arXiv subjects

Ralf Launhardt

Publications and source records attributed to Ralf Launhardt.

At least 19 recordsLinked to original sources

arXiv2024

VLBI detection of nearby (< 100 pc) young stars: Pilot observations

To increase the number of sources with Very Long Baseline Interferometry (VLBI) astrometry available for comparison with the Gaia results, we have observed 31 young stars with recently reported radio emission. These stars are all in the Gaia DR3 catalog and were suggested, on the basis of conventional interferometry observations, to be non-thermal radio emitters and, therefore, good candidates for VLBI detections. The observations were carried out with the Very Long Baseline Array (VLBA) at two epochs separated by a few days and yielded 10 detections (a $\sim$30\% detection rate). Using the astrometric Gaia results, we have extrapolated the target positions to the epochs of our radio observations and compared them with the position of the radio sources. For seven objects, the optical and radio positions are coincident within five times their combined position errors. Three targets, however, have position discrepancies above eight times the position errors, indicating different emitting sources at optical and radio wavelengths. In one case, the VLBA emission is very likely associated with a known companion of the primary target. In the other two cases, we associate the VLBA emission with previously unknown companions, but further observations will be needed to confirm this.

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arXiv2023

Twenty-Five Years of Accretion onto the Classical T Tauri Star TW Hya

Accretion plays a central role in the physics that governs the evolution and dispersal of protoplanetary disks. The primary goal of this paper is to analyze the stability over time of the mass accretion rate onto TW Hya, the nearest accreting solar-mass young star. We measure veiling across the optical spectrum in 1169 archival high-resolution spectra of TW Hya, obtained from 1998--2022. The veiling is then converted to accretion rate using 26 flux-calibrated spectra that cover the Balmer jump. The accretion rate measured from the excess continuum has an average of $2.51\times10^{-9}$~M$_\odot$~yr$^{-1}$ and a Gaussian distribution with a FWHM of 0.22 dex. This accretion rate may be underestimated by a factor of up to 1.5 because of uncertainty in the bolometric correction and another factor of 1.7 because of excluding the fraction of accretion energy that escapes in lines, especially Ly$\alpha$. The accretion luminosities are well correlated with He line luminosities but poorly correlated with H$\alpha$ and H$\beta$ luminosity. The accretion rate is always flickering over hours but on longer timescales has been stable over 25 years. This level of variability is consistent with previous measurements for most, but not all, accreting young stars.

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arXiv2023

Forbidden emission lines in protostellar outflows and jets with MUSE

Forbidden emission lines in protoplanetary disks are a key diagnostic in studies of the evolution of the disk and the host star. We report spatially resolved emission lines, [OI] 6300, 6363, [NII] 6548, 6583, H$\alpha$, and [SII] 6716, 6730 Angstrom that are believed to be associated with jets and magnetically driven winds in the inner disks. Observations were carried out with the optical integral field spectrograph of the Multi Unit Spectroscopic Explorer (MUSE), at the Very Large Telescope (VLT). With a resolution of 0.025 X 0.025 arcsec$^{2}$, we aim to derive the position angle of the outflow/jet (PA$_{outflow/jet}$) that is connected with the inner disk. The forbidden emission lines analyzed here have their origin at the inner parts of the protoplanetary disk. From the maximum intensity emission along the outflow/jet in DL Tau, CI Tau, DS Tau, IP Tau, and IM Lup, we were able to reliably measure the PA$_{outflow/jet}$ for most of the identified lines. We found that our estimates agree with PA$_{dust}$ for most of the disks. These estimates depend on the signal-to-noise level and the collimation of the outflow (jet). The outflows/jets in CIDA 9, GO Tau, and GW Lup are too compact for a PA$_{outflow/jet}$ to be estimated. Based on our kinematics analysis, we confirm that DL Tau and CI Tau host a strong outflow/jet with line-of-sight velocities much greater than 100 km s$^{-1}$, whereas DS Tau, IP Tau, and IM Lup velocities are lower and their structures encompass low-velocity components to be more associated with winds. Our estimates for the mass-loss rate, $\dot{M}_{{loss}}$, range between (1.1-6.5)X10$^{-7}$-10$^{-8}$ $M_{\odot}$ yr$^{-1}$ for the disk-outflow/jet systems analyzed here. The outflow/jet systems analyzed here are aligned within around 1 degree between the inner and outer disk. Further observations are needed to confirm a potential misalignment in IM Lup.

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arXiv2022

ISPY-NACO Imaging Survey for Planets around Young stars. The demographics of forming planets embedded in protoplanetary disks

We present the statistical analysis of a subsample of 45 young stars surrounded by protoplanetary disks (PPDs). This is the largest imaging survey uniquely focused on PPDs to date. Our goal is to search for young forming companions embedded in the disk material and to constrain their occurrence rate in relation to the formation mechanism. We used principal component analysis based point spread function subtraction techniques to reveal young companions forming in the disks. We calculated detection limits for our datasets and adopted a black-body model to derive temperature upper limits of potential forming planets. We then used Monte Carlo simulations to constrain the population of forming gas giant companions and compare our results to different types of formation scenarios. Our data revealed a new binary system (HD38120) and a recently identified triple system with a brown dwarf companion orbiting a binary system (HD101412), in addition to 12 known companions. Furthermore, we detected signals from 17 disks, two of which (HD72106 and TCrA) were imaged for the first time. We reached median detection limits of L =15.4 mag at 2.0 arcsec, which were used to investigate the temperature of potentially embedded forming companions. We can constrain the occurrence of forming planets with semi-major axis a in [20 - 500] au and Teff in [600 - 3000] K, in line with the statistical results obtained for more evolved systems from other direct imaging surveys. The NaCo-ISPY data confirm that massive bright planets accreting at high rates are rare. More powerful instruments with better sensitivity in the near- to mid-infrared are likely required to unveil the wealth of forming planets sculpting the observed disk substructures.

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arXiv2022

The JWST Early Release Science Program for the Direct Imaging & Spectroscopy of Exoplanetary Systems

The direct characterization of exoplanetary systems with high contrast imaging is among the highest priorities for the broader exoplanet community. As large space missions will be necessary for detecting and characterizing exo-Earth twins, developing the techniques and technology for direct imaging of exoplanets is a driving focus for the community. For the first time, JWST will directly observe extrasolar planets at mid-infrared wavelengths beyond 5$\mu$m, deliver detailed spectroscopy revealing much more precise chemical abundances and atmospheric conditions, and provide sensitivity to analogs of our solar system ice-giant planets at wide orbital separations, an entirely new class of exoplanet. However, in order to maximise the scientific output over the lifetime of the mission, an exquisite understanding of the instrumental performance of JWST is needed as early in the mission as possible. In this paper, we describe our 55-hour Early Release Science Program that will utilize all four JWST instruments to extend the characterisation of planetary mass companions to $\sim$15$\mu$m as well as image a circumstellar disk in the mid-infrared with unprecedented sensitivity. Our program will also assess the performance of the observatory in the key modes expected to be commonly used for exoplanet direct imaging and spectroscopy, optimize data calibration and processing, and generate representative datasets that will enable a broad user base to effectively plan for general observing programs in future cycles.

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arXiv2022

Planet populations inferred from debris discs: insights from 178 debris systems in the ISPY, LEECH and LIStEN planet-hunting surveys

We know little about the outermost exoplanets in planetary systems, because our detection methods are insensitive to moderate-mass planets on wide orbits. However, debris discs can probe the outer-planet population, because dynamical modelling of observed discs can reveal properties of perturbing planets. We use four sculpting and stirring arguments to infer planet properties in 178 debris-disc systems from the ISPY, LEECH and LIStEN planet-hunting surveys. Similar analyses are often conducted for individual discs, but we consider a large sample in a consistent manner. We aim to predict the population of wide-separation planets, gain insight into the formation and evolution histories of planetary systems, and determine the feasibility of detecting these planets in the near future. We show that a `typical' cold debris disc likely requires a Neptune- to Saturn-mass planet at 10-100 au, with some needing Jupiter-mass perturbers. Our predicted planets are currently undetectable, but modest detection-limit improvements (e.g. from JWST) should reveal many such perturbers. We find that planets thought to be perturbing debris discs at late times are similar to those inferred to be forming in protoplanetary discs, so these could be the same population if newly formed planets do not migrate as far as currently thought. Alternatively, young planets could rapidly sculpt debris before migrating inwards, meaning that the responsible planets are more massive (and located further inwards) than debris-disc studies assume. We combine self-stirring and size-distribution modelling to show that many debris discs cannot be self-stirred without having unreasonably high masses; planet- or companion-stirring may therefore be the dominant mechanism in many (perhaps all) debris discs. Finally, we provide catalogues of planet predictions, and identify promising targets for future planet searches.

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arXiv2021

Unveiling wide-orbit companions to K-type stars in Sco-Cen with Gaia EDR3

Abbreviated. We aim to identify new low-mass companions to young stars using the astrometric measurements provided by the Gaia space mission and complementary VLT/SPHERE data. We identify companion candidates from a sample of K-type, pre-main sequence stars in the Scorpius Centaurus association using the early version of the third data release of the Gaia space mission. Based on the provided positions, proper motions, and magnitudes, we identify all objects within a predefined radius whose differential proper motions are consistent with a gravitationally bound system. We derive companion masses through comparison with evolutionary tracks. For seven identified companion candidates we use additional data collected with VLT/SPHERE and VLT/NACO to assess the accuracy of the properties of the companions based on Gaia photometry alone. We identify 110 comoving companions that have a companionship likelihood of more than $95\,\%$. We identify ten especially intriguing companions that have masses in the brown dwarf regime down to $20\,M_\mathrm{Jup}$. Our high-contrast imaging data confirm both astrometry and photometric masses derived from Gaia alone. We discover a new brown dwarf companion, TYC 8252-533-1 B, with a projected separation of approximately $570\,\mathrm{au}$ from its Sun-like primary. SED modeling provides a companion mass of $52^{+17}_{-11}\,M_\mathrm{Jup}$. We show that the Gaia database can identify low-mass companions at wide separations from their host stars. For K-type Sco-Cen members Gaia can detect sub-stellar objects at projected separations larger than $300\,\mathrm{au}$ and is sensitivity limited beyond $1,000\,\mathrm{au}$ with a lower mass limit down to $20\,M_\mathrm{Jup}$. A similar analysis of other star-forming regions could significantly enlarge the sample size of such objects and test formation and evolution theories of planetary systems.

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arXiv2021

Detection of Complex Organic Molecules in Young Starless Core L1521E

Determining the level of chemical complexity within dense starless and gravitationally bound prestellar cores is crucial for constructing chemical models, which subsequently constrain the initial chemical conditions of star formation. We have searched for complex organic molecules (COMs) in the young starless core L1521E, and report the first clear detection of dimethyl ether (CH$_3$OCH$_3$), methyl formate (HCOOCH$_3$), and vinyl cyanide (CH$_2$CHCN). Eight transitions of acetaldehyde (CH$_3$CHO) were also detected, five of which (A states) were used to determine an excitation temperature to then calculate column densities for the other oxygen-bearing COMs. If source size was not taken into account (i.e., if filling fraction was assumed to be one), column density was underestimated, and thus we stress the need for higher resolution mapping data. We calculated L1521E COM abundances and compared them to other stages of low-mass star formation, also finding similarities to other starless/prestellar cores, suggesting related chemical evolution. The scenario that assumes formation of COMs in gas-phase reactions between precursors formed on grains and then ejected to the cold gas via reactive desorption was tested and was unable to reproduce observed COM abundances, with the exception of CH$_3$CHO. These results suggest that COMs observed in cold gas are formed not by gas-phase reactions alone, but also through surface reactions on interstellar grains. Our observations present a new, unique challenge for existing theoretical astrochemical models.

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arXiv2020

Pebbles in an Embedded Protostellar Disk: The Case of CB26

Planetary cores are thought to form in proto-planetary disks via the growth of dusty solid material. However, it is unclear how early this process begins. We study the physical structure and grain growth in the edge-on disk that surrounds the ~1 Myr old low-mass (~0.55 Msun) protostar embedded in the Bok Globule CB26 to examine how much grain growth has already occurred in the protostellar phase. We combine the SED between 0.9 ${\mu}$m and 6.4 cm with high angular resolution continuum maps at 1.3, 2.9, and 8.1 mm, and use the radiative transfer code RADMC-3D to conduct a detailed modelling of the dust emission from the disk and envelope of CB 26. We infer inner and outer disk radii of around 16 au and 172$\pm$22 au, respectively. The total gas mass in the disk is ~0.076 Msun, which amounts to ~14% of the mass of the central star. The inner disk contains a compact free-free emission region, which could be related to either a jet or a photoevaporation region. The thermal dust emission from the outer disk is optically thin at mm wavelengths, while the emission from the inner disk midplane is moderately optically thick. Our best-fit radiative transfer models indicate that the dust grains in the disk have already grown to pebbles with diameters of the order of 10 cm in size. Residual 8.1 mm emission suggests the presence of even larger particles in the inner disk. For the optically thin mm dust emission from the outer disk, we derive a mean opacity slope of 0.6$\pm$0.4, which is consistent with the presence of large dust grains. The presence of cm-sized bodies in the CB 26 disk indicates that solids grow rapidly already during the first million years in a protostellar disk. It is thus possible that Class II disks are already seeded with large particles and may contain even planetesimals.

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arXiv2020

Resolving the outer ring of HD 38206 using ALMA and constraining limits on planets in the system

HD 38206 is an A0V star in the Columba association, hosting a debris disc first discovered by IRAS. Further observations by Spitzer and Herschel showed that the disc has two components, likely analogous to the asteroid and Kuiper belts of the Solar System. The young age of this star makes it a prime target for direct imaging planet searches. Possible planets in the system can be constrained using the debris disc. Here we present the first ALMA observations of the system's Kuiper belt and fit them using a forward modelling MCMC approach. We detect an extended disc of dust peaking at around 180 au with a width of 140 au. The disc is close to edge on and shows tentative signs of an asymmetry best fit by an eccentricity of $0.25^{+0.10}_{-0.09}$. We use the fitted parameters to determine limits on the masses of planets interior to the cold belt. We determine that a minimum of four planets are required, each with a minimum mass of 0.64 M$_J$, in order to clear the gap between the asteroid and Kuiper belts of the system. If we make the assumption that the outermost planet is responsible for the stirring of the disc, the location of its inner edge and the eccentricity of the disc, then we can more tightly predict its eccentricity, mass and semimajor axis to be $e_{\rm{p}}=0.34^{+0.20}_{-0.13}$, $m_{\rm{p}}=0.7^{+0.5}_{-0.3}\,\rm{M}_{\rm{J}}$ and $a_{\rm{p}}=76^{+12}_{-13}\,\rm{au}$.

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arXiv2019

Detection of H$\alpha$ emission from PZ Tel B using SPHERE/ZIMPOL

H$\alpha$ is a powerful tracer of accretion and chromospheric activity, which has been detected in the case of young brown dwarfs and even recently in planetary mass companions (e.g. PDS70 b and c). H$\alpha$ detections and characterisation of brown dwarf and planet companions can further our knowledge of their formation and evolution, and expanding such a sample is therefore our primary goal. We used the Zurich IMaging POLarimeter (ZIMPOL) of the SPHERE instrument at the Very Large Telescope (VLT) to observe the known $38-72$M$_{\mathrm{J}}$ companion orbiting PZ Tel, obtaining simultaneous angular differential imaging observations in both continuum and narrow H$\alpha$ band. We detect H$\alpha$ emission from the companion, making this only the second H$\alpha$ detection of a companion using the SPHERE instrument. We used our newly added astrometric measurements to update the orbital analysis of PZ Tel B, and we used our photometric measurements to evaluate the H$\alpha$ line flux. Given the estimated bolometric luminosity, we obtained an H$\alpha$ activity (log$\mathrm{(L_{H\alpha}/L_{bol}})$) between $-4.16$ and $-4.31$. The H$\alpha$ activity of PZ Tel B is consistent with known average activity levels for M dwarf of the same spectral type. Given the absence of a known gaseous disk and the relatively old age of the system (24 Myr), we conclude that the H$\alpha$ emission around PZ Tel B is likely due to chromospheric activity.

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arXiv2019

ESA Voyage 2050 White Paper: Detecting life outside our solar system with a large high-contrast-imaging mission

In this white paper, we recommend the European Space Agency plays a proactive role in developing a global collaborative effort to construct a large high-contrast imaging space telescope, e.g. as currently under study by NASA. Such a mission will be needed to characterize a sizable sample of temperate Earth-like planets in the habitable zones of nearby Sun-like stars and to search for extraterrestrial biological activity. We provide an overview of relevant European expertise, and advocate ESA to start a technology development program towards detecting life outside the Solar system.

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arXiv2019

ISPY -- NaCo Imaging Survey for Planets around Young stars. Discovery of an M dwarf in the gap between HD 193571 and its debris ring

Context. The interaction between low-mass companions and the debris discs they reside in is still not fully understood. A debris disc can evolve due to self-stirring, a process in which planetesimals can excite their neighbours to the point of destructive collisions. In addition, the presence of a companion could further stir the disc (companion-stirring). Additional information is necessary to understand this fundamental step in the formation and evolution of a planetary system, and at the moment of writing only a handful of systems are known where a companion and a debris disc have both been detected and studied at the same time. Aims. Our primary goal is to augment the sample of these systems and to understand the relative importance between self-stirring and companion-stirring. Methods. In the course of the VLT/NaCo Imaging Survey for Planets around Young stars (ISPY), we observed HD 193571, an A0 debris disc hosting star at a distance of 68 pc with an age between 60 and 170 Myr. We obtained two sets of observations in L' band and a third epoch in H band using the GPI instrument at Gemini-South. Results. A companion was detected in all three epochs at a projected separation of 11 au (0.17 arcsec), and co-motion was confirmed through proper motion analysis. Given the inferred disc size of 120 au, the companion appears to reside within the gap between the host star and the disc. Comparison between the L' and H band magnitude and evolutionary tracks suggests a mass of 0.31 - 0.39 solar masses . Conclusions. We discovered a previously unknown M-dwarf companion around HD 193571, making it the third low-mass stellar object discovered within a debris disc. A comparison to self- and companion-stirring models suggests that the companion is likely responsible for the stirring of the disc.

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arXiv2018

The CARMENES search for exoplanets around M dwarfs: A low-mass planet in the temperate zone of the nearby K2-18

K2-18 is a nearby M2.5 dwarf, located at 34 pc and hosting a transiting planet which was first discovered by the {\it K2} mission and later confirmed with {\it Spitzer Space Telescope} observations. With a radius of $\sim 2 \, R_{\oplus}$ and an orbital period of $\sim 33$ days, the planet lies in the temperate zone of its host star and receives stellar irradiation similar to Earth. Here we perform radial velocity follow-up observations with the visual channel of CARMENES with the goal of determining the mass and density of the planet. We measure a planetary semi-amplitude of $K_b \sim 3.5$ \mpersec\ and a mass of $M_b \sim 9 \, M_{\oplus}$, yielding a bulk density around $\rho_b \sim 4 \, \mathrm{g \,cm^{-3}}$. This indicates a low-mass planet with a composition consistent with a solid core and a volatile-rich envelope. A signal at 9 days was recently reported using radial velocity measurements taken with the HARPS spectrograph. This was interpreted as being due to a second planet. We see a weaker, time and wavelength dependent signal in the CARMENES data set and thus favor stellar activity for its origin. \ktwo\ joins the growing group of low-mass planets detected in the temperate zone of M dwarfs. The brightness of the host star in the near-infrared makes the system a good target for detailed atmospheric studies with the {\it James Webb Space Telescope}.

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arXiv2017

Intensity-Corrected Herschel Observations of Nearby Isolated Low-Mass Clouds

We present intensity-corrected Herschel maps at 100 um, 160 um, 250 um, 350 um, and 500 um for 56 isolated low-mass clouds. We determine the zero-point corrections for Herschel PACS and SPIRE maps from the Herschel Science Archive (HSA) using Planck data. Since these HSA maps are small, we cannot correct them using typical methods. Here, we introduce a technique to measure the zero-point corrections for small Herschel maps. We use radial profiles to identify offsets between the observed HSA intensities and the expected intensities from Planck. Most clouds have reliable offset measurements with this technique. In addition, we find that roughly half of the clouds have underestimated HSA-SPIRE intensities in their outer envelopes relative to Planck, even though the HSA-SPIRE maps were previously zero-point corrected. Using our technique, we produce corrected Herschel intensity maps for all 56 clouds and determine their line-of-sight average dust temperatures and optical depths from modified black body fits. The clouds have typical temperatures of ~ 14-20 K and optical depths of ~ 1e-5 - 1e-3. Across the whole sample, we find an anti-correlation between temperature and optical depth. We also find lower temperatures than what was measured in previous Herschel studies, which subtracted out a background level from their intensity maps to circumvent the zero-point correction. Accurate Herschel observations of clouds are key to obtain accurate density and temperature profiles. To make such future analyses possible, intensity-corrected maps for all 56 clouds are publicly available in the electronic version.

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arXiv2016

Rotating Bullets from A Variable Protostar

We present SMA CO(2-1) observations toward the protostellar jet driven by SVS13A, a variable protostar in the NGC1333 star-forming region. The SMA CO(2-1) images show an extremely high-velocity jet composed of a series of molecular 'bullets'. Based on the SMA CO observations, we discover clear and large systematic velocity gradients, perpendicular to the jet axis, in the blueshifted and redshifted bullets. After discussing several alternative interpretations, such as twin-jets, jet precession, warped disk, and internal helical shock, we suggest that the systematic velocity gradients observed in the bullets result from the rotation of the SVS13A jet. From the SMA CO images, the measured rotation velocities are 11.7-13.7 km/s for the blueshifted bullet and 4.7+/-0.5 km/s for the redshifted bullet. The estimated specific angular momenta of the two bullets are comparable to those of dense cores, about 10 times larger than those of protostellar envelopes, and about 20 times larger than those of circumstellar disks. If the velocity gradients are due to the rotation of the SVS13A jet, the significant amount of specific angular momenta of the bullets indicates that the rotation of jets/outflows is a key mechanism to resolve the so-called 'angular momentum problem' in the field of star formation. The kinematics of the bullets suggests that the jet launching footprint on the disk has a radius of about 7.2-7.7 au, which appears to support the extended disk-wind model. We note that further observations are needed to comprehensively understand the kinematics of the SVS13A jet, in order to confirm the rotation nature of the bullets.

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arXiv2013

SMA Observations of Class 0 Protostars: A High-Angular Resolution Survey of Protostellar Binary Systems

We present high angular resolution 1.3 mm and 850 um dust continuum data obtained with the Submillimeter Array toward 33 Class 0 protostars in nearby clouds (distance < 500 pc), which represents so far the largest survey toward protostellar binary/multiple systems. The median angular resolution in the survey is 2.5 arcsec, while the median linear resolution is approximately 600 AU. Compact dust continuum emission is observed from all sources in the sample. Twenty-one sources in the sample show signatures of binarity/multiplicity, with separations ranging from 50 to 5000 AU. The numbers of singles, binaries, triples, and quadruples in the sample are 12, 14, 5, and 2, respectively. The derived multiplicity frequency (MF) and companion star fraction (CSF) for Class 0 protostars are 0.64+/-0.08 and 0.91+/-0.05, respectively, with no correction for completeness. The derived MF and CSF in this survey are approximately two times higher than the values found in the binary surveys toward Class I YSOs, and approximately three (for MF) and four (for CSF) times larger than the values found among MS stars, with a similar range of separations. Furthermore, the observed fraction of high order multiple systems to binary systems in Class 0 protostars (0.50+/-0.09) is also larger than the fractions found in Class I YSOs (0.31+/-0.07) and MS stars (< 0.2). These results suggest that binary properties evolve as protostars evolve, as predicted by numerical simulations. The distribution of separations for Class 0 protostellar binary systems shows a general trend in which companion star fraction increases with decreasing companion separation. We find that 67%+/-8% of the protobinary systems have circumstellar mass ratios below 0.5, implying that unequal-mass systems are preferred in the process of binary star formation. We suggest an empirical sequential fragmentation picture for binary star formation.

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arXiv2013

G048.66-0.29: Physical State of an Isolated Site of Massive Star Formation

We present continuum observations of the infrared dark cloud (IRDC) G48.66-0.22 (G48) obtained with Herschel, Spitzer, and APEX, in addition to several molecular line observations. The Herschel maps are used to derive temperature and column density maps of G48 using a model based on a modified blackbody. We find that G48 has a relatively simple structure and is relatively isolated; thus this IRDC provides an excellent target to study the collapse and fragmentation of a filamentary structure in the absence of complicating factors such as strong external feedback. The derived temperature structure of G48 is clearly non-isothermal from cloud to core scale. The column density peaks are spatially coincident with the lowest temperatures (~ 17.5 K) in G48. A total cloud mass of ~390Msun is derived from the column density maps. By comparing the luminosity-to-mass ratio of 13 point sources detected in the Herschel/PACS bands to evolutionary models, we find that two cores are likely to evolve into high-mass stars (M>8 Msun). The derived mean projected separation of point sources is smaller than in other IRDCs but in good agreement with theoretical predications for cylindrical collapse. We detect several molecular species such as CO, HCO+, HCN, HNC and N2H+. CO is depleted by a factor of ~3.5 compared to the expected interstellar abundance, from which we conclude that CO freezes out in the central region. Furthermore, the molecular clumps, associated with the sub-millimeter peaks in G48, appear to be gravitationally unbound or just pressure confined. The analysis of critical line masses in G48 show that the entire filament is collapsing, overcoming any internal support.

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