Searching for planets in the atmosphere of AGB stars is difficult, due to confusion with the stellar wind and pulsations. The aim here is to provide a complementary strategy for planet search in such a dense environment. The polarization properties of SiO masers, especially their circular polarization, are, under certain conditions, good tracers for rapid magnetospheric events. A Jovian planet with a magnetosphere whose dipole axis is misaligned with its rotation axis, naturally provides such conditions. Here I present several models showing that the polarization will be periodically modulated. Single-dish monitoring with a sufficiently dense time sampling and a carefully calibrated polarimeter, in combination with VLBI observations, are suited to detect and locate a periodic modulation of the circular maser polarization due to a precessing Jovian magnetosphere. The phenomenon will be rare, because a favourable arrangement of maser and magnetosphere is needed, otherwise the polarization may be below the detection threshold, especially if the maser is unsaturated. Linear polarization, though exhibiting a qualitatively similar modulation, is likely to suffer more from confusion due to beam dilution, even in VLBI observations.
Building on the detection of J=7-6 SiO maser emission in both the v=1 and v=2 vibrational states towards the symbiotic Mira, R Aquarii, we have used the James Clerk Maxwell Telescope to study the changes in the SiO maser features from R Aqr over a stellar pulsational period. The observations, complemented by contemporaneous data taken at 86 GHz, represent a test of the popular thermal-instability clump models of SiO masers. The `clump' model of SiO maser emission considers the SiO masers to be discrete emitting regions which differ from their surroundings in the values of one or more physical …
Maser emission from the SiO molecule has been widely observed in the near-circumstellar envelopes of late-type, evolved stars. VLBI images can resolve individual SiO maser spots, providing information about the kinematics and magnetic field in the extended atmospheres of these stars. This poster presents full polarization images of several SiO maser lines towards the supergiant star VY CMa. VY CMa is a particularly strong SiO maser source and allows observations of a wide range of maser transitions. We discuss implications of these observations for VY CMa morphology, polarization, and pumping …
We present full resolution (~0.2mas, ~0.1 A.U.) Very Long Baseline Interferometry maps of the v=1, J=1-0 SiO masers in the Orion-KL nebula. The morphology and turbulent nature of the maser emission argues against models in which the masers form in an expanding and rotating protostellar disk. Rather, we find that the symmetry evident in the SiO maser emission points towards its genesis in a bipolar outflow. Water masers which also appear towards Orion-KL are known to share the velocity profile and double peaked characteristics of the SiO maser emission yet form much further away from the protos…
Based on the space MSX observation in bands A(8$μ$m), C(12$μ$m), D(15$μ$m) and E(21$μ$m), and the ground SiO maser observation of evolved stars by the Nobeyama 45-m telescope in the v=1 and v=2 J=1-0 transitions, the relation between SiO maser emission and mid-IR continuum radiation is analyzed. The relation between SiO maser emission and the IR radiation in the MSX bands A, C, D and E is all clearly correlated. The SiO maser emission can be explained by a radiative pumping mechanism according to its correlation with infrared radiation in the MSX band A.
A moderately deep survey of stellar maser sources toward the Galactic center has been made in the SiO J=1-0 v=1 and v=2 transitions (~ 43 GHz) with the Nobeyama 45-m telescope of a beam size of about 40". At the Galactic center (Sgr A*), 7 (4 new) SiO maser sources were detected in one beam. In order to investigate the spatial distribution of SiO maser sources, we have also observed the offset positions by +- 40" in Galactic longitude from the Galactic center. In total, 7 (4 new) SiO maser sources were detected at the offset positions. Taking into account the shorter integration time at the of…
We present the results of an SiO maser survey for color-selected IRAS sources in the area 40 < l < 70 and |b| < 10 in the SiO J=1-0, v=1 and 2 transitions. We detected 134 out of 272 observed sources in SiO masers; 127 were new detections. A systematic difference in the detection rates between SiO and OH maser searches was found. Especially, in the color ranges with log(F_{25}/F_{12}) smaller than -0.1, the detection rate of the SiO masers is significantly higher than that of OH masers. We found a possible kinematic influence of the galactic arm on the distribution of SiO maser sources. It was…
We report on the detection of 43 GHz SiO maser emission in V838 Mon, a prototype of a new class of eruptive variables, in which a red supergiant was formed after the nova-like eruption in 2002. The detection of SiO masers indicates that the star formed after the eruption is indeed a kind of cool mass-losing object with circumstellar masers. The measured radial velocity and the intensity of maser emission are consistent with the object being located at the distance of about 7 kpc from the sun. It also suggests that a considerable percentage of SiO masing objects in the Galaxy are formed in the …
We observed v=1, J=1-0 43-GHz SiO maser emission toward the Mira variable IK Tauri (IK Tau) using the Very Long Baseline Array (VLBA). The images resulting from these observations show that SiO masers form a highly elliptical ring of emission approximately 58 x 32 mas with an axial ratio of 1.8:1. The major axis of this elliptical distribution is oriented at position angle of ~59 deg. The line-of-sight velocity structure of the SiO masers has an apparent axis of symmetry consistent with the elongation axis of the maser distribution. Relative to the assumed stellar velocity of 35 km/s, the blue…
We present the results of observations of cold IRAS sources in the Galactic disk area, -10 < l < 100 and |b|<5, in the SiO J=1-0, v=1 and 2 maser lines. SiO masers were detected in 51 out of 143 observed sources; 45 were new detections in SiO masers. The selected IRAS sources were objects with dust temperatures of between 160 and 280 K. According to a confirmation using 2MASS near-infrared images, a majority of the sample are AGB or post-AGB stars, although dense cores in the star-forming regions (or dusty HII regions) are involved in part of the sample. Among new detections, two were candidat…
Oxygen-rich Asymptotic Giant Branch (AGB) stars are intense emitters of SiO and H$_2$O maser lines at 43 (J=1-0, v=1 and 2) and 22 GHz, respectively. VLBI observations of the maser emission provides a unique tool to sample the innermost layers of the circumstellar envelopes in AGB stars. Nevertheless, the difficulties in achieving astrometrically aligned v=1 and v=2 SiO maser maps have traditionally prevented a unique interpretation of the observations in terms of physical underlying conditions, which depend on the nature of the SiO pumping mechanism. We have carried out observations of the Si…
We report the first VLBI map of the 7 mm v=0 J=1-0 maser line of the 29-SiO isotopic substitution in the long period variable star IRC+10011. We have found that this maser emission is composed of multiple features distributed in an incomplete ring, suggesting that this maser is also amplified tangentially as already proposed in other SiO circumstellar masers. We present also the results for some 28-SiO 7 mm and 3 mm maser lines. We confirm in this epoch that the 86 GHz maser v=1 J=2-1 in IRC+10011 is formed in an outer region of the circumstellar envelope compared to the other SiO masers studi…
On this paper, we present simultaneous VLBA observations of the J=1-0 and J=2-1 rotational lines in the v=1 and v=2 vibrationally excited states of SiO (at 7 and 3 mm wavelengths). We have mapped these four maser lines in the circumstellar envelopes of three AGB stars: IRC +10011, Chi Cyg and TX Cam. We study the relative spatial distribution between these maser lines. In particular, for the two v=1 transitions, we found that the J=1-0 and J=2-1 maser spot distributions are unalike, challenging all the current theoretical pumping mechanisms for SiO masers (which predict quite similar distribut…
We present a compilation and study of DENIS, 2MASS, ISOGAL, MSX and IRAS 1--25 micron photometry for a sample of 441 late-type stars in the inner Galaxy, which we previously searched for 86 GHz SiO maser emission (Messineo et al.2002). The comparison of the DENIS and 2MASS J and Ks magnitudes shows that most of the SiO targets are indeed variable stars. The MSX colours and the IRAS [12]-[25] colour of our SiO targets are consistent with those of Mira type stars with dust silicate feature at 9.7 micron feature in emission, indicating only a moderate mass-loss rate.
We present the results of SiO line observations of a sample of known SiO maser sources covering a wide dust-temperature range. The aim of the present research is to investigate the causes of the correlation between infrared colors and SiO maser intensity ratios among different transition lines. We observed in total 75 SiO maser sources with the Nobeyama 45m telescope quasi-simultaneously in the SiO J=1-0 v=0, 1, 2, 3, 4 and J=2-1 v=1, 2 lines. We also observed the sample in the 29SiO J=1-0 v=0 and J=2-1 v=0, and 30SiO J=1-0 v=0 lines, and the H2O 6(1,6)-5(2,3) line. As reported in previous pap…
We have determined extinction corrections for a sample of 441 late-type stars in the inner Galaxy, which we previously searched for SiO maser emission, using the 2MASS near-infrared photometry of the surrounding stars. From this, the near-infrared extinction law is found to be approximated by a power law A$_λ\propto λ^{-1.9\pm0.1}$. Near- and mid-infrared colour-colour properties of known Mira stars are reviewed. From the distribution of the dereddened infrared colours of the SiO target stars we infer mass-loss rates between $10^{-7}$ and $10^{-5}$ M$_\odot$ yr$^{-1}$.
IRAS 19312+1950 is a unique SiO maser source, exhibiting a rich set of molecular radio lines, although SiO maser sources are usually identified as oxygen-rich evolved stars, in which chemistry is relatively simple comparing with carbon-rich environments. The rich chemistry of IRAS 19312+1950 has raised a problem in circumstellar chemistry if this object is really an oxygen-rich evolved star, but its evolutional status is still controversial. In this paper, we briefly review the previous observations of IRAS 19312+1950, as well as presenting preliminary results of recent VLBI observations in ma…
We describe a combined dynamic atmosphere and maser propagation model of SiO maser emission in Mira variables. This model rectifies many of the defects of an earlier model of this type, particularly in relation to the infra-red (IR) radiation field generated by dust and various wavelength-dependent, optically thick layers. Modelled masers form in rings with radii consistent with those found in VLBI observations and with earlier models. This agreement requires the adoption of a radio photosphere of radius approximately twice that of the stellar photosphere, in agreement with observations. A rad…
Methanol masers are often found in linear distributions, and it has been hypothesized that these masers are tracing circumstellar accretion disks around young massive stars. However, recent observations in H2 emission have shown what appear to be outflows at similar angles to the maser distribution angles, not perpendicular as expected in the maser-disk scenario. The main motivation behind the observations presented here is to determine from the presence and morphology of an independent outflow tracer, namely SiO, if there are indeed outflows present in these regions and if they are consistent…
We report on the detection of SiO J=2--1 v=1 (86 GHz) maser emission from the red supergiant IRAS04553--6825 in the LMC. It has thereby become the first known source of SiO maser emission outside the Milky Way. We used the Swedish-ESO Submm Telescope at the European Southern Observatory at La Silla. With the help of good atmospheric conditions, the excellent performance of the brand new 3~mm SIS receiver, and 26 hours total observing time we reduced the noise level to only 63~mJy rms. This allowed us to detect the 0.28~Jy maser peak. Integrating the flux of the maser profile resulted in a 6.9~…
We report the first Very Long Baseline Array (VLBA) observations of 43 GHz v=1, J=1-0 SiO masers in the circumstellar envelope of the M-type semi-regular supergiant variable star AH Sco at 2 epochs separated by 12 days in March 2004. These high-resolution VLBA images reveal that the distribution of SiO masers is roughly on a persistent elliptical ring with the lengths of the major and minor axes of about 18.5 and 15.8 mas, respectively, along a position angle of 150^{\circ}. And the red-shifted masers are found to be slightly closer to the central star than the blue-shifted masers. The line-of…
We present 86 GHz (v = 1, J = 2 -1) SiO maser line observations with the IRAM 30-m telescope of a sample of 441 late-type stars in the Inner Galaxy (-4 degr < l < +30 degr). These stars were selected on basis of their infrared magnitudes and colours from the ISOGAL and MSX catalogues. SiO maser emission was detected in 271 sources, and their line-of-sight velocities indicate that the stars are located in the Inner Galaxy. These new detections double the number of line-of-sight velocities available from previous SiO and OH maser observations in the area covered by our survey and are, together w…
Results of an SiO maser survey for the late-type stars selected by the IRTS (Infrared Telescope in Space) are presented. We have detected SiO J=1-0, v=1 and/or v=2 lines in 27 stars out of 59 stars. The maser intensity increases with the depth of the H2O absorption in the infrared spectra and redness of the 2.2 and 12 micron color. The column densities of the water vapor in the target stars are estimated from the depth of the water absorption in the IRTS spectra. We found that the SiO maser was detected mostly in the stars with the column density of water vapor higher than 3x10^19-3x10^20 cm^-…
We report Very Long Baseline Array (VLBA) observations of 43 GHz v=1, J=1-0 SiO masers in the circumstellar envelope of the M-type semi-regular variable star VX Sgr at 3 epochs during 1999 April-May. These high-resolution VLBA images reveal a persistent ringlike distribution of SiO masers with a projected radius of ~3 stellar radii. The typical angular size of 0.5 mas for individual maser feature was estimated from two-point correlation function analysis for maser spots. We found that the apparent size scale of maser features was distinctly smaller than that observed in the previous observatio…
We present the results of SiO millimeter-line observations of a sample of known SiO maser sources covering a wide dust-temperature range. A cold part of the sample was selected from the SiO maser sources found in our recent SiO maser survey of cold dusty objects. The aim of the present research is to investigate the causes of the correlation between infrared colors and SiO maser intensity ratios among different transition lines. In particular, the correlation between infrared colors and SiO maser intensity ratio among the J=1-0 v=1, 2, and 3 lines are mainly concerned in this paper. We observe…
We present sensitive Very Large Array observations with an angular resolution of a few arcseconds of the $J= 1 - 0$ line of SiO in the $v$=1 and 2 vibrationally excited states toward a sample of 60 Galactic regions in which stars of high or intermediate mass are currently forming and/or have recently formed. We report the detection of SiO maser emission in \textit{both} vibrationally excited transitions toward only three very luminous regions: Orion-KL, W51N and Sgr B2(M). Toward all three, SiO maser emission had previously been reported, in Orion-KL in both lines, in W51N only in the $v=2$ li…
We describe an observing campaign using the Very Long Baseline Array (VLBA) to monitor the time-evolution of the v=1, J=1-0 SiO maser emission towards the Mira variable TX Cam. The data reported here cover the period 1997 May 24 to 1999 February 19, during which the SiO maser emission was imaged at approximately bi-weekly intervals. The result is an animated movie at an angular resolution of ~500 microarcsec, over a full pulsation period, of the gas motions in the near circumstellar environment of this star, as traced by the SiO maser emission. This paper serves to release the movie and is the…
We present milliarsecond-resolution maps of the SiO maser emission $v$=1 J=2--1 (3 mm) in the bipolar post-AGB nebula OH 231.8+4.2, and compare them with our previous observations of the $v$=2 J=1--0 line (7 mm). Our observations show that the SiO masers arise in several bright spots forming a structure elongated in a direction perpendicular to the symmetry axis of the nebula. This, and the complex velocity gradient observed, is consistent with the presence of an equatorial torus in rotation and with an infall of material towards the star.
We have made the first unambiguous detection of vibrational ground-state maser emission from SiO toward six evolved stars. Using the Very Large Array, we simultaneously observed the v=0, J=1-0, 43.4-GHz, ground-state and the v=1, J=1-0, 43.1-GHz, first excited-state transitions of SiO toward the oxygen-rich evolved stars IRC+10011, o Ceti, W Hya, RX Boo, NML Cyg, and R Cas and the S-type star chi Cyg. We detected at least one v=0 SiO maser feature from six of the seven stars observed, with peak maser brightness temperatures ranging from 10,000 K to 108,800 K. In fact, four of the seven v=0 spe…
A stellar hydrodynamic pulsation model has been combined with a SiO maser model in an attempt to calculate the temporal variability of SiO maser emission in the circumstellar envelope (CE) of a model AGB star. This study investigates whether the variations in local physical conditions brought about by shocks are the predominant contributing factor to SiO maser variability because, in this work, the radiative part of the pump is constant. We find that some aspects of the variability are not consistent with a pump provided by shock-enhanced collisions alone. In these simulations, gas parcels of …
We have surveyed known large-amplitude variables within 15' of the Galactic center in the SiO J=1-0 v=1 and 2 maser lines at 43 GHz, resulting in 79 detections and 58 non-detections. The detection rate of 58 percent is comparable to that obtained in Bulge IRAS source surveys. SiO lines were also detected from four other sources near the program objects. The SiO detection rate increases steeply with the period, particularly for stars with P>500 d, where it exceeds 80%. We found at a given period that the SiO detection rate is approximately double that for OH. These facts suggest that the large-…
We present milliarsecond-resolution maps of the SiO maser emission v=1 J=2-1 (3 mm) in the bipolar post-AGB nebula OH231.8+4.2, and compare them with our previous observations of the v=2 J=1-0 line (7 mm). Our observations show that the SiO masers arise in several bright spots forming a structure elongated in a direction perpendicular to the symmetry axis of the nebula. This, and the complex velocity gradient observed, is consistent with the presence of an equatorial torus in rotation and with an infall of material towards the star.
We have performed VLBA observations of the SiO v=1 and v=2 J=1-0 masers in two AGB stars, TX Cam and IRC +10011. We confirm the ring-like spatial distribution, previously found in several AGB objects, as well as the tangential polarization pattern, already reported for TX Cam. Both properties, that seem to be systematic in this kind of objects, are characteristic of radiatively pumped SiO masers. On the contrary, we do not confirm the previous report on the spatial coincidence between the J=1-0 v=1 and 2 masers, a result that would have argued in favor of collisional pumping. We find that both…
We report on the detection of SiO and water masers toward a newly found bipolar nebula, IRAS 19312+1950. This object exhibits extreme red IRAS color log (F25/F12)=0.5 and log (F60/F25)=0.7 and a nebulosity having a size of about 30" extended to the South-West in the 2MASS near-infrared image. Toward this object, we have detected emission from the H2O 6(1,6)-5(2,3) transition, the SiO J=1-0, v=1 and 2, and J=2-1, v=1 transitions, and the SO 2(2)--1(1) and H13CN J=1-0 transitions. The thermal lines of SO and H13CN are shifted by about 12 km/s in radial velocity with respect to the maser lines, i…
We have monitored the SiO (v = 1, J = 2 -> 1) maser polarization in 17 variable stars (Miras, OH-IR stars, and supergiants) to investigate the long-term persistence of masers. The 8 epochs of observations span 2.5 years, thereby sampling multiple cycles for these stars with typical periods of ~1 year. The average polarization was 23% with a typical dispersion of 7%, although the variability differed substantially from star to star. In the Stokes q and u spectra of individual stars, a few strong maser features tended to dominate the polarization, with the maser features persisting for less than…
We studied the period-K magnitude (P-K) relations of nearby Mira and Mira-like variables with relatively good Hipparcos parallaxes. They form at least two prominent sequences on the P-K plane, corresponding to the sequences C (Mira variables pulsating in the fundamental mode) and C'(Mira variables pulsating in the 1st overtone mode), that were found in the LMC. As a part of an ongoing study to see the differences between the Mira variables pulsating in the fundamental and the 1st overtone mode, we searched for SiO masers in the nearby variables on the sequences C' and C using the Nobeyama 45m …
In April 2002 an array of antennas operating at 129GHz successfully detected VLBI fringes on both continuum AGN and SiO maser sources. The 129GHz fringes on maser sources represent the highest frequency spectral line VLBI detections to date. The AGN 3C279 was detected on long baselines at both 129GHz (and at 147GHz, see Krichbaum et al in these proceedings) yielding fringe spacings of 50-56 micro arc seconds, an angular resolution record. The array consisted of the University of Arizona Kittpeak 12m antenna, the Heinrich Hertz 10m Telescope (HHT), and the IRAM 30m dish on Pico Veleta. At 129GH…
Using the 3.6/4.5/5.8/8.0 micron images with 1.2 arcsec pixel resolution from the Spitzer/GLIMPSE survey, we investigated 23 masing and 18 very red objects that were not identified in the 2MASS survey. Counterparts for all selected objects were found in the GLIMPSE images. Color indices in these IR bands suggest the presence of a high-extinction layer of more than a few tenths of a solar mass in front of the central star. Furthermore, radio observations in the SiO and H2O maser lines found characteristic maser-line spectra of the embedded objects, e.g., the SiO J=1-0 line intensity in the v=2 …
We used the Submillimeter Array to image the SiO maser emission in the $v=1$, \$J=5-4$ transition associated with the peculiar red supergiant VY Canis Majoris. We identified seven maser components and measured their relative positions and linear polarization properties. Five of the maser components are coincident to within about 150 mas ($\sim$ 200 AU at the distance of 1.5 kpc); most of them may originate in the circumstellar envelope at a radius of about 50 mas from the star along with the SiO masers in the lowest rotational transitions. Our measurements show that two of the maser components…
We report on the detection of SiO masers in Asymptotic Giant Branch variables toward bulge/disk globular clusters. In five out of six cases, the radial velocities are compatible with the optically measured radial velocities of globular clusters in the assessed uncertainty. Two sources, toward Terzan~5 and Terzan~12, lie very close to the cluster centers. The objects toward Pal~6 and Terzan~12 have luminosities appropriate to the AGB tip in globular clusters, while those toward NGC 6171, Pal~10, and Terzan~5 are brighter than expected. It is suggested that the latter three may have evolved from…
Mapping and monitoring observations of SiO maser sources near the Galactic center were made with the Nobeyama 45-m telescope at 43 GHz. Rectangular mapping an area of approximately 200'' x 100''$ in a 30'' grid, and triangular mapping in a 20'' grid toward the Galactic center, resulted in 15 detections of SiO sources; the positions of the sources were obtained with errors of 5--10'', except for a few weak sources. Three-year monitoring observations found that the component at V_lsr=-27 km/s of IRS 10 EE flared to about 1.5 Jy during 2000 March--May, which was a factor of more than 5 brighter t…
We report on the high-precision astrometric observations of maser sources around the Galactic Center in the SiO J=1--0 v=1 and 2 lines with the VLBA during 2001 -- 2004. With phase-referencing interferometry referred to the radio continuum source Sgr A*, accurate positions of masers were obtained for three detected objects: IRS 10 EE (7 epochs), IRS 15NE (2 epochs), and SiO 6 (only 1 epoch). Because circumstellar masers of these objects were resolved into several components, proper motions for the maser sources were derived with several different methods. Combining our VLBA results with those …
We study the polarization of the SiO maser emission in a representative sample of evolved stars in order to derive an estimate of the strength of the magnetic field, and thus determine the influence of this magnetic field on evolved stars. We made simultaneous spectroscopic measurements of the 4 Stokes parameters, from which we derived the circular and linear polarization levels. The observations were made with the IF polarimeter installed at the IRAM 30m telescope. A discussion of the existing SiO maser models is developed in the light of our observations. Under the Zeeman splitting hypothesi…
The study of the innermost circumstellar layers around AGB stars is crucial to understand how these envelopes are formed and evolve. The SiO maser emission occurs at a few stellar radii from the central star, providing direct information on the stellar pulsation and on the chemical and physical properties of these regions. Our data also shed light on several aspects of the SiO maser pumping theory that are not well understood yet. We aim to determine} the relative spatial distribution of the 43 GHz and 86 GHz SiO maser lines in the oxygen-rich evolved star R Leo. We have imaged with milliarcse…
We present the first VLBI images of SiO masers in the circumstellar envelope of an S-type star obtained with the newly developed capabilities of the Very Long Baseline Array (VLBA) at 86 GHz. We combine these data with those obtained quasy simultaneously at 43 GHz. These observations provide information on the structure and dynamics of the innermost circumstellar shells, where the return of large quantities of stellar material to the interstellar medium starts. Despite of the fact that these are prelimininary results, we report that the maser emission of the $v$=1 J=1--0 and J=2--1 present a v…
We present sub-milliarcsecond observations of SiO masers in the late-type stars IRC +10011 and Chi Cyg. We have used the NRAO Very Long Baseline Array (VLBA) to map the 43 GHz (v=1, 2 J=1-0) and the 86 GHz (v=1, 2 J=2-1) SiO masers. All the transitions have been imaged except the v=2 J=2-1 in IRC +10011. We report the first VLBI map of the v=1 J=2-1 28SiO maser in IRC +10011 as well as the first VLBA images of SiO masers in an S-type Mira variable, Chi Cyg. In this paper we have focused on the study of the relative spatial distribution of the different observed lines. We have found that in som…
We present the results of the first high angular resolution observations of SiO maser emission towards the star forming region W51-IRS2 made with the Very Large Array (VLA) and Very Long Baseline Array (VLBA). Our images of the water maser emission in W51-IRS2 reveal two maser complexes bracketing the SiO maser source. One of these water maser complexes appears to trace a bow shock whose opening angle is consistent with the opening angle observed in the distribution of SiO maser emission. A comparison of our water maser image with an image constructed from data acquired 19 years earlier clearl…
Menten, Reid, Eckart and Genzel (1997) accurately determined the position of Sgr A* on an infrared image, by aligning the infrared image with positions measured for SiO masers, associated with infrared-bright evolved stars, at radio wavelengths. We now report greatly improved radio positions and, for the first time, proper motions of many stellar SiO masers at the Galactic Center. These positions and motions, coupled with better infrared imaging, allow a much improved location of Sgr A* on infrared images. With current data, infrared stars can be placed in a reference frame tied to Sgr A*, to …
The theory of the generation and transfer of polarized radiation, mainly developed for interpreting solar spectropolarimetric observations, allows to reconsider, in a more rigorous and elegant way, a physical mechanism that has been suggested some years ago to interpret the high degree of polarization often observed in astronomical masers. This mechanism, for which the name of 'dichroic maser' is proposed, can operate when a low density molecular cloud is illuminated by an anisotropic source of radiation (like for instance a nearby star). Here we investigate completely unsaturated masers and s…
We present the results of simultaneous high resolution observations of v=1 and v=2, J=1-0 SiO masers toward TX Cam at four epochs covering a stellar cycle. Near maser maximum (Epochs III and IV), the individual components of both masers are distributed in ring-like structures but the ring is severely disrupted near stellar maser minimum (Epochs I and II). In Epochs III and IV there is a large overlap between the radii at which the two maser transitions occur. However in both epochs the average radius of the v=2 maser ring is smaller than for the v=1 maser ring, the difference being larger for …
In an attempt to probe the magnetic field morphology near the massive young star Orion-IRc2, we mapped the linear polarization of its J=2-1 SiO masers, in both the v=0 and v=1 vibrational levels, with 0.5 arcsec resolution. The intense v=1 masers are confined to a narrow zone 40 AU from the star. Their polarization position angles vary significantly on time scales of years. For the v=1 masers the stimulated emission rate R is likely to exceed the Zeeman splitting gΩdue to any plausible magnetic field; in this case the maser polarization need not correlate with the field direction. The much wea…
We have surveyed 401 color selected IRAS sources in the Galactic disk in the SiO J=1--0 v= 1 and 2 maser lines at 43 GHz, resulting in 254 (239 new) detections. The observed sources lie mostly in a strip of the inner Galactic disk with boundaries -10<l<40 deg and |b|<3 deg. This survey provides radial velocities of inner-disk stars for which optical measurements cannot be made due to interstellar extinction. The SiO $l$--$v$ diagram in the area $-10<l<40 deg exhibits fewer objects coincident with the molecular ring feature than the OH 1612 MHz source $l$--$v$ map does, indicating a slight diff…
We have undertaken toward 30 Mira or semi-regular variables and one OH/IR object highly sensitive observations of the v=1, J=2-1 and 3-2 transitions of SiO simultaneously with observations of the J=1-0 transition of CO during three observing sessions in the period 1995 to 1996. As in our previous observations of 1994, we observe that for several stars the SiO profiles exhibit unusually broad wings which sometimes exceed the terminal velocity of the expanding circumstellar envelope traced by the thermal CO emission. We have discovered a clear dependence of the SiO wing emission on the optical p…
We present the first contemporaneous 43GHz and 86GHz VLBI images of the v=1 J=2-1 and J=1-0 SiO masers in the Orion-KL nebula. Both maser species exhibit the same general morphology of earlier J=1-0 maser images which appear to trace the edges of a bi-polar conical outflow. Surprisingly, the J=2-1 masers form further from the central protostar than the J=1-0 masers, a fact not readily explained by current SiO maser pumping models. The average magnitude of offsets between corresponding regions of the two masing transitions is approximately 14% of the total radial extent of the SiO maser emissio…
We present the first multi-epoch study that includes concurrent mid-infrared and radio interferometry of an oxygen-rich Mira star. We obtained mid-infrared interferometry of S Ori with VLTI/MIDI at four epochs between December 2004 and December 2005. We concurrently observed v=1, J=1-0 (43.1 GHz), and v=2, J=1-0 (42.8 GHz) SiO maser emission toward S Ori with the VLBA at three epochs. 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 spa…
A comprehensive picture of high-mass star formation has remained elusive, in part because examples of high-mass YSOs tend to be relatively distant, deeply embedded, and confused with other emission sources. These factors have impeded dynamical investigations within tens of AU of high-mass YSOs--scales that are critical for probing the interfaces where outflows from accretion disks are launched and collimated. Using observations of SiO masers obtained with the VLA and the VLBA, the KaLYPSO project is overcoming these limitations by mapping the structure and dynamical/temporal evolution of the m…
OH 231.8+4.2 is a well studied preplanetary nebula (pPN) around a binary stellar system that shows a remarkable bipolar outflow. To study the structure and kinematics of the inner 10-80 AU nebular regions we performed high-resolution observations of the H$_2$O 6$_{1,6}$--5$_{2,3}$ and $^{28}$SiO $v$=2, $J$=1--0 maser emissions with the Very Long Baseline Array. The absolute position of both emission distributions were recovered using the phase referencing technique, and accurately registered in HST optical images. H$_2$O maser clumps are found to be distributed in two areas of 20 mas in size s…
We have searched for the SiO J=1--0 v= 1 and 2 maser lines at ~ 43 GHz in 277 2MASS/MSX/IRAS sources off the Galactic plane (|b|> 3 deg), which resulted in 119 (112 new) detections. Among the new detections, are two very faint objects with MSX 12 micron flux densities below 2 Jy. These are likely to be O-rich AGB-stars associated with dwarf-galaxy tidal tails. The sample also includes medium bright MSX objects at moderately high Galactic latitudes (3 deg<|b|<5 deg) and in the IRAS gap at higher latitudes. A signature of a warp of the inner Galactic disk is found for a disk subsample. This warp…
We report a result of an interferometric observation toward an SiO maser source, IRAS 19312+1950, in the HCO+ J=1-0 line with the Berkeley-Illinois-Maryland-Association (BIMA) Millimeter Array. In the spatially integrated spectrum of HCO+, two kinematic components were seen: a strong line with a narrow width (~2 km/s, narrow component), and a weak symmetric line with a broad width (~60 km/s, broad component). The line profile of HCO+ are reminiscent of that of CO. In the integrated intensity map, we found a pronounced bipolar shape consisting of lower-velocity parts of the broad component. The…
We report the results of mapping observations of the bipolar nebula with SiO maser emission, IRAS 19312+1950, in the CO (J=1-0 and J=2-1), 13CO (J=1-0 and J=2-1), C18O (J=1-0), CS (J=2-1), SO (J_K=3_2-2_1) and HCO+ (J=3-2) lines with the Berkeley-Illinois-Maryland Association array. Evolutional status of this source has been evoking a controversy since its discovery, though SiO maser sources are usually identified as late-type stars with active mass loss. In line profiles, two kinematical components are found as reported in previous single-dish observations: a broad pedestal component and a na…
We have searched for 22 GHz H2O and 43/86/129 GHz SiO masers in bright IRAS point sources in the SMC and LMC, to test whether the kinematics of the mass loss from these stars depends on metallicity. H2O masers were detected in the red supergiants IRAS04553-6825 and IRAS05280-6910, and tentatively in the luminous IR object IRAS05216-6753 and the AGB star IRAS05329-6708. SiO masers were detected in IRAS04553-6825. The outflow velocity increases between the H2O masing zone near the dust-formation region and the more distant OH masing zone from 18 to 26 km/s for IRAS04553-6825 and from 6 to 17 km/…
