Ce Senkbeil

The Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey. II. The First Four Epochs

We report on the variability of 443 flat-spectrum, compact radio sources monitored using the VLA for 3 days in four epochs at ~4 month intervals at 5 GHz as part of the Micro-Arcsecond Scintillation-Induced Variability (MASIV) survey. Over half of these sources exhibited 2%-10% rms variations on timescales over 2 days. We analyzed the variations by two independent methods and find that the rms variability amplitudes of the sources correlate with the emission measure in the ionized interstellar medium along their respective lines of sight. We thus link the variations with interstellar scintillation of components of these sources, with some (unknown) fraction of the total flux density contained within a compact region of angular diameter in the range 10-50 μas. We also find that the variations decrease for high mean flux density sources and, most importantly, for high-redshift sources. The decrease in variability is probably due either to an increase in the apparent diameter of the source or to a decrease in the flux density of the compact fraction beyond z ~ 2. Here we present a statistical analysis of these results, and a future paper will discuss the cosmological implications in detail.

A search for 22-GHz water masers within the giant molecular cloud associated with RCW 106

We report the results of a blind search for 22-GHz water masers in two regions, covering approximately half a square degree, within the giant molecular cloud associated with RCW 106. The complete search of the two regions was carried out with the 26-m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7-GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7-GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are similar to those of 6.7-GHz methanol masers, but slightly less red. We have made a statistical investigation of the properties of the 13 CO and 1.2-mm dust clumps with and without associated water masers. We find that the water masers are associated with the more massive, denser and brighter 13 CO and 1.2-mm dust clumps. We present statistical models that are able to predict those 13 CO and 1.2-mm dust clumps that are

Decrease in the orbital period of dwarf nova OY Carinae

We have measured the orbital light curve of dwarf nova OY Carinae on 8 separate nights between 1997 September and 2005 December. The measurements were made in white light using CCD photometers on the Mt Canopus 1 m telescope. The time of eclipse in 2005 December was 168±5 s earlier than that predicted by the Wood et al.(1989) ephemeris. Using the times of eclipse from our measurements and the compilation of published measurements by Pratt et al. (1999) we find that the observational data are inconsistent with a constant period and indicate that the orbital period is decreasing by 5 ±1× 10 12 s/s. This is too fast to be explained by gravitational radiation emission alone. It is possible that the change is cyclic with a period � 35 years

A Compact Extreme Scattering Event Cloud toward AO 0235+164

We present observations of a rare, rapid, high-amplitude extreme scattering event toward the compact BL Lac object AO 0235+164 at 6.65 GHz. The ESE cloud is compact; we estimate its diameter between 0.09 and 0.9 AU, with a distance of less than 3.6 kpc. Limits on the angular extent of the ESE cloud imply a minimum cloud electron density of ~4 × 103 cm−3. Based on the amplitude and timescale of the ESE observed here, we suggest that at least one of the transients reported by Bower et al. may be attributed to ESEs.

Statistics of the MASIV 5 GHZ VLA Scintillation Survey

Abstract : We are undertaking a large-scale VLA 5 GHz variability survey of the northern sky searching for rapid intra-day variability. From four epochs of observations spread over a year we find 56% of the flat-spectrum sources showed significant variability on time-scales from hours to days, with many sources varying episodically on only one epoch during the year. We find that the weaker sources show more frequent variability as well as fractionally larger amplitude variability. Fewer sources were detected at high Galactic latitude, demonstrating that inter-stellar scintillation is the principal mechanism responsible for this IDV. We also see a significant dependence on spectral index with the flatter and more inverted sources more frequently exhibiting scintillation.

Water masers within the G 333.2-0.6 giant molecular cloud

We report the results of a blind search for 22 GHz water masers in two regions, covering approximately half a square degree, within the G 333.2–0.6 giant molecular cloud. The complete search of the two regions was carried out with the 26 m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7 GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7 GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are slightly less red than those associated with methanol masers. Statistical investigation of the properties of the 13 CO and 1.2 mm dust clumps with and without associated water masers shows that the water masers are associated with the more massive, denser and brighter 13 CO and 1.2 mm dust clumps. We present statistical models that can predict those 13 CO and 1.2 mm dust clumps likely to have associated water masers.