Papers by Huib van Langevelde
In recent studies of methanol masers, a substantial fraction of the objects show maser components... more In recent studies of methanol masers, a substantial fraction of the objects show maser components aligned in large-scale elliptical configurations. These can be readily interpreted as rings centred on a high mass star in formation, seen in projection. Remarkably, most of these rings do not show signs of rotation, but rather the radial motions dominate. This must mean that their dynamics are governed by other than gravitational forces. In particular, we have studied the methanol masers around Cep A in detail, where it can be argued that the methanol masers show signs of infall. In this paper we discuss the dynamics of the Cep A methanol maser and sources from the Torun blind survey to argue that at least in a fraction of sources methanol masers could be associated with the shock interface between the large scale accretion, regulated by the magnetic field, and a 1000-AU scale circumstellar disk. We discuss the validity of such a model for the overall population of methanol maser sources.
Astrophysics and Space Science, Jan 27, 2004
The European VLBI Network (EVN) has been used to make phase referenced, wide-field (several arcmi... more The European VLBI Network (EVN) has been used to make phase referenced, wide-field (several arcminute) spectral line observations of the 6.7-GHz methanol maser emission towards W51. In the W51main region, the bulk of the methanol is offset from an UCHii region. This probably indicates the methanol emission arises at the interface of the expanding UCHii region and not from an edge-on circumstellar disc, as previously suggested. Near the W51 IRS2 region, the methanol emission is associated with a very compact, extremely embedded source supporting the hypothesis that methanol masers trace the earliest stages of massive star formation. As well as these two previously well studied sites of star formation, many previously unknown regions star formation are detected, demonstrating that methanol masers are powerful means of detection young massive stars.
arXiv: Instrumentation and Methods for Astrophysics, 2020
This white paper describes the science case for Very Long Baseline Interferometry (VLBI) and prov... more This white paper describes the science case for Very Long Baseline Interferometry (VLBI) and provides suggestions towards upgrade paths for the European VLBI Network (EVN). The EVN is a distributed long-baseline radio interferometric array, that operates at the very forefront of astronomical research. Recent results, together with the new science possibilities outlined in this vision document, demonstrate the EVN's potential to generate new and exciting results that will transform our view of the cosmos. Together with e-MERLIN, the EVN provides a range of baseline lengths that permit unique studies of faint radio sources to be made over a wide range of spatial scales. The science cases are reviewed in six chapters that cover the following broad areas: cosmology, galaxy formation and evolution, innermost regions of active galactic nuclei, explosive phenomena and transients, stars and stellar masers in the Milky Way, celestial reference frames and space applications. The document ...
Proceedings of Advancing Astrophysics with the Square Kilometre Array — PoS(AASKA14), 2015
Proceedings of The 9th European VLBI Network Symposium on The role of VLBI in the Golden Age for Radio Astronomy and EVN Users Meeting — PoS(IX EVN Symposium), 2009
We present the results of five year campaign observing 6.7 GHz methanol masers towards the Galact... more We present the results of five year campaign observing 6.7 GHz methanol masers towards the Galactic plane using European Very Long Baseline Interferometer Network (EVN). 31 out of 33 sources were imaged at milliarcsecond scale. Suprisingly, 12 of them showed an elliptical morphology which has not been detected before. We state that the recent increase of the sensitivity of EVN allowed us to detect a new type of masers. We discuss the origin of elliptically shaped methanol masers in massive star forming regions analysing their detailed structures.
Proceedings of 14th European VLBI Network Symposium & Users Meeting — PoS(EVN2018), 2019
Proceedings of 14th European VLBI Network Symposium & Users Meeting — PoS(EVN2018), 2019
With the publication of Gaia DR2, 1.3 billion stars now have public parallax and proper motion me... more With the publication of Gaia DR2, 1.3 billion stars now have public parallax and proper motion measurements. In this contribution, we compare the results for sources that have both optical and radio measurements, focusing on circumstellar masers. For these large, variable and bright AGB stars, the VLBI astrometry results can be more robust. Moreover, there are a number of applications where VLBI astrometry provides unique data for studying stellar populations and Galactic structure. The BeSSel project not only provides parallax and proper motions at much larger distances than Gaia can reach, but it also uniquely samples the spiral arms of the Galaxy. The evolved stars in the BAaDE sample can potentially constrain the dynamics and stellar content of the inner bulge and bar of the Milky Way, not reachable in the optical.
Proceedings of 14th European VLBI Network Symposium & Users Meeting — PoS(EVN2018), 2019
Proceedings of the International Astronomical Union, 2017
Ring−like sources of 6.7 GHz methanol maser emission were discovered a decade ago with the Europe... more Ring−like sources of 6.7 GHz methanol maser emission were discovered a decade ago with the European VLBI Network. In the past years we have been incessantly working to understand the nature of these rings. In general, the methanol rings do not coincide with H II regions nor they show 22 GHz water maser emission. Here, we present a proper motion study over a time baseline up to 10.5 years for the first sub-sample of methanol maser rings. Our findings suggest that in three targets G23.207−00.377, G23.389+00.185, and G23.657−00.127, such rings form in outflows or even in winds close to the central sources, and the masers trace slow proper motions of a few km s−1 typically.
Proceedings of The 9th European VLBI Network Symposium on The role of VLBI in the Golden Age for Radio Astronomy and EVN Users Meeting — PoS(IX EVN Symposium), 2009
Proceedings of 8th European VLBI Network Symposium — PoS(8thEVN), 2007
Proceedings of Advancing Astrophysics with the Square Kilometre Array — PoS(AASKA14), 2015
We discuss the unique opportunities for maser astrometry with the inclusion of the Square Kilomet... more We discuss the unique opportunities for maser astrometry with the inclusion of the Square Kilometre Array (SKA) in Very Long Baseline Interferometry (VLBI) networks. The first phase of the SKA will enable observations of hydroxyl and methanol masers, positioning the latter to an accuracy of 5 microarcseconds, and the second phase may allow water maser observations. These observations will provide trigonometric distances with errors as small as 1%. The unrivalled sensitivity of the SKA will enable large-scale surveys and, through joint operations, will turn any VLBI network into a fast astrometry device. Both evolved stars and high mass star formation regions will be accessible throughout the (Southern) Milky Way, completing our understanding of the content, dynamics and history of our Galaxy. Maser velocities and proper motions will be measurable in the Local Group of galaxies and beyond, providing new insights into their kinematics and evolution.
Monthly Notices of the Royal Astronomical Society, 2017
We present the results of multi-epoch VLBI (very long baseline interferometry) observations of wa... more We present the results of multi-epoch VLBI (very long baseline interferometry) observations of water masers in the AGFL 5142 massive star-forming region. We measure an annual parallax of π = 0.467 ± 0.010 mas, corresponding to a source distance of D = 2.14 +0.051 −0.049 kpc. Proper motion and line-of-sight velocities reveal the three-dimensional kinematics of masers in this region, most of which associate with millimetre sources from the literature. In particular, we find remarkable bipolar bowshocks expanding from the most massive member, AFGL 5142 MM1, which are used to investigate the physical properties of its protostellar jet. We attempt to link the known outflows in this region to possible progenitors by considering a precessing jet scenario and we discuss the episodic nature of ejections in AFGL 5142.
Very long baseline interferometry at millimetre/submillimetre wavelengths (mmVLBI) offers the hig... more Very long baseline interferometry at millimetre/submillimetre wavelengths (mmVLBI) offers the highest achievable spatial resolution at any wavelength in astronomy. The anticipated inclusion of ALMA as a phased array into a global VLBI network will bring unprecedented sensitivity and a transformational leap in capabilities for mmVLBI. Building on years of pioneering efforts in the US and Europe the ongoing ALMA Phasing Project (APP), a US-led international collaboration with MPIfR-led European contributions, is expected to deliver a beamformer and VLBI capability to ALMA by the end of 2014. Moreover, in Europe additional funding has become available through an ERC synergy grant (BlackHoleCam) in support of mmVLBI observations of Sgr A* and M 87. This report focuses on the future use of mmVLBI by the international users community from a European viewpoint. Firstly, it highlights the intense science interest in Europe in future mmVLBI observations as compiled from the responses to a general call to the European community for future research projects (see section 4). A wide range of research is presented that includes, amongst others: • Imaging the event horizon of the black hole at the centre of the Galaxy • Testing the theory of General Relativity an/or searching for alternative theories
Astronomy and …, 2000
The OH 1667 MHz maser in the circumstellar shell around the Mira variable U Her has been observed... more The OH 1667 MHz maser in the circumstellar shell around the Mira variable U Her has been observed with the NRAO Very Long Baseline Array (VLBA) at 6 epochs, spread over 4 years. Using phase referencing techniques the position of the most blue-shifted maser spot was monitored with respect to two extra-galactic radio sources. The absolute radio positions of the maser can be compared with the stellar optical position measured by the Hipparcos satellite to 15 mas accuracy. This confirms the model in which one of the maser spots corresponds to the stellar continuum, amplified by the maser. The stellar proper motion and the annual parallax (π VLBI = 5.3 ± 2.1 mas) were measured.
Publications of the Astronomical Society of Australia, 2013
In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telesco... more In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telescopes and upgrades are already being built around the world. These include APERTIF (The Netherlands), ASKAP (Australia),e-MERLIN (UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), MeerKAT (South Africa), and the Murchison Widefield Array. Each of these new instruments has different strengths, and coordination of surveys between them can help maximise the science from each of them. A radio continuum survey is being planned on each of them with the primary science objective of understanding the formation and evolution of galaxies over cosmic time, and the cosmological parameters and large-scale structures which drive it. In pursuit of this objective, the different teams are developing a variety of new techniques, and refining existing ones. To achieve these exciting scientific goals, many technical challenges must be addressed by the survey instruments. Given the limited reso...
Monthly Notices of the Royal Astronomical Society, 2000
We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of a sample of faint G... more We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of a sample of faint Gigahertz Peaked Spectrum (GPS) sources selected from the Westerbork Northern Sky Survey (WENSS). The 5 GHz observations involved a global array of 16 stations and yielded data on the total sample of 47 sources. A subsample of 26 GPS sources with peak frequencies ν p > 5 GHz and/or peak flux densities S p > 125 mJy was observed with the VLBA at 15 GHz. A second subsample of 29 sources, with ν p < 5 GHz, was observed at 1.6 GHz using a 14 station global VLBI array. In this way, 44 of the 47 sources (94%) in the sample were observed above and at or below their spectral peak. Spectral decomposition allowed us to identify 3, 11, 7, and 2 objects as compact symmetric objects, compact doubles, core-jet and complex sources respectively. However, many of the sources classified as compact double or core-jet sources show only two components making their classification rather tentative. This may explain why the strong morphological dichotomy of GPS quasars and galaxies found for radio-bright GPS sources, is not as clear in this faint sample.
Journal of Geophysical Research, 2006
Experimental Astronomy, 2001
A functional description is given of the new 16-station MarkIV VLBI data processor for the Europe... more A functional description is given of the new 16-station MarkIV VLBI data processor for the European VLBI Network. The data processor can operate in many configurations including sensitive continuum modes, line modes with unprecedented spectral resolution, and wide field imaging and pulsar gating modes. The EVN-MarkIV processor was developed by an international European/U.S. consortium. Several similar processors are deployed in
Uploads
Papers by Huib van Langevelde