arXiv subjects

E. Koumpia

Publications and source records attributed to E. Koumpia.

18 recordsLinked to original sources

arXiv2026

Spatial and spectral constraints on resolved mass-loss of the massive Post-RSG star IRAS 17163-3907 and its Fried Egg Nebula

The fate of massive stars during the latest stages of their evolution is highly dependent on their mass-loss rate and geometry. These processes have a significant influence on stars with masses between 25 and 40 Msun, i.e., type II SN progenitors. We aim to investigate the mass-loss history, geometry, and physical conditions of the yellow hypergiant in a post-RSG stage, IRAS 17163-3907. We place it in context with another famous yellow hypergiant, IRC+10420. We combine M-band high-resolution CRIRES+ spectroscopy with VLTI/MATISSE mid-infrared L-band interferometry, and FORS2 optical spectropolarimetry to probe both the small-scale circumstellar structure and the large-scale dusty environment of IRAS 17163. The CRIRES+ spectrum provides the first M-band coverage of IRAS 17163, revealing prominent low-excitation metal lines and hydrogen recombination features, but lacking the pronounced CO absorption seen in IRC+10420. The MATISSE observations reveal the first high angular scales of the source in the L-band and spatially resolve the Brα line-emitting region, which hints at a marginally asymmetric and variable ionised wind. FORS2 spectropolarimetry points to deviations from perfect spherical symmetry also on larger scales. The data show no evidence for a binary companion within the explored parameter space, indicating that the observed clumpy and time-variable mass loss is likely intrinsic to the star rather than companion-driven. Our results demonstrate that IRAS 17163 hosts a dense, structured, and time-variable wind, coexisting with extended dusty shells. The comparison with IRC+10420 highlights diversity among post-RSG YHGs. These findings emphasise the role of clumpy and near-symmetric mass-loss in shaping the circumstellar medium of evolved massive stars, with implications for their subsequent evolution and core-collapse supernova progenitor properties.

astro-ph.SR↗

arXiv2026

Unlocking the dynamics of Young Stellar Objects: Time-Domain Interferometry with six 4-m class telescopes

The dynamics of the inner regions of young stellar objects (YSOs) is driven by a variety of physical phenomena, from magnetospheres and accretion to the dust sublimation rim and inner disk flows. These inner environments evolve on timescales of hours to days, exactly when bursts, dips, and rapid structural changes carry the most valuable information about star and planet formations, but remain hardly reachable with current facilities. A better reactive infrastructure with six or more telescopes, combined with alerts from large time-domain surveys (e.g., at the era of LSST/Rubin type facilities), and equipped with instruments spanning from the V-band to the thermal infrared (N), would provide the instantaneous uv-coverage and spectral diagnostics needed to unambiguously interpret and image these events as they happen. Such a world's first time-domain interferometric observatory would enable qualitatively new science: directly linking optical and infrared variability to spatially resolved changes in magnetospheric accretion, inner-disk geometry, and dust and gas dynamics in the innermost astronomical unit. Crucially, connecting these processes to outer-scale unresolved information from JWST, ALMA, and the ELT would yield a complete tomography of the planet-forming region.

astro-ph.IM↗

arXiv2025

First results from ALPPS: a sub-Alfvénic streamer in SVS13A

We present the first results from the ALMA Perseus Polarization Survey (ALPPS), focusing on the magnetic field in the SVS13A circumbinary disk. The dataset includes full-Stokes dust continuum observations at $\sim0\farcs3$ and 870 $μ$m, as well as molecular line emission from C$^{17}$O$(J=3 \rightarrow 2)$ at $\sim0\farcs3$, C$^{18}$O$(J=2 \rightarrow 1)$ at $\sim0\farcs2$, and DCN$(J=3 \rightarrow 2)$ at $\sim0\farcs1$ angular resolution. Our observations resolve both a previously identified dust spiral and an infalling streamer, capturing their spatial and kinematic structures. The streamer is traced from scales $>300$ au down to the circumbinary disk. Using alignment measure (AM) maps and histograms that compare the orientations of the plane-of-sky magnetic field with local intensity and velocity gradients, we find that the AM distribution peaks at a value of 1. This AM peak strongly suggests alignment between the field and the dust total intensity emission, as well as between the field and the gas velocity, which in turn suggests grain alignment by magnetic fields. From our data, we derive a magnetic field strength, B$_{\mathrm{pos}} \sim 1.1 \pm 0.6$\, mG, and a kinetic to magnetic energy ratio of $0.5 \pm 0.4$, suggesting magnetic dominance. We also produced a map of the Alfvénic Mach number, finding $\mathcal{M}_{\rm A} < 1$ along the streamer, consistent with sub-Alfvénic infalling motions. Therefore, the field is likely facilitating the inflow of material from the envelope onto the disk by constraining movement across the field lines. This represents the first detection of a magnetically sub-Alfvénic infalling streamer in a protostellar system.

astro-ph.GA↗

arXiv2024

Unveiling accretion in the massive YSO G033.3891. Spatial and kinematic constraints from the CO bandhead emission

The inner parts of the hot discs surrounding massive young stellar objects (MYSOs) are still barely explored due to observational limitations in terms of angular resolution, scarcity of diagnostic lines and the embedded and rare nature of these targets. We present the first K-band spectro-interferometric observations toward the MYSO G033.3891, which based on former kinematic evidence via the CO bandhead emission is known to host an accreting disc. Using the high spectral resolution mode (R$\sim$4000) of the GRAVITY/VLTI, we spatially resolve the emission of the inner dusty disc and the crucial gaseous interface between the star and the dusty disc. Using detailed modelling on the K-band dust continuum and tracers known to be associated with the ionised and molecular gaseous interface (Br$γ$, CO), we report on the smallest scales of accretion/ejection. The new observations in combination with our geometric and kinematic models employed to fit former high spectral resolution observations on the source (R$\sim$30,000; CRIRES/VLTI) allow us to constrain the size of the inner gaseous disc both spatially and kinematically via the CO overtone emission at only 2 au. Our models reveal that both Br$γ$ and CO emissions are located well within the dust sublimation radius (5~au) as traced by the hot 2.2~$μ$m dust continuum. Our paper provides the first case study where the tiniest scales of gaseous accretion around the MYSO G033.3891 are probed both kinematically and spatially via the CO bandhead emission. This analysis of G033.3891 stands as only the second instance of such investigation within MYSOs, underscoring the gradual accumulation of knowledge regarding how massive young stars gain their mass, while further solidifying the disc nature of accretion at the smallest scales of MYSOs.

astro-ph.GA↗

arXiv2023

The onset of stellar multiplicity in massive star formation: A search for low-mass companions of massive young stellar objects with $L'$-band adaptive optics imaging

Given the high incidence of binaries among mature field massive stars, it is clear that multiplicity is an inevitable outcome of high-mass star formation. Understanding how massive multiples form requires the study of the birth environments of massive stars, covering the innermost to outermost regions. We aim to detect and characterise low-mass companions around massive young stellar objects (MYSOs) during and shortly after their formation phase. To investigate large spatial scales, we carried out an $L'$-band high-contrast direct imaging survey seeking low-mass companions (down to $L_{\text{bol}}\approx 10 L_{\odot}$, or late A-type) around thirteen previously identified MYSOs using the VLT/NACO instrument. From those images, we looked for the presence of companions on a wide orbit, covering scales from 300 to 56,000 au. Detection limits were determined for all targets and we tested the gravitational binding to the central object based on chance projection probabilities. We have discovered a total of thirty-nine potential companions around eight MYSOs, the large majority of which have never been reported to date. We derived a multiplicity frequency (MF) of $62\pm13$% and a companion fraction (CF) of $3.0\pm0.5$. The derived MF and CF are compared to other studies for similar separation ranges. The comparisons are effective for a fixed evolutionary stage spanning a wide range of masses and vice versa. We find an increased MF and CF compared to the previous studies targeting MYSOs, showing that the statement in which multiplicity scales with primary mass also extends to younger evolutionary stages. The separations at which the companions are found and their location with relation to the primary star allow us to discuss the implications for the massive star formation theories.

astro-ph.SR↗

arXiv2021

The first interferometric survey in the K-band of massive YSOs. On the hot dust, ionised gas, and binarity at au scales

Circumstellar discs are essential for high mass star formation, while multiplicity, in particular binarity, appears to be an inevitable outcome since the vast majority of massive stars (> 8 Msun) are found in binaries (up to 100%). We constrain the sizes of the dust and ionised gas (Brgamma) emission of the innermost regions towards a sample of six MYSOs, and provide high-mass binary statistics of young stars at 2-300 au scales using VLTI (GRAVITY, AMBER) observations. We determine the inner radius of the dust emission and place MYSOs with K-band measurements in a size-luminosity diagram for the first time, and compare our findings to T Tauris and Herbig AeBes. We also compare the observed K-band sizes to the sublimation radius predicted by three different disc scenarios. Lastly, we apply binary geometries to trace close binarity among MYSOs. The inner sizes of MYSOs, Herbig AeBe and T Tauri stars appear to follow a universal trend at which the sizes scale with the square-root of the stellar luminosity. The Brgamma emission originates from somewhat smaller and co-planar area compared to the 2.2 μm continuum emission. We discuss this new finding with respect to disc-wind or jet origin. Finally, we report an MYSO binary fraction of 17-25% at milli-arcsecond separations (2-300 au). The size-luminosity diagram indicates that the inner regions of discs around young stars scale with luminosity independently of the stellar mass. At the targeted scales (2-300 au), the MYSO binary fraction is lower than what was previously reported for the more evolved main sequence massive stars, which, if further confirmed, could implicate the predictions from massive binary formation theories. Lastly, we spatially resolve the crucial star/disc interface in a sample of MYSOs, showing that au-scale discs are prominent in high-mass star formation and similar to their low-mass equivalents.

astro-ph.SR↗

arXiv2021

K-band GRAVITY/VLTI interferometry of "extreme" Herbig Be stars. The size-luminosity relation revisited

(Abridged:) It has been hypothesized that the location of Herbig Ae/Be stars (HAeBes) within the empirical relation between the inner disk radius (r$_{in}$), inferred from K-band interferometry, and the stellar luminosity (L$_*$), is related to the presence of the innermost gas, the disk-to-star accretion mechanism, the dust disk properties inferred from the spectral energy distributions (SEDs), or a combination of these effects. This work aims to test whether the previously proposed hypotheses do, in fact, serve as a general explanation for the distribution of HAeBes in the size-luminosity diagram. GRAVITY/VLTI spectro-interferometric observations at $\sim $2.2 $ μ$m have been obtained for five HBes representing two extreme cases concerning the presence of innermost gas and accretion modes. V590 Mon, PDS 281, and HD 94509 show no excess in the near-ultraviolet, Balmer region of the spectra ($Δ$D$_B$), indicative of a negligible amount of inner gas and disk-to-star accretion, whereas DG Cir and HD 141926 show such strong $Δ$D$_B$ values that cannot be reproduced from magnetospheric accretion, but probably come from the alternative boundary layer mechanism. Additional data for these and all HAeBes resolved through K-band interferometry have been compiled from the literature and updated using Gaia EDR3 distances, almost doubling previous samples used to analyze the size-luminosity relation. We find no general trend linking the presence of gas inside the dust destruction radius or the accretion mechanism with the location of HAeBes in the size-luminosity diagram. Underlying trends are present and must be taken into account when interpreting the size-luminosity correlation. Still, it is argued that the size-luminosity correlation is most likely to be physically relevant in spite of the previous statistical warning concerning dependencies on distance.

astro-ph.SR↗

arXiv2020

Mapping the H$_{2}$D$^{+}$ and N$_{2}$H$^{+}$ emission towards prestellar cores. Testing dynamical models of the collapse using gas tracers

The study of prestellar cores is critical as they set the initial conditions in star formation and determine the final mass of the stellar object. To date, several hypotheses are describing their gravitational collapse. We perform detailed line analysis and modelling of H$_{2}$D$^{+}$ 110 -111 and N$_{2}$H$^{+}$ 4-3 emission at 372 GHz, using 2'x2' maps (JCMT). Our goal is to test the most prominent dynamical models by comparing the modelled gas kinematics and spatial distribution (H$_{2}$D$^{+}$ and N$_{2}$H$^{+}$) with observations towards four prestellar (L1544, L183, L694-2, L1517B) and one protostellar core (L1521f). We perform a detailed non-LTE radiative transfer modelling using RATRAN, where we compare the predicted spatial distribution and line profiles of H$_{2}$D$^{+}$ and N$_{2}$H$^{+}$ with observations towards all cores. To do so, we adopt the physical structure for each core predicted by three different dynamical models taken from literature: Quasi-Equilibrium Bonnor-Ebert Sphere (QE-BES), Singular Isothermal Sphere (SIS), and Larson-Penston (LP) flow. Our analysis provides an updated picture of the physical structure of prestellar cores. We find that the SIS model can be clearly excluded in explaining the gas emission towards the cores, but a larger sample is required to differentiate clearly between the LP flow, the QE-BES and the static models. All models of collapse underestimate the intensity of the gas emission by up to several factors towards the only protostellar core in our sample, indicating that different dynamics take place in different evolutionary core stages. If the LP model is confirmed towards a larger sample of prestellar cores, it would indicate that they may form by compression or accretion of gas from larger scales. If the QE-BES model is confirmed, it means that quasi hydrostatic cores can exist within turbulent ISM.

astro-ph.SR↗

arXiv2020

Optical/near-infrared observations of the Fried Egg Nebula: Multiple shell ejections on a 100 yr timescale from a massive yellow hypergiant

Context. The fate of a massive star during the latest stages of its evolution is highly dependent on its mass-loss rate/geometry and therefore knowing the geometry of the circumstellar material close to the star and its surroundings is crucial. Aims. We aim to study the nature (i.e. geometry, rates) of mass-loss episodes. In this context, yellow hypergiants are great targets. Methods. We analyse a large set of optical/near-infrared data, in spectroscopic and photometric (X-shooter/VLT), spectropolarimetric (ISIS/WHT), and interferometric GRAVITY-AMBER/VLTI) modes, toward the yellow hypergiant IRAS 17163-3907. We present the first model-independent reconstructed images of IRAS 17163-3907 at these wavelengths at milli-arcsecond scales. Lastly, we apply a 2D radiative transfer model to fit the dereddened photometry and the radial profiles of published VISIR images at 8.59 μm, 11.85 μm and 12.81 μm simultaneously, adopting the revised Gaia distance (DR2). Results. The interferometric observables around 2 μm show that the Brγ emission is more extended and asymmetric than the Na i and the continuum emission. In addition to the two known shells surrounding IRAS 17163-3907 we report on the existence of a third hot inner shell with a maximum dynamical age of only 30 yr. Conclusions. The interpretation of the presence of Na i emission at closer distances to the star compared to Brγ has been a challenge in various studies. We argue that the presence of a pseudophotosphere is not needed, but it is rather an optical depth effect. The three observed distinct mass-loss episodes are characterised by different mass-loss rates and can inform the theories on mass-loss mechanisms, which is a topic still under debate. We discuss these in the context of photospheric pulsations and wind bi-stability mechanisms.

astro-ph.SR↗

arXiv2019

Resolving the MYSO binaries PDS 27 and PDS 37 with VLTI/PIONIER

Binarity and multiplicity appear to be a common outcome in star formation. In particular, the binary fraction of massive (OB-type) stars can be very high. In many cases, the further stellar evolution of these stars is affected by binary interactions at some stage during their lifetime. The origin of this high binarity and the binary parameters are poorly understood because observational constraints are scarce, which is predominantly due to a dearth of known young massive binary systems. We aim to identify and describe massive young binary systems in order to fill in the gaps of our knowledge of primordial binarity of massive stars, which is crucial for our understanding of massive star formation. We observed the two massive young stellar objects (MYSOs) PDS 27 and PDS 37 at the highest spatial resolution provided by VLTI/PIONIER in the H-band (1.3 mas). We applied geometrical models to fit the observed squared visibilities and closure phases. In addition, we performed a radial velocity analysis using published VLT/FORS2 spectropolarimetric and VLT/X-shooter spectroscopic observations. Our findings suggest binary companions for both objects at 12 mas (30 au) for PDS 27 and at 22-28 mas (42-54 au) for PDS 37. This means that they are among the closest MYSO binaries resolved to date. Our data spatially resolve PDS 27 and PDS 37 for the first time, revealing two of the closest and most massive ($>$8 M$_\odot$) YSO binary candidates to date. PDS 27 and PDS 37 are rare but great laboratories to quantitatively inform and test the theories on formation of such systems.

astro-ph.SR↗

arXiv2017

The chemical structure of the Class 0 protostellar envelope NGC 1333 IRAS 4A

It is not well known what drives the chemistry of a protostellar envelope, in particular the role of the stellar mass and the outflows on its chemical enrichment. We study the chemical structure of NGC 1333 IRAS 4A in order to (i) investigate the influence of the outflows on the chemistry, (ii) constrain the age of our object, (iii) compare it with a typical high-mass protostellar envelope. In our analysis we use JCMT line mapping and HIFI pointed spectra. To study the influence of the outflow on the degree of deuteration, we compare JCMT maps of HCO+ and DCO+ with non-LTE (RADEX) models in a region that spatially covers the outflow activity of IRAS 4A. To study the envelope chemistry, we derive empirical molecular abundance profiles for the observed species using the radiative transfer code (RATRAN) and adopting a 1D dust density/temperature profile from the literature. We compare our best-fit observed abundance profiles with the predictions from the time dependent gas grain chemical code (ALCHEMIC). The CO, HCN, HNC and CN abundance require an enhanced UV field which points towards an outflow cavity. The abundances (wrt H2) are 1 to 2 orders of magnitude lower than those observed in the high mass protostellar envelope (AFGL 2591), while they are found to be similar within factors of a few with respect to CO. Differences in UV radiation may be responsible for such chemical differentiation, but temperature differences seem a more plausible explanation. The CH3OH modeled abundance profile points towards an age of > 4x10^4 yrs for IRAS 4A. The spatial distribution of H2D+ differs from that of other deuterated species, indicating an origin from a foreground colder layer (<20 K). The observed abundances can be explained by passive heating towards the high mass protostellar envelope, while the presence of UV cavity channels become more important toward the low mass protostellar envelope.

astro-ph.GA↗

arXiv2016

The evolutionary status of dense cores in the NGC 1333 IRAS 4 region

Protostellar evolution, following the formation of the protostar is becoming reasonably well characterized, but the evolution from a prestellar core to a protostar is not well known, although the first hydrostatic core (FHSC) must be a pivotal step. NGC 1333 IRAS 4C is a potentially very young object, that we directly compare with the nearby Class 0 IRAS 4A and IRAS 4B. Observational constraints are provided by spectral imaging from the JCMT Spectral Legacy Survey (330-373 GHz) and continuum and line observations from CARMA. We present integrated intensity and velocity maps of several species, including CO, H2CO and CH3OH. The velocity of an observed outflow, the degree of CO depletion, the deuteration of DCO+/HCO+ and gas kinetic temperatures are observational signatures that we present. We report differences between the three sources in four aspects: a) the kinetic temperature is much lower towards IRAS 4C, b) the line profiles of the detected species show strong outflow activity towards IRAS 4A and IRAS 4B but not towards IRAS 4C, c) the HCN/HNC is < 1 towards IRAS 4C, which confirms the cold nature of the source, d) the degree of CO depletion and the deuteration are the lowest towards the warmest of the sources, IRAS 4B. IRAS 4C seems to be in a different evolutionary state than the IRAS 4A and IRAS 4B sources. We can probably exclude the FHSC stage due to the relatively low Lsmm/Lbol (~6\%) and we investigate the earliest accretion phase of Class 0 stage and the transition between Class 0 to Class I. Our results do not show a consistent scenario for either case, with the major issue being the absence of outflow activity and the cold nature of IRAS 4C. The number of FHSC candidates in Perseus is ~10 times higher than current models predict, which suggests that the lifespan of these objects is greater than 1000 years, possibly due to an accretion rate lower than 4x10^-5 msun/yr.

astro-ph.SR↗

arXiv2016

Observations and modelling of CO and [CI] in disks. First detections of [CI] and constraints on the carbon abundance

The gas-solid budget of carbon in protoplanetary disks is related to the composition of the cores and atmospheres of the planets forming in them. The key gas-phase carbon carriers CO, C$^{0}$ and C$^{+}$ can now be observed in disks. The gas-phase carbon abundance in disks has not yet been well characterized, we aim to obtain new constraints on the [C]/[H] ratio in a sample of disks, and to get an overview of the strength of [CI] and warm CO emission. We carried out a survey of the CO$\,6$--$5$ and [CI]$\,1$--$0$ and $2$--$1$ lines towards $37$ disks with APEX, and supplemented it with [CII] data from the literature. The data are interpreted using a grid of models produced with the DALI code. We also investigate how well the gas-phase carbon abundance can be determined in light of parameter uncertainties. The CO$\,6$--$5$ line is detected in $13$ out of $33$ sources, the [CI]$\,1$--$0$ in $6$ out of $12$, and the [CI]$\,2$--$1$ in $1$ out of $33$. With deep integrations, the first unambiguous detections of [CI]~$1$--$0$ in disks are obtained, in TW~Hya and HD~100546. Gas-phase carbon abundance reductions of a factor $5$--$10$ or more can be identified robustly based on CO and [CI] detections. The atomic carbon detection in TW~Hya confirms a factor $100$ reduction of [C]/[H]$_{\rm gas}$ in that disk, while the data are consistent with an ISM-like carbon abundance for HD~100546. In addition, BP~Tau, T~Cha, HD~139614, HD~141569, and HD~100453 are either carbon-depleted or gas-poor disks. The low [CI]~$2$--$1$ detection rates in the survey mostly reflect insufficient sensitivity to detect T~Tauri disks. The Herbig~Ae/Be disks with CO and [CII] upper limits below the models are debris disk like systems. A roughly order of magnitude increase in sensitivity compared to our survey is required to obtain useful constraints on the gas-phase [C]/[H] ratio in most of the targeted systems.

astro-ph.SR↗

arXiv2015

Accurate fundamental parameters and distance to a massive early-type eclipsing binary in the Danks 2 cluster

We present a study of the properties of the O-type, massive eclipsing binary 2MASS J13130841-6239275 located in the outskirts of the Danks 2 cluster in the G305 star-forming complex, using near-infrared spectroscopy from VLT/ISAAC. We derive the masses and radii to be 24.5$\pm$0.9 M$_{\odot}$ and 9.2$\pm$0.1 R$_{\odot}$ for the primary and 21.7$\pm$0.8 M$_{\odot}$ and 8.7$\pm$0.1 R$_{\odot}$ for the secondary component. In addition, we evaluate the sensitivity of our parameters to the choice of the spectral features used to determine the radial velocities. Both components appear to be main-sequence O6.5$-$O7 type stars at an age of $\sim$5 Myr, which is in agreement with the age of the cluster. A high visual extinction of A$_{5495}$=11.9$\pm$0.1 mag is reported, which is likely attributed to the cold molecular gas contaminating the north-east region of the cluster. By fitting the spectral energy distribution of the system to the available $BVI_{c}JHK_{s}$ photometry, we determine a distance to the system of 3.52$\pm$0.08 kpc with a precision of 2$\%$, which is the most well-determined distance to the Danks 2 cluster and the host complex reported in the literature.

astro-ph.SR↗

arXiv2015

Outflow forces in intermediate mass star formation

Intermediate mass protostarsprovide a bridge between theories of low- and high-mass star formation. Emerging molecular outflows can be used to determine the influence of fragmentation and multiplicity on protostellar evolution through the correlation of outflow forces of intermediate mass protostars with the luminosity. The aim of this paper is to derive outflow forces from outflows of six intermediate mass protostellar regions and validate the apparent correlation between total luminosity and outflow force seen in earlier work, as well as remove uncertainties caused by different methodology. By comparing CO 6--5 observations obtained with APEX with non-LTE radiative transfer model predictions, optical depths, temperatures, densities of the gas of the molecular outflows are derived. Outflow forces, dynamical timescales and kinetic luminosities are subsequently calculated. Outflow parameters, including the forces, were derived for all sources. Temperatures in excess of 50 K were found for all flows, in line with recent low-mass results. However, comparison with other studies could not corroborate conclusions from earlier work on intermediate mass protostars which hypothesized that fragmentation enhances outflow forces in clustered intermediate mass star formation. Any enhancement in comparison with the classical relation between outflow force and luminosity can be attributed the use of a higher excitation line and improvement in methods; They are in line with results from low-mass protostars using similar techniques. The role of fragmentation on outflows is an important ingredient to understand clustered star formation and the link between low and high-mass star formation. However, detailed information on spatial scales of a few 100 AU, covering all individual members is needed to make the necessary progress.

astro-ph.SR↗

arXiv2015

Temperatures of dust and gas in S~140

In dense parts of interstellar clouds (> 10^5 cm^-3), dust & gas are expected to be in thermal equilibrium, being coupled via collisions. However, previous studies have shown that the temperatures of the dust & gas may remain decoupled even at higher densities. We study in detail the temperatures of dust & gas in the photon-dominated region S 140, especially around the deeply embedded infrared sources IRS 1-3 and at the ionization front. We derive the dust temperature and column density by combining Herschel PACS continuum observations with SOFIA observations at 37 $μ$m and SCUBA at 450 $μ$m. We model these observations using greybody fits and the DUSTY radiative transfer code. For the gas part we use RADEX to model the CO 1-0, CO 2-1, 13CO 1-0 and C18O 1-0 emission lines mapped with the IRAM-30m over a 4' field. Around IRS 1-3, we use HIFI observations of single-points and cuts in CO 9-8, 13CO 10-9 and C18O 9-8 to constrain the amount of warm gas, using the best fitting dust model derived with DUSTY as input to the non-local radiative transfer model RATRAN. We find that the gas temperature around the infrared sources varies between 35 and 55K and that the gas is systematically warmer than the dust by ~5-15K despite the high gas density. In addition we observe an increase of the gas temperature from 30-35K in the surrounding up to 40-45K towards the ionization front, most likely due to the UV radiation from the external star. Furthermore, detailed models of the temperature structure close to IRS 1 show that the gas is warmer and/or denser than what we model. Finally, modelling of the dust emission from the sub-mm peak SMM 1 constrains its luminosity to a few ~10^2 Lo. We conclude that the gas heating in the S 140 region is very efficient even at high densities, most likely due to the deep UV penetration from the embedded sources in a clumpy medium and/or oblique shocks.

astro-ph.SR↗

arXiv2011

Fundamental Parameters of four Massive Eclipsing Binaries in Westerlund 1

We present fundamental parameters of 4 massive eclipsing binaries in the young massive cluster Westerlund 1. The goal is to measure accurate masses and radii of their component stars, which provide much needed constraints for evolutionary models of massive stars. Accurate parameters can further be used to determine a dynamical lower limit for the magnetar progenitor and to obtain an independent distance to the cluster. Our results confirm and extend the evidence for a high mass for the progenitor of the magnetar.

astro-ph.SR↗

arXiv2010

Fundamental Parameters of 4 Massive Eclipsing Binaries in Westerlund 1

Westerlund 1 is one of the most massive young clusters known in the Local Group, with an age of 3-5 Myr. It contains an assortment of rare evolved massive stars, such as blue, yellow and red supergiants, Wolf-Rayet stars, a luminous blue variable, and a magnetar, as well as 4 massive eclipsing binary systems (Wddeb, Wd13, Wd36, WR77o, see Bonanos 2007). The eclipsing binaries present a rare opportunity to constrain evolutionary models of massive stars, the distance to the cluster and furthermore, to determine a dynamical lower limit for the mass of a magnetar progenitor. Wddeb, being a detached system, is of great interest as it allows determination of the masses of 2 of the most massive unevolved stars in the cluster. We have analyzed spectra of all 4 eclipsing binaries, taken in 2007-2008 with the 6.5 meter Magellan telescope at Las Campanas Observatory, Chile, and present fundamental parameters (masses, radii) for their component stars.

astro-ph.SR↗