175 research outputs found
Classifying the embedded young stellar population in Perseus and Taurus & the LOMASS database
Context. The classification of young stellar objects (YSOs) is typically done
using the infrared spectral slope or bolometric temperature, but either can
result in contamination of samples. More accurate methods to determine the
evolutionary stage of YSOs will improve the reliability of statistics for the
embedded YSO population and provide more robust stage lifetimes. Aims. We aim
to separate the truly embedded YSOs from more evolved sources. Methods. Maps of
HCO+ J=4-3 and C18O J=3-2 were observed with HARP on the James Clerk Maxwell
Telescope (JCMT) for a sample of 56 candidate YSOs in Perseus and Taurus in
order to characterize emission from high (column) density gas. These are
supplemented with archival dust continuum maps observed with SCUBA on the JCMT
and Herschel PACS to compare the morphology of the gas and dust in the
protostellar envelopes. The spatial concentration of HCO+ J=4-3 and 850 micron
dust emission are used to classify the embedded nature of YSOs. Results.
Approximately 30% of Class 0+I sources in Perseus and Taurus are not Stage I,
but are likely to be more evolved Stage II pre-main sequence (PMS) stars with
disks. An additional 16% are confused sources with an uncertain evolutionary
stage. Conclusions. Separating classifications by cloud reveals that a high
percentage of the Class 0+I sources in the Perseus star forming region are
truly embedded Stage I sources (71%), while the Taurus cloud hosts a majority
of evolved PMS stars with disks (68%). The concentration factor method is
useful to correct misidentified embedded YSOs, yielding higher accuracy for YSO
population statistics and Stage timescales. Current estimates (0.54 Myr) may
overpredict the Stage I lifetime on the order of 30%, resulting in timescales
of 0.38 Myr for the embedded phase.Comment: 33 pages, 21 figures, 6 tables, Accepted to be published in A&
High-pressure, low-abundance water in bipolar outflows. Results from a Herschel-WISH survey
(Abridged) We present a survey of the water emission in a sample of more than
20 outflows from low mass young stellar objects with the goal of characterizing
the physical and chemical conditions of the emitting gas. We have used the HIFI
and PACS instruments on board the Herschel Space Observatory to observe the two
fundamental lines of ortho-water at 557 and 1670 GHz. These observations were
part of the "Water In Star-forming regions with Herschel" (WISH) key program,
and have been complemented with CO and H2 data. We find that the emission from
water has a different spatial and velocity distribution from that of the J=1-0
and 2-1 transitions of CO, but it has a similar spatial distribution to H2, and
its intensity follows the H2 intensity derived from IRAC images. This suggests
that water traces the outflow gas at hundreds of kelvins responsible for the H2
emission, and not the component at tens of kelvins typical of low-J CO
emission. A warm origin of the water emission is confirmed by a remarkable
correlation between the intensities of the 557 and 1670 GHz lines, which also
indicates the emitting gas has a narrow range of excitations. A non-LTE
radiative transfer analysis shows that while there is some ambiguity on the
exact combination of density and temperature values, the gas thermal pressure
nT is constrained within less than a factor of 2. The typical nT over the
sample is 4 10^{9} cm^{-3}K, which represents an increase of 10^4 with respect
to the ambient value. The data also constrain within a factor of 2 the water
column density. When this quantity is combined with H2 column densities, the
typical water abundance is only 3 10^{-7}, with an uncertainty of a factor of
3. Our data challenge current C-shock models of water production due to a
combination of wing-line profiles, high gas compressions, and low abundances.Comment: 21 pages, 13 figures. Accepted for publication in A&
Water in low-mass star-forming regions with Herschel (WISH-LM): High-velocity H2O bullets in L1448-MM observed with HIFI
Herschel-HIFI observations of water in the low-mass star-forming object
L1448-MM, known for its prominent outflow, are presented, as obtained within
the `Water in star-forming regions with Herschel' (WISH) key programme. Six
H2-16O lines are targeted and detected (E_up/k_B ~ 50-250 K), as is CO J= 10-9
(E_up/k_B ~ 305 K), and tentatively H2-18O 110-101 at 548 GHz. All lines show
strong emission in the "bullets" at |v| > 50 km/s from the source velocity, in
addition to a broad, central component and narrow absorption. The bullets are
seen much more prominently in HO than in CO with respect to the central
component, and show little variation with excitation in H2O profile shape.
Excitation conditions in the bullets derived from CO lines imply a temperature
>150 K and density >10^5 cm^-3, similar to that of the broad component. The
H2O/CO abundance ratio is similar in the "bullets" and the broad component, ~
0.05-1.0, in spite of their different origins in the molecular jet and the
interaction between the outflow and the envelope. The high H2O abundance
indicates that the bullets are H2 rich. The H2O cooling in the "bullets" and
the broad component is similar and higher than the CO cooling in the same
components. These data illustrate the power of Herschel-HIFI to disentangle
different dynamical components in low-mass star-forming objects and determine
their excitation and chemical conditions.Comment: Accepted for publication in A&
Synthesis and characterization of Fe3O4@Cs@Ag nanocomposite and its use in the production of magnetic and antibacterial nanofibrous membranes
Electrospinning is a promising technique to produce polymeric as well as metal oxide nanofibers in diverse domains. In this work, different weight ratios (5%, 7.5% and 10%) of Fe3O4@Cs@Ag magnetic nanoparticles were added in PVP (polyvinylpyrrolidone) polymer and fabricated via electrospinning method to produce magnetic nanofibers (MNFs). Structural, magnetic, morphological, spectroscopic and thermal properties of produced nanofibers were characterized. Furtheremore, antibacterial effects of Fe3O4@Cs@Ag nanofibrous membrane was investigated. Obtained SEM images showed that produced nanofibers were uniform and defect free. Moreover, crystallinity and magnetic moment of fibers was tested by using X-ray diffraction and a vibrating sample magnetometer. The results showed that produced nanofibrous membranes exhibited good antibacterial activity versus Staphylococcus aureus, Bacillus subtilis, Enterococcus faecalis, Escherichia coli, Proteus mirabilis and Pseudomonas aeruginosa. © 2020National Science Foundation, NSF; Directorate for Mathematical and Physical Sciences, MPS: 1726617This work was supported in part by Scientific Research Unit of Nam?k Kemal University within NKUBAP.06.GA.19.195 coded project. Magnetic Characterization at Virginia Commonwealth University was partially supported by National Science Foundation, Award Number: 1726617.This work was supported in part by Scientific Research Unit of Namık Kemal University within NKUBAP.06.GA.19.195 coded project. Magnetic Characterization at Virginia Commonwealth University was partially supported by National Science Foundation , Award Number: 1726617
The abundance of C18O and HDO in the envelope and hot core of the intermediate mass protostar NGC 7129 FIRS 2
NGC 7129 FIRS 2 is a young intermediate-mass (IM) protostar, which is
associated with two energetic bipolar outflows and displays clear signs of the
presence of a hot core. It has been extensively observed with ground based
telescopes and within the WISH Guaranteed Time Herschel Key Program. We present
new observations of the C18O 3-2 and the HDO 3_{12}-2_{21} lines towards NGC
7129 FIRS 2. Combining these observations with Herschel data and modeling their
emissions, we constrain the C18O and HDO abundance profiles across the
protostellar envelope. In particular, we derive the abundance of C18O and HDO
in the hot core. The intensities of the C18O lines are well reproduced assuming
that the C18O abundance decreases through the protostellar envelope from the
outer edge towards the centre until the point where the gas and dust reach the
CO evaporation temperature (~20-25 K) where the C18O is released back to the
gas phase. Once the C18O is released to the gas phase, the modelled C18O
abundance is found to be ~1.6x10^{-8}, which is a factor of 10 lower than the
reference abundance. This result is supported by the non-detection of C18O 9-8,
which proves that even in the hot core (T_k>100 K) the CO abundance must be 10
times lower than the reference value. Several scenarios are discussed to
explain this C18O deficiency. One possible explanation is that during the
pre-stellar and protostellar phase, the CO is removed from the grain mantles by
reactions to form more complex molecules. Our HDO modeling shows that the
emission of HDO 3_{12}-2_{21} line is maser and comes from the hot core
(T_k>100 K). Assuming the physical structure derived by Crimier et al. (2010),
we determine a HDO abundance of ~0.4 - 1x10^{-7} in the hot core of this IM
protostar, similar to that found in the hot corinos NGC 1333 IRAS 2A and IRAS
16293-2422.Comment: 10 pages, 7 figure
Fundamental properties of the Population II fiducial stars HD 122563 and Gmb 1830 from CHARA interferometric observations
We have determined the angular diameters of two metal-poor stars, HD 122563
and Gmb 1830, using CHARA and Palomar Testbed Interferometer observations. For
the giant star HD 122563, we derive an angular diameter theta_3D = 0.940 +-
0.011 milliarcseconds (mas) using limb-darkening from 3D convection simulations
and for the dwarf star Gmb 1830 (HD 103095) we obtain a 1D limb-darkened
angular diameter theta_1D = 0.679 +- 0.007 mas. Coupling the angular diameters
with photometry yields effective temperatures with precisions better than 55 K
(Teff = 4598 +- 41 K and 4818 +- 54 K --- for the giant and the dwarf star,
respectively). Including their distances results in very well-determined
luminosities and radii (L = 230 +- 6 L_sun, R = 23.9 +- 1.9 R_sun and L = 0.213
+- 0.002 L_sun, R = 0.664 +- 0.015 R_sun, respectively). We used the CESAM2k
stellar structure and evolution code in order to produce models that fit the
observational data. We found values of the mixing-length parameter alpha (which
describes 1D convection) that depend on the mass of the star. The masses were
determined from the models with precisions of <3% and with the well-measured
radii excellent constraints on the surface gravity are obtained (log g = 1.60
+- 0.04, 4.59 +- 0.02, respectively). The very small errors on both log g and
Teff provide stringent constraints for spectroscopic analyses given the
sensitivity of abundances to both of these values. The precise determination of
Teff for the two stars brings into question the photometric scales for
metal-poor stars.Comment: accepted A&A, 8 dbl-column pages, incl. 7 tables and 4 figure
First results of the Herschel Key Program 'Dust, Ice and Gas in Time': Dust and Gas Spectroscopy of HD 100546
We present far-infrared spectroscopic observations, taken with the
Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space
Observatory, of the protoplanetary disk around the pre-main-sequence star HD
100546. These observations are the first within the DIGIT Herschel key program,
which aims to follow the evolution of dust, ice, and gas from young stellar
objects still embedded in their parental molecular cloud core, through the
final pre-main-sequence phases when the circumstellar disks are dissipated.
Our aim is to improve the constraints on temperature and chemical composition
of the crystalline olivines in the disk of HD 100546 and to give an inventory
of the gas lines present in its far-infrared spectrum. The 69 \mu\m feature is
analyzed in terms of position and shape to derive the dust temperature and
composition. Furthermore, we detected 32 emission lines from five gaseous
species and measured their line fluxes. The 69 \mu\m emission comes either from
dust grains with ~70 K at radii larger than 50 AU, as suggested by blackbody
fitting, or it arises from ~200 K dust at ~13 AU, close to the midplane, as
supported by radiative transfer models. We also conclude that the forsterite
crystals have few defects and contain at most a few percent iron by mass.
Forbidden line emission from [CII] at 157 \mu\m and [OI] at 63 and 145 \mu\m,
most likely due to photodissociation by stellar photons, is detected.
Furthermore, five H2O and several OH lines are detected. We also found high-J
rotational transition lines of CO, with rotational temperatures of ~300 K for
the transitions up to J=22-21 and T~800 K for higher transitions
Dust, Ice and Gas in Time (DIGIT) Herschel program first results: A full PACS-SED scan of the gas line emission in protostar DK Cha
DK Cha is an intermediate-mass star in transition from an embedded
configuration to a star plus disk stage. We aim to study the composition and
energetics of the circumstellar material during this pivotal stage. Using the
Range Scan mode of PACS on the Herschel Space Observatory, we obtained a
spectrum of DK Cha from 55 to 210 micron as part of the DIGIT Key Program.
Almost 50 molecular and atomic lines were detected, many more than the 7 lines
detected in ISO-LWS. Nearly the entire ladder of CO from J=14-13 to 38-37
(E_u/k = 4080 K), water from levels as excited as E_u/k = 843 K, and OH lines
up to E_u/k = 290 K were detected. The continuum emission in our PACS SED scan
matches the flux expected from a model consisting of a star, a surrounding disk
of 0.03 Solar mass, and an envelope of a similar mass, supporting the
suggestion that the object is emerging from its main accretion stage.
Molecular, atomic, and ionic emission lines in the far-infrared reveal the
outflow's influence on the envelope. The inferred hot gas can be photon-heated,
but some emission could be due to C-shocks in the walls of the outflow cavity.Comment: 4 Page letter, To appear in A&A special issue on Hersche
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