arXiv subjects

Linda Podio

Publications and source records attributed to Linda Podio.

At least 55 records · Page 3Linked to original sources

arXiv2020

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) V: Sample, overview, and demography of disk molecular emission

We present an overview of the ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT), a campaign devoted to the characterization of the molecular emission from partly embedded, young stars. The project aims at better understanding the gaseous products that are delivered to planets by means of high-resolution maps of assorted lines probing disks at the time of the planet formation (less than 1 Myr). Nine different molecules are surveyed by our observations of six Class I/flat-spectrum sources. A series of accompanying articles analyze specific targets and molecules. Here we describe the sample and provide a general overview of the results, focusing on the spatial distribution, column densities, and abundance ratios of H$_2$CO, CS, and CN. The results of this work are a first step toward the characterization of the disk chemical evolution that need to be complemented by further observations of less exceptional disks and customized thermo-chemical modeling.

astro-ph.GA↗

arXiv2020

H$_2$ mass-velocity relationship from 3D numerical simulations of jet-driven molecular outflows

Previous numerical studies have shown that in protostellar outflows, the mass-velocity distribution $m(v)$ can be well described by a broken power law $\propto v^{- γ}$. On the other hand, recent observations of a sample of outflows show that the CO intensity-velocity distribution, closely related to $m(v)$, follows an exponential law $\propto \exp(-v/v_0)$. In the present work, we revisit the physical origin of the mass-velocity relationship $m(v)$ in jet-driven protostellar outflows. We investigate the respective contributions of the different regions of the outflow, from the swept-up ambient gas to the jet. We performed 3D numerical simulations of a protostellar jet propagating into a molecular cloud using the hydrodynamical code Yguazu-a. The code takes into account atomic and ionic species and was modified to include the H$_2$ gas. We find that by excluding the jet contribution, $m(v)$ is satisfyingly fitted with a single exponential law, with $v_0$ well in the range of observational values. The jet contribution results in additional components in the mass-velocity relationship. This empirical mass-velocity relationship is found to be valid locally in the outflow. The exponent $v_0$ is almost constant in time and for a given level of mixing between the ambient medium and the jet material. In general, $v_0$ displays only a weak spatial dependence. A simple modeling of the L1157 outflow successfully reproduces the various components of the observed CO intensity-velocity relationship. Our simulations indicate that these components trace the outflow cavity of swept-up gas and the material entrained along the jet, respectively. The CO intensity-velocity exponential law is naturally explained by the jet-driven outflow model. The entrained material plays an important role in shaping the mass-velocity profile.

astro-ph.GA↗

arXiv2020

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT): I. CO, CS, CN, and H2CO around DG Tau B

The chemical composition of planets is inherited by the distribution of the various molecular species in the protoplanetary disk at thetime of their formation. As of today, only a handful of disks has been imaged in multiple spectral lines with high spatial resolution. As part of a small campaign devoted to the chemical characterization of disk-outflow sources in Taurus, we report on new ALMA Band 6 observations with 20 au resolution toward the embedded young star DG Tau B. Images of the continuum emission reveals a dust disk with rings and, putatively, a leading spiral arm. The disk, as well as the prominent outflow cavities, are detected in CO, H2CO, CS, and CN while they remain undetected in SO2, HDO, and CH3OH. From the absorption of the back-side outflow, we inferred that the disk emission is optically thick in the inner 50 au. This morphology explains why no line emission is detected from this inner region and poses some limitations toward the calculation of the dust mass and the characterization of the inner gaseous disk. The H2CO and CS emission from the inner 200 au is mostly from the disk and their morphology is very similar. The CN emission significantly differs from the other two molecules as it is observed only beyond 150 au. This ring-like morphology is consistent with previous observations and the predictions of thermochemical disk models. Finally, we constrained the disk-integrated column density of all molecules. In particular, we found that the CH3OH/H2CO ratio must be smaller than 2, making the methanol non-detection still consistent with the only such a ratio available from the literature (1.27 in TW Hya).

astro-ph.SR↗

arXiv2019

The HH 212 interstellar laboratory: astrochemistry as a tool to reveal protostellar disks on Solar System scales around a rising Sun

The investigation of star forming regions have enormously benefited from the recent advent of the ALMA interferometer. More specifically, the unprecedented combination of high-sensitivity and high-angular resolution provided by ALMA allows one to shed light on the jet/disk systems associated with a Sun-like mass protostar. Also astrochemistry enjoyed the possibility to analyze complex spectra obtained using large bandwidths: several interstellar Complex Organic Molecules (iCOMs; C-bearing species with at least 6 atoms) have been imaged around protostars. This in turn boosted the study of the astrochemistry at work during the earliest phases of star formation paving the way to the chemical complexity in planetary systems where Life could emerge. There is mounting evidence that the observations of iCOMs can be used as unique tool to shed light, on Solar System scales (< 50 au), on the molecular content of protostellar disk. The increase of iCOMs abundances occur only under very selective physical conditions, such as those associated low-velocity shocks found where the infalling envelope is impacting the rotating accretion disk. The imaging of these regions with simpler molecules such as CO or CS is indeed paradoxically hampered by their high abundances and consequently high line opacities which do not allow the observers to disentangle all the emitting components at these small scales. In this respect, we review the state-of-the art of the ALMA analysis about the standard Sun-like star forming region in Orion named HH 212. We show (i) how all the physical components involved in the formation of a Sun-like star can be revealed only by observing different molecular tracers, and (ii) how the observation of iCOMs emission, observed to infer the chemical composition of star forming regions, can be used also as unique tracer to image protostellar disks on Solar System scales.

astro-ph.SR↗

arXiv2019

Sulfur Chemistry in L1157-B1

The main carrier of sulfur in dense clouds, where it is depleted from the gas phase, remains a mystery. Shock waves in young molecular outflows disrupt the ice mantles and allow us to directly probe the material that is ejected into the gas phase. A comprehensive study of sulfur-bearing species towards L1157-B1, a shocked region along a protostellar outflow, has been carried out as part of the IRAM-30m large program ASAI. The dataset contains over 100 lines of CCS, H$_2$CS, OCS, SO, SO$_2$ and isotopologues. The results of these observations are presented, complementing previous studies of sulfur-bearing species in the region. The column densities and fractional abundances of these species are measured and together these species account for 10\% of the cosmic sulfur abundance in the region. The gas properties derived from the observations are also presented, demonstrating that sulfur bearing species trace a wide range of different gas conditions in the region.

astro-ph.GA↗

arXiv2018

Young Stars and their Variability with LSST

Young stars exhibit short-term photometric variability caused by mass accretion events from circumstellar disks, the presence of dusty warps within the inner disks, starspots that rotate across the stellar surfaces, and flares. Long-term variability also occurs owing to starspot longevity and cycles, and from changes in stellar angular momenta and activity as the stars age. We propose to observe the Carina star-forming region in different bands with a cadence of 30 minutes every night for one week per year to clarify the nature of both the short-term and long-term variability of the thousands of young stars in this region. By obtaining well-sampled multicolor lightcurves of this dense young cluster, LSST would acquire the first statistically significant data on how these objects vary on both short and long timescales. This information will allow us to relate the observed variability to stellar properties such as mass, age, binarity, and to environmental properties such as location within or exterior to the H II region, and to the presence or absence of a circumstellar disk.

astro-ph.SR↗

arXiv2018

ALMA observations of polarized emission toward the CW Tau and DG Tau protoplanetary disks: constraints on dust grain growth and settling

We present polarimetric data of CW Tau and DG Tau, two well-known Class II disk/jet systems, obtained with the Atacama Large Millimeter/submillimeter Array at 870 $μ$m and 0."2 average resolution. In CW Tau, the total and polarized emission are both smooth and symmetric, with polarization angles almost parallel to the minor axis of the projected disk. In contrast, DG Tau displays a structured polarized emission, with an elongated brighter region in the disk's near side and a belt-like feature beyond about 0."3 from the source. At the same time the total intensity is spatially smooth, with no features. The polarization pattern, almost parallel to the minor axis in the inner region, becomes azimuthal in the outer belt, possibly because of a drop in optical depth. The polarization fraction has average values of 1.2% in CW Tau and 0.4% in DG Tau. Our results are consistent with polarization from self-scattering of the dust thermal emission. Under this hypothesis, the maximum size of the grains contributing to polarization is in the range 100 - 150 $μ$m for CW Tau and 50 - 70 $μ$m for DG Tau. The polarization maps combined with dust opacity estimates indicate that these grains are distributed in a geometrically thin layer in CW Tau, representing a settling in the disk midplane. Meanwhile, such settling is not yet apparent for DG Tau. These results advocate polarization studies as a fundamental complement to total emission observations, in investigations of the structure and the evolution of protoplanetary disks.

astro-ph.SR↗

arXiv2018

A 100 au-Wide Bipolar Rotating Shell Emanating From The HH 212Protostellar Disk: A Disk Wind?

HH 212 is a Class 0 protostellar system found to host a "hamburger"-shaped dusty disk with a rotating disk atmosphere and a collimated SiO jet at a distance of ~ 400 pc. Recently, a compact rotating outflow has been detected in SO and SO2 toward the center along the jet axis at ~ 52 au (0.13") resolution. Here we resolve the compact outflow into a small-scale wide-opening rotating outflow shell and a collimated jet, with the observations in the same S-bearing molecules at ~ 16 au (0.04") resolution. The collimated jet is aligned with the SiO jet, tracing the shock interactions in the jet. The wide-opening outflow shell is seen extending out from the inner disk around the SiO jet and has a width of ~ 100 au. It is not only expanding away from the center, but also rotating around the jet axis. The specific angular momentum of the outflow shell is ~ 40 au km/s. Simple modeling of the observed kinematics suggests that the rotating outflow shell can trace either a disk wind or disk material pushed away by an unseen wind from the inner disk or protostar. We also resolve the disk atmosphere in the same S-bearing molecules, confirming the Keplerian rotation there.

astro-ph.GA↗

arXiv2018

Seeds of Life in Space (SOLIS). III. Zooming into the methanol peak of the pre-stellar core L1544

Towards the pre-stellar core L1544, the methanol (CH$_3$OH) emission forms an asymmetric ring around the core centre, where CH$_3$OH is mostly in solid form, with a clear peak 4000~au to the north-east of the dust continuum peak. As part of the NOEMA Large Project SOLIS (Seeds of Life in Space), the CH$_3$OH peak has been spatially resolved to study its kinematics and physical structure and to investigate the cause behind the local enhancement. We find that methanol emission is distributed in a ridge parallel to the main axis of the dense core. The centroid velocity increases by about 0.2~km~s$^{-1}$ and the velocity dispersion increases from subsonic to transonic towards the central zone of the core, where the velocity field also shows complex structure. This could be indication of gentle accretion of material onto the core or interaction of two filaments, producing a slow shock. We measure the rotational temperature and show that methanol is in local thermodynamic equilibrium (LTE) only close to the dust peak, where it is significantly depleted. The CH$_3$OH column density, $N_{tot}({\rm CH_3OH})$, profile has been derived with non-LTE radiative transfer modelling and compared with chemical models of a static core. The measured $N_{tot}({\rm CH_3OH})$ profile is consistent with model predictions, but the total column densities are one order of magnitude lower than those predicted by models, suggesting that the efficiency of reactive desorption or atomic hydrogen tunnelling adopted in the model may be overestimated; or that an evolutionary model is needed to better reproduce methanol abundance.

astro-ph.GA↗

arXiv2017

CALYPSO view of SVS 13A with PdBI: Multiple jet sources

Aims. We wish to clarify the origin of the multiple jet features emanating from the binary protostar SVS 13A (= VLA4A/VLA4B). Methods. We used the Plateau de Bure Interferometer to map at 0.3-0.8" (~70-190 au) dust emission at 1.4 mm, CO(2-1), SiO(5-4), SO(65-54). Revised proper motions for VLA4A/4B and jet wiggling models are computed to clarify their respective contribution. Results. VLA4A shows compact dust emission suggestive of a disk < 50 au, and is the hot corino source, while CO/SiO/SO counterparts to the small-scale H2 jet originate from VLA4B and reveal the jet variable velocity structure. This jet exhibits ~ 3" wiggling consistent with orbital motion around a yet undetected ~ 20-30 au companion to VLA4B, or jet precession. Jet wiggling combined with velocity variability can explain the large apparent angular momentum in CO bullets. We also uncover a synchronicity between CO jet bullets and knots in the HH7-11 chain demonstrating that they trace two distinct jets. Their ~ 300 yr twin outburst period may be triggered by close perihelion approach of VLA4A in an eccentric orbit around VLA4B. A third jet is tentatively seen at PA ~ 0 degrees. Conclusions. SVS13 A harbors at least 2 and possibly 3 distinct jet sources. The CO and HH7-11 jets are launched from quasi-coplanar disks, separated by 20-70 au. Their synchronous major events every 300 yr favor external triggering by close binary interactions, a scenario also invoked for FU Or outbursts.

astro-ph.GA↗

arXiv2016

H2S in the L1157-B1 Bow shock

Sulfur-bearing molecules are highly reactive in the gas phase of the ISM. However, the form in which most of the sulfur is locked onto interstellar dust grains is unknown. By taking advantage of the short time-scales of shocks in young molecular outflows, one could track back the main form of sulfur in the ices. In this paper, six transitions of H$_2$S and its isotopologues in the L1157-B1 bowshock have been detected using data from the Herschel-CHESS survey and the IRAM-30m ASAI large program. These detections are used to calculate the properties of H$_2$S gas in L1157-B1 through use of a rotation diagram and to explore the possible carriers of sulfur on the grains. The isotopologue detections allow the first calculation of the H$_2$S deuteration fraction in an outflow from a low mass protostar. The fractional abundance of H$_2$S in the region is found to be 6.0$\times$10$^{-7}$ and the deuteration fraction is 2$\times$10$^{-2}$. In order to investigate the form of sulfur on the grains, a chemical model is run with four different networks, each with different branching ratios for the freeze out of sulfur bearing species into molecules such as OCS and H$_2$S. It is found that the model best fits the data when at least half of each sulfur bearing species hydrogenates when freezing. We therefore conclude that a significant fraction of sulfur in L1157-B1 is likely to be locked in H$_2$S on the grains.

astro-ph.GA↗

arXiv2014

The protoplanetary disk of FT Tauri: multi-wavelength data analysis and modeling

Investigating the evolution of protoplanetary disks is crucial for our understanding of star and planet formation. Several theoretical and observational studies have been performed in the last decades to advance this knowledge. FT Tauri is a young star in the Taurus star forming region that was included in a number of spectroscopic and photometric surveys. We investigate the properties of the star, the circumstellar disk, and the accretion and ejection processes and propose a consistent gas and dust model also as a reference for future observational studies. We performed a multi-wavelength data analysis to derive the basic stellar and disk properties, as well as mass accretion/outflow rate from TNG-Dolores, WHT-Liris, NOT-Notcam, Keck-Nirspec, and Herschel-Pacs spectra. From the literature, we compiled a complete Spectral Energy Distribution. We then performed detailed disk modeling using the MCFOST and ProDiMo codes. Multi-wavelengths spectroscopic and photometric measurements were compared with the reddened predictions of the codes in order to constrain the disk properties. This object can serve as a benchmark for primordial disks with significant mass accretion rate, high gas content and typical size.

astro-ph.SR↗

arXiv2013

Herschel/PACS Survey of protoplanetary disks in Taurus/Auriga -- Observations of [OI] and [CII], and far infrared continuum

The Herschel Space Observatory was used to observe ~ 120 pre-main-sequence stars in Taurus as part of the GASPS Open Time Key project. PACS was used to measure the continuum as well as several gas tracers such as [OI] 63 μm, [OI] 145 μm, [CII] 158 μm, OH, H2O and CO. The strongest line seen is [OI] at 63 μm. We find a clear correlation between the strength of the [OI] 63 μm line and the 63 μm continuum for disk sources. In outflow sources, the line emission can be up to 20 times stronger than in disk sources, suggesting that the line emission is dominated by the outflow. The tight correlation seen for disk sources suggests that the emission arises from the inner disk ($<$ 50 AU) and lower surface layers of the disk where the gas and dust are coupled. The [OI] 63 μm is fainter in transitional stars than in normal Class II disks. Simple SED models indicate that the dust responsible for the continuum emission is colder in these disks, leading to weaker line emission. [CII] 158 μm emission is only detected in strong outflow sources. The observed line ratios of [OI] 63 μm to [OI] 145 μm are in the regime where we are insensitive to the gas-to-dust ratio, neither can we discriminate between shock or PDR emission. We detect no Class III object in [OI] 63 μm and only three in continuum, at least one of which is a candidate debris disk.

astro-ph.GA↗

arXiv2012

The star formation history of RCW 36

Recent studies of massive-star forming regions indicate that they can contain multiple generations of young stars. These observations suggest that star formation in these regions is sequential and/or triggered by a previous generation of (massive) stars. Here we present new observations of the star forming region RCW 36 in the Vela Molecular Ridge, hosting a young cluster of massive stars embedded in a molecular cloud complex. In the periphery of the cluster several young stellar objects (YSOs) are detected which produce bipolar jets (HH 1042 and HH 1043) demonstrating that these objects are still actively accreting. The VLT/X-shooter spectrum of the jet structure of HH 1042 provides detailed information on the physical conditions and kinematical properties of the jet plasma. From this information the YSO's accretion history can be derived. Combining the photometric and spectroscopic observations of RCW 36 gives insight into the formation process of individual stars and the star formation history of this young massive-star forming region.

astro-ph.SR↗

arXiv2011

The First X-shooter Observations of Jets from Young Stars

We present the first pilot study of jets from young stars conducted with X-shooter, on ESO/VLT. As it offers simultaneous, high quality spectra in the range 300-2500 nm X-shooter is uniquely important for spectral diagnostics in jet studies. We chose to probe the accretion/ejection mechanisms at low stellar masses examining two targets with well resolved continuous jets lying on the plane of the sky, ESO-HA 574 in Chamaleon I, and Par-Lup3-4 in Lupus III. The mass of the latter is close to the sub-stellar boundary (Mstar=0.13 Msun). A large number of emission lines probing regions of different excitation are identified, position-velocity diagrams are presented and mass outflow/accretion rates are estimated. Comparison between the two objects is striking. ESO-HA 574 is a weakly accreting star for which we estimate a mass accretion rate of log(\dot{Macc}) = -10.8 \pm 0.5 (in Msun/yr), yet it drives a powerful jet with \dot{Mout} ~ 1.5-2.7 10^-9 Msun/yr. These values can be reconciled with a magneto-centrifugal jet acceleration mechanism only assuming that the presence of the edge-on disk severely depresses the luminosity of the accretion tracers. In comparison Par-Lup3-4 with stronger mass accretion (log(\dot{Macc}) = -9.1 \pm 0.4 Msun/yr), drives a low excitation jet with about \dot{Mout} ~ 3.2 10^-10 Msun/yr in both lobes. Despite the low stellar mass, \dot{Mout} / \dot{Macc} for Par-Lup3-4 is at the upper limit of the range usually measured for young objects, but still compatible with a steady magneto-centrifugal wind scenario if all uncertainties are considered.

astro-ph.SR↗

arXiv2010

Tracing kinematical and physical asymmetries in the jet from DG Tau B

Stellar jets can be highly asymmetric and have multiple velocity components. To clarify the origin of jet asymmetries and constrain their launch mechanism we study the physical and kinematical structure of the flow emitted by DG Tau B. The analysis of deep spectra taken at the KECK telescope allows us to infer the physical properties (the electron and total density, ne and nh, the ionisation fraction, xe, and the temperature, te) and the spatial distribution of the velocity components in the two jet lobes. The presence of dust grains in the jet is investigated by estimating the gas-phase abundance of calcium with respect to its solar value. At the base of the jet the lines are broad (~100 km/s) and up to three velocity components are detected. At 5" from the source, however, only the denser and more excited high velocity components survive and the lines are narrower (~10-30 km/s). The jet is strongly asymmetric both in velocity and in its physical structure. The red lobe, slower (~140 km/s) and more collimated, presents low ionisation fractions (xe~0.1-0.4) and temperatures (te<5e3 K), while the total density is up to ~2.5e4 ccm. The blue lobe, faster (~-320 km/s) and less collimated, is also less dense (nh~1e4 ccm) but highly excited (te up to ~5e4 K and xe up to 0.9). The estimated mass loss rate is similar in the two lobes (~6-8e-9 Msol/yr), suggesting that the ejection power is comparable on the two sides of the system, as expected from a magneto-centrifugal ejection mechanism, and that the observed asymmetries are due to different mass load and propagation properties in an inhomogeneous environment. Calcium is strongly depleted, indicating that the jet contains dust grains and, therefore, should originate from a region of the disk extending beyond the dust sublimation radius. The depletion is lower for higher velocities, consistent with dust destruction by shocks.

astro-ph.SR↗

arXiv2010

Hydrogen permitted lines in the first near-IR spectra of Th 28 microjet: accretion or ejection tracers?

We report the first near-infrared detection of the bipolar microjet from TTauri star ThA 15-28 (aka Th 28). Spectra were obtained with VLT/ISAAC for the slit both perpendicular and parallel to the flow to examine jet kinematics and gas physics within the first arcsecond from the star. The jet was successfully detected in both molecular and atomic lines. The H_2 component was found to be entirely blueshifted around the base of the bipolar jet. It shows that only the blue lobe is emitting in H_2 while light is scattered in the direction of the red lobe, highlighting an asymmetric extinction and/or excitation between the two lobes. Consistent with this view, the red lobe is brighter in all atomic lines. Interestingly, the jet was detected not only in [Fe II], but also in Br gamma and Pa beta lines. Though considered tracers mainly of accretion, we find that these high excitation hydrogen permitted lines trace the jet as far as 150 AU from the star. This is confirmed in a number of ways: the presence of the [Fe II] 2.13 micron line which is of similarly high excitation; H I velocities which match the jet [Fe II] velocities in both the blue and red lobe; and high electron density close to the source of >6x10^4 cm^-3 derived from the [Fe II] 1.64,1.60 micron ratio. These near-infrared data complement HST/STIS optical and near-ultraviolet data for the same target which were used in a jet rotation study, although no rotation signature could be identified here due to insufficient angular resolution. The unpublished HST/STIS H alpha emission is included here along side the other H I lines. Identifying Br gamma and Pa beta as tracers of ejection is significant because of the importance of finding strong near-infrared probes close to the star, where forbidden lines are quenched, which will help understand accretion-ejection when observed with high spatial resolution instruments such as VLTI/AMBER.

physics.space-ph↗

arXiv2009

IR diagnostics of embedded jets: kinematics and physical characteristics of the HH46-47 jet

We present an analysis of the kinematics and physical properties of the Class I driven jet HH46-47 based on IR medium and low resolution spectroscopy obtained with ISAAC on VLT. Our aim is to study the gas physics as a function of the velocity and distance from the source and compare the results with similar studies performed on other Class I and CTTS jets, as well as with existing models for the jet formation and excitation. The ratios and luminosities of several important diagnostic lines have been used to derive physical parameters. [FeII] and H2 Position Velocity Diagrams (PVDs) have been in addition constructed to study the kinematics. Within 1000-2000 AU from the source the atomic gas presents a wide range of radial velocities. Only the gas component at the highest velocity (HVC) survives at large distances. The H2, shows, close to the source, only a single velocity component at almost zero velocity, while it reaches higer velocities further downstream. Electron densities (ne) and mass ejection fluxes (Mjet) have been measured separately for the HVC and LVC from the [FeII] lines. ne increases with decreasing velocities, while the opposite occurs for Mjet. The mass flux carried out by the molecular component, measured from the H2 lines flux, is ~4 10^-9 Msun/yr. We have estimated that the Fe gas phase abundance is significantly lower than the solar value, with ~88% of iron still depleted onto dust grains in the internal jet region. The derived densities and mass flux values are typical of Class I objects or very active TTauri stars. However, the spatial extent of the LVC and the velocity dependence of the electron density have been so far observed only in another Class I jet, the HH34 jet, and are not explained by the current models of jet launching.

astro-ph.SR↗