M. Rioja - Academia.edu (original) (raw)

Papers by M. Rioja

Research paper thumbnail of SiO MASERS AROUND WX PSC MAPPED WITH THE KVN AND VERA ARRAY (KaVA)

The Astrophysical Journal, 2016

Research paper thumbnail of Relative astrometry and phase-reference mapping in the 1636+473 system using MERLIN and Global VLBI

The authors present astrometric results and maps from simultaneous MERLIN and Global VLBI observa... more The authors present astrometric results and maps from simultaneous MERLIN and Global VLBI observations of the very weak core of the double-lobed radio source 1636+47B, using as reference the bright, compact, flat-spectrum quasar 1636+473 A, 20 arcsec away. The observations were made in May 1995 at 5 GHz. The phase-referenced VLBI map of the weak core, of resolution 1.5 mas,

Research paper thumbnail of ASTROMETRICALLY REGISTERED SIMULTANEOUS OBSERVATIONS OF THE 22 GHz H2O AND 43 GHz SiO MASERS TOWARD R LEONIS MINORIS USING KVN AND SOURCE/FREQUENCY PHASE REFERENCING

The Astronomical Journal, 2014

Research paper thumbnail of observations of radio galaxies in the S/X band with the triangle Medicina-Noto-Madrid

Research paper thumbnail of High CO depletion in southern infrared-dark clouds

Infrared-dark high-mass clumps are among the most promising objects to study the initial conditio... more Infrared-dark high-mass clumps are among the most promising objects to study the initial conditions of the formation process of high-mass stars and rich stellar clusters. In this work, we have observed the (3-2) rotational transition of C18O with the APEX telescope, and the (1,1) and (2,2) inversion transitions of NH3 with the Australia Telescope Compact Array in 21 infrared-dark clouds already mapped in the 1.2 mm continuum, with the aim of measuring basic chemical and physical parameters such as the CO depletion factor (fD), the gas kinetic temperature and the gas mass. In particular, the C18O (3-2) line allows us to derive fD in gas at densities higher than that traced by the (1-0) and (2-1) lines, typically used in previous works. We have detected NH3 and C18O in all targets. The clumps possess mass, H2 column and surface densities consistent with being potentially the birthplace of high-mass stars. We have measured fD in between 5 and 78, with a mean value of 32 and a median of...

Research paper thumbnail of First Parallax Measurements Towards a 6.7 GHz Methanol Maser with the Australian Long Baseline Array - Distance to G339.884-1.259

We have conducted the first parallax and proper motion measurements of 6.7 GHz methanol maser emi... more We have conducted the first parallax and proper motion measurements of 6.7 GHz methanol maser emission using the Australian Long Baseline Array (LBA). The parallax of G339.884-1.259 measured from five epochs of observations is 0.48± 0.08 mas, corresponding to a distance of 2.1^+0.4_-0.3 kpc, placing it in the Scutum spiral arm. This is consistent (within the combined uncertainty) with the kinematic distance estimate for this source at 2.5± 0.5 kpc using the latest Solar and Galactic rotation parameters. We find from the Lyman continuum photon flux that the embedded core of the young star is of spectral type B1, demonstrating that luminous 6.7 GHz methanol masers can be associated with high-mass stars towards the lower end of the mass range.

Research paper thumbnail of The application of MultiView Methods for High Precision Astrometric Space VLBI at Low Frequencies

High precision astrometric Space Very Long Baseline Interferometry (S-VLBI) at the low end of the... more High precision astrometric Space Very Long Baseline Interferometry (S-VLBI) at the low end of the conventional frequency range, i.e. 20cm, is a requirement for a number of high priority science goals. These are headlined by obtaining trigonometric parallax distances to pulsars in Pulsar--Black Hole pairs and OH masers anywhere in the Milky Way Galaxy and the Magellanic Clouds. We propose a solution for the most difficult technical problems in S-VLBI by the MultiView approach where multiple sources, separated by several degrees on the sky, are observed simultaneously. We simulated a number of challenging S-VLBI configurations, with orbit errors up to 8m in size and with ionospheric atmospheres consistant with poor conditions. In these simulations we performed MultiView analysis to achieve the required science goals. This approach removes the need for beam switching requiring a Control Moment Gyro, and the space and ground infrastructure required for high quality orbit reconstruction ...

Research paper thumbnail of Exploration of SFPR techniques for astrometry and observations of weak sources with high frequency Space VLBI

Space Very-Long-Baseline-Interferometry (S-VLBI) observations at high frequencies hold the prospe... more Space Very-Long-Baseline-Interferometry (S-VLBI) observations at high frequencies hold the prospect of achieving the highest angular resolutions and astrometric accuracies, resulting from the long baselines between ground and satellite telescopes. Nevertheless, space-specific issues, such as limited accuracy in the satellite orbit reconstruction and constraints on the satellite antenna pointing operations, limit the application of conventional phase referencing. We investigate the feasibility of an alternative technique, source frequency phase referencing (SFPR), to the S-VLBI domain. With these investigations we aim to contribute to the design of the next-generation of S-VLBI missions. We have used both analytical and simulation studies to characterize the performance of SFPR in S-VLBI observations, applied to astrometry and increased coherence time, and compared these to results obtained using conventional phase referencing. The observing configurations use the specifications of t...

Research paper thumbnail of 7mm VLBA observations of BL Lac object OJ287

Research paper thumbnail of ASTRONOMY AND ASTROPHYSICS Letter to the Editor Baseline errors in European VLBI Network measurements III. The dominant effect of instrumental polarization

Abstract. In this paper, we compare the results of a VLBI observation involving 7 European telesc... more Abstract. In this paper, we compare the results of a VLBI observation involving 7 European telescopes with the model by Massi et al. 1996 for the contribution of the instrumental polarization to the closure phase. The excellent agreement found between model predictions and data proves that the systematic error present in European VLBI data is in fact due to the high instrumental polarization of some of the telescopes and can be removed by data processing.

Research paper thumbnail of VLBA H 2 O observations towards IRAS 20126+4104

Research paper thumbnail of Non-closing Errors in EVN dataM

We show how the total intensity data acquired with the European VLBI telescopes are aaected by a ... more We show how the total intensity data acquired with the European VLBI telescopes are aaected by a systematic error, the physical origin of which lies in the instrumental polarization of the telescopes. The eeect on the data can be modeled and therefore removed by data processing.

Research paper thumbnail of VLBI astrometry up to 130 GHz using multi frequency calibration

2016 URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), 2016

Simultaneous observations at multiple frequency bands have the potential to overcome the fundamen... more Simultaneous observations at multiple frequency bands have the potential to overcome the fundamental limitation imposed by the atmospheric propagation in mm-VLBI observations. The propagation effects place a severe limit in the sensitivity achievable in mm-VLBI, reducing the time over which the signals can be coherently combined, and preventing the use of phase referencing and astrometric measurements. We carried out simultaneous observations at 22, 43, 87 and 130 GHz of a group of five AGNs, the weakest of which is ca. 200 mJy at 130 GHz, with angular separations ranging from 3.6 to 11 degrees, using the KVN. We analysed this data using the Frequency Phase Transfer (FPT) and the Source Frequency Phase Referencing (SFPR) techniques, which use the observations at a lower frequency to correct those at a higher frequency. The results of the analysis provide an empirical demonstration of the increase in the coherence times at 130 GHz from a few tens of seconds to about twenty minutes, w...

Research paper thumbnail of High-precision VLBI astrometry of radio-emitting stars

Astronomy and Astrophysics, 1999

Multiple-epoch phase-referenced VLBI observations of 11 radio-emitting stars have been conducted ... more Multiple-epoch phase-referenced VLBI observations of 11 radio-emitting stars have been conducted as part of an astrometric program to link the Hipparcos optical reference frame to the radio extragalactic reference frame. We present the VLBI positions, proper motions and trigonometric parallaxes from this program in the ICRF (International Celestial Reference Frame). These astrometric parameters are absolute because they are directly measured relative to the distant quasars used as VLBI phase reference calibrators. The mean astrometric precision achieved relative to the calibrators is 0.36 milliarcsecond and the highest precision is for the RS CVn close binary σ2 CrB with formal uncertainties of 0.12 milliarcsecond for its relative position, 0.05 milliarcsecond for its annual proper motion and 0.10 milliarcsecond for its trigonometric parallax. In addition to the Hipparcos link, these observations have provided several new results. The distance to the nearby TauAuriga star forming re...

Research paper thumbnail of Simultaneous multi frequency mm-VLBI on global baselines: The extended KVN

2016 URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), 2016

We present the development and efforts towards providing global baselines compatible with the inn... more We present the development and efforts towards providing global baselines compatible with the innovative Korean VLBI Network receiver system. The launching and development of the jet from an Active Galactic Nucleus is still a topic of much debate, with the detection the actual mode of jet production. The astromatric measurement of the site of the AGN core is the best diagnostic in the study. The KVN itself has a resolution too crude to trace the predicted core-shifts at millimeter wavelength, so the addition of longer, global, baselines are essential to investigate this exciting area of research.

Research paper thumbnail of Registration of H2O and SiO masers in the Calabash Nebula to confirm the planetary nebula paradigm

Monthly Notices of the Royal Astronomical Society, Jan 31, 2018

Research paper thumbnail of Registration of H2O and SiO masers in the Calabash Nebula, to confirm the Planetary Nebula paradigm

Proceedings of the International Astronomical Union

We report on the astrometric registration of VLBI images of the SiO and H2O masers in OH 231.8+4.... more We report on the astrometric registration of VLBI images of the SiO and H2O masers in OH 231.8+4.2, the iconic Proto-Planetary Nebula also known as the Calabash nebula, using the KVN and Source/Frequency Phase Referencing. This, for the first time, robustly confirms the alignment of the SiO masers, close to the AGB star, which drives the bi-lobe structure with the water masers in the out-flow.

Research paper thumbnail of LBA high resolution observations of ground- and excited-state OH masers towards G351.417+0.645

Proceedings of the International Astronomical Union

We present the results from the Australian Long Baseline Array (LBA) observations of the ground- ... more We present the results from the Australian Long Baseline Array (LBA) observations of the ground- and excited-state OH masers at high resolutions towards the massive star-forming region G351.417+0.645 in 2012. We obtain the most accurate spatial gradient of magnetic fields at ground state transitions and verify the reliability of magnetic field strengths measured from previous lower resolution observations. In comparison with previous LBA observations in 2001 at 6.0 GHz, we identified several matched Zeeman pairs. We found that the OH maser features have no significant change of magnetic field strengths and directions with small internal proper motions, implying quite stable physical conditions. Additionally, we found that 1665- and 6035-MHz OH maser features reveal the same trend of reversal of magnetic fields. Moreover, we also analyzed the physical conditions at different locations from the coincidence of different OH maser transitions based on current OH maser models.

Research paper thumbnail of Tracing the magnetic field and other properties of G351.417+0.645 at subarcsecond scales with the Long Baseline Array

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of Magnetically regulated fragmentation of a massive, dense, and turbulent clump

Research paper thumbnail of SiO MASERS AROUND WX PSC MAPPED WITH THE KVN AND VERA ARRAY (KaVA)

The Astrophysical Journal, 2016

Research paper thumbnail of Relative astrometry and phase-reference mapping in the 1636+473 system using MERLIN and Global VLBI

The authors present astrometric results and maps from simultaneous MERLIN and Global VLBI observa... more The authors present astrometric results and maps from simultaneous MERLIN and Global VLBI observations of the very weak core of the double-lobed radio source 1636+47B, using as reference the bright, compact, flat-spectrum quasar 1636+473 A, 20 arcsec away. The observations were made in May 1995 at 5 GHz. The phase-referenced VLBI map of the weak core, of resolution 1.5 mas,

Research paper thumbnail of ASTROMETRICALLY REGISTERED SIMULTANEOUS OBSERVATIONS OF THE 22 GHz H2O AND 43 GHz SiO MASERS TOWARD R LEONIS MINORIS USING KVN AND SOURCE/FREQUENCY PHASE REFERENCING

The Astronomical Journal, 2014

Research paper thumbnail of observations of radio galaxies in the S/X band with the triangle Medicina-Noto-Madrid

Research paper thumbnail of High CO depletion in southern infrared-dark clouds

Infrared-dark high-mass clumps are among the most promising objects to study the initial conditio... more Infrared-dark high-mass clumps are among the most promising objects to study the initial conditions of the formation process of high-mass stars and rich stellar clusters. In this work, we have observed the (3-2) rotational transition of C18O with the APEX telescope, and the (1,1) and (2,2) inversion transitions of NH3 with the Australia Telescope Compact Array in 21 infrared-dark clouds already mapped in the 1.2 mm continuum, with the aim of measuring basic chemical and physical parameters such as the CO depletion factor (fD), the gas kinetic temperature and the gas mass. In particular, the C18O (3-2) line allows us to derive fD in gas at densities higher than that traced by the (1-0) and (2-1) lines, typically used in previous works. We have detected NH3 and C18O in all targets. The clumps possess mass, H2 column and surface densities consistent with being potentially the birthplace of high-mass stars. We have measured fD in between 5 and 78, with a mean value of 32 and a median of...

Research paper thumbnail of First Parallax Measurements Towards a 6.7 GHz Methanol Maser with the Australian Long Baseline Array - Distance to G339.884-1.259

We have conducted the first parallax and proper motion measurements of 6.7 GHz methanol maser emi... more We have conducted the first parallax and proper motion measurements of 6.7 GHz methanol maser emission using the Australian Long Baseline Array (LBA). The parallax of G339.884-1.259 measured from five epochs of observations is 0.48± 0.08 mas, corresponding to a distance of 2.1^+0.4_-0.3 kpc, placing it in the Scutum spiral arm. This is consistent (within the combined uncertainty) with the kinematic distance estimate for this source at 2.5± 0.5 kpc using the latest Solar and Galactic rotation parameters. We find from the Lyman continuum photon flux that the embedded core of the young star is of spectral type B1, demonstrating that luminous 6.7 GHz methanol masers can be associated with high-mass stars towards the lower end of the mass range.

Research paper thumbnail of The application of MultiView Methods for High Precision Astrometric Space VLBI at Low Frequencies

High precision astrometric Space Very Long Baseline Interferometry (S-VLBI) at the low end of the... more High precision astrometric Space Very Long Baseline Interferometry (S-VLBI) at the low end of the conventional frequency range, i.e. 20cm, is a requirement for a number of high priority science goals. These are headlined by obtaining trigonometric parallax distances to pulsars in Pulsar--Black Hole pairs and OH masers anywhere in the Milky Way Galaxy and the Magellanic Clouds. We propose a solution for the most difficult technical problems in S-VLBI by the MultiView approach where multiple sources, separated by several degrees on the sky, are observed simultaneously. We simulated a number of challenging S-VLBI configurations, with orbit errors up to 8m in size and with ionospheric atmospheres consistant with poor conditions. In these simulations we performed MultiView analysis to achieve the required science goals. This approach removes the need for beam switching requiring a Control Moment Gyro, and the space and ground infrastructure required for high quality orbit reconstruction ...

Research paper thumbnail of Exploration of SFPR techniques for astrometry and observations of weak sources with high frequency Space VLBI

Space Very-Long-Baseline-Interferometry (S-VLBI) observations at high frequencies hold the prospe... more Space Very-Long-Baseline-Interferometry (S-VLBI) observations at high frequencies hold the prospect of achieving the highest angular resolutions and astrometric accuracies, resulting from the long baselines between ground and satellite telescopes. Nevertheless, space-specific issues, such as limited accuracy in the satellite orbit reconstruction and constraints on the satellite antenna pointing operations, limit the application of conventional phase referencing. We investigate the feasibility of an alternative technique, source frequency phase referencing (SFPR), to the S-VLBI domain. With these investigations we aim to contribute to the design of the next-generation of S-VLBI missions. We have used both analytical and simulation studies to characterize the performance of SFPR in S-VLBI observations, applied to astrometry and increased coherence time, and compared these to results obtained using conventional phase referencing. The observing configurations use the specifications of t...

Research paper thumbnail of 7mm VLBA observations of BL Lac object OJ287

Research paper thumbnail of ASTRONOMY AND ASTROPHYSICS Letter to the Editor Baseline errors in European VLBI Network measurements III. The dominant effect of instrumental polarization

Abstract. In this paper, we compare the results of a VLBI observation involving 7 European telesc... more Abstract. In this paper, we compare the results of a VLBI observation involving 7 European telescopes with the model by Massi et al. 1996 for the contribution of the instrumental polarization to the closure phase. The excellent agreement found between model predictions and data proves that the systematic error present in European VLBI data is in fact due to the high instrumental polarization of some of the telescopes and can be removed by data processing.

Research paper thumbnail of VLBA H 2 O observations towards IRAS 20126+4104

Research paper thumbnail of Non-closing Errors in EVN dataM

We show how the total intensity data acquired with the European VLBI telescopes are aaected by a ... more We show how the total intensity data acquired with the European VLBI telescopes are aaected by a systematic error, the physical origin of which lies in the instrumental polarization of the telescopes. The eeect on the data can be modeled and therefore removed by data processing.

Research paper thumbnail of VLBI astrometry up to 130 GHz using multi frequency calibration

2016 URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), 2016

Simultaneous observations at multiple frequency bands have the potential to overcome the fundamen... more Simultaneous observations at multiple frequency bands have the potential to overcome the fundamental limitation imposed by the atmospheric propagation in mm-VLBI observations. The propagation effects place a severe limit in the sensitivity achievable in mm-VLBI, reducing the time over which the signals can be coherently combined, and preventing the use of phase referencing and astrometric measurements. We carried out simultaneous observations at 22, 43, 87 and 130 GHz of a group of five AGNs, the weakest of which is ca. 200 mJy at 130 GHz, with angular separations ranging from 3.6 to 11 degrees, using the KVN. We analysed this data using the Frequency Phase Transfer (FPT) and the Source Frequency Phase Referencing (SFPR) techniques, which use the observations at a lower frequency to correct those at a higher frequency. The results of the analysis provide an empirical demonstration of the increase in the coherence times at 130 GHz from a few tens of seconds to about twenty minutes, w...

Research paper thumbnail of High-precision VLBI astrometry of radio-emitting stars

Astronomy and Astrophysics, 1999

Multiple-epoch phase-referenced VLBI observations of 11 radio-emitting stars have been conducted ... more Multiple-epoch phase-referenced VLBI observations of 11 radio-emitting stars have been conducted as part of an astrometric program to link the Hipparcos optical reference frame to the radio extragalactic reference frame. We present the VLBI positions, proper motions and trigonometric parallaxes from this program in the ICRF (International Celestial Reference Frame). These astrometric parameters are absolute because they are directly measured relative to the distant quasars used as VLBI phase reference calibrators. The mean astrometric precision achieved relative to the calibrators is 0.36 milliarcsecond and the highest precision is for the RS CVn close binary σ2 CrB with formal uncertainties of 0.12 milliarcsecond for its relative position, 0.05 milliarcsecond for its annual proper motion and 0.10 milliarcsecond for its trigonometric parallax. In addition to the Hipparcos link, these observations have provided several new results. The distance to the nearby TauAuriga star forming re...

Research paper thumbnail of Simultaneous multi frequency mm-VLBI on global baselines: The extended KVN

2016 URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), 2016

We present the development and efforts towards providing global baselines compatible with the inn... more We present the development and efforts towards providing global baselines compatible with the innovative Korean VLBI Network receiver system. The launching and development of the jet from an Active Galactic Nucleus is still a topic of much debate, with the detection the actual mode of jet production. The astromatric measurement of the site of the AGN core is the best diagnostic in the study. The KVN itself has a resolution too crude to trace the predicted core-shifts at millimeter wavelength, so the addition of longer, global, baselines are essential to investigate this exciting area of research.

Research paper thumbnail of Registration of H2O and SiO masers in the Calabash Nebula to confirm the planetary nebula paradigm

Monthly Notices of the Royal Astronomical Society, Jan 31, 2018

Research paper thumbnail of Registration of H2O and SiO masers in the Calabash Nebula, to confirm the Planetary Nebula paradigm

Proceedings of the International Astronomical Union

We report on the astrometric registration of VLBI images of the SiO and H2O masers in OH 231.8+4.... more We report on the astrometric registration of VLBI images of the SiO and H2O masers in OH 231.8+4.2, the iconic Proto-Planetary Nebula also known as the Calabash nebula, using the KVN and Source/Frequency Phase Referencing. This, for the first time, robustly confirms the alignment of the SiO masers, close to the AGB star, which drives the bi-lobe structure with the water masers in the out-flow.

Research paper thumbnail of LBA high resolution observations of ground- and excited-state OH masers towards G351.417+0.645

Proceedings of the International Astronomical Union

We present the results from the Australian Long Baseline Array (LBA) observations of the ground- ... more We present the results from the Australian Long Baseline Array (LBA) observations of the ground- and excited-state OH masers at high resolutions towards the massive star-forming region G351.417+0.645 in 2012. We obtain the most accurate spatial gradient of magnetic fields at ground state transitions and verify the reliability of magnetic field strengths measured from previous lower resolution observations. In comparison with previous LBA observations in 2001 at 6.0 GHz, we identified several matched Zeeman pairs. We found that the OH maser features have no significant change of magnetic field strengths and directions with small internal proper motions, implying quite stable physical conditions. Additionally, we found that 1665- and 6035-MHz OH maser features reveal the same trend of reversal of magnetic fields. Moreover, we also analyzed the physical conditions at different locations from the coincidence of different OH maser transitions based on current OH maser models.

Research paper thumbnail of Tracing the magnetic field and other properties of G351.417+0.645 at subarcsecond scales with the Long Baseline Array

Monthly Notices of the Royal Astronomical Society

Research paper thumbnail of Magnetically regulated fragmentation of a massive, dense, and turbulent clump