arXiv subjects

M. B. Areal

Publications and source records attributed to M. B. Areal.

13 recordsLinked to original sources

arXiv2022

Studying a precessing jet of a massive young stellar object within a chemically rich region

In addition to the large surveys and catalogs of massive young stellar objects and outflows, dedicated studies of particular sources, in which high-angular observations (mainly at near-IR and mm) are analyzed in depth, are needed to shed light on the processes involved in the formation of massive stars. The galactic source G079.1272+02.2782 (G79), a MYSO at about 1.4 kpc, is an ideal source to carry out this kind of studies. Near-IR integral field spectroscopic observations were carried out using NIFS at Gemini-North. The spectral and angular resolutions, allow us to perform a detailed study of the source and its southern jet, resolving structures with sizes between 200 and 300 au. As a complement, millimeter data retrieved from the JCMT and the IRAM 30m telescope databases were analyzed to study the molecular gas at a larger spatial scale. The analysis of a jet extending southwards shows cork-screw like structures at 2.2 um continuum, strongly suggesting that the jet is precessing. The jet velocity is estimated in 30-43 km/s and it is coming to us along the line of sight. We suggest that the precession may be produced by the gravitational tidal effects generated in a probable binary system, and we estimate a jet precession period of about 10^3 yr, indicating a slow-precessing jet, which is in agreement with the observed helical features. An analysis of H2 lines along the jet allows us to investigate in detail a bow-shock produced by this jet. We find that this bow-shock is indeed generated by a C-type shock and it is observed coming to us, with some inclination angle, along the line of sight. This is confirmed by the analysis of molecular outflows at a larger spatial scale. A brief analysis of several molecular species at millimeter wavelengths indicates a complex chemistry developing at the external layers of the molecular clump in which MYSO G79 is embedded.

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arXiv2022

Studying a hot molecular core embedded in a photodissociation region

At the first Galactic quadrant, at l=33.134, b=-0.091, an extended photodissociation region generated by an HII region complex lies. This region is related to abundant molecular gas, and particularly, a hot molecular core, known as G33.133-mm3, appears embedded in a molecular clump. Using data from the James Clerk Maxwell Telescope with an angular resolution of about 15", we studied the 13CO/C18O abundance ratio towards the mentioned molecular clump and its relation with the ultraviolet radiation. At smaller spatial scales, using data from the Atacama Large Millimeter Array (angular resolution about 0.7\arcsec), the hot molecular core G33.133-mm3, that has a size of about 2600 au, and is an appropriate site to form stars, was characterized. In particular, some points about its chemistry are mentioned based on the emission of the cyanide or nitrile radical (CN) and others more complex molecules, such as CH3OH, CH3CN, CH3OCHO, and CH3CCH.

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arXiv2021

Cyano radical emission at small spatial scales towards massive protostars

The cyano radical (CN), one of the first detected interstellar molecular species, is a key molecule in many astrochemical chains. Particularly, it is detected towards molecular cores, the birth places of the stars, and it is known that it is involved in the rich chemistry that takes place in these sites. At present there are not so many studies about the emission of this molecular species at small spatial scales towards massive young stellar objects. Thus, we present a high-angular resolution CN study towards a sample of massive protostars, with the aim of unveiling the spatial distribution at the small scale of the emission of this radical in relation to the star-forming processes. The interstellar CN has a strong emission line at the rest frequency 226874.764 MHz, thus, we search for observing projects in the ALMA database regarding high-mass star-forming regions observed at Band 6. A sample of ten high-mass star-forming regions were selected in base on that they present a clear emission of CN at the mentioned frequency. We found that the CN traces both molecular condensations and diffuse and extended gas surrounding them. In general, the molecular condensations traced by the maximums of the CN emission do not spatially coincide with the peaks of the continuum emission at 1.3 mm, which trace the molecular cores where the massive stars born. Based on the presence or lack of near-IR emission associated with such cores, we suggest that our sample is composed by sources at different stages of evolution. The CN is present at both, suggesting that this radical may be ubiquitous along the different star formation stages, and hence it may be involved in different chemical reactions occurring along the time in the formation of the stars. Additionally, other complex molecules were detected towards the continuum peaks of some of the analyzed cores.

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arXiv2021

Studying the interstellar medium to look for relics of triggered star formation among stellar clusters

Evidence of triggered star formation at large spatial scales involving stellar clusters is scarce. We investigate a Galactic region (l=130.0, b=0.35) populated by several open stellar clusters that according to the last GAIA data release, are located at a distance of about 2.9 kpc. By analyzing the interstellar medium (ISM) at infrared, centimeter, and millimeter wavelengths towards this group of clusters we discovered a shell of material of about 2 degree in size at the same distance. We suggest that the shell, mainly observed at 12 um and in the Hi emission at 21 cm, was generated by the action of massive stars belonging to clusters Berkeley 7 and UBC 414, that lie at its center. Five clusters (MWSC0152, Czernik 6, Czernik 7, Berkeley 6, NGC 663, and NGC 654) lie at the border of this shell. From the comparison between the dynamical time of the discovered Hi shell and the analysis of the ages of stellar populations in these clusters, we conclude that the expansion of the shell could have triggered in the past the formation of stars in some of them. We point out that in order to find physical evidence supporting a genetic connection between stellar clusters, it is necessary not only to study the individual clusters and their stellar populations, but also to investigate their surrounding ISM at a large spatial scale.

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arXiv2021

Multiple molecular outflows and fragmentation in the IRDC core G34.43+00.24 MM1

The fragmentation of a molecular cloud that leads to the formation of high-mass stars occurs on a hierarchy of different spatial scales. The large molecular clouds harbour massive molecular clumps with massive cores embedded in them. The fragmentation of these cores may determine the initial mass function and the masses of the final stars. Therefore, studying the fragmentation processes in the cores is crucial to understand how massive stars form. The hot molecular core G34-MM1, embedded in IRDC G34.34+00.24 located at a distance of 3.6 kpc, is a promising object to study both the fragmentation and outflow processes. Using data at 93 and 334 GHz obtained from the Atacama Large Millimeter Array (ALMA) database we studied G34-MM1 with great detail. The angular resolution of the data at 334 GHz allowed us to resolve structures of about 0.014 pc ($\sim$2900 au). We found evidence of fragmentation towards the molecular hot core G34-MM1 at two different spatial scales. The dust condensation MM1-A (about 0.06 pc in size) harbours three molecular subcores candidates (SC1 through SC3) detected in $^{12}$CO J=3-2 emission, with typical sizes of about 0.02 pc. From the HCO$^+$ J=1-0 emission, we identify, with better angular resolution than previous observations, two perpendicular molecular outflows arising from MM1-A. We suggest that subcores SC1 and SC2, embedded in MM1-A, harbour the sources responsible of the main and the secondary molecular outflow, respectively. Finally, from the radio continuum emission at 334 GHz, we marginally detected another dust condensation, named MM1-E, from which a young, massive, and energetic molecular outflow arises. The fragmentation of the hot molecular core G34-MM1 at two different spatial scales, together with the presence of multiple molecular outflows associated with it, would support a competitive accretion scenario.

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arXiv2020

Studying star-forming processes at core and clump scales: the case of the young stellar object G29.862-0.0044

Massive molecular clumps fragment into cores where star formation takes place, hence star-forming studies should be done at different spatial scales. Using near-IR data obtained with Gemini, data of CH3OCHO and CH3CN from the ALMA database, observations of HCN, HNC, HCO+, and C2H carried out with ASTE, and CO data from public surveys, we perform a deep study of the YSO G29.86-0.004 at core and clump spatial scales. The near-IR emission shows two nebulosities separated by a dark lane, suggesting a typical disk-jets system, but highly asymmetric. They are likely produced by scattered light in cavities carved out by jets on an infalling envelope of material, which also present line emission of H2 and [FeII]. The presence of the complex molecular species observed with ALMA confirms that we are mapping a hot molecular core. The CH3CN emission concentrates at the position of the dark lane and it appears slightly elongated from southwest to northeast in agreement with the inclination of the system as observed at near-IR. The morphology of the CH3OCHO emission is more complex and extends along some filaments and concentrates in knots and clumps, mainly southwards the dark-lane, suggesting that the southern jet is encountering a dense region. The northern jet flows more freely, generating more extended features. This is in agreement with the red-shifted molecular outflow traced by the 12CO J=3-2 line extending towards the northwest and the lack of a blue-shifted outflow. This configuration can be explained by considering that the YSO is located at the furthest edge of the molecular clump along the line of sight, which is consistent with the position of the source in the cloud mapped in the C18O J=3-2 line. The detection of HCN, HNC, HCO+, and C2H allowed us to characterize the dense gas at clump scales, yielding results that are in agreement with the presence of a high-mass protostellar object.

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arXiv2020

Three generations of stars: a possible case of triggered star formation

Evidence for triggered star formation linking three generations of stars is difficult to assemble, as it requires convincingly associating evolved massive stars with Hii regions that, in turn, would need to present signs of active star formation. We present observational evidence for triggered star formation relating three generations of stars in the neighbourhood of the star LS II +26 8. We carried out new spectroscopic observations of LS II +26 8, revealing that it is a B0 III-type star. We note that LS II +26 8 is located exactly at the geometric centre of a semi-shell-like Hii region complex. The most conspicuous component of this complex is the Hii region Sh2-90, which is probably triggering a new generation of stars. The distances to LS II +26 8 and to Sh2-90 are in agreement (between 2.6 and 3 kpc). Analysis of the interstellar medium on a larger spatial scale shows that Hii region complex lies on the northwestern border of an extended H2 shell. The radius of this molecular shell is about 13 pc, which is in agreement with what an O9V star (the probable initial spectral type of LS II +26 8 as inferred from evolutive tracks) can generate through its winds in the molecular environment. In conclusion, the spatial and temporal correspondences derived in our analysis enable us to propose a probable triggered star formation scenario initiated by the evolved massive star LS II +26 8 during its main sequence stage, followed by stars exciting the Hii region complex formed in the molecular shell, and culminating in the birth of YSOs around Sh2-90.

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arXiv2020

Studying the molecular gas towards a bright rimmed cloud at the infrared dust bubble N30

We present a study on the molecular gas towards a bright-rimmed cloud located to the north of the infrared dust bubble N30. Using the emission from the 12CO, 13CO, and C18O J=3-2 line, together with infrared and radio continuum data, we characterized the bubble and the related molecular cloud. In addition, we show an analysis of the behaviour of the abundance ratio 13CO/C18O towards the bright-rimmed cloud, and we search for clues on recent star-formation.

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arXiv2019

Kinematic study of the molecular gas associated with two cometary globules in Sh2-236

Cometary globules, dense molecular gas structures exposed to the UV radiation, are found inside HII regions. Understanding the nature and origin of these structures through a kinematic study of the molecular gas is useful to advance in our knowledge of the interplay between radiation and molecular gas. Using ASTE we carried out molecular observations towards two cometary globules (Sim129 and Sim130) in the HII region Sh2-236. We mapped two regions with the 12CO J=3-2 and HCO+ J=4-3 lines. Additionally, two single pointings of C2H (N=4-3), HNC and HCN J=4-3 were observed. We combined our observations with public infrared and optical data to analyse the distribution and kinematics of the gas. We found kinematic signatures of infalling gas in the 12CO J=3-2 and C2H J=4-3 spectra towards Sim129 . We detected HCO+, HCN, and HNC J=4-3 only towards Sim130. The HCN/HNC integrated ratio of about 3 found in Sim130 suggests that the possible star formation activity within the globule has not yet ionized the gas. The location of NVSS 052255+33315, which peaks towards the brightest border of the globule, supports this scenario. The non-detection of these molecules towards Sim129 could be due to the radiation arising from the star formation activity inside this globule. The ubiquitous presence of the C2H molecule towards both globules shows the action of nearby O-B stars irradiating their external layers. Based on mid-infrared emission, we identified two new structures: a region of diffuse emission (R1) located, in projection, in front of the head of Sim129, and a pillar-like feature (P1) placed besides Sim130. Based on 12CO J=3-2, we found molecular gas associated with Sim129, Sim130, R1 and P1 at radial velocities of -1.5, -11, +10, and +4 km/s, respectively. Therefore, while Sim129 and P1 are located at the far side of the shell, Sim130 is placed at the near side, consistent with earlier results.

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arXiv2019

Study of the 13CO/C18O abundance ratio towards the filamentary infrared dark cloud IRDC 34.43+0.24

Nowadays there are several observational studies about the 13CO/C18O abundance ratio (X) towards nearby molecular clouds. These works give observational support to the C18O selective photodissociation due to the interaction between the FUV radiation and the molecular gas. It is necessary to increase the sample of molecular clouds located at different distances and affected in different ways by nearby or embedded HII regions and OB associations to study the selective photodissociation. Using 12CO, 13CO, and C18O J=1-0 data obtained from the FOREST Survey, we analyze the filamentary infrared dark cloud IRDC34.43+0.24 located at the distance of about 3.9 kpc. This IRDC is related to several HII regions and YSOs. Assuming LTE we obtain: 0.8x10^16<N(13CO)<4x10^17cm^-2, 0.6x10^15<N(C18O)<4.4x10^16cm^-2, and 3<X<30 across the whole IRDC. Larger values of X were found towards portions of the cloud related to the HII regions associated with the N61 and N62 bubbles and with the photodissociation regions (PDRs), precisely the regions in which FUV photons are strongly interacting with the molecular gas. Our result represents an observational support to the C18O selectively photodissociation phenomenon occurring in a quite distant filamentary IRDC. Additionally, based on IR data from the Hi-GAL survey, the FUV radiation field was estimated in Habing units, and the dust temperature and N(H2) distribution was studied. Using the average of N(H2), values in close agreement with the canonical abundance ratios [H2]/[13CO] and [H2]/[C18O] were derived. However, the obtained ranges in the abundance ratios show that if an accurate analysis of the molecular gas is required, the use of the canonical values may introduce some bias. Thus, it is important to consider how the gas is irradiated by the far ultraviolet photons across the molecular cloud. The analysis of X is a good tool to perform that.

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arXiv2019

Studying star-forming processes towards G29.862-0.044

We present a multiwavelength study towards the young stellar object (YSO) G29.862-0.044 (hereafter G29), which is embedded in the massive star-forming region G29.96-0.02, located at a distance of about 6.5 kpc. The surrounding interstellar medium of G29 is studied using molecular lines data (angular resolution about 15'') obtained from the databases of the James Clerk Maxwell Telescope. The physical conditions of G29 molecular outflows and the clump where the YSO is embedded are characterized. Near-IR data is also analyzed (spatial resolution of about 0.5'') obtained with NIRI at Gemini North to have a detailed view of the circumstellar ambient of G29. The Ks emission towards G29 exhibits a cone-like feature pointing to the red molecular outflow. The aim of this work is to obtain a complete picture of this YSO, the related star-forming processes, and the interstellar medium around it. Studies like this are important because they contribute to a comprehensive understanding of star formation.

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arXiv2018

Mapping the 13CO/C18O abundance ratio in the massive star forming region G29.96-0.02

Estimating molecular abundances ratios from the direct measurement of the emission of the molecules towards a variety of interstellar environments is indeed very useful to advance in our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio (X), is studied in detail. We selected the well-studied high-mass star-forming region G29.96-0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this kind of studies. To study the X towards this region it was used 12CO J=3-2 data obtained from COHRS, 13CO and C18O J=3-2 data from CHIMPS, and 13CO and C18O J=2-1 data retrieved from the CDS database (observed with the IRAM 30m telescope). The distribution of column densities and X throughout the molecular cloud was studied based on LTE and non-LTE methods. Values of X between 1.5 to 10.5, with an average of 5, were found, showing that, besides the dependency between X and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which ones it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially across the cloud, but also along the line of sight. This kind of studies may represent a tool to indirectly estimate (from molecular lines observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

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arXiv2017

Exploring the 13CO/C18O abundance ratio towards Galactic young stellar objects and HII regions

Determining molecular abundance ratios is important not only for the study of the Galactic chemistry but also because they are useful to estimate physical parameters in a large variety of interstellar medium environments. The CO is one of the most important molecules to trace the molecular gas in the interstellar medium, and the 13CO/C18O abundance ratio is usually used to estimate molecular masses and densities of regions with moderate to high densities. Nowadays this kind of isotopes ratios are in general indirectly derived from elemental abundances ratios. We present the first 13CO/C18O abundance ratio study performed from CO isotopes observations towards a large sample of Galactic sources of different nature at different locations. To study the 13CO/C18O abundance ratio it was used 12CO J=3-2 data obtained form the CO High-Resolution Survey, 13CO and C18O J=3-2 data from the 13CO/C18O (J=3-2) Heterodyne Inner Milky Way Plane Survey, and some complementary data extracted from the James Clerk Maxwell Telescope database. It was analyzed a sample of 198 sources composed by young stellar objects (YSOs), HII and diffuse HII regions as catalogued in the Red MSX Source Survey in 27.5 < l < 46.5 and |b| < 0.5. Most of the analyzed sources are located in the galactocentric distance range 4.0-6.5 kpc. We found that YSOs have, in average, smaller 13CO/C18O abundance ratios than HII and diffuse HII regions. Taking into account that the gas associated with YSOs should be less affected by the radiation than in the case of the others sources, selective far-UV photodissociation of C18O is confirmed. The 13CO/C18O abundance ratios obtained in this work are systematically lower than the predicted from the known elemental abundance relations. These results would be useful in future studies of molecular gas related to YSOs and HII regions based on the observation of these isotopes.

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