solid materials during heat transfer on the dielectric membrane is reported for the first time as a mean to evaluate by 3-D simulation the contribution of technological processes and lay-out design to the total heat losses
A Mid-Infrared Imaging Survey of Embedded Young Stellar Objects in the Rho Ophiuchi Cloud Core
Results of a comprehensive, new, ground-based mid-infrared imaging survey of
the young stellar population of the Rho Ophiuchi cloud are presented. Data were
acquired at the Palomar 5-m and at the Keck 10-m telescopes with the MIRLIN and
LWS instruments, at 0.25 arcsec and 0.25 arcsec resolutions, respectively. Of
172 survey objects, 85 were detected. Among the 22 multiple systems observed,
15 were resolved and their individual component fluxes determined. A plot of
the frequency distribution of the detected objects with SED spectral slope
shows that YSOs spend ~400,000 yr in the Flat Spectrum phase, clearing out
their remnant infall envelopes. Mid-infrared variability is found among a
significant fraction of the surveyed objects, and is found to occur for all SED
classes with optically thick disks. Large-amplitude near-infrared variability,
also found for all SED classes with optically thick disks, seems to occur with
somewhat higher frequency at the earlier evolutionary stages. Although a
general trend of mid-infrared excess and NIR veiling exists proceeding through
SED classes, with Class I objects generally exhibiting K-veilings > 1, Flat
Spectrum objects with K-veilings > 0.58, and Class III objects with K-veilings
=0, Class II objects exhibit the widest range of K-band veiling values, 0-4.5.
However, the highly variable value of veiling that a single source can exhibit
in any of the SED classes in which active disk accretion can take place is
striking, and is direct observational evidence for highly time-variable
accretion activity in disks. Finally, by comparing mid-infrared vs.
near-infrared excesses in a subsample with well-determined effective
temperatures and extinction values, disk clearing mechanisms are explored. The
results are consistent with disk clearing proceeding from the inside-out.Comment: 18 pages + 5 tables + 7 figure
A Near-Infrared (JHK) Survey of the Vicinity of the HII region NGC 7538: Evidence for a Young Embedded Cluster
We describe the results of two near infrared (K-band) imaging surveys and a
three color (JHK) survey of the vicinity of NGC 7538. The limiting magnitudes
are K ~ 16.5 and K ~ 17.5 mag for the K-band surveys and K ~ 15 mag for the JHK
survey. We identify more than 2000 and 9000 near-infrared (NIR) sources on the
images of the two K-band surveys and 786 NIR sources in the JHK survey. From
color-color diagrams, we derive a reddening law for background stars and
identify 238 stars with NIR excesses. Contour maps indicate a high density peak
coincident with a concentration of stars with NIR excesses. We identify this
peak as a young, embedded cluster and confirm this result with the K-band
luminosity function, color histograms, and color-magnitude diagrams. The center
of the cluster is at RA = 23:13:39.34, DEC = 61:29:18.9. The cluster radius is
3' ~ 2.5 pc for an adopted distance, d ~ 2.8 kpc. For d = 2.8 kpc, and
reddening, E_{J-K} = 0.55 mag, the slope of the logarithmic K-band luminosity
function (KLF) of the cluster, s ~ 0.32 +- 0.03, agrees well with previous
results for L1630 (s = 0.34) and M17 (s = 0.26).Comment: 26 pages with 11 figures. Accepted by Astronomical Journa
Detection of Magnetohydrodynamic Shocks in the L1551 Outflow
We report the results of CO J=l—+0 mapping of portions of the blue outflow lobe of L1551 with ~ 7” (N-S) × 4” (E-W) resolution, obtained with the 3-element OVRO millimeter array. Comparison of our interferometer mosaic with lower resolution single-dish data shows that we resolve the strongest single-dish emission regions into filamentary structures, such as are characteristic of shock fronts mapped via their near-infrared H2 emission in other outflow sources
The Structure of the DoAr 25 Circumstellar Disk
We present high spatial resolution (< 0.3" = 40\Sigma
\propto r^{-p}$ with p = 0.34, significantly less steep than a steady-state
accretion disk (p = 1) or the often adopted minimum mass solar nebula (p =
1.5). Even though the total mass of material is large (M_d = 0.10 M_sun), the
densities inferred in the inner disk for such a model may be too low to
facilitate any mode of planet formation. However, alternative models with
steeper density gradients (p = 1) can explain the observations equally well if
substantial grain growth in the planet formation region (r < 40 AU) has
occurred. We discuss these data in the context of such models with dust
properties that vary with radius and highlight their implications for
understanding disk evolution and the early stages of planet formation.Comment: ApJL in pres
Detection of Magnetohydrodynamic Shocks in the L1551 Outflow
We report the results of CO J=l—+0 mapping of portions of the blue outflow lobe of L1551 with ~ 7” (N-S) × 4” (E-W) resolution, obtained with the 3-element OVRO millimeter array. Comparison of our interferometer mosaic with lower resolution single-dish data shows that we resolve the strongest single-dish emission regions into filamentary structures, such as are characteristic of shock fronts mapped via their near-infrared H2 emission in other outflow sources
Star Formation in Massive Protoclusters in the Monoceros OB1 Dark Cloud
We present far-infrared, submillimetre, and millimetre observations of bright
IRAS sources and outflows that are associated with massive CS clumps in the
Monoceros OB1 Dark Cloud. Individual star-forming cores are identified within
each clump. We show that combining submillimetre maps, obtained with SCUBA on
the JCMT, with HIRES-processed and modelled IRAS data is a powerful technique
that can be used to place better limits on individual source contributions to
the far-infrared flux in clustered regions. Three previously categorized "Class
I objects" are shown to consist of multiple sources in different evolutionary
stages. In each case, the IRAS point source dominates the flux at 12 and 25
microns. In two cases, the IRAS point source is not evident at submillimetre
wavelengths. The submillimetre sources contribute significantly to the 60 and
100 micron fluxes, dominating the flux in the 100 micron waveband. Using fluxes
derived from our technique, we present the spectral energy distribution and
physical parameters for an intermediate-mass Class 0 object in one of the
regions. Our new CO J=2-1 outflow maps of the three regions studied indicate
complex morphology suggestive of multiple driving sources. We discuss the
possible implications of our results for published correlations between outflow
momentum deposition rates and "source" luminosities, and for using these
derived properties to estimate the ratio of mass ejection rates to mass
accretion rates onto protostars.Comment: 12 pages, 11 gzipped gif figures, LaTex file and MNRAS style files,
accepted by MNRAS, v2: reference typos and author affiliation have been
correcte
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