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) & Mélisse Bonfond (2)






Monthly Discussion



 Fateme Kamali (3) & Madhuri Gaidwad (1)



Easter Monday



 Anna Mikler (3) & Chaoli Zhang (1)






May Holiday



Monthly Discussion



Jackie Ma (2) & Yuxin Lin (1)



 Efthalia Traianou (1)



 Jae-Young Kim (2) & Elaheh Hosseini (2)









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 Marzieh Parsa (3)



 Jens Erler (3)






Monthly Discussion



  Joey Martinez (3)





Henning Hilmarsson (2)





Monthly Discussion






 Maja Kierdof (3)









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 Sandra Unruh (3)






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