Monday Seminar for the year 2010

The presentations are shown in order of increasing time.

January

18

Sybille Anderl (1)

Shocks in the Interstellar Medium

 

Chair: E. Tremou

 

Abstract: Shock waves are prominent and ubiquitous structures which play a major role in the dynamics and evolution of the interstellar medium. Shocks propagate in the interstellar gas whenever kinetic energy is injected at supersonic velocities, e.g., by stellar jets, winds and outflows, near supernovae, during cloud-cloud collisions or through the non-linear dissipation of supersonic turbulence in the dense, magnetized ISM.

From an observational perspective shocks are prominent structures because they can be identified clearly from their characteristic spectral signatures. Since their emission spectrum depends upon the shock speed and the physical conditions in the pre-shock material, shocks yield important constrains on the physical conditions of the interstellar medium. The shock-induced heating and compression of the interstellar gas triggers chemical reactions in the gas-phase, and thereby leads to a different chemical composition than observed elsewhere. Processing of dust grains in shocks injects atoms and molecules into the gas-phase that set the chemistry of shocked regions apart from quiescent environments.

My talk will give an introduction to my PhD project. I will overview the theory and modeling of shock waves before I will outline the observational part of my project, which deals with shock waves caused by molecular outflows of deeply embedded, low-mass protostars.

 

 

 

 

January

25

First Black Board Lecture!

 

 

 

February

1

Marion Wienen (1)

Ammonia in high-mass star-forming regions discovered with ATLASGAL


Chair: Sybille Anderl
 
Abstract: The initial conditions of molecular clumps, in which high-mass stars form, are still poorly known in contrast to considerable advances in the understanding of early stages of low-mass star formation. In particular, progress has to be made in the investigation of the phases before ultracompact HII regions have formed and the newly formed high-mass (proto) stars emerge in the infrared. These phases are best searched for and detected by (sub)millimeter dust continuum and high-density molecular tracers. ATLASGAL, the first unbiased continuum survey of the whole Galactic plane at 870 micron, has therefore been carried out to provide a global view of cold dust and star formation at submillimeter wavelengths.


Although the earliest phases of high-mass star formation can be identified by the dust continuum, directly probing the material from which the stars form, there is still a lack of density, temperature and velocity information, which can be obtained by spectral line observations in addition to linewidths. Since especially ammonia is a good tracer of the temperature and kinematics of cold and dense molecular clumps, we have used the Effelsberg as well as Parkes telescope to measure the ammonia (1,1) to (3,3) inversion transitions of a large sample of southern and northern ATLASGAL sources. I will show correlations between ammonia line parameters and compare those with the submm dust continuum flux as will as with 13CO emission probing the low-density component of the high-mass clumps.
 

February

8

Michael Marks (1)

Evidence for top-heavy stellar initial mass functions in galactic globular clusters

Chair: Marion Wienen
 
Abstract: The stellar initial mass function (IMF) is the distribution function of stellar masses for a freshly hatched population of stars. The IMF is observationally found to be identical for nearly all dense systems in which its shape could be inferred and is hence referred to as the "standard" or "canonical" IMF. This poses a problem for star formation theories which predict a dependence on the environment where star formation takes place. One expectation from these theories would be that a larger number of high-mass stars relative to the canonical IMF (so-called "top-heavy" IMFs) form in systems with a low-metallicity (or a high-density) but which have otherwise similar properties.

Young, still gas-embedded star clusters expel their left-over gas from star formation over a time, which is primarily determined by feedback from massive stars. By changing the shape of the high-mass end of the IMF (i.e. the number of high-mass stars) one also modifies the amount of and rate by which energy is given away to the gas and therefore the speed with which the gas can be removed. Invoking a top-heavy IMF, the residual-gas is expelled faster and the cluster strongly expands as a result of the dropping potential. Since the segregation of massive stars towards the center is observed already in young, gas-embedded clusters, fast gas removal leads to the enhanced loss of preferentially low-mass stars (which are then more likely found at larger radial distances from the cluster center) over the tidal-boundary, affecting the present day /low-mass/ mass function (PDMF). /In that sense, the form of the high-mass end of the IMF can leave an imprint on the shape of the low-mass PDMF //via the expulsion of residual-gas/.

By comparison of observational data that include measurements of the low-mass PDMF with numerical simulations that include residual-gas expulsion we were able to infer the times needed to remove the gas in a sample of galactic globular clusters. We then inversely quantified the needed degree of top-heaviness in each of the clusters by applying a model for residual-gas expulsion in order to reproduce the independently constrained gas throw-out times. Our results show the above mentioned expected dependencies on the (present day) metallicity and on the density of the pre-globular cluster cloud-core. We demonstrate our results to be remarkably consistent with the (rare) observational evidence showing top-heavy IMFs in clusters and also with an independent analysis of the top-heaviness of the IMF in ultra compact dwarf galaxies.
 

February

15

  Rosenmontag

 

February

 

22

 

Monik Valencia (1)

The mystery of IRAS 01072+4954

Chair: Michael Marks
 
Abstract: Observations of active galactic nuclei (AGN) indicate that their main power supply arises from the accretion onto supermassive black holes and appear to confirm the so called ?Unified model? according the differences between the observed spectra are due to orientational effects with respect to the line of sight. However, low luminous unobscured AGN seem not to fit into the unified scheme or in any case, radiative inefficient accretion processes are require required to explain their emission.   As a case study, I present some results of the analysis of laser-guided near-infrared integral field spectroscopy of the starburst/Seyfert composite IRAS 01072+4954 whose optical/infrared emission corresponds to a star forming galaxy and its X-Ray spectrum reveals the AGN signature. 

 

March

1

Fujun Du (1)

Astrochemistry---A Preliminary Study

Chair: Monica Valencia
 
Abstract: Astrochemistry studies the chemical part of astronomical phenomena. Basically, people in this field search for various molecules in the sky and explain why they are there. Up to now more than a hundred different molecules have been detected in space, with the most complex one containing 13 atoms. It's a challenge to theorists to show how these molecules form and how the molecular complexity builds up. The molecular abundance depends strongly on the evolution history and

physical conditions, and this in turn allows to use the observed chemical composition as a diagnostic tool. In this talk after the introduction I will review how chemical modeling works, focusing mainly on the gas-phase case. Then I will talk about a special sub-topic of astrochemistry, namely the deuterium fractionation. Finally I will talk about one observation I have done and an outlook of future work.

 

March

8

Ewan Barr (1)

The Effelsberg Pulsar Survey

Chair: Fujun Du
 
Abstract: Pulsars are rapidly rotating neutron stars which emit beams of broadband radio emission from their magnetic poles. The extreme conditions found in and around pulsars make them a fantastic natural laboratory through which many aspects of fundamental physics and astronomy can be probed. As such, modern pulsar surveys provide the means through which we pave the way for new and exciting science. Whether it is an exotic pulsar which pushes the limits of the equation-of-state, a highly accurately timing millisecond pulsar (MSP) that can be used as part of an array to detect gravitational waves or a normal pulsar that will help map the interstellar medium, the discovery of new pulsars inevitably leads to an improvement in our understanding of one or more research areas. Thus we will commence a northern sky blind pulsar survey with the 100-m Effelsberg radio  telescope complimented by a twin search of the southern sky with the 64-m Parkes telescope.

 

In this talk I will outline how a blind pulsar survey is conducted, looking at the major steps involved in data processing and candidate selection. I will also take this opertunity to present some of the work that is currently being carried out with the Effelsberg telescope involving the observation of unaffiliated Fermi catalogue sources, namely the detection of Effelsbergs first new pulsar for ten years and first ever millisecond pulsar, PSR J1745+1017.

 

March

15

C.-S. Chang (3)

Cancelled

 

March

22

Fangchun Liu (1)

Water in star forming regions : tracking desorption and evaporation processes

Chair: E. Angelakis
 
Abstract: Although water is a crucial molecule in the study of star formation, unfortunately it almost can't be observed from the ground. Nevertheless deuterated water, HDO, can be a tracer to probe the water content and it can be detected with ground telescopes with better resolution than with satellites. Furthermore, HDO can provide information on the water formation and on the conditions of the observed region. In this talk, I will present our preliminary results, including HDO observations and models, towards the low-mass protostar, IRAS16293-2422, and the high-mass hot core, G327.3-0.6.

 

March

29

Rainer Rolfs (2)

Studying the Structure of Hot Cores with APEX

Chair: F.-C. Liu
 
Abstract: Hot Molecular Cores are early stages of massive star formation, where stellar feedback starts to affect the surrounding medium. Information on their structure (density, temperature, velocity, molecular abundances) is needed both for astrochemistry and for research on massive star formation. However,  this information is difficult to obtain and has to be extracted from observational data by detailed radiative transfer modeling. In this talk, I will present the first study that aims at reproducing the (self-absorbed) line shapes of various molecular lines. 12 hot cores were observed with APEX in lines of HCN, HCO+, CO, and their isotopologues, covering a wide range of excitations by including vibrationally excited HCN and high-J transitions. The models are spherically symmetric with central heating and density power law gradient, and the Monte-Carlo radiatve transfer code RATRAN is employed to compute the molecular lines. While some good fits could be achieved and the modeling procedure can constrain the radially averaged structure to a certain degree, a more realistic 3-dimensional modeling, based on interferometric data, would be needed to account for clumpiness, multiplicity of heating sources, and the complex velocity field with both infall and expansion motions present.

 

April

5

Ostermontag

 

April

 

12

 

Xun Shi (3)

Controlling intrinsic-shear alignment in three-point cosmic shear statistics

Chair: R. Rolfs

Abstract: With forthcoming large field multi-color imaging surveys, photometric redshift and shape information of a huge number of galaxies will be available, making cosmic shear one of the most promising cosmological probes. At the same time, there will be a greater demand on measuring and studying three-point (3-pt) statistics of cosmic shear. While two-point statistics fully characterizes a Gaussian random field, three-point statistics can probe non-Gaussian features.

 

I will talk about the basic concepts and ideas in cosmic shear 3-pt statistics study, and our work on controlling one of its limiting systematics: the intrinsic-shear alignment.

 

April

19

Blazar Kinematics: Reloaded
M. Karouzos (3)

 

Chair: X. Shi

Abstract: Recent radio VLBI studies of the morphology and kinematics of individual BL Lac objects (e.g., 1803+784, 0735+178) have revealed a different kinematic scenario for these objects. Most, if not all, jet components appear to be stationary with respect to the core, while exhibiting strong changes in their position angles. We use a statisticaly complete sample of almost 300 radio-loud flat-spectrum active galaxies to test this new scheme, in particular probing a possible difference between BL Lac and

quasar properties. In this talk I will first shortly describe the tools developed for this investigation. I will then focus on the results of the statistical analysis and their implications for the proposed new kinematic paradigm for BL Lac galaxies.

 

April

26

Major steps towards submission and thesis defence

Simone Pott


Chair: E. Angelakis

Abstract: Things you must know before you start the thesis submission process.

 

May

3

E. Angelakis

Discussion

 

May

10

E. Angelakis

Discussion

 

May

17

Radio detections of off-nuclear ULX sources
Mar Mezcua (2)

 

Chair: E. Angelakis

Abstract: Ultraluminous X-ray sources (ULXs) have luminosities exceeding 1039 erg/s, suggesting either the presence of black holes larger than stellar mass black holes or sources apparently radiating  above the Eddington limit.  I will present milli-arcsecond scale radio observations of some off-nuclear ULXs located within optical bright galaxies, resolving their compact radio emission, and measuring its brightness temperature and spectral properties. This allows us to uncover the nature of these sources and investigate whether they are intermediate mass black holes or supermassive black holes stripped of their accretion disks in post-merger systems.

 

 

 

E. Morales (3)

Galactic Young Star Clusters and their Molecular Surroundings


Chair: E. Angelakis

Abstract: Young star clusters, embedded in their natal molecular cloud, comprise the majority of star formation in the whole Galaxy, so the study of them is very important to understand the process of star formation itself and to test the different theories. In the last years, many new young embedded stars clusters have been discovered in the IR (mainly using 2MASS). In this project, our aim is to study the molecular environment of them, searching for correlations with submm continuum emission (ATLASGAL, survey at 870 microns with APEX-LABOCA), which traces the cold dust. We compiled a huge list of cataloged clusters to be compared with the ATLASGAL data and look for likely real cluster-environment interactions. Many objects are candidates to be interacting with their surroundings; in particular we have identified in some of them the potential presence of triggered star formation, as shown by clear ring structures seen in the mid-IR (the so called "IR bubbles") and nicely correlated with ATLASGAL emission. We also carried out a molecular map survey of a subsample of clusters, observed in CO isotopes, to probe the dynamical evolution and kinematics of the cluster’s surrounding molecular gas.

 

May

24

 Pfingstmontag

 

May

 

31

 

Ioannis Nestoras (2)

Cm to sum-mm monitoring of Fermi Gamma-ray blazars within the F-GAMMA project


Chair: E. Morales

Abstract: The blazars, being the most dramatic manifestations of of the activity sustained by a supermassive black hole in galactic nuclei, show  several exotic characteristics such as intense variability at almost all energy bands, highly super-luminal apparent motions, high brightness temperatures. Most of these characteristics are attributed to very small angles between the line-of-sight and the jet axis.

 

The blazar class is subdivided in two groups. Flat Spectrum Radio Quasars (FSRQs) and BL Lacertae objects (BL Lacs), The two subgroups differ in various properties, e.g., cosmological evolution, both exhibit similar Spectral Energy Distributions, characterized by two large humps. The first hump, peaking anywhere from IR to UV, is attributed to synchrotron emission from relativistic electrons in the jet. The second component extends up to GeV and TeV gamma-rays and its origin is more controversial. The second hump is due to Inverse Compton scattering of ambient photons, either internal to the jet (Synchrotron Self-Comtpon, SSC) or external (External Compton, EC). Because of their broad-band nature, multiwavelength observations of blazars are crucial to constrain the emission mechanisms, structure, and physical quantities of the inner jet on parsec and sub-parsec scales.

 

In this context the Fermi-GST AGN Multi-frequency Monitoring Alliance known as  F-GAMMA project is initiated. It is a program for the monthly monitoring of the spectra of ~60 Fermi-GST blazars from cm to sub-mm bands as well as optical and IR. The Effelsberg 100 m telescope is pivoting the program together with the 30m IRAM telescope as well as the APEX 12 m antenna covering roughly from 2 GHz up to 350 GHz with  precision of a few percent.

 

Here we present results including light curves, spectra, variability and statistical properties, also i will discuss the phenomenology of the sources in our sample.

 

June

7

Alex Kreplin (1)

Probing the circumstellar environment of the YSO candidate V921 Sco in the near-infrared with VLTI/AMBER


Chair: I. Nestoras

Abstract: Young stellar objects (YSOs) are surrounded by matter accumulated from its natal envelope which is bound in circumstellar dust and gas disks. Observations of circumstellar disks are therefore well suited to study the star formation process. Near-infrared observations trace the hot dust and gas in the innermost region of the circumstellar disk near the dust sublimation radius. In the case of intermediate-mass YSOs, the Herbig Ae/Be stars, the inner dust rim is expected to form a "puffed-up" inner rim which often dominates the near-infrared emission. Interferometric methods provide the required high angular resolution to study these innermost regions at a few AU from the central star. With the near-infrared interferometric instrument VLTI/AMBER the innermost region of the circumstellar environment of the YSO candidate V921 Sco has been spatially resolved. These observations suggest the existence of a circumstellar disk with a fitted ring radius of the inner rim of about 2 mas, which corresponds to a distance from the central star around the innermost 2.3 AU. The comparison of the measured size with the predicted dust sublimation radius reveals that the resolved structure is more compact than expected, which might be explained with a hot gaseous inner disk. In this talk I will briefly discuss the concept of the AMBER instrument, the data reduction, the observational V921 Sco AMBER results, and the simultaneous modeling of the visibilities and SED. 

 

June

14

Frank Schinzel (2)

 

Identification of gamma-ray emission from 3C 345 and the connection to its parsec-scale jet


Chair: Alex Kreplin

Abstract: For over 15 years, since the days of the Energetic Gamma-Ray Experiment Telescope (EGRET) aboard the Compton Gamma-Ray Observatory (CGRO; 1991-2000), it has been an open question why the prominent blazar 3C 345 has not been detected at gamma-ray energies >100 MeV. Recently, a bright gamma-ray source (0FGL J1641.4+3939/1FGL J1642.5+3947) has been detected in the region of 3C 345 by the Fermi/LAT. 20 months of Fermi/LAT monitoring data together with multi-wavelength observations from radio bands to X-rays of possible counterparts (3C 345, NRAO 512, CLASS J1641+3935), have been analysed. We identify 3C 345 as a gamma-ray loud source and the main contributor to this region. Furthermore, frequent monitoring of recent radio flaring activity, using very long baseline interferometry, has revealed a connection between the extended jet and the observed flux variability at high energies (optical, X-ray, gamma-ray). This suggests synchrotron self-Compton as the most likely process for gamma-ray production in this source.

 

 June

21

Note: today’s seminar will take place in EK0.9

 

Brenda Miranda (1)

 

Studying the outskirts of Galaxy Clusters with Suzaku


Chair: Frank Schinzel

Abstract: The outermost regions of galaxy clusters are a fascinating frontier for X-ray studies. While a wealth of information about their central regions has been obtained with high quality data, the state of the intracluster medium (ICM) at large radii still remains poorly explored. Probing regions with such a low surface brightness relative to the background noise represents an extreme instrumental challenge that is currently being overcome by the capabilities of the Suzaku satellite. This has opened up the possibility to directly study the dynamical state of the ICM in the boundary of galaxy clusters for a better understanding of the physics involved and for a more reliable use of galaxy cluster properties as a tool for precision cosmology. Observationally, temperature profiles are the key factor to derive other termodynamic variables where all the physics is included, hence the importance of extending them beyond the central regions to probe the border of galaxy clusters. So far, a handful of papers reporting Suzaku observations of galaxy cluster that succeeded on determining their temperature profiles out to the virial radius have been published. However, the number and variety of observed clusters need to be increased in order to draw general clonclusions.

I will talk about Abell 2163 and Abell 3404, the couple of clusters we have been studying and present thei temperature profiles.

 

 June

28

Gabriele Surcis (2)

 

The structure of the magnetic field in the massive star-forming region W75N


Chair: Brenda Miranta

Abstract: A number of different formation scenarios of high-mass stars have been proposed. In one of these scenarios, core accretion (Mckee & Tan 2003), massive stars form through gravitational collapse, which involves disk-assisted accretion to overcome radiation pressure. This scenario is similar to the favored picture of low-mass star formation (Shu et al. 1995), in which magnetic fields are thought to play an important role by removing excess angular momentum, thereby allowing accretion to continue onto the star (Shu et al. 1995). However, the role of magnetic fields during the protostellar phase of high-mass star formation is still a debated topic. In particular, it is still unclear how magnetic fields influence the formation and dynamics of disks and outflows. Most current information on magnetic fields close to high-mass protostars comes from polarized maser emissions, which allow us to investigate the magnetic field on small scales by using interferometers, such as EVN and VLBA. As I showed in my IMPRS seminar last year, by using maser observations at 6.7 GHz (methanol masers) I was able to detect the ordered magnetic field in the massive star-forming region W75N. In the present talk, I will only concentrate my attention on the new results of W75N. In fact, recently, by using VLBA observations at 22 GHz (water masers) I was able to detect two different magnetic fields around the two radio sources VLA1 and VLA2, which are in two different evolutionary stages. Moreover, by using polarization measurements of the water masers I was also able to identify the type of shocks originate in both sources which are responsible of the maser pumping. At the end I will try to answer one of the important questions about this region, i.e. What is the driving-source of the large-scale molecular bipolar outflow of W75N?.

 

July

5

Cancelled

 

July

12

Aarti Nagarajan (1)

 

moved to January 24th, 2011

 

July

19

Michael Marks (2)

 

Galaxy-wide binary distributions and their origin


Chair: E. Angelakis

Abstract: Stars typically form in star clusters and as members of binaries or higher-order multiple systems. Stars and binaries that are by now part of a galactic-field population have therefore once been members of a stellar cluster. Integrating the populations in all star clusters of a galaxy that have by now dissolved thus yields galactic-field binary distributions (Dynamical Population Synthesis). In order to do this we need to understand the properties of binary populations in star clusters. We therefore analyze and analytically describe the evolution of clusters with an initial binary-fraction of unity (in agreement with observations of pre-main sequence populations) in N-body calculations. Interactions between stars and binaries causes binaries to dissolve and therefore alters the binary population. It is shown that the evolution is mainly driven by the stellar density, i.e. the encounter rate, and therefore the binary populations in clusters differ in dependence of a clusters' initial conditions. Analytically this process can be described by introducing a stellar-dynamical operator which acts on the initial binary distribution and translates it into a final distribution. Once this operator is quantified we have a tool to numerically add binary populations in star clusters and predict Integrated Galaxy-wide Binary Distribution Functions (IGBDFs). The IGBDF depends on the minimal assumed star cluster mass, the star formation rate (SFR) of the galaxy (which determines the maximum cluster mass), the index (ß) of the power-law initial star cluster mass-function (CMF), and the size(-distribution) of star clusters. If each other parameter fixed, the results indicate lower field-binary fractions for larger SFR, shallower CMFs (smaller ß) and smaller cluster radii, respectively. For the Milky-Way (SFR=5 M_sun yr-1, ß=2) the model naturally produces its field-binary population, solely assuming an average initial star cluster half-mass radius of ~0.4 pc.

 

 July

26

 

August

2

 

August

9

Summer Break

August

16

 

August

23

 

 

August

 

30

 

Sybille Anderl (2)

 

Shocks in the Interstellar Medium II: Modelling and M33

 

 

September

 

6

 

Cancelled

 

September

13

Rainer Rolfs (3)

 

Structure of Hot Molecular Cores


Chair: S. Anderl

Abstract: Hot molecular cores are a short-lived phase of massive star formation: The massive stars have heated up the dense molecular gas in which they are deeply  embedded, but have not yet ionized and disrupted it. Their internal structure  (density, temperature, velocity, molecular abundances) is poorly known,  although information on that would be highly valuable both for astrochemistry  and for research on massive star formation. In this talk, I will present  observations (mainly of highly excited HCN) made with APEX, Herschel/HIFI,  the VLA and the SMA, as well as results from radiative transfer modelling,  which is necessary to constrain the structure from the observational data.  Centrally heated spheres with density power law gradient can reproduce most  of the single-dish spectra (computing the lines with RATRAN), revealing e.g.  a reversal of infall in the inner part of SgrB2-M. The interferometer data,  however, show that the small-scale structure is not spherical, and I will present early results from 3-dimensional modelling with RADMC-3D.

 

September

20

Note: today’s seminar will take place in EK0.9

 

Lilia Tremou (3)

 

Low Luminosity Quasi Stellar Objects(LLQSOs) & preparing NIR instrumentation to observe them.


Chair: R.  Rolfs

Abstract: LINC-NIRVANA is the interferometric near-infrared imaging camera for the Large Binocular  Telescope (LBT). Operating at JHK bands, LINC-NIRVANA will provide an unique and unprecedented  combination of high angular resolution, wide ?eld of view and large collecting area.  In contrast to all other large-scale interferometric telescopes the optical layout of the LBT resembles  a Fizeau interferometer, with both primary mirrors sharing a common mount. The baseline of a Fizeau  interferometer is not ?xed with respect to the ground but is ?xed with respect to the movable common mount  of the two mirrors.

 

High angular resolution targets such as LLQSOs can be observed with an instrument like LINC-NIRVANA. I present the analysis of a volume-limited sample of nearby galaxies hosting low-luminosity  quasi-stellar objects (LLQSOs). The sample has been drawn from the Hamburg/ESO QSO survey  (Wisotzki+2000), which has a well-defined flux limit of B_J<17.3. Our only selection criterion for the QSOs  was their small cosmological distance: only objects with a redshift z<0.060 were chosen. Specifically,  an optical spectroscopic study of the sample has been carrying out in order to characterize the excitation  degree of the sample and distinguish between possible LINER and Seyfert activity.  Our spectroscopic analyses results an aperture effect.

 

September

27

Jasmin Vural (3)

 

Cancelled

Single Dish School is taking place!

 

October

4

Retreat Final organization

 

October

11

Retreat Final organization

 

October

18

C. M. Fromm (1)

 

Modeling the Radio Emission from Blazars -The Case of CTA 102-

 

Chair: E. Angelakis

Abstract: We shall present the results of our study the light curve of the blazar CTA 102 at several frequencies during the major radio flare in spring 2006.  The rise and decay of flux density at all frequencies, together with minor, secondary flares, allows us to study the spectrum of the source at the extreme conditions during the flare. To interpret the observational data, we could apply the standard shock-in-jet model to derive the evolution of the physical parameters in the jet. We could find evidence for interaction between a standing and a traveling shock in the jet. This work is presented in the framework of a more ambitious program including multi-wavelength VLBI observations before and after this flaring event and relativistic (magneto-) hydrodynamical simulations.

 

October

25

Silvia Spezzano (1)

 

November

1

Allerheiligen

 

November

 

8

 

Felipe Navarrete (2)

 

Stacking (Sub)millimeter and Radio Signals in the COSMOS Survey Data

 

Chair: S. Spezzano

Abstract: The non-detected background population at 870 um and 1.4 GHz has been analyzed using the stacking technique. We analyze ~2 deg^2 of the COSMOS field that have been observed with the Large Apex  BOlometer CAmera (LABOCA) at 870 um, additionally we analyze the same region using deep observations (~10uJy/beam) at 1.4 GHz carried out with the Very Large Array Telescope (VLA). Furthermore, the inner 20 x 20 arcminutes^2 have been analyzed with the Max-Planck Bolometer Array (MAMBO) at 1.2 mm. Using the stacking technique we investigate different NIR populations, i.e. ERO, DRG, sBzK, pBzK. These populations are studied using a K band optical selected catalog, which has a completeness level of K~23. Finally we show how combining these data sets we can get insight into the evolution of the  FIR-Radio correlation.

 

 

Filomena Volino (3)

 

Strong gravitational lensing gy galaxies: the '8 o'clock arc system and MG~J0414+0524'

 

Chair: S. Spezzano

Abstract: I will split my talk in 2 parts to summarize the main results of my PhD project. In the first part I will highlight the power of gravitational lensing in detecting dust embedded high-z radio source, where star fromation is taking place. I will use as example the system 'SDSS J002240.78+143113.9' (otherwise named '8 o'clock arc system), and show the results from VLA observations. In the second part of my talk I will focus on gravitational lensing as tool to study a foreground mass distribution. I will present new global VLBI data of the system MG J0414+0534 and show results from a parametric lens modelling approach.

 

November

15

Jennifer Piel (1) 

 

Investigating Galaxy Clusters with Weak Gravitational Lensing & X-rays

 

Chair: F. Volino, F. Navarete

Abstract: I will give an overview about my PhD-project in which I analyse galaxy clusters with weak gravitational lensing and X-ray observations. The comparison between both approaches is important for deriving accurate cluster masses as both methods yields different cluster masses with respect to the cluster properties. In my thesis, I'm performing this analysis for a small sample consisting of five galaxy clusters which reveal very distinct properties. Thus, this sample is ideally suited for my project. The results will be later applied to larger cluster surveys and will help to constrain the cosmological parameters. In my talk, I will present the current state of the the weak lensing analysis. Additionally, I will also show some preliminary results from the X-ray analysis, which I have started very recently.  

 

November

22

 

Zahra Sheikbahaee (1)

 

Photometry of COMBO-17 with Softassign Procrustes Matching Algorithm

 

Chair: J. Piel

Abstract: COMBO-17 survey is an optical survey with the properties which could be suited for weak lensing studies. Weak lensing analysis could become more accurate with decreasing the uncertainties in photometric redshift estimation. Since COMBO-17 observation has been done in five broad-band filters and twelve medium bands, the determination of accurate photometric redshift with this data set could be the prominent characteristic of it.  In order to improve photoz estimation, we need to first solve the problem of photometry. Since the photometry procedure is a very tricky job, I have tackled this problem with a novel method namely, Softassign procrustes matching method. 

 

November

29

 

I. Antoniadis (1)

 

Optical studies of relativistic binary pulsars

 

Chair: Zahra Sheikbahaee

Abstract: Binary radio pulsars with optical counterparts provide a rich laboratory for a wide range of physical inquiry. Combined studies in radio and optical wavelengths can be used to address fundamental questions such as the behavior of matter at ultra-high densities,  the laws governing gravity in the strong field regime and the evolutionary history of close binary stars. In this talk I will present results from optical studies of three such binaries:

a) The photometric detection of a massive white dwarf companion to the relativistic pulsar PSR J1141-6545 and the  importance of the discovery on gravity tests performed with the system,

b) Phase-resolved spectroscopy of the low-mass white dwarf companion of PSR J1909-3744 that can be used to verify the

white dwarfs' mass-radius relationship and atmospheric models in a regime never tested before and 

c) Phase-resolved spectroscopy of the white dwarf companion to the relativistic pulsar PSR J1738+0333 that provide a GR-independent mass measurement for the pulsar, important for testing theories of gravity that try to explain the MOND phenomenology such as Bekenstein's TeVeS theory.

 

December

6

 

>>>Today’s Seminar will take place at 11:00<<<

 

Arturo Gomez (2, carried from March 2010) 

 

Warm gas in protostellar outflows: the case of L1448

 

Chair: Ioannis Antoniadis

Abstract: Traditionally low-J CO rotational transition have been used to study the outflow phenomenon in  star formation. Such transitions trace mainly the cold gas (< 40 K) present in shocked regions in outflows. On the other hand, work has started recently to study the warm component (> 50 K) in these objects thanks to the new instruments working in the submillimiter region. An example is the CHAMP+ heterodyne array at the APEX telescope in the Chajnantor plateau.  In this talk I will present the results of our program to study the properties of the warm gas in protostellar outflows. I will intruduce one of our sources under study (L1448) and show a comparison between the traditional studies of low-J CO (CO J=1-0, J=2-1) and our data taken with CHAMP+ (CO J=6-5, J=7-6).

 

December

13

 

Marion Wienen (2, carried from March 2010)

 

Ammonia in high-mass star-forming regions discovered with ATLASGAL 

 

Chair: Arturo Gomez

Abstract: The initial conditions of molecular clumps, in which high-mass stars form, are still largely unknown in contrast to considerable advances in the understanding of early stages of low-mass star formation. In particular, progress has to be made in the investigation of the phases before ultracompact HII regions have formed and the newly formed high-mass (proto) stars emerge in the infrared. These phases are best searched for and detected by (sub)millimeter dust continuum and high-density molecular tracers. ATLASGAL, the first unbiased continuum survey of the whole inner Galactic plane at 870 micron, has therefore been carried out to provide a global view of cold dust and star formation at submillimeter wavelengths. Although the earliest phases of high-mass star formation can be identified by the dust continuum, directly probing the material from which the stars form, there is still a lack of chemical as well as physical properties such as temperature, density and velocity information, which can be obtained by spectral line observations. I will describe the status of ATLASGAL and various follow up projects, in particular a large survey of clumps found with ATLASGAL in ammonia and a new mapping project of those clumps using the Mopra telescope at 3mm.  

 

December

20

 

Kirill Sokolovsky (3)

 

Synchrotron self-absorption in ultracompact AGN jets 

 

Chair: Marion Wienen

Abstract: The effect of a frequency dependent shift of the VLBI core position (known as the ``core shift'') has been predicted more than three decades ago and has since been observed in a few sources, but often within a narrow frequency range. This effect has important astrophysical and astrometric applications.  We have used the VLBA to image 20 pre-selected sources simultaneously at nine frequencies in the 1.4--15.4 GHz range. The core position at each frequency was measured by referencing it to a bright, optically thin feature in the jet. The core position, r_c, as a function of frequency, nu, is found to be consistent with a r_c ~ nu-1 law. Such behavior is predicted by the Blandford & K\"onigl model of a purely synchrotron self-absorbed conical jet in equipartition. We conclude that neither free-free absorption nor gradients in pressure and/or density in the jet itself and in the ambient medium surrounding the jet play a significant role in the sources observed within the 1.4--15.4 GHz frequency range.

 
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