Division H - Poster Abstracts


Dust reddening and diffuse ultraviolet observations near Taurus

kuzhikkatt, sathyanarayanan

We have studied the dust-distribution in Taurus molecular region with different reddening maps and analyzed the GALEX diffuse ultraviolet data to estimate the dust grain properties in the region with a Monte Carlo dust-scattering code. We find that the dust-distribution has little effects on the grain properties.

Accurate OH maser positions in SPLASH

Qiao, Hai-Hua

Masers are important astrophysical objects which can be used to understand the chemical and physical environment of the interstellar medium (ISM). The hydroxyl radical (OH) was the first molecule discovered in the ISM and can produce strong stimulated spectral line emission (OH masers). Our research measured accurate positions of OH masers based on the results from the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). SPLASH observed OH in four ground-state transitions across the inner Galactic plane (332 degrees < l < 10 degrees, |b| < 2 degrees; 358 degrees < l < 4 degrees, 2 degrees < b < 6 degrees; in total 176 square degrees). We used the Australia Telescope Compact Array to accurately determine the positions of these OH masers. We then compared these positions with the Methanol Multibeam survey, H2O Southern Galactic Plane Survey, Red MSX Source, SIMBAD and the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire maps to identify which kind of astrophysical object they are associated with. We have finished the accurate position measurements for 80 square degrees (Qiao et al. 2016a, Qiao et al. 2016b, Qiao et al. 2018, submitted). In my talk, I will present these results and some statistical work in details.

The AMBRE Project: r-process element abundances in the Milky Way thin and thick discs

Guiglion, Guillaume

Chemical evolution of r-process elements in the Milky Way disc is still a matter of debate. We took advantage of high resolution HARPS/UVES/FEROS spectra from the ESO archive in order to derive precise chemical abundances of 3 r-process elements Eu, Dy & Gd and also Ba abundance, for more than 1000 stars. The chemical analysis has been performed thanks to the automatic optimization pipeline GAUGUIN. Based on the [alpha/Fe] ratio, we chemically characterized the thin and the thick discs. We present and discuss chemical abundance patterns of such elements in both discs.

High-Resolution Empirical Profiles of Diffuse Interstellar Bands

Puspitarini, Lucky

Diffuse interstellar bands (DIBs) are a set of mysterious interstellar absorption features detected mostly in the optical and near infrared. Although we do not know utterly the carriers of the DIBs, they can be a promising tracer of the interstellar matter (ISM). DIB databases from stellar spectroscopic surveys can be used as a complementary tool for locating interstellar (IS) clouds. To perform an automated DIB fitting to the spectroscopic data, DIB shape model is needed. But unlike interstellar lines, the profiles of the DIBs are often asymmetric and have substructures. In this work, we establish new empirical individual DIB model based on the average profile of DIB by using high-resolution spectra recorded with NARVAL spectrograph. We also disscuss variations of the profiles and show correlations between individual DIBs.

ALMA Observations of Polarization from Dust Scattering in the IM Lup Protoplanetary Disk

Hull, Chat

We present 870 µm ALMA observations of polarized dust emission toward the Class II protoplanetary disk IM Lup. We find that the orientation of the polarized emission is along the minor axis of the disk, and that the value of the polarization fraction increases steadily toward the center of the disk, reaching a peak value of ~1.1%. All of these characteristics are consistent with models of self-scattering of submillimeter-wave emission from an optically thin inclined disk. The distribution of the polarization position angles across the IM Lup disk reveals that while the average orientation is along the minor axis, the polarization orientations show a significant spread in angles; this can also be explained by models of pure scattering. We compare the polarization with that of the Class I/II source HL Tau. A comparison of cuts of the polarization fraction across the major and minor axes of both sources reveals that IM Lup has a substantially higher polarization fraction than HL Tau toward the center of the disk. This enhanced polarization fraction could be due a number of factors, including scattering by larger dust grains in the more evolved IM Lup disk. However, our models yield similar maximum grain sizes for both HL Tau and IM Lup: on the order of 70 µm in both cases. This reveals continued tension between grain-size estimates from scattering models and from models of the dust emission spectrum, which find that the bulk of the (unpolarized) emission in disks is most likely due to millimeter (or even centimeter) sized grains. 

TMRT observations on H2CO & H213CO toward molecular clouds in our Galaxy

Zhang, JiangShui

We present observations of the 110-111 and 211-212 absorption lines of H2CO and the 110-111 lines of H213CO toward a large sample of more than 100 Galactic molecular clouds, through the Shanghai 65m Tianma Radio Telescope (TMRT). Complementary continuum at 2 cm and 6 cm through TMRT were also performed to determine the optical depth and further determine better the isotope abundance ratio. We got 38 sources with all lines and continuum data. Our preliminary results show that the abundance ratio of H212CO and H213CO tends to increase with increasing galacocentric distance, though the scatter of the ratio is large. Further modeling works are necessary and important to discuss the optical depth effect on the isotope ratio 12C/ 13C.

Determining the radius of an open cluster from stellar proper motions

Sanchez, Nestor

We propose a new method for calculating the radius of an open cluster in an objective way from an astrometric catalogue containing, at least, positions and proper motions. It uses the minimum spanning tree in the proper motion space to discriminate cluster stars from field stars and it quantifies the strength of the cluster-field separation. This is done for a range of different sampling radii from where the cluster radius is obtained as the size at which the best cluster-field separation is achieved. The novelty of this strategy is that the cluster radius is obtained independently of how its stars are spatially distributed. We test the reliability and robustness of the method with both simulated and real data from a well-studied open cluster (NGC 188), and apply it to UCAC4 data for five other open clusters with different catalogued radius values. NGC 188, NGC 1647, NGC 6603, and Ruprecht 155 yielded unambiguous radius values. However, ASCC 19 and Collinder 471 showed more than one possible solution, but it is not possible to know whether this is due to the involved uncertainties or due to the presence of complex patterns in their proper motion distributions.

EREBUS: the EuRopean Extinction BUmp Survey

Postel, Andreas

Dust in the interstellar medium (ISM) is intimately linked to the birth and death of stars. However, despite being of such fundamental importance to the evolution of our own and nearby galaxies, the dynamic behaviour and composition of the ISM are not yet fully understood. A number of observations by IUE of reddened Milky Way OB stars revealed a strong UV extinction feature around 2175 Å and a precipitous extinction rise to the far UV along the lines of sight. Whilst the carrier(s) for this are at present still being debated, multiple laboratory studies suggest carbonate grains to be the key constituent. EREBUS is a mission concept being developed to study the composition of the ISM in both the Milky Way and Local Group Galaxies, principally by mapping the spatial distribution of the UV extinction features. As the shape and position of both the bump and the rise are sensitive to the dust composition along the line of sight, the survey will provide a wealth of information about the spatial distribution of the carrier(s). In this way, we will be able to understand better the time evolving behaviour of the ISM, which is critical to the study of galaxy evolution. The mission proposes to deploy a satellite observatory equipped with a coarse UV spectrograph (R∼100 from 3000 to 1000 Å) to map the extinction curve variability in the Milky Way in 3 dimensions (in conjunction with data from Gaia) and in the Local Group in 2 dimensions. In this paper, we detail the scientific goals for the project, discuss a proposed observation strategy using an iterative process to develop a hierarchical map, and finally outline the instrument requirements and preliminary spacecraft architecture._x000D_ _x000D_ Keywords: Dust, UV bump, Interstellar Medium


Lopez-Martinez, Fatima

Winds and jets are key factors in the evolution of accretion disks in pre-main sequence stars, and deriving their physical properties is one of the most important steps for a full understanding of the connection among outflow, jet and accretion processes. In this work we determine the physical properties of the high velocity component (HVC) and the low velocity component (LVC) emitting region of the optical forbidden [N II], [O I] and [S II] lines for the jets of DG Tau, SZ 102, CW Tau and RW Aur. We found two well defined ranges of temperatures and densities for the gas emission lines: one with 4.125 ≤ log T e (K) ≤ 4.55 and 2.25 ≤ log n e (cm^3 ) ≤ 5.25, and another one with_x000D_ 5.25 ≤ log T e (K) ≤ 5.6 and 5.25 ≤ log n e (cm 3 ) ≤ 6.75. The LVC has high temperatures and high densities for DG Tau and CW Tau, whereas for SZ 102 it has much lower densities and temperatures. The peak velocities and full width at half maximum of the LVC pointed out that its origin is from a MHD disk wind at 0.05-1.69 AU and that Keplerian rotation is the main responsible of the broadening of the lines. The relation found between the accretion luminosity with the LVC’s temperature and density, suggests that the accretion plays an important role in the physical properties of the emitting region, likely a steady accretion is performing in the outflow driving region. We did not find evidence of Keplerian broadening for the HVC, whereas we found a correlation between the mass loss rate and accretion luminosity, probably because episodic accretion is occurring in the region where the jet is driven.

First Hydrodynamics Simulations of Radiation Forces and Photoionization Feedback in Massive Star Formation

Kuiper, Rolf

We present the first simulations of the formation of massive stars which account for radiation forces as well as photoionization feedback (along with protostellar outflows) simultaneously. We perform direct hydrodynamics simulations of the gravitational collapse of high-density mass reservoirs toward the formation of massive stars including self-gravity, stellar evolution, protostellar outflows, continuum radiation transport, photoionization, and the potential impact of ram pressure from large-scale gravitational infall. For direct comparison, we execute these simulations with and without the individual feedback components. Furthermore, each simulation series is performed starting from two different accretion scenarios, namely a finite small-scale mass reservoir such as a pre-stellar core vs. a virtually infinite reservoir which accounts for large-scale accretion flows. We determine the relative strength of the feedback components and derive the size of the reservoir from which the forming stars gained their masses. _x000D_ Photoionization and HII regions dominate the feedback ladder only at later times, after the star has already contracted down to the zero-age main sequence, and only on large scales. Specifically, photoionization yields a broadening of the bipolar outflow cavities and a reduction of the gravitational infall momentum by about 50%, but does not limit the stellar mass accretion. On the other hand, we find radiation forces restrain the gravitational infall toward the circumstellar disk, impact the gravito-centrifugal equilibrium at the outer edge of the disk, and eventually shut down stellar accretion completely. _x000D_ The most massive star formed in the simulations accreted 95 Msol before disk destruction; this mass was drawn-in from an accretion reservoir of approximately 240 Msol and 0.24 pc in radius. Concluding, in the regime of very massive stars, the final mass of these stars is controlled by their own radiation force feedback.

A statistical Study of Cluster Formation

Shimoikura, Tomomi

In order to carry out a statistical study of cluster formation, we have conducted observations toward 15 star-forming regions. We used the NRO 45m telescope to observe the regions with several molecular lines at 100 GHz (e.g., C18O) and 45 GHz (e.g., CCS). We also conducted the analyses using the 2MASS Point Source Catalog to reveal the star density distribution around the regions. We identified 24 clumps, and found that 16 of them are associated with young clusters. To characterize the clumps and clusters in terms of cluster formation, we categorized them into four types according to the spatial coincidence of gas and star density: Clumps having no associated clusters are classified as Type1, clumps showing good correlations with clusters are classified as Type2, clumps showing poor correlations with clusters are classified as Type3, and clusters with no associated clumps are classified as Type4. The Type2 clumps have a typical mass of ~103Msun and have morphologies that are similar to the clusters, suggesting that the clumps are in an early stage of cluster formation and the associated clusters are still embedded in an amount of gas and dust. We found that some of the Type2 clumps are infalling on the clump-scale to form clusters at the clump center, which should commonly occur in the beginning of cluster formation. We suggest that the clump + cluster systems should evolve from Type1 to Type4. To investigate this hypothesis in terms of chemical reactions, we examined the chemical compositions of the clumps by comparing the fractional abundances of the observed molecules with chemical models in literature. To our surprise, all of the clumps classified to Type1 are older than the Type2 clumps in terms of chemical compositions. We suggest that they are the Type1 clumps being gravitationally stable without collapsing for a long time due to the strong magnetic field. Type1 clumps younger than the observed Type2 clumps should be rare to find due to their short lifetime.

Revealing the line-of-sight structures of Taurus Molecular Cloud 1

DOBASHI, Kazuhito

In this presentation, we introduce a new method to probe into the line-of-sight structures of dense molecular clouds using the HC3N (J=5–4) and CCS(JN=43–32) lines at 45 GHz, and demonstrate results of an application to Taurus Molecular Cloud 1 (TMC-1). In TMC-1, the CCS line is moderately optically thick, and the HC3N line consists of two optically thin hyperfine lines (F=4–4 and 5–5) and three optically thick hyperfine lines (F=6–5, 5–4, and 4–3). The point of the method is to utilize the optically thin lines to identify distinct velocity components, and to utilize the optically thicker lines to infer their relative locations along the line-of-sight by solving the radiative transfer. Using the Z45 receiver and the PolariS spectrometer installed in the NRO 45m telescope (HPBW~40”), we obtained spectral data of these emission lines toward the cyanopolyyne peak in TMC-1. About 30 hours integration with these instruments brought us wonderful spectral data with a very high velocity resolution and sensitivity of 0.0004 km s-1 and 40 mK, respectively. Analyses of the optically thin hyperfine lines of HC3N indicate that there are four distinct velocity components with a narrow line width (≤0.1 km s-1) at VLSR=5.727, 5.901, 6.064, and 6.160 km s-1, which we call A, B, C, and D in the order of increasing radial velocity, respectively. Further radiative transfer analyses of the optically thicker CCS line as well as of the other hyperfine lines of HC3N show that the four velocity components are lying along the line-of-sight in the order of A, B, C, and D from far side to near side to the observer, for which we conclude that TMC-1 is shrinking, moving inward as a whole. Additional analyses based on the 13CO(J=1–0) and C18O(J=1–0) data, which are available in the data archive of the Nobeyama Radio Observatory, also support this conclusion.

Star Clusters Triggered by GS242-03+37

Palouš, Jan

We explore the star clusters found in walls of the Milky Way supershell GS242-03+37. We argue that the observed HI distribution can be explained as an expanding structure more than 100 Myr old powered by a modest energy released by an OB association. The formation of star clusters has been triggered less than 40 Myr ago when the ISM density increased due to the galactic differential rotation and vertical oscillations in the galactic disk. The sequence of ages of star clusters connected to the wall of GS242-03+37 will be compared to progression of star formation observed in the solar vicinity and in the spiral arms of the Milky Way.

SPINNAKER - The SPectral INdex Numerical Analysis of K(c)osmic-ray Electron Radio-emission

Heesen, Volker

We present SPINNAKER, the SPectral INdex Numerical Analysis of K(c)osmic-ray Electron Radio-emission. This computer program calculates non-thermal radio spectral indices for 1D cosmic ray transport of pure advection and diffusion, which can be applied to vertical intensity profiles in the haloes of edge-on galaxies. We show that advection and diffusion lead to differently shaped radio spectral index profiles, with advection resulting in a linearly steepening radio spectral index with increasing distance from the star-forming mid-plane, while diffusion leads to a more parabolical shape where the steepening occurs only at heights 1-2 kpc above the disc. Corresponding intensity profiles for exponential magnetic field distributions are exponential for advection and more Gaussian for diffusion. Our radio continuum survey of nearby edge-on galaxies using new and archival data from the radio interferometers Australia Compact Array Telescope (ATCA), Very Large Array (VLA), Westerbork Synthesis Radio Telescope (WSRT) and from the 100-m Effelsberg and 64-m Parkes single-dish telecopes shows examples for both cases. Thus, galaxies can be either described as advection dominated, where advection speeds agree within a factor of two with the escape velocity near the galactic mid-plane, or they are diffusion dominated, where the diffusion coefficients are in good agreement with the Milky Way value. Hence, the study of vertical radio spectral index profiles in galaxies is helpful in many ways, especially to detect galactic winds; they are visible as radio haloes extending over the entire disc and are related to processes connected to star formation. SPINNAKER and the Python graphical user interface (GUI) for it, Spinteractive, are free to download. Spinteractive allows the user to interactively fit advection and diffusion models to vertical intensity profiles, but also incorporates an automatic search for the best-fitting parameters.

Forming and evolution history of M31 as revealed from LAMOST M31/M33 survey


Being the largest and most luminous galaxy of the Local Group, M31 hosts a variety of interesting targets including planetary nebulae (PNe), Hii regions, supergiants and globular clusters that are easily detectable with the LAMOST. Kinematic and elemental abundance studies of those objects in M31 provide important information of the chemical composition, kinematics and structure of M31 as well as the surrounding, extremely extended and complex stellar streams revealed by the recent deep imaging surveys, and are thus of great interest for the understanding of the assemblage history of the Local Group. As part of the  LAMOST Spectroscopic Survey of the Galactic Anti-center, the LAMOST M31/M33 survey have observed M31, M33 and the vicinity fields, targeting foreground Galactic stars, accessible objects of special interests in M31 and M33, including the M31 bulge and disk, as well as background quasars. Kinematic properties of the M31 bulge and disk, Globular clusters and PNe, as well as the stellar population properties of the M31 bulge, disk  and globular clusters are derived from their LAMOST spectra. We obtain the global velocity field and calculate corresponding rotation velocities of M31. The age metallicity distributions show that there are two groups in the halo of M31, one probably formed in situ in the halo in the early epoch of M31 with a rapid process. The second group probably come from disrupted dwarf galaxies accreted by M31 in the past. The bulge of M31 was formed in a early epoch, while the disk is relatively younger and the ages of some regions along the spiral arms can reach as young as less than 1Gyr.

Far-Infrared Observations of the Circumnuclear Disk

Bryant, Aaron

At the centre of our galaxy lies a 3 x 10 M? supermassive black hole, Sgr A*. Surrounding this is a rich astrophysical laboratory of molecular clouds, dust concentrations and star clusters, a region with significantly raised ISM densities, magnetic fields, turbulences and other environmental effects. It is hence a paradox of youth that there also exists a population of massive young stars within 1 pc of the black hole, grouped into at least 2 rotating disks, subject to raised tidal forces that would normally inhibit star formation.Among the theories explaining the origin of this nuclear stellar cluster is that of a collision between two molecular cloud complexes, close to Sgr A*, enabling accretion at densities above the Roche limit. An obvious candidate for such a collision is the Circumnuclear Disk (CND), a clumpy ring of molecular gas surrounding Sgr A*, with an inner radius of ~1.5 pc and a mini-spiral of ionized gas flowing towards the black hole. However, various parameters of the CND remain unconstrained. Individual gas clumps have been characterized with a range of densities and temperature components, hence raising the question of whether these clumps are transient, or if they can surpass the Roche limit and survive to form stars in-situ. While the source of far-infrared excitation is believed to be the O/B stars of the nuclear stellar cluster, the effect of local heating and shocks cannot be ruled out.In order to attempt to address these open questions, we observed the CND at 10 far-infrared wavelengths with the Field Imaging Far-Infrared Line Spectrometer (FIFI-LS), aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). In this work we present selected fine-structure line flux and thermal continuum maps of the CND, and by modelling it as a PDR, derive its density and susceptibility to tidal forces. We also outline dynamical properties of the cold gas, and present a model explaining these features.

The temperature and density from permitted O II lines in the planetary nebula NGC 7009

Torres-Peimbert, Silvia

We have used spatially- and velocity-resolved spectroscopy of NGC 7009 to determine the electron temperature and density structure based upon O II lines. We find a strong gradient in the O II -based electron temperature. It agrees with the electron temperature determined by collisionally-excited lines in part of the nebular volume, but also differs by more than 6,000K in other parts of the nebular volume. This result supports the hypothesis that NGC 7009 contains two plasma components, one of which emits collisionally-excited lines and the other that does not. For the component that does not emit collisionally-excited lines, we find a lower limit to the electron density of 104 cm-3 from the O II lines, which is higher than derived from collisionally-excited lines. We are unable to determine whether the two plasma components are in pressure equilibrium from our data, but there exist temperature and density combinations that allow this equilibrium for temperatures between 600 K and 6,000 K. For most of the temperature and density conditions allowed for the component without collisionally-excited lines, its mass of O+2 is less than that of the plasma component that emits collisionally-excited lines.

MopraCO – the CO Southern Galactic Plane Survey

Burton, Michael

The Mopra CO survey of the southern Galactic Plane (MopraCO) covers ~115°x2°, extending from Galactic longitude l = +257° – +11_x000E_° and latitude b = ±1°_x000E_. These data have been taken at 0.6 arcminute spatial resolution and 0.1 km/s spectral resolution, providing an unprecedented view of the molecular clouds and gas of the southern Galactic Plane in the 109–115 GHz J = 1–0 transitions of 12CO, 13CO and C18O.The data is being released in a series of papers (Burton et al 2013, Braiding et al 2015, Braiding et al 2018) in longitude ranges, plus selected regions of interest (Rebolledo et al 2016 for Carina, Blackwell et al 2018 for the Central Molecular Zone). The final survey fields will be taken during the 2018 austral winter.We present a series of velocity-integrated maps, spectra and position-velocity plots that illustrate Galactic arm structures and trace masses on the order of _x0018_106 Msun per square degree.  These data will be available from the Mopra CO website (www.phys.unsw.edu.au/mopraco/) and the PASA data store.

The relation between the O/H ratio and the total mass of the galaxies

Peimbert, Manuel

We compare different calibrations of the  O/H abundance ratio measured from H II regions at the effective radius of galaxies of the CALIFA sample. Most calibrations are based on the collisional lines, ignore the ADF problem, ignore the results based on O recombination lines, and do not include the fraction of O atoms embedded in dust grains. Our calibration is consistent with the O recombination lines and present a mechanism that explains the cause of the ADF. This explanation is consistent will all the observational data for H II regions including the O recombination and the O collisional excited lines. The calibration is also consistent with the O/H values derived from  Cepheids, B stars,  the Sun and H II regions in our Galaxy (Carigi, Peimbert, and Peimbert 2018).

NIR High-Resolution Spectroscopy of MWC 1080 by IGRINS: Detection of New Outflows?

Kim, il-joong

Through MIRIS Paa Galactic plane survey, a lot of Paa blobs were found along the plane. To reveal their characteristics, we are planning to collect NIR high-resolution spectroscopic data for the Paa blobs by using Immersion GRating INfrared Spectrograph (IGRINS). Here, we present the IGRINS results for the Herbig Be star MWC 1080, which is one of the Paa blobs detected in Cepheus. This Herbig Be star is known to have many young stellar objects (YSOs) and bright MIR (10-20 µm) nebulosity in its vicinity. From IPHAS Ha data, we found large extended Ha features that correlate well with MIR and 13CO morphologies around MWC 1080. A part of the Ha features shows a bow shock shape to the northeast of the primary star MWC 1080A, which seems to be due to an outflow from the star. We detected faint [Fe II] ?1.644 µm and H2 1-0 S(1) ?2.122 µm emission lines around the bow shock feature. To the east region of MWC 1080A, we also detected strong [Fe II] and H2 emission lines with a couple of velocity components, which suggests the detection of a new outflow from another YSO. Broad Br? ?2.1662 µm line and H2 lines with various velocity components were detected around the bright MIR and Ha nebulosity as well.

An Origin of Accelerating Star Formation

Inutsuka, Shu-ichiro

Recent theoretical work on phase transition dynamics of ISM has shown that the formation of molecular clouds requires multiple episodes of supersonic compression. This finding enables us to create a scenario of molecular cloud formation as the interacting shells or bubbles in galactic scale. This picture naturally explains the accelerated star formation over many million years that was previously reported by stellar age determination in nearby star forming regions.

Spatially-resolved Measurement of Hydrogen Volume Density in the Central Molecular Zone of the Milky Way

Tanaka, Kunihiko

Star formation in the Galactic central molecular zone (CMZ) exhibits several characteristics that are rare elsewhere in the Galaxy:   formation of young massive clusters,  mini-starburst in the Sgr B2 complex, and low star formation efficiency in the vast majority of the GMCs.  We present the result of spatially resolved measurement of hydrogen volume density in the CMZ, which is one of the most important parameters in the dynamical processes of the GMCs.  We have measured the three-dimensional (position-position-velocity) distributions of volume density,  gas column density, kinetic temperature, and fractional abundances of eight molecules (HCN, HCO+, CS, H2CO, SiO, N2H+, HC3N, HNC), through excitation study using various published survey data and the HCN 4-3 data newly obtained with the ASTE 10-m telescope. The hierarchical parameter inference technique is used to suppress artificial correlations among the parameters due to the deficiency in simple one-zone LVG analysis.  The main results are summarized as follows: (1) the typical volume density and temperature are measured to be 104.1 cm-3 and 101.8 K, respectively, for the gas visible in high-density tracer lines; meanwhile, low-J CO lines are likely to originate from gas with lower density and temperature, whose mass is comparable to that of the high-density gas.   (2) CMZ clouds are generally affected by shockwaves, as indicated by the spatial correlation between the temperature variation and that in the abundances of shock-tracer molecules.  (3) the parameters that distinguish the clouds with signatures of SF (water masers and HII regions) from quiescent clouds are found to be the virial parameter and volume density, through linear discriminant analysis.  These results are consistent with the picture that the CMZ clouds generally have high density typical of SF clouds in the Galactic disk, but their star formation is suppressed by high internal pressure support provided by interaction with shocks.

The debris disc around 49 Ceti

Pawellek, Nicole

Dust grains in debris discs are important tracers of the planetesimal formation mechanisms and physical processes operating in these systems. Two main forces influencing the particle orbits are gravity and radiation pressure leading to typical appearances of debris belts including asymmetries. High angular resolution observations at near-infrared wavelengths can provide key constraints on the radial and azimuthal distribution of the small dust grains helping us to better understand where most of the dust particles are released upon collisions. In contrast to near-infrared data, sub-mm observations trace the larger parent bodies. Thus, we are able to get more information on the distribution of the dust grains by using both wavelength ranges for our analysis. Here, we present near-infrared and sub-mm radial profiles of the 49~Ceti debris disc and compare them to our theoretical model taking into account the stellar radiation pressure. 

Chemistry, masses and ages of RAVE-K2 metal poor stars

Valentini, Marica

Metal poor stars are key to understanding the history of our Galaxy. In their element abundances pattern is encoded the chemical composition of the first stars and therefore, when the stellar age is available, hints on the chemical enrichment and evolution of the Milky Way. However, obtaing precise ages for field metal poor stars is a challenging task: at present only an handful of very metal-poor stars have ages, derived by using nucleo-cosmo-chronology (via Thorium and Uranium abundances).Asteroseismology in recent years demonstrated to be a powerful tool to derive masses, and hence ages, of red giant stars. By applying this technique to metal poor stars we hope to increase the number of metal poor objects with an age measurement.For this purpose we selected 5 giants ([Fe/H]<-1.5 dex) from RAVE survey flagged as metal poor candidates by Matijevic et al. 2017. We obtained seismic information from the light curves collected by the K2 space mission, and detailed chemical abundances, from ESO-UVES high resolution spectra.  We derived iteratively the atmospheric parameters, by taking into account the seismic surface gravity. We then derived precise abundances taking into account NLTE effects. The final atmospheric parameters and abundances, together with the seismic information and, when available, Gaia parallaxes, were used for  infer stellar masses, radii and ages, via Bayesian fitting on a set of isochrones.We obtained a unique set of metal poor stars, for which we determined precise ages. For the first time a consistent and complete approach have been adopted, in order to quantify the impact of temperature shifts, different mass-loss approaches, alpha-enrichment and corrections on seismic scaling relations. This exploratory sample, obtained from the first K2 Campaigns, shows how it is possible to obtain ages for field metal poor giants, and therefore add a chronology to the chemical enrichment of the Galactic halo.

OGLE-ing the Magellanic System: Three-Dimensional Structure

Jacyszyn-Dobrzeniecka, Anna

I will present a three-dimensional structure of the Magellanic System using over 9000 Classical Cepheids (CCs) and almost 23000 RR Lyrae (RRL) stars from the OGLE Collection of Variable Stars. Given the vast coverage of the OGLE-IV data and very high completeness of the sample we were able to study the Magellanic System in great details.Lately, we have very carefully studied once again the distribution of both types of pulsators in the Magellanic Bridge area. We showed that there is no evidence of an actual physical connection between the Clouds in RRL stars distribution. We only see the two halos overlapping. There are few CCs in the Magellanic Bridge area that seem to form a genuine connection between the Clouds. Their on-sky locations are very well correlated with young stars and neutral hydrogen distribution.CCs in the LMC are situated mainly in the bar that shows no offset from the galaxy plane. The norther arm is also very prominent. Moreover, it is located closer to us than the entire sample. The CCs in the SMC have a non-planar distribution that can be described as an ellipsoid extended almost along the line of sight. RRL stars revealed a very regular distribution in both Magellanic Clouds. We fitted triaxial ellipsoids to our LMC and SMC RRL samples.

Temperature-Dependent Laboratory Measurements of the Far-Infrared to Millimeter Opacity of Carbonaceous Dust-Analogues

Greif, Jonas

We are measuring and analysing the FIR- and THz- Spectra of pyrolysed micro-crystalline cellulose as an analogue of carbonaceous interstellar dust. We are using cellulose-powder with a crystal size of 20µm  and are heating it up to temperatures of 1000°C. First results of the mass normalised extinction are presented and compared to Jäger et al. (1998). The temperature dependent measurements took place in a dry environment at cooling temperature between Tc=300K (room temperature;RT) and Tc=10K.Our aim is to assess carbonaceous dust analogues in terms of structure, nature and morphology. For theoretical and observational investigation we are going to determine their optical constants. Furthermore, we are going to calculate the emission cross section of particles with different geometries to compare them with the measured results.

The Near-infrared Optimal Distances Method Applied to Galactic Classical Cepheids Tightly Constrains Mid-infrared Period–Luminosity Relations


Classical Cepheids are well-known and widely used distance indicators. Since distance and extinction are usually degenerate, it is important to develop suitable methods to robustly anchor the distance scale. Here, we introduce a near-infrared (near-IR) optimal distance method to determine both the extinction values of and distances to a large sample of 289 Galactic classical Cepheids. The overall uncertainty in the derived distances is less than 4.9%. We compare our newly determined distances to the Cepheids in our sample with previously published distances to the same Cepheids with Hubble Space Telescope parallax measurements and distances based on the IR surface brightness method, Wesenheit functions, and the main-sequence fitting method. The systematic deviations in the distances determined here with respect to those of previous publications is less than 1-2%. We hence constructed Galactic mid-IR period-luminosity (PL) relations for classical Cepheids in the four Wide-Field Infrared Survey Explorer (WISE) bands (W1, W2, W3, and W4) and the four Spitzer Space Telescope IRAC bands ([3.6], [4.5], [5.8] and [8.0]). Based on our sample of hundreds of Cepheids, the WISE PL relations have been determined for the first time; their dispersion is approximately 0.10 mag. Using the currently most complete sample, our Spitzer PL relations represent a significant improvement in accuracy, especially in the [3.6] band which has the smallest dispersion (0.066 mag). In addition, the average mid-IR extinction curve for Cepheids has been obtained: A_W1/A_Ks=0.560, A_W2/A_Ks=0.479, A_W3/A_Ks=0.507, A_W4/A_Ks=0.406, A_[3.6]/A_Ks=0.481, A_[4.5]/A_Ks=0.469, A_[5.8]/A_Ks=0.427, and A_[8.0]/A_Ks=0.427 mag.

An extremely low mid-infrared extinction law toward the Galactic Center and 4% distance precision to 55 classical Cepheids

Chen, Xiaodian

Distances and extinction values are usually degenerate. To refine the dis- tance to the general Galactic Center region, a carefully determined extinction law (taking into account the prevailing systematic errors) is urgently needed. We collected data for 55 classical Cepheids projected toward the Galactic Center region to derive the near- to mid-infrared extinction law using three different ap- proaches. The relative extinction values obtained are AJ /AKs = 3.005, AH /AKs = 1.717,A[3.6]/AKs = 0.478,A[4.5]/AKs = 0.341,A[5.8]/AKs = 0.234,A[8.0]/AKs = 0.321, AW 1/AKs = 0.506, and AW 2/AKs = 0.340. We also calculated the cor- responding systematic errors. Compared with previous work, we report an ex- tremely low and steep mid-infrared extinction law. Using a seven-passband ‘op- timal distance’ method, we improve the mean distance precision to our sample of 55 Cepheids to 4%. Based on four confirmed Galactic Center Cepheids, a solar Galactocentric distance of R0 = 8.1 ± 0.1 ± 0.2 kpc is determined, which is close to the limiting distance accuracy (3%) for Galactic Center Cepheids. 

The Role of the Magnetic Field in the Molecular Inflow in the Central 10 pc of the Galactic Center - Implications From 850 micron Polarization Data

Hsieh, Pei-Ying

Utilizing James Clark Maxwell Telescope (JCMT) 850 micron  dust polarization data, weinvestigate the configuration of the magnetic (B-) field in the circumnuclear disk (CND) of the Galactic Center (GC).  Overall on a large scale, the B-field shows a clear predominantly toroidal morphology in the 2-pc ring rotating with respect to supermassive black hole SgrA*. In general, the observed B-field morphology is well described by a self-similar axisymmetric disk model where the radial infall velocity is one quarter of the rotational velocity. A detailed comparison with higher-resolution interferometric maps from the Submillimeter Array (SMA) further reveals that the B-field aligns with the neutral gas streamers where they are connecting to the CND.  Moreover, the innermost observed B-field structure also appears to trace and align with  the ionized mini-spirals located inside the CND.  This suggests that there might be one underlying B-field structure that is connecting the CND with its streamers and the inner mini-spirals. An estimate of beta_Plasma~0.02-0.04 -- based on the global B-field morphology that constrains  the azimuthal-to-vertical field strength ratio to be around 40 combined with a measurement of the azimuthal velocity -- indicates that the B-field appears dynamically significant towards the CND and also onwards to the inner mini-spirals.

The Expansion of the SMC SNR 1E 0102.2-7219 as Seen in X-rays

Plucinsky, Paul

We measure the expansion of the forward shock of the Small Magellanic Cloud supernova remnant 1E 0102.2-7219 in X-rays based on  Chandra X-Ray Observatory on-axis Advanced CCD Imaging Spectrometer (ACIS) observations from 1999 through 2017. We estimate a blast wave global expansion rate of 0.0253% +/- 0.0044% yr-1 (~ 1/4 of the previous X-ray measurement). We combine the expansion rate with the blast wave and reverse shock radii to generate a grid of one dimensional shock models for a range of ejecta masses and swept-up masses to constrain the progenitor mass, explosion energy, age, circumstellar density and unshocked ejecta mass. We find a constant density ambient medium does not reproduce the observed values. Models with a power-law density profile  ~r-2  (appropriate for a uniform steady progenitor stellar wind) better reproduce the observed values of forward/reverse shock radii and forward shock velocity.  For ejecta masses 6-12 solar masses and swept-up masses 10-30 solar masses, we find a range of progenitor masses 16-42 solar masses with explosion energies 0.22-0.58x1051 erg, ages ~2700-3300 yr, ambient interstellar densities 0.13-0.40 cm-3, and unshocked ejecta masses of 0.40-3.9 solar masses. The explosion energies are consistently below 1.0x1051 erg for the range of assumed values indicating a relatively low explosion energy for this supernova.  Our blast wave velocity implies a lower limit on the post shock electron temperature of 0.7 keV, assuming Coulomb heating, which is consistent with the estimate from X-ray spectral analysis.  This indicates a significantly smaller amount of energy going into accelerating cosmic rays  than previously estimated.

The Fossil Nuclear Outflow in the Central 30 pc of the Galactic Center

Hsieh, Pei-Ying

In Hsieh+ (2015, 2016, ApJ), we report a new 1 pc (30?) resolution CS(J=2-1) line map of the central 30 pc of the Galactic center (GC), made with the Nobeyama 45 m telescope. We revisit our previous study of an extraplanar feature called the polar arc (PA), which is a molecular cloud located above SgrA*, with a velocity gradient perpendicular to the galactic plane. We find that the PA can be traced back to the galactic disk. This provides clues to the launching point of the PA, roughly 6x10^6 years ago. Implications of the dynamical timescale of the PA might be related to the Galactic center lobe at parsec scale. Our results suggest that, in the central 30 pc of the GC, the feedback from past explosions could alter the orbital path of molecular gas down to the central tenth of a parsec. In the follow-up work of our new CS(J=2-1) map, we also find that, near systemic velocity, the molecular gas shows an extraplanar hourglass-shaped feature (HG-feature) with a size of ~13 pc. The latitude-velocity diagrams show that the eastern edge of the HG-feature is associated with an expanding bubble B1, ~7 pc away from SgrA*. The dynamical timescale of this bubble is ~3x10^5 years. This bubble is interacting with the 50 km/s cloud. Part of the molecular gas from the 50 km/s cloud was swept away by the bubble to b=-0.2 degree (27 pc from SgrA*). The western edge of the HG-feature seems to be molecular gas entrained from the 20 km/s cloud toward the north of the galactic disk. Our results suggest a fossil explosion in the central 3 0 pc of the GC, a few 10^5 years ago.

Molecular Gas Feeding the Circumnuclear Disk of the Galactic Center

Hsieh, Pei-Ying

The interaction between a supermassive black hole (SMBH) and the surrounding material is of primary importance in modern astrophysics. The detection of the molecular 2 pc circumnuclear disk (CND) immediately around the Milky Way SMBH, SgrA*, provides a unique opportunity to study SMBH accretion at subparsec scales. Our new wide-field CS(J = 2 - 1) map toward the Galactic center (GC) reveals multiple dense molecular streamers that originated from the ambient clouds 20 pc further out, and that are connected to the central 2 pc of the CND. These dense gas streamers appear to carry gas directly toward the nuclear region and might be captured by the central potential. Our phase-plot analysis indicates that these streamers show a signature of rotation and inward radial motion with progressively higher velocities as the gas approaches the CND and finally ends up corotating with the CND. Our results might suggest a possible mechanism of gas feeding the CND from 20 pc around 2 pc in the GC. In this paper, we discuss the morphology and the kinematics of these streamers. As the nearest observable Galactic nucleus, this feeding process may have implications for understanding the processes in extragalactic nuclei. The results were published in the astrophysical journal (2017, ApJ, 847, 3).

Polycyclic Aromatic Hydrocarbon Space Telescope (PAHST): Towards a complete view of star formation in the early Universe at z = 4.5 - 6.0

Postel, Andreas

This paper presents the Polycyclic Aromatic Hydrocarbons Space Tele-scope (PAHST) mission concept which is designed to probe star formationin the Early Universe by detecting Polycyclic Aromatic Hydrocarbon (PAH)features and emission lines redshifted to 30 – 200 µm at 4.5 < z < 6.0, aregion where no earlier measurements exist. The mission will reveal the his-tory of star formation in the early Universe by probing star formation indistant galaxies. Secondary science objectives are the study of the structureof high density filaments in the Interstellar Medium (ISM) of our Galaxy, andan investigation into the nature of cool brown dwarfs and their surroundingdusty disks. These science objectives require an ESA L-class infrared spacetelescope. The spacecraft will be launched by an Ariane 6 launcher to anoperational orbit around Lagrange point L2. The telescope is an on-axis de-sign with a 8 m segmented, foldable mirror. Detectors are a high sensitivityspectrometer and photometer. This paper presents the science case for theprimary and secondary science objectives and details a feasible spacecraftdesign concept. The mission concept, science case and technical feasibilitystudy were carried out during the Alpbach Summer School 2017, “The DustyUniverse,” and its five-day follow-up session “Post Alpbach Event” at theESA Academy Training and Learning Centre in Redu, using the concurrentengineering approach.

ATLASGAL - Kinematic distances and the dense gas mass distribution of the inner Galaxy

Wienen, Marion

High-mass stars and clusters form in the densest regions within giant molecular clouds. The initial conditions of the process are still little understood. Further progress requires to study objects in these early evolutionary stages, which are so cold that they can only be probed at far-infrared and longer wavelengths. The APEX Telescope Large Area Survey of the Galaxy, ATLASGAL, the first unbiased dust continuum survey of the whole inner Galactic plane at 870 micron, has therefore been carried out. It provides a statistically representative sample of molecular clumps at various stages of high-mass star formation.Molecular line observations are an essential tool to obtain important parameters such as temperatures, linewidths and distances. Especially the high density tracer ammonia is an excellent probe of massive clumps with low temperatures. Using the Effelsberg and Parkes telescope we thus followed up a large sample of ATLASGAL sources in the (1,1) to (3,3) ammonia inversion transitions. We derive a large range of linewidths from 1 to 7 km/s and of rotational temperatures between 10 and 25 K. The determination of masses and sizes requires the derivation of distances using the measured ammonia velocities and further velocities from the literature. We identify about 700 complexes consisting of about 3500 ATLASGAL sources based on spatial and kinematic information. From their radial velocities and a rotation curve model we determine their distances. For complexes within the solar circle two distances are possible and HI data are used to resolve these ambiguities. A correlation between the source number as a function of galactocentric radius and the position of the spiral arms reveals a link between them. Most clumps exceed the mass-size threshold for massive star formation and are likely to be unstable to gravitational collapse. Our results show that most ATLASGAL sources are already forming massive stars or have the potential to form high-mass stars in the future.

Galactic foreground of extragalactic objects based on high angular resolution multi-wavelength observations

Pinter, Sandor

We estimate the column density of the Galactic foreground interstellar medium (GFISM) in the direction of selected extragalactic sources. All-sky Planck survey data in six wavebands might be used to trace the GFISM with a resolution of 9.7 – 32.3 arcminutes, while in selected areas Herschel PACS/SPIRE gives us additional 6 wavebands towards the shorter wavelength with a magnitude higher (5 – 36 arcseconds) resolution. High spatial resolution observations of the GFISM may be important recalculating the physical parameters of gamma-ray burst (GRB) host galaxies (e.g. star formation rate, stellar & dust mass) using the updated foreground parameters. The resolution of the Planck/Herschel maps is better than other available all sky survey data on the Galactic ISM. We show how much that resolution gain matters calculating the actual foreground column densities, and then deriving an intrinsic column density.


Yin, Qian-Qing

The diffuse Galactic gamma-ray emission is resulted from the interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way; the main radiation mechanisms are proton-proton collisions, electron bremsstrahlung, and inverse Compton scattering. Observations of these diffuse emissions provide a tool to study some spatial structures, i.e, the anisotropy of cosmic rays. The pearson correlation coefficient method are used to do correlation analysis between the diffuse Galactic gamma-ray maps and the the cosmic ray maps, and then some correlation spectra are obtained. These spectra show that the spatial correlations between two maps vary as energies of gamma-ray. Hence, the variations of the spectra help to understand the possible radiation mechanisms in the anisotropy of cosmic rays.

New HI Absorption Distances for Galactic Supernova Remnants

Leahy, Denis

 We use absorption by neutral hydrogen from the ISM and emission from CO to obtain new distances for Galactic supernova remnants (SNRs). The area of the Galaxy studied is between longitudes of 15 and 60 degrees. An updated Galactic rotation curve for this region of the Galaxy is used to convert absorption and emission line velocities into distance limits for the SNRs. We are able to obtain new distances for 30 SNRs in the surveyed area. Implications of the new distances are discussed.

Gas infalling motions in the envelopes of Very Low Luminosity Objects

Kim, Mi-Ryang

We present the results of observations toward 95 VeLLOs in optically thick (HCN 1-0) and thin (N2H+ 1-0) lines using both the Korean VLBI Network (KVN) and Mopra telescopes to study inward motions in the envelopes of the VeLLOs. The normalized velocity differences (dV) between the peak velocities of the thick and thin lines were derived from 44 VeLLOs detected in both lines. The dV distribution of these VeLLOs is found to be significantly skewed to the blue, like the case of starless cores, but not as much as that of normal protostars.We selected 25 infall candidates showing infall asymmetry in the line profiles and derived their infall speeds of 0.03  km s-1 to 0.3  km s-1 with a trimmed mean value of 0.15 km s-1 using a HILL5 radiative transfer model. The mass infall rates calculated from these infall speeds are mostly of the order of 10-6 Msun yr-1 with a 10% trimmed mean value of 4.0 x 10-6 Msun yr-1. Thirteen sources out of the infall candidates were found to show typical outflow wing features in HCN profiles. The mass accretion rates for these sources were derived and found to be smaller by 1-2 orders of magnitude than the mass infall rate. This may imply that most of the VeLLOs are currently accreting only a small fraction of mass accumulated from infalling processes. In this process, a major fraction of the infalling material from the envelopes may be accumulated somewhere in accretion disk for the future massive inflow to the central source in an episodic manner. Alternatively, the infalling material may be being mostly ejected in the form of outflow winds before reaching to the central object.

Full-Disk CII Mapping of the Star Forming Nearby Disk Galaxy NGC6946 with SOFIA/FIFI-LS

Bigiel, Frank

Our poster presents results from our analysis in progress of one of thefirst, complete CII maps at high (15") resolution across the entire starforming disk of the nearby spiral galaxy NGC6946. This data set fromFIFI-LS onboard SOFIA allows us to study CII emission and key ratios,like CII-to-CO (a tracer of the CO-dark gas) or CII-to-TIR (a measure of thephotoelectric heating efficiency), across the galaxy disk and as a functionof local conditions (dust properties, radiation field, etc.). By means ofstacking the large number of independent spectra provided by the full diskmapping data, we also perform high significance arm-interarm comparisonsof these quantities to study the impact of dynamical environment. Finally,we compare CII emission to accurately calibrated, canonical SFR tracers(e.g. H-alpha+IR) and assess its use as a star formation rate tracer acrossdisk galaxies.

Gemini Observations of Two Candidate Planetary Nebulae toward the Galactic Center

Hong, Jihye

We present high-resolution near-infrared (IR) spectra of two candidate planetary nebulae (PNe) that were serendipitously found toward the Galactic center (GC). Our spectra obtained using GNIRS on Gemini North reveal strong Br ? and He I recombination lines. In one of the targets, we confidently detect Pa ß and Pa ? emissions. Based on Br ? and Pa ß lines, we estimate a foreground extinction Av ~ 20 mag for SSTGC 588220 and Av > 28 mag for SSTGC 580183. Given the large foreground extinction toward the GC, our extinction estimates plausibly indicate that they are located at the GC distance. Along with the presence of high excitation emission lines such as [S IV], [Ne III], [Ne V], and [O IV] detected in the mid-IR spectra from the Spitzer Space Telescope, and the extended emission in the Pa a narrow-band image from the Hubble Space Telescope, our observations suggest that they are the first spectroscopically confirmed PNe in the GC.

PDR Analysis with Far-infrared Diagnostic Lines in M17-SW

Klein, Randolf

Photo-dissociation regions (PDRs) are the places where molecular clouds are destroyed by UV radiation of forming massive stars (eg. Hollenbach & Tielens 1999). The molecular gas is photo-dissociated and then ionized by UV radiation. Photo-electric heating heats the gas in the PDRs. Cooling happens through the dust continuum and a handful of far infrared (FIR) fine-structure lines. FIFI-LS (Colditz et al. 2012), the FIR spectrometer onboard the US-German airborne observatory, SOFIA, can map these main cooling lines efficiently. To study the heating, cooling, physical conditions and destruction rates, we observed the well-studied edge-on PDR, M17-SW with high spatial resolution in all major FIR cooling lines of the ionized and neutral medium. In this pre- sentation, we discuss the fine-structure line and continuum maps observed by SOFIA/FIFI-LS showing the layering in this edge-on PDR. The data allows us to infer physical conditions and the energetics of the interface regions. The continuum maps together with literature data allow us to construct complete spectral energy distributions of the PDR material and the sources embedded in the PDR.

Star Cluster Systems of the Andromeda Galaxy

Naujalis, Rokas

We continue studies of the M31 galaxy’s star clusters (de Meulenaer et al. 2017; A&A, 602, A112) using photometry data from the HST PHAT multicolour survey. A significant improvement in the accuracy of star cluster physical parameters – age, mass, metallicity and extinction – was achieved by combining resolved, semi-resolved, and unresolved cluster photometry. Special care has been taken to account for contaminating foreground stars. Based on a new synthetic star cluster parameter database we derived star cluster parameters in the M31 galaxy.

Chemistry of hydrogen isotopologues in the ISM: similarities and differences

Kochina, Olga

Since observational technologies allow astronomers to get detailed molecular spectra of cold dense clouds, the presence of isotopologues in the ISM is being discovered. A common approach to taking into account such extraordinary species in numerical modeling is computing chemistry of the main isotopologue and then considering the abundance of a specific isotopologue being a fraction of the main one corresponding the isotope ratio for a definite atom. In order to validate the accuracy of such approach, the detailed chemistry of deuterium-bearing species was studied. Evolution of abundance of the species was compared to that of main isotopologues. As surface chemistry is highly important for evolution of molecular compound in cold dense cloud, chemistry was additionally detailed by considering complex dust compound [1] in the simulations. The results show that for some of the deuterium-bearing species evolution differs from the one for main isotopologues, and ratios of abundances of isotopologues on each step do vary and may differ from general isotope ratio. Evolutionary ways of some astrochemicaly important isotopologues and origins of the differences were studied and are presented here. The study was supported by RFBR, research project No. 16-02-00834 a.[1] Different-sized dust grains and the chemical evolution of protostellar objects. Kochina, O.V. & Wiebe, D.S. Astron. Rep. (2014) 58: 228.

The Early Dynamical Evolution of Young Massive Clusters near the Galactic Centre

Park, So-Myoung

     We examine the dynamical evolution of both Plummer sphere and substructured (fractal) star forming regions in Galactic Centre (GC) strong tidal fields to see what initial conditions could give rise to an Arches-like massive star cluster by ~ 2 Myr. We find that any initial distribution has to be contained within its initial tidal radius to survive, which sets a lower limit of the initial density of the Arches of ~ 600 M pc-3 if the Arches is at 30 pc from the GC, or ~ 200 M pc-3 if the Arches is at 100 pc from the GC. Plummer spheres that survive change little other than to dynamically mass segregate, but initially fractal distributions rapidly erase substructure, dynamically mass segregate and by 2 Myr look extremely similar to initial Plummer spheres, therefore it is almost impossible to determine the initial conditions of clusters in strong tidal fields.

The Distance to and the Near-infrared Extinction of the Monoceros Supernova Remnant

Zhao, He

Supernova remnants (SNRs) contain information on the influence of supernova explosions on dust properties. Based on the color indices from the Two Micron All Sky Survey and the stellar parameters from the SDSS–DR12/Apache Point Observatory Galactic Evolution Experiment and LAMOST-DR2/LAMOST Experiment for Galactic Understanding and Exploration spectroscopic surveys, the near-infrared extinction law of and the distance to the Monoceros SNR are derived together with those of two nebulae close to it, the Rosette Nebula and NGC 2264. The distance is found at the position of the sharp increase of the interstellar extinction with distance, and the nebular extinction is calculated by subtracting the foreground interstellar extinction. The distance to the Monoceros SNR is determined to be 1.98 kpc, larger than previous values. Meanwhile, the distance to the Rosette Nebula is 1.55 kpc, which is generally consistent with previous work. The distance between these two nebulae suggests no interaction between them. The distance to NGC 2264, 1.20 kpc, exceeds previous values. The color excess ratio, EJH/EJKs, is 0.657 for the Monoceros SNR, consistent with the average value of 0.652 for the Milky Way. This consistency results from the fact that the SNR material is dominated by interstellar dust rather than by supernova ejecta. EJH/EJKs is equal to 0.658 for the Rosette Nebula, further proving the universality of the near-infrared extinction law.

Metallicity Mapping of the Milky Way with Large Photometric Surveys

An, Deokkeun

We present a metallicity map of the Milky Way Galaxy within 10 kpc from the Sun, based on extensive sets of ugriz photometry from the Sloan Digital Sky Survey (SDSS), the Southern Galactic Cap u-band Sky Survey (SCUSS), and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). We obtain metallicities for individual stars by applying a set of stellar isochrones, which have been calibrated against observations of main-sequence stars in clusters and  tested using spectroscopic data. Our metallicity scale has been further checked using Gaia priors for relatively nearby stars. Our metallicity map has a continuous spatial coverage and thus is less susceptible to sampling bias, and can be used as an independent check on results from recent spectroscopic survey data. Combining with proper motion measurements from Gaia, our metallicity estimates reveal a long tail of stars with retrograde rotation in the Galactic halo. These stars exhibit systematically lower metallicities than those in prograde rotation, consistent with previous findings based on smaller photometric data samples.

CO molecular line observations of HII region G84.9+0.5

Jeong, Il-Gyo

We present the results of the multiple transitions of CO molecular line observations toward the Galactic HII region G84.9+0.5. The low transition 12CO and 13CO molecular line observations are executed with the Taeduk Radio Astronomy Observatory (TRAO) 13.7-m radio telescope in order to explore the distributions of molecular clouds and search for the star-forming activity along the H II region.  We mapped 20’ x 20’ area with On-The-Fly mapping mode of the TRAO to cover the whole area of H II region. Several molecular clumps are detected in the vicinity of the H II region, and the velocity component at ~-41 km/s these clumps seem to strongly correlated with the H II region spatially. The estimated kinematic distance toward the H II  region is about 5.5 kpc. Thus, 12CO J=3-2 molecular line observation was performed in order to investigate the spatial correlation between these clumps and the H II region G84.9+0.5. The observation results indicate that the molecular cloud distributions are well matched along the H II region identified as the distinct ring-like morphology with a small radius (~3'). The infrared images from Spitzer and Herschel clearly show the ring-like H II region shape and the point sources are associated with molecular dense clumps. At the northern part of the H II region, we were able to detect the broadened CO velocity profiles might imply the existence of the young stellar objects as well as the outflow feature. We show the detailed observation results and present the characteristics and properties of the HII region G84.9+0.5.

Near-infrared observations of supernova remnants in M33

Lee, Ho-Gyu

We present near-infrared imaging and spectroscopic observations of supernova remnants (SNRs) in M33. The SNRs are detected by our UKIRT near-infrared [Fe II] and H2 narrow band imaging of M33. For the detected SNRs, we perform follow-up spectroscopic observations using GNIRS on Gemini. The shock-heated SNR is clearly detected in the narrow band [Fe II] image, while the photoionized giant H II region is undistinguished even to the larger scale. We also detect H2 emission for some of the SNRs, suggesting that the SNRs are interacting with molecular clouds and significantly impact their surrounding conditions. We compare our results to the cases of SNRs in Milky Way. The spatially resolved distributions of two emission lines indicate that the line-emitting gases are in different conditions, resulting from the influence of evolution of massive star through stellar wind and interaction with surrounding. Additional observations including integral field unit spectroscopy and ALMA molecular line observations are needed to understand the SNRs and their effects to the environments simutaneously.

Confirmation of Benzonitrile in the Interstellar Medium

Langston, Glen

Complex organic molecules are found in cold clouds in the interstellar medium (ISM) of our Milky Way galaxy.[1][2] Frequently, if one isomer of a molecule is detected, then other isomers will also be found, but with different relative abundances. The formation pathway for these molecules is deduced the relative abundance of different sub-component molecules. The measurement of the relative abundances of isotopomers strongly tests interstellar chemical models.  These chemical models are relevant to understanding the origin of line on Earth, because the initial conditions for chemical phenomena on Earth were formed in the ISM. Our observations further extend interstellar chemistry by the first detection of benzene ring through microwave spectroscopy of cold molecular clouds. Here we report the detection in the ISM of benzonitrile, C6H5CN.   This is the first individual polycyclic aromatic hydrocarbon identified in the ISM by microwave spectroscopic observations. The Taurus Molecular Cloud 1 (TMC) is long known[3] to be a prime candidate for search for this molecule due to the high abundance of the linear cyanopolyyne molecule, HC7N, with similar molecular mass to benzonitrile. Benzonitrile molecular lines are expected to be much weaker than those for HC7N, due to the complexity of the benzonitrile microwave spectrum.[4]   We identify benzonitrile by the weighted sum of a number of spectral lines.   This process is described by Langston and Turner 2007[5].[1] Herbst,  1[2] Tielens, A.G.G.M., 2013, Reviews of Modern Physics, 85, 1021[3] Feeman, A. & Millar, T. J. (1983), Nature301, 402[4] J. M. Hollis, Anthony J. Remijan, P. R. Jewell, and F. J. Lovas (2006), Ap. J. 642:933[5] Langston, G. I. and Turner, Barry (2007), Astronomical Journal

Chemistry in HCL2

Tóth, L. Viktor

While there are excellent models for star formation it is till a challenge to test the duration of the phases of the evolution of clouds from the low density diffuse phase to the dense star forming cores. One possibility to derive the ages of interstellar clouds is to use the fact that the chemical composition of these objects is also varying with time.One of the most important environmental effects on the actual chemistry of an interstellar cloud is the energy density of the ultraviolet radiation field it is exposed to, other important parameters are density and temperature. We observed lines and derived the column densities of two time sensitive chemical species NH3, and HCO+ in the most massive part of the Taurus Molecular Cloud complex, the HCL 2. We may assume that the UV field is approximately the same for the parts of HCL 2. The other physical conditions were derived from multi-wavelength archival data, including Herschel far-infrared and CO spectral line data.We used the UMIST-2012 gas phase network with 467 species and the 6173 possible reactions between them to determine the time dependent chemical evolution in clouds with physical parameters similar to the parts of HCL 2. We compared the derived time dependent relative abundances of NH3, and HCO+ to our observed density ratios, and estimated the chemical ages of the sub-clouds of HCL 2.

VLT / KMOS view of the explosive outflow in Orion BL/KL

Itrich, Dominika

Orion BL/KL hosts a unique outflow containing more than 100 individual jets resembling those of young stellar objects. The directions of the jets strongly suggest an explosive origin linked to the decay of a non-hierarchical system of massive stars (Youngblood et al. 2016). Here, we present near-IR (1.4-2.4 µm) spectral maps of these "Orion fingers" using the K-band Multi Object Spectrograph (KMOS) at VLT. The H2 and [FeII] lines are used to determine gas physical conditions and dynamics. The observations reveal the properties of the shocks in this unique region at unprecedented detail.

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