116 research outputs found
Far infrared CO and HO emission in intermediate-mass protostars
Intermediate-mass young stellar objects (YSOs) provide a link to understand
how feedback from shocks and UV radiation scales from low to high-mass star
forming regions. Aims: Our aim is to analyze excitation of CO and HO in
deeply-embedded intermediate-mass YSOs and compare with low-mass and high-mass
YSOs. Methods: Herschel/PACS spectral maps are analyzed for 6 YSOs with
bolometric luminosities of . The maps
cover spatial scales of AU in several CO and HO lines located
in the m range. Results: Rotational diagrams of CO show two
temperature components at K and
K, comparable to low- and high-mass protostars
probed at similar spatial scales. The diagrams for HO show a single
component at K, as seen in low-mass protostars, and
about K lower than in high-mass protostars. Since the uncertainties in
are of the same order as the difference between the
intermediate and high-mass protostars, we cannot conclude whether the change in
rotational temperature occurs at a specific luminosity, or whether the change
is more gradual from low- to high-mass YSOs. Conclusions: Molecular excitation
in intermediate-mass protostars is comparable to the central AU of
low-mass protostars and consistent within the uncertainties with the high-mass
protostars probed at AU scales, suggesting similar shock
conditions in all those sources.Comment: Accepted to Astronomy & Astrophysics. 4 pages, 5 figures, 3 table
Warm gas towards young stellar objects in Corona Australis - Herschel/PACS observations from the DIGIT key programme
The effects of external irradiation on the chemistry and physics in the
protostellar envelope around low-mass young stellar objects are poorly
understood. The Corona Australis star-forming region contains the R CrA dark
cloud, comprising several low-mass protostellar cores irradiated by an
intermediate-mass young star. We study the effects on the warm gas and dust in
a group of low-mass young stellar objects from the irradiation by the young
luminous Herbig Be star R CrA. Herschel/PACS far-infrared datacubes of two
low-mass star-forming regions in the R CrA dark cloud are presented. The
distribution of CO, OH, H2O, [C II], [O I], and continuum emission is
investigated. We have developed a deconvolution algorithm which we use to
deconvolve the maps, separating the point-source emission from the extended
emission. We also construct rotational diagrams of the molecular species. By
deconvolution of the Herschel data, we find large-scale (several thousand AU)
dust continuum and spectral line emission not associated with the point
sources. Similar rotational temperatures are found for the warm CO (
K), hot CO ( K), OH ( K), and H2O ( K) emission,
respectively, in the point sources and the extended emission. The rotational
temperatures are also similar to what is found in other more isolated cores.
The extended dust continuum emission is found in two ridges similar in extent
and temperature to molecular mm emission, indicative of external heating from
the Herbig Be star R CrA. Our results show that a nearby luminous star does not
increase the molecular excitation temperatures in the warm gas around a young
stellar object (YSO). However, the emission from photodissociation products of
H2O, such as OH and O, is enhanced in the warm gas associated with these
protostars and their surroundings compared to similar objects not suffering
from external irradiation.Comment: 37 pages, accepted for publication in A&
Spectroscopic Diagnostics of the Mid-Infrared Features of the Dark Globule, DC 314.8-5.1, with the Spitzer Space Telescope
We present an analysis of the mid-infrared spectra, obtained from the Spitzer
Space Telescope, of the dark globule, DC 314.8--5.1, which is at the onset of
low-mass star formation. The target has a serendipitous association with a
B-type field star, which illuminates a reflection nebula in the cloud. We focus
on the polycyclic aromatic hydrocarbon (PAH) emission features prevalent
throughout the mid-infrared range. The analysis of the spectra with the PAHFIT
software as well as pypahdb package, shows that (i) the intensities of PAH
features decrease over distance from the ionizing star toward the cloud center,
some however showing a saturation at larger distances; (ii) the relative
intensities of the 6.2 and 8.6 features with respect to the 11.2 micron feature
remain high throughout the globule, suggesting a larger cation-to-neutral PAH
ratio of the order of unity; the breakdown from pypahdb confirms a high ionized
fraction within the cloud; (iii) the pypahdb results display a decrease in
large PAH fraction with increased distance from HD 130079, as well as a
statistically significant correlation between the large size fraction and the
ionized fraction across the globule; (iv) the 7.7 PAH feature displays a peak
nearer to 7.8 microns, suggesting a chemically processed PAH population with a
small fraction of UV-processed PAHs; (v) the H2 S(0) line is detected at larger
distances from the ionizing star. All in all, our results suggest divergent
physical conditions within the quiescent cloud DC 314.8--5.1 as compared to
molecular clouds with ongoing starformation.Comment: Accepted for publication by the Astrophysical Journa
OH far-infrared emission from low- and intermediate-mass protostars surveyed with Herschel-PACS
OH is a key species in the water chemistry of star-forming regions, because
its presence is tightly related to the formation and destruction of water. This
paper presents OH observations from 23 low- and intermediate-mass young stellar
objects obtained with the PACS integral field spectrometer on-board Herschel in
the context of the Water In Star-forming Regions with Herschel (WISH) key
program. Most low-mass sources have compact OH emission (< 5000 AU scale),
whereas the OH lines in most intermediate-mass sources are extended over the
whole PACS detector field-of-view (> 20000 AU). The strength of the OH emission
is correlated with various source properties such as the bolometric luminosity
and the envelope mass, but also with the OI and H2O emission. Rotational
diagrams for sources with many OH lines show that the level populations of OH
can be approximated by a Boltzmann distribution with an excitation temperature
at around 70 K. Radiative transfer models of spherically symmetric envelopes
cannot reproduce the OH emission fluxes nor their broad line widths, strongly
suggesting an outflow origin. Slab excitation models indicate that the observed
excitation temperature can either be reached if the OH molecules are exposed to
a strong far-infrared continuum radiation field or if the gas temperature and
density are sufficiently high. Using realistic source parameters and radiation
fields, it is shown for the case of Ser SMM1 that radiative pumping plays an
important role in transitions arising from upper level energies higher than 300
K. The compact emission in the low-mass sources and the required presence of a
strong radiation field and/or a high density to excite the OH molecules points
towards an origin in shocks in the inner envelope close to the protostar.Comment: Accepted for publication in Astronomy and Astrophysics. Abstract
abridge
Multiwavelength Study of Dark Globule DC 314.8-5.1: Point Source Identification and Diffuse Emission Characterization
We present an analysis of multi-wavelength observations of the dark globule
DC\,314.8--5.1, using data from the Gaia optical, 2MASS near-infrared, and WISE
mid-infrared surveys, dedicated imaging with the Spitzer Space Telescope, and
X-ray data obtained with the Swift-XRT Telescope (XRT). The main goal was to
identify possible pre-main sequence stars (PMSs) and young stellar objects
(YSOs) associated with the globule. For this, we studied the infrared colors of
all point sources within the boundaries of the cloud. After removing sources
with non-stellar spectra, we investigated the Gaia parallaxes for the YSO
candidates, and found that none are physically related to DC\,314.8--5.1. In
addition, we searched for X-ray emission from pre-main sequence stars with
Swift-XRT, and found no 0.5--10\,keV emission down to a luminosity level
erg\,s, typical of a PMS with mass\,.
Our detailed inspection therefore supports a very young, ``pre-stellar core''
evolutionary stage for the cloud. Based on archival Planck and IRAS data, we
moreover identify the presence of hot dust, with temperatures \,K,
in addition to the dominant dust component at 14\,K, originating with the
associated reflection nebula.Comment: Accepted to A
Los juegos: una herramienta para aprender algebra
El siguiente Trabajo Fin de Máster recoge una propuesta de mejora, con respecto a la unidad didáctica presentada en el período de prácticas, basada en la utilización de juegos y de actividades de corte cooperativo.
En primer lugar se realiza un análisis de los referentes teóricos como base sobre la que se apoya esta propuesta. Posteriormente se presenta la nueva unidad didáctica.
Por último, las conclusiones nos llevan a una crítica razonada acerca de lo que aporta la propuesta presentada, una valoración de posibles nuevas mejoras y un pequeño análisis sobre la formación del docente.The following Master’s Thesis contains a proposal for improvement of a teaching unit. The proposal is based on the use of games and cooperative learning. First an analysis of the theoretical framework is done. These justify the improvement proposal. Secondly the new unit is exposed.
Finally, the conclusions lead us to a reasoned criticism about the results of the new unit, an assessment of the possible future improvements and a small analysis on teacher training
Shockingly low water abundances in Herschel / PACS observations of low-mass protostars in Perseus
Protostars interact with their surroundings through jets and winds impacting
on the envelope and creating shocks, but the nature of these shocks is still
poorly understood. Our aim is to survey far-infrared molecular line emission
from a uniform and significant sample of deeply-embedded low-mass young stellar
objects in order to characterize shocks and the possible role of ultraviolet
radiation in the immediate protostellar environment. Herschel/PACS spectral
maps of 22 objects in the Perseus molecular cloud were obtained as part of the
`William Herschel Line Legacy' survey. Line emission from HO, CO,
and OH is tested against shock models from the literature.
Observed line ratios are remarkably similar and do not show variations with
source physical parameters. Observations show good agreement with the shock
models when line ratios of the same species are compared. Ratios of various
HO lines provide a particularly good diagnostic of pre-shock gas
densities, cm, in agreement with typical
densities obtained from observations of the post-shock gas. The corresponding
shock velocities, obtained from comparison with CO line ratios, are above 20
km\,s. However, the observations consistently show one-to-two orders of
magnitude lower HO-to-CO and HO-to-OH line ratios
than predicted by the existing shock models.
The overestimated model HO fluxes are most likely caused by an
overabundance of HO in the models since the excitation is
well-reproduced. Illumination of the shocked material by ultraviolet photons
produced either in the star-disk system or, more locally, in the shock, would
decrease the HO abundances and reconcile the models with
observations. Detections of hot HO and strong OH lines support
this scenario.Comment: 28 pages, 12 figures, accepted to Astronomy & Astrophysic
CO in Protostars (COPS): -SPIRE Spectroscopy of Embedded Protostars
We present full spectral scans from 200-670m of 26 Class 0+I
protostellar sources, obtained with -SPIRE, as part of the
"COPS-SPIRE" Open Time program, complementary to the DIGIT and WISH Key
programs. Based on our nearly continuous, line-free spectra from 200-670
m, the calculated bolometric luminosities () increase by 50%
on average, and the bolometric temperatures () decrease by 10% on
average, in comparison with the measurements without Herschel. Fifteen
protostars have the same Class using and /. We identify rotational transitions of CO lines from J=4-3 to J=13-12,
along with emission lines of CO, HCO, HO, and [CI]. The ratios
of CO to CO indicate that CO emission remains optically
thick for < 13. We fit up to four components of temperature from
the rotational diagram with flexible break points to separate the components.
The distribution of rotational temperatures shows a primary population around
100 K with a secondary population at 350 K. We quantify the correlations
of each line pair found in our dataset, and find the strength of correlation of
CO lines decreases as the difference between -level between two CO lines
increases. The multiple origins of CO emission previously revealed by
velocity-resolved profiles are consistent with this smooth distribution if each
physical component contributes to a wide range of CO lines with significant
overlap in the CO ladder. We investigate the spatial extent of CO emission and
find that the morphology is more centrally peaked and less bipolar at high-
lines. We find the CO emission observed with SPIRE related to outflows, which
consists two components, the entrained gas and shocked gas, as revealed by our
rotational diagram analysis as well as the studies with velocity-resolved CO
emission.Comment: 50 pages, 18 figures, accepted to ApJS. Revised for Table 6 and
Figure
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