Instituto Argentino De Radioastronomia Research Articles

GASS: the Parkes Galactic all-sky survey

The Parkes Galactic All-Sky Survey (GASS) is a survey of Galactic atomic hydrogen (HI) emission in the southern sky observed with the Parkes 64-m Radio Telescope. The first data release was published by McClure-Griffiths et al. (2009). We remove instrumental effects that affect the GASS and present the second data release. We calculate the stray-radiation by convolving the all-sky response of the Parkes antenna with the brightness temperature distribution from the Leiden/Argentine/Bonn (LAB) all sky 21-cm line survey, with major contributions from the 30-m dish of the Instituto Argentino de Radioastronomia (IAR) in the southern sky. Remaining instrumental baselines are corrected using the LAB data for a first guess of emission-free baseline regions. Radio frequency interference is removed by median filtering. After applying these corrections to the GASS we find an excellent agreement with the Leiden/Argentine/Bonn (LAB) survey. The GASS is the highest spatial resolution, most sensitive, and is currently the most accurate HI survey of the Galactic HI emission in the southern sky. We provide a web interface for generation and download of FITS cubes.

A radio continuum and neutral hydrogen counterpart to the IRAS Vela shell

Aims. We look for radio-continuum and atomic neutral hydrogen (Hi) counterparts of the IRAS Vela shell (IVS). Methods. Neutral hydrogen (Hi) and 1410 MHz radio continuum surveys carried out with the Instituto Argentino de Radioastronomia (IAR) dishes are the main databases used in this investigation. Results. A good morphological correlation was found between arc-shaped structures at radio wavelengths and in the 100 μ m IR emission. This correlation is observed at velocities of the Hi between –17.5 and –2.1 km s -1 , in agreement with the velocities of the molecular gas detected in the region. The radial distribution of the different components is consistent with the presence of an expanding shell that is being ionized from inside. Assuming a distance of 400 pc, the amount of ionized and atomic gas associated with the IVS is $2.3 \times 10^4$ and $6.8 \times 10$ 4 solar masses, respectively. The origin of the expansion of the IVS could not be identified.

The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI

We present the final data release of observations of lambda 21-cm emission from Galactic neutral hydrogen over the entire sky, merging the Leiden/Dwingeloo Survey (LDS: Hartmann & Burton, 1997) of the sky north of delta = -30 deg with the Instituto Argentino de Radioastronomia Survey (IAR: Arnal et al., 2000, and Bajaja et al., 2005) of the sky south of delta = -25 deg. The angular resolution of the combined material is HPBW ~ 0.6 deg. The LSR velocity coverage spans the interval -450 km/s to +400 km/s, at a resolution of 1.3 km/s. The data were corrected for stray radiation at the Institute for Radioastronomy of the University of Bonn, refining the original correction applied to the LDS. The rms brightness-temperature noise of the merged database is 0.07 - 0.09 K. Residual errors in the profile wings due to defects in the correction for stray radiation are for most of the data below a level of 20 - 40 mK. It would be necessary to construct a telescope with a main beam efficiency of eta_{MB} > 99% to achieve the same accuracy. The merged and refined material entering the LAB Survey of Galactic HI is intended to be a general resource useful to a wide range of studies of the physical and structural characteristices of the Galactic interstellar environment. The LAB Survey is the most sensitive Milky Way HI survey to date, with the most extensive coverage both spatially and kinematically.

Jupiter's Synchrotron Emission Induced by the Collision of Comet Shoemaker-Levy 9

From July 13 to August 21, 1994, we observed Jupiter at 1420 MHz using one of the 30-m single dishes of the Instituto Argentino de Radioastronomia. After the impact of fragment G, we detected a rapid increase of the 21cm-continuum flux, which reached the maximum (≈ 20% of Jupiter's flux) at the end of the impact period. The nature of this radiation is clearly synchrotron. We interpret it in terms of a new population of relativistic electrons (≈ 2 × 1029) injected into the Jovian magnetosphere as a consequence of the impact explosions. The proposed mechanism is that the relativistic plasma was blown as magnetic clouds that flowed along the magnetic lines of force towards the jovimagnetic equator. We constructed a model in which the energies of the fresh electrons, generated within the magnetized clouds with a power law energy spectrum, were highly degraded by the comet dust grains attached to the magnetized plasma. The model can account for the spectral shape based on observations at several frequencies (de Pater et al., 1995, Science 268, 1879; Venturi et al., 1996, Astron. Astrophys. 316, 243). The energy released by the explosions under the form of relativistic electrons is of ≈ 2 × 1025 erg, which represents a fraction of about 1–3 per cent of the explosion energy. The efficiency in converting the explosion energy into the relativistic electron energy is, therefore, of the same order of magnitude as that of supernova explosions. An alternative model is considered. This gives figures for the total energy and number of relativistic electrons that are similar to the corresponding ones of the favoured model. Finally, we suggest that the behavior of the flux decay in the various observed frequencies is the result of the diffusion of electrons into the loss-cone due to the resonant scattering of the electrons by Alfven waves.

Observation of the OH 1667 MHz line toward Comet Halley from the Southern Hemisphere

Halley's comet has been tracked for observing at the Instituto Argentino de Radioastronomia (IAR) in the 1667 MHz line of OH, 4 hr a day, from February 6 to May 1, 1986. It has been detected in absorption from March 24 to April 23. A detail of the observations and of the results is given here. The mean velocities show that there have not been any significant asymmetries in the profile shapes. The total number of OH molecules has been estimated for each day from the observed profiles and compared with the values predicted by Schloerb and Gerard (1985) using the same model. The observational results for this number, for the period March 23 to April 12, are, on average, 2.4 times larger than the predicted values, but it shows rapid variations with maximum-to-minimum ratios of the order of 1.7. The average of the OH production rate derived from these observations is (4.6 + or - 0.2) x 10 to the 29th molecules/s.

The Magellanic Stream. II

New high-sensitivity observations of the Magellanic Stream have been carried out from the Instituto Argentino de Radioastronomia. The Stream was surveyed between dec. -44 deg and -20 deg. The data are presented in the form of maps of H I column density distribution and velocity distribution. They reveal the extreme complexity of the gas distribution: here, the main Stream is present as a continuous feature of several concentrations (MSI-III, Mathewson's (1974) clouds) linked by low emission gas. The observations also show other components overlapping the main Stream. Several of these seem to be typical high-velocity clouds. 34 references.