arXiv subjects

Robert Estalella

Publications and source records attributed to Robert Estalella.

At least 37 records · Page 2Linked to original sources

arXiv2013

Interferometric observations of nitrogen-bearing molecular species in the star-forming core ahead of HH 80N

We present VLA NH3 and PdBI NH2D and H13NC observations of the star forming core ahead of HH 80N, the optically obscured northern counterpart of the Herbig-Haro objects HH 80/81. The main goal is to determine the kinematical information of the high density regions of the core ($n\lesssim 10^5$ cm$^{-3}$), missed in previous works due to the depletion of the species observed (e.g. CS). The obtained maps show different kinematical signatures between the eastern and western parts of the core, suggesting a possible dynamical interaction of the core with the HH 80/81/80N outflow. The analysis of the Position-Velocity (PV) plots of these species rules out a previous interpretation of having a molecular ring-like structure of $6\times 10^4$ AU of radius traced by CS infalling onto a central protostar found in the core (IRS1). High degree of deuteration, with respect to the central part of the core harboring IRS1, is derived in the eastern part, where a dust condensation (SE) is located. This deuteration trend of NH3 suggests that SE is in a prestellar evolutionary stage, earlier than that of the IRS1. Since SE is the closest condensation to the HH 80N/81/80N outflow, in case of having outflow-core dynamical interaction, it should be perturbed first and be the most evolved condensation in the core. Therefore, the derived evolutionary sequence for SE and IRS1 makes the outflow triggered star formation on IRS1 unlikely.

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arXiv2013

Properties of dense cores in clustered massive star-forming regions at high angular resolution

We aim at characterising dense cores in the clustered environments associated with massive star-forming regions. For this, we present an uniform analysis of VLA NH3(1,1) and (2,2) observations towards a sample of 15 massive star-forming regions, where we identify a total of 73 cores, classify them as protostellar, quiescent starless, or perturbed starless, and derive some physical properties. The average sizes and ammonia column densities are 0.06 pc and 10^15 cm^-2, respectively, with no significant differences between the starless and protostellar cores, while the linewidth and rotational temperature of quiescent starless cores are smaller, 1.0 km/s and 16 K, than those of protostellar (1.8 km/s, 21 K), and perturbed starless (1.4 km/s, 19 K) cores. Such linewidths and temperatures for these quiescent starless cores in the surroundings of massive stars are still significantly larger than the typical values measured in starless cores of low-mass star-forming regions, implying an important non-thermal component. We confirm at high angular resolutions the correlations previously found with single-dish telescopes between the linewidth, the temperature of the cores, and the bolometric luminosity. In addition, we find a correlation between the temperature of each core and the incident flux from the most massive star in the cluster, suggesting that the large temperatures measured in the starless cores of our sample could be due to heating from the nearby massive star. A simple virial equilibrium analysis seems to suggest a scenario of a self-similar, self-graviting, turbulent, virialised hierarchy of structures from clumps (0.1-10 pc) to cores (0.05 pc). A closer inspection of the dynamical state taking into account external pressure effects, reveal that relatively strong magnetic field support may be needed to stabilise the cores, or that they are unstable and thus on the verge of collapse.

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arXiv2013

Deciphering the ionized gas content in the massive star forming complex G75.78+0.34

We present sub-arcsecond observations toward the massive star forming region G75.78+0.34. We used the Very Large Array to study the centimeter continuum and H2O and CH3OH maser emission, and the Owens Valley Radio Observatory and Submillimeter Array to study the millimeter continuum and recombination lines (H40alpha and H30alpha). We found radio continuum emission at all wavelengths, coming from three components: (1) a cometary ultracompact (UC) HII region with an electron density 3.7x10^4 cm^{-3}, excited by a B0 type star, and with no associated dust emission; (2) an almost unresolved UCHII region (EAST), located 6 arcsec to the east of the cometary UCHII region, with an electron density 1.3x10^5 cm^{-3}, and associated with a compact dust clump detected at millimeter and mid-infrared wavelengths; and (3) a compact source (CORE), located 2 arcsec to the southwest of the cometary arc, with a flux density increasing with frequency, and embedded in a dust condensation of 30 Msun. The CORE source is resolved into two compact and unresolved sources which can be well-fit by two homogeneous hypercompact HII regions each one photo-ionized by a B0.5 ZAMS star, or by free-free radiation from shock-ionized gas resulting from the interaction of a jet/outflow system with the surrounding environment. The spatial distribution and kinematics of water masers close to the CORE-N and S sources, together with excess emission at 4.5 mum and the detected dust emission, suggest that the CORE source is a massive protostar driving a jet/outflow.

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arXiv2012

Unveiling a network of parallel filaments in the Infrared Dark Cloud G14.225-0.506

We present the results of combined NH3(1,1) and (2,2) line emission observed with the Very Large Array and the Effelsberg 100m telescope of the Infrared Dark Cloud G14.225-0.506. The NH3 emission reveals a network of filaments constituting two hub-filament systems. Hubs are associated with gas of rotational temperature Trot \sim 25 K, non-thermal velocity dispersion ~1.1 km/s, and exhibit signs of star formation, while filaments appear to be more quiescent (Trot \sim 11 K, non-thermal velocity dispersion ~0.6 km/s). Filaments are parallel in projection and distributed mainly along two directions, at PA \sim 10 deg and 60 deg, and appear to be coherent in velocity. The averaged projected separation between adjacent filaments is between 0.5 pc and 1pc, and the mean width of filaments is 0.12 pc. Cores within filaments are separated by ~0.33 pc, which is consistent with the predicted fragmentation of an isothermal gas cylinder due to the 'sausage'-type instability. The network of parallel filaments observed in G14.225-0.506 is consistent with the gravitational instability of a thin gas layer threaded by magnetic fields. Overall, our data suggest that magnetic fields might play an important role in the alignment of filaments, and polarization measurements in the entire cloud would lend further support to this scenario.

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arXiv2012

Early stages of cluster formation: fragmentation of massive dense cores down to ~1000 AU

In order to study the fragmentation of massive dense cores, which constitute the cluster cradles, we observed with the PdBI in the most extended configuration the continuum at 1.3 mm and the CO(2-1) emission of four massive cores. We detect dust condensations down to ~0.3 Msun and separate millimeter sources down to 0.4" or ~1000 AU, comparable to the sensitivities and separations reached in optical/infrared studies of clusters. The CO(2-1) high angular resolution images reveal high-velocity knots usually aligned with previously known outflow directions. This, in combination with additional cores from the literature observed at similar mass sensitivity and spatial resolution, allowed us to build a sample of 18 protoclusters with luminosities spanning 3 orders of magnitude. Among the 18 regions, ~30% show no signs of fragmentation, while 50% split up into ~4 millimeter sources. We compiled a list of properties for the 18 massive dense cores, such as bolometric luminosity, total mass, and mean density, and found no correlation of any of these parameters with the fragmentation level. In order to investigate the combined effects of magnetic field, radiative feedback and turbulence in the fragmentation process, we compared our observations to radiation magneto-hydrodynamic simulations, and found that the low-fragmented regions are well reproduced in the magnetized core case, while the highly-fragmented regions are consistent with cores where turbulence dominates over the magnetic field. Overall, our study suggests that the fragmentation in massive dense cores could be determined by the initial magnetic field/turbulence balance in each particular core.

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arXiv2012

Centimeter continuum observations of the northern head of the HH 80/81/80N jet: revising the actual dimensions of a parsec scale jet

We present 6 and 20 cm JVLA/VLA observations of the northern head of the HH 80/81/80N jet, one of the largest collimated jet systems known so far, aimed to look for knots further away than HH 80N, the northern head of the jet. Aligned with the jet and 10 arcmin northeast of HH 80N, we found a radio source not reported before, with a negative spectral index similar to that HH 80, HH 81 and HH 80N. The fit of a precessing jet model to the knots of the HH 80/81/80N jet, including the new source, shows that the position of this source is close to the jet path resulting from the modeling. If the new source belongs to the HH 80/81/80N jet, its derived size and dynamical age are 18.4 pc and >9000 yr, respectively. If the jet is symmetric, its southern lobe would expand beyond the cloud edge resulting in an asymmetric appearance of the jet. Based on the updated dynamical age, we speculate on the possibility that the HH 80/81/80N jet triggered the star formation observed in a dense core found ahead of HH 80N, which shows signposts of interaction with the jet. These results indicate that pc scale radio jets can play a role on the stability of dense clumps and the regulation of star formation in the molecular cloud.

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arXiv2012

The counterjet of HH 30: new light on its binary driving source

We present new [SII] images of the HH 30 jet and counterjet observed in 2006, 2007, and 2010 that allowed us to measure with improved accuracy the positions and proper motions of the jet and counterjet knots. Our results show that the motion of the knots is essentially ballistic, with the exception of the farthest knots, which trace the large scale C-shape bending of the jet. The observed bending of the jet can be produced by a relative motion of the HH 30 star with respect to its surrounding environment, caused either by a possible proper motion of the HH 30 star, or by the entrainment of environment gas by the red lobe of the nearby L1551-IRS 5 outflow. Alternatively, the bending can be produced by the stellar wind from a nearby CTTS, identified in the 2MASS catalog. The proper motion velocities of the knots of the counterjet show more variations than those of the jet. In particular, we identify two knots of the counterjet that have the same kinematic age but whose velocities differ by almost a factor of two. Thus, it appears that counterjet knots launched simultaneously can be ejected with very different velocities. We confirm that the observed wiggling of the jet and counterjet arises from the orbital motion of the jet source in a binary system. Precession is of secondary importance in shaping the jet. We derive an orbital period $τ_o=114\pm2$ yr and a mass function $mμ_c^3=0.014\pm0.006$ $M_\odot$. For a mass of the system of $m=0.45\pm0.04$ $M_\odot$ (the value inferred from the disk kinematics) we obtain a mass $m_j=0.31\pm0.04$ $M_\odot$ for the jet source, a mass $m_c=0.14\pm0.03$ $M_\odot$ for the companion, and a binary separation of $a=18.0\pm0.6$ AU. This binary separation coincides with the value required to account for the size of the inner hole observed in the disk, attributed to tidal truncation in a binary system.

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arXiv2012

Probing the physical and chemical structure of the CS core in LDN 673. Multitransitional and continuum observations

High-angular resolution observations of dense molecular cores show that these cores can be clumpier at smaller scales, and that some of these clumps can also be unbound or transient. The use of chemical models of the evolution of the molecular gas provides a way to probe the physical properties of the clouds. We study the properties of the clump and inter-clump medium in the starless CS core in LDN 673 by carrying out a molecular line survey with the IRAM 30-m telescope toward two clumps and two inter-clump positions. We also observed the 1.2-mm continuum with the MAMBO-II bolometer at IRAM. The dust continuum map shows four condensations, three of them centrally peaked, coinciding with previously identified sub-millimetre sources. We confirm that the denser clump of the region, $n\sim3.6 \times10^5$\cmt, is also the more chemically evolved, and it could still undergo further fragmentation. The inter-clump medium positions are denser than previously expected, likely $n\sim1\times10^3$--1$\times10^4$\cmt\ due to contamination, and are chemically young, similar to the gas in the lower density clump position. We argue that the density contrast between these positions and their general young chemical age would support the existence of transient clumps in the lower density material of the core. We were also able to find reasonable fits of the observationally derived chemical abundances to models of the chemistry of transient clumps.

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arXiv2012

VLBI multi-epoch water maser observations toward massive protostars

VLBI multi-epoch water maser observations are a powerful tool to study the gas very close to the central engine responsible for the phenomena associated with the early evolution of massive protostars. In this paper we present a summary of the main observational results obtained toward the massive star-forming regions of Cepheus A and W75N. These observations revealed unexpected phenomena in the earliest stages of evolution of massive objects (e.g., non-collimated "short-lived" pulsed ejections in different massive protostars), and provided new insights in the study of the dynamic scenario of the formation of high-mass stars (e.g., simul- taneous presence of a jet and wide-angle outflow in the massive object Cep A HW2, similar to what is observed in low-mass protostars). In addition, with these observations it has been possible to identify new, previously unseen centers of high-mass star formation through outflow activity.

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arXiv2011

Intermediate-mass hot cores at 500 AU: disks or outflows?

Observations with the Plateau de Bure Interferometer in the most extended configuration toward two intermediate-mass star-forming regions, IRAS22198+6336 and AFGL5142, reveal the presence of several complex organic molecules at ~500 AU scales, confirming the presence of hot cores in both regions. The hot cores are not rich in CN-bearing molecules, as often seen in massive hot cores, and are mainly traced by CH3CH2OH, (CH2OH)2, CH3COCH3, and CH3OH, with additionally CH3CHO, CH3OD and HCOOD for IRAS22198+6336, and C6H, and O13CS for AFGL5142. The emission of complex molecules is resolved down to sizes of ~300 and ~600 AU, for IRAS22198+6336 and AFGL5142, respectively, and most likely is tracing protostellar disks rather than flattened envelopes or toroids as usually found. This is specially clear for the case of IRAS22198+6336, where we detect a velocity gradient for all the mapped molecules perpendicular to the most chemically rich outflow of the region, yielding a dynamic mass >4 Msun. As for AFGL5142, the hot core emission is resolved into two elongated cores separated 1800 AU. A detailed comparison of the complex molecule peaks to the new CO(2-1) data and H2O maser data from literature suggests that also for AFGL5142 the complex molecules are mainly associated with disks, except for a faint and extended molecular emission found to the west, which is possibly produced in the interface between one of the outflows and the dense surrounding gas.

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arXiv2011

A multi-wavelength study of the star-forming core ahead of HH 80N

We present observations of continuum emission in the MIR to mm wavelength range, complemented with ammonia observations, of the dense core ahead of the radio Herbig Haro object HH 80N, found in the GGD 27 region. The continuum emission in all the observed bands peaks at the same position, consistent with the presence of an embedded object, HH 80N-IRS1, within the core. The distribution of the VLA ammonia emission is well correlated with that of the dust, suggesting that photochemical effects caused by the nearby Herbig Haro object do not play an important role in shaping this particular molecular emission. In order to unveil the nature of HH 80N-IRS1 we analyzed the continuum data of this source, using self-consistent models of protostellar collapse. We find that a young protostar surrounded by a slowly rotating collapsing envelope of radius $\sim$0.08 pc and 20 \msun\ plus a circumstellar disk of radius $\sim$300 AU and 0.6 \msun\ provide a good fit to the observed spectral energy distribution and to the maps at 350 \micron, 1.2 mm and 3.5 mm of HH 80N-IRS1. Besides, the APEX and PdBI continuum maps at 350 \micron\ and 3.5 mm, respectively, reveal additional clumps in the continuum emission. Given the modeling results and the observed morphology of the emission, we propose a scenario consisting of a central embedded Class 0 object, HH 80N-IRS1, with the rest of material of the HH 80N core possibly undergoing fragmentation that may lead to the formation of several protostars

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arXiv2010

N2H+ depletion in the massive protostellar cluster AFGL 5142

We aim at investigating with high angular resolution the NH3/N2H+ ratio toward the high-mass star-forming region AFGL 5142 in order to study whether this ratio behaves similarly to the low-mass case, for which the ratio decreases from starless cores to cores associated with YSOs. CARMA was used to observe the 3.2 mm continuum and N2H+(1-0) emission. We used NH3(1,1) and (2,2), HCO+(1-0) and H13CO+(1-0) data from the literature and we performed a time-dependent chemical modeling of the region. The 3.2 mm continuum emission reveals a dust condensation of ~23 Msun associated with the massive YSOs, deeply embedded in the strongest NH3 core (hereafter central core). The N2H+ emission reveals two main cores, the western and eastern core, located to the west and to the east of the mm condensation, and surrounded by a more extended and complex structure of ~0.5 pc. Toward the central core the N2H+ emission drops significantly, indicating a clear chemical differentiation in the region. We found low values of the NH3/N2H+ ratio ~50-100 toward the western/eastern cores, and high values up to 1000 in the central core. The chemical model indicates that density, and in particular temperature, are key parameters in determining the NH3/N2H+ ratio. The high density and temperature reached in the central core allow molecules like CO to evaporate from grain mantles. The CO desorption causes a significant destruction of N2H+, favoring the formation of HCO+. This result is supported by our observations, which show that N2H+ and HCO+ are anticorrelated in the central core. The observed values of the NH3/N2H+ ratio in the central core can be reproduced by our model for times t~4.5-5.3x10^5 yr (central) and t~10^4-3x10^6 yr (western/eastern). The NH3/N2H+ ratio in AFGL 5142 does not follow the same trend as in regions of low-mass star formation mainly due to the high temperature reached in hot cores.

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arXiv2010

Young starless cores embedded in the magnetically dominated Pipe Nebula

The Pipe Nebula is a massive, nearby dark molecular cloud with a low star-formation efficiency which makes it a good laboratory to study the very early stages of the star formation process. The Pipe Nebula is largely filamentary, and appears to be threaded by a uniform magnetic field at scales of few parsecs, perpendicular to its main axis. The field is only locally perturbed in a few regions, such as the only active cluster forming core B59. The aim of this study is to investigate primordial conditions in low-mass pre-stellar cores and how they relate to the local magnetic field in the cloud. We used the IRAM 30-m telescope to carry out a continuum and molecular survey at 3 and 1 mm of early- and late-time molecules toward four selected starless cores inside the Pipe Nebula. We found that the dust continuum emission maps trace better the densest regions than previous 2MASS extinction maps, while 2MASS extinction maps trace better the diffuse gas. The properties of the cores derived from dust emission show average radii of ~0.09 pc, densities of ~1.3x10^5 cm^-3, and core masses of ~2.5 M_sun. Our results confirm that the Pipe Nebula starless cores studied are in a very early evolutionary stage, and present a very young chemistry with different properties that allow us to propose an evolutionary sequence. All of the cores present early-time molecular emission, with CS detections toward all the sample. Two of them, Cores 40 and 109, present strong late-time molecular emission. There seems to be a correlation between the chemical evolutionary stage of the cores and the local magnetic properties that suggests that the evolution of the cores is ruled by a local competition between the magnetic energy and other mechanisms, such as turbulence.

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arXiv2010

IRAS 22198+6336: Discovery of an Intermediate-Mass Hot Core

We present new SMA and PdBI observations of the intermediate-mass object IRAS 22198+6336 in the millimeter continuum and in several molecular line transitions. The millimeter continuum emission reveals a strong and compact source with a mass of around 5 Msun and with properties of Class 0 objects. CO emission shows an outflow with a quadrupolar morphology centered on the position of the dust condensation. The CO outflow emission seems to come from two distinct outflows, one of them associated with SiO outflow emission. A large set of molecular lines has been detected toward a compact dense core clearly coincident with the compact millimeter source, and showing a velocity gradient perpendicular to the outflow traced by CO and SiO. The chemically rich spectrum and the rotational temperatures derived from CH$_3$CN and CH$_3$OH (100-150 K) indicate that IRAS 22198+6336 is harbouring one the few intermediate-mass hot cores known at present.

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arXiv2009

The molecular emission of the irradiated star forming core ahead of HH 80N

We present a Berkeley-Illinois-Maryland Association (BIMA) Array molecular survey of the star forming core ahead of HH 80N, the optically obscured northern counterpart of the Herbig-Haro objects HH 80/81. Continuum emission at 1.4 mm and 8 micron is detected at the center of the core, which confirms the presence of an embedded very young stellar object in the core. All detected molecular species arise in a ring-like structure, which is most clearly traced by CS(2-1) emission. This molecular ring suggests that strong molecular depletion occurs in the inner part of the core (at a radius of ~0.1 pc and densities higher than ~5 x 10^4 cm^{-3}). Despite of the overall morphology and kinematic similarity between the different species, there is significant molecular differentiation along the ring-like structure. The analysis of the chemistry along the core shows that part of this differentiation may be caused by the UV irradiation of the nearby HH 80N object, that illuminates the part of the core facing HH 80N, which results in an abundance enhancement of some of the detected species.

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arXiv2007

Unveiling the nature and interaction of the intermediate/high-mass YSOs in IRAS 20343+4129

In order to elucidate the nature of the brightest infrared sources associated with IRAS 20343+4129, IRS1 and IRS3, we observed with the Submillimeter Array (SMA) the 1.3 mm continuum and CO(2-1) emission of the region. Faint millimeter dust continuum emission was detected toward IRS1, and we derived an associated gas mass of ~0.8 Msun. The IRS1 spectral energy distribution agrees with IRS1 being an intermediate-mass Class I source of about 1000 Lsun, whose circumstellar material is producing the observed large infrared excess. We have discovered a high-velocity CO bipolar outflow in the east-west direction, which is clearly associated with IRS1, and the outflow parameters are similar to those of intermediate-mass young stellar objects. Associated with the blue large scale CO outflow lobe, detected with single-dish observations, we only found two elongated low-velocity structures on either side of IRS3. The large-scale outflow lobe is almost completely resolved out by the SMA. Our detected low-velocity CO structures are coincident with elongated H2 emission features. The strongest millimeter continuum condensations in the region are found on either side of IRS3, where the infrared emission is extremely weak, and the CO and H2 elongated structures follow the border of the millimeter continuum emission that is facing IRS3. All these results suggest that the dust is associated with the walls of an expanding cavity driven by IRS3, estimated to be a B2 star. Within and beyond the expanding cavity, the millimeter continuum sources can be sites of future low-mass star formation.

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arXiv2007

Proper Motions of the Jets in the Region of HH 30 and HL/XZ Tau. Evidence for a Binary Exciting Source of the HH 30 Jet

We present [SII] images of the HH 30 and HL/XZ Tau region obtained at two epochs, as well as long-slit optical spectroscopy of the HH 30 jet. We measured proper motions of about 100-300 km/s for the HH 30 jet and counterjet, and of about 120 km/s for the HL Tau jet. Inclination angles with respect to the plane of the sky are 0-40 deg for the HH 30 jet and 60 deg for the HL Tau jet. Comparison with previous observations suggests that most of the jet knots consist of persisting structures. Also, we corroborate that the HH 30-N knots correspond to the head of the HH 30 jet. The overall HH 30 jet structure can be well described by a wiggling ballistic jet, arising either by the orbital motion of the jet source around a primary or by precession of the jet axis because of the tidal effects of a companion. In the first scenario, the orbital period would be 53 yr and the total mass 0.25-2 solar masses. In the precession scenario, the mass of the jet source would be 0.1-1 solar masses, the orbital period <1 yr, and the mass of the companion less than a few times 0.01 solar masses, thus being a substellar object or a giant exoplanet. In both scenarios a binary system with a separation <18 AU (<0.13 arcsec) is required. Since the radius of the flared disk observed with the HST is about 250 AU, we conclude that this disk appears to be circumbinary rather than circumstellar, suggesting that the search for the collimating agent of the HH 30 jet should be carried out at much smaller scales.

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arXiv2007

Star formation in a clustered environment around the UCHII region in IRAS 20293+3952

We aim at studying the cluster environment surrounding the UCHII region in IRAS 20293+3952, a region in the first stages of formation of a cluster around a high-mass star. BIMA and VLA were used to observe the 3 mm continuum, N2H+(1-0), NH3(1,1) and (2,2), and CH3OH(2-1) emission of the surroundings of the UCHII region. We studied the kinematics of the region and computed the rotational temperature and column density maps by fitting the hyperfine structure of N2H+ and NH3. The dense gas traced by N2H+ and NH3 shows two different clouds, a main cloud to the east of the UCHII region, of 0.5 pc and 250 Msun, and a western cloud, of 0.15 pc and 30 Msun. The dust emission reveals two strong components in the northern side of the main cloud, associated with Young Stellar Objects (YSOs) driving molecular outflows, and two fainter components in the southern side, with no signs of star forming activity. Regarding the CH3OH, we found strong emission in a fork-like structure associated with outflow B, as well as emission associated with outflow A. The rotational temperature is higher in the northern side of the main cloud, around 22 K, where there are most of the YSOs, than in the southern side, around 16 K. There is strong chemical differentiation in the region, since we determined low values of the NH3/N2H+ ratio, around 50, associated with YSOs in the north of the main cloud, and high values, up to 300, associated with cores with no detected YSOs, in the south of the main cloud. Such a chemical differentiation is likely due to abundance/depletion effects. Finally, interaction between the different sources in the region is important, mainly through their UV radiation and outflows (abridged).

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