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L. -A. Nyman

Publications and source records attributed to L. -A. Nyman.

At least 19 recordsLinked to original sources
arXiv2018

G331.512-0.103: An Interstellar Laboratory for Molecular Synthesis I. The Ortho-to-para Ratios for CH$_3$OH and CH$_3$CN

Spectral line surveys reveal rich molecular reservoirs in G331.512-0.103, a compact radio source in the center of an energetic molecular outflow. In this first work, we analyse the physical conditions of the source by means of CH$_3$OH and CH$_3$CN. The observations were performed with the APEX telescope. Six different system configurations were defined to cover most of the band within (292-356) GHz; as a consequence we detected a forest of lines towards the central core. A total of 70 lines of $A/E$-CH$_3$OH and $A/E$-CH$_3$CN were analysed, including torsionally excited transitions of CH$_3$OH ($ν_t$=1). In a search for all the isotopologues, we identified transitions of $^{13}$CH$_3$OH. The physical conditions were derived considering collisional and radiative processes. We found common temperatures for each $A$ and $E$ symmetry of CH$_3$OH and CH$_3$CN; the derived column densities indicate an $A/E$ equilibrated ratio for both tracers. The results reveal that CH$_3$CN and CH$_3$OH trace a hot and cold component with $T_k \sim$ 141 K and $T_k \sim$ 74 K, respectively. In agreement with previous ALMA observations, the models show that the emission region is compact ($\lesssim$ 5.5 arcsec) with gas density $n$(H$_2$)=(0.7-1) $\times$ 10$^7$ cm$^{-3}$. The CH$_3$OH/CH$_3$CN abundance ratio and the evidences for pre-biotic and complex organic molecules suggest a rich and active chemistry towards G331.512-0.103.

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arXiv2015

An Overview of the 2014 ALMA Long Baseline Campaign

A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ~15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from September to late November 2014, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ~350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

astro-ph.IM↗
arXiv2015

ALMA Observations of Asteroid 3 Juno at 60 Kilometer Resolution

We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum images of the asteroid 3 Juno obtained with an angular resolution of 0.042 arcseconds (60 km at 1.97 AU). The data were obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. A sequence of ten consecutive images reveals continuous changes in the asteroid's profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the Database of Asteroid Models from Inversion Techniques. We measure a geometric mean diameter of 259pm4 km, in good agreement with past estimates from a variety of techniques and wavelengths. Due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. The median peak brightness temperature is 215pm13 K, while the median over the whole surface is 197pm15 K. With the unprecedented resolution of ALMA, we find that the brightness temperature varies across the surface with higher values correlated to the subsolar point and afternoon areas, and lower values beyond the evening terminator. The dominance of the subsolar point is accentuated in the final four images, suggesting a reduction in the thermal inertia of the regolith at the corresponding longitudes, which are possibly correlated to the location of the putative large impact crater. These results demonstrate ALMA's potential to resolve thermal emission from the surface of main belt asteroids, and to measure accurately their position, geometric shape, rotational period, and soil characteristics.

astro-ph.EP↗
arXiv2015

First Results from High Angular Resolution ALMA Observations Toward the HL Tau Region

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0.075 arcseconds (10 AU) to 0.025 arcseconds (3.5 AU), revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72pm0.05 degrees) and position angle (+138.02pm0.07 degrees). We obtain a high-fidelity image of the 1.0 mm spectral index ($α$), which ranges from $α\sim2.0$ in the optically-thick central peak and two brightest rings, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation include an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO+ (1-0) which exhibits a pattern over LSR velocities from 2-12 km/s consistent with Keplerian motion around a ~1.3 solar mass star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protostars XZ Tau (A/B) and LkHa358 at 2.9 mm.

astro-ph.SR↗
arXiv2015

ALMA Long Baseline Observations of the Strongly Lensed Submillimeter Galaxy HATLAS J090311.6+003906 at z=3.042

We present initial results of very high resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the $z$=3.042 gravitationally lensed galaxy HATLAS J090311.6+003906 (SDP.81). These observations were carried out using a very extended configuration as part of Science Verification for the 2014 ALMA Long Baseline Campaign, with baselines of up to 15 km. We present continuum imaging at 151, 236 and 290 GHz, at unprecedented angular resolutions as fine as 23 milliarcseconds (mas), corresponding to an un-magnified spatial scale of ~180 pc at z=3.042. The ALMA images clearly show two main gravitational arc components of an Einstein ring, with emission tracing a radius of ~1.5". We also present imaging of CO(10-9), CO(8-7), CO(5-4) and H2O line emission. The CO emission, at an angular resolution of ~170 mas, is found to broadly trace the gravitational arc structures but with differing morphologies between the CO transitions and compared to the dust continuum. Our detection of H2O line emission, using only the shortest baselines, provides the most resolved detection to date of thermal H2O emission in an extragalactic source. The ALMA continuum and spectral line fluxes are consistent with previous Plateau de Bure Interferometer and Submillimeter Array observations despite the impressive increase in angular resolution. Finally, we detect weak unresolved continuum emission from a position that is spatially coincident with the center of the lens, with a spectral index that is consistent with emission from the core of the foreground lensing galaxy.

astro-ph.GA↗
arXiv2014

ALMA observations of alpha Centauri: First detection of main-sequence stars at 3mm wavelength

The precise mechanisms that provide the non-radiative energy for heating the chromosphere and the corona of the Sun and those of other stars constitute an active field of research. By studying stellar chromospheres one aims at identifying the relevant physical processes. Defining the permittable extent of the parameter space can also serve as a template for the Sun-as-a-star. Earlier observations with Herschel and APEX have revealed the temperature minimum of alpha Cen, but these were unable to spatially resolve the binary into individual components. With the data reported here, we aim at remedying this shortcoming. Furthermore, these earlier data were limited to the wavelength region between 100 and 870mu. In the present context, we intend to extend the spectral mapping to longer wavelengths, where the contrast between stellar photospheric and chromospheric emission becomes increasingly evident. ALMA is particularly suited to point sources, such as unresolved stars. ALMA provides the means to achieve our objectives with both its high sensitivity of the collecting area for the detection of weak signals and the high spatial resolving power of its adaptable interferometer for imaging close multiple stars. This is the first detection of main-sequence stars at a wavelength of 3mm. Furthermore, the individual components of the binary alpha CenAB are clearly detected and spatially well resolved at all ALMA wavelengths. The high S/N of these data permit accurate determination of their relative flux ratios. The previously obtained flux ratio of 0.44, which was based on measurements in the optical and at 70mu, is consistent with the present ALMA results, albeit with a large error bar. Given the distinct difference in their cyclic activity, the similarity of their submm SEDs appears surprising.

astro-ph.SR↗
arXiv2013

Silicon isotopic abundance toward evolved stars and its application for presolar grains

Galactic chemical evolution (GCE) is important for understanding the composition of the present-day interstellar medium (ISM) and of our solar system. In this paper, we aim to track the GCE by using the 29Si/30Si ratios in evolved stars and tentatively relate this to presolar grain composition. We used the APEX telescope to detect thermal SiO isotopologue emission toward four oxygen-rich M-type stars. Together with the data retrieved from the Herschel science archive and from the literature, we were able to obtain the 29Si/30Si ratios for a total of 15 evolved stars inferred from their optically thin 29SiO and 30SiO emission. These stars cover a range of masses and ages, and because they do not significantly alter 29Si/30Si during their lifetimes, they provide excellent probes of the ISM metallicity (or 29Si/30Si ratio) as a function of time. The 29Si/30Si ratios inferred from the thermal SiO emission tend to be lower toward low-mass oxygen-rich stars (e.g., down to about unity for W Hya), and close to an interstellar or solar value of 1.5 for the higher-mass carbon star IRC+10216 and two red supergiants. There is a tentative correlation between the 29Si/30Si ratios and the mass-loss rates of evolved stars, where we take the mass-loss rate as a proxy for the initial stellar mass or current stellar age. This is consistent with the different abundance ratios found in presolar grains. We found that older objects (up to possibly 10 Gyr old) in our sample trace a previous, lower 29Si/30Si value of about 1. Material with this isotopic ratio is present in two subclasses of presolar grains, providing independent evidence of the lower ratio. Therefore, the 29Si/30Si ratio derived from the SiO emission of evolved stars is a useful diagnostic tool for the study of the GCE and presolar grains.

astro-ph.GA↗
arXiv2012

Unexpectedly large mass loss during the thermal pulse cycle of the red giant R Sculptoris!

The asymptotic giant branch star R Sculptoris is surrounded by a detached shell of dust and gas. The shell originates from a thermal pulse during which the star undergoes a brief period of increased mass loss. It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse - parameters that determine the lifetime on the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3 arcsec. What was hitherto thought to be only a thin, spherical shell with a clumpy structure, is revealed to contain a spiral structure. Spiral structures associated with circumstellar envelopes have been seen previously, from which it was concluded that the systems must be binaries. Using the data, combined with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse approximately 1800 years ago, lasting approximately 200 years. About 0.003 Msun of mass was ejected at a velocity of 14.3 km s-1 and at a rate approximately 30 times higher than the prepulse mass-loss rate. This shows that approximately 3 times more mass is returned to the interstellar medium during and immediately after a pulse than previously thought.

astro-ph.SR↗
arXiv2009

ATLASGAL - The APEX Telescope Large Area Survey of the Galaxy at 870 microns

(Abridged) Studying continuum emission from interstellar dust is essential to locating and characterizing the highest density regions in the interstellar medium. In particular, the early stages of massive star formation remain poorly understood. Our goal is to produce a large-scale, systematic database of massive pre- and proto-stellar clumps in the Galaxy, to understand how and under what conditions star formation takes place. A well characterized sample of star-forming sites will deliver an evolutionary sequence and a mass function of high-mass, star-forming clumps. This systematic survey at submm wavelengths also represents a preparatory work for Herschel and ALMA. The APEX telescope is ideally located to observe the inner Milky Way. The Large APEX Bolometer Camera (LABOCA) is a 295-element bolometer array observing at 870 microns, with a beam size of 19". Taking advantage of its large field of view (11.4') and excellent sensitivity, we started an unbiased survey of the Galactic Plane, with a noise level of 50-70 mJy/beam: the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). As a first step, we covered 95 sq. deg. These data reveal 6000 compact sources brighter than 0.25 Jy, as well as extended structures, many of them filamentary. About two thirds of the compact sources have no bright infrared counterpart, and some of them are likely to correspond to the precursors of (high-mass) proto-stars or proto-clusters. Other compact sources harbor hot cores, compact HII regions or young embedded clusters. Assuming a typical distance of 5 kpc, most sources are clumps smaller than 1 pc with masses from a few 10 to a few 100 M_sun. In this introductory paper, we show preliminary results from these ongoing observations, and discuss the perspectives of the survey.

astro-ph.GA↗
arXiv2009

Physical properties of Southern infrared dark clouds

It is commonly assumed that cold and dense Infrared Dark Clouds (IRDCs) likely represent the birth sites massive stars. Therefore, this class of objects gets increasing attention. To enlarge the sample of well-characterised IRDCs in the southern hemisphere, we have set up a program to study the gas and dust of southern IRDCs. The present paper aims at characterizing the continuuum properties of this sample of objects. We cross-correlated 1.2 mm continuum data from SIMBA@SEST with Spitzer/GLIMPSE images to establish the connection between emission sources at millimeter wavelengths and the IRDCs we see at 8 $μ$m in absorption against the bright PAH background. Analysing the dust emission and extinction leads to a determination of masses and column densities, which are important quantities in characterizing the initial conditions of massive star formation. The total masses of the IRDCs were found to range from 150 to 1150 $\rm M_\odot$ (emission data) and from 300 to 1750 $\rm M_\odot$ (extinction data). We derived peak column densities between 0.9 and 4.6 $\times 10^{22}$ cm$^{-2}$ (emission data) and 2.1 and 5.4 $\times 10^{22}$ cm$^{-2}$ (extinction data). We demonstrate that the extinction method fails for very high extinction values (and column densities) beyond A$_{\rm V}$ values of roughly 75 mag according to the Weingartner & Draine (2001) extinction relation $R_{\rm V} = 5.5$ model B. The derived column densities, taking into account the spatial resolution effects, are beyond the column density threshold of 3.0 $\times 10^{23}$ cm$^{-2}$ required by theoretical considerations for massive star formation. We conclude that the values for column densities derived for the selected IRDC sample make these objects excellent candidates for objects in the earliest stages of massive star formation.

astro-ph.SR↗
arXiv2007

A centimetre-wave excess over free-free emission in planetary nebulae

We report a centimetre-wave (cm-wave, 5-31GHz) excess over free-free emission in PNe. Accurate 31 and 250GHz measurements show that the 31GHz flux densities in our sample are systematically higher than the level of optically thin free-free continuum extrapolated from 250GHz. The 31GHz excess is observed, within one standard deviation, in all 18 PNe with reliable 31 and 250GHz data, and is significant in 9 PNe. The only exception is the peculiar object M2-9, whose radio spectrum is that of an optically thick stellar wind. On average the fraction of non-free-free emission represents 51% of the total flux density at 31GHz, with a scatter of 11%. The average 31-250GHz spectral index of our sample is = -0.43+-0.03 (in flux density, with a scatter of 0.14). The 31--250 GHz drop is reminiscent of the anomalous foreground observed in the diffuse ISM by CMB anisotropy experiments. The 5--31 GHz spectral indices are consistent with both flat spectra and spinning dust emissivities, given the 10% calibration uncertainty of the comparison 5GHz data. But a detailed study of the objects with the largest cm-excess, including the low frequency data available in the literature, shows that present spinning dust models cannot alone explain the cm-excess in PNe. Although we have no definitive interpretation of our data, the least implausible explanation involves a synchrotron component absorbed by a cold nebular screen. We give flux densities for 37 objects at 31GHz, and for 26 objects at 250GHz.

astro-ph↗
arXiv2007

Sub-millimeter Observations of Giant Molecular Clouds in the Large Magellanic Cloud: Temperature and Density as Determined from J=3-2 and J=1-0 transitions of CO

We have carried out sub-mm 12CO(J=3-2) observations of 6 giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) with the ASTE 10m sub-mm telescope at a spatial resolution of 5 pc and very high sensitivity. We have identified 32 molecular clumps in the GMCs and revealed significant details of the warm and dense molecular gas with n(H2) $\sim$ 10$^{3-5}$ cm$^{-3}$ and Tkin $\sim$ 60 K. These data are combined with 12CO(J=1-0) and 13CO(J=1-0) results and compared with LVG calculations. We found that the ratio of 12CO(J=3-2) to 12CO(J=1-0) emission is sensitive to and is well correlated with the local Halpha flux. We interpret that differences of clump propeties represent an evolutionary sequence of GMCs in terms of density increase leading to star formation.Type I and II GMCs (starless GMCs and GMCs with HII regions only, respectively) are at the young phase of star formation where density does not yet become high enough to show active star formation and Type III GMCs (GMCs with HII regions and young star clusters) represents the later phase where the average density is increased and the GMCs are forming massive stars. The high kinetic temperature correlated with \Halpha flux suggests that FUV heating is dominant in the molecular gas of the LMC.

astro-ph↗
arXiv2006

Detection of HCO+ Emission toward the Planetary Nebula K 3-35

We report the detection, for the first time, of HCO+ (J=1-0) emission as well as marginal CO (J=1-0) emission toward the planetary nebula (PN) K3-35 as a result of a molecular survey carried out toward this source. We also report new observations of the previously detected CO (J=2-1) and water maser emission, as well as upper limits for the emission of the SiO, H13CO+, HNC, HCN, HC3OH, HC5N, CS, HC3N, 13CO, CN, and NH3 molecules. From the ratio of CO (J=2-1) to CO (J=1-0) emission we have estimated the kinetic temperature of the molecular gas, obtaining a value of ~20 K. Using this result, we have estimated a molecular mass for the envelope of ~ 0.017 M_Sun, and an HCO+ abundance relative to H_2 of 6 X 10^-7, similar to the abundances found in other PNe. K~3-35 is remarkable because it is one of the two PNe reported to exhibit water maser emission, which is present in the central region as well as at a distance of $\simeq$ 5000 AU away from the center. The presence of molecular emission provides some clues that could help to understand the persistence of water molecules in the envelope of K 3-35. The HCO$^{+}$ emission could be arising in dense molecular clumps, that may provide the shielding mechanism which protects water molecules in this source.

astro-ph↗
arXiv2006

Molecular excitation in the Eagle nebula's fingers

Context: The M16 nebula is a relatively nearby Hii region, powered by O stars from the open cluster NGC 6611, which borders to a Giant Molecular Cloud. Radiation from these hot stars has sculpted columns of dense obscuring material on a few arcmin scales. The interface between these pillars and the hot ionised medium provides a textbook example of a Photodissociation Region (PDR). Aims: To constrain the physical conditions of the atomic and molecular material with submillimeter spectroscopic observations. Methods: We used the APEX submillimeter telescope to map a ~3'x3' region in the CO J=3-2, 4-3 and 7-6 rotational lines, and a subregion in atomic carbon lines. We also observed C18O(3-2) and CO(7-6) with longer integrations on five peaks found in the CO(3-2) map. The large scale structure of the pillars is derived from the molecular lines' emission distribution. We estimate the magnitude of the velocity gradient at the tips of the pillars and use LVG modelling to constrain their densities and temperatures. Excitation temperatures and carbon column densities are derived from the atomic carbon lines. Results: The atomic carbon lines are optically thin and excitation temperatures are of order 60 K to 100 K, well consistent with observations of other Hii region-molecular cloud interfaces. We derive somewhat lower temperatures from the CO line ratios, of order 40 K. The Ci/CO ratio is around 0.1 at the fingers tips.

astro-ph↗
arXiv2006

Warm Molecular Gas in the Outflow and Envelope of IRAS 12496-7650 (DK Cha)

Aims:To obtain insight into the physical structure of the warm gas in the inner envelope of protostars and the interaction with the outflow. Methods: Sub-millimeter observations of 12CO, 13CO and/or C18O in J=3-2, J=4-3 and J=7-6 were obtained with the APEX Telescope towards IRAS 12496-7650, an intermediate mass young stellar object. The data are compared to ISO-LWS observations of CO J=14-13 up to J=19-18 lines to test the different proposed origins of the CO lines. Results: The outflow is prominently detected in the 3-2 and 4-3 lines, but not seen at similar velocities in the 7-6 line, constraining the temperature in the high-velocity (> 5 km/s from line center) gas to less than 50 K, much lower than inferred from the analysis of the ISO-LWS data. In addition, no isothermal gas model can reproduce the emission in both the 7-6 and the higher-J ISO-LWS lines.The 7-6 line probably originates in the inner (<250 AU) region of the envelope at ~150 K. Detailed radiative transfer calculations suggest that the ISO-LWS lines are excited by a different mechanism, possibly related to the larger-scale outflow. All possible mechanisms on scales smaller than 8 " are excluded. High-resolution continuum as well as high-J 12CO and isotopic line mapping are needed to better constrain the structure of the warm gas in the inner envelope and the interaction with the outflow.

astro-ph↗
arXiv2006

The evolutionary state of the southern dense core Cha-MMS1

Aims: Our goal is to set constraints on the evolutionary state of the dense core Cha-MMS1 in the Chamaeleon I molecular cloud. Methods: We analyze molecular line observations carried out with the new submillimeter telescope APEX. We look for outflow signatures around the dense core and probe its chemical structure, which we compare to predictions of models of gas-phase chemistry. We also use the public database of the Spitzer Space Telescope (SST) to compare Cha-MMS1 with the two Class 0 protostars IRAM 04191 and L1521F, which are at the same distance. Results: We measure a large deuterium fractionation for N2H+ (11 +/- 3 %), intermediate between the prestellar core L1544 and the very young Class 0 protostar L1521F. It is larger than for HCO+ (2.5 +/- 0.9 %), which is probably the result of depletion removing HCO+ from the high-density inner region. Our CO(3-2) map reveals the presence of a bipolar outflow driven by the Class I protostar Ced 110 IRS 4 but we do not find evidence for an outflow powered by Cha-MMS1. We also report the detection of Cha-MMS1 at 24, 70 and 160 microns by the instrument MIPS of the SST, at a level nearly an order of magnitude lower than IRAM 04191 and L1521F. Conclusions: Cha-MMS1 appears to have already formed a compact object, either the first hydrostatic core at the very end of the prestellar phase, or an extremely young protostar that has not yet powered any outflow, at the very beginning of the Class 0 accretion phase.

astro-ph↗
arXiv2005

Millimeter-wave emission during the 2003 low excitation phase of eta Carinae

In this paper we present observations of eta Carinae in the 1.3 mm and 7 mm radio continuum, during the 2003.5 low excitation phase. The expected minimum in the light curves was confirmed at both wavelengths and was probably due to a decrease in the number of UV photons available to ionize the gas surrounding the binary system. At 7 mm a very well defined peak was superimposed on the declining flux density. It presented maximum amplitude in 29 June 2003 and lasted for about 10 days. We show that its origin can be free-free emission from the gas at the shock formed by wind-wind collision, which is also responsible for the observed X-ray emission. Even though the shock strength is strongly enhanced as the two stars in the binary system approach each other, during periastron passage the X-ray emission is strongly absorbed and the 7 mm observations represent the only direct evidence of this event.

astro-ph↗