89 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 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
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
Formaldehyde Densitometry of Galactic Star-Forming Regions Using the H2CO 3(12)-3(13) and 4(13)-4(14) Transitions
We present Green Bank Telescope (GBT) observations of the 3(12)-3(13) (29
GHz) and 4(13)-4(14) (48 GHz) transitions of the H2CO molecule toward a sample
of 23 well-studied star-forming regions. Analysis of the relative intensities
of these transitions can be used to reliably measure the densities of molecular
cores. Adopting kinetic temperatures from the literature, we have employed a
Large Velocity Gradient (LVG) model to derive the average hydrogen number
density [n(H2)] within a 16 arcsecond beam toward each source. Densities in the
range of 10^{5.5}--10^{6.5} cm^{-3} and ortho-formaldehyde column densities per
unit line width between 10^{13.5} and 10^{14.5} cm^{-2} (km s^{-1})^{-1} are
found for most objects, in general agreement with existing measurements. A
detailed analysis of the advantages and limitations to this densitometry
technique is also presented. We find that H2CO 3(12)-3(13)/4(13)-4(14)
densitometry proves to be best suited to objects with T_K >~ 100 K, above which
the H2CO LVG models become relatively independent of kinetic temperature. This
study represents the first detection of these H2CO K-doublet transitions in all
but one object in our sample. The ease with which these transitions were
detected, coupled with their unique sensitivity to spatial density, make them
excellent monitors of density in molecular clouds for future experiments. We
also report the detection of the 9_2--8_1 A^- (29 GHz) transition of CH3OH
toward 6 sources.Comment: 17 pages; 6 figures; Accepted by Ap
Triggering Collapse of the Presolar Dense Cloud Core and Injecting Short-Lived Radioisotopes with a Shock Wave. I. Varied Shock Speeds
The discovery of decay products of a short-lived radioisotope (SLRI) in the
Allende meteorite led to the hypothesis that a supernova shock wave transported
freshly synthesized SLRI to the presolar dense cloud core, triggered its
self-gravitational collapse, and injected the SLRI into the core. Previous
multidimensional numerical calculations of the shock-cloud collision process
showed that this hypothesis is plausible when the shock wave and dense cloud
core are assumed to remain isothermal at ~10 K, but not when compressional
heating to ~1000 K is assumed. Our two-dimensional models (Boss et al. 2008)
with the FLASH2.5 adaptive mesh refinement (AMR) hydrodynamics code have shown
that a 20 km/sec shock front can simultaneously trigger collapse of a 1 solar
mass core and inject shock wave material, provided that cooling by molecular
species such as H2O, CO, and H2 is included. Here we present the results for
similar calculations with shock speeds ranging from 1 km/sec to 100 km/sec. We
find that shock speeds in the range from 5 km/sec to 70 km/sec are able to
trigger the collapse of a 2.2 solar mass cloud while simultaneously injecting
shock wave material: lower speed shocks do not achieve injection, while higher
speed shocks do not trigger sustained collapse. The calculations continue to
support the shock-wave trigger hypothesis for the formation of the solar
system, though the injection efficiencies in the present models are lower than
desired.Comment: 39 pages, 14 figures. in press, Ap
Results from DROXO. III. Observation, source list and X-ray properties of sources detected in the "Deep Rho Ophiuchi XMM-Newton Observation"
X-rays from very young stars are powerful probes to investigate the
mechanisms at work in the very first stages of the star formation and the
origin of X-ray emission in very young stars. We present results from a 500 ks
long observation of the Rho Ophiuchi cloud with a XMM-Newton large program
named DROXO, aiming at studying the X-ray emission of deeply embedded Young
Stellar Objects (YSOs). The data acquired during the DROXO program were reduced
with SAS software, and filtered in time and energy to improve the signal to
noise of detected sources; light curves and spectra were obtained. We detected
111 sources, 61 of them associated with rho Ophiuchi YSOs as identified from
infrared observations with ISOCAM. Specifically, we detected 9 out of 11 Class
I, 31 out of 48 Class II and 15 out 16 Class III objects. Six objects out of 21
classified Class III candidates are also detected. At the same time we suggest
that 15 Class III candidates that remain undetected at log Lx < 28.3 are not
related to the cloud population. The global detection rate is ~64%. We have
achieved a flux sensitivity of ~5 x 10^{-15} erg s^{-1} cm^{-2}. The Lx to
L_bol ratio shows saturation at a value of ~ -3.5 for stars with T_eff <= 5000
K or 0.7 M_sun as observed in the Orion Nebula. The plasma temperatures and the
spectrum absorption show a decline with YSO class, with Class I YSOs being
hotter and more absorbed than Class II and III YSOs. In one star (GY 266) with
infrared counterpart in 2MASS and Spitzer catalogs we have detected a soft
excess in the X-ray spectrum which is best fitted by a cold thermal component
less absorbed than the main thermal component of the plasma. Such a soft
component hints to the presence of plasma heated by shocks due to jets outside
the dense circumstellar material.Comment: Accepted for publication on Astronomy & Astrophysics journa
A new scheme of radiation transfer in H II regions including transient heating of grains
A new scheme of radiation transfer for understanding infrared spectra of H II
regions, has been developed. This scheme considers non-equilibrium processes
(e. g. transient heating of the very small grains, VSG; and the polycyclic
aromatic hydrocarbon, PAH) also, in addition to the equilibrium thermal
emission from normal dust grains (BG). The spherically symmetric interstellar
dust cloud is segmented into a large number of "onion skin" shells in order to
implement the non-equilibrium processes. The scheme attempts to fit the
observed SED originating from the dust component, by exploring the following
parameters : (i) geometrical details of the dust cloud, (ii) PAH size and
abundance, (iii) composition of normal grains (BG), (iv) radial distribution of
all dust (BG, VSG & PAH).
The scheme has been applied to a set of five compact H II regions (IRAS
18116- 1646, 18162-2048, 19442+2427, 22308+5812 & 18434-0242) whose spectra are
available with adequate spectral resolution. The best fit models and inferences
about the parameters for these sources are presented.Comment: 16 pages total including 3 tables and 2 figure
A Near-Infrared Multiplicity Survey of Class I/Flat-Spectrum Systems in Six Nearby Molecular Clouds
We present new near-IR observations of 76 Class I/flat-spectrum objects in
the nearby (d < 320 pc) Perseus, Taurus, Chamaeleon I and II, rho Ophiuchi, and
Serpens dark clouds. These observations are part of a larger systematic
infrared multiplicity survey of self-embedded objects in the nearest dark
clouds. When combined with the results of our previously published
near-infrared multiplicity survey, we find a restricted companion star fraction
of 14/79 (18% +/- 4%) of the sources surveyed to be binary or higher order
multiple systems over a separation range of ~300 - 2000 AU with a magnitude
difference K <= 4, and with no correction for background contamination
or completeness. This is consistent with the fraction of binary/multiple
systems found among older pre-main-sequence T Tauri stars in each of the
Taurus, rho Ophiuchi, and Chamaeleon star-forming regions over a similar
separation range, as well as the combined companion star fraction for these
regions. However, the companion star fraction for solar-type, and lower mass M
dwarf, main-sequence stars in the solar neighborhood in this separation range
(11% +/- 3%) is approximately one-half that of our sample. Together with
multiplicity statistics derived for previously published samples of Class 0 and
Class I sources, our study suggests that a significant number of
binary/multiple objects may remain to be discovered at smaller separations
among our Class I/flat-spectrum sample and/or most of the evolution of
binary/multiple systems occurs during the Class 0 phase of early stellar
evolution.Comment: 23 pages, 8 figures, to appear in the March 2004 A
Dynamical Masses of Young Stars I:Discordant Model Ages of Upper Scorpius
We present the results of a long term orbit monitoring program, using sparse
aperture masking observations taken with NIRC2 on the Keck-II telescope, of
seven G to M-type members of the Upper Scorpius subgroup of the Sco-Cen OB
association. We present astrometry and derived orbital elements of the binary
systems we have monitored, and also determine the age, component masses,
distance and reddening for each system using the orbital solutions and
multi-band photometry, including Hubble Space Telescope photometry, and a
Bayesian fitting procedure. We find that the models can be forced into
agreement with any individual system by assuming an age, but that age is not
consistent across the mass range of our sample. The G-type binary systems in
our sample have model ages of ~11.5 Myr, which is consistent with the latest
age estimates for Upper Scorpius, while the M-type binary systems have
significantly younger model ages of ~7 Myr. Based on our fits, this age
discrepancy in the models corresponds to a luminosity under-prediction of
0.8-0.15 dex, or equivalently an effective temperature over-prediction of
100-300 K for M-type stars at a given premain-sequence age. We also find that
the M-type binary system RXJ 1550.0-2312 has an age (~16 Myr) and distance (~90
pc) indicating that it is either a nearby young binary system or a member of
the Upper-Centaurus-Lupus subgroup with a 57% probability of membership.Comment: 16 pages, 8 figures, 9 tables, accepted for publication in Ap
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