Monday Seminar for the year 2017

    The presentations are shown in order of increasing time.









    Monthly Discussion Room 002



    Natalya Porayko (2)

    chair: Ann Kathrin Baczko

    Measuring RM variations with LOFAR: ISM vs ionosphere

    Magnetic fields play a crucial role in the magneto-hydrodynamic (MHD) heating of the interstellar medium (ISM) and the density fragmentation of cold molecular clouds, thus regulating the process of star formation. They are also known to be important in particle ray acceleration, which can provide the pressure to drive galactic outflows. However, many important characteristics of the magnetic fields, such as their origin and evolution, strength and structure, and their influence on Galactic dynamics remain unknown. Using the data from highly polarized pulsars observed with German LOFAR stations, we will investigate long-term Rotation Measure (RM) variations. Our goal is to update our knowledge about the small-scale turbulent structure of the magnetic fields and the electron density in the ISM of our Galaxy. These variations arise as the pulsar moves along the tangent plane and, thus, the pulsar beam intersects different parts of the ISM. Besides being sensitive to the ISM effects due to LOFAR low-frequency range, our data are also susceptible to ionospheric effects that are undesirable for our investigation. Using long pulsars' observations we can carefully investigate accuracy of the GPS ionospheric maps and independently estimate parameters of the noise, generated by imperfect ionospheric modeling. After careful subtraction of ionospheric contribution the residual RM data is expected to show the presence of red noise, whose parameters will depend on the regime of ISM turbulence.



     Won Ju Kim (3)

    chair: N. Porayko

    Millimeter hydrogen radio recombination lines from HII regions in molecular clumps

    I would like to mainly present millimeter hydrogen radio recombination line surveys with IRAM and Mopra telescopes,
    and then shortly to show preliminary results from submillimeter hydrogen RRL surveys with APEX telescope.

    We carried out millimeter radio recombination lines (mm-RRLs, 39 ≤ n ≤ 65 and ∆n = 1, 2, 3, and 4) surveys using the IRAM 30m and MOPRA 22m telescopes toward 976 compact dust clumps of the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey.
    The (sub)millimeter RRLs can be used to derive physical propoerties of HII regions and to provide velocity information of ionized gas.
    Therefore, these mm-RRLs surveys aim at searching for embedded HII regions in the dust clumps and studying the characteristics of the HII regions. The targeted dust clumps were an unbiased sample without any specific criteria and half of the sample were also selected to be mid infrared dark to cover very young clumps.
    We detected mm-RRLs toward 178 HII regions; 178 Hnα, 65 Hnβ, 23 Hnγ, and 22 Hnδ mm-RRLs were detected. It is the largest sample of mm-RRLs to date. All sources were searched subsequently for radio continuum source and mid infrared source counterparts. There are eight clumps having potential HII regions based on only mm-RRL detections. Nine clumps have broad RRL features (FWHM > 40 km/s). Such broad recombination line objects (BRLOs) imply the existence of significant turbulent motions. Except for detecting the BRLOs, we also found an evidence that the dynamics of the mm-RRLs are related to turbulent motions in the parental molecular clouds to compare to their H13CO+(1-0) FWHM linewidths with detection (a mean linewidth of 4.18 km/s) and non-detection (a mean linewidth of 3.08 km/s) of mm-RRLs.
    We present a significant correlation (correlation coefficient, 0.72 and slope, 0.86) between integrated fluxes of mm-RRL and 6 cm continuum
    emission. The good correlation shows that the mm-RRLs trace the radio continuum sources detected by high-resolution observations. By calculating the electron densities we find the mm-RRL emission is associated with HII regions with electron density < 10^5 cm^-3 and HII region diameter > 0.03 pc.






    Monthly Discussion



     Henning Hilmarsson (1) & Vivien Thiel (2)



     Andrew Cameron (3)

    chair: V. Thiel

    The Most Relativistic Binary Pulsar, and other news from the HTRU-S LowLat Pulsar Survey

    Pulsars, rapidly-rotating highly-magnetised neutron stars, can serve as fantastic natural laboratories for testing theories of gravity when discovered as part of binary systems. The most prominent example of such a binary has been the Double Pulsar, PSR J0737-3039A/B, which has been used to test General Relativity to within uncertainties of just 0.05%. The HTRU-South Low Latitude pulsar survey represents the most sensitive blind pulsar survey taken of the southern Galactic plane to date, and has resulted in the discovery of 104 additional pulsars thus far. With long integration times and a custom acceleration search pipeline, one of the primary aims of this survey has been to discover new relativistic binary pulsars which may be able to produce even stronger tests of gravity theories. Here I will present our binary pulsar searching strategy and report on the discovery highlight of the survey, a new relativistic binary pulsar. With a short orbital period of 4.4 hours and an eccentricity of 0.606, this double neutron star system represents the most relativistic binary pulsar discovered in our Galaxy to date, and has potential to exceed the tests set down and by the Double Pulsar and place new limits on gravitational theories such as General Relativity.









    Monthly Discussion



     Marilyn Cruces (1)

    Chair: A. Cameron

    HTRU-North data reprocessing

    Pulsars are strongly magnetized neutron stars detected mainly through the pulses of electromagnetic emission emitted from their poles, and modulated by the stable rotation of the object. They have become a fascinating research area, since their discovery in 1967, as they are fundamental tools for understanding stellar evolution, the behavior of matter at extreme conditions, to test theories of gravity, among others. The more pulsars we find, the more we can understand and advance  in these areas. During the talk I will discuss about the “High Time Resolution Survey (HTRU)-North” being held by MPIfR with the use of the “100m-Effelsberg Telescope”, the reprocessing of the  624 TB of data collected since the beginning of the survey in 2010 and future prospects.

    Weiwei Chen (1)

    chair: M. Cruces

    Beamforming with MeerKAT

    Since the discovery of the First Radio Bursts(FRBs), it has been a research focus in the recent decade. This kind of radio transient has a much larger dispersion measurement than other transient sources, indicating a potentially extragalactic source. FRBs could act as a probe for intergalactic medium and a tool for studying universe in cosmic scale. Currently only a dozen of FRBs are discovered and published, multiple follow up observations have been carried out. However, hindered by the indistinctness location and distant of the sources, it’s difficult to perform an explicit search. A better searching and observation strategy is imminent. In this PHd research project, an implement of beamforming with MeerKAT is introduced which will obtain a large field of view, create hundreds of synthesized beams and with the equipped transient buffer make it very suitable for searching and localizing transient sources such as FRBs. To meet the demand of computing power, parallel technology such as GPU computing is used in the beamforming process.



     Michal Zajacek (3)

    chair: Weiwei Chen

    Nature of the Galactic centre NIR-excess sources

    The Dusty S-cluster Object (DSO/G2) orbiting the supermassive black hole (Sgr A*) in the Galactic centre has been monitored in both near-infrared continuum and line emission. There has been a continued discussion about the character of the object: interpreting it as either a core-less gas cloud or a dust-enshrouded star. A recent analysis of polarimetry data in K_s-band (2.2 μm) by Shahzamanian et al. (2016) allows us to put further constraints on the geometry of the DSO (Zajacek et al. 2017, A&A, submitted). In addition, several other well-localized reddened sources are present in the central arcsecond from Sgr A*. The nature and the possible relation of these sources has not been determined yet. It is clear, however, that these "red" sources are peculiar in comparison with the prevailing population of main-sequence B-type stars (so-called S stars) in the central S-cluster. I will present our recent results of the radiative transfer modelling, including NIR polarized continuum, and discuss possible models of the DSO/G2 and other sources in the context of Galactic centre stellar populations.

    Kevin Harrington (1)

    chair: M. Zajacek

    Observing the Interstellar Medium of IR Luminous SF Galaxies at z >1

    With the recent all-sky Planck survey at sub-mm wavelengths we have been able to identify the brightest sources observed to date, with log(LIR) > 13-14 L_sun. The high apparent luminosities are believed to be a result of strong lensing effects that amplify the light from the galactic systems we are interested in, particularly at the epoch of galaxy assembly: 1 < z < 4. This allows for more efficient spectroscopic studies, and insights into the fainter population of SF galaxies that are more challenging to study in detail without the aid of lensing. I will present initial work done thus far on studying the galaxy integrated molecular gas measurements using the LMT/GBT/IRAM 30m. I will then present my ideas for a roadmap forward in studying the various phases of the ISM in these galaxies at high-z.



     Michael Mattern (3)

    chair: K. Harrington

    Filaments in the early phases of star formation

    Current studies show that filamentary structures in the ISM play an important role in the process of star formation. However, our knowledge is mainly based on nearby star-forming regions and a few more distant structures. I will present the first systematic analysis of massive filaments across the Galaxy and some of the first results.
    In the full ATLASGAL survey, Li et al. (2016) identified 517 filaments employing the DisPerSE algorithm. This defines an unbiased and representative catalog of dense, filamentary, molecular clouds. The SEDIGISM survey (Structure, Excitation, and Dynamics of the Inner Galactic Inter Stellar Medium, Schuller et al. 2017) conducted with APEX covers 78 deg^2 of the southern Galactic Plane: −60 ° ≤ l ≤ 18 ° , with |b| ≤ 0.5 ° , at 30” resolution. This allows us to follow up about 280 of these filaments, trace their larger, diffuse structure, analyze their kinematics and connect them to the larger scale Galactic structure.

    Mélisse Bonfond (2)

    chair: M. Mattern

    Exploring molecular complexity with ALMA: Characterizing the hot core population in Sgr B2(N)

    The Sagittarius B2 molecular cloud is one of the most prominent regions forming high-mass stars in our Galaxy. It is located in the Central Molecular Zone, close to the Galactic center. The cloud contains two major centers of activity called Sgr B2(M) and Sgr B2(N). They both host a cluster of (ultra)compact HII regions and class II methanol masers, both phenomena providing strong evidence of on-going high-mass star formation. In addition the high density of molecular lines and the continuum emission detected toward this region highlight the presence of a large amount of material to form new stars. The target of my PhD project is Sgr B2(N), which contains two already known hot molecular cores, called Sgr B2(N1) and Sgr B2(N2). They are both in the early stage of the star formation process when complex organic molecules (COMs) are detected in the gas phase. Many of the first detections of interstellar molecules at radio and (sub)millimeter wavelengths were made toward Sgr B2. Sgr B2(N) thus appears to be one of the best targets for searching and studying COMs and also to investigate the high mass star formation process. In my talk I will present the discovery of 3 new hot cores in Sgr B2(N), made possible thanks to the high sensitivity of the EMoCA survey conducted with ALMA. Through the investigation of the chemical composition of these hot cores, I will show how to derive their physical properties. I will also discuss their evolutionary stages, comparing their chemical abundances to the predictions of chemical models and taking into account their associations with ultracompact HII regions and class II methanol masers.






    Monthly Discussion






    Easter Monday



     Anna Mikler (3)

    chair: M. Bonfand

    The Pressure Profile Shape and the Dynamical States of Galaxy Clusters

    Galaxy cluster properties are generally characterized using universal templates without keeping into consideration the dynamical states of the individual systems. This assumption leads to systematic errors that limits the accuracy for precision cosmology when using galaxy cluster counts from large surveys. In our work, we combine high-resolution Sunyaev-Zel'dovich (SZ) effect data from the APEX-SZ experiment, together with low-resolution data from Planck, to get a precise understanding of the shape of the intra-cluster gas pressure and its relationship with the cluster's dynamical state. The goal is to improve the current working templates for the cluster SZ signal extraction and modeling for precision cosmology.

    Chaoli Zhang (1)

    chair: A. Mikler

    Galaxy clusters at high redshift (z>2) as seen by ATHENA

    ATHENA (Advanced Telescope for High Energy Astrophysics) is the next generation of X-ray observatories, it will address some fundamental questions in modern astrophysics and cosmology including the formation and evolution of the largest gravitationally bound object: galaxy groups and clusters. ATHENA will help to answer the questions of how and when the first galaxy groups in the Universe, massive enough to bind more than 10^7 K gas, formed. For the first year of PhD project, we investigate on the capabilities of detecting the early galaxy groups (290% at all redshifts and all off-axis angles.






    May Holiday



    Monthly Discussion



    Jackie Ma (2) & Yuxin Lin (1)



     Efthalia Traianou (1)

    chair: Yuxin Lin

    Tracing the fundamental jet properties in the gamma-ray active blazars

    Blazars, a subclass of jetted AGN, show extreme flux variability across all electromagnetic wavelengths from radio to gamma-ray. In particular, their extremely rapid flares (< months) at GeV regime are hard to understand because of (i) the associated ultra-compact emission region size (< sub-pc) and (ii) bizarre high-energy radiation mechanism. The prime objective of the PhD thesis project is therefore to identify such gamma-ray emitting regions and constrain their physical conditions by multi-epoch high resolution VLBI imaging. In this talk, I will present a case study of the gamma-ray flaring events which occurred in the compact blazar 2013+370 during 2002-2012. Preliminary analysis of gamma-ray light curves sampled by the Fermi space satellite and multi-epoch VLBI imaging from 15 to 86 GHz reveal the following: (a) the flaring events are clearly correlated with the VLBI-scale jet structure and (b) the VLBI core radio flux as well. Tentative interpretation of our results will be presented.

    Madhuri Gaikwad (1)

    chair. E. Traianou

    Precision Timing of Pulsars using EPTA and LEAP

    Pulsars are rapidly rotating neutron stars with very strong magnetic fields. They are very stable clocks in space which have many applications to problems in physics and astrophysics. Pulsars can be used to study the inter-stellar medium, galactic structures and test the effects of gravity. We have begun an exciting era for gravitational wave (GW) detection, where Pulsar timing arrays (PTAs) have emerged as possible tool to detect GW. I will discuss the observations from the Large European Array for Pulsars which will allow us to detect or limit errors in the Solar System ephemerides used in pulsar timing analysis. I will briefly describe techniques being employed to possibly detect GW.



     Jae-Young Kim (2)

    chair: M. Gaikwad

    Imaging the Nuclear Region of Radio Galaxies M87 and 3C 84 by Global-VLBI Observations at 86 GHz

    Understanding how mass accretion and jet formation occurs near the central engine of AGN has been one of major challenges in modern astrophyiscs. The apparent size of the jet forming region is desperately small even for an extraordinary massive BH system (10Rs=0.001pc for a BH mass of 10^9Msun), making a direct comparison of theories and observations difficult. Therefore, it is indispensable to image the vicinity of the SMBH and the accretion disk with ultra-high resolution VLBI technique. In this talk, I will present an observational study of the innermost region (7 - 100s of Rs) of nearby radio galaxies M87 and 3C 84 within the context of ongoing PhD thesis project. The data obtained by global VLBI observations at 86 GHz, with high-sensitivity stations such as the 100m GBT and the IRAM 30m being included, reveal several new features which were not seen by previous VLBI at lower-resolution and/or lower-frequency. Analysis and interpretation of the total intensity and linear polarization structures will be mainly presented.









    Monthly Discussion



     Basilio Solis (1)

    Chair J.-Y. Kim

    Exploring the ISM properties in nearby galaxies: PAHs and CO

    I used a sample of 33 galaxies from the SINGS (Spitzer IR), KINGFISH (Herschel IR) and HERACLES (IRAM CO) surveys to study the relations between infrared and millimeter bands within the galaxies. I analyzed the specific intensity of the polycyclic aromatic hydrocarbons (PAHs), traced by the stellar continuum-subtracted emission at 8 μm, and molecular gas, traced by carbon monoxide (CO), as a function of different wavelengths ranging from 3.6 to 500 μm.  We found that PAHs (8 μm) are highly correlated with star formation (24 μm) and cold dust (250 μm), which confirms previous studies of some individual galaxies. Additionally we found there are galaxies that present bimodalities in their correlations that can be observed at the 3.6 and 24 μm bands. These bimodal effects show us how strong interstellar radiation fields (ISRF) can affect the life cycle of PAHs and their production/destruction processes.
    In the case of CO, we found a strong correlation with PAHs indicating the close relationship between molecular gas and dust in the ISM. This correlation is even stronger for SA-type and higher SFR galaxies. The molecular gas correlates with others star formation tracers as well. The bimodality detected for PAHs can also be observed on the CO emission, which confirms their close relation.









    Monthly Discussion



     V. Yankelevich (2)

    chair: Basilio Solis

    Cosmology with the Euclid galaxy bispectrum

    The last decades witnessed huge progress in understanding the large-scale structure of the Universe. While homogeneous and isotropic on the largest scales, the matter and galaxy distributions display complex patterns on smaller scales where we observe elongated filaments, compact clusters and volume-filling underdense regions.  These features are not captured by studies of two-point statistics like the power spectrum that does not retain information on the phases of the Fourier modes of the density field. Therefore, higher-order statistics like the bispectrum should provide additional information. The Euclid galaxy redshift survey will cover a large enough volume to provide robust measurements of the galaxy bispectrum as a function of redshift. The potential of these measurements as a mean to extract additional cosmological information has never been investigated properly. In this talk we present detailed forecasts for the Euclid mission. Our study
    shows that there is a clear advantage in combining the power spectrum and the bispectrum to infer the galaxy bias parameters and constrain the dark-energy equation of state.






     Enrico Garaldi

    chair: Victoria Yankelevich

    Dissecting assembly bias using the ZOMG simulations

    The clustering properties of dark matter haloes are influenced by their formation history, in what is known as assembly bias. I investigated its origin and effects on the baryonic content of haloes using a dedicated suite of high-resolution simulations named ZOMG –Zooming On a Mob of Galaxies. I will show how the environment of a halo
    determines its assembly history, and how the latter affects the properties of the central galaxy and its satellites. Finally, I will present an way to link observed properties to the dark matter assembly history.



     Jens Erler (3)

    chair: V.Yankelevich

    Observations of the Sunyaev-Zel'dovich effect spectral shape with Planck

    The Sunyaev-Zel’dovich (SZ) Effect is a spectral distortion of the cosmic microwave background (CMB) caused by inverse Compton scattering of CMB photons by free electrons in a hot plasma such as the intracluster medium (ICM) found in clusters of galaxies. Its signal is proportional to the line of sight integral of the thermal gas pressure and not dimmed with redshift. Due to the high temperatures of several keV found in the ICM, relativistic effects are expected to distort the SZE spectrum, which allows to measure the temperature of the scattering gas. These relativistic corrections are well known in theory, but have only recently been observed. In my talk, I will present a stacking analysis of a large sample of galaxy clusters with data from the Planck mission. With its nine frequency channels, Planck allows to probe the entire spectrum of the SZE, making it an ideal instrument for its study. Furthermore, I will provide an outlook on future studies of the SZE with the recently granted CCAT-prime telescope.






    Monthly Discussion



      No seminar



    Fateme Kamali (3)

    Radio Continuum of Galaxies with Water Megamaser Disk

    Galaxies with H2O megamaser disks are active galaxies in whose edge-on accretion disks 22 GHz H2O maser emission has been detected. They are a unique sample of targets to study accretion disk-jet paradigm since their circumnuclear disk is viewed edge-on and their rotation axis is oriented parallel to the plane of the sky. We have studied the radio continuum of 24 such galaxies with the VLA at 33 GHz and 200 - 500 mas resolution, and with VLBA at 5 GHz and 2 mas resolution. The aim of our studies was to investigate the nuclear environment of these galaxies and to relate the maser and host galaxy properties to those of its radio continuum emission.
    In my talk I will present the radio continuum maps of our sample and I will discuss the radio morphologies and other properties of these galaxies. Furthermore I will present recent high resolution maps of a few detected sources in our VLBA observations.

    Joey Martinez (3)

    Pulsar Searching and TIming with Arecibo and Effelsberg Radio Telescopes

    Pulsars have been used to study our galaxy, uncovering secrets that have helped scientists investigate theories of gravity, the interstellar medium, neutron star population, and binary system dynamics. Even after discovering over ∼2300 radio pulsars, many large scale surveys are still on the hunt for these exotic stars to help us further understand the laws that govern our universe. In this talk I will present my discoveries, two double neutron star systems: J0453+1559, J1411+2551 and 4 Millisecond pulsars.



     Sac Medina (2)

    Feedback of HII regions in their parental turbulent molecular clouds

    Turbulence plays a major role in the lifetime of Molecular Clouds (Formation, Fragmentation, Collapse) and its characterization is high important. I will show some results about the turbulence characterization in molecular clouds of 13CO emission from the SEDIGISM survey using the Velocity Channel Analysis technique (VCA). Also, the strategy to relate HII regions from GLOSTAR survey with the 13CO emission from Galactic Ring survey using other statistical tools.







     Monthly Discussion



     Maja Kierdof (3)

    chair: Sac Medina

    Probing the Magnetized Medium of AGNs and Galaxies using Wideband

    Wideband radio polarimetry is a powerful tool to reveal magnetic fields on different scales in different environments: in galaxies and in Active Galactic Nuclei (AGNs). I observed polarized emission from unresolved point sources, selected from the NVSS catalog which seems to have very high fractional polarizations (> 30%). Except for the high degree of polarization, those sources appear to have normal AGN properties. Therefore, they could represent a class of sources with very well ordered magnetic fields. Forthis, I am conducting a deep, high resolution, broad band polarization survey of 77 of those sources to make one more step towards
    understanding the origin of the unusual high degree of polarization. Another perfect laboratory for studying  well ordered magnetic fields provide the grand design spiral galaxy M51. To complete the study at
    several frequency ranges I observed this galaxy with the VLA at 2-4 GHz where currently no polarization data of M51 exists. Data in this frequency range allow us to probe the disk-halo interaction region that
    has never been done so far to see how the magnetic field structure behave in the layer between disk and halo of M51.

    Eric Faustino (2)

    chair. Maja Kierdorf

    Radio continuum size evolution of star-forming galaxies in the COSMOS field

    In order to better constrain the physical mechanisms which drive star formation at high redshift, we are studying the evolution of the star-forming size of a large mass- complete sample of Main Sequence (MS) and starburst galaxies (0 < z < 2.25) for the first time. We benefit from the JVLA-COSMOS map at 3GHz (2sq degs, 0.75 arcsec resolution, rms=2.3μJy/beam) to estimate the star formation rate (SFR) and intrinsic size of 3463 star-forming galaxies (SFGs) in the COSMOS field. We find that the overall star-forming component of typical SFGs on the MS is more extended (median Reff ~2 kpc) than in starburst galaxies (median Reff ~1–2 kpc). This size dichotomy suggests that the star formation is driven by different mechanisms in MS and starburst galaxies, where mergers may play a major role in producing a compact star-forming region. Finally, at all redshift, we found that the stellar component of the massive SFGs studied here (Reff ~5–10 kpc) is more extended than their global star-forming region.



     M. Tiwari (2)

    chair: Eric Faustino

    Unveiling the remarkable Photodissociation region of M8

    Photodissociation regions (PDRs) are predominantly neutral regions of the interstellar medium (ISM) in which the heating and chemistry are regulated by far UV photons emitted by near by stars. The region closest to the star is radiated with UV photons which are energetic enough to ionize the hydrogen present hence the name HII (ionized hydrogen) region while the cooler molecular clouds are shielded from the strong radiation. PDRs are at the interface between the molecular cloud and the HII region where the presence of far-UV photons, which are not energetic enough to ionize hydrogen and create HII regions, but which can dissociate most molecules and can ionize carbon. The study of PDRs is basically the study of the effects of stellar far-UV (6 eV < hυ <13.6 ev="" photons="" on="" the="" structure="" chemistry="" thermal="" balance="" and="" evolution="" of="" ism="" galaxies="" br="">
    We are carrying out a comprehensive survey in millimeter-and submillimeter regime of Messier 8 which is an emission nebula in our galaxy, with APEX, IRAM 30m and SOFIA telescopes. M8 is heated by the nearby hot star Herschel 36 and has one of the brightest PDRs in our galaxy. In this talk, I will introduce my research and will present the results obtained from APEX, SOFIA and IRAM 30m telescopes' observations and the outlook of this research.

    Joseph Kuruvilla (2)

    chair: M. Tiwari

    Small-scale modelling of redshift-space distortions

    Peculiar velocities affects the redshifts of distant galaxies and introduces distortions in all statistical measures of the reconstructed large-scale structure. These distortions are in general complex to model. In this talk, we focus on the streaming model which is often used to model these distortions in configuration space. Current phenomenological models based on the streaming equation do not work well at small scales. Using N-body simulations, we take a deeper look into the pairwise velocity distributions and show how field and halo particles contribute to these distribution. We also model these distortions to small scales and thus paving a way to obtain precise cosmological constraints from planned future surveys like EUCLID.






    Monthly Discussion



     Nina Brinkmann (2)



     Tilemachos Athanasiadis (1)

    chair: Nina Brinkmann

    A Targeted Survey for Binary Pulsars

    Pulsar mass measurements provide crucial information for a wide range of astrophysical problems and open questions in fundamental physics. Some of the most useful systems for precision mass NS mass measurements are millisecond pulsars with low-mass white dwarf companions.
    I will cover some basic concepts and techniques of a recently commenced targeted survey with the Effelsberg telescope, which is specifically designed to find such binaries.  I will also present some preliminary results based on a dataset collected during a small-scale pilot survey.



     Sandra Unruh (2)

    chair: Tilemachos Athanasiadis

    Shear-ratio test in lensing and the large-scale structure bias

    Weak gravitational lensing is one of the most powerful methods to explore Dark energy. However, the distortions induced by weak lensing are subject to systematics which can be tedious to control. In recent surveys null tests have been used (among other methods) to check for systematic errors in the data. An apparently easy null test involves shear-ratios. In this talk I will show, that the shear-ratio test leads to faulty conclusions. This is due to a bias induced by a non-vanishing matter-galaxy correlation function.









    Monthly Discussion








    Prajwal Padmanabh (1)






    Monthly Discussion



     Fatimah Mohd Raihan (1)

    Testing 3D-HST photo-zs for weak lensing

    Weak lensing has been proven to be a crucial method to study cosmology by giving an unbiased measurement of
    galaxy clusters. However, the systematic, especially the redshift distribution of galaxies that serve as the source of the weak lensing signal, needs to
    be controlled. In this talk, I will present you the problem that we found while testing the accuracy of the 3D-HST photometric redshift catalogue and a
    possible solution towards fixing it.



     Henning Hilmarsson (2) &

    Abel Schootemeijer (2)

    Wolf-Rayet stars in the Small Magellanic Cloud as testbed for massive star evolution

    Wolf-Rayet (WR) stars are hot, luminous and massive objects that approach the end of their stellar lifetime. We simulate stellar models which we compare with observed WR stars in the Small Magellanic Cloud (SMC). This is a metal-poor but nearby satellite galaxy of the Milky Way. Therefore, the SMC is a unique laboratory to study stellar evolution in conditions which resemble those of high-redshift galaxies. We find a dichotomy between apparently single and binary WR stars. While the properties of binary WR stars follow theoretical predictions, we infer thin hydrogen envelopes with steep hydrogen gradients for the apparently single WR stars. Arguably, this implies a common envelope formation scenario for these stars, where a lower mass companion stripped the WR star’s hydrogen envelope late in the evolution. If confirmed, this would be a step towards understanding the formation of binary black holes at low metallicity – i.e., the progenitor systems of the recently detected gravitational waves.




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