We present first results of the H2O Southern Galactic Plane Survey (HOPS), using the Mopra Radio Telescope with a broad-band backend and a beam size of about 2 arcmin. We have observed 100 deg2 of the southern Galactic plane at 12 mm (19.5-27.5 GHz), including spectral line emission from H2O masers, multiple metastable transitions of ammonia, cyanoacetylene, methanol and radio recombination lines. In this paper, we report on the characteristics of the survey and H2O maser emission. We find 540 H2O masers, of which 334 are new detections. The strongest maser is 3933 Jy and the weakest is 0.7 Jy, with 62 masers over 100 Jy. In 14 maser sites, the spread in the velocity of the H2O maser emission exceeds 100 km s-1. In one region, the H2O maser velocities are separated by 351.3 km s-1. The rms noise levels are typically between 1 and 2 Jy, with 95 per cent of the survey under 2 Jy. We estimate completeness limits of 98 per cent at around 8.4 Jy and 50 per cent at around 5.5 Jy. We estimate that there are between 800 and 1500 H2O masers in the Galaxy that are detectable in a survey with similar completeness limits to HOPS. We report possible masers in NH3 (11,9) and (8,6) emission towards G19.61-0.23 and in the NH3 (3,3) line towards G23.33-0.30.

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The H2O Southern Galactic Plane Survey (HOPS) – I. Techniques and H2O maser data

We present a second update of the Arcetri Catalog of water masers (Comoretto et al. [CITE]; Brand et al. [CITE]). The present study reports the results of the observations carried out with the Medicina 32-m radiotelescope from January 1993 to April 2000 on a sample of 300 sources. This compilation consists of newly discovered maser sources that did not appear in the previous Arcetri Catalogs and is made of: a) detections from the literature, and b) unpublished detections obtained with the Medicina antenna. Overall, 83 out of 300 sources were detected. The detection rate is low (28% ) and we attribute this result to the inclusion in our survey of a rather large number of spurious maser detections that have appeared in one particular paper. The observational parameters are reported in tabular form for all the 300 sources and the spectra of the detected masers are presented. We discuss the global properties of the complete Arcetri Catalog based on Comoretto et al. ([CITE]), Brand et al. ([CITE]) and the present observations, which now contains 1013 galactic water maser sources. Of these, 937 have an IRAS counterpart within 1 arcmin from the nominal position of the maser. We establish a classification scheme based on the IRAS flux densities which allows to distinguish between water masers associated with star forming regions and late-type stars. The Arcetri Catalog represents a useful data base for systematic studies of galactic water maser sources.

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The Arcetri Catalog of H2O maser sources: Update 2000

Aims. We present the first multi-epoch study that includes concurrent mid-infrared and radio interferometry of an oxygen-rich Mira star. Methods. We obtained mid-infrared interferometry of S Ori with VLTI/MIDI at four epochs in December 2004, February/March 2005, November 2005, and December 2005. We concurrently observed v = 1, J = 1-0 (43.1 GHz), and v = 2, J = 1-0 (42.8 GHz) SiO mascr emission toward S Ori with the VLBA in January, February, and November 2005. The MIDI data are analyzed using self-excited dynamic model atmospheres including molecular layers, complemented by a radiative transfer model of the circumstellar dust shell. The VLBA data are reduced to the spatial structure and kinematics of the maser spots. Results. The modeling of our MIDI data results in phase-dependent continuum photospheric angular diameters of 9.0±0.3mas (phase 0.42), 7.9 ±0.1 mas (0.55), 9.7 ±0.1 mas (1.16), and 9.5±0.4mas (1.27). The dust shell can best be modeled with Al 2 O 3 grains using phase-dependent inner boundary radii between 1.8 and 2.4 photospheric radii. The dust shell appears to be more compact with greater optical depth near visual minimum (τ V ∼ 2.5), and more extended with lower optical depth after visual maximum (τ V ∼ 1.5). The ratios of the 43.1 GHz/42.8 GHz SiO maser ring radii to the photospheric radii are 2.2 ± 0.3/2.1 ± 0.2 (phase 0.44), 2.4 ±0.3/2.3 ±0.4 (0.55), and 2.1 ±0.3/1.9 ±0.2 (1.15). The maser spots mark the region of the molecular atmospheric layers just beyond the steepest decrease in the mid-infrared model intensity profile. Their velocity structure indicates a radial gas expansion. Conclusions. S Ori shows significant phase-dependences of photospheric radii and dust shell parameters. Al 2 O 3 dust grains and SiO mascr spots form at relatively small radii of ∼ 1.8-2.4 photospheric radii. Our results suggest increased mass loss and dust formation close to the surface near the minimum visual phase, when Al 2 O 3 dust grains are co-located with the molecular gas and the SiO maser shells, and a more expanded dust shell after visual maximum. Silicon does not appear to be bound in dust, as our data show no sign of silicate grains.

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The Mira variable S Orionis: relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs

A study is made of a sample of 58 dust-enshrouded asymptotic giant branch (AGB) stars (including two possible post-AGB stars), of which 27 are carbon-rich and 31 are oxygen-rich. These objects were originally identified by Jura & Kleinmann as nearby (within about 1 kpc of the Sun) AGB stars with high mass-loss rates (M˙>10−6 M⊙ yr−1). Ground-based near-infrared photometry, data obtained by the IRAS satellite and kinematic data (radial and outflow velocities) from the literature are combined to investigate the properties of these stars. The light amplitude in the near-infrared is found to be correlated with period, and this amplitude decreases with increasing wavelength. Statistical tests show that there is no reason to suspect any difference in the period distributions of the carbon- and oxygen-rich stars for periods less than 1000 d. There are no carbon-rich stars with periods longer than 1000 d in the sample. The colours are consistent with those of cool stars with evolved circumstellar dust shells. Luminosities and distances are estimated using a period–luminosity relation. Mass-loss rates, estimated from the 60-μm fluxes, show a correlation with various infrared colours and pulsation period. The mass-loss rate is tightly correlated with the K−[12] colour. The kinematics and scaleheight of the sample show that the sources with periods less than 1000 d must have low-mass main-sequence progenitors. It is argued that the three oxygen-rich stars with periods over 1000 d probably had intermediate-mass main-sequence progenitors. For the other stars an average progenitor mass of about 1.3 M⊙ is estimated with a final white dwarf mass of 0.6 M⊙. The average lifetime of stars in this high mass-loss AGB phase is estimated to be about 4×104 yr, which suggests that these stars will undergo at most one more thermal pulse before leaving the AGB, if current theoretical relations between thermal interpulse period and core mass are correct.

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Dust-enshrouded asymptotic giant branch stars in the solar neighbourhood

The space motions of Mira variables are derived from radial velocities, Hipparcos proper motions and a period–luminosity relation. The previously known dependence of Mira kinematics on the period of pulsation is confirmed and refined. In addition, it is found that Miras with periods in the range 145–200 d in the general Solar neighbourhood have a net radial outward motion from the Galactic Centre of 75±18 km s−1. This, together with a lag behind the circular velocity of Galactic rotation of 98±19 km s−1, is interpreted as evidence for an elongation of their orbits, with their major axes aligned at an angle of ∼17° with the Sun–Galactic Centre line, towards positive Galactic longitudes. This concentration seems to be a continuation to the Solar circle and beyond of the bar-like structure of the Galactic bulge, with the orbits of some local Miras probably penetrating into the bulge. These conclusions are not sensitive to the distance scale adopted. A further analysis is given of the short-period (SP) red group of Miras discussed in companion papers in this series. In Appendix A the mean radial velocities and other data for 842 oxygen-rich Mira-like variables are tabulated. These velocities were derived from published optical and radio observations.

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Mira kinematics from Hipparcos data: a Galactic bar to beyond the Solar circle

Almost 3000 stellar sources which have been searched for maser emission from the H2O, SiO, and/or OH molecules are catalogued. Of the sources listed, 368 were detected in H2O, 209 in SiO, and 713 in OH. The catalog includes basic information about the stars including alternate names, the 1950 epoch position, velocity, spectral type, variability type, and period, as well as the references for both the detections and nondetections for each of the three molecules.

Kristin A. Blais

Papers

A Catalog of Observations for Stellar Masers