Monday Seminar for the year 2013

The talks are shown in order of increasing time.

7-Jan-2013

 

Nadeen Sabha (1)

The Diffuse NIR Emission in the Inner Tenth of a Parsec of the Galactic Center

Chair: E. Angelakis

Abstract:
 
Sagittarius A* (Sgr A*), the super-massive black hole at the center of the Milky Way, is surrounded by a small cluster of high velocity stars, known as the S-stars. In my talk I discuss our efforts in constraining the amount and nature of the stellar and dark mass associated with the cluster in the immediate vicinity of Sgr A*. We use near-infrared imaging to determine the Ks-band luminosity function of the S-star cluster members, and use the distribution of the diffuse background emission and the stellar number density counts around the central black hole. This allows us to determine the stellar light and mass contribution that we can expect from the faint members of the cluster. We then use post-Newtonian N-body techniques to investigate the effect of stellar perturbations on the motion of S2, as a means of detecting the number and masses of the perturbers.

 

 

 

14-Jan-2013

 

Sameera Salim (3)

Laboca Survey of the COSMOS Field

Chair: Nadeen Sabha

Abstract:
 
 The Cosmological Evolution Survey (COSMOS) field covers 2 sq.deg., and it has been observed in a wavelength range that spans from the X-rays to the radio.LABOCA survey is the first (sub)millimeter survey of the COSMOS field at 870 microns which covers the inner ~0.7 sq.deg. This data set is complementary to previous millimeter surveys of the same field, MAMBO (1.2 mm), BOLOCAM (1.1mm), and AzTEC (1.1mm). In this talk I will mainly present the different methods for SMG counterpart association since it is comparatively difficult to  identify counterparts precisely at other wavelengths and to take up subsequent analysis of their physics, with more emphasis given to the new method we are testing on the Laboca sources ie. SED fitting technique.

 

 

 

21-Jan-2013

 

Silvia Spezzano (3)

First Interstellar Detection of c-C3D2

Chair: Sameera Salim

Abstract:
 
 I will report the first interstellar detection of c-C3D2: the doubly deuterated cyclopropenylidene has been detected towards the starless cores TMC-1C and L1544 using the IRAM 30m telescope. The J(Ka,Kc) = 3(0,3) - 2(1,2), 3(1,3) - 2(0,2) and 2(2,1) - 1(1,0) transitions of this species, a doubly deuterated carbene, have been observed at 3 mm in both sources. The abundance of doubly deuterated cyclopropenilydene with respect to the normal species is found to be (0.3 - 0.4)% in TMC-1C and (1.0 - 1.5)% in L1544.

The importance of c-C3D2 as a probe for deuterium interstellar chemistry will be discussed.

 

 

 

28-Jan-2013

 

Lisa Zimmermann (3)

Broad band radio observations of the outburst in the periodic gamma-ray binary LS I +61°303

Chair: Mariangela Vitale

Abstract:
 
 The periodic radio source LS I +61◦303 is one of the four established massive X-ray binaries that emit also at high/very high energies. Recent radio spectral index analysis at two frequencies by Massi Kaufman Bernado 2009 from LS I +61◦303 give new evidence for the two peak microquasar model and weaken the alternative pulsar model. The results are corroborated by high energy results from Fermi-Lat. We extended these analysis to several radio frequencies in order to get new and complete spectral index information and to compare those with the continuously running observations at high energies (e.g. with Fermi-Lat). In this talk, I present the results from these broad band radio observations of LS I +61◦303 with the Effelsberg 100m telescope, covering the large radio outburst of the source towards apastron.

 

Jeff Hodgson (1)

 

 

Zooming into the highest resolutions: Studying gamma-ray blazars with mm-VLBI

Chair: Mariangela Vitale

Abstract:
 
 The Global mm-VLBI Array (GMVA) is the highest angular resolution imaging interferometer currently available as a common user facility. It is capable of angular resolutions on the order of 40 microarcseconds. Currently consisting of 14 stations in the United States and Europe, the GMVA is used for continuum and spectroscopic imaging, probing the central regions of active galaxies and the origin of jets. In this talk I will discuss the challenges and opportunities of mm-VLBI and also present some early results of a 3 mm survey of gamma-ray blazars.

 

4-Feb-2013

 

Monthly Discussion 

Zahra Sheikbahaee (3)

 

 

 

11-Feb-2013

 

Rosenmontag

 

 

 

18-Feb-2013

 

Guang-Xing Li (3)

A Spiral-Shaped Molecular Cloud and The Formation of Stars

Chair: Zahra Sheikbahaee

Abstract:
 
 Star formation take place in molecular cloud. It is still unclear how molecular clouds fragment and produce stars. Turbulence have been proposed as a major ingredient in controlling the fragmentation. In this talk, I will report our observational study of a spiral-shaped molecular cloud. I will show that for this spiral-shaped molecular, the fragmentation process is dominated by rotation and gravity, and the star formation is controlled by gravity. Turbulence does not seems to be important at the large scale but may be important at smaller scales.

 

 

 

25-Feb-2013

 

Nicolas Caballero (2)

Timing Stability of Millisecond Pulsars and Gravitational Wave Detection

Chair: E. Angelakis

Abstract:
 
 Millisecond (radio) pulsars (MSPs) have remarkable rotational stabilities that allows them to be used as accurate cosmic clocks. One of their most exciting applications is their use for direct Gravitational Wave (GW) detection. Due to the long frequency of the GWs we can observe with MSPs, we require that they have long-term timing stability, i.e. the time of arrivals of signal should not show unexplained irregularities.

I will give an overview of the GW detection method, and the approach we use to examine the long-term timing stability of MSPs. Further, I will present the work done in this direction in the framework of the European Pulsar Timing Array project.

 

 

 

4-Mar-2013

 

Monthly Discussion

 

 

 

11-Mar-2013

 

Cherry Ng (3)

The all-sky High Time Resolution Universe Pulsar Survey (HTRU) - MSP discoveries and further timing study

 Chair: Nicolas Caballero

Abstract:
 
 In this talk I will provide an overview of the HTRU Pulsar Survey. I will present the pulsar timing work I am carrying out on 12 of the HTRU discovered millisecond pulsars (MSPs). Discovery highlights include the "Planet-pulsar" J1719-1438 and two Black widow pulsars. I will also discuss the Fermi associations detection of two MSPs found just last week and the use of MSPs as a tool for test of General Relativity.

 

 

 

18-Mar-2013

 

 Sutirtha Sengupta (1)

The origin of carbon-rich stars in the Galactic halo

 Chair: Cherry Ng

Abstract: The Galactic halo contains many carbon-rich stars, according to some surveys up to 20% of halo red giants are carbon rich. These stars defy an explanation in standard stellar evolution theory because carbon is made during helium-burning while these stars are still hydrogen-burning. One solution is that they accrete material from a binary companion which is now a white dwarf, but models predict about 2% should be carbon rich.

The most recent observations suggest there may in fact be two populations in the halo with different carbon-rich stellar fractions. The aim of this project is to understand the origin of this difference and, in turn, identify why there are so many carbon-rich stars in the Galactic halo. Is the binary model applicable for most of them? Is another source of carbon required? Are stellar mergers important? Is star formation different in the halo? This will lead to an understanding of the oldest stars in our Galaxy and hence shed light on the origin of the Milky Way itself.

 

 

 

25-Mar-2013

 

Kostas Markakis (1)

Near-Infrared A.O. Variability study of Sagittarius A*

 Chair: Sutirtha Sengupta

Abstract: We present results of the reduction of SUBARU polarization data in near infrared (Ks filter) of the Super Massive Black Hole at the center of our own Milky Way Galaxy, Sagittarius A*. The observations were conducted using the HiCIAO instrument at the Mauna Kea, HAWAII, during 15 to 17 of May 2012. With these observations we intend to further study the polarized radiation of Sagittarius A* during its short period radiation outbursts. SGRA* is considered to be the best laboratory to observe an Active Galactic Nucleus (AGN). Detection of high level of linear polarization at the Ks band can provide us with vital information of the physical conditions of the accretion of mass in the vicinity of SGRA*. We plan to compare our results with previous studies in the same and other wavelengths, which can help us to better understand the nature of the emission mechanisms causing the radiation detected from SGRA*.

 

 

 

1-Apr-2013

 

Ostermntag

 

 

 

8-Apr-2013

 

Monthly Discussion

 

Abhijeet Borkar (1)

ATCA Observations of the Galactic Center

 Chair: Kostas Markakis

 

Abstract:  Radio interferometric observations can provide important insights into the conditions near the Galactic Center (GC). We have observations of the GC at 3mm wavelength ( ~ 86 GHz ) from 3 epochs taken by the Australian Telescope Compact Array (ATCA). I will present the primary results of the positions and proper motions of the SiO maser sources. I will discuss the planned study of the variability of Sagittarius A*. I will also talk about the periapse of the infrared excess source DSO/G2, and the upcoming observations from ATCA.

 

 

 

15-Apr-2013

 

Zeinab Shafiee (3)

Weak Gravitational Lensing Study on Six Galaxy Clusters from 400d X-ray Survey”

Chair: Kostas Markakis

 

Abstract:  Determination of mass function of galaxy clusters specially at high redshifts significantly improves the constrains on cosmological parameters. Weak gravitational lensing is a promising method to determine masses of galaxy clusters and its results could be compared with the results of X-ray studies as an independent test. In this weak lensing project we select a subsample of six galaxy clusters from 400d X-ray selected galaxy cluster survey with redshifts from 0.35 to 0.47 to  measure their masses. The data is observed with the ground based 2.2m Wide Field Imager (WFI) ESO optical telescope. For data reduction we use THELI

pipeline and in order to find the shear estimation we will use KSB method. In this talk I will mainly concentrate on the KSB shape measurement method.

 

Behnam Javanmardi (1)

Studying (an)isotropy of the universe using type Ia supernovae

 Chair: Kostas Markakis

 

Abstract:  Isotropy of the Universe is one of the assumptions of the cosmological principle which standard model of cosmology is founded on. Some previous observations of the anomalies in WMAP data suggested that this assumption might need reconsideration. This issue can no longer be neglected since the Planck results confirm that the CMB sky deviates from isotropy in large scales. I try to study the subject of isotropy using the Union2.1 (2011) type Ia supernova data set.

 

 

 

22-Apr-2013

 

Axel Buddendiek (1)

Constraining Cosmological Parameters by combining Galaxy-Galaxy Lensing and Galaxy Clustering

 

 Chair: B. Javanmardi

Abstract:  During my talk I will first give a short introduction to the cosmological standard model. Afterwards I will present a newly proposed method for cosmology (Baldauf et al. 2010). This method combines galaxy-galaxy lensing with galaxy clustering in order to recover the statistical properties of the dark matter distribution in our Universe. Since the dark matter distribution contains an incredible amount of information we are able to put constraints on several cosmological parameters. This new way of doing cosmology is complementary to cosmic shear while at the same time it has different and maybe less complicated systematic errors. My main PhD project will be the application of this new method to optical multi band surveys  and finding ways to improve it.

 

 

 

29-Apr-2013

 

 Biagina Boccardi (1)

High resolution mm-VLBI imaging of Cygnus A

 Chair: Axel Buddendiek

 Abstract:  The prototypical radio galaxy Cygnus A is an ideal target for high resolution VLBI studies aimed at

a deeper understanding of the mechanism of launching, acceleration and collimation of relativistic jets. Due to its relatively close proximity (z=0.056), CygA can be imaged with mm-VLBI on scales of up to ~ 200 Schwarzschild radii, providing a unique opportunity to test MHD models in the vicinity of the central engine.

Results from a kinematical and spectral study at 43 and 86 GHz are shown here. The analysis of the proper motions of components at 7 mm shows higher velocities compared to those measured at lower frequencies. This could be related to the presence of velocity stratification due to instabilities, with faster layers appearing more prominently at higher frequencies. Spectral index analysis reveals deviations from the typical spectral characteristics of synchrotron dominated sources. The flat spectrum towards the counter-jet side suggests the presence of a "donut-like" free-free absorber partially obscuring it.

 

Banafsheh Shahzamanian (2)

Near-infrared polarization observations of Sagittarius A*

 Chair: Axel Buddendiek

 Abstract:  In this talk I will provide an overview of polarized near-infrared (NIR) observations of Sagittarius A* (SgrA*) which is associated with the super massive black hole at the center of the Milky Way. The observations have been carried out using NACO adaptive optics instrument at the VLT(ESO) and CIAO NIR camera on the Subaru telescope (from 2004 to 2012). I will present several polarized flares that have been observed during these observations and the statistical properties of NIR polarization of SgrA*. Linear polarization at 2.2 micron and its variations can help us to constrain the physical conditions of the accretion process around this SMBH.

 

 

 

6-May-2013

 

 Monthly Discussion

 

Lijing Shao (2)

Best tests of local Lorentz invariance of gravity from pulsars

 Chair: Banafsheh Shahzamanian 

Abstract:  Local Lorentz invariance (LLI) of gravity is a fundamental symmetry of spacetime in general relativity. Some alternative gravity theories predict a violation of LLI. We constrained such kinds of violation to a great precision, by using binary pulsar timing experiments, and solitary pulsar profile analysis. Some results on local position invariance of gravity from pulsars will also be present. Our constraints on the spacetime symmetries of gravitational interaction are significantly better than those from terrestrial experiments and Solar system observations.

 

 

 

13-May-2013

 

 Alice Pasetto (1)

Searching for radio sources with high rotation measures

 Chair:  L. Shao

Abstract:  This project aims at searching for high Rotation Measures (RM) in a sample of strong and compact radio sources at high redshifts. Our sample has been compiled of those sources in the NVSS catalogue without detected polarisation at 1.4 GHz. The non-detection in polarisation strongly suggests a depolarisation in a dense medium of the source itself or from the intracluster medium of a primordial cluster. An important class of objects discovered to have strong Faraday rotation are the Giga-Hertz Peaked Spectrum (GPS) sources, young clusters at their early stage of evolution or damped Ly-alpha systems. Here we present the source selection, background in some detail and some first results from the follow-up observations performed now using the 100-m Effelsberg telescope.

 

Luca Grassitelli (1)

Instabilities in the envelope of Wolf-Rayet stars

Chair: L. Shao

Abstract:  We investigate the effect of instability to convection in the outer layer of Wolf-Rayet (WR) stars, using a stellar evolution code called BEC. WR stars are very hot, highly luminous stars which have lost almost all their H-rich envelope, which allows us to model them as Helium stars. Therefor, we study the sub-surface convective zones, which arise thanks to the iron opacity peak, and from the average convective velocities we estimate the velocity field propagated to the surface. The results show that a velocity field - turbulence - at the surface may be observable for masses above 10Msun and may be accounted as the origin of wind clumping. Moreover, we investigate the occurrence of instabilities against 'strange modes' pulsation in WR stars, their origin and the influence of mass-loss on them.

 

 

 

20-May-2013

 

 Pfingsmintag

 

 

 

27-May-2013

 

 Gerrit  Schellenberger (1)

Individual Mass Determination of the HIFLUGCS Clusters

Chair:

 Abstract:  Clusters of galaxies are the most massive gravitationally relaxed systems in the universe, so the observed cluster mass function is a sensitive probe of cosmological parameters. The greatest challenge in measuring the cluster mass function is obtaining sufficiently accurate mass estimates. We are in the process of deriving the mass function by the determination of the individual masses for the 64 objects of the HIFLUGCS sample using high quality data from Chandra. By studying the two dimensional cluster shape we can obtain more accurate masses and investigate the presence of substructure and the consequent impact on the determination of the cosmological parameters. Furthermore we will check systematic uncertainties in mass determination between all instruments (XMM EPIC and Chandra ACIS). We investigate the calibration uncertainty by determining the cluster temperature in specified regions.

 

Marina Berezina (1)

 

 

tba

Chair:

 

Abstract:  tba

 

3-Jun-2013

 

 Monthly Discussion

 

Borm, Katharina (1)

X-ray Galaxy Cluster Observations with eROSITA

 

Chair:

 Abstract:  eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the German core instrument aboard the Russian Spektrum-Roentgen-Gamma satellite which is scheduled for launch in 2014. The main driver for eROSITA is studying the nature of dark energy, which is especially imprinted in the redshift and mass distribution of galaxy clusters. eROSITA is expected to detect around 100,000 clusters of galaxies in

X-rays up to redshifts of z~2.0. By means of simulations of galaxy cluster spectra, we quantify the accuracy and the precision with which two of the main cluster characteristics, the temperature and the redshift, will be obtained from eROSITA data. At the same time, we compute the number of clusters for which these two properties will be available. With the help of eROSITA we expect to increase the current sample of clusters with known characteristics by a factor of the order of ~15. This improved sample will then allow for the definition of tightest constraints on the cosmological parameters, especially on the nature of dark energy.

 

 

 

10-Jun-2013

 

 Fachbeirat visiting

 

 

 

17-Jun-2013

 

 Milan  den Heijer (1)

The Tully-Fisher relation for early-type galaxies and the Bluedisk project

 

Chair:

Abstract:  For 16 galaxies, deep Westerbork Synthesis Radio Telescope H I-observations and 2MASS K-band magnitudes are used to study the Tully-Fisher (TF) relation for early-type galaxies (ETGs). Using velocity field-based tilted-ring analyses, including the decomposition of the velocity field into its harmonic terms complemented by modeling the full data cube in order to extract the kinematical information has been applied. Moreover, the baryonic Tully-Fisher (BTF) relation is constructed using mass-to-light ratios based on models of stellar dynamics as well as star formation histories. I have found that for this sample, the K-band TF relation shows a large amount of scatter. If the TF relation is fitted to the data, the parameters indicate a much shallower relation with respect to the established spiral relation. The BTF relation yields a much tighter TF relation. It is found that variation in the mass-to-light ratios for ETGs are an essential component in explaining the offset from the K-band relation. Apart from that, the size of the galaxies and to a lesser extent the distance uncertainties play a role.

 Moreover, I will introduce the Bluedisk project, which focusses on studying the accretion mechanism of atomic gas in nearby galaxies. It consists of a multi-wavelength survey of 25 HI-rich spiral galaxies with a blue outer-disk and a control sample, consisting of 25 'normal' spirals, matched in inclination, stellar mass, size and redshift. By studying their kinematics I will investigate the question whether or not these gas-rich galaxies show signs of ongoing gas accretion, such as warps, lopsidedness or strong radial motions.

 Lars Flöer (3)

Exploration of the Local Universe in HI

 

Chair:

Abstract:  Since fall of 2008, the Effelsberg-Bonn HI Survey (EBHIS) is carried out with the 7 feed array at the Effelsberg 100-m telescope. The now finished survey covers the whole sky north of declination -5° and maps both the galactic and extragalactic HI emission out to a redshift of 0.07. In my last IMPRS talk, I will review the methods for automated source finding and parametrization I developed for the survey. I will then introduce the concept of neural networks, which I'm currently investigating to help with the last remaining task, the automated classification of detected sources.

 

 

 

24-Jun-2013

 

Florent Mertens (2)

Longitudinal and transverse velocity fields in parsec-scale jets

 

Chair:

Abstract:  Radio-loud AGN typically manifest powerful relativistic jets extending up to millions of light years and often showing superluminal motions organised in a complex kinematic pattern.  A number of physical models are still competing to explain the jet structure and kinematics revealed by radio images using the VLBI technique. Robust measurements of longitudinal and transverse velocity field in the jets would provide crucial information for these models. This is a difficult task, particularly for transversely resolved jets in objects like 3C273 and M87.  To address this task, we have developed a new technique for identifying significant structural patterns (SSP) of smooth, transversely resolved flows and obtaining a velocity field from cross-correlation of these regions in multi-epoch observations. Detection of individual SSP is performed using the wavelet decomposition and multiscale segmentation of the observed structure. The cross-correlation algorithm combines structural information on different scales of the wavelet decomposition, providing a robust and reliable identification of related SSP in multi-epoch images. The algorithm enables recovering structural evolution on scales down to ~0.25 FWHM of the image PSF. We present here the results from application of this algorithm to obtaining the first detailed transverse velocity fields and studying the kinematic evolution in the parsec-scale jets in 3C273 and M87.

 

Maria Strandent (1)

 

 

Spectral Energy Distributions of Lensed Dusty Star forming Galaxies

 

Chair:

Abstract:  A hitherto unknown population of rare (n~0.1 deg^2) and extremely bright (S1.4mm > 20 mJy) mm-selected galaxies has been uncovered (Vieira et al. 2010) with the South Pole Telescope (SPT) from a 2500 deg^2 survey at 1.4 & 2.0 mm. Follow up observations with the HST, Herschel, ALMA and other ground based facilities have shown that these sources are strongly lensed members of the high redshift submm galaxy population (see Fig. 1, Greve et al. 2012, Vieira et al. 2013) with gravitational amplification factors of _ > 10 (Hezaveh et al. 2013). Our comprehensive multi-wavelength follow-up campaign have identified over 120 SPT-SMGs. One key result from our survey comes from ALMA CO redshifts of a subsample of 28 SPT sources. These observations show that the mean redshift of SPT-SMGs is _z = 3.5, significantly larger than those of radio identified SMGs (z = 2.3, Chapman et al. 2005) and that the redshift distribution is almost flat between redshift z = 2-4 (see Fig. 2, Weiss_ et al. 2013). As such the SPT survey has uncovered the long missing high-redshift tail of the submm galaxy population which is due to our long selection wavelength of 1.4mm combined with unbiased CO redshift measurements. This demonstrates the uniqueness of our strongly lensed SMG sample to study key parameters of galaxy evolution out to the highest redshifts.

In this talk I will focus on how we obtain photometric redshifts of the sample using data from SPT, APEX, Herschel and ALMA.

 

M. Broockamp (3)

Erosion of Globular Cluster Systems by SMBHs

 

Chair:

Abstract:  Globular clusters (GCs) belong to the oldest fossils of galaxy formation. The spatial distribution of GCs might contain valuable information about the dynamics and properties of their host galaxies. To read out this information, the surviving fraction of globular clusters in arbitrary elliptical galaxies can now be investigated by means of a new software which was developed during the last 2 years. It can handle various physical effects like the influence of the generalized dynamical friction force, the degree of radial anisotropy of the initial GC distribution and the presence of central supermassive black holes as well as much beyond that. I will discuss first promising results and answer the question if the central core profiles of globular cluster systems can be explained by eroding GCs.

 

 

 

1-Jul-2013

 

Monthly Discussion

 

 

 

8-Jul-2013

 

H. Sagiha (2)

GALAXY-GALAXY-GALAXY LENSING

Chair: E. Angelakis

 Abstract:  Gravitational lensing has proven to be a significant and powerful technique to study the matter distribution in the Universe. Lensing effect induced by galaxies, galaxy-galaxy lensing, studies the statistical properties of matter environment of individual lens galaxies. In comparison to galaxy-galaxy lensing, the new technique of third-order galaxy-galaxy lensing (G3L) provides additional information on the galaxy-matter connection. More specifically, G3L gives insight into the average distribution of matter around galaxy pairs -- it is thus a probe for galaxy pairs rather than individual galaxies. Observationally, it has recently been shown that there is an excess in surface mass density around an average galaxy pair compared to the sum of surface mass around two individual galaxies. This excess mass depends on the separation of the galaxies and their type. I present my results for the theoretically expected excess mass for different galaxy populations in the Millennium Simulation.

 

 

 

 

15-Jul-2013

 

Franz Kirsten (2)

High precision astrometry of compact objects in M15

 Chair: H. Saghiha

 Abstract:  The globular cluster (GC) M15 is among the oldest and most massive globular clusters known to reside in the Milky Way. The strong peak in brightness distribution towards the central arc second accompanied with an increase in stellar velocity dispersion gave reason for speculations that M15 could be host to an intermediate mass black hole (IMBH). Eight millisecond pulsars (MSPs) have thus far been confirmed to belong to the GC, four of which are located within 4.5 arcsec of the cluster core. Within the same core region one low mass X-ray binary (LMXB) has also been detected in radio observations. In this project, we measure the proper motion of the brightest MSPs - one of them being a member of a double neutron star system, and of the LMXB AC211. Additionally, we try and detect new radio point sources in the cluster that could potentially be pulsars missed in previous observations. To these ends we observe the central region (~ 2 arcmin) of M15 in seven epochs spread over more than two years with a global VLBI array comprised of several EVN antennas, the Arecibo telescope and the GBT. In this talk I will present our proper motion results along with a discussion of the nature of thus far unclassified sources that are within our field of view. Additionally, I will discuss the indications of outflow activity in the case of the LMXB AC211 which reveals a double peaked structure in one of our observations.

 

 

Natasa Tsitali (3)

A spectral survey of the starless core population in the molecular clouds Chamaeleon I and III: core dynamics and kinematics

 Chair: H. Saghiha

 Abstract:  The molecular clouds Chamaeleon I and III contain a relatively large population of starless condensations (60 and 29, respectively) at nearby distances, thus providing us favourable candidates for pre-protostellar studies. They both belong to the same molecular cloud complex but Chamaeleon I is an active star forming cloud while there is no known sign of star formation in Chamaeleon III. Yet their populations of starless cores as detected in continuum emission with LABOCA have very similar properties. The difference in star-formation acivity is bewildering given their proximity. One of the main goals of the spectral survey is, therefore, to study the kinematics of these cores to understand this apparent contradiction and gain further insight into the cores' dynamical state and their future evolution. We thus hope to shed some light into the physical processes that have so far governed the early phase of star formation in Chamaeleon I and the processes that have hindered it taking place in Chamaeleon III.

 

 

 

22-Jul-2013

 

Denise Keller (1)

Chemical Modeling of Envelopes of Evolved Stars 

 Chair: A. Tsitali

 Abstract:  Circumstellar envelopes of AGB stars are crucial in the understanding of the evolution of low- and intermediate-mass stars. These stars have initial masses less than 8 solar masses and are the most common type of stars in the Universe. Mostly all intermediate-mass stars go through the AGB phase before they turn into white dwarfs. AGB stars are a unique site for a rich nucleosynthesis which is observable in their circumstellar envelopes. To deepen the understanding of the physics and chemistry of the circumstellar envelopes and their interaction with the interstellar medium we perform spectroscopy of the molecular emission and model the radiative transfer. I started to work with mm-data from the APEX telescope and the JVLA to explore the molecular emission of the carbon-star IRC+10216.

 

Cosmos Yeh (1)

Multiwavelength Analyses of Luminous Star Forming Regions in the Carina Arm

 Chair: A. Tsitali

 Abstract:  We present a progress report for our study of massive star forming regions in the carina arm. Sources detected from the extended APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey are selected for the follow-up CO line survey. The APEX line observation from both 13CO(2-1) and C18O(2-1) provides velocity measurements of them, enabling us to identify sources in the Carina Arm. We further compare sources in the Carina arm with multi-wavelength archives from WISE, Herschel, and ATLASGAL images. The connections between images and velocities can be used to extract fluxes of sources from multiwavelength observations, such that physical properties of star forming regions in the carina can be constrained.

 

 

 

29-Jul-2013

 

Philip Schmidt (2) + Jeff Hodgson (2 moved up)

 

 

 

5-Aug-2013

 

Monthly Discussion

 

 

 

12-Aug-2013

 

Katharina Immer (2) + Naftali Kimani (1) + Carolina Mora (2)

 

 

 

19-Aug-2013

 

Sandra Martin (2)

Testing the Halo Model

 Chair: Katharina Immer

Abstract:  A widely accepted model for structure formation in a LambdaCDM universe is the “Halo Model”. It assumes that the whole dark matter content of the Universe is bound to spherically symmetric halos which host its luminous tracers, the galaxies. It is a semi-analytic model, which combines results from simulations for the number density of dark matter halos with a certain halo mass, the dark matter halo profile and the clustering behaviour of dark matter, with theoretical results for the formation of dark matter halos and the halo occupation distribution of galaxies, which accounts for the clustering of galaxies. A wide range of physical information might be recovered by calculating the Galaxy-galaxy-galaxy lensing signal for the Halo Model and by fitting the theoretically predicted signal to the observations. This is the second part of my Ph.D. project in which I want to test the Halo Model, respectively the physical concepts the model is based on.  

 

 

 

26-Aug-2013

 

Jan Wagner (3)

Water Megamasers and Megamaser Cosmology -- The sub-parsec AGN Disk Masers in IC 2560

 Chair: Sandra Martin

Abstract:  Radio interferometric imaging of "nuclear water masers" is currently the only means of directly mapping structures <1 pc="" surrounding="" supermassive="" black="" holes="" certain="" active="" galaxies="" like="" ngc="" 4258="" contain="" disk="" masers="" in="" an="" edge-on="" accretion="" around="" a="" central="" massive="" 10="" 6="" to="" 8="" msun="" and="" highly="" compact="compact" object="" extensive="" past="" vlbi="" studies="" of="" 4285="" have="" constrained="" thickness="" magnetic="" fields="" determined="" precise="" distance="" density="" hole="" mass="" several="" maser="" are="" studied="" under="" the="" nrao="" key="" science="" megamaser="" cosmology="" project="" addition="" filling="" low-mass="" end="" m-sigma="" relation="" is="" instrumental="" it="" offers="" independent="" measurement="" hubble="" constant="" h0="" may="" also="" give="" insight="" into="" disagreement="" between="" derived="" from="" cmb="" anisotropies="" via="" cepheids="" sn="" ia="" this="" third="" part="" my="" phd="" which="" i="" searched="" for="" new="" water="" three="" will="" present="" results="" search="" one="" galaxy="" ic="" 2560="" --1--="">

 

 

 

2-Sep-2013

 

Monthly Discussion

 

 

 

9-Sep-2013

 

M. Vitale (3)

Galaxy evolution across optical emission-line diagnostic diagrams

 Chair: Jan Wagner

 Abstract:  Optical emission-line diagnostic diagrams have been proven as a useful tool to select AGN from large spectroscopic surveys like the SDSS. A cross-correlation of the SDSS with the FIRST radio survey at 20cm allows us to study radio-emitters with observed optical counterparts. The triggering of radio AGN activity has been found to be a strong function of host galaxy properties and it is possibly linked to different stages of massive galaxy formation. Our work aims to a better understanding of the interplay between optical and radio emission. In particular, we make use of Effelsberg 2.8 and 6cm data to calculate spectral indexes and polarization degrees of the brightest sources of FIRST (~150 galaxies). We study the differences between star-forming galaxies, composite galaxies, Seyferts and LINERs, looking for a galaxy evolutionary sequence across the optical emission-line diagnostic diagrams.

 

 

 

16-Sep-2013

 

 

 

 

23-Sep-2013

 

M. Tomassetti (3)

Molecular Hydrogen Formation in high redshift galaxies

 Chair: E. Angelakis

 Abstract:  The main goal of this project is to implement an improved treatment of  the cold interstellar medium for high-redshift galaxies. We perform ``zoom-in'' cosmological simulations of a Milky-Way-sized galaxy at $z=2$ (physical resolution of $\sim$130 pc) with the RAMSES code and use it to study the impact of molecular-hydrogen-based star formation laws on basic galaxy properties. In order to compute H$_2$ abundances we assume a chemical-equilibrium model as well as propose a novel sub-grid treatment of H$_2$ formation on dust grains and destruction by the interstellar UV field, based on the assumption of a lognormal sub-grid density distribution in each cell. Our findings show that the main properties of the $z=2$ galaxy are not particular influenced by the type of star formation prescription used. However, most of the low-mass halos simulated with the molecular-regulate prescription show a significant delay in the star formation rate and an increase cold gas mass at $z=2$.

 

Ioannis Miserlis (2)

Blazar physics through multi-band linear and circular polarization monitoring

 Chair: E. Angelakis

Abstract:  Blazars comprise the class of Active Galactic Nuclei (AGN) that emit a remarkably broad Spectral Energy Distribution (SED) from long cm wavelengths to GeV and TeV energies. They  exhibit rapid flux density variations, practically over the entire electromagnetic spectrum, high superluminal motions and significant optical polarization. The observed emission is attributed to incoherent synchrotron radiation from the magnetized plasma that forms a relativistic jet, powered by an accreting supermassive black hole (SMBH) and directed at small angles to the line-of-sight. Multi-band linear and circular polarimetry is an invaluable tool in the investigation of the wealth of their physical properties, such as the topology and magnitude of their magnetic fields, the composition of their jets and structural characteristics of their galactic environments. High cadence monitoring programs furthermore, allow the exploration of the dynamics of such parameters on the one hand, while they provide a unique probe of the models developed to explain the variability-producing mechanisms and the spectral evolution of outbursts.

The F-GAMMA monitoring program by utilizing the Effelsberg 100m, the IRAM 30m and the APEX 12m telescopes, provides monthly sampled light curves for some 60 selected Fermi blazars at 12 radio frequencies ranging from 2.6 GHz to 345 GHz since 2007. The dataset includes polarization information for at least 5 of the observed frequencies which are currently being extracted and analyzed. In parallel, the F-GAMMA team has co-initiated the construction of an optical polarimeter, which is mounted on the 1.3m Skinakas telescope (University of Crete) aiming at measuring and parametrizing the optical polarization behaviour of AGNs especially during gamma-ray outbursts (RoboPol monitoring program). The RoboPol program is designed to observe a large number of γ-ray bright blazars (~100) at high cadence and in a dynamic manner by increasing the sampling rate while the sources show rapid polarization variability.

I will start the talk with a general discussion of the great potential that high cadence polarization monitoring holds for probing the physical conditions of blazars. Subsequently, a  description of the F-GAMMA and RoboPol monitoring programs will follow, including: (a) the sample selection, (b) the system description and (c) important observational facts. Then, the focus will be put on the radio polarization measurements and the method followed for the necessary determination and correction of the instrumental polarization. Such measurements can be very challenging, especially for circular polarization, since most AGN exhibit low levels of radio polarization (~5% linear and <1% circular) due to incoherent emission, beam depolarization and so on. Nevertheless, preliminary analysis of the radio monitoring data has revealed sources which show significant Stokes V measurements persistently (3C84, 3C454.3). These findings are very promising because circular polarization measurements can give us a direct insight into the magnetic field ordering, the composition and other features of the jet. Finally, some first results from the radio and optical polarimetric data analysis in progress will be discussed. Such results can also be combined to investigate the correlation between the two regions of the jet which are probed by optical and radio emission.

 

 

 

30-Sep-2013

 

Semir Smajic (2)

LINC-NIRVANA and The NuGa Project

 Chair: I. Myserlis

Abstract:  LINC-NIRVANA is the LBT INterferometric Camera and Near-InfraRed/Visible Adaptive iNterferometer for Astronomy. The instrument is being built for the Large Binocular Telescope (LBT) in Arizona. The LBT has two light collecting mirrors (binocular) and both are situated in the same plane which enables Fizeau interferometry that is used by LINC-NIRVANA. I will show you the contribution of the I. Physical Institute of the University of Cologne for this instrument, the Fringe and Flexure Tracking System (FFTS). The NuGa project concentrates on local universe active galaxies and investigates the gas motion in these galaxies. The goal is to find how gas can be made (angular momentum problem) to fall from outer parts of the galaxy towards the nucleus and on smaller scales from the nuclear region towards the active nucleus. The investigations were mainly done using the Plateau de Bure telescope and IRAM to look at the cold gas distribution. With the implementation of ALMA the NuGa sample is being expanded to the southern hemisphere where we can use the capabilities of the VLT instruments like SINFONI to further investigate the NuGa galaxies in the NIR and at similar resolution as ALMA. I will show you a few problems I had with our SINFONI data (OH sky lines and detector issues) and some freshly brewed line maps.

 

 

 

7-Oct-2013

 

Monthly Discussion

 

 

 

14-Oct-2013

 

Vassilis Karamanavis (2)

Broadband emission and structure dynamics of PKS 1502+106 during a prominent γ-ray flare

 Chair: Semir Smajic

Abstract:  Blazars are the most variable and most broad-band emitters of radiation in the Universe. The processes that give rise to those characteristics, though, remain still unclear. In this talk an introduction to the blazar phenomenon will be given. The tools used in their study will also be introduced, namely broad-band variability studies and the F-GAMMA program, but also the Very Long Baseline Interferometry technique will be discussed. Then I will give an account of the scope of my thesis which is the application of both techniques to PKS1502+106, a prominent Fermi detected gamma-ray blazar. The final part of this talk will be focused on Narrow line Seyfert 1 galaxies, my VLBI imaging attempts and their applications to the study of this new type of gamma-ray emitting AGN.

 

 

 

21-Oct-2013

 

 Tobias Roehser (1)

The dynamical transition from atomic to molecular intermediate-velocity clouds

 Chair: Vassilis Karamanavis

Abstract:  Towards the high galactic latitude sky the far-infrared (FIR) intensity is tightly correlated to the HI 21-cm line emission. Intermediate-velocity clouds (IVCs) contain a large reservoir of neutral gas that may be important in the star formation history of our Galaxy. How IVCs evolve during their infall is essential as to how they are accreted onto the galactic disk. We analyse gas and dust properties of IVCs in the lower galactic halo to explore their transition from the atomic to the molecular phase.  Data of the Effelsberg-Bonn HI-Survey and the Westerbork-Synthesis Radio Telescope is correlated and compared to FIR wavebands of the Planck satellite. Two IVCs show different FIR properties despite their similarity in singledish-HI such as narrow spectral lines and large column densities: A FIR bright IVC is associated with H_2 while the other IVC is FIR dim indicating the absence of molecular hydrogen. The molecular IVC shows much more substructure in its HI distribution than the FIR dim IVC. We propose that these two IVCs probe the transition between the atomic and molecular gas phase. The most natural driver is ram pressure exerted onto the cloud by the increasing halo density. Small and dense condensations are formed in which the formation time-scale of H_2 is reduced by the increased pressure.

 

 

 

28-Oct-2013

 

Miriam Ramos Ceja (2)

Detection of high-z galaxy groups with Athena+

 Chair: Tobias Roehser

 Abstract:  The Advanced Telescope for High-energy Astrophysics (Athena+) is being proposed to ESA as the L2 mission (for a launch in 2028) and is specifically designed to answer two of the most pressing questions for astrophysics in the forthcoming decade: How did ordinary matter assemble into the large scale structures we see today? and how do black holes grow and shape the Universe? For addressing these two issues, Athena+ will provide transformational capabilities in terms of angular resolution, effective area, spectral resolution, grasp, etc. In this talk, I will focus on the detection of high-z galaxy groups with Athena+. 

 

Alberto Doria (2)

The 400d Survey Cosmological Sample: IMACS@Magellan data reduction

 Chair: Tobias Roehser

Abstract:  One of the major challenges of today's astrophysics and cosmology is to constrain Dark Energy. The study of galaxy clusters evolution, in particular of the behavior of number density of massive clusters with redshift, allows us to constrain cosmological parameters. For this purpose, the comparison of independent approaches, such as X-ray and gravitational lensing analysis, yields the most accurate results in tracing the cosmic evolution. We are working on the mass estimation of the weak lensing follow-up of a complete sample of high-redshift (0.35<z<0.89) clusters in order to obtain more precise mass models, correcting for possible biases on the X-ray measurements. After having obtained the shear catalogs for the six clusters observed with the WFI@MPG/ESO camera, also the optical data reduction of four more clusters observed with the IMACS@Magellan camera is complete. I will show how the many issues due to the instrument characteristics were faced and solved during the data reduction process, leading to an improvement and expansion of the THELI pipeline.

 

 

 

4-Nov-2013

 

Monthly Discussion

 

 

 

11-Nov-2013

 

Pablo Torne (2)

Looking for pulsars with new receivers

 Chair: Alberto Doria / Miriam Ramos Ceja

Abstract:  The modern technologies for radio astronomical applications are opening new ways of observing the sky and are enabling new, very exciting science. The Max-Planck-Institute for Radio Astronomy has always been at the forefront of technological developments for their use in radio telescopes, and currently efforts on several new promising instruments are taking place here in Bonn. Two of those projects are the Ultra-Broad-Band receiver and the Phased Array Feed, both instruments covering low frequency ranges and mainly driven by the pulsar science. In this talk, I will give an overview about pulsar science and present the key points faced when searching for new pulsars. I will then present these two innovative receivers, their new capabilities and main challenges, and comment about the future of pulsar astronomy.

 

 

 

18-Nov-2013

 

Sebastian Kielhmann (2)

Probing the magnetic field of 3C279

 Chair: Pablo Torne

Abstract:  Magnetic fields play a major role in the launching, acceleration, collimation, and radiation properties of extragalactic jets. The only direct way to observationally access magnetic fields in jets is to measure their polarization imprint on the emitted synchrotron radiation. 3C 279 exhibits strong variation of the optical electric vector position angle (EVPA), showing continuous EVPA rotations larger than 360 degrees in both clockwise and counterclockwise directions. I will present a method to discriminate between stochastic and deterministic EVPA variation processes and a model that explains two-directional EVPA swings as observed in 3C 279.

 

 

 

25-Nov-2013

 

Nadeen Sabha (2)

Mid-infrared observations of the Galactic Center

 Chair: Sebastian Kielhmann

 Abstract:  I will present our mid-infrared data of the Galactic Center obtained with VLT VISIR and discuss our  ecent finding of a convex-like feature at a distance of ~0.68 pc from the center where the supermassive black hole, Sgr A*, lies. This feature resembles a stellar bowshock with a symmetry axis pointing to the center, and it is aligned with other sources that are believed to be caused by the interaction with a wind originating from the center of the cluster.

 

 

 

2-Dec-2013

 

Monthly Discussion

 

 

 

9-Dec-2013

 

Sutirtha Sengupta (2)

BONNFIRES framework for modelling CEMP stars

 Chair: E. Angelakis

Abstract:  I will describe our progress towards devolping the population synthesis code BONNFIRES for modelling the chemically peculiar class of carbon enhanced metal poor (CEMP) stars that constitute a significant fraction (upto ~20%) of the oldest stars in our Galaxy. My current work focusses on the AGB binary mass-transfer scenario proposed to explain both carbon and heavy element (e.g. s-process) enhancements observed in majority of these CEMP stars. Our interpolated grids of low-mass stellar models, at metallicity of Z=0.0001 evolved upto the first giant-branch, include both mixing (convective/non-convective) and nuclear processing of the accreted carbon-rich material and can thus predict the surface composition of AGB-polluted CEMP stars with varying levels of carbon enhancemnt depending on their evolutionary status (sub-giant/giant) and amount of accreted material. Such predictions should be testable in the near future with data from the GAIA mission and can improve our understanding of nucleosynthesis of the very generation of stars that shaped the chemical history of our Galaxy. 

 

 

 

16-Dec-2013

 

Jana Koehler (3)

Study of large-scale galactic magnetic fields at low frequencies

 Chair: S. Sengupta

Abstract:  The main aim of this project is to map out the large-scale total and polarized intensity of the entire northern sky, concentrating on the Faraday spectrum of the polarized emission. In this way the polarization properties of the Milky Way can be studied, as well as special targets like CasA, CygA and TauA. The use of RM synthesis will help to study the structures and turbulent regions in the Milky Way ISM. With the use of LOFAR it is now possible to study polarization below 250 MHz, which gives the oppertunity to study the weak magnetic fields in the Galactic halo and outer disc, about which little has been measured to date. In this talk I will give an short overview about what we already know about large-scale structures in total and polarized intensity, talk about the polarization calibration of LOFAR Single Station data and I will show some first results from my observations and data reduction.

 

 

 

23-Dec-2013

 

 
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