arXiv subjects

T. Stanke

Publications and source records attributed to T. Stanke.

At least 19 recordsLinked to original sources

arXiv2025

Dust scattering halo of 4U 1630-47: High resolution X-ray and mm observations constrain source and molecular cloud distances

We re-investigated the distance to the black hole X-ray binary 4U 1630-47 by analyzing its dust scattering halo (DSH) using high-resolution X-ray (Chandra) and millimeter (APEX) observations. Dust scattering halos form when X-rays from a compact source are scattered by interstellar dust, creating diffuse ring-like structures that can provide clues about the source's distance. Our previous work suggested two possible distances: 4.9 kpc and 11.5 kpc, but uncertainties remained due to low-resolution CO maps. We developed a new methodology to refine these estimates, starting with a machine learning approach to determine a 3D representation of molecular clouds from the APEX dataset. The 3D maps are combined with X-ray flux measurements to generate synthetic DSH images. By comparing synthetic images with the observed Chandra data through radial and azimuthal profile fitting, we not only measure the source distance but also distinguish whether the molecular clouds are at their near or far distances. The current analysis again supported a distance of 11.5 kpc over alternative estimates. While the method produced a lower reduced chi-squared for both the azimuthal and radial fits for a distance of 13.6 kpc, we ruled it out as it would have produced a bright ring beyond the APEX field of view, which is not seen in the Chandra image. The 4.85 kpc estimate was also excluded due to poor fit quality and cloud distance conflicts. The systematic error of 1 kpc, arising from uncertainties in determining molecular cloud distances, dominates the total error.

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arXiv2025

The pre-eruption state of T CrB as observed with ALMA in 2024

T CrB is a nearby symbiotic binary and a recurrent nova with a period of ca. 80 years. The next eruption is expected to take place in 2025 or 2026. We present our pre-eruption observations made in ALMA frequency Bands 1, 3, 4, 6, 7, and 8 in August to November 2024 and constrain the properties of the environment into which the imminent next nova will erupt. We find that in the second half of 2024, the quiescent T CrB was a faint mm source with a spectral energy distribution well described by a powerlaw with index $\alpha=$0.56$\pm$0.11 and a flux density of ca. 0.1 mJy at 44 GHz and 0.4 mJy at 400 GHz. There is no significant line emission. This is in agreement with expectations for free-free emission from the partially ionized wind of the red giant donor star and, in extrapolation to 35 GHz, a factor 5 fainter than the emission observed in 2016/17 during the latest high state. Comparing the spectra from that high-state between 13.5 GHz and 35 GHz with our spectrum from 2024, our spectrum is softer. The spectral index is on average lower by 0.34$\pm$0.11 . Our per-band and aggregate bandwidth images of T CrB show an unresolved point source with no evidence for extended structure. A simple model of a free-free emitting, fully-ionized stellar wind seems to describe well the 2016/17 high state of T CrB but not our 2024 ALMA measurements with their low flux and high turnover frequency suggesting that in 2024, the wind was far from fully ionized. (See the unabridged version of the abstract in the paper.)

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arXiv2024

Hunt for complex cyanides in protostellar ices with JWST: Tentative detection of CH$_3$CN and C$_2$H$_5$CN

Nitrogen-bearing complex organic molecules have been commonly detected in the gas phase but not yet in interstellar ices. This has led to the long-standing question of whether these molecules form in the gas phase or in ices. $\textit{James Webb}$ Space Telescope ($\textit{JWST}$) offers the sensitivity, spectral resolution, and wavelength coverage needed to detect them in ices and investigate whether their abundance ratios are similar in gas and ice. We report the first tentative detection of CH$_3$CN, C$_2$H$_5$CN, and the simple molecule, N$_2$O, based on the CN-stretch band in interstellar ices toward three (HOPS 153, HOPS 370, and IRAS 20126+4104) out of the five protostellar systems observed as part of the Investigating Protostellar Accretion (IPA) GO program with $\textit{JWST}$-NIRSpec. We also provide upper limits for the two other sources with smaller luminosities in the sample. We detect OCN$^-$ in the ices of all sources with typical CH$_3$CN/OCN$^-$ ratios of around 1. Ice and gas column density ratios of the nitrogen-bearing species with respect to each other are better matched than those with respect to methanol, which are a factor of ${\sim}5$ larger in the ices than the gas. We attribute the elevated ice column densities with respect to methanol to the difference in snowline locations of nitrogen-bearing molecules and of methanol, biasing the gas-phase observations toward fewer nitrogen-bearing molecules. Moreover, we find tentative evidence for enhancement of OCN$^-$, CH$_3$CN, and C$_2$H$_5$CN in warmer ices, although formation of these molecules likely starts along with methanol in the cold prestellar phase. Future surveys combining NIRSpec and MIRI, and additional laboratory spectroscopic measurements of C$_2$H$_5$CN ice, are necessary for robust detection and conclusions on the formation history of complex cyanides.

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arXiv2022

The molecular gas properties in local Seyfert 2 galaxies

We present a multi-wavelength study of the molecular gas properties of a sample of local Seyfert 2 galaxies to assess if, and to what extent, the presence of an active galactic nucleus (AGN) can affect the Interstellar Medium (ISM) properties in a sample of 33 local Seyfert 2 galaxies. We compare the molecular gas content (MH2), derived from new and archival low-J CO line measurements of a sample of AGN and a control sample of star-forming galaxies (SFGs). Both the AGN and the control sample are characterised in terms of host-galaxy properties (e.g., stellar and dust masses, Mstar and Mdust, respectively; and star formation rate, SFR). We also investigate the effect of AGN activity onto the emission of polycyclic aromatic hydrocarbon (PAH) molecules in the mid-infrared (MIR), a waveband where the dust-reprocessed emission from the obscured AGN contributes the most. The AGN hosted in less massive galaxies (i.e., log(Mstar/Msun)<10.5; log(Mdust/Msun)<7.5) show larger molecular gas content with respect to SFGs matched in stellar and dust mass. When comparing their depletion time(tdep~MH2/SFR), AGN show tdep~0.3-1.0 Gyr, similar to those observed in the control sample of SFGs. Seyfert 2 galaxies show fainter PAH luminosity at increasingly larger dominance of the nuclear activity in the MIR. We find no clear evidence for a systematic reduction of the molecular gas reservoir at galactic scale in Seyfert galaxies with respect to SFGs. This is in agreement with recent studies showing that molecular gas content only is reduced in regions of sub-kpc size, where the emission from the accreting supermassive black hole dominates. Nonetheless, we show that the impact of AGN activity on the ISM is clearly visible as suppression of the PAH luminosity.

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arXiv2020

An APEX survey of outflow and infall toward the youngest protostars in Orion

We aim to characterize the outflow properties of a sample of early Class 0 phase low-mass protostars in Orion first identified by the Herschel Space Observatory. We also look for signatures of infall in key molecular lines. CO $J$=3-2 and $J$=4-3 maps toward 16 very young Class 0 protostars were obtained using the Atacama Pathfinder EXperiment (APEX) telescope. We search the data for line wings indicative of outflows and calculate masses, velocities, and dynamical times for the outflows. We use additional HCO$^+$, H$^{13}$CO$^+$, and NH$_3$ lines to look for infall signatures toward the protostars. We estimate the outflow masses, forces, and mass-loss rates based on the CO $J$=3-2 and $J$=4-3 line intensities for 8 sources with detected outflows. We derive upper limits for the outflow masses and forces of sources without clear outflow detections. The total outflow masses for the sources with clear outflow detections are in the range between 0.03 and 0.16 $M_\odot$ for CO $J$=3-2, and in the range between 0.02 and 0.10 $M_\odot$ for CO $J$=4-3. The outflow forces are in the range between $1.57\times10^{-4}$ and $1.16\times10^{-3}$ $M_\odot$ km s$^{-1}$ yr$^{-1}$ for CO $J$=3-2 and in the range between $1.14\times10^{-4}$ and $6.92\times10^{-4}$ $M_\odot$ km s$^{-1}$ yr$^{-1}$ for CO $J$=4-3. Nine protostars in our sample show asymmetric line profiles indicative of infall in HCO$^+$, compared to H$^{13}$CO$^+$ or NH$_3$. The outflow forces of the protostars in our sample show no correlation with the bolometric luminosity, unlike those found by some earlier studies for other Class 0 protostars. The derived outflow forces for the sources with detected outflows are similar to those found for other - more evolved - Class 0 protostars, suggesting that outflows develop quickly in the Class 0 phase.

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arXiv2018

Characterising the high-mass star forming filament G351.776--0.527 with Herschel and APEX dust continuum and gas observations

G351.776-0.527 is among the most massive, closest, and youngest filaments in the inner Galactic plane and therefore it is an ideal laboratory to study the kinematics of dense gas and mass replenishment on a large scale. In this paper, we present far-infrared (FIR) and submillimetre wavelength continuum observations combined with spectroscopic C$^{18}$O (2-1) data of the entire region to study its temperature, mass distribution, and kinematics. The structure is composed of a main elongated region with an aspect ratio of $\sim 23$, which is associated with a network of filamentary structures. The main filament has a remarkably constant width of 0.2 pc. The total mass of the network (including the main filament) is $\geq 2600$ M$_\odot$, while we estimate a mass of $\sim 2000$ M$_\odot$ for the main structure. Therefore, the network harbours a large reservoir of gas and dust that could still be accreted onto the main structure. From the analysis of the gas kinematics, we detect two velocity components in the northern part of the main filament. The data also reveal velocity oscillations in C$^{18}$O along the spine in the main filament and in at least one of the branches. Considering the region as a single structure, we find that it is globally close to virial equilibrium indicating that the entire structure is approximately in a stable state.

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arXiv2017

HOPS 108: Star-formation triggered by a non-thermal jet?

The nature of the far-IR source HOPS 108 has been a matter of debate in the last years. Previous radio observations detected a 3.6 cm source (VLA 12), coincident with HOPS 108, that was interpreted as a radio jet from this protostar. We present new multi-wavelength (0.7-5 cm), multi-configuration VLA observations as well as archive data (3.6 cm) that reveal VLA 12 as three knots of non-thermal emission, with HOPS 108 close to the central knot. We show that these knots have not been ejected by HOPS 108. We propose that the VLA 12 knots are actually part of a radio jet driven by VLA 11 (HOPS 370), a strong nearby source clearly elongated in the direction of the knots. The position of HOPS 108 in the path of the VLA 11-VLA 12 jet suggests an appealing new scenario: the triggered formation of HOPS 108 by the interaction of the jet with the surrounding medium.

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arXiv2016

The Herschel Orion Protostar Survey: Spectral Energy Distributions and Fits Using a Grid of Protostellar Models

We present key results from the Herschel Orion Protostar Survey (HOPS): spectral energy distributions (SEDs) and model fits of 330 young stellar objects, predominantly protostars, in the Orion molecular clouds. This is the largest sample of protostars studied in a single, nearby star-formation complex. With near-infrared photometry from 2MASS, mid- and far-infrared data from Spitzer and Herschel, and sub-millimeter photometry from APEX, our SEDs cover 1.2-870 $μ$m and sample the peak of the protostellar envelope emission at ~100 $μ$m. Using mid-IR spectral indices and bolometric temperatures, we classify our sample into 92 Class 0 protostars, 125 Class I protostars, 102 flat-spectrum sources, and 11 Class II pre-main-sequence stars. We implement a simple protostellar model (including a disk in an infalling envelope with outflow cavities) to generate a grid of 30400 model SEDs and use it to determine the best-fit model parameters for each protostar. We argue that far-IR data are essential for accurate constraints on protostellar envelope properties. We find that most protostars, and in particular the flat-spectrum sources, are well-fit. The median envelope density and median inclination angle decrease from Class 0 to Class I to flat-spectrum protostars, despite the broad range in best-fit parameters in each of the three categories. We also discuss degeneracies in our model parameters. Our results confirm that the different protostellar classes generally correspond to an evolutionary sequence with a decreasing envelope infall rate, but the inclination angle also plays a role in the appearance, and thus interpretation, of the SEDs.

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arXiv2016

Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A with sparse aperture masking and spectroastrometry

Contemporary theory holds that massive stars gather mass during their initial phases via accreting disk-like structures. However, conclusive evidence for disks has remained elusive for the most massive young objects. This is mainly due to significant observational challenges. Incisive studies, even targeting individual objects, are therefore relevant to the progression of the field. NGC 3603 IRS 9A* is a young massive stellar object still surrounded by an envelope of molecular gas. Previous mid-infrared observations with long-baseline interferometry provided evidence for a disk of 50 mas diameter at its core. This work aims at a comprehensive study of the physics and morphology of IRS 9A at near-infrared wavelengths. New sparse aperture masking interferometry data taken with NACO/VLT at Ks and Lp filters were obtained and analysed together with archival CRIRES spectra of the H2 and BrG lines. The calibrated visibilities recorded at Ks and Lp bands suggest the presence of a partially resolved compact object of 30 mas at the core of IRS 9A, together with the presence of over-resolved flux. The spectroastrometric signal of the H2 line shows that this spectral feature proceeds from the large scale extended emission (300 mas) of IRS 9A, while the BrG line appears to be formed at the core of the object (20 mas). This scenario is consistent with the brightness distribution of the source for near- and mid-infrared wavelengths at various spatial scales. However, our model suffers from remaining inconsistencies between SED modelling and the interferometric data. Moreover, the BrG spectroastrometric signal indicates that the core of IRS 9A exhibits some form of complexity such as asymmetries in the disk. Future high-resolution observations are required to confirm the disk/envelope model and to flesh out the details of the physical form of the inner regions of IRS 9A.

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arXiv2015

Massive envelopes and filaments in the NGC 3603 star forming region

The formation of massive stars and their arrival on the zero-age main-sequence occurs hidden behind dense clouds of gas and dust. In the giant Hii region NGC 3603, the radiation of a young cluster of OB stars has dispersed dust and gas in its vicinity. At a projected distance of 2:5 pc from the cluster, a bright mid-infrared (mid-IR) source (IRS 9A) had been identified as a massive young stellar object (MYSO), located on the side of a molecular clump (MM2) of gas facing the cluster. We investigated the physical conditions in MM2, based on APEX sub-mm observations using the SABOCA and SHFI instruments, and archival ATCA 3 mm continuum and CS spectral line data. We resolved MM2 into several compact cores, one of them closely associated with IRS 9A. These are likely infrared dark clouds as they do not show the typical hot-core emission lines and are mostly opaque against the mid-IR background. The compact cores have masses of up to several hundred times the solar mass and gas temperatures of about 50 K, without evidence of internal ionizing sources. We speculate that IRS 9A is younger than the cluster stars, but is in an evolutionary state after that of the compact cores.

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arXiv2015

The VISTA Orion mini-survey: star formation in the Lynds 1630 North cloud

The Orion cloud complex presents a variety of star formation mechanisms and properties and it is still one of the most intriguing targets for star formation studies. We present VISTA/VIRCAM near-infrared observations of the L1630N star forming region, including the stellar clusters NGC 2068 and NGC 2071, in the Orion molecular cloud B and discuss them in combination with Spitzer data. We select 186 young stellar object (YSO) candidates in the region on the basis of multi-colour criteria, confirm the YSO nature of the majority of them using published spectroscopy from the literature, and use this sample to investigate the overall star formation properties in L1630N. The K-band luminosity function of L1630N is remarkably similar to that of the Trapezium cluster, i.e., it presents a broad peak in the range 0.3-0.7 M$_\odot$ and a fraction of sub-stellar objects of $\sim$20%. The fraction of YSOs still surrounded by disk/envelopes is very high ($\sim$85%) compared to other star forming regions of similar age (1-2 Myr), but includes some uncertain corrections for diskless YSOs. Yet, a possibly high disk fraction together with the fact that 1/3 of the cloud mass has a gas surface density above the threshold for star formation ($\sim$129 M$_\odot$ pc$^{-2}$), points towards a still on-going star formation activity in L1630N. The star formation efficiency (SFE), star formation rate (SFR) and density of star formation of L1630N are within the ranges estimated for galactic star forming regions by the Spitzer "core to disk" and "Gould's Belt" surveys. However, the SFE and SFR are lower than the average value measured in the Orion A cloud and, in particular, lower than that in the southern regions of L1630. This might suggest different star formation mechanisms within the L1630 cloud complex.

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arXiv2014

A necklace of dense cores in the high-mass star forming region G35.20-0.74N: ALMA observations

The present study aims at characterizing the massive star forming region G35.20N, which is found associated with at least one massive outflow and contains multiple dense cores, one of them recently found associated with a Keplerian rotating disk. We used ALMA to observe the G35.20N region in the continuum and line emission at 350 GHz. The observed frequency range covers tracers of dense gas (e.g. H13CO+, C17O), molecular outflows (e.g. SiO), and hot cores (e.g. CH3CN, CH3OH). The ALMA 870 um continuum emission map reveals an elongated dust structure (0.15 pc long and 0.013 pc wide) perpendicular to the large-scale molecular outflow detected in the region, and fragmented into a number of cores with masses 1-10 Msun and sizes 1600 AU. The cores appear regularly spaced with a separation of 0.023 pc. The emission of dense gas tracers such as H13CO+ or C17O is extended and coincident with the dust elongated structure. The three strongest dust cores show emission of complex organic molecules characteristic of hot cores, with temperatures around 200 K, and relative abundances 0.2-2x10^(-8) for CH3CN and 0.6-5x10^(-6) for CH3OH. The two cores with highest mass (cores A and B) show coherent velocity fields, with gradients almost aligned with the dust elongated structure. Those velocity gradients are consistent with Keplerian disks rotating about central masses of 4-18 Msun. Perpendicular to the velocity gradients we have identified a large-scale precessing jet/outflow associated with core B, and hints of an east-west jet/outflow associated with core A. The elongated dust structure in G35.20N is fragmented into a number of dense cores that may form massive stars. Based on the velocity field of the dense gas, the orientation of the magnetic field, and the regularly spaced fragmentation, we interpret this elongated structure as the densest part of a 1D filament fragmenting and forming massive stars.

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arXiv2014

On the nature of the deeply embedded protostar OMC-2 FIR 4

We use mid-infrared to submillimeter data from the Spitzer, Herschel, and APEX telescopes to study the bright sub-mm source OMC-2 FIR 4. We find a point source at 8, 24, and 70 $μ$m, and a compact, but extended source at 160, 350, and 870 $μ$m. The peak of the emission from 8 to 70 $μ$m, attributed to the protostar associated with FIR 4, is displaced relative to the peak of the extended emission; the latter represents the large molecular core the protostar is embedded within. We determine that the protostar has a bolometric luminosity of 37 Lsun, although including more extended emission surrounding the point source raises this value to 86 Lsun. Radiative transfer models of the protostellar system fit the observed SED well and yield a total luminosity of most likely less than 100 Lsun. Our models suggest that the bolometric luminosity of the protostar could be just 12-14 Lsun, while the luminosity of the colder (~ 20 K) extended core could be around 100 Lsun, with a mass of about 27 Msun. Our derived luminosities for the protostar OMC-2 FIR 4 are in direct contradiction with previous claims of a total luminosity of 1000 Lsun (Crimier et al 2009). Furthermore, we find evidence from far-infrared molecular spectra (Kama et al. 2013, Manoj et al. 2013) and 3.6 cm emission (Reipurth et al 1999) that FIR 4 drives an outflow. The final stellar mass the protostar will ultimately achieve is uncertain due to its association with the large reservoir of mass found in the cold core.

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arXiv2013

A candidate circumbinary Keplerian disk in G35.20-0.74 N: A study with ALMA

We report on ALMA observations of continuum and molecular line emission with 0.4" resolution towards the high-mass star forming region G35.20-0.74 N. Two dense cores are detected in typical hot-core tracers, such as CH3CN, which reveal velocity gradients. In one of these cores, the velocity field can be fitted with an almost edge-on Keplerian disk rotating about a central mass of 18 Msun. This finding is consistent with the results of a recent study of the CO first overtone bandhead emission at 2.3mum towards G35.20-0.74 N. The disk radius and mass are >2500 au and 3 Msun. To reconcile the observed bolometric luminosity (3x10^4 Lsun) with the estimated stellar mass of 18 Msun, we propose that the latter is the total mass of a binary system.

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arXiv2012

The thermal state of molecular clouds in the Galactic Center: evidence for non-photon-driven heating

We used the Atacama Pathfinder Experiment (APEX) 12 m telescope to observe the J_KaKc=3_03-2_02, 3_22-2_21, and 3_21-2_20 transitions of para-H_2CO at 218 GHz simultaneously to determine kinetic temperatures of the dense gas in the central molecular zone (CMZ) of our Galaxy. The map extends over approximately 40 arcmin x 8 arcmin (~100x20 pc^2) along the Galactic plane with a linear resolution of 1.2 pc. The strongest of the three lines, the H_2CO (3_03-2_02) transition, is found to be widespread, and its emission shows a spatial distribution similar to ammonia. The relative abundance of para-H_2CO is 0.5-1.2 10^{-9}, which is consistent with results from lower frequency H_2CO absorption lines. Derived gas kinetic temperatures for individual molecular clouds range from 50 K to values in excess of 100 K. While a systematic trend toward (decreasing) kinetic temperature versus (increasing) angular distance from the Galactic center (GC) is not found, the clouds with highest temperature (T_kin > 100 K) are all located near the nucleus. For the molecular gas outside the dense clouds, the average kinetic temperature is 65+/-10 K. The high temperatures of molecular clouds on large scales in the GC region may be driven by turbulent energy dissipation and/or cosmic-rays instead of photons. Such a non-photon-driven thermal state of the molecular gas provides an excellent template for the more distant vigorous starbursts found in ultraluminous infrared galaxies (ULIRGs).

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arXiv2011

The molecular distribution of the IRDC G351.77-0.51

Infrared dark clouds are massive, dense clouds seen in extinction against the IR Galactic background. Many of these objects appear to be on the verge of star and star cluster formation. Our aim is to understand the physical properties of IRDCs in very early evolutionary phases. We selected the filamentary IRDC G351.77 - 0.51, which is remarkably IR quiet at 8μm. As a first step, we observed mm dust continuum emission and rotational lines of moderate and dense gas tracers to characterise different condensations along the IRDC and study the velocity field of the filament. Our initial study confirms coherent velocity distribution along the infrared dark cloud ruling out any coincidental projection effects. Excellent correlation between MIR extinction, mm continuum emission and gas distribution is found. Large-scale turbulence and line profiles throughout the filament is indicative of a shock in this cloud. Excellent correlation between line width, and MIR brightness indicates turbulence driven by local star formation.

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arXiv2010

Hier ist wahrhaftig ein Loch im Himmel - The NGC 1999 dark globule is not a globule

The NGC 1999 reflection nebula features a dark patch with a size of ~10,000 AU, which has been interpreted as a small, dense foreground globule and possible site of imminent star formation. We present Herschel PACS far-infrared 70 and 160mum maps, which reveal a flux deficit at the location of the globule. We estimate the globule mass needed to produce such an absorption feature to be a few tenths to a few Msun. Inspired by this Herschel observation, we obtained APEX LABOCA and SABOCA submillimeter continuum maps, and Magellan PANIC near-infrared images of the region. We do not detect a submillimer source at the location of the Herschel flux decrement; furthermore our observations place an upper limit on the mass of the globule of ~2.4x10^-2 Msun. Indeed, the submillimeter maps appear to show a flux depression as well. Furthermore, the near-infrared images detect faint background stars that are less affected by extinction inside the dark patch than in its surroundings. We suggest that the dark patch is in fact a hole or cavity in the material producing the NGC 1999 reflection nebula, excavated by protostellar jets from the V 380 Ori multiple system.

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arXiv2010

Herschel/PACS Imaging of Protostars in the HH 1-2 Outflow Complex

We present 70 and 160 micron Herschel science demonstration images of a field in the Orion A molecular cloud that contains the prototypical Herbig-Haro objects HH 1 and 2, obtained with the Photodetector Array Camera and Spectrometer (PACS). These observations demonstrate Herschel's unprecedented ability to study the rich population of protostars in the Orion molecular clouds at the wavelengths where they emit most of their luminosity. The four protostars previously identified by Spitzer 3.6-40 micron imaging and spectroscopy are detected in the 70 micron band, and three are clearly detected at 160 microns. We measure photometry of the protostars in the PACS bands and assemble their spectral energy distributions (SEDs) from 1 to 870 microns with these data, Spitzer spectra and photometry, 2MASS data, and APEX sub-mm data. The SEDs are fit to models generated with radiative transfer codes. From these fits we can constrain the fundamental properties of the protostars. We find luminosities in the range 12-84 L_sun and envelope densities spanning over two orders of magnitude. This implies that the four protostars have a wide range of envelope infall rates and evolutionary states: two have dense, infalling envelopes, while the other two have only residual envelopes. We also show the highly irregular and filamentary structure of the cold dust and gas surrounding the protostars as traced at 160 microns.

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