356 research outputs found
Unveiling the circumstellar environment towards a massive young stellar object
As a continuation of a previous work, in which we found strong evidence of
massive molecular outflows towards a massive star forming site, we present a
new study of this region based on very high angular resolution observations
with the aim of discovering the outflow driven mechanism. Using near-IR data
acquired with Gemini-NIRI at the broad H- and Ks-bands, we study a region of
22" x 22" around the UCHII region G045.47+0.05, a massive star forming site at
the distance of about 8 kpc. To image the source with the highest spatial
resolution possible we employed the adaptative optic system ALTAIR, achieving
an angular resolution of about 0.15". We discovered a cone-like shape nebula
with an opening angle of about 90 degree extending eastwards the IR source
2MASS J19142564+1109283, a very likely MYSO. This morphology suggests a cavity
that was cleared in the circumstellar material and its emission may arise from
scattered continuum light, warm dust, and likely emission lines from
shock-excited gas. The nebula, presenting arc-like features, is connected with
the IR source through a jet-like structure, which is aligned with the blue
shifted CO outflow found in a previous study. The near-IR structure lies ~3"
north of the radio continuum emission, revealing that it is not spatially
coincident with the UCHII region. The observed morphology and structure of the
near-IR nebula strongly suggest the presence of a precessing jet. In this study
we have resolved the circumstellar ambient (in scale of a thousand A.U.) of a
distant MYSO, indeed one of the farthest cases.Comment: Accepted in A&A Letters (October 2013
Studying the Molecular Ambient towards the Young Stellar Object EGO G35.04-0.47
We are performing a systematic study of the interstellar medium around
extended green objects (EGOs), likely massive young stellar objects driving
outflows. EGO G35.04-0.47 is located towards a dark cloud at the northern-west
edge of an HII region. Recently, H2 jets were discovered towards this source,
mainly towards its southwest, where the H2 1-0 S(1) emission peaks. Therefore,
the source was catalogued as the Molecular Hydrogen emission-line object MHO
2429. In order to study the molecular ambient towards this star-forming site,
we observed a region around the aforementioned EGO using the Atacama
Submillimeter Telescope Experiment in the 12CO J=3--2, 13CO J=3--2, HCO+
J=4--3, and CS J=7--6 lines with an angular and spectral resolution of 22" and
0.11 km s-1, respectively. The observations revealed a molecular clump where
the EGO is embedded at v_LSR ~ 51 km s-1, in coincidence with the velocity of a
Class I 95 GHz methanol maser previously detected. Analyzing the 12CO line we
discovered high velocity molecular gas in the range from 34 to 47 km s-1, most
likely a blueshifted outflow driven by the EGO. The alignment and shape of this
molecular structure coincide with those of the southwest lobe of MHO 2429
mainly between 46 and 47 km s-1, confirming that we are mapping its CO
counterpart. Performing a SED analysis of EGO G35.04-0.47 we found that its
central object should be an intermediate-mass young stellar object accreting
mass at a rate similar to those found in some massive YSOs. We suggest that
this source can become a massive YSO.Comment: accepted to be published in PASJ - 24 September 201
A view of Large Magellanic Cloud HII regions N159, N132, and N166 through the 345 GHz window
We present results obtained towards the HII regions N159, N166, and N132 from
the emission of several molecular lines in the 345 GHz window. Using ASTE we
mapped a 2.4' 2.4' region towards the molecular cloud N159-W in the
CO J=3-2 line and observed several molecular lines at an IR peak very
close to a massive young stellar object. CO and CO J=3-2 were
observed towards two positions in N166 and one position in N132. The CO
J=3-2 map of the N159-W cloud shows that the molecular peak is shifted
southwest compared to the peak of the IR emission. Towards the IR peak we
detected emission from HCN, HNC, HCO, CH J=4-3, CS J=7-6, and
tentatively CO J=3-2. This is the first reported detection of these
molecular lines in N159-W. The analysis of the CH line yields more
evidence supporting that the chemistry involving this molecular species in
compact and/or UCHII regions in the LMC should be similar to that in Galactic
ones. A non-LTE study of the CO emission suggests the presence of both cool and
warm gas in the analysed region. The same analysis for the CS, HCO, HCN,
and HNC shows that it is very likely that their emissions arise mainly from
warm gas with a density between to some cm. The
obtained HCN/HNC abundance ratio greater than 1 is compatible with warm gas and
with an star-forming scenario. From the analysis of the molecular lines
observed towards N132 and N166 we propose that both regions should have similar
physical conditions, with densities of about 10 cm.Comment: accepted in MNRAS (October 5, 2015
ASTE observations in the 345 GHz window towards the HII region N113 of the Large Magellanic Cloud
N113 is an HII region located in the central part of the Large Magellanic
Cloud (LMC) with an associated molecular cloud very rich in molecular species.
Most of the previously observed molecular lines cover the frequency range
85-270 GHz. Thus, a survey and study of lines at the 345 GHz window is required
in order to have a more complete understanding of the chemistry and excitation
conditions of the region. We mapped a region of 2.5' x 2.5' centered at N113
using the Atacama Submillimeter Telescope Experiment in the 13CO J=3-2 line
with an angular and spectral resolution of 22" and 0.11 km/s, respectively. In
addition, we observed 16 molecular lines as single pointings towards its
center. For the molecular cloud associated with N113, from the 13CO J=3-2 map
we estimate LTE and virial masses of about 1x10^4 and 4.5x10^4 M_sun,
respectively. Additionally, from the dust continuum emission at 500 micron we
obtain a mass of gas of 7x10^3 M_sun. Towards the cloud center we detected
emission from: 12CO, 13CO, C18O (3-2), HCN, HNC, HCO+, C2H (4-3), and CS (7-6);
being the first reported detection of HCN, HNC, and C2H (4-3) lines from this
region. The CS (7-6) which was previously tentatively detected is confirmed in
this study. By analyzing the HCN, HNC, and C2H, we suggest that their emission
may arise from a photodissociation region (PDR). Moreover, we suggest that the
chemistry involving the C2H in N113 can be similar to that in Galactic PDRs.
Using the HCN J=4-3, J=3-2, and J=1-0 lines in a RADEX analysis we conclude
that we are observing very high density gas, between some 10^5 and 10^7 cm-3.Comment: accepted for publication in A&A, September 9, 201
The molecular environment of the pillar-like features in the HII region G46.5-0.2
At the interface of HII regions and molecular gas peculiar structures appear,
some of them with pillar-like shapes. Understanding their origin is important
for characterizing triggered star formation and the impact of massive stars on
the interstellar medium. In order to study the molecular environment and the
influence of the radiation on two pillar-like features related to the HII
region G46.5-0.2, we performed molecular line observations with the Atacama
Submillimeter Telescope Experiment, and spectroscopic optical observations with
the Isaac Newton Telescope. From the optical observations we identified the
star that is exciting the HII region as a spectral type O4-6. The molecular
data allowed us to study the structure of the pillars and a HCO+ cloud lying
between them. In this HCO+ cloud, which have not any well defined 12CO
counterpart, we found direct evidence of star formation: two molecular outflows
and two associated near-IR nebulosities. The outflows axis orientation is
perpendicular to the direction of the radiation flow from the HII region.
Several Class I sources are also embedded in this HCO+ cloud, showing that it
is usual that the YSOs form large associations occupying a cavity bounded by
pillars. On the other hand, it was confirmed that the RDI process is not
occurring in one of the pillar tips.Comment: Accepted in MNRAS (2017 June 13
Measuring the physical imprints of gas flows in galaxies I: Accretion rate histories
Galaxies are expected to accrete pristine gas from their surroundings to
sustain their star formation over cosmic timescales. Its lower abundance
affects the metallicity of the ISM in which stars are born, leaving chemical
imprints in the stellar populations. We measure the amount of pristine gas that
galaxies accrete during their lifetime, using information on the ages and
abundances of their stellar populations and a chemical evolution model. We also
aim to determine the efficiency of star formation over time. We derived star
formation histories and metallicity histories for a sample of 8523 galaxies
from the MaNGA survey. We use the former to predict the evolution of the
metallicity in a closed-box scenario, and estimate for each epoch the gas
accretion rate required to match these predictions with the measured stellar
metallicity. Using only chemical parameters, we find that the history of gas
accretion depends on the mass of galaxies. More massive galaxies accrete more
gas and at higher redshifts than less massive galaxies, which accrete their gas
over longer periods. We also find that galaxies with a higher star formation
rate at z = 0 have a more persistent accretion history for a given mass. The
star formation efficiency shows similar correlations: early-type galaxies and
higher-mass galaxies had a higher efficiency in the past, and it declined such
that they are less efficient in the present. Our analysis of individual
galaxies shows that compactness affects the peak star formation efficiency that
galaxies reach, and that the slope of the efficiency history of galaxies with
current star formation is flat. Our results support the hypothesis that a
steady and substantial supply of pristine gas is required for persistent star
formation in galaxies. Once they lose access to this gas supply, star formation
comes to a halt.Comment: 17 pages, 11 figures. Accepted at A&
Bone Morphogenetic Protein and its Option as an Alveolar Cleft Treatment
Indexación: Scopus; Scielo.Bone morphogenetic protein (BMP) is an endogenous protein that has shown significant effects in the promotion of bone formation. BMP also has been described in the reconstruction of traumatic and pathological bone defects, including alveolar cleft, alveolar ridge augmentation, maxillary sinus elevation, and applications in post-extraction alveolus graft, and peri-implant surgery among others. Despite the advantages associated with the use of BMP, currently is applied in combination with collagen matrices, which has certain properties such as low mechanical resistance and a high burst initial release that diminish its effectiveness in bone formation. In this context, the development of novel systems with greater mechanical resistance and prolonged release of BMP, that lead to chemotaxis of mesenchymal cells, following by its differentiation to osteoblasts represents a major challenge that holds outstanding clinical potential for the stimulation of bone formation. In this paper, we describe the use of BMP for the reconstruction of alveolar clefts, and its advantages being administrated in polymeric microparticles as sustain release system with promising applications in the stimulation of bone formation.http://ref.scielo.org/ps5w6
A charge-coupled device photometric study of south hemispheric contact binary ae phoenicis
The complete charge-coupled device light curves in B, V, R, and I bands of the short-period binary system, AE Phe, are presented. It is found that the light curves of AE Phe belong to typical EW-type light variation. Photometric solutions were derived by using the 2003 version of the Wilson-Devinney code. It showed that AE Phe is a W-subtype shallow-contact system (f = 14.6%(0.5%)) with a mass ratio of q = 2.5491(0.0092). The temperature difference between the two components is 227 K. Analysis of the O - C curve suggests that the period of AE Phe shows a long-term continuous increase at a rate of dP/dt = +6.17(0.44) × 10-8 days year-1. The long-term period increase, the marginal-contact configuration, and the astrophysical parameters of the binary system, all suggest that it is a shallow-contact binary undergoing a thermal relaxation oscillation evolving into a detached binary.Facultad de Ciencias Astronómicas y GeofÃsicasInstituto de AstrofÃsica de La Plat
A charge-coupled device photometric study of south hemispheric contact binary AE Phoenicis
The complete charge-coupled device light curves in B, V, R, and I bands of the short-period binary system, AE Phe, are presented. It is found that the light curves of AE Phe belong to typical EW-type light variation. Photometric solutions were derived by using the 2003 version of the Wilson–Devinney code. It showed that AE Phe is a Wsubtype shallow-contact system (f = 14.6%(±0.5%)) with a mass ratio of q = 2.5491(±0.0092). The temperature difference between the two components is 227 K. Analysis of the O − C curve suggests that the period of AE Phe shows a long-term continuous increase at a rate of dP /dt = +6.17(±0.44) × 10−8 days year−1. The longterm period increase, the marginal-contact configuration, and the astrophysical parameters of the binary system, all suggest that it is a shallow-contact binary undergoing a thermal relaxation oscillation evolving into a detached binary.Fil: He, J. J.. Chinese Academy of Sciences; República de ChinaFil: Qian, S. B.. Chinese Academy of Sciences; República de ChinaFil: Fernandez Lajus, Eduardo Eusebio. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto de AstrofÃsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y GeofÃsicas. Instituto de AstrofÃsica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y GeofÃsicas; ArgentinaFil: Fariña, Cecilia. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto de AstrofÃsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y GeofÃsicas. Instituto de AstrofÃsica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y GeofÃsicas; Argentin
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